[012] The neuromuscular junction Flashcards
This a microscopic picture of a neuromascular junction ,, define the regions
Action potential carried by voltage-gated sodium channels reaches the nerve ending causing depolarization and opening of………… in active zones regions
voltage-gated Ca++ channels
Acetylcholine binds to its…… receptors on the motor endplate
nicotinic
Explain the end-plate potential (EPP)
When Inward Na+ conductance is greater than outward K +conductance so muscle membrane depolarizes.
Following muscle contraction , Acetylcholine is degraded rapidly by……(enzyme) present in high density in the synaptic cleft into…. (Products)
acetylcholinesterase ,,,, choline and acetate.
Some of the released Ach is ….. before reaching any receptor
hydrolyzed
Through uptake of ….. , the vesicles are refilled & reused to discharge Ach
choline
….. is a receptor that penetrate all the way through the muscle fiber from one side of the fiber to the other
dihydropyridine
Activated dihydropyridine receptors activate the sarcoplasmic reticulum through ….. receptors
ryanodine
Factors affecting force generation in the skeletal muscle ?
- Type of muscle fibers
• 2. Frequency of muscle electrical stimulation
• 3. Strength of the muscle stimulation
• 4. Length-tension relationship (preload)
• 5. Force-velocity relationship (afterload)
Fast twitch muscle fibers are ….(respiartion) and aid in …. Movements
Mainly anerobic ,,,powerful bursts of movements
Fast twitch muscle fibers are ….(respiartion) and aid in …. Movements
Anerobic ,,, strong push
During aerobic exercises such as running or swimming,….. fibers are the first to contract
slow-twitch
When the……. fibers become tired,….. fibers begin to take over
slow-twitch ,,, fast-twitch
Muscles rely on two physiological principles to bring a productive motion ?
• Recruitment
• Summation
Recruitment is…….. when the stimulation…. is increased, resulting in the increase in tension in the whole muscle
increasing the number of motor units responding to a single stimulus
‘’’
amplitude (strength)
Summation is the …… that results when a muscle fiber is unable to relax between twitches due to increased……
Increase in tension ,,,,, stimulation frequency
…….is a response of repeated stimulation, where cytosolic calcium remains highly elevated with continuous repeated activation of the contractile mechanism
tetanus
Two types of tetanus ?
• Partially fused or incomplete tetanus
• Complete tetanus
Partially fused or incomplete tetanus ?
when there are periods of INCOMPLETE relaxation between the summated stimuli
• Complete tetanus ?
when there is no relaxation between stimuli
Increasing the stimulus strength (amplitude) will increase the…… in the muscle
number of activated muscle fibers
Aka: recruitment
passive tension ?
exerted by the unstimulated muscle
total tension ?
the tension that a muscle develops when stimulated to contract isometrically
Active tension ?
= total tension - passive tension
…..of the muscle optimizes the overlap between actin and myosin cross bridges
Stretching
The length of the muscle at which the active tension is maximal is called its….
“resting length”
Increasing the length of the muscle beyond its resting length will…… the overlap of actin and myosin
decrease
…….the length of the muscle below its resting length will reduce the distance at which the actin can move over the myosin decreasing the developed active tension
Decreasing
……..Is a competitor inhibitor to acetylcholine on the Ach receptors
Atracurium
…. Is another competitor inhibitor to acetylcholine of plant origins
Curare
insecticides effect on motor end plate ?
block acetylcholine receptors
….. and …… are examples of anticholinesterase are used to reduce degradation of acetylcholine
neostigmine, edrophonium
Complications of Myasthenia gravis are improved with …..(drugs)
anticholinesterase
……..is a neurotoxin that binds competitively and in a relative irreversible manner to the nicotinic acetylcholine receptors
Alpha-bungarotoxin
…….. is a neurotoxin that can cause paralysis, respiratory failure and death
Alpha-bungarotoxin
Venom of Australian Eastern brown snake ?
Pseudonaja textilis
The venom of ……. snake selectively blocks the release of acetylcholine
Australian Eastern brown snake
…… is a depolarizing neuromuscular blocker used to cause short relaxation ,,,, as during anesthesia ;; to allow intubation and in electroconvulsive therapy
Suxamethonium chloride (succinylcholine)
…..is an ACH antagonists that is not subject to degradation by acetylcholinesterase
succinylcholine
Mention Side effects of succinylcholine :
-increase plasma potassium and intraocular pressure
- muscle twitches
-followed by paralysis and respiratory arrest
