Session 2 - Muscle Structure, Morphology and Mechanics Flashcards
List the arrangement of muscles from bone to myofilaments
-Bone, tendon, muscle, fascicle, fibre. myofibril, myofilaments
What are the possible arrangements of skeletal muscle?
- Circular
- Convergent
- Multipennate
- bipennate
- Unipennate
- Parallel
- Fusiform
What are the main functions of skeletal muscle?
- Movement
- Posture
- Joint stability
- Heat generation
What is fasciculation?
-Muscle twitch
What is the agonist muscle during a movement?
-The prime mover which exerts a force or effect (main muscle responsible for movement)
What is the antagonist during a movement?
-The muscle which opposes the prime mover, allowing control of a movement
What does a synergist muscle do in a movement?
-Assists prime mover by neutralising extra motion, eg sideways motion
What is the function of a fixator during a movement?
-A muscle which stabilises the action of the prime mover eg fixes a non-moving joint when prime mover acts over two joints
What is a 1st class lever?
-The load is on the opposite side to the muscle, central to the fulcrum eg skull
What is a second class level?
-The load is on the same side to the muscle but close to the fulcrum
What is a third class lever?
-The load is on the same side of the muscle far away from the fulcrum
What is compartment syndrome?
- Compartments of limbs surrounded by non-expandable fascia
- Anything which causes a large increase in pressure in the compartment can lead to compression of the blood supply and nerves, possible leading to necrosis of compartment
What is isotonic contraction?
-Contraction of the muscle resulting in constant muscle tension and varying muscle length
What is the difference between concentric and eccentric isotonic muscle contraction?
- Concentric muscle shortens in length
- Eccentric muscle extends in length
What is delayed-onset muscle soreness, what is a common cause?
- Muscle soreness wich becomes symtomatic a few days after the causing factor
- Walking down hill
What is isometric contraction?
-Contraction of muscle where muscle stays the same length but there is varying tension eg hand grip
Why can isometric contraction be important in the elderly or those with hypertension?
-There is a small muscle mass involved in isometric contraction, however it has a large effect on blood pressure
Describe type I muscle fibres
-Aerobic, red with rich capillaries, many mitochondria and fatigue resistant, slow oxidative with endurance
Describe type IIa muscle fibres
-Aerobic, red/pink with rich capillary supply, many mitochondria and moderately fatigue resistant, fast oxidative,
Describe type IIb muscle fibres
-Anaerobic, white with poor capillary supply, few mitochondria and fatigue rapidly, short intense movements
What is proprioception?
-Awareness of self
How does proprioception work?
- Feedback control by proprioceptors
- Proprioreceptor muscle spindles send messages about tension and stretch being exerted on the muscle to the brain
What is a motor unit?
-A motor neurone and the muscle fibres it innervates (ie each axon innervates several muscle fibres
How is the number of muscle fibres per axon determined?
-Depends on how fine of control needed for the movement
What can atrophy of a nerve/muscle cause on its corresponding nerve/muscle? Why?
-Atorphy due lack of chemical signals, eg neurotrophins/cytokines
What is muscle tone?
-The continuous and passive part-contraction of muscles
What determines baseline muscle tone?
-Baseline motor neurone activity and muscle elasticity
What controls tone which occurs above baseline?
- Motor control centres in the brain
- Afferent muscle fibre signals
- Negative feedback from muscle spindles
What are four possible causes of hypotonia?
- Lesions of sensory afferents
- Cerebral/spinal shock
- Primary degeneration of muscles
- Lesion of lower motor neurones
What is a synaptic bouton?
-Flattened terminal of axon at NMJ used to increase SA
How many molecules of Ach bind to NachR?
-2 ach -> 2 a-subunits
What is a depolarising blockade anaesthetic?
-An anaesthetic which mimics ach, which in excess causes an initial depolarisation followed by a block of the NMJ and ultimately muscle relaxation
What is a non-depolarising anaesthetic?
-One which blocks the nicotinic receptors
What is recruitment?
-The more neurones activated, the more muscle fibres are recruited to develop more force
What is unfused tetanus?
-A series of action potentials causes a series of twitches together
What is fused tetanus?
-Action potentials become more frequent and muscle doesnt get time to relax so contraction becomes continuous
What is tetanus?
-Clostridium tetani’s exotoxin causes muscle spasms and rigidity by interfering with feedback control of muscle tension
What is an electromyography?
-A diagnostic tool where electrodes are placed above or in muscles to measure the electrical activity
NB:recruitment of muscle fibres should match the force of contraction
How does relaxation of muscle occur?
- Ca2+ is pumped back into the sarcoplasmic reticulum by SERCA
- Some calcium binds to calmodulin
Why is ATP needed in continual muscle contraction?
-In order to detach myosin heads from actin filaments
Where do muscles get their ATP from?
- Oxidative phosphorylation
- Glycolysis
- Creatine phosphate
- Anaerobic glycolysis
What is a contracture?
-State of continuous contraction
Why does contracture occur when ATP is depleted?
-Myosin heads remain bound to actin filaments so muscle stays contracted
