chapter 7 the nervous system. functions of the nervous system 1. sensory input – gathering...
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Chapter 7The Nervous System
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Functions of the Nervous SystemFunctions of the Nervous System1. Sensory input – gathering
information
monitor changes inside and outside the body
Changes = stimuli
2. Integration
process and interpret input and decide on action
3. Motor output
response to stimuli
activates muscles or glands
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Structural ClassificationStructural Classification
1. Central nervous system (CNS)
Brain
Spinal cord
2. Peripheral nervous system (PNS)
Nerves outside the brain & spinal cord
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2 Divisions of the PNS2 Divisions of the PNSSensory (afferent) division
Nerve fibers that carry information to the central nervous system
Motor (efferent) division
Nerve fibers that carry impulses away from the central nervous system
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2 Parts of Motor Division2 Parts of Motor Division1. Somatic = voluntary
2. Autonomic = involuntaryWhich side is fight or flight response?
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Neuroglia : Support CellsNeuroglia : Support Cells
1. Astrocytes
Abundant, star-shaped cells
Brace neurons
Form barrier between capillaries and neurons
Control chemical environment of brain
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2. Microglia
Spider-like phagocytes
Dispose of debris
3. Ependymal cells
Line cavities of brain and spinal cord
Circulate cerebrospinal fluid
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4. Oligodendrocytes
Produce myelin sheath around nerve fibers in CNS
5. Satellite cells
Protect neuron cell bodies
6. Schwann cells
Form myelin sheath in the peripheral nervous system
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Neurons = nerve cellsNeurons = nerve cells
1. specialized to transmit messages
2. Major regions
Cell body – nucleus and metabolic center of the cell
Processes – fibers that extend from the cell body
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Neuron AnatomyNeuron Anatomy Cell body
a. Nissl substance – specialized rough endoplasmic reticulum
b. Neurofibrils – intermediate cytoskeleton that maintains cell shape
c. Nucleus
d. Large nucleolus
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Processes -Extensions outside the cell body
a. Dendrites – conduct impulses toward the cell body
b. Axons – conduct impulses away from the cell body
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Axons and Nerve ImpulsesAxons and Nerve Impulses
Axons end in axonal terminals
terminals contain vesicles with neurotransmitters
Synaptic cleft – gap between adjacent neurons
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Nerve Fiber CoveringsNerve Fiber Coverings Schwann cells –
produce myelin sheaths in jelly-roll like fashion
Nodes of Ranvier – gaps in myelin sheath along the axon
Figure 7.5
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Neuron Cell Body LocationNeuron Cell Body Location In CNS (Most)
1. Gray matter – cell bodies and unmylenated fibers
2. Nuclei – clusters of cell bodies within the white matter of the central nervous system
Outside CNS
1. Ganglia – collections of cell bodies
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1. Sensory (afferent) neurons
Carry impulses from sensory receptors to CNS
a. Cutaneous sense organs
b. Proprioceptors – detect stretch or tension
2. Motor (efferent) neurons
Carry impulses from CNS
3. Interneurons (association neurons)
Found in neural pathways in CNS
Connect sensory and motor neurons
Functional Classification of NeuronsFunctional Classification of Neurons
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Structural Classification of NeuronsStructural Classification of Neurons
1. Multipolar neurons – many extensions from cell body
2. Bipolar neurons – one axon and one dendrite
3. Unipolar neurons –short single process leaving cell body
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Properties of NeuronsProperties of Neurons1. Irritability –respond to stimuli
2. Conductivity –transmit impulses
plasma membrane at rest is polarized
Fewer + ions inside than outside the cell
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Starting a Nerve ImpulseStarting a Nerve Impulse
Depolarization – a stimulus depolarizes the neuron’s membrane
allows Na+ to flow inside membrane
exchange of ions initiates an action potential in neuron
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The Action PotentialThe Action Potential
If action potential (nerve impulse) starts, it is propagated over the entire axon
K+ rush out after Na+ rush in, which repolarizes the membrane
Sodium-potassium pump restores the original configuration - requires ATP
Impulse moves toward the cell body
Impulses travel faster when fibers have a myelin sheath
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Impulses are able to cross the synapses
Neurotransmitter released from nerve’s axon terminal
Dendrite of the next neuron has receptors that are stimulated by neurotransmitter
Action potential is started in the dendrite
Continuation between NeuronsContinuation between Neurons