Chapter 15: The Autonomic Nervous System

Compare/contrast the basic characteristics of the somatic and autonomic nervous system

somatic:

• sensory & motor neurons

• voluntary

autonomic:

• receives input from sensory receptors located in organs, blood vessels, muscles, & nervous system

• involuntary

Compare the sensory input of the SNS vs. ANS

SNS → somatic senses & special senses

ANS → interoceptors; some somatic & some special senses

Compare the control of motor output for SNS vs. ANS

SNS → voluntary; from cerebral cortex (contributions from corpus striatum, cerebellum, brainstem, spinal cord)

ANS → involuntary; from hypothalamus, limbic system, brainstem, & spinal cord

Compare the motor neuron pathway for SNS vs. ANS

SNS → one-neuron pathway; somatic motor neurons extending from CNS synapse directly with effector

ANS → usually two-neuron pathway; preganglionic neurons extending from CNS synapse with postganglionic neurons in autonomic ganglion, & postganglionic neurons extending from ganglion synapse with visceral effector

Compare the neurotransmitter & hormones of the SNS vs. ANS

SNS → all somatic motor neurons only release ACETYLCHOLINE (ACh)

ANS → all sympathetic/parasympathetic preganglionic neurons release ACh. Most sympathetic postganglionic neurons release NE; those to most sweat glands release ACh. All parasympathetic postganglionic neurons release ACh. Chromaffin cells of suprarenal medullae release epinephrine & norepinephrine (NE)

Compare the effectors of the SNS vs. ANS

SNS → skeletal muscle

ANS → smooth muslce, cardiac muscle, & glands

Compare the responses of the SNS vs. ANS

SNS → contraction of skeletal muscle

ANS → contraction/relaxation of smooth muscle; increased or decreased rate & force of contraction of cardiac muscle; increased or decreased secretions of glands

Which parts of the brain provide regulation for ANS reflexes?

hypothalamus & brain stem

What are interoceptors? Where are they located and what is their function? Provide two examples of an interoceptor

interoceptors

• location: blood vessels, visceral organs, muscles, & nervous system

• function: monitor conditions in the internal environment

• example 1: chemoreceptors → monitor blood CO2 level

• example 2: mechanorecepetors → detect the degree of stretch in walls of organs/blood vessels

How do autonomic motor neurons regulate visceral activities?

either increasing (Exciting) or decreasing (inhibiting) ongoing activities in thier effector tissues

Most autonomic motor pathways consist of two motor neurons in series. Name and briefly describe them

1. preganglionic neuron → cell body is in CNS & axon extends to an autonomic ganglion

2. postganglionic neuron → unmyelinated axon extending from ganglion to effector

What is dual ANS innvervation?

most body organs receive impulses from both sympathetic & parasympathetic neurons

What is the difference between the sympathetic and parasympathetic nervous system?

sympathetic → “flight-or-flight”; stimulation leads to increased alertness & metabolism

parasympathetic → “rest-and-digest”; stimulation slows down most body activity

Where are the cell bodies of the preganglionic neurons located in the sympathetic division?

lateral gray horns of the gray matter in the T1-L3 segments

List the ganglion of the sympathetic division

1. celiac ganglion

2. aorticorenal ganglion

3. superior mesenteric ganglion

4. renal ganglion

5. inferior mesenteric ganglion (?)

What is another name for the sympathetic division?

thoracolumbar

Name the 2 major types of sympathetic ganglia & briefly describe them

1. sympathetic trunk ganglia → lie in vertical row on either side of the vertebral column

2. prevertebral ganglia → lie anterior to vertebral column & close to large abdominal arteries

What does the sympathetic division stimulate that the parasympathetic division does not?

skin & kidney

Where are the cell bodies of the preganglionic neurons in the parasympathetic division?

in the nuclei of 4 cranial nerves (III, VII, IX, X) in the brain stem & in lateral gray matter in S2-S4 segments of the spinal cord

__% of parasympathetic flow goes through the __ nerve

80%; vagus

What is another name for the parasympathetic division?

craniosacral

List the ganglia of the parasympathetic nervous system

1. terminal ganglia

2. ciliary ganglion

3. pterygopalatine ganglion

4. submandibular ganglion

5. otic ganglion

List the 4 ways that axons of sympathetic preganglionic neurons connect with postganglionic neurons

1. Axon may synapse w/ postganglionic neurons in the 1st ganglion is reaches

2. Axon may ascend or descend to a higher or lower ganglion before synapsing w/ postganglionic neurons

3. axon may continue w/o synapsing, thru the sympathetic trunk ganglion to end at a prevertebral ganglion & synapse w/ postganglionic neurons

4. axon may pass w/o synapsing, thru the sympathetic trunk ganglion & a prevertebral ganglion, then extend to adrenal medullae

what is the adrenal medullae?

central part of adrenal gland, on top of kidneys; activates fight or flight

The abdomen & pelvis contain major autonomic plexuses which are often named after the artery along which they are distributed. Name them

1. celiac (solar) plexus

2. superior mesenteric plexus

3. inferior mesenteric plexus

4. renal plexus

5. hypogastric plexus

mnemonic → Cats Sleep More In Rainy Houses

Where are the sympathetic trunk ganglia?

anterior & lateral to vertebral column

• 2 cervical

• 11-12 thoracic

• 4-5 lumbar

• 4-5 sacral

• 1 coccygeal

Based on the neurotransmitter they produce and release, autonomic neurons are considered as either ___ or ___. What neurotransmitters does each release?

cholinergic → release acetylcholine (ACh)

adrenergic → release norepinephrine (noadrenalin)

What are 2 cholinergic receptors?

• nicotinic receptors

• muscarinic receptors

List the 3 major locations of nicotinic receptors and the effects of each

1. Plasma membrane of postganglionic sympathetic & parasympathetic neurons → excitation = impulses in postganglionic neurons

2. chromaffin cells of suprarenal medullae → epinephrine & norepinephrine secretion

3. sarcolemma of skeletal muscle fibers (motor end plate) → excitation = contraction

List the 3 major locations of muscarinic receptors and the effects of each

1. effectors innervated by parasympathetic postganglionic neurons → in some, excitation; in others, inhibition

2. sweat glands innervated by cholinergic sympathetic postganglionic neurons → increased sweating

3. skeletal muscle blood vessels innervated by cholinergic sympathetic postganglionic neurons → inhibition to relaxation to vasodilation

what are beta blockers? how do they work? provide an example.

• AKA “beta-adrenergic blocking agents”

• medications that reduce blood pressure

  • work by blocking the effects of epinephrine (adrenaline)

  • cause heart to beat slower & w/ less force → lowers BP

  • widens veins/arteries to improve blood flow

• e.g. propanolol

Compare the distribution of sympathetic vs. parasympathetic division

symp → wide regions; skin, sweat glands, arrector muscles of hair, adipose tissue, smooth muscle of blood vessels

para → mainly to head & viscera of thorax, abdomen, & pelvis; some blood vessels

Compare the location of preganglionic neuron cell bodies & site of outflow for symp vs. para divisions

symp → lateral gray horns of spinal cord segments T1-L2 or L3.

para → nuclei of cranial nerves III, VII, IX & X (3, 7, 9, 10)

Compare the associated ganglia of the symp vs. para divisions

symp → sympathetic trunk ganglia & prevertebral ganglia

para → parasympathetic ganglia

Compare the ganglia locations of the symp vs. para divisions

symp → close to CNS & distant from visual effectors

para → typically near or within wall of vicsceral effectors

Compare the axon length & divergence of the symp vs. para divisions

symp → preganglionic neurons w/ short axons synapse with many postganglionic neurons with long axons that pass to many visceral effectors

para → preganlionic neurons w/ long axons usually synapse w/ 4-5 postganglionic neurons w/ short axons that pass to a single visceral effector

Compare the white & gray communicating rami of the symp vs. para divisions

symp → bost present; white contains myelinated preganglionic axons; gray contains unmyelinated postganglionic axons

para → neither present

Compare the neurotransmitters of the symp vs. para divisions

symp → preganglionic neurons release acetylcholine (ACh) which is excitatory & stims postganglionic neurons; most postganglionic neurons release norepineprine (NE); postganglionic neurons that innervate mosr sweat glands & some blood vessels in skeletal muscle release ACh

para → preganglionic neurons release ACh, which is also excitatory and stims postganglionic neurons; postganglionic neurons release ACh

Compare the physiological effects of the symp vs. para divisions

symp → fight-or-flight

para → rest-and-digest

What is Autonomic Tone? What is it regulated by?

balance between sympathetic & parasympathetic nervous system activity

• regulated by hypothalamus

• effects body organs differently

• when sympathetic input increases, parasympathetic input decreases & vice versa (equilibrium)

What does Sympathetic Stimulation lead to?

• secretion of norepinephrine by adrenal glands

• increase in rate & strength of the heartbeat

• constriction of blood vessels of non-essential organs

• dilation of vessels of essential organs (skeletal muscle & cerebral cortex)

• increase in rate & depth of breathing

• hepatic conversion of glycogen → glucose

• decrease in GI activity

SLUDD is an acronym used to describe the responses of the prasympathetic nervous system. What does it stand for?

Salivation (increased)

Lacrimation (increased)

Urination (increased)

Digestion (increased)

Defecation (increased)

• & 3 decreases (rate/force of heart beat, airway size, rate of breathing, & pupil size)

What is controlled when nerve impulses pass through an autonomic reflex arc?

• heart rate & force of ventricular contraction

• blood pressure & blood vessel diameter

What is the autonomic reflex arc composed of?

• receptor

• sensory neuron

• integrating center

• motor neurons

• effector

What is Raynaud Phenomenon?

• occurs due to excessive sympathetic stimulation of smooth muscle in arterioles of digits

• vasoconstriction leads to numbness & ischemia in digits