Week 8 the autonomic nervous system

Question 1

Autonomic nervous system

Answer 1

->Maintains internal environment
->Mostly involuntary
->Controls visceral functions
- circulation
- digestion
- excretion
->Modulates endocrine function

Question 2

ANS Input (afferent)

Answer 2

Autonomic nervous system: afferent
Sensory neurones from peripheral organs to centres in e.g., hypothalamus, medulla

Question 3

ANS Output (efferent)

Answer 3

->Sympathetic or Parasympathetic neurons
- Organs innervated by both (often)
- Generally opposing actions
May be Linked by reflex arcs
(afferent and efferent)

Question 4

Outputs: What do ANS nerves control

Answer 4

Mainly smooth muscle, cardiac muscle and secretory glands

Question 5

Divisions of the ANS

Answer 5

-Sympathetic
-Parasympathetic

Question 6

Sympathetic

Answer 6

->’Fight or flight’
->Short term survival
->Generally increases energy availability/ capacity and usage e.g.,
– Increase heart rate
– Increase lung capacity
– Increase blood flow to some skeletal muscles
– Increase blood glucose

Question 7

Parasympathetic

Answer 7

->‘Rest and digest’
->Long term survival
->Generally reduces energy availability/capacity and usage e.g.,
– Decrease heart rate
– Decrease lung capacity
– Increase blood flow to digestive system
– Increase fat/glycogen stores

Question 8

Homeostasis

Answer 8

->SNS and PNS are active
constantly - modulating
DYNAMIC BALANCE

Question 9

Autonomic nervous system functions

Answer 9

->Each organ controlled by
branches of both
parasympathetic and
sympathetic NS
->Stimulation of the
parasympathetic NS has
broadly opposite effect to stimulation of the sympathetic in that organ (and vice versa)

Question 10

ANS neurons vs motor (somatic NS) neurons

Answer 10

-Neurons bundle together to form nerves

Question 11

Anatomical differences in PNS and SNS

Answer 11

->Where nerves originate (leave CNS)
->Where the ganglia (cell
bodies) are, i.e., where 2
neurons synapse
->Differences in
neurotransmitters and
receptor subtypes

Question 12

SNS and PNS

Answer 12

Each organ receives input from both the parasympathetic and the sympathetic nervous system -> Each organ is controlled by both divisions but each division has broadly opposite effects

Question 13

Arrangement of PNS and SNS neurons

Answer 13

PNS is made up of spinal nerves that leave the spinal cord between the vertebra
SNS is made up of cranial nerves that leave the CNS below the base of the brain and the base of the spinal cord (sacral region)

Question 14

Anatomical similarities in PNS and SNS

Answer 14

Consist of two neurons that exist in series

Question 15

Autonomic ganglion

Answer 15

Where neurons synapse, lots of neurons synapse in this place
They leave the CNS at their relevant location, enter the periphery and synapse onto a second neuron, the point where they synapse is called an autonomic ganglion -> where the second neuron ends it will synapse onto an effector organ where you will see the effect
->1st neuron is called a preganglionic neuron (myelinated)
->2nd neuron is called a postganglionic neuron (unmyelinated)

Question 16

Cranial nerves

Answer 16

10 cranial nerves -> one of these is the vagus nerve, critial parasympathetic nerve, cranial nerve 10, carries most of the parasympathetic messages to the body and controls most of our main organs

Question 17

Neurotransmitters involved in SNS

Answer 17

1st neuron releases acetylcholine onto the 2nd neuron within the sutonomic ganglion
When acetylcholine is released it binds to receptors on the post synaptic membrane and stimulate the second neuron -> it stimulates the second neuron to release noradrenaline (norepinephrine) onto the smooth muscle (effector) to cause a contraction

Question 18

Neurotransmitters involved in PNS

Answer 18

1st neuron releases acetylcholine onto the 2nd neuron, the 2nd neuron also releases acetylcholine

Question 19

Adrenal gland exception

Answer 19

The adrenal gland in the SNS, exception to the neurotransmitters released by SNS neurons
1st neuron will release acetylcholine onto the adrenal gland but it stimulates the adrenal gland to release a epinephrine and norepinephrine which will travel in blood vessels and have an effect on the effector organ

Question 20

Adrenal gland

Answer 20

Adrenal gland located: On top of kidneys
-Adrenal medulla (inside part) is a major organ of the sympathetic nervous system
-Synapse/ganglia in gland
-Can cause body-wide release
of epinephrine / adrenaline
and norepinephrine/
noradrenaline in an extreme
emergency (adrenaline “rush” or surge)

Question 21

Receptors

Answer 21

Protein structures that receive and transduce signals
-Include ligand gated ion channel-linked (ionotropic) receptors
-G protein coupled (metabotropic) receptors

Question 22

Ionotropic receptors

Answer 22

Binding site and channel
combined, have a binding site and a channel down the middle of the receptor that are combined, no downstream signalling molecules (no 2nd messenger) so you get a rapid response

Question 23

Metabotropic receptors

Answer 23

GPCR
-Binding site not combined
with a channel, don’t have an obvious channel that ions can travel through associated with them but they do have a secondary messenger system
-2nd messenger/GPCR
-Slower response
May have another channel opening

Question 24

PNS overview

Answer 24

Preganglionic nerves - cholinergic
Postganglionic nerves - cholinergic
Effector Neurotransmitter = ACETYLCHOLINE
Two types of acetylcholine receptors; (distrabuted differently in the ANS)
->Nicotinic
->Muscarinic

Question 25

Nicotinic

Answer 25

Ionotropic ligand gated channel
-5 subunits
-2 ACh binding sites
-(Skeletal muscle), autonomic
ganglia, adrenal medulla

Question 26

Muscarinic

Answer 26

GPCR
3 subtypes;
– M1 - brain, parietal cells (excitatory)
– M2 – heart (inhibitory)
– M3 - smooth muscle, glands,
(excitatory)

Question 27

Post-synaptic receptors (targets) -> PNS

Answer 27

1st neuron releases acetylcholine onto nicotinic receptors
Nicotinic receptors on the dendrites of the second neuron in series
In the PNS, the receptor that sits on the smooth muscle of the effector, is a muscarinic receptor
Nicotinic receptor in the autonomic ganglion and a muscarinic receptor on the effector tissue

Question 28

SNS overview

Answer 28

Preganglionic nerves - cholinergic
Postganglionic nerves - adrenergic
Effector Neurotransmitter = NORADRENALINE (NOREPINEPHRINE)

Question 29

Post-synaptic receptors (targets) -> SNS

Answer 29

1st neuron releases acetylcholine onto 2nd neuron, we have a nicotinic receptor in the autonomic ganglion
On the smooth muscle we have adrenoceptors receptors -> respond to noradrenaline and adrenaline –» important for drug specificity, agonists can be designed to bind to specific receptors

Question 30

Drug specificity

Answer 30

If you have a drug that binds to a nicotinic cholinergic receptor, you will either block or stimulate the sympathetic nervous system and the parasympathetic nervous system to the same extent -> problematic as if you stimulate both you would have no effect

Question 31

Adrenoceptors

Answer 31

G-protein coupled receptors
(metabotropic)
-2 types: alpha (alpha 1 and alpha 2) and beta (beta 1 and beta 2)
-Respond to adrenaline,
noradenaline
-Have diverse actions depending on the target tissue, that depends on the downstream molecules that these receptors stimulate
-> Some of these receptors are inhibitory and some of these receptors are excitatory

Question 32

Diverse actions of adrenoceptors

Answer 32

e.g., Some of these receptors have conflicting effects despite being SNS, for example the SNS overall causes the bronchi to dilate, but there are two types of adrenoceptors, alpha 1 and beta 2 receptors -> alpha causing constriction and beta causing dilation - most of the adrenoceptors are beta 2 receptors, so the overall effect on the bronchi by the SNS is dilation (there are some alpha 1 receptors)

Question 33

PNS vs SNS

Answer 33

Organs have inputs from both PNS and SNS -> broadly opposite effects
Individual cells generally have inputs from both PNS and SNS

Question 34

Autonomic: smooth muscle neuro muscular junction

Answer 34

Controls;
-Vascular smooth muscle
-Bronchial smooth muscle
-Intestinal peristalsis
Specialised neuro muscular junction
Where the second neuron of the ANS makes contact with the smooth muscle
Axons end with a series of swollen areas called varicosity contains vesicles filled with neurotransmitter -> release neurotransmitter