BSC 2085 ANS

Autonomic Nervous System

Lecture Notes

General function -- portion of nervous system that automatically (reflexively) regulates activities of smooth muscle, cardiac muscle, exocrine glands (sweat), endocrine glands (adrenal) and adipose tissue.

I. Differences between somatic nervous system (SNS) and autonomic nervous system (ANS)

A. Effectors controlled
SNS skeletal muscles
ANS smooth muscle, cardiac muscle, endocrine and exocrine glands

B. Control
SNS usually voluntary via motor cortex
ANS involuntary via hypothalamus (or medulla oblongata)

C. Neural pathway (motor portion of arc)
SNS only 1 motor neuron to effector cell
ANS has 2 motor neurons axons to effector cell, i.e., preganglionic and postganglionic cells. ganglion represents synapses along motor pathway.

D. Action on effector
SNS always excitatory
ANS excitatory or inhibitory (depending on which division , sympathetic or parasympathetic, provides the stimulation
dual innervation = both divisions affect an organs--all visceral organs but not sweat glands, adipose tissue and smooth muscle in blood vessels.

E. Neurotransmitters
SNS -ACh (Acetylcholine) released by both pre- and post-ganglionic neurons (to effector cell). Acetylcholinesterase (ACHase) rapidly removes ACh from synaptic gaps.
ANS -usually ACh released by preganglionic neurons and norepinephrine (NE) released by postganglionic neuron to effector cell. sweat gland is exception. Monoamine oxidase (MAO) slowly removes NE from synaptic gaps.

F.Typical autonomic reflex arc

1 visceral receptors

2 sensory neurons for input

3. CNS association areas (brain or spinal cord)

4. Motor output
    a. Myelinated preganglionic neurons exit, with SNS neurons, as cranial/spinal nerves
    b. Ganglion (clusters of cell bodies outside of CNS)
    c. Unmyelinated postganglionic neuron

5. Effector (smooth and cardiac muscle, exocrine and endocrine glands)

Distinguish important differences between SNS and ANS systems.

G. Examples of Autonomic reflexes
    1. smooth muscles of GI tract (gastric and intestinal mobility)
    2. cardiac muscle (heart rate)
    3. smooth muscles of blood vessels (vasomotor responses)
    4. Ventilation rate and bronchomotor responses)
    5. Urination and defecation
    6. production of epinephrine
    7. regulation of blood glucose

II. Structure of autonomic divisions

A. Parasympathetic division ( known as the craniosacral division)
    1. cranio region (4 cranial nerves)
        a. oculomotor (pupil constriction and cilary lens focusing)
        b. facial ( nasal mucous production as well as lacrimal and salivary glands)
        c. glossopharyngeal (saliva production)
        d. vagus nerve (affect functions of liver, gallbladder, stomach, intestines, pancreas, heart (slow HR), lungs.)

2. saccral region (4 pelvic splanchnic spinal nerves) to innervate
intestine, ureters, urinary bladder and reproductive organs.

3. distribution pattern limited to thorax and abdomen, mostly

a. Long preganglionic neuron
b. Terminal ganglion (in or near effector)
b. Few and short postganglionic neurons
Result: single effectors are stimulated with one pathway-localized stimulation.

C. Sympathetic Division ( known as the thoracolumbar division)
1.neurons exit via all thoracic spinal nerves and several lumbar spinal nerves to ALL organs innervated by parasympathetic division and MORE ( e.g., sweat glands, adipose tissue and blood vessels)

2.distribution more widespread than parasympathetic division

a. Short preganglionic neurons
b. Ganglion typical near vertebrae
c. Long and many postganglionic neurons
Result: widely diverging pathways increase number of effectors stimulated by one pathway-global stimulation.Distinguish important differences in structure of the two divisions of ANS.

III. Physiology of ANS A. Neurotransmitters and their receptors (chemically gated channels) 1. Cholinergic neurons release ACh neurotransmitter to cholinergic receptors a. ACh released from: all preganglionic neurons; all parasympathetic postganglionic neurons; sympathetic postganglionic to most sweat glands.

b. Cholinergic effects are short lived due to ACh destruction by Acetylcholinesterase (ACHase)

c. two types of Cholinergic receptors (on effectors)
nicotinic effects (mimic effect of nicotine in tobacco):excites skeletal muscle contraction; increases adrenal medula gland's production of epinephrine (or NE); in CNS causes addiction.

muscarinic (mimic effect of mushroom poisoning): inhibits smooth muscle in GI tract but excites smooth muscle in iris (pupil constriction) and sweat and salivary gland production.

2. Adrenergic neurons release NE (norepinephrine) neurotransmitter to adrenergic receptors a. NE released from most sympathetic postganglionic neurons

b. NE is removed slowly by MAO (monoanine oxidase), also stays in blood and secreted by adrenal glands therefore adrenergic effects last longer
c. two types of andrenergic receptors (alpha and beta)
alpha and Beta 1 receptors (effectors) tend to be excited by increased NE
alpha and beta 2 effectors tend to be inhibited by increased NE (work with parasympathetic division)

Relate the general pattern of neurotranmitters in the ANS

3. The activity of certain amine hormones (NE, dopamine, serotonin) can be regulated by drugs:
a) MAO inhibitors (MAOIs) remove the inhibitory effect of the MAO enzyme so the neurotransmitter concentrations stay high
b) inhibition of re-uptake. Many hormones are modified when they bond to receptors (on the postsynaptic neuron) and then are recycled by being moved back into (i.e., re-uptake) the pre-synaptic neuron. Selective re-uptake inhibitor drugs also keep the neurotransmitter concentrations high. B. Physiological responses due to Sympathetic stimulation
1. triggered by emotional or physical stress (4E's = Exercise, Emergency, Embarrasment, excitement)
2) specific actions
a). increases heart rate and blood pressure
b. respiration rate and bronchodilation (more oxygen) increases
c. vasodilation (more blood) to acting organs (heart, skeletal muscle, liver, adipose) increases
d. vasoconstriction (less blood) to not needed organs (skin, kidney, GI tract) and less mobility to GI tract
e. increased blood sugar due to increased liver and adipose function
f. pupil dilation
g. increased secretion of NE by adrenal glands (provides hormonal amplication of nervous stimulation actions)

3) General result
a) supports activities that burn energy and allow vigorous physical activity
b) short term reduction of stress
c) longer lasting (due to slow NE removal) but wider distributed (more divergent motor pathways) than parasympathetic

C. Physiological responses due to Parasympathetic stimulation
1) triggered by resting and feeding "rest and digest"
2) specific actions
a. increased Salivation
b. increased Lacrimation
c. vasodilation to kidneys and GI tract (Urinary system, Digestion and Defecation)
d. also decreased heart and respiratory rates
e. pupil constriction

3) General result
a) supports activities that conserve and store energy (SLUDD)|
b) "paradoxical fear" =massive activation of parasympathetic division, therefore loss of control of urination and defecation.
c) shorter lasting (due to fast AChremoval) but narrower distributed (less divergent motor pathways) than sympathetic

Distinguish the specific actions and general response patterns of each division.

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Professor Thomas M. Lancraft
Human Anatomy and Physiology Courses
at St. Petersburg College
St. Petersburg/Gibbs Campus

5/24/2003