John Peters:- An introduction to Pain slide 11 Flashcards
What innervates skeletal muscle?
Motor neurones
What happens to the motor neuron when it is nearing its muscle?
It loses its myelen sheaf and splits up into different branches all having their own terminal button forming a chemical synapse
What is the neurotransmitter found at the terminal boutons ?
Acetylcholine
What are the four key features of the skeletal neuromuscular junction?
- Terminal bouton and schwann cell
- Synapic vesicles
- Synaptic cleft
- End plate region
Where woud you find nicotinic acetlycholine receptors?
At region of the junctional folds of the end plate region that face the active zones
What happens at the neuromuscular junction?
Action potential
Ca2+ channels open and calcium rushes in
Depolarization
Acetlycholine is released
Acetlycholine is broken down
Choline is returned to the cell
What breaks down Acetlycholine?
Acetylcholinesterase
What is acetylcholine broken down into?
Acetate and Choline
How is choline transported in to the bouton?
Alongside Na+
Where is Acetlycholine synthesised?
in the Cytosol
What is the reaction to make Acetlycholine?
Choline + acetyl coenzyme A = Acetylcholine
What enzyme is required to make acetylcholine?
Choline acetyltransferase
What concentrates acetylcholine in vesicles?
Vesicular ACh transporter
What happens in the post-synaptic process?
2 actelycholine molecules bind
Channel opens for cations only
Na+ influx and K+ eflux
Infflux of sodium is greater than efflux of potassium resulting in deporelization
What is a “quantum”?
A quantum is the amount of neurotransmitter contained in one vesicle
What does a quantum of acetlycholine cause?
a miniature endplate potential
What is the “all or none” theory?
You need a certain nummber of M.E.P.P in quick succession in order to produce one muscle action potential
The E.P.P must exceed the therhold.
What does the end plate potential do?
Triggers the opening of voltage activated sodium channels causing a muscle action potential
How does the action potential make the muscle contract?
Action potential travels down the T-tubules triggering the release of calcium ions which interact with troponin associated with the myofibrils
What happens in Myasthenia Gravis?
Autoimmune destruction of nicotinic acetylcholine receptors in the endplate.
What does Botulinum Toxin do?
Irreversibly inhibits Ach release
What is Neuromytonia also known as ?
Isaac’s syndrome
What is Neuromyonia?
Autoimmune hyperexcitabilty of volatge activated K+ channels
Define Pain?
An unspleasent sensory and emotional experiance, associated with actual tissue damage or described in terms of such damage
What are the three forms of pain?
Nociceptive pain
Inflammatory Pain
Pathological pain
What are Nociceptors?
Peripheral primary sensory afferent neurones which are activated by intesne noxious stimuli
What are the two characterisitcs of Nociceptive pain?
It is adaptive
It has a high thershold
What does the Nocieptive Pain actually do?
It is responsible for the withdrawal reflex
What does inflammatory pain do?
It causes pain hypersensitvity
and
Allodynia (Innocuous stimuli now causes pain)
Why is inflammatory pain necessary?
Assits in wound healing by:
Discouraing physical contact
Discouraging movement
What is Pathaological pain?
Maladaptive pain with no protective function
How is pain like a burgelar alarm?
Nociceptive pain - oh shit its begby, run
Inflamatory pain - Whats that noise… its probably begby
Pathological pain - False alarms all the time
What are the two types of Nociceptors?
A-fibres
C-fibres
How do the two types of Nociceptors differ?
A-fibres are myelinated and respond fast but only to mechanical or thermal injury
C-fibres are unmyelinated so respond slower but can respond to all sources of pain
