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Chapter 10
The Nervous System
Introduction, Spinal Cord and
Spinal Nerves
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Introduction
• Control center and communication
network
– Directs functions of body’s organs and
systems
– Interprets external environment
– Determines reaction to change
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Introduction (cont’d.)
• Homeostasis: balanced internal
environment
– Controlled by nervous and endocrine systems
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Organization
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Organization (cont’d.)
• Central nervous system: brain and spinal
cord
• Peripheral nervous system
– Afferent peripheral system
• Sensory neurons
– Efferent peripheral system
• Somatic
• Autonomic - sympathetic and parasympathetic
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Organization (cont’d.)
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Classification of Nerve Cells
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Neuroglia Cells
• Astrocytes: support, connection, blood
brain barrier
• Oligodendroglia: support, myelin sheath
formation
• Microglial: phagocytosis
• Ependymal: line the ventricles of the brain
• Schwann: myelin sheaths in peripheral
nervous system
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The Structure of a Neuron
• Cell body
• Dendrites: receptive areas
• Axon: extension of cell body
– Schwann cells
– Nodes of Ranvier
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The Structure of a Neuron (cont’d.)
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The Structure of a Neuron (cont’d.)
• Multipolar: several dendrites coming off
cell body
• Bipolar: one dendrite and one axon
• Unipolar: one process extending from cell
body
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The Structure of a Neuron (cont’d.)
• Receptors: detect environmental stimuli
• Sensory: receive impulse from receptor
site
• Internuncial: transmit impulse for
interpretation and processing
• Motor: reaction to the stimulus
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The Physiology of the Nerve
Impulse
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The Physiology of the Nerve
Impulse (cont’d.)
• Nerve cell fiber resting potential
– Na+ concentration higher on outside
– K+ concentration higher on inside
– Negative charge on inside
– Positive charge on outside
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The Physiology of the Nerve
Impulse (cont’d.)
• Depolarization: Na+ rush inside cell
• Repolarization: K+ rush out to restore
balance
• Depolarization: Repolarization moves in
one direction
• Myelinated vs. unmyelinated
• All-or-none law
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The Synaptic Transmission
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The Synaptic Transmission
(cont’d.)
• Synapse: axon terminal branches close to
next dendrites
• Impulse reaches axon terminals
• Triggers neurotransmitter release into
synaptic cleft
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The Synaptic Transmission
(cont’d.)
• Neurotransmitters
– Acetylcholine
• Most common
– Epinephrine
– Norepinephrine
– Serotonin
– Dopamine
– Endorphins
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Animation – Firing of
Neurotransmitters
• This animation illustrates the physiology of
the nerve impulse
• [Insert FiringofNeurotransmitters.swf]
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The Reflex Arc
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The Reflex Arc (cont’d.)
• Knee-jerk reflex
• Maintain homeostasis
– Heartbeat/breathing rates
– Digestion
– Coughing
– Sneezing
– Swallowing
– Vomiting
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The Reflex
Arc (cont’d.)
• Involuntary
reaction to
external
stimulus
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Grouping of Neural Tissue
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Grouping of Neural Tissue (cont’d.)
• White matter
– Groups of myelinated axons
– Forms nerve tracts in CNS
• Gray matter
– Nerve cell bodies and dendrites
– Unmyelinated axon bundles
– Cortex: gray matter on surface of brain
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Grouping of Neural Tissue (cont’d.)
•
•
•
•
Nerve: bundle of fibers outside CNS
Ganglia: nerve cell bodies outside CNS
Tract: bundle of fibers inside CNS
Nucleus: nerve cell bodies and dendrites
inside CNS
• Horns: areas of gray matter in spinal cord
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The Spinal Cord
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Introduction
• Continuation of medulla oblongata
• 31 segments each with pair of spinal
nerves
• Protected by meninges
– Dura mater
– Arachnoid
– Pia mater
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Functions of the Spinal Cord
• Conveys sensory impulses to the brain
• Integrates reflexes
• Spinal nerves connect at roots
– Dorsal root: sensory
– Ventral root: motor
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The Spinal Nerves
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The Spinal Nerves (cont’d.)
• All 31 pairs arise from union of dorsal and
ventral roots
• Mixed nerves consisting of motor and
sensory fibers
• Most exit vertebral column between
vertebrae
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The Spinal Nerves (cont’d.)
• Named and numbered according to region
and level of spinal cord
– Cervical: 8 pairs
– Thoracic: 12 pairs
– Lumbar: 5 pairs
– Sacral: 5 pairs
– Coccygeal: 1 pair
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Summary
• Named the major division of the nervous
system
• Classified neurons and neuroglial cells
• Discussed the physiology of the nerve
impulse and transmission at synapses
• Named the different types of neural tissue
• Discussed the structure of the spinal cord
• Named the spinal nerves
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