Autonomic Nervous System

Question 1

Structural features of the SOMATIC Nervous System

Answer 1

sensory input comes in synapse of MYELINATED motor neuron extends out to the dorsal root to striated muscle (effector) where Ach is released, causing contraction of the muscle
- innervation of target DIRECTLY

Question 2

Structural features of the AUTONOMIC Nervous System

Answer 2

sensory input comes in through dorsal horn and descending innervation from higher brain centers; MYELINATED preganglionic neuron transmits signal to efferent neuron in an intermediate zone (not the target) and instead synapses onto a ganglion–> from ganglion UNMYELINATED postganglionic neuron sends its axon out to target where Ach (parasympathetic) or NorE (sympathetic) is then released
- innervation of target thru pre and postganglionic fibers and intermediate ganglion

Question 3

What neurotransmitter is released in the Sympathetic NS?

Answer 3

Norepinephrine

Question 4

What neurotransmitter is released in the Parasympathetic NS?

Answer 4

Acetylcholine for smooth muscle movements (“rest and digest”)

Question 5

Adrenal Medulla

Answer 5

serves as intermediate ganglion in the ANS; contains cells that release norepinephrine into the blood in response to an action potential where it then can act on targets

Question 6

Why are different neurotransmitters used in the sympathetic and parasympathetic nervous systems?

Answer 6

Both act on the same targets so different NT are needed to communicate the appropriate messages

Question 7

Pre and postganglionic fibers of the Sympathetic NS

Answer 7

preganglionic fibers: SHORT (ganglia are right next to the spinal cord T-L spine)
postganglionic fibers: LONG (have to extend the rest of the way to reach the target)

Question 8

Pre and postganglionic fibers of the Parasympathetic NS

Answer 8

preganglionic fibers: LONG (ganglia are closer to the TARGET)
postganglionic fibers: SHORT

Question 9

why can sweat glands utilize both ACH and NE to send signals?

Answer 9

Sweat glands are ONLY innervated by the sympathetic NS so either NT will communicate that message (dual innervation)

Question 10

Fibers of the Sympathetic trunk

Answer 10

• preganglionic fibers can synapse onto each other and add onto each other in same direction, or axon can split and some go up or down the trunk and then some at that level
  = more DIVERGENCE
• one preganglionic fiber can split and synapse onto on avg 20 postganglionic fibers

Question 11

Fibers of the Parasympathetic trunk

Answer 11

preganglionic neurons often synapse with just ONE other postganglionic neuron in 1:1 fashion,
= LITTLE TO NO DIVERGENCE
- 1preganglionic fiber:3 postganglionic fibers ON AVG

Question 12

Agonist

Answer 12

binds to receptor and activates it

Question 13

Inverse Agonist

Answer 13

substance that when bound to receptor decreases its basal activity of receptor
- in the absence of its ligand it typically binds to the receptor which usually has SOME activity, so the inverse agonist REDUCES that

Question 14

Antagonist

Answer 14

substance that when bound does not do anything BY ITSELF, BUT in the presence of an agonist it will decrease activity of the agonist or inverse agonist (may actually be antagonist or really an inverse agonist just incorrectly named)

Question 15

hexamethonium

Answer 15

NICOTINIC receptor antagonist at the ganglia in the AUTONOMIC NS but no effect on the muscle in the NMJ (somatic NS) so we know they can respond to the same substance (nicotine) but have diff receptors

Question 16

curare

Answer 16

NICOTINIC antagonist at the ganglia in the SOMATIC NS, has no effect on AUTONOMIC NS unless added in very large concentrations

Question 17

Atropine

Answer 17

MUSCARINIC receptor antagonist at the POSTganglion of the PARASYMPATHETIC NS, has no effect on nicotinic receptors
- used to dilate pupils

Question 18

Preganglionic Receptors in the Sympathetic and Parasympathetic NS

Answer 18

NICOTINIC ONLY

Question 19

Postganglionic Receptors in the Sympathetic NS

Answer 19

NICOTINIC and MUSCARINIC
- beta1 receptors: increase heart rate and contractility
- beta2 receptors reduce gut motility

Question 20

Postganglionic Receptors in the Parasympathetic NS

Answer 20

ONLY Muscarinic

Question 21

Dopamine

Answer 21

precursor to norepinephrine so will be some present in any synapse that releases NE even from the adrenal medulla
- also serotonin, histamine, GABA

Question 22

Other molecules with signaling abilities

Answer 22

NO (nitric oxide) and purines (i.e ATP)

Question 23

En Passant Synapse

Answer 23

axon may not stop at target in ANS –> just has swellings (varicosities) along the way as it goes to its true target
–> = EN PASSANT synapses

Question 24

alpha 2 receptor

Answer 24

receptor on the postganglionic decrease norepinephrine if too much NE (negative feedback mechanism)

Question 25

what other substances have receptors that can release NE?

Answer 25

Angiotensin II and

Question 26

Negative feedback between parasympathetic and sympathetic NS

Answer 26

when parasympathetic activity is high, sympathetic NS will signal by releasing norepinephrine to signal to stop producing ACH; when sympathetic activity is high, parasympathetic NS sends over some ACH and that binding to muscarinic receptor DECREASES norepinephrine release and slows sympathetic ns activity
–> PARASYMP and SYMP work TOGETHER to maintain homeostasis

Question 27

Pattern of Neuronal Activity: Somatic NS

Answer 27

• initiates activity in muscle that is otherwise inactive (muscle will not contract unless stimulated)
• motoneurons are inactive until stimulated

Question 28

Pattern of Neuronal Activity: Autonomic NS

Answer 28

• modulates targets with autogenic activity (most targets don’t need any neural stimulation to work)
• efferent neurons maintain tonic discharge (always active at a slow rate; will just increase or decrease the firing rate of pre/postganglionic neurons)
• can affect targets individually (more typical of parasympathetic since typically only synapse to 1-3 other postganglionic fibers)
• can affect targets in concert (more typical of sympathetic since synapse to ~20 postganglionic fibers- basis of polygraph testing)

Question 29

consensual pupillary response

Answer 29

By shining light into one eye, retinal preganglion stimulate both eyes (negative feedback reflex)

Question 30

Regulating orthostatic hypotension

Answer 30

baroreceptors combat orthostatic hypotension bc ACH production on the heart needs to slow and NE production to the heart must INCREASE to pump the heart and restore blood circulation

Question 31

Horner’s Syndrome

Answer 31

Condition in which lesion/defect in SYMPATHETIC system leads to one- eye droop (miosis), decreased sweating on one side of the face, increased blushing/heat on one side of the face
- sweat glands ONLY receive sympathetic innervation so must be where lesion is