Lecture 9: Skeletal Muscle Neurophysiology 1 Flashcards
What is another name for skeletal muscle? Why is this?
striated muscle because of its striated appearance due to the thick and thin filaments
Flexion _________ the angle between joints and extension _______ the angle between the joints
decreases
increase
What is being activated and what is being relaxed during flexion?
activation of flexor muscles and relaxation of extensor muscles
What is being activation and what is being relaxed during extension?
activation of extensor muscles and relaxation of flexor muscles
Muscles need to span the joint. What is the name of the proximal attachment of the muscle to bone? What is the name of the distal attachment of muscle to bone?
the origin
the insertion
What do tendons connect?
muscle to bone
What do ligaments connect?
bone to bone
Both tendons and ligaments are made of what?
collagen
A group of muscle fibres is called a ________
fasciculus
What is a fasciculus made of?
lots of individual muscle fibres
What are muscle fibres?
the individual muscle cell
What do muscle fibres/cell have lots of?
nuclei
Muscle cells/fibres consist of lots of what?
myofibrils
What two things make up the myofibril? What does this cause?
thick and thin filaments (myosin and actin) which causes an ordered striated appearance
Which is the thick filament, actin or myosin?
myosin
Which is the thin filament, actin or myosin?
actin
What is an individual contractile unit of a myofibril called?
a sarcomere
What region makes up the sarcomere?
in between the two Z lines
What does the sarcomere consist of?
actin filaments going inwards from the Z line interlinked with the thick myosin filaments
What is the I band of the myofibril?
between the myosin filaments so it contains only actin
What is the A band of the myofibril?
between the regions of only actin filaments so this contains both the actin and myosin
What is the H zone of the myofibril?
the very middle part of the sarcomere which only contains myosin when resting
When the sarcomere is resting, there are balls of myosin right in the middle of the H zone which contains proteins. What are these proteins used for?
they organise and align myosin
When contracting, what changes in the sarcomere?
- the Z discs become closer together
- the myosin slides over the actin
- the H zone becomes much smaller and the actin is coming closer together
- I band becomes smaller as the myosin is coming closer together
Skeletal muscles respond rather than thinking. What does this means that they have?
no intrinsic spontaneous activity
Muscle fibres should contract near simultaneously along their _______ ______
entire length
Because skeletal muscles have no intrinsic spontaneous activity, what do they require?
innervation from the CNS
We need all the muscle fibres to contract nearly simultaneously along their entire length, true or false?
Why is this?
true
to allow precise, controlled movements of our skeleton
What allows the muscle fibres to contract nearly simultaneously along their entire length?
the motor neurons in the spinal cord which innervate skeletal muscle and a single motor neuron can innervate up to 1000 muscle fibres at once
Lots of axon potentials in a single motor neuron which can drive the coordinated, simultaneous contraction of many skeletal muscles just from one what?
motor neuron
Apart from one motor neuron innervating thousands of muscle fibres at once, what is the other reason why the muscle fibres can contract simultaneously?
because one action potential in the motor neuron causes 1 action potential in the skeletal muscle (there is no threshold) and there is a 1:1 ratio for signal transduction
What is another name for the NMJ?
the motor endplate
In the CNS, what wraps around the synapse?
astrocytes
In the PNS, what wraps around the synapse?
What is its purpose?
Schwann cells
this is to regulate synaptic transmission by sensing the neurotransmitter being released, and sometimes release gliotransmitter
Where are the ACh containing vesicles mainly located?
close to the release sites close to the synaptic cleft
some are tethered to the membrane
Why is it important that the vesicles are close to the synaptic celft?
so that when an AP comes along and there is an influx of Ca2+ ions, the docked vesicles can immediately be released in a highly synchronised way
What causes the release of the vesicles?
the action potential opens the voltage gated Ca2+ channels which causes the influx of Ca2+ ions to release the vesicles by exocytosis
What is at the active zone of the NMJ?
there are proteins that bind to the vesicles to allow the fusion and release of the vesicles
What is the purpose of the active zone?
so that you can control where the vesicles are released so that they are released into the right place (synaptic cleft)
Why is the length of the synaptic cleft very small?
so that the diffusion distance is minimised so the speed of neurotransmission is very fast
What is the sarcolemma?
the plasma membrane of the muscle cell that has a high density of nicotinic ACh receptors
Why are there in-folds in the sarcomere?
to increase the surface area to that there can be more nicotinic ACh receptors
and because there is an enzyme ACh esterase for regulating the ACh levels to breakdown ACh
What is the NMJ?
the synapse between the motor neuron axon terminal and a muscle fibre
The depolarisation of fibers triggers what?
an action potential
The action potential in muscle fibres propagates in which direction?
both directions
Acetyl CoA and Choline is converted to ACh (and CoA) by which enzyme?
Choline acetyltransferase (ChAT)
What is the role of choline acetyltransferase (ChAT)?
to convert acetyl CoA and choline to ACh and CoA
ACh is converted to acetic acid and choline by which enzyme?
acetylcholinesterase
What is the role of acetylcholinesterase?
to convert ACh to acetic acid and choline
Describe the Acetylcholine life cycle
An AP triggers the release of the vesicles to bind to ACh receptors which triggers a depolarisation of the post-synaptic cell. AChE quickly breaks down ACh into choline and acetic acid to ACh can’t bind anymore.
Choline is pumped back into the cell using the electrochemical gradient of Na+
ChAT uses this choline and combines it with Acetyl CoA to reform ACh which is pumped into the vesicles using active transport
