T2L6 autonomic nervous system

Question 1

basics

3 main roles

3 divisions

Answer 1

part of peripheral nervous system

involuntary control

1. regulates operation of internal organs
2. maintains internal environment
3. innervates smooth muscle, cardiac muscle, glands

3 divisions:

• sympathetic
• parasympathetic
• enteric

Question 2

map of ans

Answer 2

s4

parasympathetic - brainstem, S2-S4 of spinal chord

sympathetic - T1-L2 of spinal chord

Question 3

ANS nervous structure

Answer 3

axons do not pass directly to effector organs
- they form disynaptic pathways

s5 crucial

myelinated axon from cranial nerve nuclei (cranial/spinal nerves) synapse at ganglion. an unmyelinated postganglionic axon then goes to the effector organ

except for sympathetic supply to adrenal medulla

Question 4

neurotransmissions

1. within ganglia
2. postganglionic sympathetic
3. within adrenal medulla (exception)
4. postganglionic parasympathetic

Answer 4

1. within autonomic ganglia s6
   - acetylcholine binds to nicotinic receptors on postganglionic neurons

ionotropic ligand gated channel (fast)

• acetylcholine opens pore
• depolarises neuron

2. postganglionic sympathetic s7
   - noradrenaline binds to adrenergic receptors on effector organ

metabotropic G-protein coupled (slow)
many subtypes : α1, α2, β1, β2 and β3

3. adrenal medulla s8
   - acetylcholine binds to nicotinic receptors on chromaffin cells
   - causes release of adrenalin/noradrenaline into circulation
   - activates sympathetic effector organs
4. postganglionic parasympathetic s9
   - acetylcholine binds to muscarinic receptors on effects organ
   - metabotropic g protein coupled (slow)

Question 5

sympathetic trunk

Answer 5

• interconnected paravertebral ganglia
• extends from cervical to sacral levels
• preganglionic fibres enter sympathetic trunk through white rami communicans

s11,12

lateral horn = cell bodies of preganglionic neurons
white ramus communicans = myelinated preganglionic
grey ramus communicans = unmyelinated postganglionic

Question 6

sympathetic trunk preganglionic fibres

Answer 6

on entering the trunk, they either:

1. synapse in ganglion
2. pass through ganglion into splanchnic nerves to synapse in prevertebral ganlia

s13 orrid

Question 7

sympathetic trunk postganglionic fibres

Answer 7

• much more numerous than preganglionic
  1:10
  sympathetic responses are mass responses
• coordinated activity at multiple levels

follow 2 routes:

1. to periphery
   - sweat glands, vessels, hair follicles
   - via grey rami communicans back into spinal nerves
2. to the viscera
   - heart, lungs, head
   - via medial branches/plexus

from the prevertebral ganglia, postganglionic fibres form plexus around viscera (s15)

Question 8

cervical sympathetic

Answer 8

3 ganglia in cervical sympathetic trunk

• superior
• middle
• inferior cervical ganglia

postganglionic:

1. exit via grey rami communicans to spinal nerves (supply sympathetic to upper limbs)
2. go down common carotid to heart (supply sympathetic to heart)
3. go up internal/external carotid artery to head:
   - internal carotid plexus (dilates pupil, inhibits lacrimal gland)
   - external carotid plexus (inhibit secretions at submandibular and parotid glands)

s18

Question 9

horners syndrome

Answer 9

disruption of sympathetic supply to head

can be any part of pathway; hypothalamus to preganglionic neurons- eg lesion in brainstem, spinal chord

pupil/eyelid/skin of face

Question 10

sympathetic trunk thoracic ganglia

Answer 10

12

postganglionic fibres
- exit via grey rami communicans to spinal nerves or medial branches to heart and lungs

preganglionic fibres

• exit via thoracic splanchnic nerves to abdomen (greater, lesser, least) to prevertebral ganglia
• synapse in prevertebral ganglia: (celiac ganglion, superior mesenteric ganglion, aorticorenal ganglion), close to abdominal aorta

Question 11

sympathetic trunk lumbar ganglia

Answer 11

4

postganglionic fibres:
- exit via grey rami communicans to spinal nerves

preganglionic fibres:
- exit via lumbar splanchnic nerves to pelvis

Question 12

sympathetic trunk sacral ganglia

Answer 12

postganglionic fibres exit via:

1. grey rami communicans to spinal nerves (lower limbs)
2. sacral splanchnic nerves to pelvic organs

Question 13

parasympathetic preganglionic fibres

Answer 13

within brainstem and grey matter spinal chord

s27

brainstem > cranial nerves > head, lungs, abdo, heart
spinal chord > pelvic splanchnic nerves > pelvic organs

Question 14

cranial parasympathetic

Answer 14

preganglionic neuronal cell bodies in cranial nerve nuclei
s28

CN 3, 7, 9, 10

preganglionic axons pass through cranial nerves to ganglia

ganglia all close to target organ (eg ciliary ganglion for pupil control)

vagus nerve 10 passes to heart, lungs, abdominal viscera

Question 15

sacral parasympathetic

Answer 15

from sacral spinal chord

preganglionic fibres:

• exit via pelvic splanchnic nerves to pelvic organs
• form pelvic plexus over viscera
• synapse in walls of target organs

function:

1. bladder
   - contraction of bladder wall
   - inhibition of bladder sphincter
2. rectum
   - inhibition of rectal sphincter
3. sexual function
   - vasodilation of erectile tissues

Question 16

enteric nervous system

Answer 16

in walls of GI tract

2 plexi:

1. auerbachs
   - between muscle layers
   - regulates muscle contraction
2. meissners
   - regulates glandular secretions
   - on inside wall

retains function after all central connections severed ie very autonomic

Question 17

central control

Answer 17

s35