CVS - Autonomic Nervous System Flashcards Preview

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Flashcards in CVS - Autonomic Nervous System Deck (46):
1

What does the autonomic nervous system exert control over?

Smooth muscle
Exocrine secretion (salivary glands)
Rate and force of contraction in the heart

2

What are the two divisions of the ANS?

What is the third division sometimes mentioned?

Parasympathetic

Sympathetic

Enteric nervous system - network of neurones surrounding GI tract, normally controlled by sympathetic and parasympathetic fibres

3

Where is the cell body of the preganglionic neurone located?

And post ganglionic?

CNS

PNS

4

What is the origin of the sympathetic division?

What segments do the preganglionic neurones arise from?

Where do they synapse with the post ganglionic neurones?

Thoracolumbar origin
- preganglionic in the thoracic spinal cord and lumbar spinal cord

Arise from segments T1 to L2

Most synapse in Paraverterbal chain of ganglia

Some synpase in a number of prevertebral ganglia

** Short preganglionic, long post ganglionic neurones **

5

What is the origin of the parasympathetic division?

Where do the preganglionic fibres travel?

Where do they synapse with the post ganglionic neurones?

Craniosacral origin

In cranial nerves or sacral outflow

Ganglia - close to target cells

Long pre-ganglionic, short post ganglionic.

6

What do preganglionic neurones release?

What receptors does it act on?

What type of ion channel do these receptors have?

Acetylcholine

Nicotinic Ach receptors on post ganglionic cell

Integral ion channel - which is permeable to K+ and Na+

7

What causes an action potential to be fired down the axon?

Influx of Na+ ions, depolarises the cell.

Reaches threshold and action potential fired down the axon

8

What type of receptors do the post ganglionic neurones of the

a) sympathetic neurones

b) parasympathetic neurones

Have?

What is the exception?

Sympathetic - noradrenergic (noradrenaline as transmitter)

Parasympathetic - cholinergic (Ach as transmitter)

Sweat glands (sympathetic) - post ganglionic release Ach which acts on muscarinic ACh receptors

9

What cells of the adrenal medulla are like specialised post ganglionic sympathetic neurones?

What do they release? Where does it circulate?

Chromaffin cells

Release adrenaline - which circulates in the blood stream

10

What is the type of receptors to noradrenaline and adrenaline?

What are their types? And subtypes?

Adrenoreceptors which are G protein coupled receptors

alpha adrenoreceptors = a1-adrenoreceptor, a2-adrenoreceptor

Beta adrenoreceptors = b1-adrenoreceptors, b2-adrenoreceptor

11

Why do different tissues have different subtypes of receptors?

Allows for diversity of action

Selectivity of drug action

12

What is a co-transmitter?


Name two types of Co- transmitter

Other transmitters released with noradrenaline and adrenaline at the synpase of the post ganglionic neurone with the effector cells

NPY and ATP

13

What receptors does ACh act on?

What type of receptors are they?

Is there an integral ion channel?

Muscarinic receptors

G protein coupled receptors (M1, M2, M3)

No integral ion channel

14

What receptors have an integral ion channel?

And which don't?

Nicotinic receptors

Muscarinic receptors - G protein coupled receptors DONT.

15

In the parasympathetic nervous system what receptors are on the post synaptic and effector cells?

Pre ganglionic releases Acetylchloline

Post ganglionic = Has nicotinic receptors on (with integral ion channel)

Effector cells = have Muscarinic receptors (M1, M2, M3) NO integral ion channel

16

In the sympathetic nervous system what receptors are on the post synaptic and effector cells?

Pre ganglionic releases ACh

Post ganglionic = nicotinic ACh receptors

Effector cell = adrenogenic receptors

17

What are the functions of the autonomic nervous system?

Regulates physiological functions e.g. BP

SNS and PNS innervate a tissue they often have opposite effects

18

When is sympathetic activity increased?

When is parasympathetic system more dominant?

Under stress

Under basal conditions

They work together to maintain balance

19

Is sympathetic drive to different tissues independently regulated?

Yes e.g. Sympathetic activity to the heart can be increased without increasing activity to the GI tract

On some occasions (fight or flight) there can be a more coordinated sympathetic response

20

What does the autonomic nervous system control in the CVS?

Heart rate
Force of contraction of the heart
Peripheral resistance of blood vessels - controls arterioles constriction and how much resistance there is to the blood flow

21

What influence is the heart under at rest?

What happens if you denervate the heart (remove all innervation)?

Vagal influence - PNS dominates and keeps HR down

Heart will beat to 100bmp

22

Where are the preganglionic fibres in the parasympathic input to the heart?

Where do the preganglionic neurones synapse with the post ganglionic neurones?

What do the postganglionic cells release?

Which receptors do they act on?

What are the effects?

Pre ganglionic fibres at 10th cranial nerve vagus

On epicardial surface of at SA and AV node

ACh

M2 receptors

Decrease heart rate and decrease AV node conduction velocity

*note - not much effect on force of contraction*

23

Where do the post ganglionic fibres from the sympathetic input to the heart come from?

What do they innervate?

What do they release?

What receptors does it act on?

What are the effects?

Sympathetic trunk

Innervate SA node, AV node and myocardium

Noradrenaline

Acts mainly on Beta 1 adrenoreceptors

Increase heart rate
Increase force of contraction

24

How do cells in the SA node set the pace of the heart?

What sets the rhythm of the heart?

They steadily depolarise towards the threshold
Slow depolarising pacemaker potential
Turning on of a slow Na+ conductance (If - funny current)
Opening of Ca2+ channels

Action potentials firing in the SA node

25

What is the sympathetic effect of the ANS on pacemaker potentials?

Mediated by B1 receptors

Gs protein coupled receptors (S=stimuli)

Increase cAMP, active the HCN channels, more channels open, faster the slope back to threshold

Speeds up pacemaker potential

26

What is the parasympathetic effect of the ANS on pacemaker potentials?

Parasympathetic effect mediated by M2 receptors

Gi (i= inhibitory) protein coupled receptor

Increase K+ conductance, pulls resting potential more negative from threshold so takes longer to get back to threshold.

Decrease cAMP - cAMP will deactive the HCN channels

27

How does noradrenaline increase force of contraction?

Noradrenaline acting on B1 receptors in myocardium causes an increase in cAMP --> activates PKA

Phosphorylation of Ca2+ channels increases Ca2+ entry during the plateau of the action potential

Increased uptake of Ca2+ in sarcoplasmic recticulum

Increased sensitivity of contractile machinery

28

What type of innervation do most vessels receive?

What is the exception?

Sympathetic

Some specialised tissue e.g. Erectile tissue has parasympathetic innervation

29

What types of receptors are in most arteries and veins?

Alpha 1 adrenorecptors

Coronary arteries just from b2 receptors

Skeletal muscle has alpha 1 adrenorecptors and b2 receptor

Some blood vessels have B2 receptors as well as adrenoreceptors

30

What allows vasodilation to occur?

Vasomotor tone

31

What receptor does adrenaline have a greater affinity for?

What will happen at high concentrations?

B2 receptors than alpha 1 adrenoreceptors.

It will activate alpha 1 receptors

32

What effect will adrenaline have on activating b2 receptors?

Vasodilation - increases cAMP -->PKA -->opens K+channels and inhibits MLCK --> relaxation of smooth muscle

33

What effect will adrenaline have on activating alpha 1 adrenoreceptors?

Vasoconstriction - stimulates IP3 production

Increase in Ca2+ from stores via influx of extracellular calcium binds to calmodulin --> contraction of smooth muscle

34

What is the role of local metabolites?

What effect do local increases in metabolites have?

Active tissue produces more metabolites e.g. K+, H+, adenosine, incrase PCO2.

Strong vasodilator effect

More important for ensuring adequate perfusion of skeletal and coronary
muscle than activation of B2 receptors

35

How are changes in the state of the CVS communicated to the brain?

What is their role?

What receptors are found on the high pressure and low pressure side of system?

Via afferent nerves

Alters activity of efferent nerves

Baroreceptors - high pressure side
Atrial receptors - low pressure side

36

Where are the nerve endings of baroreceptors found?

What are they sensitive to?

Where is the control centre located?

Carotid sinus and aortic arch

Sensitive to stretch

Higher the BP, wider the walls of the artery will stretch, cause more AP to be fired.

Adrenal medulla

37

What drugs act on the ANS?

Sympathomimetics - alpha adrenoreceptor and beta adrenoreceptor

Adrenorecptors antagonists

Cholinergics - muscarinic agonist and antagonists

38

What uses do sympathomimetric drugs have on the CVS?

When do you administer adrenaline?

What is dobutamine? When may it be given?

What drug is given for asthma and why?

To restore function in cardiac arrest, along with electric shocks to restart heart
Also administered for anaphylactic shock

B1 agonist - given in cardiogenic shock (pump failure)

Salbutamol - B2 agonist - causes relaxation of bronchiole smooth muscle so you can breathe better

39

Give an example of a alpha one antagonists and describe how it works?

Give two examples of a beta adrenoreceptor antagonist. What effects does the drug have on the beta 1 and beta 2 receptors?

Prazosin - anti hypertensive. Inhibits noradrenaline action on vascular smooth muscle a1 receptors = vasodilation.

Propranolol - non selective B1/B2 antagonist. Slows heart rate and reduces force of contraction (b1) but also acts on bronchial smooth muscle causing bronchoconstriction (b2)

Atenolol - selective B1 (cardio-selective) - less risk of bronchoconstriction

40

Name a muscarinic agonist and when it is used.

Name a muscarinic antagonists and when it's used. When may it be used in examination.

Agonist - pilocarpine, used in treatment of glaucoma - activates constrictor papillae muscle

Antagonist - atropine/tropicamide - increases HR and bronchial dilation - used to dilate pupils for examination.

41

Where are alpha adrenoreceptor found?

Where are beta adrenoreceptors found?

Smooth muscle

Heart, smooth muscle of airways of lung, adipose and some blood vessels - particularly in skeletal muscle

42

What is cardiac output the product of?

Heart rate

Stroke volume

43

What is the principal means by which distribution of flow around the CVS is controlled?

Interplay between the sympathetic vasoconstrictor tone and the action of vasodilator substances

44

What is the normal resting heart rate?

60bpm

45

How is the action of the parasympathetic system on heart rate mediated?

How it the action of the sympathetic system on heart rate mediated?

Via acetylcholine acting on M2 muscarinic receptors

Noradrenaline acting on Beta 2 adrenoreceptors

46

What is the autonomic nervous system important for?

Regulating many physiological functions e.g. Heart rate, BP, body temperature (homeostasis)

Coordinating the body's response to exercise

Outside of voluntary control