LM 1.1: Introduction to the Autonomic Nervous System Flashcards
what is the autonomic nervous system?
the peripheral nervous system that functions outside of our conscious awareness!
what is the distinctive feature of the autonomic nervous system?
the two-step output pathway involving centrally located preganglionic neurons and peripherally located postganglionic neurons (all are called general visceral efferent (GVE) fibers
the preganglionic neuron cell bodies are located in the brainstem and in the lateral gray horn of the spinal cord
the cell bodies of the postganglionic neurons are located in a peripherally located ganglia
so the preganglionic neuron is the in the CNS while the posganglionic neuron is in the peripheral nervous system –> they communicate with each other and
what is the function of visceral efferent neurons?
aka GVEs, visceral motor neurons
they provide efferent (motor) innervation to smooth muscle, cardiac muscle and exocrine/ endocrine glands
what is the function of visceral afferent neurons?
aka GVAs, visceral sensory neurons
they are similar in morphology and function to somatic neuron = they connect the CNS to the organs, muscles, and skin
what is the unsettled debate about the autonomic nervous system?
most physiology textbooks consider the ANS to be solely a visceral efferent (motor) system
however, most gross anatomy textbooks consider Visceral Afferent Neurons (VANs) to be part of the autonomic nervous system
what are the 3 divisions of the autonomic nervous system?
- sympathetic
- parasympathetic
- enteric
the division is based on structural, chemical, and functional differences –> organs generally receive innervation from both divisions
what is the enteric nervous system,?
a division of the autonomic nervous system that exists only within the muscular walls of the esophagus, stomach, small intestine and large intestine
the enteric nervous system receives inputs from the parasympathetic nervous system
what is the anatomical distinction between the parasympathetic and sympathetic systems?
the location of their ganglia
what is the functional distinction between the parasympathetic and sympathetic systems?
it relates to the type of neurotransmitters released by the postganglionic neurons and the character of the response their stimulation evokes increased ability to react versus increased ability to restore metabolic resources
what are the steps from the origin to the target of the somatic nervous system?
there’s just one neuron that starts in the CNS and goes directly to the target which is skeletal muscle
this causes a releases of ACh which goes and binds to a nicotinic acetylcholine receptor
what are the steps from the origin to the target of the parasympathetic nervous system?
there’s a neuron that starts in the CNS and it goes and synapses in a smooth muscle, cardiac muscle, or gland ganglion and causes the release of ACh
ACh then binds to an N2 receptor which activates another neuron that again releases ACh
what are the steps from the origin to the target of the sympathetic nervous system?
a preganglionic fibers from the CNS goes and synapses in a ganglion and releases ACh which binds to the N2 receptors on the postganglionic neuron
the postganglionic neuron then goes and releases norepinephrine which binds to alpha and beta adrenergic receptors
OR
the preganglionic neuron from the CNS goes and synapses in the adrenal medulla and releases ACh which binds to an N2 receptor on a chromatin cell
the chromatin cell then releases epinephrine
what is the sympathetic nervous system?
it’s a branch of the autonomic nervous system that is responsible for regulating many homeostatic mechanisms
fibers from the SNS innervate tissues in almost every organ system and provide physiological regulation over diverse body processes including pupil diameter, gut motility (movement), and urinary output
it’s best known for mediating the neuronal and hormonal stress response commonly known as the fight-or-flight response, also known as sympatho-adrenal response of the body
what is the fight or flight response?
it’s caused by the sympathetic nervous system
it occurs occurs as the preganglionic sympathetic fibers that end in the adrenal medulla secrete acetylcholine, which activates the secretion of adrenaline (epinephrine), and to a lesser extent noradrenaline (norepinephrine)
so this response is mediated directly via impulses transmitted through the sympathetic nervous system, and also indirectly via catecholamines that are secreted from the adrenal medulla, and acts primarily on the cardiovascular system
what are the functions of the sympathetic nervous system?
- stimulates metabolism; expends energy (lipid, glucose) reserves
- increases alertness
- prepares the body to deal with emergencies; the sympathetic nervous system is sometimes referred to as “fight or flight” system because it is primarily activated in times when a quick and energetic response might be necessary (fright, flight, fight, exercise, or trauma)
- all visceral organs and glands are innervated by the sympathetic system and most are innervated by the parasympathetic system
what are the major components of the sympathetic nervous system?
- vascular
- visceral
the vasculature like blood vessels and exocrine glands (e.g. sweat glands) of the body wall and skeletal muscles are innervated by the SYMPATHETIC DIVISION of the ANS ONLY (NOT the parasympathetic)
what are the characteristics of the sympathetic efferent motor system?
- cell bodies of the preganglionic VEN are located in the lateral grey horn of the thoracic and upper lumbar spinal cord (from T1 to L2 or L3)
- cell bodies of the postganglionic VEN are found in either the paravertebral or the prevertebral ganglia, or the adrenal (suprarenal gland) medulla
- a single preganglionic sympathetic VEN innervates up to 32 postganglionic sympathetic VENs
what are the anatomical components of the sympathetic nervous system?
- lateral gray horn
- ventral roots
- spinal nerves
preganglionic axons course along corresponding spinal nerves to reach the white communicating rami
- rami communicantes
- paravertebral ganglia/sympathetic chain ganglia
- sympathetic chain
- ventral and dorsal rami
- prevertebral ganglia
- adrenal gland
where are the preganglionic cell bodies of the sympathetic nervous system located?
in the lateral horn of grey mayor of the spinal cord segments between T1 and L2 or L3
where do the axons of the preganglionic neurons of the sympathetic nervous system leave the spinal cord?
ventral roots T1-L2 or L3
what are the white and grey rami communicates?
the preganglionic axons of the sympathetic nervous system course along corresponding spinal nerves to reach the white communicating rami:
- the white rami communicantes carry myelinated preganglionic fibers from the spinal nerve directly into the paravertebral ganglia
they also carry sensory processes from vasculature and viscera back to the spinal nerve
- the post ganglionic axons gain access to the spinal nerves by passing over the gray rami communicantes
all the paravertebral ganglia gives rise to gray rami and each spinal nerve receives at least one gray ramps
what is the sympathetic trunk?
part of the sympathetic nervous system
they are the long chains of paravertebral ganglia located on either side of the vertebral column
what are the paravertebral ganglia?
part of the sympathetic nervous system
the paravertebral ganglia form two long chains called sympathetic trunks and they resemble a string of beads which lie along each side of the vertebral column against the vertebral bodies, from C1 to the coccyx
what are the 4 regions of paravertebral ganglia of the sympathetic nervous system?
- cervical region
has 3 ganglia on each side = superior cervical ganglion, middle cervical ganglion, and inferior cervical ganglion
- thoracic region
2-5 ganglia on each side
- sacral region
4-5 ganglia on each side
- coccygeal region
1 ganglion; the two sympathetic chains unite forming a single midline ganglion (ganglion impar)
what are the 3 prevertebral ganglia of the sympathetic nervous system?
- celiac
- superior mesenteric
- inferior mesenteric
they are found in the abdominal cavity and they are somewhat anatomically distinct masses that surround the origin of the major branches of the abdominal aorta
so ganglionic neurone with axons innervating abdominal and pelvis verger are found in these ganglia! the prevertebral ganglia receive their preganglionic axons through splanchnic nerves
what is the function of the celiac ganglion and plexus?
it’s a prevertebral ganglia of the sympathetic nervous system that innervates the distal esophagus, stomach, liver, and pancreas
what is the function of the superior mesenteric ganglion and plexus?
it’s a prevertebral ganglia of the sympathetic nervous system that innervates the small intestine
what is the function of the inferior mesenteric ganglion and plexus?
it’s a prevertebral ganglia of the sympathetic nervous system that innervates the large intestine, rectum, urinary and reproductive organs
what is the pathway of the sympathetic efferent nervous system?
- the axons of preganglionic VENs whose cell bodies are located in the lateral gray horn exit the spinal cord via the ventral roots and course along spinal nerves to reach white rami communicantes
- the preganglionic axon has a number of options after passing through a white ramus commicantes to enter a paravertebral ganglion
it can synapse with the cell body of a postganglionic VEN in the paravertebral ganglion at its spinal cord level of entry (ultimately terminate in the head, neck, body wall, limbs, or thoracic cavity)
OR
it can either ascend or descend in the sympathetic trunk to synapse with a cell body of a postganglionic VEN in a paravertebral ganglion at a higher or lower spinal cord level (ultimately terminate in the head, neck, body wall, limbs, or thoracic cavity)
OR
it can pass through the sympathetic trunk without synapsing, join a splanchnic nerve to travel to a prevertebral ganglia, and subsequently synapse with a cell body of a postganglionic VEN (ultimately terminate in the viscera of the abdominopelvic cavity)
OR
it can pass through the sympathetic trunk without synapsing and subsequently synapse on special modified postganglionic cells in the medullary portion of the adrenal (suprarenal) gland (a special case of a neuron that has lost its axon and secretes catecholamines into the bloodstream)
- the postganglionic VENs that re-enter the spinal nerve do so via gray rami commicantes and are distributed via the spinal nerves to the body wall
go look at the link picture you sent angela….
what is the function of the postganglionic VENs of the sympathetic nervous system that re-enter the spinal nerve?
- stimulate constriction of blood vessels by causing contraction of smooth muscle
- produce contraction of arrector pili muscle found in hair follicles causing goose bumps
- stimulate sweat glands
where are the white vs. grey rami communicantes found?
white rami communicantes are ONLY found at spinal levels T1-L2 while gray rami are found at all vertebral levels
what innervates the viscera of the thoracic cavity?
the heart and lungs are innervated by autonomic nervous system through the cardiopulmonary splanchic nerves
what is the cardiopulmonary plexus?
the POSTganglionic sympathetic VENs originate (i.e. cell bodies located) in the cervical ganglia and upper thoracic sympathetic trunk
these POST ganglionic sympathetic VENs form nerves called cardiopulmonary splanchnic nerves and intermix to form a nerve network called the cardiopulmonary plexus
the cardiopulmonary plexus is found on and around the aortic arch and the bifurcation of the trachea ultimately terminates in the lungs and heart
what does the cardiopulmonary plexus innervate?
the postganglionic sympathetic VENs of the cardiopulmonary plexus provide motor innervation to the smooth muscle of:
- bronchopulmonary tree (increases airway resistance)
- lung vasculature (control blood flow)
- lung mucus glands (controls secretion)
- heart vasculature (control blood flow)
- heart muscle cells (increases contraction)
- heart pacemaker cells (increases heart rate)
what are the abdominopelvic splanchnic nerves?
PREganglionic sympathetic VENs that pass through the sympathetic trunk without synapsing travel in visceral nerves called abdominopelvic splanchnic nerves, which terminate in the prevertebral ganglia
after synapsing in the prevertebral ganglia (celiac, superior mesenteric, inferior mesenteric), fibers of POSTganglionic neurons form plexuses around arteries and travel with these vessels and their branches to their final destination (smooth muscle and glands of viscera)
what are some of the main abdominopelvic splanchnic nerves?
- greater thoracic splanchiics
- lesser thoracic splanchinics
- lumbar splanchinics
what are the greater thoracic splanchnics?
an abdominopelvic splanchinic nerve = PREganglionic sympathetic VENs that pass through the sympathetic trunk without synapsing travel in visceral nerves called abdominopelvic splanchnic nerves, which terminate in the prevertebral ganglia
the greater thoracic splanchnics carry preganglionic sympathetic VENs to the celiac ganglion located in the celiac plexus
what are the lesser thoracic splanchnics?
an abdominopelvic splanchinic nerve = PREganglionic sympathetic VENs that pass through the sympathetic trunk without synapsing travel in visceral nerves called abdominopelvic splanchnic nerves, which terminate in the prevertebral ganglia
the lesser thoracic splanchnics carry preganglionic sympathetic VENs to the aorticorenal ganglion located in aorticorenal plexus and the superior mesenteric ganglion located in the superior mesenteric plexus
what are the lumbar splanchnics?
an abdominopelvic splanchinic nerve = PREganglionic sympathetic VENs that pass through the sympathetic trunk without synapsing travel in visceral nerves called abdominopelvic splanchnic nerves, which terminate in the prevertebral ganglia
the lumbar splanchnics carry preganglionic sympathetic VENs to the inferior mesenteric ganglion located in the inferior mesenteric plexus
what is the difference between cardiopulmonary splanchnic nerves and abdominopelvic splanchnic nerves?
cardiopulmonary splanchnic nerves they arise from the cervical ganglia of the paravertebral column and carry POSTganglionic sympathetic VENs
abdominopelvic splanchnic nerves arise from the thoracic or lumbar ganglia of the paravertebral column and carry PREganglionic sympathetic VENs
what are VANs?
VANs = visceral afferent neurons and they travel antiparallel to sympathetic VENs
so VANs travel in the thoracic, abdominal, and lumbar splanchnic nerves back to the CNS!
like SANs, the VANs have their cell bodies in the Dorsal Root Ganglion and terminate in the dorsal horn of the spinal cord where they make synaptic contact with interneurons that take the information to the brainstem, thalamus, and higher brain centers
also like SANs, VANs are a single neuron from the periphery to the CNS
VANs that travel antiparallel to the two-neuron sympathetic VEN chain generally carry the sensations of pain and stretch
what is the peripheral nervous system?
it is responsible for regulating the internal organs and glands, which occurs unconsciously
its roles include stimulation of rest-and-digest activities that occur when the body is at rest, including sexual arousal, salivation, lacrimation (tears), urination, digestion, and defecation
so you can kind of tell that the sympathetic and parasympathetic divisions typically function in opposition to each other
what are the functions of the parasympathetic nervous system?
- known as the rest , digest, and repose system; in general it conserves and restores energy reserves by promoting sedentary activities, such as digestion
- innervates ONLY visceral organs and blood vessels in the head, neck, thorax, abdomen, and pelvis
- DOES NOT innervate the peripheral vasculature of the extremities and trunk
what are the two divisions of the parasympathetic nervous system?
- cranial
- sacral
based on the location of PREganglionic neurons
where are the cell bodies of the preganglionic parasympathetic VENs located?
in the brainstem OR spinal segments S2 through S4
axons of PREganglionic parasympathetic VENs originating in the brainstem travel in cranial nerves to their destination –> CN 3, CN7, CN 9, CN 10 –> PREganglionic parasympathetic VENs from these cranial nerves ultimately reach their destinations by hitching rides with other nerve branches
axons of PREganglionic VENs originating in the sacral spinal cord exit via ventral roots, enter the ventral rami, then split off to form the pelvic splanchnics which innervate the pelvic viscera
which cranial nerves are associated with the parasympathetic nervous system?
CN 3
CN 7
CN 9
CN 10
where are the cell bodies of the postganglionic VENs of the parasympathetic nervous system located?
cell bodies of POSTganglionic VENs are located within the walls of target tissues (intramural ganglia) AND/OR near* (terminal ganglia) the target organs found in the head, neck, or throughout the viscera
POSTganglionic VENs terminate on smooth muscle, cardiac muscle, or glands
what is the relationship between preganglionic and postganglionic VENs in the parasympathetic nervous system?
one PREganglionic VEN innervates 6-8 POSTganglionic VENs
what are some general difference between the parasympathetic and sympathetic divisions of the autonomic nervous system?
dffects of parasympathetic system are more specific and localized than the sympathetic division
parasympathetic system has a much more restricted distribution as contrasted to the sympathetic system (only the head, visceral cavities, and erectile tissues of the male/female external genitalia)
where are the cell bodies of the parasympathetic VANs located?
the VANs have their cell bodies in the Dorsal Root Ganglion and terminate in the dorsal horn of the spinal cord where they make synaptic contact with interneurons that take the information to the brainstem, thalamus, and higher brain centers
VANs travel in the Vagus cranial nerves or pelvic splanchnic nerves back to the CNS
VANs are a single neuron from the periphery to the CNS. VANs that travel antiparallel to the two-neuron parasympathetic VEN chain generally carry the sensations of nausea or hunger and sometimes chemoreception (e.g. oxygen content or pH of the blood)
what is the enteric nervous system?
a division of the autonomic nervous s system that is the “brain of your belly”
it consists of an intricate network of microscopic non-myelinated neurons found between the muscular layers of the esophagus, stomach, small intestine, and large intestine
the ENS has both efferent and afferent VENS and can work independently (i.e. in a localized visceral reflex of the digestive tract) of the CNS or parasympathetic or sympathetic nervous systems
the ENS often acts as the postsynaptic network of neurons for presynaptic parasympathetic neurons
what is the summary of the parasympathetic vs. sympathetic nervous system?
MOST ACTIVE
P = rest, digest and repose
S = fear, flight, fight, exercise or trauma
GENERAL CHARACTERISTICS
P = narrowcast message to specific regions of an organ or organ system
S = broadcast message to several organs at one time
TYPES OF EFFECTOR ORGANS INNERVATED
P = smooth muscle, cardiac, exocrine and endocrine glands
S = smooth muscle, cardiac, and exocrine glands
LOCATION OF CELL BODIES OF PREGANGLIONIC VEN
P= brainstem and sacral S2=S4 spinal cord segments
S = lateral gray horn of thoracic and upper lumbar spinal cord (T1-L2)
LENGTH OF PREGANGLIONIC VEN AXON
P= long preganglionic VEN
S = short preganglionic VEN axon
LOCATION OF PERIPHERAL AUTONOMIC GANGLIA
P = very near or within target organ, terminal ganglia, or intramural ganglia
S = distant from target organ, paravertebral ganglia, or prevertebral ganglia
aka the synapse between the preganglionic VEN and postganglionic VEN
LENGTH OF POSTGANGLIONIC VEN AXON
P = short postganglionic VEN axon
S = long postganglionic VEN axon
TYPICAL SESNSATION THAT A VAN TRAVELING ANTIPARALLEL TO THESE VENS WOULD CARRY
P = nausea, hunger
S = pain, stretch
