Physiology Of Muscles Flashcards
Muscle tissues types
- Skeletal
- Cardiac
- Smooth Muscle
Skeletal muscle
Allows us to voluntarily move our bones (or not). This type of muscle tissue has striatum’s when viewed with a microscope
Cardiac muscle tissue
Also striated but not under voluntary control
Smooth muscle tissue
Found in the wall of hollow organs (eg digestive system) and blood vessels. Also involuntary
Characteristics of muscle tissue
ECEE
- excitability
- contractility
- extensibility
- elasticity
Excitability
Myocytes receive stimuli and respond
Contractibility
Muscles shorten when they receive stimulus
Extensibility
Muscles can be stretched beyond their resting length
Elasticity
Muscles recoup and resume their resting length after being stretched
Fascicle
A section of muscle fibres surrounded by perimysium
Isotonic contraction
Muscle length changes to move a load, two types
Concentric isotonic contraction
Muscle shortens
Epimysium- structure of muscle
Dense layer of connective tissue and surrounds the whole muscle
Perimysium - structure of muscle
Dense layer of connective tissue surrounding each muscle fascicle
Endomysium - structure of muscle
A thin sheath of fine connective tissue surrounding each individual muscle fibre (muscle cell)
Direct attachment of muscle to other tissue
Epimysium of muscle fuses straight onto periosteum of bone or cartilage fairly uncommon
Indirect attachment of muscle tissue
Muscle connective tissue forms a tendon or aponeurosis to anchor to bone or cartilage. These are more common as they are smaller and more durable
Eccentric isotonic contraction
Muscle contracts but lengthens
Isometric contraction
Tension is produced but the length does not change
Nerve supply to muscles
1 nerve to provide stimulus needed for contraction
Arterial network in muscles is comprised of how many artery per muscle?
1 artery for oxygen and nutrients which reaches extensively into a network to supply whole muscle.
Sarcomere- myosin
Rich filament (thick)
Sarcomere- Titin
Elastic filaments that tie myosin to the Z disc
Sarcomere- Z discs
End of the Sarcomere (actin only)
Sarcomere- M-line
The middle (myosin only)
Sarcomere- I-band
Actin rich filaments (light)
Sarcomere- A band
Where the myosin rich filaments are situated
Sarcomere- H-Zone
A band of protein called myomesin which bisects the H zone
Sarcomere- thick filament (myosin)
Rod like tail, flexible hinge next region, two heads which bind to actin or ATP which supplies chemical energy. Whole filament looks like a golf club.
Sarcomere- thin filament (actin)
Two strands of grape-like actin subunits with active binding sites. Two strands of long tropomyosin which covers the active binding sites. Small troponin molecules which bind to troponin, tropomyosin and calcium. Helix shaped
Sarcolemma (intercellular structures)
Specialised cell membrane for skeletal muscle fiber cells
Sarcoplasm (intercellular structures)
Contains more nutrients and oxygen than normal cytoplasm as well as 3 specialised additions. Component of a muscle fibre cell
Components of sarcoplasm
Myofibrils
Sarcoplasmic reticulum
T tubules
Myofibrils (sarcoplasm of muscle fibres)
Hundreds of these rods make up 80% of the cell volume of a muscle fibre, enable contraction via Sarcomeres
Sarcoplasmic reticulum (sarcoplasm of muscle fibre cells)
Smooth endoplasmic reticulum which stores and releases calcium in demand, hence regulating intercellular calcium levels
T tubules (sarcoplasm of muscle fibre cells)
An extensions of the sarcolemma deep into the fibre which means each fibre has a massive surface to facilitate calcium intake
Sarcomeres (functional unit of a muscle)
Region of a Myofibrils between two successive Z discs
Neuromuscular junction
Where the nerve end (axon) and muscle fibre combine
Motor unit (neurons)
Consists of one motor neuron and all the muscle fibres it innervates. Arrival of stimulus triggers calcium release
Step 1 of muscle contraction
An action potential reaches the neuromuscular junction (chemical signal)
Step 2 of muscle contraction
Causes release do the neurotransmitter acetylcholine from the axon
Step 3 of muscle contraction
Arrival of acetylcholine to muscle fibre starts a new action potential which travels along sarcolemma and down t tubules
Step 4 of muscle contraction
The arrival of the action potential to the Sarcoplasmic reticulum causes release of calcium into the cell
In muscle contraction calcium bonds to
Troponin which moves the tropomyosin which allows myosin and actin to bind, initiating contraction
Botox inhibits
Acetylcholine at the neuromuscular junction which means no calcium and no muscle contraction = flaccid paralysis
Excitation-contraction coupling
Sarcoplasmic reticulum releases calcium, enters cell and binds to troponin.
Troponin rolls tropomyosin away from the actin binding sites allowing myosin to bind
What starts the cross bridge cycle
Excitation-contraction coupling of allowing myosin to bind to actin
Cross Bridge Cycle, what is it
Series of 4 events during which my doing heads pull actin towards the centre of the Sarcomere
Cross Bridge cycle step 1 Formation
Once troponin has moved tropomyosin off the acting binding sites, the myosin head binds to actin
Cross Bridge cycle step 2 power stroke
ADP is released from the myosin head, causing a change in shape of myosin which becomes more bent which pulls actin towards M-line
Cross Bridge cycle step 3 Detachment
Myosin head has lost all energy and a new ATP molecule binds allowing myosin to detach from actin, this destroys actin + myosin cross bridge
Cross Bridge cycle step 4 cocking of the myosin head
Energy from ATP is released as it splits into ADP and phosphate which allows the myosin head to swing back to starting position
Muscle twitch phase 1 - Latent
When the excitation- contraction coupling is occurring and the cross bridges begin to cycle but tension has not yet developed so immeasurable
Muscle twitch phase 2 - Contraction
Cross bridges are still cycling but now tension development within the muscle can be measured. Muscle length may or may not change if contractile force overcomes load
Muscle twitch phase 3 - Relaxation
Occurs when calcium starts to enter SR. Contractile force starts to decrease as less cross bridges are present, producing force. If muscle had changed length it now returns to resting length
Twitch summation Unfused
If a new stimulus arrives before all cross bridges have detached and more tension develops- summation of the force the muscle is producing (calcium released due to new stimulus)
Twitch summation Fused
If lots of stimuli occur frequently enough the twitches add together to produce maximum possible tensions the muscle can produce. FUSED TETANUS
Motor unit recruitment refers to
The number of motor units increases the amount of force a muscle develops. Stimulus strength= increased recruitment of motor units
Why are capillaries long and winding?
Capillaries are long and winding to allow for muscle contractions
