Lecture 10-Neural regulation of the heart and vasculature

Question 1

what is autoregulation?

Answer 1

intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure
-intrinsic to the organ –> occur in absence of neural / hormonal influence

Question 2

what is reflex neural control

Answer 2

adjustment of cardiovascular function to meet the bodies needs

• allows rapid change in BP / CO
• essential to meet demand of brain / heart

Question 3

where does parasympathetic and sympathetic afferents go to

Answer 3

medullary regulatory center

Question 4

where do PNS and SNS efferents go to?

Answer 4

autonomic ganglia

sympathetic also goes to spinal centers`

Question 5

what does the autonomic ganglia act on?

Answer 5

intrinsic nerves of the heart and vessels

Question 6

what does sympathetic activity do to the heart?

Answer 6

increases HR and contraction rate
increases strength of contraction
releases adrenaline
vasoconstriction and vasodilation in certain places

Question 7

what does parasympathetic activity do to the heart?

Answer 7

slows HR
slows rate of conduction
dilation in some vascular beds

Question 8

what leads to HTN and heart failure

Answer 8

imbalance of sympathetic and parasympathetic NS

Question 9

what receptors does the sympathetic nervous system act on?

Answer 9

B1
B2
A1
A2

Question 10

what receptors does the parasympathetic nervous system act on

Answer 10

Muscarinic receptors

M1-3

Question 11

What receptors are cardiac specific

Answer 11

Sympathetic = adrenergic B1 receptors
Parasympathetic = M2 receptors

Question 12

What receptors act peripherally?

Answer 12

SNS =B2 + A1 + A2

Question 13

How does the Vagus nerve affect the heart?

Answer 13

Role in the parasympathetic efferent
Slow rate of conduction / lower HR / relax smooth muscle
1. Right Vagus
-innervates SA node
2. Left vagus
-AV node

Question 14

what other cranial nerves relax smooth muscle?

Answer 14

III , VII , IX

Question 15

what are the characteristics of parasympathetic efferent fibres?

Answer 15

• maintain physiological rest
• long preganglionic fibres
• short post-ganglionic fibres
• ganglia near or in visceral organ
• released AcH

Question 16

what is the parasympathetic efferent pathway

Answer 16

via thoracic vagus nerve in medulla
AcH released and acts on nicotinic receptors of ganglion cells
Post-ganglionic neuron transmit signal and releases AcH to act on M2 receptors and slow conduction in SA / AV nodes

Question 17

where do vagal efferent neurones originate in the brainstem?

Answer 17

1. Dorsal vagal nucleus
2. nucleus ambiguus (80%)
3. intermediate reticular zone

Question 18

give an overview how the baroreceptor reflex responds to an increase in blood pressure?

Answer 18

1. Increase in arterial pressure
2. Detection by arterial baroreceptors in the aortic arch / carotid sinus
3. Sensory afferent nerves ( glossopharyngeal / vagus nerve ) carry the impulse to the NTS in the medulla oblongata
4. Increase pressure relayed to the parasympathetic NA
5. Inhibits the impulses from the sympathetic tracts CVLM / RVLM
6. The NA directly along the parasympathetic efferent sends impulses to the SA node

Question 19

How does the baroreceptor reflex vary for the sympathetic nerve?

Answer 19

1. From the medulla it goes to the RVLM or CVLM

2. The efferent from these locations then goes to down the thoracic spinal cord

Question 20

Describe the Dil tracer applied to the hearts of rats

Corbett et al

Answer 20

localisation of vagal parasympathetic efferent cell bodies within the medulla oblongata
Neuron tracer Dil applied to the SA node of the rats
Immunochemistry can also be used to visualise the location of AcH using chAT

Question 21

what are the differences in the type of axons exist in the vagal efferent centres?

Answer 21

1. Different motor axons –> myelinated or unmyelinated
2. Different terminals in the heart
3. Functional differences

Question 22

Role of the vagus nerve as a parasympathetic afferent?

Answer 22

• sensory afferent neurones have cell bodies in the nodose ganglia
• innervate baroreceptors in the aortic arch
• potentially innervate chemoreceptors

Question 23

Role of the glosso-pharyngeal nerve as a parasympathetic afferent?

Answer 23

• sensory afferent neurones have cell bodies in the petrosal ganglia
• innervate baroreceptors in the carotid sinus
• innervate chemoreceptors in the carotid sinus

Question 24

Describe the experiment used to show the structure of receptors in the aortic arch
Cheng et al

Answer 24

Dil inserted in the Nodose ganglia
- Dil travels down to the sensory axon where the receptors exist
-the receptors can then be identified using a fluorescent microscope
BF = flower-spray or end-net terminals in walls of great vessels

Question 25

what has still not been identified in terms receptors and channels of the aortic arch?

Answer 25

type of channels responsible for signal transduction not resolved

Question 26

what is the role of the NTS?

Answer 26

brain's reception, processing and integration center for the entire CVS

Question 27

what are important features of the NTS shown by Spyer KM, 1982)

Answer 27

- Lesioning studies --> damage to the NTS and observe changes in reflexes - receives central termination of all vagal and glosso-pharngeal sensory fibres - NTS organised into distinct functional units

Question 28

what experiments have been done on the transmission of information to the NTS cellss

Answer 28

1. NTS response to cardiovascular signals in neurones with tracers show that small interneurones with long dendrites extend throughout the NTS 2. NTS neurones act differently to BP changes --> this suggests different functional types 3. Glutamate is the main transmitter released by cardiovascular afferents via NMDA and non-NMDA

Question 29

What are key features of the sympathetic pathway?

Answer 29

``` Flight or fight mainly thoracic / lumbar ganglia short pre-ganglionic and long post ganglionic fibres may be branched supply the entire heart Nor(adrenaline) released ```

Question 30

Describe the transmission of an impulse from preganglionic to heart muscle cell in the sympathetic pathway

Answer 30

1. Pre-ganglionic neuron in the spinal IML 2. AcH released from the axon to act on nictonic receptors on the ganglion 3. Post ganglion cell releases Noradrenaline at the axon 4. HR increases / SA conduction / AV conduction / and contraction strength 5. This occurs through activation of B1 and A1 receptors and blocking B2

Question 31

what have sympathetic nerve tracing studies shown about sympathetic preganglionic neurons?

Answer 31

recieve and are controlled by descending projections in the brain stem They exist in the IML of the thoracic ganglia Preganglionic axons pass through the ventral root

Question 32

describe the Geurtzenstein and silver(1974) studies regarding sympathetic activity

Answer 32

applied inhibitory glycine to the ventral medulla of cats and saw that the BP dropped - inhibition here suggests that neurons here regulate blood pressure - this area is called the RVLM

Question 33

describe the Dampney 1985 study regarding sympathetic activity

Answer 33

applied glutamate to the RVLM blood pressure responses coincided with the area of the RVLM that contained catecholamine producing neurones (the ‘C1’ adrenaline cell group, identified by immunohistochemistry) and also contained ‘bulbospinal’ neurones projecting down to the IML of the spinal cord

Question 34

what happens when neurons in the caudal CVLM are activated

Answer 34

sympathetic efferent outflow is inhibited and BP decreases

Question 35

how does activation of neurons in CVLM lead to inhibition of the RVLM

Answer 35

inhibitory neurons that originate in the CVLM and terminate in the RVLM are activated and they secrete GABA which is inhibitory

Question 36

how was it shown that activation of neurons in CVLM lead to inhibition of the RVLM

Answer 36

- injection of glutmate in the CVLM - sympathetic activity is inhibited - release of GABA in the RVLM

Question 37

what did the hainsworth review state about sympathetic afferents

Answer 37

Supply coronary vessels rather than great vessels Respond to chemical stimuli (nociceptors) rather than stretch or volume Response – can  HR & BP rather than  HR & BP Fibres run in cardiac & spinal nerves rather than cranial nerves Cell bodies in C8-T4 dorsal root ganglia rather than cranial ganglion Central terminals in dorsal horn rather than NTS

Question 38

What is the hearts little brain?

Answer 38

cardiac ganglion cells and intrinsic nerve fibre network within the heart