Lecture 10-Neural regulation of the heart and vasculature Flashcards
what is autoregulation?
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
what is reflex neural control
adjustment of cardiovascular function to meet the bodies needs
- allows rapid change in BP / CO
- essential to meet demand of brain / heart
where does parasympathetic and sympathetic afferents go to
medullary regulatory center
where do PNS and SNS efferents go to?
autonomic ganglia
sympathetic also goes to spinal centers`
what does the autonomic ganglia act on?
intrinsic nerves of the heart and vessels
what does sympathetic activity do to the heart?
increases HR and contraction rate
increases strength of contraction
releases adrenaline
vasoconstriction and vasodilation in certain places
what does parasympathetic activity do to the heart?
slows HR
slows rate of conduction
dilation in some vascular beds
what leads to HTN and heart failure
imbalance of sympathetic and parasympathetic NS
what receptors does the sympathetic nervous system act on?
B1
B2
A1
A2
what receptors does the parasympathetic nervous system act on
Muscarinic receptors
M1-3
What receptors are cardiac specific
Sympathetic = adrenergic B1 receptors Parasympathetic = M2 receptors
What receptors act peripherally?
SNS =B2 + A1 + A2
How does the Vagus nerve affect the heart?
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
what other cranial nerves relax smooth muscle?
III , VII , IX
what are the characteristics of parasympathetic efferent fibres?
- maintain physiological rest
- long preganglionic fibres
- short post-ganglionic fibres
- ganglia near or in visceral organ
- released AcH
what is the parasympathetic efferent pathway
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
where do vagal efferent neurones originate in the brainstem?
- Dorsal vagal nucleus
- nucleus ambiguus (80%)
- intermediate reticular zone
give an overview how the baroreceptor reflex responds to an increase in blood pressure?
- Increase in arterial pressure
- Detection by arterial baroreceptors in the aortic arch / carotid sinus
- Sensory afferent nerves ( glossopharyngeal / vagus nerve ) carry the impulse to the NTS in the medulla oblongata
- Increase pressure relayed to the parasympathetic NA
- Inhibits the impulses from the sympathetic tracts CVLM / RVLM
- The NA directly along the parasympathetic efferent sends impulses to the SA node
How does the baroreceptor reflex vary for the sympathetic nerve?
- From the medulla it goes to the RVLM or CVLM
2. The efferent from these locations then goes to down the thoracic spinal cord
Describe the Dil tracer applied to the hearts of rats
Corbett et al
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
what are the differences in the type of axons exist in the vagal efferent centres?
- Different motor axons –> myelinated or unmyelinated
- Different terminals in the heart
- Functional differences
Role of the vagus nerve as a parasympathetic afferent?
- sensory afferent neurones have cell bodies in the nodose ganglia
- innervate baroreceptors in the aortic arch
- potentially innervate chemoreceptors
Role of the glosso-pharyngeal nerve as a parasympathetic afferent?
- sensory afferent neurones have cell bodies in the petrosal ganglia
- innervate baroreceptors in the carotid sinus
- innervate chemoreceptors in the carotid sinus
Describe the experiment used to show the structure of receptors in the aortic arch
Cheng et al
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
what has still not been identified in terms receptors and channels of the aortic arch?
type of channels responsible for signal transduction not resolved
what is the role of the NTS?
brain’s reception, processing and integration center for the entire CVS
what are important features of the NTS shown by Spyer KM, 1982)
- 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
what experiments have been done on the transmission of information to the NTS cellss
- NTS response to cardiovascular signals in neurones with tracers show that small interneurones with long dendrites extend throughout the NTS
- NTS neurones act differently to BP changes –> this suggests different functional types
- Glutamate is the main transmitter released by cardiovascular afferents via NMDA and non-NMDA
What are key features of the sympathetic pathway?
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
Describe the transmission of an impulse from preganglionic to heart muscle cell in the sympathetic pathway
- Pre-ganglionic neuron in the spinal IML
- AcH released from the axon to act on nictonic receptors on the ganglion
- Post ganglion cell releases Noradrenaline at the axon
- HR increases / SA conduction / AV conduction / and contraction strength
- This occurs through activation of B1 and A1 receptors and blocking B2
what have sympathetic nerve tracing studies shown about sympathetic preganglionic neurons?
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
describe the Geurtzenstein and silver(1974) studies regarding sympathetic activity
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
describe the Dampney 1985 study regarding sympathetic activity
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
what happens when neurons in the caudal CVLM are activated
sympathetic efferent outflow is inhibited and BP decreases
how does activation of neurons in CVLM lead to inhibition of the RVLM
inhibitory neurons that originate in the CVLM and terminate in the RVLM are activated and they secrete GABA which is inhibitory
how was it shown that activation of neurons in CVLM lead to inhibition of the RVLM
- injection of glutmate in the CVLM
- sympathetic activity is inhibited
- release of GABA in the RVLM
what did the hainsworth review state about sympathetic afferents
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
What is the hearts little brain?
cardiac ganglion cells and intrinsic nerve fibre network within the heart
