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Lecture 20 - The Autonomic Nervous System
System
58
Anatomy
Undergraduate 1
11/20/2010

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Term
Somatic nervous system
Definition
Skeletal muscles are controlled by the motor side of the somatic nervous system. Movement of skeletal muscles occurs in response to commands that are usually under conscious control (exceptions are certain postural and spinal reflexes)
Term
The enteric branch
Definition
is represented by a highly complex network of neurons found in the walls of the gut.
Term
The autonomic nervous system controls the following effectors:
Definition

-cardiac muscle

-smooth muscle

-glandular epithelium

Term
In the somatic nervous system...
Definition
a motor neuron in the spinal cord sends an axon through a peripheral nerve and make a direct synapse with skeletal muscle fibers.
Term
Preganglionic neurons
Definition
The axons of the first neurons are called pregalionic axons, and neurons themselves are called preganglionic neurons.
Term
Postganglionic axons
Definition
The axons of the second-order neuron are called post ganglionic axons. The neurons themselves are called postganglionic neurons, even though their cell bodies are within the ganglia
Term
Spinal cord Autonomic ganglia
Definition
The first motor neurons of the sympathetic and parasympathetic branches of the autonomic nervous system are in the spinal cord, as in the case of the somatic nervous system. However, the efferent pathways of the sympathetic and parasympathetic autonomic nervous system involve groups of second-oder neurons that are located in autonomic ganglia outside of the CNS. The axons of the first motor neurons synapse with these second-order neurons, which in turn send their axons to the visceral effectors, i.e. cardiac muscle, smooth muscle or glandular epithelium.
Term
There are three general goups of ganglia in the parasympathetic and sympathetic branches of the autonomic nervous .
Definition

-Paravertebral ganglia

-Collateral ganglia

-Terminal ganglia/Intramural ganglia

Term
Paravertebral ganglia sympathetic trunk
Definition
The paravertebral ganglia are arranged like a string of beads along either side of the vertebral column. The beads are the ganglia, and the whole string is the sympathetic trunk
Term
Collateral ganglia
Definition
The second group also associated with sympathetic division. Ganglia in this group are called collateral ganglia.
Term
Terminal ganglia (intramural ganglia)
Definition
The third group associated with parasympathetic division. They belong to the parasympathetic division, and are located wither very close to the organ be innervated or are actually within the walls of the organ itself. In the gut, neurons in these ganglia input into the enteric branch of the autonomic nervous system.
Term
Myelinated preganglionic axons of the sympathetic
Definition
exit with somatic efferents through ventral roots of spinal cord segements T1-T12 and L1-L2.
Term
White rami Paravertebral ganglion
Definition
Once outside the vertebral column, white rami branch away from spinal nerve and connect with a paravertebral ganglion. The white rami are white because their fibers are myelinated.
Term
Gray rami
Definition
Once they have entered the parabertebral ganglion, the preganglionic fibers may: Form synapses with second-oder neurons in the paravertebral ganglion. The fibers of these second-order neurons are unmyelinated. These postganglionic fibers (=axons) emerge from the paravertebral ganglia in the gray rami and join the spinal nerve again. They innervate many organs, including the iris of the eye, the salibary glands, lungs, heart.
Term
once they entered the paravertebral ganglion, the preganglionic fibers may: alternatively
Definition
the preganglionic fibers may pass straight through the paravetabral ganglion without synapsing ( they are still called preganglionic because they haven’t synapsed yet). There after, these preganglionic fibers may do one of many things.
Term
Preganglionic fibers that do not synapse in paravertebral ganglion.
Definition
The preganglionic fibers may emerge from the paravertebral ganglion and pass up or down the sympathetic trunk before forming synapses with second-order neurons in other paravertebral ganglia. The unmyelinated axons of the postganglionic, second-order neurons rejoin the spinal nerves via the gray rami
Term
Slanchinic nerves Colateral ganglia
Definition
Instead of passig up and down the sympathetic trunk, the preganglionic fibers may emerge from the paravertebral ganglion in nerves called the splanic nerves, and form their first synapses with second-order neurons in the collateral ganglia.
Term
Collateral ganglia include
Definition

celia ganglion

the superior mesenteric ganglion

the inferior mesenteric ganglion.

Term
From second-oder neurons in the the collateral ganglia...
Definition
unmyelinated post ganglionic axons distribute themselves to many organs. In the case of the celia ganglia, these organs include the stomach, spleen, liver, kidney and small intestine
Term
The adrenal glands
Definition
is one apparent exception to the general rule of two neurons in the efferent pathways of the symptheti and parasympthetic branches of the autonomic nervous system, some preganglionic axons from first neurons in the sympathetic nerves synapse directly on cells in the adrenal medulla.
Term
Neurosecretory cells
Definition
Secrete their neurotransmitters into the bloodstream. These neurotransmitters, more correctly called hormones, are norepinephrine and its close relative epinephrine (= adrenalin).
Term
Parasympathetic Division
Definition

The parasympathetic division of the autonomic nervous system has its first neurons in two widely-sepatated locations of the central nervous system:

 

the head (cranial) end

the tail (sacral) end.

Term
The cranial group of parasympathetic neurons is found
Definition
in certain cranial nerve nuclei of the midbrain, pons and medulla
Term
The sacral group of the parasympathetic neurons is found
Definition
in the gray matter of the spinal cord segments S2-S4
Term
Cranial end of the parasympathetic division
Definition
Parasympathetic preganglionic fibers exit cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal) and X (the vagys).
Term
Parasympathetic: Cranial Nerve III (oculomotor)
Definition

ganglion:

- ciliary organ

- iris

Term
Parasympathetic: Cranial Nerve VII (facial)
Definition

ganglion: pterygopalatine organs

-lacrimal (tear) glands and nasopharyngeal mucosa

-subamandibular organ

-salivary

Term
Parasympathetic: Cranial X (the vagus)
Definition
Ganglion: has its second neurons in the walls of organs (intramural ganglia) organs - lungs, heart, liver, stomach, small intestine, ascending colon
Term
Sacral end of the parasympathetic division
Definition
Collectively, the sacral parasympathetic outflow as preganglionic fibers from the ventral roots of S2-S4. These fibers constitute the pelvic splanchnic nerves. They synapse with second, postnglionic neurons in the walls of the urinary bladder, rectum, genital organs. These synapses are called intramural synapses.
Term
Acetylcholine binds to two types of cell surface receptor:
Definition

-nicotinic receptors

-muscarinic receptors

Term
Norepinephrine binds to two types of cell surface receptors:
Definition

-alpha-adrendergic receptors

-beta-adrenergic receptors

Term
Distribution of neurotransmitter receptors
Definition
-The membranes of sympathetic and parasympathetic postganglionic neurons have nicotinic acetylcholine receptors. -alpha and beta-adrenergic receptors are found on the membranes of cells that respond to norepinephrine. -Muscarinic acetylcholine receptors are found on the cells that respond to acetylcholine released from autonomic nerve endings.
Term
Adrenal medulla
Definition
The cells of the adrenal medulla are modified postganglionic sympathetic neurons. When stimulated by preganglionic neurons they release catecholamines epinephrine (80%) and norepinephrine (20%) into the blood (epinephrine is another word for adrenalin). From the adrenal medulla, these catecholamines are swept by the bloodstream to many tissues and organs, so that sympathetic stimulation of the adrenal can have widespread action throughout the body.
Term
Nicotinic Receptors
Definition
One receptor for acetylcholine is found in the postsynaptic membrane of both sympathetic and parasympatheic postganglionic neurons, and is called a nicotinic receptor. The motor endplate of the neuromuscular junction also has nicotinic receptors. nicotinic acetylcholine receptors are also found in the brain, where they are responsible for the effects of nicotine and nicotine addiction from cigarette smoking. The nicotinic receptor is an example of a ligand-gated ion channel.
Term
Muscarinic receptors
Definition
The second receptor for acetylcholine is found in the postsynaptic membrane of synapses formed by the second neurons of the parasympathetic division with visceral effectors. This receptor is called the muscarinic (so called because the toadstool toxin called muscarine acts as an agonist)
Term
Alpha-adrenergic
Definition
Bind both epinephrine and norepinephrine. Alpha receptors are found in the walls of blood vessels
Term
Beta-adrenergic receptors
Definition
bind norepinephrine and epinephrine. Certain blood vessels have Beta receptors as well as alpha receptors in their walls. Beta-adrenergic receptors mediate the increase in force and rate of contraction of the heart when the sympathetic system is stimulated.
Term
Sympathetic is involved in the fight-orflight response:
Definition

1) Pupils dilate

2) Heart rate and force of contraction increase

3) Blood vessels in skin and viscera contract.

4) dilation of bronchioles to allow faster movements of air into and out of the lungs

5) Blood vessels in skeletal muscles dilate

6) Liver glycogen is converted to glucose

7) Epinephrine and norepinephrine are secreted by the adrenal medulla 8) “Non-essential” activities are inhibited (e.g. activity of the gastrointestinal tract, such as digestive secretion and movement.)

Term
Action of sympathetic and parasympathetic stimulation: pupil of eye
Definition

Symp - dialated

 

Para - constricted

Term
Action of sympathetic and parasympathetic stimulation: glands (lacrimal, salivary)
Definition

sympathetic - no action or slight stimulation

 

parasympathetic - strong stimulation sweat

 

symp - strong stimulation (cholinergic)

 

para - no action Gastric symp - inhibition parasy - stimulation

Term
Action of sympathetic and parasympathetic stimulation: stomach
Definition

symp - dcreased motility

 

para - increased motility

Term
Action of sympathetic and parasympathetic stimulation: Heart
Definition

Symp - increased rate and force of contraction

 

Para - decreased rate (strong stimulation causes “vagal arrest”)

Term
Action of sympathetic and parasympathetic stimulation: Lungs (smooth muscle in the bronchi and bronchioles)
Definition

symp - dilated

 

para - constricted

Term
Action of sympathetic and parasympathetic stimulation: arterioles (skin, viscera)
Definition

symp - constricted

 

para - not innervated

Term
Action of sympathetic and parasympathetic stimulation: veins and muscular venules
Definition

symp - constricted

 

para - not innervated

Term
Action of sympathetic and parasympathetic stimulation: basal metabolism
Definition

symp - increased

 

para - not innervated

Term
Action of sympathetic and parasympathetic stimulation: penis
Definition

Sym - ejaculation

 

Para - erection (also of clitoris in female)

Term
Action of sympathetic and parasympathetic stimulation: liver
Definition

symp - glycogen --> glucose

 

para - moderate glycogen

Term
Action of sympathetic and parasympathetic stimulation: intestine
Definition

Symp - decreased mobility, tone

 

Para - strongly increased mobility, tone

Term
The autonomic reflex involves
Definition

1) a receptor

2) a sensory afferent neuron

3) one or more interneurons

4) a preganglionic motor neuron

5) a postganglionic motor neuron in an autonomic ganglion

6) an effector (smooth muscle, cardiac muscle, glandular)

Term
The difference between somatic and autonomic reflexes
Definition
The only real difference is the presence of two motor neurons in the efferent motor pathway, the second on being housed in a sympthetic or parasympathetic autonomic ganglion
Term
Baroceptor reflex
Definition

1) A fall of blood pressure causes special stretch receptors (baroceptors) in the aortic arch and carotid artery to become less strech and to reduce their firing rate. this reduses the frequency of action potentials passing up the sensory axons neurons in the medulla.

 

2) this increases the firing rate of a group of neurons in the medulla

 

3) The neurons in the medulla signal to sympatheric motor neurons, which (via postganglionic neurons) cause the heart to increase its rate and force of contraction.

 

4) The sympathetic motor neurons also cause smooth muscle contraction in the blood vessels, narrowing them (=vasoconstriction).

Term
Medula actions
Definition

-cardiac

-respiratory

-vasomotor

-swallowing

-vomiting

Term
hypothalamus
Definition
temperature regulation
Term
Autonomic system: Cerebral cortex
Definition
Control of the sympathetic and parasympathetic branches of the autonomic nervous system by the cerebral cortex seems to occur primarily during emotional stress (fear, anxiety, etc)
Term
Autonomic: Limbic system
Definition
the cerebral cortex operates through the limbic system. Note, however, that some components of the limbic system are actually cerebral cortex (e.g. the cingulate gyrus,)
Term
Autonomic System: Hypothalamus
Definition
The hypothalamus is the major output pathway of the limbic system, and the hypothalamus controls and integrates the autonomic nervous system.
Term
Pons and medulla
Definition
The hypothalamus in turn can stimulate centers in the pons and medulla. For example, the cardiac and vasometor centers in the medulla can increase heart rate, force of heart contraction, and ma rise the blood pressure. The micturition center in the pons regulates micturition. respiratory centers are found in the pons and medulla.
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