Topic 13 - Muscles Flashcards
Learning Outcomes
- Describe the basic structure og muscle and the role of Actin and Myosin
- Differentiate between smooth muscle, skeletal muscle and myocardium in terms of their location in the body and generak structural characteristics.
- Explain the basic process of muscle contraction and how tension is developed in a muscle (including how nerves control muscle contraction, how some muscle types control their own contractile activity, and cross bridge cycling theory of muscle contraction)
- Explain the differences between fast and slow twitch muscle fibres and how fibre type relates to muscle function
- Describe how the musculoskeletal system interacts with other body systems to enable movement to occur
6.Describe how training impacts upon movement
- Describe the psychological differences between an elite sprinter and an elite marathon runner
Roles of Muscle
Movement of:
- Bones
- Food
- Fluids
- Blood
Thermal regulation
Energy metabolism and storage
Appetite regulation
Endocrine functions
Properties of muscle
Muscle mass declines over ager
Men are approx. 40% muscle mass. Women are 30%
Mostly made of water (75%) and protein (18%)
- Contracility
- Excitability
- Extensibilty
- Elasticity
Contracibilty
- Ability to shorten with a force
- Requires energy
- Relaxes passively
Excitability
- Capacity to respond to stimuli (nerves)
- Electrical stimulation of the heart
Extensibilty
Ability for a muscle to be stretched beyond its normal resting length to a limiting degree
- Stomach/ Bladder as it fills
Elasticity
Muscle havinf the capacity to return to its resting position
Types of muscle
Skeletal:
- Attached to skeleton
- Responsible for movement
- Voluntary
- Straited
Cardiac(Myocardium):
- Forms the heart
- Involuntary
- Striated
Smooth:
- In tussues of organs
- Controlls diabetre of structures and peristalsis
- Involuntary
- Non-striated
Skeletal muscle structure
- Muscle
- Fascicle
- Cell
Diagram in Notes
Muscle Fibre structure
Actin:
- Thin myofilament
Myosin:
- Thick myofilament
Sarcomere:
- made up of Actin and myosin to provide striations on the cell in longitudinal direction
- Allows the muscle to contract
Diagram in notes
Muscle contraction process
- An action potensial reaches the muscle
- Calcium ions diffuse into the sarcolemma.
- Calcium ions bind to Troponin on the actin filaments. This causes the Tropomyosin to move, opening the binding sites for the myosin heads.
- The Myosin heads then attatch to the binding site forming a cross-bridge by using ADP + P (Adenosine Diphosphate + Phosphate)
- The Phosphate breaks off from the myosin head and goes back to the Mitochondria causing the myosin heads to pull forming the powerstroke and sliding of the filaments. ADP then goes back to the mitochondria
- The muscle stays contracted unitl ATP (Adenosine Triphosphate) attatches to the myosin head.
- The ATP turns into ADP + P. This causes the crossbridge/ myosin heads to break off from their binding sites.
- The Myosin deatatches from the actin filament and is resting until another action potensial arrives.
Cardiac Vs Skeletal Muscle
Table diagram in Notes
Skeletal Muscle fibre types
Type 1 Slow twitch
Type 2 Fast twitch
Type 1 muscle fibre
- Slow twitch
- Contract slowly, and is slow to fatigue
- Supplied by nerves to activate contraction
- Uses aerobic metabolism to generate large amounts of ATP
- Full of myoglobin to facilitate O2 (appearing red)
Type 2 Muscle fibre
- Fast twitch
- Conracts quickly, and is fast to fatigue
- Uses anaerobic metabolism generating less ATP
- Not adapted to deliver O2 to the mitochondria
Marathon Runner Vs. Sprinter
Marathon runners tend to have more Type 1 Slow twitch muscle fibres allowing them to run with more endurance at and undergo aerobic metabolic pathways
Sprinters tend to have more Type 2 Fast twitch muscle fibres allowing them to run at faster speeds at short periods, and undergo anaerobic metabolic pathways.
Smooth muscle
- Has no striations and is spindle shaped
- Contains a single nuclei
- Contracts slower and weaker than skeletal muscle
- Respond to hormones, neural stimulations and stretch
2 Types of contraction:
- Phasic (rapid)
- Tonic (Slower and longer)
Where is smooth muscle found
- Walls of organs
- Recipiratory tract
- Eye (Dilation of pupils)
- Skin
- Kidneys
Smooth muscle contraction
- Ca2+ influx into the cell from sarcoplasmic reticulum and extracellular sources via L-type Ca2+ channels
- Ca2+ binds to calmodulin in sarcoplasm
- Activating MLCK, phosphorolating myosin head for cross-bridge formation
- If there is no influx, the muscle relaxes
- Ca2+ concentration determines the force of the contraction
Smooth Vs Skeletal Muscle
Calmodulin Vs Tropomyosin
MLCK phosphorylation
Smooth = 100-1000x slower
Smooth stimulous is varied
Diagram in Notes
Controlling Muscle Tension: Motor Units
Small Motor units:
- Innervale less fibres
- Generate less tension
- Enable fine control
- Fatigue resistent
- Type 1 (Sustained contraction)
Large Motor Units:
- Generate more tension
- Fatigue quickly
- Type 2 (Large rapid force)
Increase in force of muscle contraction is generated by activating more motor units simultaneously
Muscle Tension
Latent Period:
- Action potential propgated along membrane
- Ca2+ released from SR.
Contraction phase:
- Period of cross-bridge formation
Relaxation Phase:
- Ca2+ pumped back into SR and cross-bridge stops
Summation
If a muscle cell is stimulated while a previous twitch is occuring, the second twitch is stronger
Second stimulous releases more Ca2+ ions, allowing more cross bridge formation
Tetanic Contraction:
* A sustained muscle contraction evoked by a motor nerve that emits action potentials at a very high rate
