W7 Functioning Of The Autonomic Nervous System

Question 1

Autonomic sensory components

Answer 1

Sensory receptors within the viscera (soft internal tissues)

Somatosensory/external environment

Question 2

Does sensory input control somatic or autonomic changes?

Answer 2

A single piece of sensory input might result in somatic and autonomic changes, because information is integrated within the CNS.

Question 3

How are autonomic motor components different to somatic motor components?

Answer 3

• the effectors innervated
• the number of neurones between CNS and effector
• neurotransmitter release and the nature of neurotransmitters

Question 4

What are the effectors of the autonomic nervous system?

Answer 4

Autonomic neurones will innervate smooth and cardiac muscles, and glands (viscera).

Question 5

What can the autonomic nervous system be split into?

Answer 5

Sympathetic, parasympathetic, enteric

Question 6

How do neurones communicate with effectors in the autonomic NS?

Answer 6

There is a 2-neurone chain between the CNS and effector tissue
Pre-ganglionic and Post-ganglionic neurones communicating at a synapse existing in collections known as ganglia

Question 7

What is a preganglionic neurone?

Answer 7

The neurone whose cell body is in the CNS and terminals in the ganglia.

Question 8

What is a postganglionic neurone?

Answer 8

Cell bodies in the ganglia and terminates in the effector tissue

Question 9

What is the functional important of having a 2-neurone chain between the CNS and effector tissue?

Answer 9

Preganglionic neurones might branch and be in contact with multiple postganglionic neurones, resulting in widespread activation of postganglionic neurones and thus can control a large area of effector tissue.

Question 10

What acts like the NMJ a of the somatic NS in the autonomic NS?

Answer 10

There are a series of small swellings, which each contrail vesicles of neurotransmitter. ‘Beads on a string’. Refer to image. Allows a single postganglionic neurone to release neurotransmitter at many sites and thus over a large area.

Question 11

What are the functional implications of the ‘beads on a string’ arrangement?

Answer 11

A small number of postganglionic autonomic neurones can influence a large number of effector cells. So within an organ we can organise the change in activity in a large number of smooth muscle cells, allowing a high level of coordination.

Question 12

Sympathetic neurotransmitters

Answer 12

Within the ganglion = ACh

Released at nerve endings = NA

Question 13

Parasympathetic neurotransmitters

Answer 13

Within the ganglion = ACh

Release at nerve terminals = ACh

Question 14

What exceptions are there to the sympathetic and parasympathetic neurotransmitters.

Answer 14

Sweat glands and adrenal medulla

Question 15

How are the sweat glands exceptions to the autonomic NS?

Answer 15

They have sympathetic function however release ACh at the postganglionic nerve endings.

Question 16

How is the adrenal medulla an exception to the autonomic NS?

Answer 16

Receives normal sympathetic input via ACh. But adrenal medulla cells are endocrine cells which release adrenaline (and NA in humans), not postganglionic cells (neuroendocrine organ).
So NA and Ad are released and able, via blood transport, to activate non-innervated receptors. They act at adrenergic receptors. Can be found in smooth muscle of bronchioles/blood vessels etc.

Question 17

Role of the sympathetic and parasympathetic NS

Answer 17

Homeostasis, vision, reproduction

Question 18

When are the SNS or PNS responsible?

Answer 18

SNS = responsible when we are alert and active. In emergency or as a defence (fight or flight)
PNS = rest and digest. Energy conservation, digestion and emptying.

Question 19

How are most organs innervated by the autonomic NS? Give example

Answer 19

Most organs and tissues are dual innervated with an antagonistic SNS and PNS
E.g., GIT, activation of the SNS decreases motility due to action on the smooth muscle cells of the GIR but activation of PNS increases motility

Question 20

What are the different ways the autonomic NS can innervate structures?

Answer 20

Dual innervation with antagonistic SNS and PNS
Overall antagonistic dual innervation but innervation is of different parts of the structure
Dual innervation but not antagonistic
Single innervation

Question 21

Give an example of where an overall structure has antagonistic dual innervation but the innervation is of different parts of the structure

Answer 21

The pupil (smooth muscle)

Question 22

Describe the arrangement of the iris

Answer 22

Formed of 2 layers of muscle:

• inner layer next to pupil where the long smooth muscles are arranged point to point in circular arrangement, circular muscle
• outside layer where smooth muscle cells are labelled end to end, radial muscle

Question 23

What causes pupil dilation?

Answer 23

SNS is activated causing contraction of the radial muscle

Smooth muscle cell contraction in the outer layer will pull open the pupil

Question 24

What causes pupil constriction?

Answer 24

PNS aids activated causing contraction of the circular muscle.
Smooth muscle cell contraction in the inner layer will constrict the pupil.

Question 25

Give an example of dual autonomic innervation but not antagonistic

Answer 25

Salivary glands

Sympathetic and parasympathetic innervation promote the production of saliva

Question 26

What does the SNS do in respect to salivary glands?

Answer 26

Increased SNS to blood vessels supplying the salivary glands would cause vasoconstriction and thus less blood flow. So less constituents are delivered to the salivary glands, so saliva is low in volume but more sticky.

Question 27

What does the PNS do in respect to salivary glands?

Answer 27

Increase PNS activity to blood vessels supplying salivary glands causes vasodilatation. More constituents can flow to the salivary gland, producing lots of watery saliva.

Question 28

Functional significance of the salivary glands innervation

Answer 28

PNS - rest and digest = more saliva to start digestion process
SNS - alert state = not as much saliva needed. ‘Dry mouth’ = less serous saliva

Question 29

What are the salivary glands like in normal situations?

Answer 29

PNS input dominates over SNS input meaning average quantity of reasonably watery saliva.

Question 30

Give 2 examples of single autonomic innervation

Answer 30

Sweat glands have sympathetic nervous input only

Most blood vessels also only have sympathetic innervation

Question 31

Describe single sympathetic innervation of blood vessels

Answer 31

Smooth muscle in most blood vessels is only innervated by SNS. An increased sympathetic activity causes more vasoconstriction and decreased sympathetic activity causes vasodilation. Vasomotor tone.

Question 32

Which blood vessels are not singly innervated?

Answer 32

Blood vessels of the head and reproductive organs. Receive SNS (vasoconstriction) and PNS (vasodilation) with antagonistic effects.

Question 33

When do the SNS and PNS work together?

Answer 33

Make sex organs (doesn’t fit fight or flight and rest and digest)
PNS = erection
SNS = ejaculation
Dual innervation but timing of activity is important

Question 34

What happens if there is widespread sympathetic activation?

Answer 34

Blood vessels of skeletal muscle and cardiac muscle will vasodilate
Most other blood vessels and skin vessels will constrict

Question 35

What happens in body-wide increased sympathetic activity?

Answer 35

Most vessels (e.g., in skin):
- NA acts on alpha adrenergic receptors
- acts to vasoconstrict
Some blood vessels (skeletal and cardiac muscle):
- adrenal medulla releases adrenaline acting on beta adrenergic receptors
- when activated on smooth muscle, they relax and thus vasodilation

Thus there is a balance

Question 36

Which blood vessels express which receptors and how many?

Answer 36

Most blood vessels primarily express alpha receptors, showing vasoconstriction
Skeletal muscle vessels express more beta receptors, showing dilatations

Question 37

How does focusing the eyes on a near object changed by somatic and autonomic NS?

Answer 37

ANS - pupil/lens adjustments

Somatic - eyeball movements

Question 38

How is the response to cold controlled by autonomic and somatic NS?

Answer 38

ANS - vasoconstriction in the skin (to conserve heat, direct blood flow elsewhere)
Somatic - shivering