Comprehensive Review

Unit 1

Neurons• There are hundreds of different types of neurons, each one is

specialized for a particular task• Sensory nerves receive and transmit sensory information, and

there are several different types of them, with receptors for touch, light, smell, etc.

• Motor neurons transmit signals for muscle contraction, etc.• They all share certain characteristics.

– Longevity (can last a lifetime)– High metabolic rate– Cannot divide to reproduce– Cannot survive without oxygen

Neuron Anatomy

Axon hillock (trigger zone)

Soma (cell body)

Axon (transmits signals)

Axon terminals (stimulate another cell)

Dendrites (receive signal)

Neuron Anatomy

• DENDRITES function to receive the signal and carry the nerve conduction toward the cell body.

• SOMA (cell body) is where the nucleus, ribosomes, and most organelles are located

• AXON HILLOCK is the area on the soma where the action potential of the neuron builds up before it transmits the signal down the axon.

• AXON function is to transmit signals. Some cells have many axons, some have one, some are short, and some are long.

• AXON TERMINALS (also called terminal boutons or synaptic knobs) contain a neurotransmitter which, when released, stimulates another cell.

• A synapse is where one neuron touches another neuron. Neurons may have a couple of synapses, or hundreds.

Structure of a Synapses

Figure 12.8a, b

Chemical substances released from the presynaptic terminal:

•May inhibit or stimulate an action in the postsynaptic cell

•May be broken down by enzymes

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Cell Membranes• What two conditions must be met for

diffusion of a substance across a semipermeable membrane?– Is the membrane permeable to it?– Does it have a concentration

gradient?

• If the answer is yes to both questions, then the substance will diffuse (Which way? Down it’s gradient)

• Each cell in our body is surrounded by a cell membrane composed of a phospholipid BI-LAYER. That means that our cell membranes have two layers: an outer layer, and an inner layer.

• The inside layer of each cell membrane in the body, (including each neuron) has a charge (usually negative), and the outside layer of each cell membrane has a charge (usually positive).

• The reason for the charge difference is that there are many proteins inside of cells, and proteins are made of amino acids, most of which have a negative charge. Because proteins are negatively charged, the inside layer of the cell membrane has a negative charge.

• Outside of the cell, there are many electrolytes, especially sodium (Na+), which have a positive charge. They stay outside of the cell because they cannot get in unless sodium channels in the cell membrane are open, which they usually are not. That’s why the outside of the cell membrane usually has a positive charge.

• What is a sodium channel? Proteins embedded in the cell membranes form channels which only allow certain ions to cross the cell membrane.

• A sodium ion can only get into the cell by way of a sodium channel. A potassium ion can only get in by way of a potassium channel, etc.

• Charged ions, such as potassium (K+), sodium (Na+), calcium (Ca+

+), and chloride (Cl-) are called electrolytes. When they move from one side of the cell membrane to the other (when their channels are open), they carry their electrical charge with them.

• When sodium channels open during neuron stimulation, it changes the overall charge of the inside and outside of the cell membrane.

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Sidedness “Sidedness” of the membrane •Sidedness means that the electrical charges on one side of the membrane (positive or negative) are different than on the other side. Why does sidedness exist?•The cell membrane has different permeabilities to each ion; for instance the cell is more permeable to K+ than any other ion.•Pumps exist which force particular ions into or out of the cell•Channels made out of protein selectively allow particular ions into or out of the cell. These channels may be open or closed at any given time.

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Not just separation of solutes, but charges, too!

• Inside of the cell is negative due to :– Abundance of proteins,

which have a negative charge

– The cell membrane is very permeable (“leaky”) to K+, so it can LEAVE the cell whenever it wants. That leaves the inside of the cell more negative.

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_ _ _ __ _ _ __ _ _ _

++++

++++

++++

++++

• Every cell has a positive charge on the outside of the membrane and a negative charge on the inside of the cell membrane, when the cell is at rest (not being stimulated).

• K+ constantly leaks out of the cell because it wants to diffuse down its concentration gradient. That means it wants to go from its area of high concentration (the inside of the cell) to an area where it is in low concentration (the outside of the cell).

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• But once it leaks out of the cell, the positive charge of K+ is combined with the positive charge of Na+, and this collection of positive charges makes K+ want to go back into the cell, since positive charges are attracted to negative charges. Na+ wants to get into the cell, too, but it’s channel is closed.

• We use this electricity to do work. Blood pressure, peristalsis of intestines, muscles, etc, use this electricity for work.

Because of this separation of chemicals and electrical charges, every cell has a Resting Membrane

“Potential”

• There is a difference in electrical charge across the membrane (a potential difference)

• More negative inside; more positive outside

• Our cells are like batteries and some cells can tap into this “potential energy” to do work (“kinetic energy”)

• What generates it?– Mainly, ion concentration gradients and

differences in membrane permeability (leaky to K+ but not to anything else)

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Resting Membrane Potential• The resting membrane potential is how negative

or positive the charge of the cell membrane is when it is not being stimulated by a neuron

• Resting membrane potential is minus70 to minus 90mV

• Why is the resting membrane potential negative? Because K+ has leakiness, so it constantly escapes with its positive charge, leaving the inside of the cell more negative.

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• As K+ leaves the cell, it takes a positive charge outside with it, so the inside is more negative.

• However, as the inside of the cell is becoming more negative, the outside of the cell is becoming more positive, and the positive charges will want to flow back inside of the cell since they are attracted to the negative charges.

• This is what keeps K+ from just leaving the cell until it is in equal numbers on both sides of the cell. Before it can reach such an equilibrium, it gets pulled back into the cell because its positive charges are drawn into the inside of the cell, where the charge has become strongly negative (because proteins are on the inside of the cell and they have a negative charge).

• Other positively charged ions, like Na+, want to go into the cell also, but they are blocked by protein gates that only K+ can get through.

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MEMBRANE POTENTIAL• The MEMBRANE POTENTIAL (how negative or positive the charge of the

cell membrane is) is a number that is a reflection of the ion with the greatest permeability.

• Our cells’ resting membrane potential is minus 70 mV because they are most permeable to K+. Therefore, K+ will diffuse out its concentration gradient, taking its positive charges with it, leaving the inside of the cell more negative.

• What if the cell was more permeable to Na+? • Sodium would diffuse down its concentration gradient to the inside of

the cell, taking its positive charges with it, making the inside of the cell more positive.

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What if…..• What if a membrane suddenly became

MORE PERMEABLE to Na+?????• Even for just a moment in time…..• What would Na+ do? (Ask yourself the 3

questions)

Which way is the electrochemical gradient for Na+?

Electrical: inwardChemical: inwardAnswer:Most definitely INWARDSodium WANTS IN!

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-

+

-70 mV

- - -

+++

Na+

Na+

Cl-

Cl-

Na+

Cl-

Na+

Na+

Cl-

Cl-

Na+

Na+

Cl-

Cl-

What would happen to the membrane potential of the cell when this event occurs?

• What would happen to the membrane potential of the cell when you open up a sodium channel?

• If we instantly increase sodium permeability, sodium will enter the cell, changing the charge of the inside of the cell so that it goes from negative to positive. The outside layer of the cell membrane would then go from positive to negative (the charges flip). This is called DEPOLARIZATION.

• However, when this occurs, Na+ will be in higher concentration on the inside of the cell, so it wants to diffuse back out of the cell.

• Once it leaves the cell again, the membrane potential of the inside of the cell membrane will return to a negative charge. This is called REPOLARIZATION.

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Excitable Cells• Cells that can experience a momentary change in

membrane voltage are “excitable” cells• That temporary change in voltage is due to a momentary

change in permeability of Na+• The membrane, for only a moment, becomes more

permeable to Na+ than to K+

• When the outside and inside of the cell membrane reverse their charges (inside becomes positive and outside becomes negative), and then reverts back to normal, this process (depolarization + repolarization) is called an ACTION POTENTIAL.

• The reversal of charges (action potential) is carried like a wave down the length of the cell, and into the next cell touching it, and so on.

ACTION POTENTIAL• The action potential occurs when the membrane potential (how

negatively charged the inside of the cell is) reaches a certain threshold.

• When the Na+ rushes into the cell, the membrane potential becomes less and less negative. Eventually, it reaches zero charge, and as more Na+ enters the cell, the inside of the cell becomes positively charged.

• At this threshold, when the inside of the cell membrane has become positive, the outside of the cell membrane will become negative, and this reversal of charges sweeps down the length of the cell membrane, like a wave of electricity. This is the action potential. This is how one neuron stimulates a cell (a muscle cell, gland, or another neuron).

• If the neuron stimulates a muscle cell, it contracts. If it stimulates a gland, it secretes. If it stimulates another neuron, the action potential is carried further along the nerve pathway, until it reaches the target organ.

Functional Classification of Neurons• Neurons are grouped functionally according to the

direction the nerve impulse travels relative to the CNS.• Sensoroy Neurons (afferent neurons) transmit impulses

toward the CNS. They originate in the PNS and terminate in the CNS.

• Motor Neurons (efferent neurons) transmit impulses from the CNS to effector organs (muscles and glands). They originate in the CNS and terminate in the PNS.

• Interneurons (association neurons) connect sensory neurons to motor neurons within the spinal cord and brain. They originate and terminate in the CNS, and form complex neuronal pathways. They make up 99.98% of the neurons in the body, reflecting the vast amount of information processed in the CNS.

Sensory Input and Motor Output• Sensory (afferent) neurons are those that pick

up sensory signals from receptors in the fingers, toes, etc– Bundles of the same kind of sensory neurons travel

together as NERVES, and go from the PNS to the CNS

• Motor (efferent) neurons originate in the brain, and the signals are carried away from the CNS and go to the muscles and glands.

Neurons Classified by Function: Sensory vs. Motor Neurons

Figure 12.11

Sensory neurons enter the spinal cord. Motor neurons leave the spinal cord. Interneurons connect the sensory and motor neurons.

Neurons are only one type of cell; there are others, which are supporting cells, with a special name:

GLIA (neuroglia, meaning “nerve glue”) are the supporting cells of the nervous system. These are only brain cells that can reproduce. Since cancerous cells are those that reproduce, all brain tumors originate from glial cells.

There are four types of glial cells that we will cover: 1. Oligodendrocytes2. Schwann cells3. Astrocytes4. Microglia

Types of Glial Cells

1. OLIGODENDROCYTES (“few branches”). They are found only in the CNS, are very large and complex cells. Oligodendrocytes form MYELIN SHEATHS. This sheath is a covering around an axon to speed up the nerve conduction.

• The action potential jumps BETWEEN Nodes of Ranvier (it skips the bare areas), speeding up the overall nerve conduction.

• Therefore, a myelinated axon conducts impulses faster than an unmyelinated axon.

MULTIPLE SCLEROSIS is an autoimmune disease where the oligodendrocytes (the myelin sheaths) are destroyed (axon demyelination), interfering with the neuron functions in the CNS. Oligodendrocytes cannot regenerate.

MS is the most common neurological disease of young adults. Starts to manifest in late teens and early 20’s.

It progresses to paralysis and sometimes death. One in 1000 people get it. There are treatments, but no

cure.

2. SCHWANN CELL is another cell that forms myelin sheaths, but in the PNS. Each cell only forms one myelin sheath.

One cell may form 3 nodes, another cell may form 2 nodes

One cell always forms only one node.

Difference between oligodendrocytes and Schwann cells

Found in CNS only Found in PNS only

3. ASTROCYTE is another very large, complex cell, in the CNS. Its function is to wrap around capillaries while it also is physically supporting and wrapping around neurons.– Physically supports the neurons– Transmits materials from capillaries to neurons– Forms blood-brain barrier (BBB)

Supporting Cells in the CNS

Figure 12.12a

Blood-Brain-Barrier• The BBB prevents a lot of certain types of materials from

leaving the blood and entering the brain (e.g. hormones, drugs).

• The brain still gets its nourishment from the blood, without the toxins.

• The continuous capillaries have leakage, but are surrounded by astrocytes, so not everything can leak out.

• Certain antibiotics can’t cross the BBB, so they can’t be used for brain infections.

• The only function of the blood-brain barrier is to help protect the central nervous system.

4. MICROGLIA (one word, two errors!). These are not micro, nor are they glia.

They are macrophages, the same size as everywhere else in the body.

They are called micro because they are much smaller than real glia cells.

They pick up bacteria and dead cell, etc.

Supporting Cells in the CNS

Figure 12.12b

TERMINOLOGY

•GREY MATTER: that portion of the CNS that is unmyelinated (cell bodies of neurons, some types of glia (neuroglia), and dendrites)•WHITE MATTER: that portion of the CNS with myelinated axons; the myelin makes the area look white.•NERVE: collection of axons in the PNS. No cell bodies, dendrites, or synapses; just axons.•TRACT: collection of axons in the CNS e.g. conveys information (axons) from the left to the right side of the brain.•SYNAPSES: Where information is processed. Most synapses are in the CNS

TERMINOLOGY

•GANGLION: A collection of cell bodies in the PNS•NERVE PLEXUS: A network of nerves (nerves don’t run by themselves, they go in groups)•MOTOR NEURON: Nerves that leave the CNS to effect a muscle or gland•SENSORY NEURON: goes from body to CNS, carrying sensory information.•INTERNEURON is a small neuron found only in the CNS; it connects two other neurons. There is a large number of interneurons in the CNS, this is what makes the CNS complex.

• MAJOR ANATOMICAL REGIONS OF THE BRAIN – Cerebrum– Diencephalon– Brain Stem– Cerebellum

CEREBRUM•The brain is divided into parts, and is bilaterally symmetrical. •In general, the left side controls the right half of the body, and the right side of the brain controls the left half of the body. •The largest portion is the CEREBRUM, which makes up 80% of the brain. •The cerebrum controls logical thought and conscious awareness of the environment.•It is also the area responsible for the highest sensory and motor activity. •The cerebrum is made up mostly of grey matter (cell bodies, dendrites, and unmyelinated axons).

The Cerebral Hemispheres and lobes

• The FRONTAL LOBE and PARIETAL LOBE are separated by the CENTRAL SULCUS.

• The TEMPORAL LOBE is between the parietal and frontal lobe, separated by the LATERAL SULCUS.

• The OCCIPITAL LOBE does not have a real border; it’s just a region.

• These are the anatomical areas, but the functional areas are more important.

Central sulcus

Lateral sulcus

CORPUS CALLOSUM

• The CORPUS CALLOSUM is the area that connects the right and left halves of the brain.

DiencephalonConsists of two parts:• Thalamus• The superior portion of the diencephalon• Processes sensory information according to importance• Major relay station for sensory impulses to the cerebrum

• Hypothalamus– The inferior portion of the diencephalon– Provides homeostatic control over the body (maintains the

homeostasis of the body)– Controls hunger/thirst body temperature

THALAMUS

•The THALAMUS functions to sort out all the sensory information. •It compares the input and determines what information is worth sending to the cortex. •Your body ignores most sensory information.•Up until now, have you noticed the sound of the air conditioner? It’s not important, so it goes unnoticed. •This area also compares information from the right and left eyes for stereoscopic vision, and the right and left ear to determine direction of sound.

Pituitary gland

Hypothalamus

Thalamus

HYPOTHALAMUSThis small area exerts more control over autonomic functioning

than any other part. Provides homeostatic control over the body (maintains the

homeostasis of the body)• It maintains homeostasis by controlling the autonomic

nervous reflexes, glucose and hormone levels. • It is also the main visceral control center, so it controls

body temperature, hunger and thirst, and blood pressure.

The hypothalamus is part of the limbic system, so that’s why a painful memory can increase blood pressure.

• BRAIN STEM– MIDBRAIN– PONS– MEDULLA OBLONGATA

Midbrain• The top of the brain stem is the MIDBRAIN. • It controls automatic behaviors (fight or flight) • The midbrain also contains a pigmented area called the

substantia nigra.• The Substantia nigra is involved in addictions and in initiating

body movement. • The substantia nigra secretes the neurotransmitter dopamine.• When the neurons in the substantia nigra become damaged,

dopamine levels decrease, causing Parkinson's Disease.• Treatment is to replace the dopamine

Dopamine• Remember that acetylcholine is the neurotransmitter that

functions to contract skeletal muscles?• There are many other types of neurotransmitters as well. One is

called dopamine.• Dopamine is the neurotransmitter that controls the flow of

information between various areas of the brain. • Dopamine is lacking in Parkinson's Disease, in which the

person has muscular rigidity and tremors, so they lose the ability to start movements. They need a service dog to help them get out of a chair or to take a first step. They have a pill-rolling tremor at rest.

Pons

Farther down the brainstem is the PONS, which relays sensory information between the cerebellum and cerebrum.

Pons

Midbrain

Medulla Oblongata

Medulla Oblongata

• At the base of the brainstem is the MEDULLA OBLONGATA, which contains areas for heart rate, blood pressure, and breathing.

• Damage here causes coma. Swelling from an injury causes pressure, which can damage this area, which can cause a coma.

• Concussions cause nausea and a decrease in blood pressure; patients with these symptoms need an MRI to see if this is early signs of damage to medulla oblongata

• Boxers who are knocked out can recover, but repeated knock-outs can cause permanent brain damage.

PINEAL BODY

• The PINEAL BODY secretes melatonin.• How much it secretes depends on the sensory

information it receives from the eyes about how many hour of daylight are present.

• The amount of melanin secreted and circulating in the blood then determines the circadian rhythm, or the biological clock (cycles influenced by light).

• Therefore, the pineal body detects the number of hours of light and dark, and sets the body’s 24-hour clock.

ThalamusPineal body

Pineal body

CEREBELLUM

• The cerebellum is the second largest portion of the brain, is responsible for balance and muscle coordination, and is a comparator.

FUNCTIONAL REGIONS

• A. MOTOR AREAS• B. SENSORY AREAS • C. HIGHER FUNCTIONS

MOTOR AREAS

• PRIMARY MOTOR CORTEX • PRIMARY MOTOR ASSOCIATION AREA

CORTEX AND ASSOCIATION AREAS• Each area of the brain has a region where the

sensory information comes in, and another area where the information is understood.

• The area where the information comes in is a cortex, and the area where it is understood is the association area.

• Therefore, there will be a motor cortex and association area, a visual cortex and association area, an auditory cortex and association area, and a somatic (sense of touch) cortex and association area.

MOTOR AREAS

• 1. PRIMARY MOTOR CORTEX • 2. PRIMARY MOTOR ASSOCIATION AREA

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PRIMARY MOTOR CORTEX

Contains UPPER MOTOR NEURONS, which extend down the spinal cord and synapse on LOWER MOTOR NEURONS which then leave the spinal cord to innervate every skeletal muscle.

Some muscles have more motor units than others (hands, eyes, etc).

Upper and Lower Motor Neurons

Figure 12.11

Lower motor neuron is here. The upper motor neuron comes down from the brain and synapses on this neuron.

PRIMARY MOTOR ASSOCIATION AREA

Located just anterior to the primary motor cortex.

A. Learned motor skills: these are preprogrammed skills, like when you know how to type or swing a golf club. You practiced it so often, it’s now automatic.

– When someone asks you how to spell a word, but you can’t do it until you write it out, it’s because that memory is now a motor skill.

– The same happens when you know how to tie your own shoelace or necktie, but can’t tie another’s; it initially is learned by repetition.

– Then, to do it later triggers a series of information which turns on those muscles in the right order.

PRIMARY MOTOR ASSOCIATION AREA

B. Planning movement: This is when you plan to reach for a new item.

You have not rehearsed it, but you know to extend your forearms, lift, etc.

A signal is sent to the primary motor cortex to turn on specific motor units to do that.

Damage from a stroke= loose function to that area, but you can compensate by using other muscles, and re-learn that movement.

Pre-Central Gyrus

Pre-Central Gyrus• Within the primary motor area of the brain, there is a structure called the

pre-central gyrus which contains a precise map of the different body parts.• This map is called a motor homunculus (Latin: little man)• All the neurons that innervate the lips would have their cell bodies in one

particular region in this area. All the neurons that innervate the hands have their cell bodies in this area. All those that innervate the back have their cell bodies here.

• However, we don’t have as many neurons innervating the back as we do for the lips and hands.

• The homunculus is drawn to represent how many neuron cell bodies we have that innervate each region of our body.

FUNCTIONAL REGIONS

• A. MOTOR AREAS• B. SENSORY AREAS • C. HIGHER FUNCTIONS

SENSORY AREAS

• PRIMARY SOMATOSENSORY CORTEX Somatic = touch

• SOMATOSENSORY ASSOCIATION AREA • PRIMARY VISUAL CORTEX • VISUAL ASSOCIATION AREA

• PRIMARY AUDITORY CORTEX • AUDITORY ASSOCIATION AREA

SOMATOSENSORY AREAS

1. Primary somatosensory cortex2. Somatosensory association areaThe primary somatosensory cortex receives

signals for touch and pressure. The somatosensory association area interprets the sensation. When I put my hand in my pocket, I know that is my keys I am feeling.

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VISUAL AREAS

1. Primary visual cortex2. Visual association areaThe primary visual cortex receives signals from

the optic nerves.The visual association area interprets the signals. When I look at my keys, I can identify them as keys.

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VISUAL ASSOCIATION AREAWithin the visual association area is a region called Brodmann areas

18 +19. Damage to this area results in an inability to recognize what one

sees. The person can see a chair in their way, move around it, but they

can’t identify the object as a chair. Some people with this damage can’t distinguish one person from

another because they can’t recognize their faces.For more information on these types of brain damages, there’s a

book called The Man Who Mistook his Wife for a Hat.

HEARING AREAS

1. Primary auditory cortex2. Auditory association areaThe primary auditory cortex receives signals from

the ear.The auditory association area interprets the signals. When I hear a sound, I can tell you what it is that I am hearing.

1 2

Auditory Association Area• The auditory association area contains two special regions• BROCA'S AREA is a region of the brain that allows for

speech.– Injury (stroke) in this location causes impairment of

speaking certain words. They know what they want to say, they just cannot get the words out. Not being able to speak at all is called aphasia.

• WERNICKE’S AREA is the region of the brain that allows understanding of words.

• It does not affect a person’s speech.• They can say what they want to, but they cannot comprehend someone else’s speech.

FUNCTIONAL REGIONS

• A. MOTOR AREAS• B. SENSORY AREAS • C. HIGHER FUNCTIONS

• For a great video of a neurologist describing what it felt like when she had a stroke:

http://www.ted.com/talks/lang/eng/jill_bolte_taylor_s_powerful_stroke_of_insight.html

HIGHER FUNCTIONS

1. PLANNING AND JUDGMENT2. MEMORY3. EMOTIONS

PLANNING AND JUDGMENT• How much time do you need to be ready for the

test? This is calculated by the frontal lobe.• Damage to the frontal lobe causes people to

become docile and do what they are told. • 1930’s when people were overly aggressive,

they did a frontal lobotomy by going up the eyelid, crack through the skull, and stirring up the brain. The problem is that it permanently altered their personalities.

• Stopped in 1960’s; we do it with drugs now (Ritalin).

MEMORY: HIPPOCAMPUS

• We talked about motor memory. You can also have memory of events.

• This is controlled by the HIPPOCAMPUS (“sea horse”; that’s its shape). The hippocampus plays a major role in storing and retrieving memories.

• But memories are not stored there or in any other single site in the brain. They are stored throughout the brain, especially in the cerebral cortex.

Memory: Hippocampus

Hippocampus

Mammilary Bodies• A pair of small round bodies at the anterior end of

the fornix• Part of the diencephalon; they form part of the

limbic system. • They relay information (recognition memory) from

the hippocampus. They also add the element of smell to memories.

• Damage to the mammillary bodies due to thiamine deficiency or alcohol causes Wernicke-Korsakoff syndrome (anterograde amnesia)

Fornix

Sheep brain

Mammilary body

Fornix

Mammilary body

Fornix

• Carries signals from the hippocampus to the mammillary bodies.

ANTEROGRADE AMNESIA• Damage to the mammillary bodies or hippocampus;

they remember things before the injury occurred, but all new information is lost within minutes.

• Nemo’s fish friend, Dori, has this type of amnesia.• You can get around it by motor memory. Give an

amnesiac a new puzzle; they’ll do it in 30 mins. The next day, they don’t recognize the puzzle, but they do it in 20 mins, the next day in 10. Therefore, they are learning by motor memory. They can learn their route from home to the market by repetition. But they can’t make a detour, and if anything bumps them off track, they’ll be lost.

RETROGRADE AMNESIA• Retrograde amnesia is a form of amnesia where someone is

unable to recall events that occurred before the development of the amnesia.

• Retrograde amnesia is caused by trauma that results in brain injury.

• Retrograde amnesia is often temporally graded, meaning that remote memories are more easily accessible than events occurring just prior to the trauma.

• Events nearest in time to the event that caused memory loss may never be recovered.

• They can remember new things.

STROKES

• A hemorrhage in the brain (broken blood vessel) deprives an area of the brain of oxygen.

• This is called a stroke.• It is one of the most likely causes of amnesia. • Amnesia that is caused by a blow to the head is

not cured by a second blow!

ALZHEIMER’S DISEASE

• Dementia is a symptom, not a disease. Dementia is loss of memory.

• Alzheimer’s disease is the most common form of dementia.

• About 10% of people over the age of 65 and 50% of people over the age 85 suffer from it.

• It is irreversible, incurable, and fatal (6th leading cause of death in the USA, surpassing diabetes). The person dies because they can no longer eat, swallow, etc. There are treatments to delay symptoms.

EMOTIONS: LIMBIC SYSTEM

• The prefrontal lobe and the hippocampus are part of a system of structures in the brain.

• The LIMBIC SYSTEM also includes the olfactory nerves (sense of smell). Therefore, memory, emotion, and smell are linked.

• Crayolas are created today with the same scent because it reminds people of their happy times in childhood.

• Why is the brain formed so that smell and emotions are tied together?

• Because pheromones are tied to emotions and behavior, so they need the link.

The Limbic System(everything in orange)

Figure 13.23

Limbic System

• The limbic system includes the olfactory cortex (sense of smell), and portions of the diencephalon and cerebrum

• It influences emotions, motivations, and mood• It is functionally associated with the

hypothalamus• It initiates responses necessary for survival,

such as hunger and thirst.

MENINGES• These are tissues that cover the entire CNS.

They are three layers that serve to protect and cushion the brain.

Meninges 1. DURA MATER is the thickest and most superficial of the

meninges. 2. ARACHNOID MATER is the middle layer and is not nearly as

dense. It also does not go down into the sulci, it only covers over the top of the gyri.

3. PIA MATER is the thin, shiny layer that DOES follow the brain surface into the sulci.

• SUBDURAL SPACE is between the dura mater and the arachnoid mater.

• The SUBARACHNOID SPACE is between the arachnoid and pia mater, and is filled with CEREBRAL SPINAL FLUID (CSF).

1. DURA MATER (“Tough mother”)Dense regular connective tissue. It consists of two layers. Under the skull is the first layer of dura mater, called the

PERIOSTEAL LAYER. Just under this is the second layer, called the MENINGEAL LAYER. There are these two layers everywhere except around the spinal cord, where it’s just one layer, the meningeal layer of the dura mater; no periosteal layer.

Between the meningeal and periosteal layers of the dura mater are DURAL SINUSES, which are filled with venous blood which is drained from the brain.

Dural sinus and subarachnoid space

Clinical Significance• In the spinal cord, between L3 and L4, a doctor can

inject anesthetic above the dura mater, so only the nerves are affected. What is that called?

The dura and arachnoid mater both have lots of blood vessels, which might rupture in an injury, called a SUBDURAL or SUBARACHNOID HEMORRHAGE, which is potentially fatal. Blood accumulates and squeezes the brain.

Treatment = drill a hole.

Epidural.

VENTRICLES OF THE BRAIN • The brain and spinal cord are hollow, filled with CSF = ventricles They are

extensive. The names are simple.• LATERAL VENTRICLE is the largest, extends throughout the cerebrum.• THIRD VENTRICLE: in a sheep, it forms a figure “3” under the fornix and

around the corpora quadrigemina. In a human model, it looks like a cavity between the fornix and a red arch.

• FOURTH VENTRICLE is at the base of the cerebellum; it is continuous with the central canal of the spinal cord, and also with the subarachnoid space.– CEREBRAL AQUEDUCT: connects the 3rd and 4th ventricles.

• The ventricles, subarachnoid space , and cerebral aqueduct are filled

with CSF. The subdural space is NOT filled with CSF; it is filled with venous blood.

Figure 13.6a, b

VENTRICLES OF THE BRAIN (blue)

CerebroSpinal Fluid (CSF)

• CSF is similar to plasma because it is derived from plasma.

• CSF is made in the ventricles by a group of capillaries called the CHOROID PLEXUS.

• The choroid plexus capillaries have holes that allow the blood plasma to leak into the subarachnoid space. It is now called cerebrospinal fluid (CSF).

CerebroSpinal Fluid (CSF)• The CSF that has been depleted of its nutrients is absorbed back

into the blood through the ARACHOID GRANULATIONS. • Arachnoid granulations are small protrusions of the arachnoid

mater (the thin second layer covering the brain) through the dura mater (the thick outer layer).

• They protrude into the venous sinuses of the brain, and allow cerebrospinal fluid (CSF) to exit the brain, and enter the blood stream.

• 800ml of CSF is made per day, but there is actually only 150 ml there because the extra is continually absorbed in the dural sinus through the arachnoid villa, which are valves that release the CSF back into the blood.

PROBLEMS WITH MENIGES• HYDROCEPHALY is accumulation of CSF inside the ventricles.• It is usually congenital, caused by a blockage of the cerebral

aqueduct. The CSF is made but can’t leave, and the brain gets expanded.

• The skull bones in a newborn can expand, so although it CAN damage the brain, it does NOT cause mental retardation. The head becomes enlarged.

• Treatment is to put in a tube to drain it.• Hydrocephaly in adults can be caused by a tumor, and since the

skull no longer expands, it’s very dangerous.

MENINGITIS• Meningitis is inflammation of the meninges. • Can be caused from bacteria (can be fatal in 24 hours) or virus

(fatal in a week or more). • The main symptom is a headache, so when this occurs in an

infant, they can’t say where they hurt. • So when an infant presents with a high fever of 104˚ with no

other symptoms, they might test for meningitis, because if they miss it, it’s fatal.

• The test is a SPINAL TAP, where a needle is inserted between L4 and L5 because that is below the level of the spinal cord.

• They draw the CSF to look at. It it’s cloudy or bloody, it’s usually meningitis. Untreated meningitis can lead to this next one:

ENCEPHALITIS• This is inflammation of the brain. • It can be caused by mosquito-borne illnesses, or

bacteria. • Why is infection of the brain so dangerous? The

swelling crushes the brain. • Any injury may lead to brain swelling.• Treatment is to remove a piece of the skull

bone to allow the swelling.

The 12 Pairs of Cranial Nerves

Figure 14.8

I. Olfactory Nerves

• Sensory nerves of smell

Table 14.2

II. Optic Nerve

• Sensory nerve of vision

Table 14.2

III Occulomotor Nerve

• This controls most of the extrinsic muscles of the eye (that move the eyeball).

• They also have parasympathetic innervation in the iris (pupil) and cilliary muscles (controls the lens).

IV. Trochlear Nerve

• Innervates an extrinsic eye muscle

Table 14.2

V. Trigeminal Nerve

• This is the main sensory nerve of the face. It has a large branch that passes through the foramen ovale of the skull. It has three parts.

• When a dentist numbs the lower teeth, he injects the mandibular branch. For the upper teeth, he injects the maxillary branch.

• The superior branch is the opthalmic branch.• Problems with CN-V are called TRIGEMINAL

NEURALGIA, which is excruciating pain in the face from nerve inflammation.

V. Trigeminal Nerve

Table 14.2

VI. Abducens Nerve

• Abducts the eyeball

Table 14.2

VII Facial Nerve

•This innervates the muscles of facial expression.•A person who cannot blink or smile may have damage to this nerve. •Someone with a damaged facial nerve can not easily taste sweet, sour, or salty substances.•It also supplies parasympathetic innervation to most salivary glands. •BELL’S PALSY is damage of the facial nerve causing paralysis on one side. The nerves swell from infection by herpes simplex virus, but only the motor nerves are involved, not the sensory, so it’s painless. Needs to be distinguished from a stroke.

VII. Facial Nerve• Innervates muscles of facial expression

Table 14.2

VIII. Vestibulocochlear Nerve• Sensory nerve of hearing and balance

Table 14.2

IX: GLOSSOPHARYNGEAL• Along with CN X, the Glossopharyngeal nerve

carries information from the baroreceptors in the head and neck to the brainstem.

• Baroreceptors sense how much arteries are being stretched, and use this to measure the blood pressure so the brain can adjust BP as needed.

• Signals the pharynx to constrict (along with CN-X) during swallowing.

Baroreceptors

• Baroreceptors are sensors located in the blood vessels of the human body. They detect the pressure of blood flowing through them, and can send messages to the central nervous system to increase or decrease total peripheral resistance and cardiac output.

• Baroreceptors act immediately as part of a negative feedback system (called the baroreflex) as soon as there is a change from the usual blood pressure, returning the pressure to a normal level.

• Baroreceptors detect the amount of stretch of the blood

vessel walls, and send the signal to the nervous system.

IX. Glossopharyngeal Nerve• Innervates structures of the tongue and

pharynx

Table 14.2

X Vagus Nerve• (vagrant = “wanders”). • 90% of all parasympathetic fibers are in this cranial nerve. • This is the only cranial nerve that travels into the abdomen. • This is the most important cranial nerve because it innervates

all of the organs in the thoracic and abdominal cavities: heart, lungs, GI tract, etc, with parasympathetic innervation.

• It also moves the larynx during speech and signals the pharynx to constrict (along with IX) during swallowing.

• The majority of the parasympathetic outflow from the head is by the vagus nerve.

X. Vagus Nerve

• A mixed sensory and motor nerve The only cranial nerve

that “Wanders” into thorax and abdomen

Table 14.2

XI: ACCESSORY NERVE

• Enters the skull through foramen magnum and leaves through the jugular foramen.

• It just supplies the shoulder muscles.

XI. Accessory Nerve• An accessory part of the vagus nerve

XII. HYPOGLOSSAL NERVE

• Supplies the tongue. • Damage causes impairment of speech.

XII. Hypoglossal Nerve• Runs inferior to the tongue– Innervates the tongue muscles

Table 14.2

Need to know all of the cranial nerves

• Hint: use the first letter of each nerve to make a sentence: “OOOTTAFVGVAH”. OOO, Tommy Turtle Always Finds Vegetable Gardens Very Attractive, Heavenly!

Spinal Cord Cross Section

Dorsal root Dorsal root

Ventral root

Dorsal root ganglion

Ventral horn

Dorsal horn

Ventral horn

Dorsal root ganglion

Dorsal root

Posterior median sulcus

Dorsal horn

White matter

Grey matter

Central canal

Ventral root

Anterior median fissure

White Matter

• White matter of the nervous system forms conduction pathways called NERVE TRACTS.

• The white matter in each half of the spinal cord is organized into three columns:– Dorsal (posterior) column– Ventral (anterior) column– Lateral column

• Each column has ascending tracts, which consist of axons conducting impulses toward the brain and descending tracts, which consist of axons conducting impulses away from the brain.

1 1

2 2

33

1. Dorsal (posterior) column2. Ventral (anterior) column3. Lateral column

Terms• GANGLION is the term for a group of neuron

cell bodies (both sensory and motor) found in the peripheral nervous system only.

• SENSORY NEURONS come in (via the spinal nerve) through the dorsal root; their cell body is in the dorsal root ganglion, and its axon goes into the dorsal horn and synapses in the grey matter.

• It also sends a branch to an area of the white matter called the DORSAL COLUMN PATHWAY, which goes into the brain (thalamus).

Neurons Classified by Function

Figure 12.11

Upper motor neuron

Dorsal column pathway

Lower motor neuron

Terms• LOWER MOTOR NEURONS have their cell body in the ventral horn, their

axon goes out the ventral root, and synapses in a skeletal muscle. Symptoms of a lower motor neuron disorder is when the patient has paralysis including their reflexes.

• UPPER MOTOR NEURONS have their cell body in the brain, and they synapse on a lower motor neuron. Symptom of an upper motor neuron disorder is when the patient cannot move their hand (paralysis) but reflexes work

• INTERNEURONS: These are found in the brain and spinal cord. The ones in the spinal cord have their cell bodies in the dorsal half of the gray matter. They receive signals from the sensory neuron and then synapse on the cell body of the motor neuron. In this way, the interneurons (sometimes called association neurons) transmit signals from the sensory pathways to the motor pathways. The complexity of the CNS can be attributed to the large number of interneurons in the CNS.

Spinal Cord Reflexes• Stretch Reflex (knee-jerk; patellar reflex)– Muscle contracts in response to a sudden stretch force

(with a reflex hammer).– After a severe spinal cord injury, all spinal reflexes are lost

below the level of the injury for 2 weeks. Then the patellar reflex returns but it is often exaggerated (hyper-reflexic), indicating damage is still present.

• Withdrawal Reflex– The body part is quickly removed from a painful stimulus.– Sensory neurons carry the information to the spinal cord, and the

muscles remove the limb immediately, before the brain receives the pain information.

Sensory Tracts

• Now the signal has to go to the brain via a TRACT.• A tract is a collection of axons inside the central

nervous system. • Sensory axons send a branch to the thalamus

portion of the brain. • SENSORY TOUCH SPINAL NERVE POSTERIOR

ROOT POSTERIOR ROOT GANGLION POSTERIOR HORN TRACT THALAMUS

Tracts to the Brain• These tracts have various names, depending

on what types of neurons are traveling within them.

• For example, the SPINOTHALAMIC TRACT transmits pain and temperature.

• The SPINOCEREBELLAR tract transmits signals of balance and position to the cerebellum.

• There are many other tracts as well. Some tracts send sensory information to the brain, and some tracts send motor commands from the brain to the muscles.

SOMATIC MOTOR NEURON• Sends commands to the skeletal muscle to

contract. • When the nerves leave the spinal cord, they

travel together in what is called a plexus. One of these is known as the brachial plexus (in the armpit; innervates the muscles of the upper extremity).

• Starting at the spinal cord and preceding laterally, the subdivisions of a plexus start out in the ROOTS (RAMI), then form a TRUNK, which then branches into DIVISIONS, which then become CORDS, which become the plexus.

Upper and Lower Motor Neuron Diseases

• Some diseases only effect the UMN, and some only effect the LMN.

• Lower motor neuron disorders: – Multiple Sclerosis– Polio

• Upper motor neuron disorder:– Cerebral palsy

• Upper and Lower motor neuron disease– ALS

Amyotrophic Lateral Sclerosis (ALS)• Also known as Lou Gehrig's disease• Physicist Stephen Hawking also has this disease.• A progressive motor neuron disease. • The disorder causes muscle weakness and atrophy throughout the body

as both the upper and lower motor neurons degenerate, ceasing to send messages to muscles.

• The muscles gradually weaken, develop fasciculations (twitches) because of denervation, and eventually atrophy .

• Eye muscles are usually spared.• Cognitive function is generally spared.• Death usually occurs in 2-4 years, although Stephen Hawking has had it

for the longest period of time, almost 50 years.

PROPRIOCEPTION NEURONS• Sensors within the muscles that measure the amount of force

and movement (sensory). • Proprioception neurons travel up the spinocerebellar tract.

The brain can then interpret whether you are off balance, then send a command to the muscles to contract and straighten yourself up so you don’t fall.

• Note that this sense of balance is NOT the same as the sense of balance from equilibrium in the ears. Proprioception neurons are located within the muscles.

• During a physical exam, a doctor will test the patient’s proprioception ability by telling them to close their eyes and place their finger on their nose. This may indicate a lesion in the cerebellum. Who else may ask you to do this test? Alcohol disrupts the cerebellum.

Proprioceptors•Sensory receptors that report on internal events in your muscles and joints.

•They report on muscle stretch and joint position.

•They generate electrical impulses that will travel up neurons to the CNS.

Proprioception Disorders

• Damage to proprioceptors can occur from consuming excess vitamin B6 (pyridoxine).

• Patients cannot tell where their body parts are unless they look at them.

• They have difficulty with all motor tasks including walking, eating, dressing, etc.

• They must use their vision to watch each body part to make it move in the right direction.

Structure of a Nerve

Figure 12.16a

Each neuron is surrounded by a sheath called the endoneurium. Some axons have an additional sheath called myelin.

A bundle of neurons travel together in a fascicle, and are surrounded by perineurium.

A bundle of fascicles is surrounded by epineurium

DAMAGE TO THE NERVOUS SYSTEM

• If a person has a spinal cord injury in their cervical region, they could have quadriplegia (arms and legs paralyzed).

• If a person has a spinal cord injury in their thoracic region, they could have paraplegia (just legs are paralyzed).

SOME CLINICALLY IMPORTANT PERIPHERAL NERVES:

• Note: an epidural nerve block during child birth will numb the mother from her navel to her knees.

• PUDENDAL NERVE: this is the nerve that can be anesthetized during childbirth as an alternative to an epidural (a pudendal nerve block is also called a saddle block because the numb areas are where you would be touching a saddle).

• PHRENIC NERVE: allows the diaphragm to contract. If it gets severed, the person can no longer breathe without assistance.

Nerve Plexus

A PLEXUS is a network of nerves that primarily serves the limbs. There are four major plexi: cervical, brachial, lumbar, and sacral.

1. CERVICAL PLEXUS comes out of the neck and are cutaneous nerves (sensory input of the skin) of the neck and back of the head.

BRACHIAL PLEXUS

2. BRACHIAL PLEXUS• This is the major group of nerves that supply

the upper limbs. It runs through the axilla. • If a person leans their armpits on their

crutches, they can damage this plexus and lose the use of their arms.

• The nerves in the brachial plexus change names as they go to different regions in the arm.

Major Nerves of the Upper

Extremity

Axillary

Musculocutaneus

Axillary Nerve

• Deltoid

Musculocutaneus Nerve

• Supplies anterior muscles of the arm

Median Nerve

• Supplies no muscles of the arm• Supplies anterior forearm (except flexor carpi

ulnaris)• Carpal Tunnel Syndrome– Hand of benediction

Carpel Tunnel Syndrome

• The median nerve travels under the transverse carpal ligament.

• The nerve is pinched in carpal tunnel syndrome.

MEDIAN NERVE

• This is the nerve that gets cut when people try to slit their wrists.

• The arteries are so small in the wrist; people rarely die from this type of suicide attempt. However, they live with a lot of tissue damage. They are not able to move the thumb towards the little finger, so it is hard to pick up small objects. This is called “ape hand”.

Ulnar Nerve

• Supplies flexor carpi ulnaris• “Funny Bone”• Damage can cause claw hand; cannot adduct

or abduct fingers

Radial Nerve

• Supplies muscles on the posterior arm and forearm

• Damage can cause wrist drop

Carpel Tunnel Syndrome

Axillary, Radial, Ulnar, Median Nerves

Figure 14.4

Brachial Plexus

• Damage to Brachial Plexus– Klumpke’s paralysis (brachial plexus damaged during

birth)– Acquired Brachial Plexus injuries• Crutch paralysis (total upper extremity paralysis)• Claw Hand / Ape hand • Hand of benediction • Wrist Drop (Waiter’s Hand)

LUMBAR PLEXUS

3. LUMBAR PLEXUS• FEMORAL NERVE is the main nerve to the

anterior thigh.

Sacral Plexus4. SACRAL PLEXUS Some of the fibers from the lumbar plexus mix with the sacral

plexus, so these are often referred to together as the lumbosacral plexus.

• SCIATIC NERVE is the largest branch of the sacral plexus and the largest nerve in the body; it leaves the pelvis through the sciatic notch.

• A short, thick muscle (Piriformis muscle) covers the sciatic notch, and when it contracts, it can pinch the sciatic nerve, causing a type of sciatica (sciatic nerve irritation) known as piriformis syndrome.

• This can be alleviated by stretching exercises. However, sciatica can also be caused if there is a herniated lumbar disc, in which case stretching exercises make it worse.

Nerves of the Lower

ExtremityFemoral

Obturator

The sciatic nerve supplies the back of the thigh, then branches out into the TIBIAL and FIBULAR (peroneal) nerves, which supply the leg and foot.The fibular nerve branches into superficial and deep.

Lower Extremity NervesObturator Nerve

Supplies adductor musclesSciatic Nerve

Supplies back of thigh, leg and footFemoral Nerve

Supplies anterior ThighTibial Nerve

Supplies posterior leg and footCommon Fibular Nerve

Superficial branch Supplies lateral side of leg

Deep branchSupplies anterior leg Injury causes “Foot Drop”

Tibial Nerve

• Sometimes a small branch of the tibial nerve in the foot gets pinched between the metatarsal heads, and the irritation causes nerve swelling and pain.

• It is called a neuroma (“nerve tumor”) and manifests as pain in the ball of the foot, made worse with high heels.

• An injury to the fibular nerve may result in “foot drop”, where the foot cannot be dorsiflexed.

AUTONOMIC NERVOUS SYSTEM

• We don’t have voluntary control over these nerves.

• They are involved digestion, blood flow, urination, defecation, glandular secretion.

• Therefore, the ANS supplies the glands, smooth muscle, and cardiac muscle, but NOT the skeletal muscle.

• For this reason, the ANS is also called the general visceral motor system.

ANS

• All of the neurons of the ANS are motor neurons (there are no sensory neurons in the ANS).

• The ANS differs from the CNS reflex arc because the ANS has two lower motor neurons in the periphery (the cell body of one is in the spinal cord and the cell body of the other is in the periphery), whereas the CNS has one lower motor neuron, and its cell body is within the spinal cord, not in the periphery.

Ganglia

• The area where the two neurons come together is the AUTONOMIC GANGLIA.

• The first neuron is the PRE-GANGLIONIC NEURON.

• The second neuron is the POST-GANGLIONIC NEURON.

• Some of these ganglia (those in the sympathetic division of the ANS) are lined up along the vertebral column, called a structure called the sympathetic trunk ganglia.

ANS

• The ANS motor unit is characterized by having more than one lower motor neuron, the axons may be myelinated or unmyelinated, conduction is slow, and the axons are thin.

• The ANS has two divisions: sympathetic and parasympathetic.

ANS has TWO lower motor neuronsPreganglionic

neuron

Post-ganglionic neuron

Ganglion (where the cell bodies of the post-

ganglionic neurons are)

CNS has just one lower motor neuron

SYMPATHETIC DIVISION

• ↑heart rate and blood pressure, • ↑metabolic activity (increased blood

glucose), • decreased peristalsis (decreased food

digestion) • dilation of bronchioles• control of blood flow to the skin• sweating

Sympathetic Division

• E.g. when running, ↑heart rate = sympathetic.

• When hot sweat = sympathetic. • The term “Fight or Flight” is inaccurate; it

refers to the ↑ heart rate, etc, but the sympathetic division is also active when relaxing on a nice beach with a cool drink on a hot day, because whenever you’re sweating, that’s the sympathetic division.

ANATOMY OF THE SYMPATHETIC DIVISION

• The sympathetic neurons exit the spinal cord at the thorax and lumbar regions.

• The axons of most pre-ganglionic neurons in the sympathetic division are fairly short, and they synapse quickly on a ganglia.

• All these ganglia together are the SYMPATHETIC TRUNK (CHAIN) GANGLIA.

• Therefore, the postganglionic cell bodies of the sympathetic nervous system are in the chain ganglia.

• There are also nerves that connect the ganglia to each other.

Sympathetic Division

In Sympathetic division, preganglionic axons are SHORT because they terminate in ganglia that are close to the spinal cord

That means the post-ganglionic axons are LONG, because they have to reach all the way to the target muscle.

Sympathetic Division

• The axons of POST-GANGLIONIC NERVES are very long, and go to the target organs.

• Some pre-ganglionic neurons bypass the sympathetic chain ganglia and go directly to the abdomen.

• They create a group of ganglia in the abdomen called the SOLAR PLEXUS (“sun”). When you get punched in the abdomen, you are punched in the solar plexus, and get the wind knocked out of you.

PARASYMPATHETIC DIVISION

• Unlike the sympathetic division, the axons of the preganglionic neurons of the parasympathetic division are long, and the axons of the postganglionic neurons are short.

• The nerve cell bodies (peripheral ganglia) of the parasympathetic division are closer to the organs being innervated than in the sympathetic division.

• In fact, the cell bodies are either next to or inside of the target organs. Therefore, they have short post-ganglionic fibers.

Parasympathetic Division

In the Parasympathetic division, preganglionic axons are LONG because they terminate in ganglia that are close to the target organ

That means the post-ganglionic axons are SHORT

PARASYMPATHETIC DIVISION

• Involved in vegetative activities, such as digestion, urination, defecation

• Has postganglionic cell bodies in terminal ganglia, located either near or within target organs

• Has both preganglionic and postganglionic neurons that secrete acetylcholine

• Has preganglionic cell bodies located in the cranial and sacral areas.

Parasympathetic Division

• The function of this division is often antagonistic (opposite) of the sympathetic, but actually, they work together.

• The parasympathetic division inhibits cardiac contraction, so there is: ↓heart rate, constricts bronchioles, activates digestive system, and causes salivation, urination, and defecation.

• When you are lounging on the beach, the heart rate decreases (parasympathetic), but the sweat increases (sympathetic).

Vagus Nerve

• The parasympathetic neurons come out of either the brain or the sacral region of the spinal cord.

• The majority of the parasympathetic outflow from the head is by the vagus nerve.

Vasovagal Syncope (Fainting)

• The most common type of fainting.• After a stressful trigger, the parasympathetic nervous

system is enhanced by the Vagus nerve.• The heart rate speeds up, then suddenly drops. • Then the blood pressure drops.• Unconsciousness results.• Treatment: elevate the legs above the heart for a few

minutes, and make sure the airway remains open.• A cold, wet cloth on the forehead and back of the neck

may make the person feel better as they recover.

VISCERAL (“organ”) SENSES

• A visceral nerve innervates involuntary effectors (smooth muscles in organs).

• A somatic motor nerve innervates voluntary effectors (skeletal muscle). – (don’t confuse this with a somatic sensory nerve for

the sense of touch; sensory nerves are not part of the ANS)

VISCERAL (“organ”) SENSES

• Internal organs also have sensory nerves that tell you when you have eaten enough or your bladder is full. These are not part of the ANS because they are sensory.

• Not all organs have sensory nerves, for instance, you can’t feel when you have high blood pressure.

• You can also have visceral reflexes, which trigger the parasympathetic system to contract the bladder when full, etc.

• Reflexes are hard to localize.

Referred Pain

• Pain in an organ may not be where the organ is.

• Heart pain usually manifests in the left side of chest, the left shoulder, arm, but not the heart.

• This is REFERRED PAIN. • Pain in the lungs usually shows up as neck

pain.• These areas of referred pain are important to

know, but not for this class.