Muscle structure Flashcards
What type of nerve control is smooth muscle
Involuntary
What type of nerve control is cardiac muscle
Autonomous
Autonomic nervous system and circulating chemicals
What type of nerve control is skeletal
Voluntary control - soamtic nervous system
Attached to bones and contract to bring about movement
Arrangement of muscle fibres
Structure of skeletal muscles
Structure of skeletal muscles
Plasma membrane - sarcolemma
T-tubules tunnel into the centre
Sarcoplasm- cytoplasm
Network of fluid filled tubules - sarcoplasmic reticulum
Structure of skeletal muscles myofibrils
Sacomere - repeating pattern from Z to Z disc
Thin filament - actin (I band)
Thick filament - myosin (A band)
Light and dark bands give striated appearance
Cause contraction - changes in filaments overlap
Structure of skeletal muscles - actin and myosin
Structure of skeletal muscles - myosin
Two globular heads
Move using ATP
Cause sliding
Two a helices tail
Structure of skeletal muscles - actin
Actin molecule twisted into helix
Each molecule has myosin binding site
Filaments also contain troponin and tropomyosin
Initiation of muscle contraction
- Action potential open voltage gated Ca
- Ca enters pre-synaptic terminal
- Ca triggers exocytosis of vesicles
- Acetylcholine diffuses
- Binds to acetylcholine receptors and induces action potentials in muscle
- Local currents flow from depolarised region and adjacent region
- Acetylcholine broken down by acetylcholine esterase
Initation of muscle contraction - activation inside muscle
- AP propagates along surface membrane and into T-tubules
- Dihydropyridine receptor in T tubules sense voltage and changes shape of protein linked to ryanodine receptor which opens ryanodine receptor Ca channel in sarcoplasmic reticulum
- Ca released from SR into space around the filaments and binds to troponin which allows tropomyosin to move
- Crossbridges attach to actin
- Ca is actively transported continuously while action potentials continue
Excitation contraction coupline
- In the presence of Ca - movement of troponin from tropomyosin chain
- Movement exposes myosin binding site on surface of actin
- Myosin head binds to exposed site on actin filament
- Binding and discharge of ADP cause myosin head to pivot
- ATP binding - releases myosin head from actin chain
- ATP hydrolysis - recharge
Neural control of muscle contraction
Upper motor neurons in the brain
lower motor neurons in brainstem or spinal cord
Diagram of the motor unit
A single motor unit causes contraction of all the muscle fibres in that unit
No 2 motor neurons innervate the same muscle fibre
Slow motor units
Smallest diameter cell bodies
Small dendritic trees
Thinnest axons
Slowest conduction velocity
High myoglobin content
Red colour
High aerobic capcity
Low anaerobic capacity
Fast, fastigue resistant (FR, type IIA)
Fast, fatiguable (FF, type IIB)
Larger diameter cell bodies
Larger dendritic trees
Thicker axons
Faster conduction velocity
What is the difference between fast, fatigue resistant (FR, type IIA) and fast, fatiguable (FF, type IIB)
Myoglobin content - FR - HIGH, FF - LOW
Colour - FR - PINK, FF - WHITE
Aerobic capacity - FR - MODERATE, FF - LOW
Anaerobic capacity - FR - HIGH, FF, HIGH
Force graph of the different types of motor units
Fatigue graph of the different types of motor units
Regulation of muscle force - recruitment
Smaller units are recruited first (slow twitch units)
As more force required, more units are recruited which allows fine control under which low force levels are required
Regulation of muscle force - rate coding
Motor unit can fire a range of frequencies, slow units fire at lower frequency
Firing rate increases, force produced by the unit increases
Summation occurs when firing too fast to allow muscle to relax in between action potentials
Effect of transferring nerves from different muscle fibres
Fast and slow twitch muscle are cross innervates, slow one becomes fast and vice versa
Motor neuron has some effect on the properties of the muscle fibres it innervates
What are neurotrophic factors
Food
Type of growth factor
Prevent neuronal death
Promote growth of neurons after injury
What is an isometric contraction
Muscle produces force but doesn’t change length
What is a concentric muscles
Shorten muscles to produce movement
Eccentric muscles
Muscles becomes longer
More force produced
Plastivity of motor units
Type IIB to IIA - following training
Type 1 and 2 possibel in severe deconditioning or spinal cord injury
Microravity results in shift from slow to fast
Ageing associated with loss of type 1 and 2, preferentionally type 2 fibres, slower movements
