The Nervous SystemCh. 12-17

The Nervous System Introduction Composed of

Brain Spinal Cord Nerves

2 Major Subdivisions CNS (Central Nervous System)

Brain, Spinal Cord PNS (Peripheral Nervous System)

Cranial and Spinal Nerves2 Major Subdivisions

Afferent incoming pathwaysEfferent Outgoing pathways

Neurons Remember neuron structure:

The Cell Body or Soma Contains a nucleus surrounded by cytoplasm along with

all other organelles found within a cell The Dendrites

Extensions from Cell Body/Soma Receives information

The Axon Single, long extension from Cell Body/Soma Branch out into telodendria and end at synaptic/axon

terminals

Structure of a Neuron

The Synapse Each synaptic/axon terminal is part of a

synapse Site where the neuron communicates with

another cellPresynaptic Cell: sends the message

(usually a neuron)Postsynaptic Cell: receives the message

(any cell type) After a series of electrical signals is

transmitted through the neuron, the axon/synaptic terminals release chemicals or neurotransmitters to the dendrite of another cell to continue the message

Synapse

Synaptic Cleft

Neuron Video http://www.youtube.com/watch?v=r71R

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Neuroglia Higher quantity and variation in CNS than

PNS Central Nervous System

1. Ependymal Cells2. Astrocytes3. Microglia4. Oligodendrocytes

Peripheral Nervous System1. Schwann Cells2. Satellite Cells

Ependymal Cells Line ventricles in

the brain and spinal cord

Aid in producing, circulating and monitoring of cerebrospinal fluid

Microglia Removes cell

debris, wastes, and pathogens by phagocytosis

CNS Neuroglia

Astrocytes Provide structural

support Regulate ion, nutrient,

and dissolved gas concentrations

Absorb and recycle neurotransmitters

Form scar tissue after injury

Oligodendrocytes Myelinate axons Provide structural

framework

CNS Neuroglia

Schwann Cells Surround all axons Responsible for

myelination Participate in

repair process after injury

Satellite Cells Surround neuron

cell bodies Regulate gas,

nutrient, and neurontransmitter levels

PNS Neuroglia

Synaptic ActivityMessages move from 1 location to another

in the form of action potentials along neuronsAlso known as nerve impulsesMessages move across the synapse

Can be electricalCan be chemical (use of neurotransmitter)

Electrical SynapsesPresynaptic and postsynaptic cell

membranes are locked togetherLocal electrical currents and

directly transferred from cell to cell = very rapid electrical impulse Efficient action potential transfer

from cell to cell

Chemical SynapsesPresynaptic and postsynaptic cell

membranes are NOT locked togetherMessage not guaranteed to be transferred

to the next cell dependent on the amount of neurotransmitters released Different neurotransmitters:

Acetocholyne: found at neuromuscular junctionNorepinephrine: excitatory effect, adrenalineDopamine: Parkinson’s disease (rigidity of

muscles) Serotonin: attention, emotion, responsible for

depressionGABA: reduce anxiety

Spinal Cord and Spinal NervesChapter 13

Spinal Cord Anatomy Posterior/Anterior/Lateral Horn of Gray matter Anterior Median Fissure Posterior Median Sulcus Spinal Nerve (Posterior/Anterior Roots) Spinal Ganglion

Spinal Cord Anatomy

Adult – 18 inches in length Only reaches down to L1-

L2 Spinal Meninges:

specialized membranes that surround the spinal cord Dura Mater Arachnoid Pia Mater

Bacterial or vial infections of the Meninges Meningitis

Meninges

Dura Mater Tough, fibrous

outermost layer Collagen fibers Covered with

blood vessels and adipose tissue

Epidural Space

Arachnoid Filled with

cerebrospinal fluid (SPF)—shock absorber

Spinal tap

Pia Mater Meshwork of

connective tissue Dense area of

vessels

Nerve Plexuses Complex interwoven network of nerves Plexus. 1. Cervical Plexus

1. C1-C5 (muscles of neck, thoracic cavity)2. Brachial Plexus

1. C5-T1 (muscles of pectoral girdle and upper limb)3. Lumbar Plexus

1. T12-L4 4. Sacral Plexus

1. L4-S4

Day 2

RefluxesChapter 13

Reflexes Rapid automatic responses to a specific

stimuli made by a receptor Preserve homeostasis Rapid adjustments

The Reflex Arc: wiring of a single reflex Beings at the receptor Ends at peripheral effector (ex: muscle

fiber)

Reflexes Sensory Receptors

Proprioreceptors: provide info about body position and muscle control

Vestibular Receptors: provide a sense of equilibrium

Cutaneous Receptors: touch, pressure, heat and cold

Photoreceptors: respond to light Chemoreceptors: respond to taste Nocioreceptors: pain receptors

Reflexes1. Arrival of a stimulus and activation of receptor (pain)2. Activation of a Sensory Neuron (action potential

along axons of neurons spinal cord)3. Information Processing (neurotransmitter released

and sensation related to brain)4. Activation of Motor Neuron (axons carry action

potential back towards the origin of pain)5. Response of Peripheral Effector (release of

neurotransmitter to skeletal muscle fiber contraction pulls hand away from pain)

http://www.youtube.com/watch?v=wLrhYzdbbpE

Reflexes Receptor Density

More dense the receptors = more “sensitive” the area Upon stimulation…

Phasic: receptors respond with an initial burst of action potentials and rapidly decrease, even though stimulus continues

Tonic: receptors firing at a constant rate as long as the stimulus is applied

1. Lab on reflexes

The Brain and Cranial NervesChapter 14

Human Brain Contains 98% of neural tissue Weighs about 3 lbs Covered by a neural cortex (superficial layer of

gray matter Main Areas

Cerebrum Cerebellum Diencephalon Brain Stem

Cerebrum Largest portion of the brain 2 hemispheres

Controls thoughts, sensations, intellect, memory, and complex movements

Lobes (correspond with cranial bones) Frontal Parietal Occipital Temporal

Cerebrum Landmarks

Longitudinal fissure (separates the 2 hemispheres)

Central Sulcus (separates the frontal from parietal lobes)

Lateral Sulcus (separates the frontal from temporal)

Parieto-occipital sulcus (separates the parietal from the occipital)

White Matter Dense region of axons

Cerebrum Motor and Sensory Areas

Frontal Lobe = Voluntary control of skeletal muscles

Parietal Lobe = conscious perception of touch, pressure, vibration, pain, temperature, and taste

Occipital Lobe = conscious perception of visual stimuli

Temporal Lobe = conscious perception of auditory and olfactory stimuli, speech

All Lobes = Integration and processing of sensory data and motor activities

stop

Cerebellum 2nd Largest portion of the brain 2 hemispheres 2 Primary Functions

Adjusting Postural muscles of the body Programming and fine-tuning movements

Other Major Regions of the Brain Diencephalon:

Thalamus: relay and processing centers for sensory information

Hypothalamus: emotions, autonomic function, hormone production, body temp regulation

Other Major Regions of the Brain Brain Stem :link between cerebrum and brain stem

Mesencephalon: aka “midbrain”; visual and auditory information

Pons: sleep & respiration Medulla Oblongata: regulate heart rate, blood pressure,

digestion

Ventricles of the Brain Chambers filled with cerebrospinal

fluid (CSF) Lateral Ventricles (2 in each

hemisphere of cerebrum) Third Ventricle Interventricular Foramen

(connection between the lateral ventricles and third ventricle)

Cerebral Aqueduct (connection between the third

ventricle and fourth ventricle) Fourth Ventricle

Narrows and opens into the spinal cord

Protection and Support Protected by

1. Bones of cranium: mechanical protection (car)

2. Cranial Meninges: anchor (seat belt)

Dura Mater: outer layer Arachnoid: middle layer Pia Mater: surface of brain

3. Cerebrospinal Fluid: cushions against shocks/jolts (air bag)

Cerebrospinal Fluid (CSF) Function:

Cushion Support Transport

nutrients/chemical messengers/waste products

Formation: Choroid plexus (in all

ventricles): specialized cells that produce CSF

Blood Supply to the Brain Brain requires a tremendous amount of blood Receives 15-20% of blood pumped by heart Interruption unconsciousness/irreversible brain

damage Dependent on constant supply of oxygen &

glucose Receives blood through arteries

Hydrocephalus Condition with infants

Prior to fusion of cranial bones Excess CSF (due to blockage or

constriction of the meninges)causes the skull to enlarge

Infants suffer some degree of mental retardation

Cranial Nerves Part of the PNS Connected to the brain and branch out 12 of them Attaches the brain near a sensory or

motor neuron 2 of each

Cranial Nerves1. Olfactory Nerves smell2. Optic Nerves Vision3. Oculomotor Nerves Eye Movements4. Trochlear Nerves Eye movements5. Trigeminal Nerves Sensory/Motor to face6. Abducens Nerves Motor eye movements7. Facial Nerves Sensory/Motor to face8. Vestibulocochlear Nerves balance/equilibrium and

hearing9. Glossopharyngeal Nerves Sensory/Motor to head

and neck10. Vagus Nerves Sensory/Motor to thorax and abdomen11. Accessory Nerves Motor to muscles of neck and

upper back12. Hypoglossal Nerves Motor for tongue movements

“Oh, once one takes the anatomy final, very good vacations are heavenly”

Sleep

Conscious/Unconscious Conscious = state of awareness of

external stimuli Unconscious = number of conditions,

deep, unresponsive state drifting into sleep

Levels of Sleep 2 levels, patterns of brain activity

1. Slow wave sleep Deep sleep/non-REM sleep Entire body relaxed Cerebral cortex activity at minimum Heart rate, blood pressure, respiratory rate, energy

utilization decline by 30%2. Rapid Eye Movement (REM sleep)

Active dreaming Changes in blood pressure/respiratory rate Muscle tone decreases Neurons controlling eye muscles stop regulation = eyes

move rapidly as dream events unfold

Sleeping Cycles REM and Deep sleep

alternate throughout the night

Starts with Deep sleep = 1.5 hours

REM last on average 5 minutes

Determined by an EEG Electroencephalogram:

graphic record of the electrical activities of the brain

Alzheimer’s Disease Loss of cerebral functions Symptoms appear around 50-60 years

old Can affect younger individuals but is rare

Currently affects 2 million ppl in USA 100,000 deaths each year Chromosome 14, 19, and 21

Majority of Downs Syndrome develop it (21)

Composed of: Brain Spinal Cord Nerves

Sense of smell activity

Sense of smell optionsCinnamonLemonOrangeRootbeerStrawberry

GrapesCherryPeppermintBaby powderRose

Sense of Smell Key1. Baby

powder2. Cinnamon3. Rose4. Lemon5. Strawberry

6. Cherry7. Root beer8. Peppermint9. Orange10.Grape

Action Potential= The membrane potential of a neuron that is conducting an impulse (nerve impulse)

Action potential is an all-or-none response

Resting membrane potential (RMP) at -70mV. Na+ on outside and K+ on inside of cell

Stimulus at dendrites triggers Na+ channels to open, causing local depolarization. If the opening is sufficient to drive the interior

potential from -70 mV up to -55 mV, the process of depolarization continues.

As depolarization reaches threshold of -55mV, the action potential is triggered and Na+ rushes into cell until membrane potential reaches +30mV on action potential

Propagation of the action potential at 100 m/sec (which is 225 mph)

Repolarization occurs with K+ exiting the cell to return to -70mV RMP

Return of ions (Na+ and K+) to their extracellular and intracellular sites by the sodium potassium (Na+K+) pump

Continues until RMP is met

Action Potential Video Video 2