BIOLOGICAL SCIENCE 102 – ANIMAL BIOLOGY – NOTES & VOCABULARY
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¾ NERVOUS SYSTEM: THE EFFERENT NERVOUS SYSTEM
¾ AUTONOMIC AND SOMATIC RESPONSES
autonomic nervous system = the involuntary branch of the peripheral nervous system
somatic nervous system = the voluntary branch of the peripheral nervous system
gray matter = neuronal cell bodies and their dendrites, short interneurons and glial cells
white matter = tracts of bundled nerve cell axons
ascending tract = carry information to the brain
descending tract = carry information from the brain
The gray matter of the spinal cord is divided into a dorsal (or posterior) horn, a ventral (or
anterior) horn and a lateral horn.
dorsal horn = contains cell bodies of interneurons upon which afferent (sensory) neurons
terminate
lateral horn = contains cell bodies of autonomic efferent nerve fibers
ventral horn = contains cell bodies of somatic efferent nerve fibers
spinal nerve = where the dorsal and ventral roots meet to form a nerve that connects a
particular region of the body to the spinal cord
nerve = a bundle of efferent and afferent peripheral neuronal axons
dorsal root ganglion = a cluster of afferent neuronal cell bodies located adjacent to the spinal
cord on the dorsal roots; the cell bodies of sensory neurons are found here
simple reflex = a built-in and unlearned response such as pulling your hand away from a hot
object
acquired or conditioned reflex = develops as a result of practice and learning such as playing
a musical instrument
reflex arc (as in figure 5-31 of the text) = the neural pathway responsible for a reflex that
involves: a receptor, an afferent (or sensory) neuron, an interneuron (integrating center), an
efferent (or motor) neuron, and an effector organ or muscle
sympathetic nervous system = the subdivision of the autonomic nervous system that
dominates in emergency, “fight or flight” or stressful situations and prepares the body for
strenuous physical activity (the active state)
parasympathetic nervous system = the subdivision of the autonomic nervous system that
dominates in quiet, relaxed situations and promotes body maintenance activities such as
digestion and emptying of the urinary bladder (the resting state)
BIOLOGICAL SCIENCE 102 – ANIMAL BIOLOGY – NOTES & VOCABULARY
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preganglionic neuron (or fiber) = the first neuron in the two-neuron autonomic nerve pathway;
originates in the CNS and terminates on a sympathetic ganglion or parasympathetic ganglion.
Preganglionic neurons always release acetylcholine.
postganglionic neuron (or fiber) = the second neuron in the two-neuron autonomic nerve
pathway; originates in a sympathetic or parasympathetic ganglion and terminates on an
effector organ.
Parasympathetic postganglionic neurons release acetylcholine while sympathetic
postganglionic neruons release norepinephrine.
ganglion (= singular; ganglia is plural) = a collection of nerve cell bodies found outside the CNS
sympathetic ganglia = the series of ganglia located along either side of the spinal cord where
the preganglionic and postganglionic neurons of the sympathetic system synapse together
parasympathetic ganglion (a type of terminal ganglion) = the ganglia located near or on the
individual effector organs where the preganglionic and postganglionic neurons of the
parasympathetic system synapse together
terminal ganglion = a ganglia that lies in or near an effector organ
acetylcholine = the neurotransmitter released from both sympathetic and parasympathetic
preganglionic neurons, parasympathetic postganglionic fibers, and all motor neurons (of the
somatic nervous system)
epinephrine (or adrenaline) = the primary hormone secreted by the adrenal medulla;
epinephrine is important in preparing the body for “fight or flight” responses and helps regulate
arterial blood pressure (it increases blood pressure and heart rate)
norepinephrine (or noradrenaline) = the neurotransmitter released from sympathetic
postganglionic neurons