muscle control and reflexes Flashcards
outline the structure of the spinal cord
formed from segments, has spinal roots in between the vertebrae, which form the peripheral nerves which innervate muscle. has sensory (afferent) neurones on the dorsal root, and motor (efferent) neurones on the ventral root
what is found within white and grey matter?
white: contains all ascending and descending neuronal pathways
grey: contains neuronal cell bodies
what is a motor unit?
an alpha motor neurone and the group of muscle fibres it innervates
why does unfused tetanus allow prolonged contraction over full tetanus?
full tetanic contraction compresses the capillaries, cutting off supply of oxygen = muscle fatigues quickly
what is the effect of age on motor units?
number of motor units decreases, number of fibres per unit increases. reduced fine control of muscles
give the features of S, FR, and FF muscle fibres
S: slow contracting, v fatigue resistant, v small force. oxidative
FR: faster contracting, fatigue resistance, small force, oxidative/glycolytic
FF: fast contracting, fast fatigue, high force, glycolytic
what does contractile force depend on?
- number of muscle fibres in the motor unit
- proportion of motor unit types in the muscle
- number of motor units activated
- frequency of activation
describe the muscle architecture of parallel fibres
- individual fibres are long
- have capacity for extensive shortening
- few fibres/volume
- low force
describe the structure of pennate fibres
- slow and limited shortening
- many fibres/volume
- high force
what is meant by proprioception?
our knowledge of where our limbs are in space
what is kinaesthesia?
awareness of movement
what are the four main proprioceptors?
- muscle spindle
- tendon organ
- joint receptors
- skin
what is the muscle spindle?
a complex sense organ which has a core of specialised muscle fibres called intrafusal muscle fibres
what does the muscle spindle measure?
the length and change of length of the muscle
outline sensory input/output from the muscle spindle
- Ia afferent axon carries information to spinal cord. forms spiral endings which wrap around the the intrafusal fibres. sensitive to velocity of stretch
- type II afferent; sensitive to absolute length
- innervated by a Gamma motor neurone
how does the the Ia afferent in the muscle spindle provide feedback?
when intrafusal fibres are stretched, the primary sensory ending is distorted, opening the ion channels causing depolarisation
what does the tendon organ measure?
force production across the muscle
describe the structure of the tendon organ
strands of collagen enclosed in a capsule. has a Ib afferent axon, which branches and supplies terminals which wrap around the collagen
what does proprioceptive flow to the: spinal cord, cerebellum, and cerebral cortex control?
spinal cord: spinal reflexes
cerebellum: movement control, planning and error correction
cerebral cortex: movement control, planning, error correction and conscious sensation
outline a spinal reflex
sense organ -> afferent axon -> spinal cord (synapse) -> efferent axon -> effector
outline the mechanisms for control of reflexes
- fusimotor system: alteration of muscle spindle sensitvity via the gamma motor neurones
- alteration of alpha motor neurone excitability
- alteration of neurotransmitter released by Ia and II afferents
give examples of 2 negative feedback pathways for reflex control
reciprocal inhibition: interneurones synapse with antagonist muscles, occurs at same time as stretch in agonist, causing relaxation of antagonist
autogenic inhibition: involves tendon organ, balances production of force in the muscle by selectively inhibiting muscle fibres
give an example of a positive feedback pathway for reflex control
withdrawal reflex
what do the otolith organs respond to?
linear acceleration