Nervous System

Components of the Nervous System

• The nervous system includes the brain, cranial nerves, spinal cord, spinal nerves, ganglia, enteric plexuses, and sensory receptors.

CNS

• Brain

• Spinal Cord

PNS• includes all nervous tissue outside the

CNS.

• Cranial Nerves = 12 X 2 =

• Spinal Nerves = 31 X 2

• Enteric plexuses

• Sensory receptors

Function

• Sensory function. Sensory receptors detect internal stimuli, such as an increase in blood acidity, and external stimuli, such as a raindrop landing on your arm.

• This sensory information is then carried into the brain and spinal cord through cranial and spinal nerves.

Intergration

• Integrative function. The nervous system integrates (processes) sensory information by analyzing and storing some of it and by making decisions for appropriate responses.

• An important integrative function is perception, the conscious awareness of sensory stimuli. Perception occurs in the brain.

Motor Neuron

• Motor function. Once sensory information is integrated, the nervous system may elicit an appropriate motor response by activating effectors (muscles and glands) through cranial and spinal nerves. Stimulation of the effectors causes muscles to contract and glands to secrete.

Which types of neurons carry input to the

CNS and output from the CNS?

Neuron

• Structure of a typical neuron

• The arrows indicate the direction of information flow: dendrites → cell body → axon → axon terminals → synaptic end bulbs.

• The basic parts of a neuron are: dendrites, a a cell body, and a single axon

Neuroglia in the CNS and PNS

• Astrocytes

• Microglia

• Oligodendrocytes

• Schwann Cells

Gray and White Matter

• White matter is composed primarily of myelinated axons.

• The whitish color of myelin gives white matter its name.

• The gray matter of the nervous system contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia.

• It appears grayish, rather than white, because the cellular organelles impart a gray color and there is little or no myelin in these areas.

Membrane Potential

is due to a small buildup of negatively charged ions, mainly organic phosphates (PO43-) and proteins, in the cytosol just inside the membrane and an equal buildup of positively charged ions, mainly sodium ions (Na+), in the interstitial fluid just outside the membrane.

Membrane Potential

Action Potential (AP)

• When a stimulus depolarizes the membrane to threshold, an action potential is generated.

• An action potential consists of depolarizing and repolarizing phases.

Which channels are open during depolarization?

During repolarization?

• What are the meanings of the terms:

• resting membrane potential

• depolarization

• repolarization

• nerve impulse

• refractory period?

• How is saltatory conduction different from continuous conduction?

Events at a Synapse

• A nerve impulse arrives at a synaptic end bulb of a presynaptic axon.

 

• The depolarizing phase of the nerve impulse opens voltage-gated Ca2+ channels, which are present in the membrane of synaptic end bulbs.

• Because calcium ions are more concentrated in the interstitial fluid, Ca2+ flows into the synaptic end bulb through the opened channels.

• An increase in the concentration of Ca2+ inside the synaptic end bulb triggers exocytosis of some of the synaptic vesicles, which releases thousands of neurotransmitter molecules into the synaptic cleft.  

• The neurotransmitter molecules diffuse across the synaptic cleft and bind to neurotransmitter receptors in the postsynaptic neuron's plasma membrane.

• Binding of neurotransmitter molecules opens ion channels, which allows certain ions to flow across the membrane.

 

• As ions flow through the opened channels, the voltage across the membrane changes.

• Depending on which ions the channels admit, the voltage change may be a depolarization or a hyperpolarization.  

• If a depolarization occurs in the postsynaptic neuron and reaches threshold, then it triggers one or more nerve impulses.

Human Brain

Sensory Receptors

• Exteroceptors

• Interoceptors

Types of Sensory Receptors

• Chemoreceptors

• Pain receptors –nociceptors

• Photoreceptors

• Mechanoreceptors

• Thermoreceptors

Other types of Sensory Receptors

• Proprioceptors are mechanoreceptors- involved in reflex actins to maintain muscle tone, equilibrium and posture

• Cutaneous Receptors, which make the skin sensitive to touch, pressure, pain, and temperature (warmth and cold)

Senses

• Nose-smell

• Eyes-vision

• Ears-hearing

• Mouth-taste

• Skin -touch

Sense of Taste and Smell

• Sense of taste : taste buds are located on the tongue

• Others are located in the hard palate, pharynx, epiglottis

• There are four primary types of taste: sweet, sour, salty, and bitter.

Taste Buds

• open at a taste pore

• Have supporting cells and taste cells

• The taste cells have extensions: microvilli

• Sensory nerve fiber

Microvilli

• When you eat, the chemical molecules in your food bind to the chemoreceptors of the microvilli.

• Nerve signals are generated in sensory nerve fibers that go to the brain.

• The signal is sent to the parietal lobe-the area that interprets taste.

Chemoreceptors

Sense of Smell

• Approximately 80-90% of what we receive as “taste” actually is due to the sense of smell.

• Our sense of smell depends on between 10 and 20 million olfactory cells located within olfactory epithelium high in the roof of the nasal cavity.

Chemoreceptors

• Olfactory cells are modified neurons.• Each cell ends in a tuft of about five olfactory

cilia, which bear receptor proteins for odor molecules.

• When you smell a rose, the odor molecules(chemicals) bind to the olfactory cilia. The sensory neuron generates a nerve impulse that moves along the sensory nerve which reaches the olfactory bulb

Photoreceptors

• Are located in the retina

• Cone cells-black and white vision

• Rod cells-color vision

• See table 14.2

• The neurons communicate this information via the olfactory tract to the olfactory area of the cerebral cortex.

• The olfactory area is located in the temporal lobe.

• When the action potential reaches the temporal lobe (olfactory area) you know you have smelled a rose.

Eye

Sense of Hearing

• The ear has three division: outer ear, middle ear and inner ear.

• See figure 14.12

Inner Ear

• Has three areas:

• semicircular canals-equilibrium

• Vestibule-equilibrium

• Cochlea-hearing

• White matter

• Gray matter

• HypothalamusThalamus

• Cerebellum

• Brain stem: midbrain, medulla oblongata, pons

• The reticular formation

• Limbic System

• Sympathetic and parasympathetic

• CNS• PNS• Crania nerves• Spinal nerves• Sensory receptors• Sensory neurons• Interneurons• Motor neurons• Motor receptors• Effectors

• Dendrites• Axon• Myelin sheath• Node of Ranvier• Axon terminal• Cell body• See figure 13.2• How do the three different types of

neurons differ in structure?• Neuroglia cells out number neurons

9:1(know all four)

• Resting membrane• Action potential• Depolarization• Repolarization• Sodium-potossium pump• Sodium ion• Potassium ion • Saltatory conduction• Refractory period • The Synapse see figure 13.4

Neurotrnsmitter Molecules

• Acetycholine• Norepinephrine• Dopamine• Serotonin• Glutamate• GABA

• Acetylcholinesterase