Muscle physiology and histology Flashcards
What are the four levels found in a muscle?
Whole muscle Fascicle Muscle fibre Myofibril Sarcomere
What types of cells are found in the whole muscle?
Muscle fibres
Connective tissue
Blood vessels and lymph
What is a muscle fibre?
One muscle cell
Name three unique features of a muscle fibre.
Multinucleate
Contain myofibrils
Very long.
How big are muscle fibres?
10-100microM in diameter
1000-2000microM in length
What are myofibrils?
Collections of sarcomeres packaged together.
What is a sarcomere?
Basic functional unit of the muscle that allows for contraction.
What two proteins make up a sarcomere?
Myosin (heavy chain)
Actin (light chain)
What are the five regions of a sarcomere called and what do they represent?
A Band- From one end of myosin to the other I Band- Area w/ no myosin H Zone- Area w/ no actin Z Line- Area linking actin M Line- Area linking myosin
What are the five stages of a muscle contraction?
Resting Binding- requires Ca2+ Bending- ADP+Pi dissociate Detachment- Fresh ATP binds Energised- with ATP bound ready for next stroke
How does Ca2+ allow binding?
Binds to troponin to move it out the way allowing myosin to bind to tropomyosin on actin.
What is a muscle fascicle?
A collection of muscle fibres in found in the whole muscle.
What is the connective tissue round the whole muscle called?
Epimysium
What is the connective tissue around the fascicle called?
Perimysium
What is the connective tissue around a single muscle fibre called?
Endomysium
What are the three types of muscle fibres?
Type I
Type IIa
Type IIb
Describe Type I muscle fibres.
Aerobic red fibres with lots of mitochondria and myoglobin. Slow contracting but resistant to fatigue.
Describe Type IIa fibres.
Intermediate fibres. Relatively fast contracting but relatively fatigue resistant.
Describe Type IIb fibres.
Anaerobic white fibres with little mitochondria and myoglobin. Fast contracting but fatigue easily.
How many nerves synapse onto a singe muscle fibre?
One
What is a neuromuscular unit?
An alpha motor neuron and all the muscle fibres it innervates.
What is the neurotransmitter in somatic motor neurons?
ACh
What ions does nAChR let through?
Na in and K out
What is an EPP?
The sum of all the mepp caused by each quanta of ACh binding.
How many ACh molecules does it take to open a nAChR?
Two
Describe the presynaptic events that lead to ACh release.
An AP travels down the nerve fibre to the bouton where it activates VGCC allowing Ca in which allows for binding of ACh vesicles.
Describe how ACh is recycled.
ACh is broken down by AChesterase to choline and acetate. Choline is reuptaken into the presynaptic cell where it is combined with acetyleCoA to form ACh.
How does the EPP propagate a contraction?
It allows opening of VCSC to propagate the depol across the cell. This travels down the T-tubules to allow Ca2+ release from the SR.
What two factors does the generation of muscle tension rely on?
Number of fibres recruited
Tension developed per muscle fibre.
What three things determine the tension developed per muscle fibre?
Frequency of stimulation
Thickness of fibre
Length of starting contraction
Is the length of contraction in skeletal muscle long or short?
Long
What is summation of contraction?
When another AP arrives before the muscle has finished contracting and relaxing it can cause it to contract further thus generating extra force.
What is tetanising a muscle?
When it is fully contracted and can contract no further.
What is the maximal tetanic contraction?
The maximum length change for each muscle. This is described as 100% of its length. If it is shorter than this you won’t get full length contraction and longer won’t get full power.
What are isotonic contractions?
Contractions used for body movement.
What are isometric contractions?
Contractions used to fix an object in space.
What are the origins of the two potential motor inputs to a muscle?
UMN and LMN from brain giving conscious control
Reflex arc of somatic sensory, interneuron and somatic motor.
Describe the stretch reflex arc.
Resists passive change to the muscle length to maintain optimal muscle length. Important for walking. Muscle stretch activates stretch receptors thus causing reflex muscle contraction.
What senses muscle stretch?
Muscle spindles/intrafusal fibres. Annulospiral fibres in them do the sensing.
What are extrafusal fibres?
Normal muscle fibres
Where are muscle spindles usually found?
In the middle of the muscle.
How do they detect stretch?
Increase stretch causes increase discharge.
What neurons synapse onto muscle spindles?
Gamma MN to adjust level of tension.
What do ligaments do?
Attach bone to bone.
What do tendons do?
Attach muscle to bone.
Describe tendons.
Parallel collagen fibres
Type 1 Collagen 99%
Type 2 Collagen 1%
Describe ligaments
Nearly parallel collagen fibres
Type 1 Collagen 90%
Type 2 Collagen 10%
What are the four stages of tendons entering bone?
Parallel collagen fibres
Unmineralised fibrocartilage
Mineralised fibrocartilage
Cortical bone
What are the five morphologies of skeletal muscle and give examples of them.
Flat- External obliques Fusiform- Biceps brachii Circular- Orbicularis oculi Pennate- Deltoid Quadrate- Rectus abdominis.
