Muscle 2 Flashcards
what shortens during contraction
sarcomere
what happens with actin and myosin as a contraction takes place in a sarcomere
actin and myosin slide past each other, but don’t change length
which zones and bands shorten during contraction? which stay constant?
H zone and I band shorten
A band remains constant
what is the force generated by a contracting skeletal muscle referred to as ?
muscle tension
what is the order of initiation of skeletal muscle contraction? (3)
events in the CNS (brain responds to voluntary movement)
neuromuscular junction (synaptic contact between somatic motor neuron and individual muscle fibre)
excitation- contaction coupling (an action potential In skeletal muscle fibre results in an increase in intracellular (sarcoplasmic) Ca2+)
what is the output system towards skeletal muscle
primary motor cortex
what is the corticospinal tract
descending tract (ventral and interior)
what is an upper motor neuron (what does it travel through)
brain to brainstem or spinal cord
where does an alpha motor neuron travel? what is unique about it
it goes from the spinal cord to muscle and it can be very long
what is an alpha motor neuron
it is a lower neuron that goes from the spinal cord to muscle
what is a single motor neuron and all the muscle fibres it activates known as
motor unit
what is the area where the motor neuron makes synaptic contact with the muscle fibre known as
the neuromuscular junction
how does one motor unit contract
all parts of it contract together
what happens to muscle fibres if their motor unit becomes active
they all respond simultaneously
what are the 3 components of a neuromuscular junction
- presynaptic motor neuron filled with synaptic vesicles
- the synaptic cleft
- the postsynaptic membrane of the skeletal muscle fibre
what is the motor end plate ?
the region of sarcolemma at the end of the neuromuscular junction
what do junctional folds do
increase surface area on sarcolemma
what do motor neuron vesicles contain
acetylcholine
what does the muscle fibre sarcolemma contain (motor end plate)
nicotinic acetylcholine receptors
what causes voltage gated Ca2+ channels to open
an action potential arriving at the axon terminal
what is acetylcholine metabolized by? (Broken down)
acetylcholinesterase
what is required for nicotinic ACh receptors to open
two acetylcholine molecules bound to it
What is a neuromuscular junction?
Synapse of a lower motor neuron to a muscle fibre
What kind of receptors does the muscle sarcolemma contain
Nicotine acetylcholine receptors
What is a monovalent cation channel? What is it permeable to?
It is a ligand gated ion channel
Permeable to NA and K
What does Na entry through nicotinic ACh receptors generate? What does the response generated do?
An excitatory end plate potential
It spreads to adjacent voltage gated Na channels and initiates un action potential
What does myasthenia gravis mean?
Severe weakness of muscle
True or false: a single muscle fibre can be controlled by multiple alpha motor neurons
False
Where do action potentials start from and go to in muscle?
From the sarcolemma to the interior of muscle fibres along the transverse tubules
What is the specialized calcium storing organelle in muscles?
Sarcoplasmic reticulum
What triggers contraction in all muscle types?
A rise in intracellular calcium
Where do t-tubules surround a sarcomere?
A and I band junctions
What is a DHP receptor?
L-type Ca channel → voltage sensitive
What is a ryanodine receptor? (RyR)
Ca release channel on sarcoplasmic reticulum
What initiates an action potential in t tubules?
Entry of Na through acetylcholine receptors
What type of gate is a ryanodine receptor
Mechanical, it is opened by the DHP
Where are DHP receptors located
T-Tubules
Where are DHP receptors located
T-Tubules
