Lecture 6: Autonomic Nervous System

Question 1

Nervous system divisions

Answer 1

NS = CNS + PNS
PNS = somatic + autonomic
Autonomic = sympathetic + parasympathetic + enteric

Question 2

What does the autonomic nervous system do?

Answer 2

Involuntary innervation of tissues other than skeletal muscle/GI tract (enteric)

Question 3

How do autonomic nerves connect to the CNS?

Answer 3

2 neurons in series synapsing at the autonomic ganglion outside the CNS. Pre-ganglionic cell body is in the CNS.

Question 4

How are sympathetic neurons/ganglia placed?

Answer 4

Sympathetic ganglia run in 2 chains close alongside the length of spinal cord in sympathetic trunks or are closer to organs in the abdominal cavity (collateral ganglia). Sympathetic nerves leave CNS at thoracic/lumbar spinal cord.

Question 5

Sympathetic trunks (paravertebral ganglia)

Answer 5

Bundled nerve fibers running alongside the vertebral column containing the sympathetic ganglia. Allows pre-ganglionic sympathetic nerves to travel up/down before synapsing

Question 6

How are parasympathetic nerves/ganglia placed?

Answer 6

Parasympathetic ganglia are placed very close to or within innervated organs. Parasympathetic nerves leave CNS at brain stem/sacral spinal cord.

Question 7

Collateral (pre-vertebral) ganglia

Answer 7

Sympathetic ganglia in the abdominal cavity placed closer to innervated organs compared to other sympathetic ganglia. Specifically the celiac and superior/inferior mesenteric ganglia.

Question 8

Autonomic nervous divisions

Answer 8

-Sympathetic (AKA thoracolumbar) division
-Parasympathetic (AKA craniosacral) division
-Enteric NS

Question 9

Pattern of sympathetic innervation

Answer 9

Sympathetic NS typically affects targets in concert due to higher pre-ganglionic divergence and circulating epi/norepi.

Question 10

Pattern of parasympathetic innervation

Answer 10

Parasympathetic NS typically affects targets individually in a finely-tailored pattern due to less pre-ganglionic divergence.

Question 11

General somatic NS efferent pathway

Answer 11

Large diameter, myelinated axons of motor neurons directly innervate skeletal muscle with ACh; faster transmission

Question 12

General autonomic NS efferent pathway

Answer 12

Medium diameter, myelinated pre-ganglionic neurons release ACh onto small, unmyelinated post-ganglionic neurons which innervate targets with NE (symp.) or ACh (parasymp.), or synapse onto adrenals. Apparently no evolutionary need for faster transmission.

Question 13

Autonomic innervation of the adrenal medulla

Answer 13

The adrenal medulla acts like a ganglion. Chromaffin cells receive ACh from pre-ganglionic fibers and then release NE and epi into circulation.

Question 14

Primary autonomic neurotransmitters

Answer 14

In general, pre-ganglionic fibers release ACh and post-ganglionic release NE (sympathetic/adrenal medulla) or ACh (parasympathetic).

Question 15

Cholinergic receptor types

Answer 15

Named for agonists.
Nicotinic: skeletal muscle, autonomic post-ganglionic dendrites
Muscarinic: parasympathetic targets + sweat glands/blood vessels (sympathetic)

Question 16

Antagonists for cholinergic receptors

Answer 16

Curare = somatic nicotinic antagonist
Hexamethonium = autonomic ganglia nicotinic antagonist
Atropine = muscarinic antagonist

Question 17

Adrenergic receptor types

Answer 17

Adrenergic receptors are not named for agonists.

α1, α2, β1, β2 on smooth/cardiac muscle and glands (autonomic)

Question 18

Agonist

Answer 18

Substance that binds a receptor and activates it

Question 19

Inverse agonist

Answer 19

Substance that binds a receptor and decreases its (basal) activity in the absence of ligands

Question 20

Antagonist

Answer 20

Substance that reduces the efficacy of agonists/inverse agonists

Question 21

Reciprocal innervation

Answer 21

Most autonomic targets are innervated in opposition by both sympathetic and parasympathetic nerves. Exceptions include skin hair, sweat glands, adrenal medulla, some blood vessels

Question 22

Reciprocal innervation exceptions

Answer 22

Likely allows separate regulation separate from circulating NE/epi. Piloerectors, sweat glands, adrenals, some blood vessels receive ACh and NE from sympathetic post-ganglionic nerves.

Question 23

Nonadrenergic, noncholinergic neurons

Answer 23

Many autonomic post-ganglionic neurons use other NTs/factors like NO for many functions.

Question 24

Sympathetic and parasympathetic purposes

Answer 24

Sympathetic = fight or flight, gas pedal
Parasympathetic = rest and digest, brakes
(in general)

Question 25

Varicosities

Answer 25

AKA “en passant” synapses. Swellings along axon branches form many autonomic synaptic junctions (rather than axon terminals)

Question 26

Patterns of somatic innervation

Answer 26

Somatic motor neurons are inactive until stimulated, and initiate activity in otherwise inactive muscle

Question 27

Patterns of autonomic innervation

Answer 27

Autonomic neurons typically maintain a basal tonic activity and modulate targets that have autogenic activity.

Question 28

Horner’s syndrome

Answer 28

Caused by a sympathetic defect -> inactivating several muscles, resulting in partial eyelid droop (ptosis) and uneven pupils (miosis)