Sensory motor neurotransmission (finished) Flashcards
Where are the cell bodies of sensory nerves located?
dorsal root ganglion
Where are the terminals of sensory nerves located?
2 terminals
- Various tissues and organs round the body e.g. skin = peripheral terminal
- Other ending is within the CNS = central terminal
What is the basic role of sensory neurons?
Pick up information and convey to CNS- part of reflex arc, then motor nerves are activated to illicit a response e.g. pain
Name + define the 2 types of functions of sensory nerves
Afferent function = sensation and reflex homeostasis
Efferent function = motor function involves release of neurotransmitter from peripheral terminals (typically neuropeptides) in response to a stimulus that can also illicit a response that travels through collaterals so neurotransmitter can be released at adjacent terminals e.g. skin- antidromic vasodilation = neurotransmitter released at blood vessels and causes them to dilate
What are the different names for sensory nerves?
C and A delta fibres
sensory-motor
Primary afferent
How were sensory nerves discovered (1876-1927)?
- 1876- Stricker (scientist) found if you cut nerve trunk to separate endings from cell bodies- then stimulate bottom half of nerve fibre = response in the periphery = suggests nerves could convey information in efferent direction
- 1901- Bayliss (scientist) found if you destroyed dorsal root ganglion = prevent response (vasodilatation) but if you did this to sympathetic ganglion = did not prevent vasodilatation
- 1927- Lewis = 1st person to ascribe phsyiological role to these nerves as he showed stimulation of these nerves linked with neurogenic inflammation- as inflammatory response didnt occur when skin was denervated
What are the causes of an insect bite response?
Insect bite reponse =
- site of bite = raised area from sensory nerves releasing neurotransmitter onto blood vessels = become leaky and white blood cells accumulate
- Redness caused by sensory nerves releasing neurotransmitter into skin = blood vessels dilate
- Area is hotter = increased blood flow
- Pain = involves sensory function of sensory nerves
Name some other diseases that have been linked to sensory nerves
- Asthma
- Eczema
- Psoriasis
- Migraine
What was the compound used to discover most of what is known about sensory neurons?
capsaicin
What vegetable is capsaicin found?
Hot peppers
Historically, how was capsaicin used?
Added to sensory nerves =
- Low doses (µg/kg) – transient excitation
High doses (mg/kg) – long lasting damage in vivo = desensitises them
What is capasicin?
Vanilloid
What does capsaicin act on?
TRPV1 = non-selective cation channel that gets depolarised result in neurotransmitter release = desensitisation
What does capsaicin select for?
Selective for “capsaicin-sensitive” sensory nerves = Non-myelinated (C fibre) and some thin myelinated (Ad) axons
Capsaicin is not often present in the body, so what acts at TRPV1 channels?
endocannabinoids
Hydrogen ions
Where are sensory neurons found?
Can be found throughout the body- lungs, bladder i.e. in most organs and tissues
Describe the distribution of sensory motor nerves in the cardiovascular system
Wide distribution in cardiovascular system- many blood vessels and heart
Mainly adventitial (some medial) localisation.
Density of fibres generally higher in arteries than veins.
Capsaicin treatment
removes SP and CGRP
immunoreactivity
What are the neurotransmitters of the sensory nerves in the cardiovascular system?
substance P (SP)- and calcitonin gene-related peptide (CGRP)-containing fibres (more CGRP)
Where are sensory nerve fibres located on blood vessels?
Mainly adventitial (some medial) localisation.
What is the adventitia?
Outermost layer of blood vessels
Compare the density of sensory nerve fibres in arteries and veins
Density of fibres generally higher in arteries than veins
What happens when capsaicin is added to sensory nerves in cardiovascular system?
Capsaicin treatment
removes SP and CGRP
immunoreactivity