Functional anatomy Flashcards
Muscle belly
- Contains many fascicles.
- Surrounded by epimysium.
Fascicle
- Contains many muscle fibres.
- Surrounded by perimysium.
Muscle fibre
- Individual strand of muscle fibre.
- Contains myofibrils.
- Surrounded by endomysium.
Myofibril
- Made up of myofilaments.
- Chain of sarcomeres (contractile units of skeletal muscle).
Myofilaments
- Proteins which cause muscle to contract.
- Actin and myosin are contractile filaments which change length of sarcomere.
Label this diagram
Label a sarcomere
How can muscle contracted one moment, then be able to recontract?
- Once contraction is finished, myosin releases grip on actin.
- Release of grip and elastic energy stored in tendons, allows sarcomere and subsequent muscle fibre to relax and lengthen to resting length, ready for another contraction.
Types of muscular contractions
Isotonic contraction: Muscle length changes during contraction. Concentric and Eccentric.
Isometric: Muscle length doesn’t change when generating a force.
Isokinetic: Change in muscle length against a varying load.
Agonist and Antagonistic pairs
Origin - Attachment to stationary bone. Attachment points on proximal end.
Insertion - Attachment to moving bone. Attachment points on distal end.
Synergist
Muscle that stabilises a joint around which movement is occurring.
Recipricol inhibition
Coordinated relaxing of muscles on one side of a joint to accommodate to contraction on other side of that joint.
3 functions of the nervous systems
- Receives info about changes in body and environment; sends information to spinal cord and brain.
- Brain determines suitable response.
- Brain sends commands to muscles to carry out selected response.
PNS divisions
Sensory division
Motor division
Carries messages from body and environment to CNS. Made up of sensory neurons.
Carries messages from brain to muscles.
Made up of motor neurons.
Parts of a motor neuron
Dendrites
Pass impulse from sensory receptors to sensory neurons.
Cell body
Directs neuron’s messages to axon.
Axon
Carries nerve impulses away from cell body.
Motor unit
- The motor neuron and muscle fibres that it innervates.
- A single motor neuron joins with muscle fibres – activates a contraction.
- A whole muscle contains many separate motor units which allows muscle to generate different amounts of force to meet demands of situation.
Label a motor unit
All or none principle
All fibres in a motor unit will either contract at maximum capacity or not contract all.
When a motor unit is stimulated by a signal which exceeds its stimulus threshold, all muscle fibers in that motor unit contract with maximal force at same time.
If stimulus threshold is not reached, no fibres in motor unit will contract.
When all motor units are stimulated, they contract at 100%. To decrease force, requit fewer motor units.
Stages of neuromuscular junction nerve impulse to muscle contraction
- Action potential arrives at neuromuscular junction.
- Voltage gated calcium channels open, calcium flows into cytosol of motor neuron.
- Calcium binds to synaptic vesicles filled acetylcholine, causing vesicles to migrate towards membrane.
- Exocytosis occurs, acetylcholine is released into synaptic cleft.
- Acetylcholine diffuses through synaptic cleft and bind to receptor proteins on post synaptic membrane.
- Sodium and potassium channels open allowing sodium in and potassium out. Depolarisation occurs.
- Depolarisation spreads across surface of t tubules, triggering release of calcium ions from sarcoplasmic reticulum.
- Calcium attaches to troponin causing tropomyosin to unveil.
- This exposes binding sight of actin.
- Myosin cross bridges attaches to active site on actin.
- Myosin springs forward, creating a power stroke which pulls on actin fibres.
- As actin and myosin slide across each other, sarcomeres shorten bringing Z-lines closer together.
- As sarcomere shortens, muscle fibres shorten which causes a muscle contraction.
Fill in the table - Twitch fibres
Force velocity
- Relationship between force production and velocity of movement.
- Force produced by a muscle depends on velocity of a muscle contraction.
Force velocity - Concentric contraction
When velocity of contraction increases, force that can be produced decreases.
More force = Slower contraction speed. Less force = Faster contraction speed.
Due to rate of cross bridge connections. Myosin cross bridges have to attach and detach more rapidly as velocity of contraction increases.
Force velocity - Eccentric contraction
As load on muscles increases, it reaches a point where external force on muscle is greater than force they can generate. Even though muscle may be fully activated, it is forced to lengthen due to high external force.
Due to elastic component. Faster muscle contracts near its resting length, more force is produced.
Increasing velocity of an eccentric contraction increases force muscles can resist. Greater force required, faster velocity of contraction.
Less force required, slower velocity of contraction.
Force - length
Amount of muscle force that can be produced at varying muscle lengths.
Length of a muscle affects how much force it can generate.
Maximum tension is best achieved when muscle is at its normal resting length, due to an increased number of cross bridges attached between myosin and actin.
- When muscle is fully contracted, only a small force can be generated.
- When muscle is at its optimal length, greatest force is generated.
- When muscle is fully lengthened, only a small force can be generated.
