Kinesiology: Physiology - Skeletal Muscle

structure

• muscle is an organ

• large group of tissues that aid each other in performing a function

• multi-nucleate

• have many mitochondria

epimysium

membrane that bounds muscles together

fasicles

smaller groups of muscle cells found within the epimysium

• allow for more fine tuned control

• within each fascicle, there are a number of muscle cells

muscle fibres

extremely long part of the muscle found in the middle of the muscle

myofibres

long strands of protein that mainly fills cell

action and myosin

2 proteins that are bundled within myofibres

sliding filament theory

in a contraction, overlap increases and eliminates the I-band and therefore shortens the muscle

physiology of a contraction

• motor nerves synapse with sarcolemma of individual muscle cells

• acetylcholine is released into the synaptic cleft and causes an action potential in the sarcolemma

• acetylcholine travels down the T-tubules and at the ends of the tubules are cisternae (structures)

• Ca2+ ions are released by the cisternae and binds to a protein on actin called troponin

• myosin cross bridges grab and pull on the active actin fibres pulling each other close together and shortening the muscle

• once the contraction is over, the myosin releases the actin, troponin releases the Ca2+ and gets reabsorbed by cisternae and waits for the next contraction

graded response of a muscle contraction

• muscles operate on a sliding scale between twitch and tetanus

• allows complicated, fine tuned movements

graded response of a muscle contraction - twitch

brief contraction of just a few fibres in a muscle that are often involuntary and due to brief stimulusg

graded response of a muscle contraction - tetanus

intense prolonged contraction of a muscle involving as many fibres as possible

reflex

rapid, automatic response to a stimulus

spinal reflex

• typically involuntary

• don’t require action from brain

  • could involved some lower centers of brain

cerebral reflex

• involves brain

interneuron

nerve in spinal column with a high threshold value

• only creates an impulse for a very strong stimuli

• causes an impulse in efferent nerve faster than brain will

simple reflex arc

• receptor responds to stimuli and takes an Energy and transforms its energy

• sensory neuron (afferent) takes electrical energy and sends it to the CNS

• control centre (integration centre) where interneuron takes signal from sensory neuron and sends it to where it needs to go

• motor neuron (efferent signal) goes to the effector

• effector is the muscle

proprioception

body’s ability to sense position, spatial orientation, angles of joints and influence from surrounding

proprioceptors

organs that sense proprioception

muscle spindle

muscle fibre that lies parallel to other fibres in the muscle (leader)

• each one has 2 motor neurons and 1 sensory neuron associated with it

  • sensitive to changes in the muscle fibre length and provides feedback to brain and is capable of rapid adjustment

golgi tendon organ

• proprioceptor located in the tendons

• sensitive to changes in tension in a muscle

• when it is activated, it causes associated muscle to relax

  • if it doesn’t, it could cause tears - happens to prevent injury

specific reflexes

• occurs when stretch in muscle is detected by muscle spindle and results associated mucle contracting

• at the same time a message is sent to the antagonist muscle to relax

  • coordinates movement

withdraw reflex

pull away from something hot/sharp

startle reflex

flailing when startled

stretch reflex

“knee jerk”

tension reflex

• tension is detected by the golgi organ

  • message is sent for that muscle to relax - injury prevention

crossed-extensor

when you step on a tack with 1 foot and hop to the other

• poly-synaptic