Lecture 9 - Skeletal Muscle Neurophysiology Flashcards
what is the appearance of skeletal muscle?
a striated appearance due to the arrangement of thick filaments (myosin) and thin filaments (actin)
what does skeletal muscle interact with?
interacts with the skeleton
what is the origin of skeletal muscle?
the most proximal skeletal muscle insertion
what is the insertion of skeletal muscle?
the most distal skeletal muscle insertion
where do the skeletal muscle origin and insertion insert into?
insert into the bone via tendons
what is the function of tendons?
connect muscle to bone to allow the muscle to exert force on the skeleton
what is fascicles?
a group of muscle fibres that are bundled together
what are muscle fibres?
multi nucleated muscle cell that is between 10-80um but up to 25cm in length
what are myofibrils?
long filaments composed of myosin (thick filament) and actin (thin filament) that make up the inside of muscle fibres
what is the sacromere?
the contractile unit of skeletal muscle that is the region between the ‘Z’ lines
what is a ‘Z’ line?
a zig zag arrangement of actin (thin filaments) that project to the centre of the sarcomere
what is the ‘I’ band?
the region between the myosin filaments (thick) that only contains actin (thin filament)
what is the ‘A’ band?
the region in-between each I band region that contains both actin and myosin filaments
what is the ‘H’ zone?
when the muscle is at resting length, the actin filaments do not project all the way into the centre of the sarcomere creating a gap where there is only myosin and no actin
what is the ‘M’ line?
the centre of the myosin that contains proteins which organise and align myosin allowing for the ordered arrangement
what is the relationship between the bands/zones/lines and skeletal muscle contraction?
all of the different bands change in length depending on whether the muscle is at rest or shortening as it contracts
what occurs at the sarcomere as skeletal muscle contracts in term of the Z line, H zone, I band and the A band?
As the muscle starts to contract, the Z lines come close together by shortening.
Myosin slides over actin and the H zone becomes much smaller because the actin filaments slide across each other.
The I band becomes smaller as myosin partially comes together.
The A band stays the same
when does maximally contracted skeletal muscle occur?
occurs when actin filaments have slide so far they can not go any further and are pushed right up against the myosin.
- the H zone is gone
- the I band is really tiny
- the A band remains the same
what is the relationship between motor neurons in the spinal cord and skeletal muscle?
motor neurons in the spinal cord innervate skeletal muscle to generate voluntary control (non intrinsic spontaneous activity)
what does a single motor neuron innervate?
can innervate up to a thousand muscle fibres at once
what is the 1:1 relationship between an AP in a motor neuron and an AP in a muscle fibre?
a single AP in a motor neuron drives a single AP in a muscle fibre and that single AP drives a twitch
what is the NMJ?
neuromuscular junction
where is the NMJ located?
located on a motor neuron axon on a muscle fibre
what is another name for the NMJ?
motor endplate
what is the NMJ?
the synapse between a motor neuron axon terminal and a muscle fibre
what do AP’s in the motor neuron lead to?
depolarisation of a muscle fibre via the release of Ach
what does depolarisation of muscle fibre trigger?
triggers an AP
what does the muscle fibre AP trigger?
triggers contraction through excitation-contraction coupling
what is the synthesis of acetylcholine?
acetyl CoA + choline –> Ach
catalysed by the enzyme choline acetyltransferase (ChAT)
what is the breakdown of acetylcholine?
Ach –> acetic acid + choline
catalysed by the enzyme acetylcholineasterase
what is the lifecycle of acteylcholine?
Begins with the synthesis of Ach through the reaction of choline with acetyl coenzyme A. Much of the choline used in this process is recycled but it can also be synthesised in the neuron. This reaction is catalysed by the enzyme choline acetyl transferase.
Once Ach has combined with the receptor site, it must be rapidly removed from the synapse for the repolarisation to occur. It is therefore catalysed by the enzyme acetylcholinesterase to produce choline and acetate.
The choline is then recycled back into the terminal to produce new molecules of Ach
