Sensory motor nurotransmission Flashcards
What is sensory motor neurotansmission?
- Nerves that have duel sensory and motor functions
- Other names include:
1. C- and A-delta fibres, sensory motor and primary afferent.
What else do sensory motor fibres do?
- In addition to sending info from periphery to CNS they also have a motor function which elicits motor effects.
- E.g. The release of peptides onto blood vessels to control blood vessel contractility
What is capsacin?
- Used to charcterise sensory motor nerves
- Afferent neurons involved in blood flow regulation are sensitive to capsacin
- Capsacin creates the hot feeling by acting on TRPV1 receptors, whcih release neuropeptides to elicit sensation
What is the distribution of sensory motor nerves in cardiovascular system?
- Wide distribution in cardiovascular system
- Overlap of SP and calcitonin gene related peptide (CGRP)-containg fibres
- Mainly adventitial (some medial) localisation
- Density of fibres genrally higher in arteries than veins
- Capsacin treatment removes SP + CGRP immunoreactivity
What is sensory motor nerve co-transmission?
- Classical sensory NTs are CGRP, SP
- CGRP and SP stored in same vesicles
- Half lives minutes
- Other co-transmitters: e.g. ATP, enkephalin etc
- CGRP, SP removed by proteases
Explain activation of sensory motor nerves
- Sensory nerve fibre has 2 varicosities, and within them are vesicles
- Below sensory fibre is smooth muscle cell
- Shows histamine, bradykinin, prostaglandins etc are inf mediators
- Once neuropeptides are released, they initiate a response
- —In the case of blood vessels its genrally a vasorelaxant response.
What are the roles of sensory motor nerves in cardiovascular system?
- Defence against challenges to homeostasis (Neurogenic inflammation)
- Vasodilation & regulation of blood flow
- Regulation of cardiac function
- Trophic effects
- Ageing, hypertension, diabetes
How do they defend against challenges to homeostasis?
- Vasoactive afferent neurons are a system of first line defence agaisnt trauma
- Afferent function - Pain sensation & nocifensive reflexes
- Efferent function - Vasodilation & plasma extravasation:
- Neurogenic inflammation
Hyperemia & increased vascular permeability - facilitates delivery of leukocytes to tissues —-> Resistance against further damage and aids repair
What is Neurogenic inflammation?
- Arteriolar vasodilation
* Facilitates delivery of leukocytes
2.Increase in Vascular permeability
* By SP and other tachkinins
* Protein leakage into interstitial space
- Modulation by co-released sensory neuropeptides
* Inc in permeability - Effects of SP & CGRP on monocytes/macrophages
* Release stuff which: - Inc vessel diameter, permeability & afferent excitability
What happens in chronic inflammation?
Sensory motor nerves become hyperactive & contribute to hyperalgesia & perpetuation of inflammatory response
How do sensory motor nerves help vasodilation & regulation of blood flow?
- Some evidence that sensory motor nerves participate in moment-to-moment control of blood vessel diameter
- CGRP - Potent prolonged vasodilation
- SP - Vasodilatation
- NKA - Contraction
What is the evidence for a role of CGRP in sensory motor vasodilation?
- Neurogenic relaxation
1. Abolished by capsacin
2. Blocked by CGRP antagonist
3. Mimicked by exogenous CGRP - Release of CGRP
- Immunohistochemial localisatin of CGRP-Cont nerves
How do sensory motor nerves help regulate cardiac function?
- Capsacin is a potent cardiostimulant - Positive inotropic & chronotropic effects due to activation of sensory motor nerves
- CGRP, SP, NKA co-released from cardiac sensory motor nerves
- CGRP mimicks action of capsacin
- Cardiac sensory motor nerves activated by mediators of inflammation & ischaemia
What are the trophic effects of Sensory motor nerves?
- Maintenance of tissue integrity and ability to repair in response to injury
- Wound healing:
1. Destruction of sensory nerves reduces the survival of skin flaps and leads to appearance of skin wounds
2. SP,NKA, and CGRP stimulates proliferation of endothelial, smooth muscle cells and skin fibrolasts - Influence on sympathetic nerves:
1. Decreased sensory-motor nerves -> Incd sympathetic nerves
How does ageing effect sensory-motor nerves?
- Ageing - ↓ CGRP content and vasorelaxation by sensory nerves in rat mesenteric arteries
- Hypertension - ↓ Sensory neurogenic vasorelaxation in mesenteric arteries of hypertensive rats
- Diabetes - ↓ Sensory nerve conduction velocity, NP content & neurogenic vasorelaxation
- Migraine - CGRP-mediated vasodilation: Triptans
