OVERVIEW

Defined

1. Autonomic nervous system - subdivision of PNS; involuntary

Somatic versus autonomic

1. Effectors – target

-a. Somatic - skeletal muscle

-b. Autonomic - cardiac, smooth muscle, and glands

2. Efferent pathway – motor

-a. Somatic - single neuron chain conduct impulses very rapidly

-b. Autonomic– 2 neuron chain; preganlionic and postganglionic

3. Neurotransmitter effects – excitatory or inhibitory

-a. Somatic - acetylcholine always excites skeletal muscle

-b. Autonomic – norepinephrine, acetylcholine excitatory or inhibitory

4. Overlap - most spinal nerves contain both somatic and autonomic fibers

Autonomic nervous system: divisions

1. Parasympathetic division – during resting

-a. Digestion - salivation and digestive juice production are stimulated

-b. Resting - conserves energy; heart rate and respiration decrease

-c. Non-stressful times - a time of relaxation, such as right after having a meal

2. Sympathetic division – during stress

-a. Flight or fight - run away or tooth and claw your way out of a situation

-b. Stress - such as fear, injury, or fear of injury

-c. Protection - adaptation to protect us against harm

ANATOMY OF THE AUTONOMIC NERVOUS SYSTEM

Parasympathetic (craniosacral) division

1. Fibers - preganglionic fibers tend to be longer than postganglionic fibers

-a. Terminal (intramural) ganglion - very close to or in target organ

2. Cranial outflow - cell bodies of the cranial nerves are found in the brain stem

3. Oculomotor nerve (III) - pupils constrict; lens accommodate to close vision

-a. Ciliary ganglion - cell bodies of postganglionic fibers; orbit

4. Facial nerve (VII) - stimulates lacrimal gland, nasal glands, some salivary glands

-a. Pterygopalatine ganglion - posterior to maxillae; lacrimal and nasal glands

-b. Submandibular ganglion - deep to mandible angles; submandibular, sublingual

5. Glossopharyngeal nerve (IX) - salivary gland stimulation

-a. Otic ganglion – inferior to foramen ovale of sphenoid; parotid glands

6. Trigeminal nerve (V) – preganglionic axons these 3 synapse, postganglionic

7. Vagus nerve (X) - most ventral body cavity, except the most distal parts

-a. Plexuses – cardiac, pulmonary, esophageal, and aortic

-b. Organs served – all except distal large intestine and pelvic organs

8. Sacral outflow - provides the rest of the parasympathetic outflow

-a. Organs served – distal large intestine and pelvic organs

9. Pelvic splanchnic nerves – preganglionic axons of the sacral outflow

Sympathetic (thoracolumbar) division: preganglionic fibers

1. Cell bodies - in spinal cord segments T1 through L2

2. White rami communicantes - preganglionic axons; both para and pre

3. Splanchnic nerves – T5-L2; do not synapse with paravertebral ganglion

-a. Include – thoracic, lumbar, and sacral splanchnics

-b. Area served – all abdominopelvic cavity

Sympathetic (thoracolumbar) division: ganglia

1. Paravertebral (chain) ganglia - cell bodies of the postganglionic neurons

-a. Sympathetic chain - chain of beads; flank vertebral column on both sides

-b. Paravertebral pathway - preganglionic postganglionic synapse paravertebral

-c. Sympathetic trunk – preganglionic axon; up or down sympathetic chain

2. Prevertebral ganglia - postganglionic that synapse with splanchnic nerves

-a. Abdominal aortic plexus - abdominal aorta has prevertebral ganglia

Sympathetic (thoracolumbar) division: postganglionic fibers

1. Gray rami communicantes – postganglionic axons from the paravertebral ganglia

-a. Unmyelinated – reason called gray

-b. Spinal nerve – mix and branch with these

-c. Sympathetic connection – to head, neck, thoracic organs, skin, blood vessels

2. Prevertebral ganglia postganglionic axons – usually follow arteries serving target

-a Sympathetic connections – to abdominopelvic organs

Sympathetic (thoracolumbar) division: adrenal medulla

1. Thoracic splanchnic nerve – some fibers synapse with adrenal medulla

2. Hormones released – norepinephrine and epinephrine

Visceral reflex arc

1. Visceral reflex arc – same components as somatic reflex arc

2. Visceral sensory neurons – sensory component

-a. Peripheral processes – VII, IX, X; splanchnic, spinal nerves; sympathetic trunk

-b. Cell bodies – dorsal root ganglion or sensory ganglia of cranial nerves

3. Integration center – as usual, located in the CNS

4. Motor chain – chief difference, 2 motor neurons (preganglionic, postganglionic)

5. Referred pain – sensed some where else

-a. Common pathways – for both somatic and visceral sensory neurons

-b. Brain interpretation – visceral pain as somatic; medial left arm, heart attack

6. Stimuli – usually pain, irritation, and/or stretch

AUTONOMIC NERVOUS SYSTEM PHYSIOLOGY

Neurotransmitters

1. Acetylcholine – most studied neurotransmitter

-a. Cholinergic fibers – axons which secrete acetylcholine

-b. Somatic axons – skeletal muscle; somatic nervous, always excitatory

-c. Preganglionic axons – sympathetic and parasympathetic; always excitatory

-d. Postganglionic parasympathetic axons – excitatory, inhibitory

2. Norepinephrine – also epinephrine released by adrenal medulla

-a. Adrenergic fibers – axons which secrete norepinephrine

-b. Postganglionic sympathetic axons – most, some exceptions

Cholinergic receptors

1. Cholinergic receptors – acetylcholine; two types; named after drugs which bind

2. Nicotinic receptors – are always stimulatory

-a. Skeletal muscle – not autonomic

-b. Postganglionic neurons – in the ganglia for both sympathetic, parasympathetic

-c. Adrenal medulla – cells which secrete epinephrine and norepinephrine

3. Muscarinic receptors – can be inhibitory or stimulatory

-a. Parasympathetic target organs – all

-b. Sympathetic target organs – few; eccrine activation; muscle vessel dilation

-c. Stimulatory – smooth muscle of the gastrointestinal tract

-d. Inhibitory – cardiac muscle of the heart

Adrenergic receptors

1. Adrenergic receptors – most sympathetic and adrenal medulla target cells

-a. Alpha receptors – most stimulatory; vasoconstriction skin, mucosa, viscera

-b. Beta 1 receptors – on heart; excitatory; heart to beat faster and harder

-c. Beta 2 receptors – in lungs; inhibitory; smooth muscles of bronchioles to dilate

Drug effects

1. Cholinergic drugs – effects on receptors which bind acetylcholine

-a. Atropine – stops salivation; dries up respiratory system; before surgery

2. Adrenergic drugs – effects on receptors which bind norepinephrine

-a. Tricyclic antidepressants – prolong activity of norepinephrine

-b. Beta-blockers – Beta 1; reduce heart rate; arrhythmia

AUTONOMIC DIVISION INTERACTIONS

Antagonistic interactions

1. Notable organs – heart, respiratory system, and digestive system

2. Flight or fight response – sympathetic ↑heart rate, respiration; ↓digesting

3. Resting – parasympathetic ↓ heart rate, respiration; ↑digesting, elimination

Sympathetic and parasympathetic tone

1. Sympathetic (vasomotor) tone – with few exception; blood vessels are entirely

-a. Blood pressure – blood vessels constrict; increased delivery to body

2. Parasympathetic tone – heart, digestive system, urinary system

-a. Heart rate – decreases it

-b. Smooth muscle – of urinary and digestive system; increased activity

Cooperative effects

1. External genitalia

-a. Parasympathetic control – dilate blood vessels; cause erection penis and clitoris

-b. Sympathetic control – ejaculation in males; reflex peristalsis of the female vagina

Sympathetic division: unique roles

1. Unique roles – regulates many functions not subject to parasympathetic influences

2. Thermoregulation – body temperature control

-a. Heat – blood vessels reflex dilation help cool body off

-b. Sweat glands – activated to increase cooling of body

-c. Blood vessels – reflex constriction to conserve heat

-d. Errector pilli muscles – contract to cause hair to rise; not very useful in humans

3. Renin – released by kidney; renin-angiotensin; increased blood pressure

4. Metabolic effects – include

-a. Adrenal medulla – epinephrine, norepinephrine; augments sympathetic response

-b. Body cells – causes them to increase metabolic rate

-c. Liver – stimulates the release of glucose to blood

-d. Adipose tissue – stimulates fat breakdown (lipolysis)

-e. Reticular activating system – is activated causing increased mental alertness

Localized versus diffuse effects

1. Parasympathetic division – tends to be much more localized

-a. Synapses – postganglionic usually synapse with 1 or a few preganglionic neurons

-b. Acetylcholine – is quickly degraded so its effects are short lasting

2. Sympathetic division – diffuse and highly integrated way; together feeling

-a. Synapses – one preganglionic axon with a number of postganglionic neurons

-b. Norepinephrine – not degraded, take up by axonal terminal, its effects are longer

-c. G protein linked receptor – second messenger mechanisms, exerts effects slower

-d. Adrenal medulla – epi, norepi to blood; 25 - 50% sympathetic effect on body

MISCELLANEOUS

Control of autonomic functioning

1. Reticular formation – most direct influence over autonomic functions

2. Medullary centers – HR, blood vessel diameter (CV centers) and respiration

3. Pons – respiratory centers which communicate with those in the medulla

4. Midbrain – oculomotor nuclei which control pupil diameter

5. Spinal cord reflexes – for defecation and micturition

6. Hypothalamus – overall integration center for autonomic nervous system; the boss

-a. Reticular formation – hypothalamus uses this to exert its effects over brain stem –b. Hypothalamic centers – heart, BP, temperature, water balance, endocrine

-c. Limbic system – mediates various emotional states; autonomic effect

3. Cortical control – higher brain

-a. Subconscious level – cortical control is not on a conscious level

-b. Limbic system – cortical communicates a scary situation to the hypothalamus

Homeostatic imbalances

1. Hypertension – overactive sympathetic nervous system; stress keeps BP high

2. Raynaud’s disease – exaggerated vasoconstriction; fingers, toes; pale, cyanotic

-a. Gangrene – tissue death can result

-b. Sympathectomy – severing the preganglionic sympathetic fibers controlling area

3. Mass reflex reaction – spinal cord injury above T6

-a. Autonomic reflex – without mediation of higher CNS input

-b. Somatic effects – skeletal muscle spasms

-c. Arterial blood pressure – very high; can cause stroke

-d. Other effects – bladder, rectal emptying; sweating

4. Hirschsprung’s disease – parasympathetic doesn’t move feces

-a. Congenital megacolon – to the ballooning of the more distal segment

5. Aging – several effects on ANS

-a. Constipation – resulting from decrease in gastrointestinal tract motility

-b. Dry eyes – resulting from decrease in tear production

-c. Orthostatic hypertension – dizzy getting up; low BP less responsive sympathetic