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Neurology > S1: Physiology of the Parasympathetic Nervous System > Flashcards

S1: Physiology of the Parasympathetic Nervous System Flashcards

1
Q

The parasympathetic nervous system control our ‘rest and digest’ system.

List some changes to the body

A
  • slowing of heart rate: rest
  • accommodation of the eye
  • bladder controlling urination
  • GI tract motility/secretion : time for eating and digestion
  • bronchoconstriction during rest when less o2 required

These mechanisms in eye, bladder, GI and lungs are caused by contraction of smooth muscle

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2
Q

Where do the pre-ganglionic fibres of the parasympathetic system exit the spinal cord?

A

They exit the spinal cord from the cranio-sacral outflow

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3
Q

From the brain stem there are 4 parasympathetic nerves

Name them (and numbers)

A

CN III = oculomotor nerve
CN VII= facial
CN IX= glossopharyngeal
CN X= vagus

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4
Q

What does the occulomotor nerve innervate?

A

Eye

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5
Q

What does the facial nerve innervate?

A

The salivary glands:

Lacrimal glands
Submandibular glands
Sublingual glands

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6
Q

What does the glossopharyngeal nerve innervate?

A

Parotid gland

Pharynx

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7
Q

What does the vagus nerve innervate?

A 
Airway
Heart 
Stomach 
Liver
Pancreas
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8
Q

What modulates cranial nerves?

A

The higher centres of the brain can feed in information to change the activity of these neurones

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9
Q

Compare the length of pre and post ganglionic parasympathetic fibres

A

The parasympathetic preganglionic fibres are long
They enter the ganglia and synapse with the post ganglionic fibres much closer to target structure

The parasympathetic post ganglionic fibre are short

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10
Q

What neurotransmitter is used in the preganglionic terminal and postganglionic terminal ?

A

Acetylcholine choline

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11
Q

What receptors do Ach bind to in preganglionic terminal?

A

Nicotinic receptors

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12
Q

What receptors do Ach bind to in post ganglionic terminal?

A

Muscarinic receptors (M)

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13
Q

In the the sacral region, what does the postganglionic fibres innervate?

A

Bladder
Genetalia
Large intestine

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14
Q

What nerve releases Ach at M2 receptors?

A

Vagus nerve

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15
Q

What happen when M2 receptors are stimulated by parasympathetic NS in the heart?

A

Vagus nerve releases Ach at M2 receptors which are found at the SA node.
Stimulation of them decreases pacemaker potential at the SAN resulting in a reduction of heart rate (bradycardia)

It also decreases the rate of electrical conduction as M2 receptors are found in conduction pathway through AVN to balance reduction in heart rate contraction.

Stimulation of vagus nerve therefore decreases cardiac output as heart rate is decreases and CO= HR x SV

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16
Q

Where are M2 receptors in the heart found?

A

SAN

AVN

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17
Q

Do parasympathetic nerves innervate ventricles and most blood vessel?

A

No the sympathetic system does

They therefore do not affect heart contractility SV or total peripheral resistance (BP)

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18
Q

What happen when M3 receptors are stimulated by parasympathetic NS in the eye?

A

Stimulation of M3 receptors leads to construction of circular smooth muscle of iris (constrictor pupillary) so pupil diameter decreases (miosis)

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19
Q

What is miosis?

A

Construction of pupil

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20
Q

What is the secondary action of miosis?

A

It opens the canal of schlemm at the back of the pupil.

This drains aqueous humour from the eye reducing intra-ocular pressure within the eye

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21
Q

What happens when the M3 receptors on the ciliary muscled are not stimulated by occulomotor nerves (III)?

A

The ciliary muscles are relaxed and the suspensory ligaments which attach the muscles to the lens are taunt. This results in a long thin lens allowing long focal length (distance vision)

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22
Q

What happens when the M3 receptors on the ciliary muscled are stimulated by occulomotor nerves (III)?

A

It causes ciliary muscles to contract and therefore relaxes the suspensory ligaments causing the lens to bulge in shape allowing reduced focal length (close vision)

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23
Q

Where are mechano-sensitive afferent fibres found?

A

In the bladder wall in the detrusor muscles

24
Q

How does bladder ‘know’ it is full?

A

When the bladder fills up, stretch receptors and mechano-sensory fibres detect this and send to information to the brainstem micturition centre in the brain.

25
Q

What does the brain stem miturition centre do?

A

It is the control centre for urination and controls the parasympathetic and sympathetic system innervating the bladder

26
Q

Where is the brain stem micturition centre found?

A

In the medulla in the brain

27
Q

Name the three systems involved with the control of our bladder and briefly describe their role

A

The sympathetic system= they relax the bladder muscles to let it fill and contracting internal sphincter to prevent urination

The parasympathetic system= contracts the detrusor muscles to make you want to urinate

Motor system= we are aware of this as we were ‘potty trained’. We can control our urination by controlling our external sphincter. This is governed by the higher centres.

28
Q

How will parasympathetic system promote urination?

A

It activates M3 receptors by releasing Ach which contracts detrusor muscles

29
Q

How will sympathetic system promote holding in urine?

A

It activates B2 receptors in the detrusor muscles by releasing noradrenaline while relaxes it allowing bladder to fill.

30
Q

What happens when the M3 receptors on the GI tract are stimulated by vagus nerve?

A

Acetylcholine acts on M3 receptors which causes contraction of circular and longitudinal smooth muscle in the GI tract. This increases GI motility, by reducing size and pushing the contents down the lumen.

31
Q

What controls our peristaltic reflexes?

A

The afferent vagus sensory fibres

32
Q

What other nervous system controls the movements of the gut (not sym or para)

A

Enteric nervous system

33
Q

What parasympathetic nerves stimulate salivary glands?

A 
CN IV (facial)
CN IX (glossopharyngeal)
34
Q

What cells in salivary glands are stimulated by parasympathetic nerves and what do they secrete?

A

Facial and glossopharyngeal nerves stimulate acinar cells

They increase the secretion if amylase/mucins

35
Q

What nerve stimulates gastric glands?

A

CN X (vagus)

36
Q

What cells in gastric glands are stimulated by parasympathetic nerves and what do they secrete?

A

Vagus nerve stimulates parietal cells

They secrete HCl

37
Q

What nerve stimulates pancreatic gland?

A

Vagus nerve

CN X

38
Q

What cells in pancreatic gland are stimulated by parasympathetic nerves and what do they secrete?

A

Acinar and islet increased secretion of pancreatic enzymes e.g. insulin

39
Q

Why are the salivary glands, gastric glands and pancreatic glands stimulated by the parasympathetic nervous system?

A

They are required for eating and digestion

40
Q

What happens when the M3 receptors on the bronchi are stimulated by parasympathetic nerves?

A

It causes smooth muscle cells to contract causing bronchoconstriction

41
Q

What special nerves innervate erectile tissue?

A

Specialised sacral parasympathetic ‘vasodilator’ nerves

42
Q

What do the nerves that innervate erectile tissue release?

A

They release nitrous oxide (NO)

Not ach - this is an exception to parasympathetic rule

43
Q

How does NO cause an erection?

A

No is a lipophilic, membrane permeable gas so NO causes relaxation of vascular smooth muscle cells composing the corpus cavernosum.

The corpus cavernosum dilates and fills with blood

44
Q

How does viagra work?

A

Viagra is a erectile disfunction drug

It prevents the breakdown of the actions of NO increasing its vasodilator effects

45
Q

What is the alpha subunit in M3?

A

Gq/11

46
Q

How does stimulation of M3 receptors cause contraction of smooth muscle?

A
  1. Ach binds to M3 receptor and it interacts with the enzyme phospholipase C (PLC)
  2. PLC breaks down PIP2 into IP3
  3. IP3 binds to IP3 receptor on sarcoplasmic reticulum stimulating Ca2+ release into cytosol
  4. DAG stimulates Na+ ion channels to open increasing membrane excitability as Na+ influxes in
  5. This causes depolarisation of the smooth muscle which activates VGCCs inducing Ca2+ influx
  6. Ca2+ from the SR and from VGCCs bind to camodulin.
  7. The Ca2+/CaM complex activates myosin light chain kinase (MLCK)
  8. MLCK phosphorylase myosin light chains which then allows contraction to occur
47
Q

What enzyme breaks down PIP2 into IP3 and DAG?

A

Phospholipase C (PLC)

48
Q

What happens when IP3 binds to the IP3 receptor?

A

This simulates Ca2+ release into cytosol

49
Q

Where is the IP3 receptor found?

A

On the sarcoplasmic reticulum membrane

50
Q

What stimulates Na ion channels to open?

A

DAG

51
Q

What activates VGCCs?

A

Depolarisation of smooth muscle caused by Na+ ion channels opening

52
Q

What two things induce Ca2+ influx into cytosol?

A
  1. IP3 binding to IP3 receptors of SR

2. Activation of VGCC

53
Q

What does calcium bind to in order to form a Ca2+/CaM complex?

A

Calmodulin

54
Q

What does the Ca2+/CaM complex activate?

A

Myosin light chain kinase (MLCK)

55
Q

What does MLCK do?

A

Phosphorylase the myosin light chain allowing contraction of smooth muscle to occur

Neurology (29 decks)

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