Anatomy Lecture Notes Chapter 15

Anatomy Lecture Notes Chapter 15

ANS = general visceral motor portion of PNS

sympathetic division / "fight or flight" / prepares body for emergencies and intense muscular activity
parasympathetic division / "rest and digest" / maintains body, conserves and stores energy

both divisions innervate cardiac m., smooth m., and glands (dual innervation)

divisions usually cause opposite effects in effector organs

A. ANS pathway has 3 components

1. preganglionic neuron - CNS to ganglion

2. ganglion (autonomic motor)

3. postganglionic neuron - ganglion to effector

B. anatomical comparison

1. origin (location of preganglionic neuron cell bodies)

S: lateral gray horn, thoracic and lumbar spinal cord

P: brain stem and sacral spinal cord

2. relative length of pre- and postganglionic neurons

sympathetic / parasympathetic
preganglionic
postganglionic

3. location of ganglia

a. sympathetic

paravertebral (sympathetic chain) ganglia - chain lateral to spinal column

prevertebral (collateral) ganglia - ventral body cavity

b. parasympathetic

terminal (intramural) ganglia in effector organs

cranial ganglia

4. divergence of preganglionic neurons

a. sympathetic - extensive

b. parasympathetic - minimal

C. neurotransmitters

cholinergic neurons - acetylcholine (Ach)

adrenergic neurons - norepinephrine (NE)

preganglionic / postganglionic
sympathetic
parasympathetic

* except in skeletal blood vessels and sweat glands

D. parasympathetic outflow

1. cranial nerves

a. oculomotor

preganglionic neurons in midbrain

ganglion = ciliary ganglion

postganglionic neurons innervate intrinsic muscles of eye: ciliary and iris

b. facial nerve

preganglionic neurons in pons

ganglia = pterygo-palatine and submandibular

postganglionic neurons innervate :

submandibular & sublingual salivary glands

lacrimal gland

nasal mucus glands

c. glossopharyngeal nerve

preganglionic neurons in medulla oblongata

ganglion = otic

postganglionic neurons innervate parotid gland

d. vagus nerve

preganglionic neurons from medulla via plexuses

ganglia = intramural

postganglionic neurons innervate most visceral organs of thorax and abdomen

2. sacral

preganglionic neurons in S2-S4

pelvic splanchnic nerves

ganglia = intramural

postganglionic neurons innervate pelvic organs

E. sympathetic outflow

1. preganglionic neuron cell bodies in lateral gray horn of segments T1-L2

axons leave spinal nerve in white ramus

2. pathways of preganglionic neurons

a. synapse with postganglionic neuron in paravertebral ganglion; return to spinal nerve in gray ramus

same segment

inferior or superior segment

b. pass through paravertebral ganglia to synapse with postganglionic neuron in a prevertebral ganglion

splanchnic nerves

F. adrenal medulla

specialized sympathetic ganglion

chromaffin cells are modified postganglionic cells without axons

secrete norepinephrine and epinephrine into circulation

G. control of ANS

1. reticular formation contains vital reflex centers that control organs via autonomic nerves

2. hypothalamus integrates both ANS divisions and links ANS to limbic system

3. cerebral cortex can be used to indirectly and temporarily control some autonomic functions

H. visceral sensory neurons

general visceral sensory neurons monitor viscera for pain, temperature, chemicals, stretch

neuron cell bodies are in dorsal root ganglia

axons project to thalamus and cerebral cortex

Strong/Fall 2008 page 5