muscle control and reflexes

Question 1

outline the structure of the spinal cord

Answer 1

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

Question 2

what is found within white and grey matter?

Answer 2

white: contains all ascending and descending neuronal pathways
grey: contains neuronal cell bodies

Question 3

what is a motor unit?

Answer 3

an alpha motor neurone and the group of muscle fibres it innervates

Question 4

why does unfused tetanus allow prolonged contraction over full tetanus?

Answer 4

full tetanic contraction compresses the capillaries, cutting off supply of oxygen = muscle fatigues quickly

Question 5

what is the effect of age on motor units?

Answer 5

number of motor units decreases, number of fibres per unit increases. reduced fine control of muscles

Question 6

give the features of S, FR, and FF muscle fibres

Answer 6

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

Question 7

what does contractile force depend on?

Answer 7

• number of muscle fibres in the motor unit
• proportion of motor unit types in the muscle
• number of motor units activated
• frequency of activation

Question 8

describe the muscle architecture of parallel fibres

Answer 8

• individual fibres are long
• have capacity for extensive shortening
• few fibres/volume
• low force

Question 9

describe the structure of pennate fibres

Answer 9

• slow and limited shortening
• many fibres/volume
• high force

Question 10

what is meant by proprioception?

Answer 10

our knowledge of where our limbs are in space

Question 11

what is kinaesthesia?

Answer 11

awareness of movement

Question 12

what are the four main proprioceptors?

Answer 12

• muscle spindle
• tendon organ
• joint receptors
• skin

Question 13

what is the muscle spindle?

Answer 13

a complex sense organ which has a core of specialised muscle fibres called intrafusal muscle fibres

Question 14

what does the muscle spindle measure?

Answer 14

the length and change of length of the muscle

Question 15

outline sensory input/output from the muscle spindle

Answer 15

• 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

Question 16

how does the the Ia afferent in the muscle spindle provide feedback?

Answer 16

when intrafusal fibres are stretched, the primary sensory ending is distorted, opening the ion channels causing depolarisation

Question 17

what does the tendon organ measure?

Answer 17

force production across the muscle

Question 18

describe the structure of the tendon organ

Answer 18

strands of collagen enclosed in a capsule. has a Ib afferent axon, which branches and supplies terminals which wrap around the collagen

Question 19

what does proprioceptive flow to the: spinal cord, cerebellum, and cerebral cortex control?

Answer 19

spinal cord: spinal reflexes
cerebellum: movement control, planning and error correction
cerebral cortex: movement control, planning, error correction and conscious sensation

Question 20

outline a spinal reflex

Answer 20

sense organ -> afferent axon -> spinal cord (synapse) -> efferent axon -> effector

Question 21

outline the mechanisms for control of reflexes

Answer 21

• 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

Question 22

give examples of 2 negative feedback pathways for reflex control

Answer 22

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

Question 23

give an example of a positive feedback pathway for reflex control

Answer 23

withdrawal reflex

Question 24

what do the otolith organs respond to?

Answer 24

linear acceleration

Question 25

what do the semi-circular canals respond to?

Answer 25

rotational/angular acceleration

Question 26

how do the semi-circular canals cause a response to acceleration?

Answer 26

when the head is turned, the endolymph does not initially move as it has its own inertia. this causes the endolymph to press against the cupula, distorting the hair cells and causing an action potential to fire

Question 27

how do the otolith organs cause a response to acceleration?

Answer 27

hair cells are projecting up into a gel, above this gel there is a membrane containing CaCl2 crystals. when the head is accelerated, gravity bends the hair cells

Question 28

what are static reflexes?

Answer 28

maintenance of body position with respect to gravity

Question 29

what are statokinetic reflexes?

Answer 29

restoration of head position with respect to gravity