Muscle Physiology Flashcards
What are the 3 types of muscle cells
Skeletal
Smooth
Cardiac
What are the characteristics of skeletal muscle
Multi-nucleated
Long, unbranched fibres
Voluntary contraction
Striated
Transverse tubules
Sarcoplasmic reticulum
What are characteristics of smooth muscle
Uninucleated
Unbranched fibres
Involuntary contraction
Unstriated
What are the characteristics of cardiac muscle
Branched fibres
Intercalated discs
Purkinje fibres
Faintly striated
Inherent rhythm
What is a muscle fascicule
Bundle of muscle fibres
What is a myofibril
Bundle of interconnected protein filaments of striated muscles
What filaments are found in the myofibrils
Thick filaments - myosin
Thin filaments - actin
What is the contractile functional unit of the myofibril
The sarcomere
What are a bands
Dark bands that contain thick filaments myosin
What are i bands
Light bands that contain only thin filaments actin
Where are i bands found
Between 2 thick filaments
What are z discs
The area that transverse i bands that mark the point of connection between two actin filaments
What is an m line
Middle of the sarcomere containing protein myomesin
What is the h zone
Area between the m line and the z disc
Only contains myosin
What is the main function of a myofibril
Produce a muscular contraction
Where is a muscular contraction induced from
The neuromuscular junction
What is the neurotransmitter involved in muscle contractions
Acetylecholine
What helps to regulate the muscle contraction
2 proteins
Troponin and tropomyosin
What is crucial to be present in a muscle contraction
Calcium
How is calcium regulated within the muscle cell
The sarcoplasmic reticulum
Where can you find endomysium
Surrounding individual muscle fibres
Where can you find perimysium
Surrounding a bundle of muscle fibres forming a fascicle
Where can you find epimysium
Surrounding the entire muscle
What are the 3 types of skeletal muscle
Type I - slow oxidative
Type IIa - fast oxidative
Type IIx - fast glycolytic
Describe the fibre size, contraction speed, force generated, susceptibility to fatigue, type of metabolism and role of Type I skeletal muscle fibres
Fibre size - small
Contraction speed - slow
Force generated - low
Susceptibility to fatigue - low
Type of metabolism - oxidative so high mitochondrial content
Role - low intensity, high duration eg postural muscles
Describe the fibre size, contraction speed, force generated, susceptibility to fatigue, type of metabolism and role of Type IIa skeletal muscle fibres
Fibre size - large
Contraction speed - fast
Force generated - high
Susceptibility to fatigue - medium
Type of metabolism - primarily oxidative but can switch to glycolysis
Role - short high intensity
Describe the fibre size, contraction speed, force generated, susceptibility to fatigue, type of metabolism and role of Type IIx skeletal muscle fibres
Fibre size - very large
Contraction speed - very fast
Force generated - very high
Susceptibility to fatigue - high
Type of metabolism - Anaerobic glycolysis
Role - very short maximal intensity
What are skeletal muscles innervated by
Alpha-motor neurons
What is a neuromuscular junction
Specialised synapse which connects a alpha-motor neuron and a skeletal muscle fibre
What triggers a skeletal muscle contraction
An action potential arriving at the neuromuscular junction causing the opening of voltage gated calcium channels
What does the increase in intracelluar calcium cause
Cause vesicles containing acetylecholine to be released into the synaptic cleft
What does acetylecholine in the synaptic cleft trigger
It activates the nicotinic ACh receptors in the muscle fibre plasma membrane
When the ligand ion channels in the muscle fibre plasma membrane are active what does this cause
Influx of sodium ions and depolarisation of the muscle fibre membrane potential which activates voltage sensitive sodium channels resulting in a action potential in the muscle fibre
How does the membrane of the muscle fibre repolarise
Acetylecholine is rapidly broken down in the cleft by Acetylecholinesterase which terminates the signal and allows for repolarisation
Describe the process of excitation contraction coupling
Action potential is generated and it travels along the sarcolemma and Down the t-tubule to depolarise the membrane
Depolarisation triggers voltage gated l-type calcium channels which allows calcium to enter the cell
Calcium influx leads to activation of ryanodine receptors located in the sarcoplasmic reticulum allowing for calcium to flow into the cytoplasm increasing the concentration more
Calcium binds to troponin-c which reveals a binding site on actin for the myosin head through a conformational change
Binding results in ATP hydrolysis providing energy for actin and myosin to slide past each other and shorten the sarcomere length initiating muscle contraction
How does relaxation of the muscle fibre occur
Calcium is pumped back into the sarcoplasmic reticulum to reverses the conformational change removing the binding site and so restoring the sarcomere length
