spinal reflexes

Question 1

lower motor neuron

Answer 1

motor neuron that has cell body in ventral horn.

Question 2

upper motor neuron

Answer 2

nerve cells that are higher in the brain and send axons down the spinal cord in descending tracts, synapsing with dendrites of the lower motor neurons.

Question 3

motor unit

Answer 3

smallest unit of contraction

motor neurone together with its cell body in the dorsal horn, its motor axon and set of muscle fibres that it innervates

Question 4

how is a twitch generated

Answer 4

single AP contracts one motor unit.

Question 5

Tetanic Contraction

Answer 5

smooth contraction: initiated by a train of action potentials at high frequency

Question 6

is tetanic contraction healthy

Answer 6

yes

Question 7

how is a fused contraction produced

Answer 7

tetanic fusion frequency

Question 8

which type of fibres have all or nothing activity

Answer 8

motor

Question 9

how are muscles for fine control different to other muscles

Answer 9

more small motor units

Question 10

Pyramidal System

Answer 10

upper motor neurone cell bodies: project directly from frontal lobe (mainly motor cortex) to spinal cord. They travel via the corticospinal tract.

Question 11

Extrapyramidal System

Answer 11

Upper motor neurone cells travel to the brainstem, synapse, and then project to the spinal cord. These are regulated by the motor cortex.

Question 12

reflex

Answer 12

Involuntary motor action triggered by a sensory input

Question 13

where are reflexes stored

Answer 13

dorsal and ventral grey matter in forms of patterns of synaptic connections

Question 14

monosynaptic reflex

Answer 14

reflex with no interneurons neurons between muscle spindle afferent and motorneuron efferent

Question 15

homonymous reflex

Answer 15

muscle sending sensory information is the one that contracts

Question 16

reciprocal inhibition

Answer 16

1 muscle contracts, another relaxes

Question 17

which muscle contracts when patella tapped

Answer 17

quadriceps

hamstrings relax

Question 18

proprioceptor/muscle spindle

Answer 18

Receptor that mediates tendon reflexes

Question 19

what makes up a proprioceptor/muscle spindle

Answer 19

stretch receptor inside a connective tissue sheath

Question 20

what is the main sensory nerve fibre from muscle spindle

Answer 20

la afferent

Question 21

what do muscle spindles detect

Answer 21

muscle length

Question 22

how many muscle spindle Ia nerve fibre synapses must be active to fire a motor neurone

Answer 22

2+

Question 23

what does a single Ia sensory nerve fibre produce in a motor neuron

Answer 23

Excitatory post-synaptic potential

Question 24

Spatial Summation

Answer 24

Two synaptic inputs are active at the same time and the EPSPS are summed together

Question 25

Temporal Summation

Answer 25

single Ia nerve fibre fires a high frequency burst of action potentials so that the EPSPs sum together to trigger an action potential.

Question 26

what is a muscle spindle made up of

Answer 26

modified skeletal muscle fibres with contractile tissue at the end and the centre of the spindle with no actin or myosin

Question 27

what type of motor neuron supplies a muscle spindle

Answer 27

gamma motor neuron

Question 28

how does the brain keep muscle spindle feedback at the right level during movement

Answer 28

activates both alpha and gamma motor neurons

Question 29

how is constant muscle length maintained despite fatigue

Answer 29

muscle spindles give continuous feedback to motor neurons and continually adjust the motor neuron output during normal movement

Question 30

mechanism of maintaining muscle length despite fatigue

Answer 30

Holding something: initially there is input to motor neurons from descending axons and from muscle spindle Ia afferents. The combined input keeps it in positon. However, biceps fatigue after a while: they contract less strongly and start to stretch. This stretch increases the activity of the muscle spindles, which increases input to biceps motor neurons as well as spinal cord Increased contraction: arm moves back into place.

Question 31

golgi tendon organ

Answer 31

Second major proprioceptor.

Question 32

what activates golgi tenson organ

Answer 32

tension

Question 33

what does golgi tendon organ do

Answer 33

Prevents muscles from contracting too strongly

Question 34

what type of motor neuron does golgi tendon organ connect to

Answer 34

glycinergic inhibitory neuron

Question 35

what activates a flexion relfex

Answer 35

activation of small myelinated nociceptor afferents

Question 36

are flexor reflexes polysynaptic or monosynaptic

Answer 36

polysynaptic

Question 37

what type of reflex can the brain supress

Answer 37

polysynaptic

Question 38

what is a crossed extensor reflex

Answer 38

Activation of extensors in the other leg during flexion reflex to take weight

Question 39

how are crossed extensor reflexes produced

Answer 39

afferent fibres cross stimulated side of body to contralateral side of spinal cord. There they synapse with interneuron

Question 40

muscle tone

Answer 40

small amount of contraction in muscles when these are moved passively

Question 41

what does lower motor neuron damage cause

Answer 41

flaccid paralysis - decr tone, paralysed muscles

Question 42

what does upper motor neuron damage cause

Answer 42

spasticity - incr tone