ANS - Composition Flashcards by Cal Schiller

The autonomic nervous system is a system of visceral sensory (____) and visceral motor (____) neurons that regulates the activity of smooth muscle, cardiac muscle, and many glands

afferent

efferent

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Like the somatic nervous system, the autonomic nervous system operates via ___

reflex arcs

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A continual flow of nerve impulses from autonomic sensory neurons in visceral organs and blood vessels propagate into integrating centers in the central nervous system, and impulses in autonomic ___ propagate to various effector tissues (smooth muscle, cardiac muscle, many glands)

motor neurons

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The ___ part of the autonomic nervous system consists of two branches: sympathetic division and parasympathetic division

motor

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Most input to the autonomic nervous system comes from autonomic sensory neurons, which are mostly ___

interoceptors, such as . . .
Chemoreceptors that monitor blood CO2 levels
Mechanoreceptors that detect the degree of stretch in walls of organs (stomach, urinary bladder, intestines, uterus) or blood vessels

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The signals are not consciously perceived most of the time, but intense activation of interoceptors may produce conscious sensation

such as angina pectoris from inadequate blood flow to the heart

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Autonomic neurons regulate visceral activities by increasing (____) or decreasing (___) activities in their effector tissues (cardiac muscle, smooth muscle, glands)

exciting

inhibiting

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Unlike skeletal muscle, tissues innervated by the ANS often have an intrinsic function that enables them to continue to operate even if their ___ is damaged (heart beat, gastrointestinal tract contractions)

nerve supply

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Whereas a single myelinated somatic motor neuron extends from the CNS to the skeletal muscle fibers in its motor unit, autonomic motor pathways consist of __ motor neurons in series

two

slide 7

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The first neuron has its cell body in the ___, and its myelinated axon extends from the CNS to an autonomic ganglion. This is the pre-ganglionic neuron

CNS

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All pre-synaptic in the ANS are?

myelinated

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The second neuron has its cell body in the ganglion, and its unmyelinated axon extends from the ganglion to the ___. This is the post-ganglionic neuron

effector

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autonomic motor neurons release either ____ or ___

acetylcholine or norepinephrine.

An additional difference between somatic and autonomic motor neurons is that somatic motor neurons release only acetylcholine (Ach) as their neurotransmitter

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motor part of the autonomic nervous system has two main components:

Sympathetic division
Parasympathetic division

Most organs have dual innervation, meaning they receive impulses from both sympathetic and parasympathetic neurons

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As a general principle, nerve impulses from one division of the ANS stimulate increased activity in an organ (excitation), and impulses from the other division decrease activity (inhibition),

The heart rate is increased by an increased rate of nerve impulses from sympathetic division, and decreased by an increased rate of nerve impulses from the parasympathetic division

Muscular movements of the GI tract are slowed by sympathetic stimulation, and increased by parasympathetic stimulation

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Autonomic motor pathways consist of two neurons:

Preganglionic neuron

Postganglionic neuron

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Cell body is in the brain or spinal cord

Axon exits the CNS as part of a cranial nerve or spinal nerve

Conveys nerve impulses from the CNS to autonomic ganglia

Preganglionic neuron

The first of the two motor neurons in any autonomic motor pathway

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Cell body and dendrites are in an autonomic ganglion

Relays nerve impulses from autonomic ganglia to visceral effectors

Postganglionic neuron

The second of the two motor neurons in any autonomic motor pathway

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Preganglionic neurons of the ____ have their cell bodies in the lateral gray horns of the 12 thoracic segments and the first 2 lumbar segments of the spinal cord

sympathetic division

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Preganglionic neurons of the parasympathetic division have their cell bodies in the nuclei of cranial nerves III, VII, IX, and X of the ____ , and in the lateral gray horns of the second through the ____ sacral segments of the spinal cord

brain stem

fourth

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Sympathetic ganglia are of two major types

Sympathetic trunk ganglia

Prevertebral ganglia

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Also called vertebral chain ganglia, or paravertebral ganglia

Ganglia lie in a vertical row on each side of the vertebral column

(sympathetic)

Sympathetic trunk ganglia

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Preganglionic axons are usually short

Postganglionic axons are generally fairly long

Postganglionic axons mostly innervate organs above the diaphragm

(sympathetic)

Sympathetic trunk ganglia

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The ganglia are anterior to the vertebral column, close to the large abdominal arteries

(sympathetic)

Prevertebral ganglia

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Postganglionic axons mostly innervate organs below the ___ (Prevertebral ganglia) (sympathetic)

diaphragm

As with paravertebral ganglia, preganglionic axons are usually short and postganglionic axons are generally fairly long (sympathetic)

Prevertebral ganglia | part of sympathetic

Celiac ganglion Superior mesenteric ganglion Inferior mesenteric ganglion Aorticorenal ganglion Renal ganglion (sympathetic)

five major prevertebral ganglia

five major prevertebral ganglia | sympathetic

Celiac ganglion Superior mesenteric ganglion Inferior mesenteric ganglion Aorticorenal ganglion Renal ganglion

Preganglionic axons of the parasympathetic division synapse with postganglionic neurons in terminal ganglia Most terminal ganglia are located close to or within the wall of the visceral organ Preganglionic axons are typically long Postganglionic axons are short, or seemingly non-existent

Parasympathetic ganglia "terminal ganglia"

Parasympathetic ganglia of the head have specific names:

Ciliary ganglion Pterygopalatine ganglion Submandibular ganglion Otic ganglion

Parasympathetic ganglia

Parasympathetic splanchnic nerves extend to ____

viscera

Axons of parasympathetic neurons extend to parasympathetic postganglionic neurons in terminal ganglia in the walls of the colon, ureters, urinary bladder, and reproductive organs by means of pelvic ___

splanchnic nerves

Sympathetic preganglionic neurons arriving at sympathetic trunk ganglia may connect with postganglionic neurons by . . . (4 options)

Synapsing in the ganglion it first reaches, OR BY… Ascending or descending before synapsing, OR BY… Continuing, without synapsing, through the trunk ganglion to a prevertebral ganglion and synapsing there with postganglionic neurons, OR BY… Continuing without synapsing through both the sympathetic trunk ganglion and a prevertebral ganglion to extend to chromaffin cells of the adrenal medullae

Sympathetic preganglionic fibers have many axon ___, and synapse with a number of postganglionic neurons (20 or more)

collaterals This is a divergent projection pattern Explains in part why sympathetic responses typically affect almost the entire body, and why they do so simultaneously

Postganglionic axons of the sympathetic division usually terminate in several ___ after leaving their ganglia

effectors

Parasympathetic preganglionic neurons have ___ collaterals, and synapse with a limited number of postganglionic neurons, all of which are in the same visceral effector

few axon This is technically a divergent projection pattern (but not much divergence) Explains in why parasympathetic responses can be localized to a single effector

Parasympathetic postganglionic axons terminate in the __ effector after leaving their ganglia (rather than branching out to different effectors)

same

tangled networks of neurons formed jointly by the sympathetic and parasympathetic nervous systems

Autonomic plexuses

They are present in the thorax, abdomen, and pelvis Many of them lie along major arteries Visceral afferent fibers are commonly also present?

Autonomic plexuses

at the base of the heart, it surrounds the large blood vessels emerging from the heart. It is contributed to by both post-ganglionic sympathetic and pre-ganglionic parasympathetic nerves. Sympathetic neurons to this plexus increase heart rate and contractility. Parasympathetic innervation, provided by the vagus nerve, supplies fibers to the heart that slow heart rate

Cardiac plexus

posterior to each lung, sympathetic and parasympathetic branches of the autonomic nervous system serve the lungs, bronchi, and pulmonary blood vessels. Sympathetic innervation causes bronchodilation. Parasympathetic pathway causes bronchoconstriction and increased secretion from mucous glands of the bronchial tree

Pulmonary plexus

(AKA solar plexus): the largest autonomic plexus, it surrounds the celiac and superior mesenteric arteries, and is at the level of the last thoracic / first lumbar vertebrae

Celiac plexus

supplies the small and large intestine Celiac plexus

Superior mesenteric plexus

innervates the large intestine Celiac plexus

Inferior mesenteric plexus

Cell bodies are part of the ___ horns of all thoracic segments plus the first two or three lumbar segments of the spinal cord Sympathetic Preganglionic Neurons

lateral (The axons are myelinated) Sympathetic Preganglionic Neurons

Preganglionic axons leave the spinal cord through the ___ root of a spinal nerve along with somatic motor neurons at the same level, and exit through the intervertebral foramina Sympathetic Preganglionic Neurons

The myelinated axons pass through a white ___ to enter an adjoining paravertebral (chain) ganglion, thereby forming part of the sympathetic trunk, AKA sympathetic chain Sympathetic Preganglionic Neurons

ramus communicans

White rami communicantes are present only in the _____, since those are the only regions with sympathetic outflow

thoracic and first two lumbar nerves (T1-L2)

Sympathetic trunk ganglia are paired, one on each side of the vertebral column, typically consisting of:

``` 3 cervical ganglia 11 or 12 thoracic ganglia 4 or 5 lumbar ganglia 4 or 5 sacral ganglia 1 coccygeal ganglion (fused at midline) ```

Cervical ganglia (Sympathetic preganglionic ) fibers that serve the head and neck emerge from spinal cord segments T1 – T6, and ascend to synapse with postganglionic neurons within cervical ganglia in the neck, comprising

Superior cervical ganglion Middle cervical ganglion Inferior cervical ganglion

Superior cervical ganglion postganglionic sympathetic fibers supply the head and heart

``` Sweat glands Smooth muscle of the eye Blood vessels of the face Salivary glands Pineal gland Lacrimal glands Heart ```

Middle cervical ganglion and inferior cervical ganglion postganglionic sympathetic fibers supply the ___

heart

The thoracic region receives most of the sympathetic ___ axons (sympathetic)

preganglionic

Postganglionic fibers from the thoracic sympathetic trunk innervate . . .

``` Heart Lungs Bronchi Sweat glands Blood vessels of the skin Arrectores pilorum muscles ```

``` Heart Lungs Bronchi Sweat glands Blood vessels of the skin Arrectores pilorum muscles ``` innervated by what of the sympathetic trunk?

Postganglionic fibers from the thoracic sympathetic trunk

Axons leave the sympathetic trunk in four possible ways

Enter spinal nerves Form cephalic periarterial nerves Form sympathetic nerves Form splanchnic nerves

Sympathetic trunk pathways: enter a spinal nerve...

Some incoming sympathetic preganglionic neurons synapse with postganglionic neurons either in the ganglion at the level of entry, or farther up or down the sympathetic chain Axons of those postganglionic neurons leave the trunk by means of a gray ramus (gray ramus communicans), then merge with the anterior ramus of a spinal nerve

Axon collaterals from preganglionic neurons may pass up or down the ___ for a variable distance, forming sympathetic chains, which are the fibers on which the ganglia are located

sympathetic trunk

Unmyelinated postganglionic axons pass through a ____ to connect the ganglia of the sympathetic trunk to spinal nerves

gray ramus communicans | gray ramus communicans are all the way up and down the spine

Since gray rami communicantes are associated with all spinal nerves, they outnumber white rami communicantes, which are associated with only the _____

thoracic nerves and two or three lumbar nerves

Some preganglionic neurons ascend in the sympathetic trunk to the superior _____, where they synapse with postganglionic neurons

cervical ganglion

Those postganglionic neurons (from the cervical ganglion) extend to the head by wrapping around and following certain arteries (such as the carotid artery) from the neck to the head, forming _____ (sympathetic)

cephalic periarterial nerves

Cephalic periarterial nerves supply sympathetic innervation to: (sympathetic)

skin of the face (sweat glands, smooth muscle of blood vessels, arrectores pilorum muscles) visceral effectors of the head (smooth muscles of the eye, lacrimal glands, pineal gland, nasal mucosa, salivary glands)

After synapsing with preganglionic neurons, some postganglionic neurons form sympathetic nerves that extend to visceral effectors in the thoracic cavity, providing: (sympathetic)

Sympathetic nerves to the heart (the superior, middle, and inferior cervical ganglia, and first through fourth thoracic ganglia) Sympathetic nerves to smooth muscle of bronchi and lungs

Some sympathetic preganglionic neurons pass through the trunk without terminating in it. They then form nerves called ____ that generally extend to prevertebral ganglia

splanchnic nerves

Splanchnic nerves are formed by preganglionic axons that pass through the ____ without terminating in it, then terminate in prevertebral ganglia

sympathetic trunk | generally innervate organs below the diaphragm

Postganglionic neurons of the greater splanchnic nerve supply . . .

``` Liver Stomach Spleen Small intestine Kidney ```

Postganglionic neurons of the lesser splanchnic nerve innervate . . .

Small intestine | Colon

Postganglionic neurons of the lumbar splanchnic nerve innervate . . .

Colon Rectum Genitals Urinary bladder

Although there are no postganglionic neurons from the adrenal medullae, developmentally the adrenal medullae are derived from the same type of precursor cell, called ____, that gives rise to postganglionic neurons elsewhere in the body

chromaffin cell

In effect, then, the adrenal medullae themselves comprise a large complex of _____, the cells of which release hormones into the blood (mostly epinephrine, some norepinephrine, a trace of dopamine)

postganglionic neurons

Cell bodies are in nuclei in the brain stem and in the ___ horns of the second through fourth sacral segments of the spinal cord (Parasympathetic Preganglionic Neurons)

lateral

Axons emerge as part of a cranial nerve, or as part of the anterior root of a spinal nerve: (Parasympathetic Preganglionic Neurons)

cranial parasympathetic outflow consists of preganglionic axons, from the brain stem in four of the cranial nerves sacral parasympathetic outflow, comprises preganglionic axons in anterior roots of the second through fourth sacral spinal nerves

(Parasympathetic Preganglionic Neurons)

The axons are myelinated, and end in terminal ganglia close to the organ they innervate

(Parasympathetic Preganglionic Neurons)

located near the posterior aspect of each eyeball; preganglionic axons from oculomotor nerves (CN III); postganglionic axons innervate smooth muscles in eyeball Cranial parasympathetic ganglia

Ciliary ganglia

preganglionic axons from facial (VII) nerves; postganglionic axons to nasal mucosa, pharynx, and to lacrimal glands Cranial parasympathetic ganglia

Pterygopalatine ganglia

located near submandibular salivary gland ducts; preganglionic axons from facial (VII) nerves; postganglionic axons to submandibular salivary glands and sublingual salivary glands Cranial parasympathetic ganglia

Submandibular ganglia

inferior to each foramen ovale; pregangliionic axons from glossopharyngeal (IX) nerves; postganglionic axons to parotid salivary glands Cranial parasympathetic ganglia

Otic ganglia

Most (80%) of the total craniosacral outflow is carried by preganglionic axons that leave the brain as part of the ____

vagus nerves (cranial nerve X)

The vagus nerve sends axons to the . . .

``` Heart Airways of the lungs Liver Gallbladder Stomach Pancreas Small intestine Large intestine ```

innervated by Vagus nerve

Preganglionic neurons of the sacral parasympathetic outflow form pelvic splanchnic nerves, the postganglionic neurons of which innervate smooth muscle and glands in . . . (PARASYMPATHETIC)

Colon Ureters Reproductive organs Urinary bladder