Autonomic Nervous System

Question 1

ANS controls what?

Answer 1

Not under conscious control 
Controls non-skeletal peripheral function:
Cardiac muscle
Smooth muscle
Internal organs
Skin

Question 2

Two types of afferent neurones

Answer 2

Somatic sensory - respond to external stimuli
Visceral sensory - responds to internal stimuli
Relay to the brain through cranial nerves then to efferent neurones

Question 3

Describe the motor (efferent) division

Answer 3

Somatic motor - external response
Visceral motor - parasympathetic (routine maintenance + digestion) and sympathetic (mobilisation and increased metabolism)

Question 4

Parasympathetic vs Sympathetic Effects on:
Pupil
Heart
Stomach

Answer 4

Pupil:
Parasympathetic - constriction
Sympathetic - dilation
Heart:
Parasympathetic - reduces rate and contraction
Sympathetic - increases rate and contraction
Stomach:
Parasympathetic - increases motility and secretions
Sympathetic - decreases motility and secretions

Question 5

Parasympathetic vs Sympathetic effects on:
Lungs
Liver
Bladder

Answer 5

Lungs:
PS - constrict
S - dilate
Liver:
PS - increased bile release (digestion)
S - increased glucose release (for fight/flight)
Bladder:
PS - contraction
S - relaxation

Question 6

Example of where only one NS affects both increase and decrease in the body

Answer 6

Sympathetic nervous system controls blood vessels with regards to constriction and dilation

Question 7

Describe the process of altering heart rate in relation to baroreceptors

Answer 7

Baroreceptors in visceral sensory division (internal environment)
Higher the heart rate higher the blood pressure and so the baroreceptor’s firing rate which is sent up afferent division to PNS+CNS then to efferent division to visceral motor.
Higher firing rate means heart rate must be reduced so para’s effect is increased
Lower firing rate means heart rate must be increased so symp’s effect is increased

Question 8

Location of visceral neurones

Answer 8

Visceral motor nuclei originate in hypothalamus

Visceral motor neurons project towards the brainstem/spinal chord where they synapse with autonomic neurones

Question 9

Autonomic neurones consist of two neurones…..

Describe their characteristics with regards to PNS and SNS

Answer 9

Pre-ganglionic and post ganglion neuron
(Ganglion is a nerve cell cluster)
Long pre-ganglionic fibre and short post-ganglionic fibre in PNS (ganglions close to effector tissue)
Short pre-ganglionic fibre and long post-ganglionic fibre in SNS (ganglions close to spinal chord) lots of sympathetic nerves to allow mass activation

Question 10

What neurotransmitters do each neurone release at their synapses?

Answer 10

Pre-ganglionic and Post-ganglionic fibres on PNS release acetylcholine
Pre-ganglionic fibres on SNS release acetylcholine
Post-ganglionic fibres on SNS release Noradrenaline

Question 11

Adrenal Gland is different how?

Answer 11

Has only one sympathetic nerve instead of two neurones
Secretes a hormone (adrenaline and some noradrenaline) not a neurotransmitter
Screwed into bloodstream not through synapses

Question 12

How does the PNS and SNS control lung function?

Answer 12

Only PNS have nerves innervating the lung tissue (no SNS) which causes bronchoconstriction
SNS influences lung function through the adrenal gland by releasing adrenaline which causes bronchodilation

Question 13

Other nervous system to control gut function?

Answer 13

Enteric nervous system adds layer of complexity to gut responses

Question 14

Describe the micturition reflex?

Answer 14

Pressure builds up in bladder - sensory info relayed up to brain
PNS controls destructor muscle initially relaxed now contracts to force urine out
SNS controls internal sphincter initially contracting to stop urine release now relaxes so urine can leave bladder

Question 15

What type of receptors would be wanted at autonomic ganglia?

Answer 15

Ion channel receptor for fast response (between neurones)

Nicotinic acetylcholine receptor to mediate fast excitatory and inhibitory transmission

Question 16

Purpose of adrenergic receptors

Answer 16

G-protein coupled receptor

Adrenergic (SNS) respond to noradrenaline release from post-gang SNS fibres or adrenaline via blood

Question 17

Purpose of Muscarinic receptors?

Answer 17

G-protein coupled receptor

Responds to acetylcholine release from post-gangling PNS fibres

Question 18

Journey of NTs at synaptic transmission with reference to acetylcholine

Answer 18

Precursor (choline and acetyl CoA) enzymatically converted to neurotransmitter (acetylcholine) which is the. Packaged into vesicles. AP causes Ca2+ influx and exocytosis of neurotransmitters.
Receptor (muscarinic or nicotinic) is then activated as NTs bind.
Removal of NT from synapse via uptake into pre-synaptic terminal or glial cell, can be metabolised in synapse prior to uptake
(Acetylcholine broken down by acetylcholinesterase in synapse, choline taken up into presynaptic terminal by choline uptake protein)

Question 19

What happens if acetylcholinesterase is blocked?

Answer 19

Acetylcholine is stopped from being metabolised and so accumulates in synapse

Question 20

Noradrenaline’s pathway in synaptic transmission

Answer 20

Tyrosine converted to DOPA by tyrosine hydroxylase. DOPA converted to dopamine by DOPA decarboxlase. Dopamine packaged into vesicles with dopamine beta hydroxylase. Noradrenaline is the product.
AP causes Ca2+ influx and exocytosis of NT, adrenergic receptor are activated.
MOA-O breaks down noradrenaline in presynaptic terminal or COMT. Reads down noradrenaline in glial cell.

Question 21

What is the process for the adrenal gland and adrenaline release?

Answer 21

Tyrosine (tyrosine hydroxylase) -> DOPA (DOPA decarboxylase) -> dopamine
Dopamine packaged into vesicles with dopamine beta hydroxylase, noradrenaline as product.
Noradrenaline converted to adrenaline in the cytoplasm by phenylethanol methyl transferase in adrenal gland
AP causes Ca2+ influx and exocytosis of adrenaline
Adrenaline diffuses into capillary and transported to tissues in the blood