exam 5: autonomic nervous system

afferent (visceral sensory) pathways

feedback

regulate effectors

efferent (viscera motor) pathways

sympathetic division

parasympathetic division

dual innervation (most structures)

enteric nervous system

visceral reflexes ( bypass spinal cord)!

regional “command center”

regulated by ANS

sympathetic division overview

origin: preganglionic neurons originate in lateral horns of T1-L2 segments of spinal cord (thoracolumbar)

Functions:

maintains body during conditions of “flight-or-fight”

increases alertness and metabolic activities

sympathetic preganglionic fibers

arise from cell bodies in thoracolumbar lateral gray horns

exit cord via ventral nerve root → ventral rami T1- L2

exit ventral rami via white rami communications

sympathetic postganglionic fibers- spinal nerve pathway

preganglionic fibers synapse in sympathetic chain ganglia @ same level, level above or level below

postganglionic fibers return to ventral ramus via gray rami comminicans

continues through spinal nerves

innervates neck, torso & limb skin effectors

sympathetic postganglionic fibers- sympathetic nerve pathway

reganglionic fibers synapse in sympathetic chain ganglia @ same level, level above or level below

postganglionic fibers pass through sympathetic chain

sympathetic nerves join upper cervical spinal nerves & cranial nerves

innervate head & face skin effectors, organs of cervical region & thoracic cavity

sympathetic postganglionic fibers- splanchnic nerve pathway

preganglionic fibers pass through sympathetic chain ganglia @ same level, level above or level below

form splanchnic nerves

synapse @ prevertebral ganglia

postganglionic fibers innervate abdominal & pelvic organs

parasympathetic divison

preganglionic neurons

arise from brain stem nuclei

• exit brain stem via CN III, VII, IX & X

arise from sacral lateral gray horns

• exit cord via ventral nerve roots S2- 4 & travel through ventral rami

postganglionic neurons

• terminal ganglia: near or imbedded within effectors

parasympathetic divison overview:

origin: preganglionic neurons originate in brainstem nuclei and S2-4 segments of spinal cord (craniosacral)

functions: maintain body during conditions of “rest-and-digest”

converses energy and replenishes nutrient stores

visceral reflex arc

visceral sensory neurons ( not somatic sensory)

2 motor neurons ( not just one)

effectors (not skeletal muscle)

• smooth

• cardiac

• glands

Acetylcholine (AcH): ANS neurotransmitters

cholinergic fiber

• all pre & postganglionic parasympathetic neurons

• all preganglionic sympathetic neurons

• some postganglionic sympathetic neurons

Norepinephrine (NE) : ANS neurotransmitters

Adrenergic fibers

most postganglionic sympathetic neurons

ANS receptors

an effectors (target organ) response to neurotransmitter is dependent on what kind of receptors are on that effector cell

most effector cells have > 1 receptor type

pharm treatment:

• medications to block receptors & minimize neurotransmitters effect

• medications to inhibit reuptake of neurotransmitters to maximize its effect

Nicotinic cholingeric receptors

all post-ganglionic autonmic dendrite & cell bodies: excitatory

adrenal medial- excitatory

motor endplate skeletal muscle- excitatory

muscarinic cholinergic 1

all parasympathetic target organs

• smooth muscle walls of hallow organs- excitatory

• glandular tissue- excitatory

• visceral sphincters- inhibitory

is the visceral sphincters inhibitory or excitatory of the muscarinic cholinergic?

inhibitory

muscarinic cholinergic 2

all parasympathetic target organs

• cardiac muscle- inhibitory

  • decrease heart rate

• pupillary sphincter- excitatory

sweat glands: muscarinic cholinergic

excitatory

SYMPATHETIC innervation only

alpha adrenergic reporters

smooth muscle in blood vessel walls- excitatory

smooth muscle in visceral sphincters- excitatory

smooth muscle of dilator pupillae muscle- excitatory

smooth muscle of arrestor pili muscles- excitatory

beta adrenergic receptors

smooth muscle walls of hallow viscera- inhibitory

• digestive organs

• urinary organs

• reproductive organs

• respiratory organs

cardiac muscle: beta adrenergic receptors

excitatory

increase heart rate

increase strength of contraction

beta blockers- decrease heart strain

sympathetic functions

“flight or fight”

faster, stronger heartbeat

vasoconstriction: sympathetic tone or vasomotor tone

bronchodilation:

• increase glycogenolysis

• increase lipolysis

• increase sweat

stimulates adrenal medulla

• epinephrine

  • prolonged & widespread effects

adrenal glans

pre-ganglionic sympathetic connection

acts like post-ganglionic neuron

secretes epinephrine & norepinephrine

ANS- endocrine link!

parasympathetic functions

“rest & digest”

• smooth muscle contraction

  • lining of viscera

  • digestion

  • elimination

• increase gland secretions

• vasodilation (genitalia)

• pupillary constriction

effects are shorter duration & more localized

parasympathetic tone (heart, digestive & urinary tracts)

important point

sympathetic innervation only

• smooth muscle walls of most blood vessels

• sweat glands

• arrector pili muscles

• adrenal medulla