Autonomic Nervous System

Question 1

What is the autonomic nervous system (ANS) a subdivision of?

Answer 1

Peripheral nervous system

Question 2

What non-skeletal peripheral functions does the ANS control? (4)

Answer 2

Cardiac muscle

Smooth muscle

Internal organs

Skin
Not under conscious control

Question 3

What are the 2 afferent neurones of the sensory division, and which of these is part of the ANS?

Answer 3

• Somatic sensory → responds to external stimuli e.g. skeletal muscle responding to you walking
• Visceral sensory afferent (part of ANS) → responds to internal stimuli

Question 4

What are the 2 efferent neurones of the motor division, and which of these is part of the ANS?

Answer 4

Visceral motor efferent
Somatic motor

Question 5

Parasympathetic vs sympathies

Answer 5

Rest and digest
Fight or flight

Question 6

How do the 2 systems interact with pupils, heart, stomach, lungs?

Answer 6

• Pupil → sympathetic causes dilation, para causes constriction
• Heart → sympathetic increases rate and contractility, para decreases rate and contractility
• Stomach → sympathetic decreases motility and secretions, para increases motility and secretions
• Lungs → sympathetic causes dilation, para causes constriction

Question 7

Effect of SNS and PNS on liver

Answer 7

• Liver → sympathetic increases glucose release, para increases bile release

Question 8

effect of SNS and PNS on bladder

Answer 8

Bladder → sympathetic causes relaxation, parasympathetic causes contraction

Question 9

When do para and sympathetic not have opposing effects?

Answer 9

e.g. SNS controls blood vessel tone → both constriction and dilation

Question 10

Explain how the 2 systems balanced (e.g. with heart rate & bp)?

Answer 10

With autonomic control, generally either para or sympathetic is dominant over the other, particularly when both innervate the same tissue e.g. baroreceptors detect high blood pressure, send this to brain, brain sends signal to para neurones to lower bp and turns sympathetic off to stop further increase in bp

If bp drops, baroreceptors fire less often (baroreceptor firing is proportional to bp) so there is less signal through visceral motor neurones so parasympathetic effect drops and the SNS that is normally inhibited by baroreceptor firing, aren’t anymore as that stimulus has decreased, so SNS switches on (disinhibition) so now SNS is dominant

Question 11

Where is the autonomic sensory (afferent) info relayed to

Answer 11

Hypothalamus

Question 12

Where do visceral motor nuclei originate

Answer 12

Hypothalamus
Project to the brain stem or spinal chord

Question 13

What do autonomic neurones consist of?

Answer 13

2 neurones → a pre-ganglionic (originating in brain/spinal cord) and a post-ganglionic neurone

Question 14

Ganglion

Answer 14

A group of nerve cell bodies in PNS

Question 15

What does the paraNS look like in terms of these?

Answer 15

• Long pre-ganglionic fibres
• Ganglions close to/embedded within effector tissues
• Short post-ganglionic fibres

Question 16

What does the SNS look like in terms of these?

Answer 16

• Short pre-ganglionic fibres (sympathetic)
• Ganglions close to spinal cord
• Long post-ganglionic fibres

Question 17

Exception to 2 neurone arrangement

Answer 17

Adrenal gland
Only has single sympathetic nerve innervating adrenal gland

Question 18

Which neurotransmitters do pre-ganglionic nerves of both SNS & PNS release, and what are the receptors?

Answer 18

Acetylcholine (ACh)

nicotinic ACh receptor

Question 19

Parasympathetic NS, what neurotransmitter is released from the post-ganglionic nerve, and what are the receptors?

Answer 19

ACh but detected by the muscarinic ACh receptors

Question 20

In SNS, what neurotransmitter is released from the post-ganglionic nerve, and state the exception to this rule?

Answer 20

Noradrenaline (NA) is released into effector organ

The sweat glands where ACh is the neurotransmitter released

Question 21

What does the adrenal gland secrete?

Answer 21

Does not release neurotransmitter

Instead secretes hormone, Adrenaline (and some noradrenaline)

Released into bloodstream NOT a synapse

Question 22

After smelling food, is the PNS or the SNS more dominant?

Answer 22

PNS - gastrointestinal tract needs to be ready to undergo process of digesting

Question 23

What is the name of the complex neural network within the gut?

Answer 23

Enteric nervous system - largely responds to gut function and stimuli received within the gut without engaging the brain

Question 24

What is the unusual situation with the lung in terms of innervation?

Answer 24

There are parasympathetic neurons in the lung which cause bronchocontrictuon via ACh but in synoayhic neurones
Adrenaline causes bronchodilation

Question 25

Describe the micturition reflex

Answer 25

Bladder slowly fills and moderate pressure in the bladder, SNS is in charge at this point

Internal sphincter controlled by SNS is contracted to prevent urine leaving the bladder

Once pressure gets to certain point, sensory information is relayed to the brain

PNS switched on and SNS is switched off

PNS contracts detrusor muscle to squeeze bladder and force urine out

Internal Sphincter is relaxed as SNS is turned off so urine can leave the bladder

• Somatic NS also gives voluntary level of control for when you want to empty bladder through control of external sphincter

Question 26

Which receptors mediate the effects at all autonomic ganglia?

Answer 26

Nicotinic acetylcholine (nACh) receptor- is an ion channel linked receptor that gives fast response

These are found at all ANS ganglion- need that fast propagation of signal

Question 27

Which receptors mediate the effects of NT released from postganglionic fibres?

Answer 27

• G protein coupled receptors- muscarinic receptors for ACh (in PNS) and adrenergic receptors for NA (in SNS)
• G protein coupled receptors have a slower onset than ion channel linked receptor

Question 28

How is ACh made at synapses and released etc?

Answer 28

• etc?
  
  • Choline and acetyl CoA enzymatically converted by choline acetyl transferase (into ACh)
  • ACh is packaged into vesicles
  • Action potential causes Ca2+ influx and exocytosis
  • Exocytosis and neurotransmitter release
  • ACh binds onto muscarinic/nicotinic receptors
  • Acetylcholine rapidly degraded by acetylcholinesterase in the synapse. Choline taken up into presynaptic terminal by choline uptake protein (or in a glial cell)

Question 29

• What happens if acetylcholinesterase is blocked?

Answer 29

ACh accumulates in synaptic cleft and there is a much more powerful ACh effect

Question 30

How is NA made at synapses and released etc?

Answer 30

Tyrosine hydroxylated to form Dopa, by tyrosine hydroxylase

Dopa decarboxylated to form Dopamine, by DOPA decarboxylase

Dopamine hydroxylated to form noradrenaline, by dopamine Beta hydroxylase, noradrenaline packaged into vesicles

Action potential causes Ca2+ influx and exocytosis

Exocytosis and neurotransmitter release

Receptor activation (Adrenergic)

Removal of neurotransmitter from synapse via uptake into pre-synaptic terminal or glial cell; can be metabolised in the synapse prior to uptake

Question 31

What are the 2 enzymes that metabolise noradrenaline into breakdown products, and where are they found?

Answer 31

Monoamine oxidase A within pre-synaptic terminal

Catechol-O-methyltransferase (COMT) in glial cells

Question 32

• Describe the biosynthesis & action & release of Adrenaline in the nerve innervating the Adrenal gland

Answer 32

Tyrosine hydroxylated to form Dopa, by tyrosine hydroxylase

Dopa decarboxylated to form Dopamine, by DOPA decarboxylase

Dopamine hydroxylated to form noreadrenaline, by dopamine Beta hydroxylase

Noradrenaline methylated to form adrenaline, by phenylethanol methyltransferase

Action potential causes Ca2+ influx & Exocytosis

Exocytosis & Neurotransmitter release

Adrenaline diffuses into capillaries and is transported to tissues in the blood