Structure Of Skeletal Muscle Flashcards
What are the three types of muscle in body? And where they found
Cardiac muscle - heart
Smooth muscle- walls of blood vessels and gut
Skeletal muscle - it is attached to bone and acts involuntary, conscious control
What are muscles made up of
Millions of tiny muscle fibres called myofibrils
What’s within the sarcoplasm
Large concentration of mitochondria and endoplasmic reticulum
What do the muscle fibres share when separate cells have become fused together into muscle fibres
They share nuclei and cytoplasm, called sarcoplasm
What are the I bands ?
The light bands. They appear lighter because the thick and thin filaments do not overlap in this region
What are the A bands
The dark bands. They appear darker because the thick and thin filaments overlap in this region
What’s at the centre of each A band?
A lighter coloured region called the H zone
What’s at the centre of each I band
The Z line
What’s the distance between adjacent Z lines
A sacromere
What happens when a muscle contract to the sacromere
It shortens and the pattern of light and dark bands changes
What is tropomyosin
An important protein found in muscles
Which forms a fibrous strand around the actin filament
What are slow twitch fibres
These contract mite slowly than fast twitch fibres and provide less powerful contractions but over a longer period
What type of work are slow twitch fibres adapted for
Endurance work such as a marathon
How are they adapted for aerobic respiration to avoid build up of lactic acid
Large myoglobin stores ( stores oxygen)
Rich supply of blood vessels to deliver oxygen and glucose for aerobic respiration
Numerous mitochondria to produce ATP
What are fast twitch fibres
These contract more rapidly and produce powerful contractions but only for a short period
What are fast twitch fibres adapted for
Intense exercise such as weight lifting
How are fast twitch fibres adapted to their role
They have thicker and more numerous myosin filaments
A high concentration of glucose
A high concentration of enzymes involved in anaerobic respiration which provides ATP rapidly
A store of phosphocreatine, a molecule that can rapidly generate ATP from ADP in anaerobic conditions and so provide energy for muscle contractions
What is a neuromuscular junction
Is the point where a motor neurone meets a skeletal muscle fibre
How is the control over he force exerted controlled
As all muscle fibres supplied by w single motor neurone act together as a single functional unit (motor unit)
If only a slight force is needed, only a few units are stimulated
If a greater force is required, a larger number of units are stimulated
What happens before muscle contraction when a nerve impulse is received at the neuromuscular junction
The synaptic vesicles fuse with the presynaptic membrane and release their acetylcholine.
The acetylcholine diffuses to the post synaptic membrane (membrane of muscle fibre), altering its permeability to sodium ions, which enter rapidly, depolarising the membrane.
The acetylcholine is broken down by acetylcholinesterase to ensure that the muscle is not over stimulated
The resulting choline and acetyl (etanoic acid) diffuse back into the neurone, where they are recombined to form acetylcholine using energy provided by mitochondria found there
How is a neuromuscular junction similar to a cholinergic synapse
Have neurotransmitters that are transported by diffusion
Have receptors, that on binding with the neurotransmitter, cause an influx of sodium ions
Use a sodium potassium pump to repolarise the axon
Use enzymes to breakdown the neurotransmitter
What are the differences between a neuromuscular junction and cholinergic synapse
N- only excitatory
C- may be excitatory or inhibitory
N- only links neurones to muscles
C- links neurones to neurones, or neurones to other effect organs
N- only motor neurones involved
C- motor, sensory and intermediate neurones may be involved
N- the action potential ends here
C- a new action potential may be produced along another neurone
N- acetylcholine binds to receptors on membrane muscle fibre
C- acetylcholine binds to receptors on membrane post synaptic neurone
What are the two types of protein filament
Actin - thinner and consists of two strands twisted around one another
Myosin - which is thicker and consists of long rod shaped tails with bulbous heads that project to the side
