AUTONOMIC SYSTEM - LECTURE 1

Question 1

Nerve and muscle cells are considered to be excitable tissues because

Answer 1

they are able to produce an electrical signal when exited

Question 2

where does the autonomic nervous system come from

Answer 2

nervous system= peripheral system=efferent division =autonomic nervous system

Question 3

the autonomic system is divided into

Answer 3

1. sympathetic division

2. parasympathetic division

Question 4

AS system innervates

Answer 4

1. smooth muscles
2. cardiac muscles
3. glands(Exo/endocrine)

Question 5

what is AS?

Answer 5

→ ANS regulates activities of systems not under voluntary control
e.g. respiration, circulation, digestion, body temperature, metabolism, sweating, some endocrine

Question 6

AS helps maintain

Answer 6

maintain a constant internal body environment (homeostasis)

Question 7

The cell bodies of the primary neurons (presynaptic/ preganglionic neurons) are located in the

Answer 7

the intermediolateral (IML) gray column of the spinal cord or in the brain stem nuclei

Question 8

These cell bodies send axons which are usually

Answer 8

usually small-diameter, myelinated, relatively slow conducting B fibers, out to synapse with the secondary neuron (postsynaptic/ postganglionic, neuron) located in one of the autonomic ganglia.

From there, the postganglionic axon (mostly unmyelinated C fibers) passes to its target organ

Question 9

Because the postganglionic fibers outnumber the preganglionic neurons by a ratio of about 32:1, a single preganglionic neuron may

Answer 9

control the autonomic functions of a rather extensive terminal area

Question 10

comparison of the somatic nervous system from AS

Answer 10

• innervates the skeletal muscle.

no neuron on neuron synapse outside CNS.

may not be tonically active.

larger, thicker fibers – faster.

simple Arch-based NT communication

Question 11

comparison of AS from somatic system

Answer 11

• usually more complex- requires 2nd messenger systems

→ receptor-activated → starts a chain of events

Question 12

somatic AP vs AS AP

Answer 12

Somatic AP originate in CNS & sometimes (not often) from reflexes

Vs.

ANS actions originate from CNS, but most often through reflexes.
(in-built control system for homeostasis)

ANS pathway from CNS to target has a set (chain) of two fibers.

Question 13

effects on effector organ from SS and AS

Answer 13

1. SS can only stimulate

2. AS can stimulate and inhibit

Question 14

length of neuron in SS

Answer 14

the neuron is very long, its cell body originates from the CNS, and its axon terminal releases ACH at the effector organ.

Question 15

length of a neuron is AS- parasympathetic

Answer 15

long pre-ganglionic neuron releases ACH at the ganglion to the short post-ganglionic neuron in the ganglion which then releases the ACH at the effector organ

Question 16

length of a neuron in AS- sympathetic

Answer 16

a pre-ganglionic neuron shorter than that of parasympathetic releases ACH at the ganglion to the post-ganglionic neuron that is longer than that of parasympathetic, which releases norepinephrine at the effector organ

Question 17

length of neuron in the adrenal medulla

Answer 17

1. the pre-ganglionic neuron is very very short.
2. ! The adrenal medulla is essentially a sympathetic ganglion in which the postganglionic cells have lost their axons and secrete norepinephrine and epinephrine directly into the bloodstream. The cholinergic preganglionic neurons to these cells have consequently become the secretomotor nerve supply of this gland

Question 18

Noradrenaline (NA) is the same as norepinephrine (NE

Answer 18

true

Question 19

autonomic nerve pathway

Answer 19

the pre-ganglion neuron of which its cell body is in the CN releases pre-ganglionic neurotransmitter in the autonomic ganglion where synapse occurs

the neurotransmitter will then attach to the receptors of a post-ganglionic neuron using the lock and key method which then releases post-ganglionic neurotransmitter from varicosity to the receptors of an effector organ

Question 20

ganglion is

Answer 20

a cluster of cell bodies that lie outside the CNS

Question 21

varicosity

Answer 21

= areas of stored neurotransmitter- spread out for greater surface area compared to the axon terminal

Question 22

endocrine gland

Answer 22

the hormone released into the bloodstream and reaches target receptors by blood (eg insulin)

Question 23

exocrine gland

Answer 23

secretions not into the bloodstream but into the duct to get to target receptors (eg digestive enzymes of pancreas via a duct to the small intestine)

Question 24

sympathetic system

Answer 24

SNS (thoracolumbar) division:

Preganglionic cell bodies are located in the intermediolateral (IML) gray column – 12 thoracic segments (T1 to T12) & upper 2 lumbar segments (L1 and L2) of the spinal cord

t1-t12 synapse at the sympathetic ganglion chain

L1-L2 synapse at the collateral ganglion

Question 25

parasympathetic nervous system

Answer 25

sometimes called the craniosacral division (location of its preganglionic neurons).

preganglionic cell bodies in the gray matter of the brainstem (medial part of the oculomotor nucleus, Edinger–Westphal nucleus, superior & inferior salivatory nuclei) AND the middle three segments of the sacral cord (S2–4)

PNS nerves supply the visceral structures in the head via the oculomotor, facial, & glossopharyngeal nerves, & those in the thorax & upper abdomen via the vagus nerve.

The sacral outflow supplies the pelvic viscera via branches of S2-S4 spinal nerves.

The parasympathetic distribution is confined entirely to visceral structures

Question 26

cranial nerves

Answer 26

• oculomotor (III)
• facial (VII)
• glossopharyngeal (IX)
• vagus (X)

Question 27

Note the differences in the origin of fibers in the two divisions of ANS

Answer 27

(PNS: cell bodies in the brainstem and sacrum, whereas SNS: thoracic (T1-T12) and lumbar (L1-L2) segments of the spinal cord)

PNS and SNS have similar pathways autonomic nervous system pathways: ie, preganglionic, postganglionic, but the differences are in the length of fibers and origin of fibers.

Question 28

PNS nerves supply the visceral structures in the head and thorax and upper abdomen via

Answer 28

the oculomotor, facial, & glossopharyngeal nerves

& those in the thorax & upper abdomen via the vagus nerve.

Question 29

The sacral outflow supplies the pelvic viscera via

Answer 29

via branches of S2-S4 spinal nerves.

The parasympathetic distribution is confined entirely to visceral structures

Question 30

when both the SNS and PNS are partially active

Answer 30

this is known the as sympathetic and parasympathetic tone

Question 31

tonically active

Answer 31

PNS and ANS can have antagonist (opposite) effects or complementary effects

Question 32

SNS activation

Answer 32

SNS activation is also known as the “Fight or flight” response or the “fight, flight or freeze” response as it prepares the body for physical activity/coping with stress/emergency situations.

“freeze” (or acting as if you are dead), is also a reaction that one may choose for survival under circumstances of excessive stress- e.g. if one sees a wild animal close by, they may freeze (so as not to attract attention or be seen as a threat to the animal.

Stimuli include: stress, low blood pressure (BP), low blood glucose (BG), anxiety

Question 33

stimulation of SNS leads to

Answer 33

mobilization of energy, ↑ CVS function, ↑ respiratory function,↓ digestion

i.e. SNS = catabolic nervous system.
dilates the pupils (letting more light into the eyes), accelerates the heartbeat & raises the BP (providing better perfusion of the vital organs & muscles), & constricts the BVs of the skin (which limits bleeding from wounds).

Noradrenaline (NA) discharge due to SNS activation also leads to elevated plasma glucose & free fatty acid levels (supplying more energy)

Question 34

PNS activation

Answer 34

PNS- concerned with the vegetative aspects of day-to-day living.

PNS dominates in quiet, relaxed situations- PNS is the body’s response to a “rest and digest” state.

PNS is important for maintenance/normal functioning.

Eg, PNS action favors digestion and absorption of food by increasing the activity of the intestinal musculature, increasing gastric secretion, and relaxing the pyloric sphincter.
For this reason, the cholinergic PNS division is sometimes called the anabolic nervous system

Stimuli: high blood glucose and other metabolites, restful situations

→ conserve and store energy, ↑ digestion, ↓ CVS function, and ↓ respiratory function

Question 35

PNS and SNS

Answer 35

Bearing in mind that TONE will change according to one’s current state: fight/flight (SNS) or rest/digest (PNS).

Say, for example, you were taking a hike and you have just come across a snake in your path.
This will obviously put you into fight/flight mode- this means SNS will take over (so there will no longer be balance between the two divisions) and you will get all the physiological SNS responses (which we will go through shortly) and your PNS responses will “back down”

(which makes sense, since, mostly the two ANS divisions have opposite effects (are antagonistic)- which you will learn as we move on).
In this circumstance (with the snake), when the SNS takes over, the SNS “dominates” – known as “sympathetic dominance”.

On the other hand, when one is relaxed (e.g. reading a book), they are in a state of “Parasympathetic dominance”.