The Autonomic Nervous System

Key Terms

acetylcholine (ACh)
neurotransmitter that binds at a motor end-plate to trigger depolarization
adrenal medulla
interior portion of the adrenal (or suprarenal) gland that releases epinephrine and norepinephrine into the bloodstream as hormones
adrenergic
synapse where norepinephrine is released, which binds to α- or β-adrenergic receptors
afferent branch
component of a reflex arc that represents the input from a sensory neuron, for either a special or general sense
agonist
any exogenous substance that binds to a receptor and produces a similar effect to the endogenous ligand
alpha (α)-adrenergic receptor
one of the receptors to which epinephrine and norepinephrine bind, which comes in three subtypes: α1, α2, and α3
antagonist
any exogenous substance that binds to a receptor and produces an opposing effect to the endogenous ligand
anticholinergic drugs
drugs that interrupt or reduce the function of the parasympathetic system
autonomic tone
tendency of an organ system to be governed by one division of the autonomic nervous system over the other, such as heart rate being lowered by parasympathetic input at rest
baroreceptor
mechanoreceptor that senses the stretch of blood vessels to indicate changes in blood pressure
beta (β)-adrenergic receptor
one of the receptors to which epinephrine and norepinephrine bind, which comes in two subtypes: β1 and β2
cardiac accelerator nerves
preganglionic sympathetic fibers that cause the heart rate to increase when the cardiovascular center in the medulla initiates a signal
cardiovascular center
region in the medulla that controls the cardiovascular system through cardiac accelerator nerves and vasomotor nerves, which are components of the sympathetic division of the autonomic nervous system
celiac ganglion
one of the collateral ganglia of the sympathetic system that projects to the digestive system
central neuron
specifically referring to the cell body of a neuron in the autonomic system that is located in the central nervous system, specifically the lateral horn of the spinal cord or a brain stem nucleus
cholinergic
synapse at which acetylcholine is released and binds to the nicotinic or muscarinic receptor
chromaffin cells
neuroendocrine cells of the adrenal medulla that release epinephrine and norepinephrine into the bloodstream as part of sympathetic system activity
ciliary ganglion
one of the terminal ganglia of the parasympathetic system, located in the posterior orbit, axons from which project to the iris
collateral ganglia
ganglia outside of the sympathetic chain that are targets of sympathetic preganglionic fibers, which are the celiac, inferior mesenteric, and superior mesenteric ganglia
craniosacral system
alternate name for the parasympathetic division of the autonomic nervous system that is based on the anatomical location of central neurons in brain-stem nuclei and the lateral horn of the sacral spinal cord; also referred to as craniosacral outflow
dorsal longitudinal fasciculus
major output pathway of the hypothalamus that descends through the gray matter of the brain stem and into the spinal cord
dorsal nucleus of the vagus nerve
location of parasympathetic neurons that project through the vagus nerve to terminal ganglia in the thoracic and abdominal cavities
Eddinger–Westphal nucleus
location of parasympathetic neurons that project to the ciliary ganglion
efferent branch
component of a reflex arc that represents the output, with the target being an effector, such as muscle or glandular tissue
endogenous
describes substance made in the human body
endogenous chemical
substance produced and released within the body to interact with a receptor protein
epinephrine
signaling molecule released from the adrenal medulla into the bloodstream as part of the sympathetic response
exogenous
describes substance made outside of the human body
exogenous chemical
substance from a source outside the body, whether it be another organism such as a plant or from the synthetic processes of a laboratory, that binds to a transmembrane receptor protein
fight-or-flight response
set of responses induced by sympathetic activity that lead to either fleeing a threat or standing up to it, which in the modern world is often associated with anxious feelings
G protein–coupled receptor
membrane protein complex that consists of a receptor protein that binds to a signaling molecule—a G protein—that is activated by that binding and in turn activates an effector protein (enzyme) that creates a second-messenger molecule in the cytoplasm of the target cell
ganglionic neuron
specifically refers to the cell body of a neuron in the autonomic system that is located in a ganglion
gray rami communicantes
(singular = ramus communicans) unmyelinated structures that provide a short connection from a sympathetic chain ganglion to the spinal nerve that contains the postganglionic sympathetic fiber
greater splanchnic nerve
nerve that contains fibers of the central sympathetic neurons that do not synapse in the chain ganglia but project onto the celiac ganglion
inferior mesenteric ganglion
one of the collateral ganglia of the sympathetic system that projects to the digestive system
intramural ganglia
terminal ganglia of the parasympathetic system that are found within the walls of the target effector
lesser splanchnic nerve
nerve that contains fibers of the central sympathetic neurons that do not synapse in the chain ganglia but project onto the inferior mesenteric ganglion
ligand-gated cation channel
ion channel, such as the nicotinic receptor, that is specific to positively charged ions and opens when a molecule such as a neurotransmitter binds to it
limbic lobe
structures arranged around the edges of the cerebrum that are involved in memory and emotion
long reflex
reflex arc that includes the central nervous system
medial forebrain bundle
fiber pathway that extends anteriorly into the basal forebrain, passes through the hypothalamus, and extends into the brain stem and spinal cord
mesenteric plexus
nervous tissue within the wall of the digestive tract that contains neurons that are the targets of autonomic preganglionic fibers and that project to the smooth muscle and glandular tissues in the digestive organ
muscarinic receptor
type of acetylcholine receptor protein that is characterized by also binding to muscarine and is a metabotropic receptor
mydriasis
dilation of the pupil; typically the result of disease, trauma, or drugs
nicotinic receptor
type of acetylcholine receptor protein that is characterized by also binding to nicotine and is an ionotropic receptor
norepinephrine
signaling molecule released as a neurotransmitter by most postganglionic sympathetic fibers as part of the sympathetic response, or as a hormone into the bloodstream from the adrenal medulla
nucleus ambiguus
brain-stem nucleus that contains neurons that project through the vagus nerve to terminal ganglia in the thoracic cavity; specifically associated with the heart
parasympathetic division
division of the autonomic nervous system responsible for restful and digestive functions
parasympathomimetic drugs
drugs that enhance or mimic the function of the parasympathetic system
paravertebral ganglia
autonomic ganglia superior to the sympathetic chain ganglia
postganglionic fiber
axon from a ganglionic neuron in the autonomic nervous system that projects to and synapses with the target effector; sometimes referred to as a postganglionic neuron
preganglionic fiber
axon from a central neuron in the autonomic nervous system that projects to and synapses with a ganglionic neuron; sometimes referred to as a preganglionic neuron
prevertebral ganglia
autonomic ganglia that are anterior to the vertebral column and functionally related to the sympathetic chain ganglia
referred pain
the conscious perception of visceral sensation projected to a different region of the body, such as the left shoulder and arm pain as a sign for a heart attack
reflex arc
circuit of a reflex that involves a sensory input and motor output, or an afferent branch and an efferent branch, and an integrating center to connect the two branches
rest and digest
set of functions associated with the parasympathetic system that lead to restful actions and digestion
short reflex
reflex arc that does not include any components of the central nervous system
somatic reflex
reflex involving skeletal muscle as the effector, under the control of the somatic nervous system
superior cervical ganglion
one of the paravertebral ganglia of the sympathetic system that projects to the head
superior mesenteric ganglion
one of the collateral ganglia of the sympathetic system that projects to the digestive system
sympathetic chain ganglia
series of ganglia adjacent to the vertebral column that receive input from central sympathetic neurons
sympathetic division
division of the autonomic nervous system associated with the fight-or-flight response
sympatholytic drug
drug that interrupts, or “lyses,” the function of the sympathetic system
sympathomimetic drug
drug that enhances or mimics the function of the sympathetic system
target effector
organ, tissue, or gland that will respond to the control of an autonomic or somatic or endocrine signal
terminal ganglia
ganglia of the parasympathetic division of the autonomic system, which are located near or within the target effector, the latter also known as intramural ganglia
thoracolumbar system
alternate name for the sympathetic division of the autonomic nervous system that is based on the anatomical location of central neurons in the lateral horn of the thoracic and upper lumbar spinal cord
varicosity
structure of some autonomic connections that is not a typical synaptic end bulb, but a string of swellings along the length of a fiber that makes a network of connections with the target effector
vasomotor nerves
preganglionic sympathetic fibers that cause the constriction of blood vessels in response to signals from the cardiovascular center
visceral reflex
reflex involving an internal organ as the effector, under the control of the autonomic nervous system
white rami communicantes
(singular = ramus communicans) myelinated structures that provide a short connection from a sympathetic chain ganglion to the spinal nerve that contains the preganglionic sympathetic fiber