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Introduction to Nerves and the
Nervous System
Chapter 19
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Role of the Nervous System
• Controlling the functions of the human body
• Analyzing incoming stimuli
• Integrating internal and external responses
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Make Up of the Nervous System
• Central Nervous System (CNS)
– Composed of the brain and spinal cord
• Peripheral Nervous System (PNS)
– Sensory receptors bring information into the CNS
– Motor nerves carry information away from the CNS
• Autonomic Nervous System (ANS)
– Uses components of the CNS and PNS to regulate
automatic or unconscious responses to stimuli
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Function of the Cells that Make Up the Nervous
System
• Allow movement
• Allow realization of various sensations
• Provide response to internal and external stimuli
• Stimulate learning, thinking, and emotions
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Neuron
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Types of Axons
• Afferent Fibers
– Nerve axons that run from peripheral receptors into
the CNS
• Efferent Fibers
– Nerve axons that carry nerve impulses from the CNS
to the periphery to stimulate muscles or glands
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Action Potential
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Electrolytes Involved in Nerve Cell Action
• Sodium
• Potassium
• Calcium
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Movement of Electrolytes with Action
• Rest/Repolarization
– Membrane is impermeable to sodium
– Permeable to potassium
• Action/Depolarization
– Sodium goes into the cell
– Potassium leaves the cell
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Formation of Myelin Sheath
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Nerve Synapse
• Presynaptic Nerve
• Synaptic Cleft
• Postsynaptic Effector Cell
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Question
What nerve axons carry nerve impulses from the central
nervous system to the peripheral nervous system?
a. Somatic axons
b. Efferent fibers
c. Afferent fibers
d. Sensory axons
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Answer
b. Efferent fibers
Rationale: Efferent fibers: Nerve axons that carry nerve
impulses from the CNS to the periphery to stimulate
muscles or glands
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Neurotransmitters
• Acetylcholine
– Communicates between nerves and muscles
• Norepinephrine and Epinephrine
– Catecholamines released by nerves in the
sympathetic branch of the ANS
• Dopamine
– Involved in the coordination of impulses and
responses
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Neurotransmitters (cont.)
• Gamma-aminobutyric Acid (GABA)
– Inhibits nerve activity and is important in preventing
over-excitability or stimulation such as seizure
activity
• Serotonin
– Important in arousal and sleep and in preventing
depression and promoting motivation
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Central Nervous System
• Made up of brain and spinal cord
• Structures are covered by meninges
• Blood brain barrier
• Blood supply to the brain
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Anatomy of the Brain
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Hindbrain
• Runs from the top of the spinal cord into the midbrain
• Most primitive part of the brain - contains the brainstem
• Controls basic vital functions:
– Breathing
– Blood pressure
– Swallowing
– RAS
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Midbrain
• Contains the thalamus, the hypothalamus, and the limbic
system
• The thalamus sends direct information into the cerebrum to
transfer sensations
• Hypothalamus acts as major sensor activity in the body
– Temperature regulation
– Water balance
– Appetite
– Endocrine function
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Limbic System
• Contain high levels of the neurotransmitters
– Epinephrine
– Norepinephrine
– Serotonin
• Controls expression of emotions
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Forebrain
• Made up of two cerebral hemispheres joined together by
the corpus callosum
• Receives and sends nerve impulses, coordinates speech
and communication, and facilitates learning
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Spinal Cord
• Made up of 31 pairs of spinal nerves
• Each spinal nerve has two components or roots
– Sensory fiber (dorsal root)
• Brings information into the CNS from the periphery
– Motor fiber (ventral root)
• Causes movement or reaction
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Function of Central Nervous System
• Sensory Functions
• Motor Functions
• Intellectual and Emotional Functions
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Intellectual and Emotional Function
• Two hemispheres of the brain process information
differently
• Right Side
– Artistic
• Left Side
– Analytical
• When learning takes place and actual change occurs in a
neuron
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Intellectual and Emotional Function (cont.)
• Some degree of stress helps facilitate learning
• Increased stress inhibits learning
• The limbic system plays a role in learning
• Emotions associated with memory as well as the present
have an impact on stimulus response.
• The placebo effect is a documented effect of the mind on
drug therapy: If a person perceives that a drug will be
effective, it is much more likely to actually be effective.
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Question
What is a documented phenomenon of the mind affecting
drug therapy?
a. Action potential
b. Placebo effect
c. Expectation effect
d. Learning
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Answer
b. Placebo effect
Rationale: The placebo effect is a documented effect of the
mind on drug therapy: If a person perceives that a drug
will be effective, it is much more likely to actually be
effective.
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