sensory motorneurotransmission in vasculatur Flashcards
function of sensory nerves
project from the dorsal root gangion in the spinal cord.
Efferent: release of peptides, and blood vessel control.
Afferent: conveys sensation from stimulus and pivotal role in reflex homeostasis
C- and Adelta- fibres carry these signals. They are the primary afferents.
Capsaicin in sensory motor nerves
Low doses cause transient excitation, and high doses cause long lasting damage.
Vanilloid is an ingredient in chilli peppers and acts at capsaicin-sensitive non-myelinated C-fibres, and some thin myelinated Adelta-fibres.
Acts at TRPV1, which is a nonselective LGIC, which depolarsies the neroune. Endocannabinoids and H+ ions are endogenous ligands.
what other compounds can be Cotransmissited and what compounds can activate sensory motor nerves
CGRP and substance P (and neurokinin A (NKA)) play a role (then metabolised by proteases). ATP cholecystokinin, NO, VIP, and dynorphin also can act as cotransmitters. They are synthesised in the cell body and then transported to the peripheral endings.
Many of the activators are inflammatory mediators, such as bradykinin, prostaglandins, histamines, etc…
Sensory nerves then release the CGRP, SP, and NKA to mediate vasorelaxation of the vascular smooth muscle.
Defence against challenges to homeostasis - effects in physical trauma (cardiovascular)
Vasoactive afferent neurones are a first line defense against trauma.
the afferent functions mediate pain sensation and nocifensive reflexes.
The efferent functions mediate vasodilatation, and plasma extravasation (to leave the vessels), this facilitates delivery of leukocytes to the surrounding tissue, which provides resistance against further damage
Vasodilatation mediated by CGRP, SP and mast cell histamine.
Increased vascular permeability primarily mediated by SP and tachykinins.
CGRP synergystically mediates the SP induced increase in permeability, despite not increasing permeability alone.
CGRP and SP stimulate the release of cytokines, PGs, leukotrienes, and thromboxanes from macrophages.
Vasodilation and regulation of blood flow (cariovascular)
CGRP is a potent and prolonged vasodilator. acts at CGRP receptor
SP is a vasodilator that acts at NK1 recepors.
NKA contracts SM, acts at NK2.
Neurogenic relaxation of the vasculature is abolished by capsaicin, and can be blocked by an CGRP receptor antagonist. Also the vasodilation can be mimicked by exogenous CGRP.
Regulation of cardiac function (cardiovascular)
Capsaicin is a potent cardiostimulant. increases contractile force.
CGRP, SP and NKA are coreleased onto the heart by cardiac sensory motor nerves.
CGRP mimicks this.
The cardiac sensory nerves are activated by inflammatory and ischaemic mediators.
Trophic effects (cardiovascular): effects for repair of tissue
It plays a role in the maintenece of tissue integrity and its ability to repair following injury.
SP, NKA and CGRP all stimulate proliferation of endothelial, SM, and fibroblast (connective tissue) cells. As such, destruction of sensory nerves saw reduced healing.
A decrease in sensory motor nerves sees an increase in sympathetic nerves - homeostasis.
What effect on motorneurotransmission is seen in Aging, hypertension, diabetes, migraine (cardiovascular)
With age, there are decreases in CGRP, leading to a decrease in vasodilatation. This can be attributed to increased hypertension with ageing.
A decrease in sensory nerve conduction velocity has been associated with diabetes.
CGRP is released in migraines, and may play a causal role in migraines.
