Proprioceptors

Question 1

what motor neurone cause contractility of skeletal muscle?

Answer 1

alpha - motor neurons

lower motor neurone

Question 2

where do a motor neurone have their cell bodies

Answer 2

in the anterior horn of the spinal cord

Question 3

where do a motor neurone axons project out to (2)

Answer 3

muscle fibres with a single synapse

Question 4

can a single fibre have many nerves innervating it?

Answer 4

nope it can only have one

Question 5

whats a motor unit

Answer 5

an a MN innervating a muscle fibre

Question 6

what are the 3 ways of modifying force of contraction

Answer 6

1. frequency of action potential firing
2. number of active motor units
3. change type of active motor units

Question 7

whats the general rule in terms of size of motor neurones cell body

Answer 7

the bigger the neurone cell body, the bigger the stimulation you have to give it to get it up fire an action potential. (smallest and weakest will always be active)

Question 8

what is the balance of whether a cell produces an AP based on?

Answer 8

balance of excitatory and inhibitory inputs - allows very fine control of movement

Question 9

what does the arm sagging down to the effect of gravity cause? (muscle spindle fibres)

Answer 9

unintended stretch of a muscle due to the muscle contracting too little
spindle gets stretched and this will cause the sensory afferents to send signals to the spinal cord and will increase excitation of the MN pool innervating the same muscle.
so increased AP firing and contraction of more and bigger myofibrils and so muscle will contract with more force allowing to maintain position.

Question 10

what are the two nerves of the muscle spindle fibre

Answer 10

gamma motor neurone axons

stretch sensitive afferents

Question 11

what are intrafusal fibres

Answer 11

modified muscle fibres

Question 12

where do intrafusal fibres have their contractile machinery

Answer 12

at the poles (ends)

so poles are contractile and change length at same time as main muscle

Question 13

what are the sensory stretch afferents associated with

Answer 13

the elastic inner bit - so if that stretches, spindles will be activated to try and stop it

Question 14

what are the poles of the intrafusal fibres innervated by

Answer 14

gamma motor neurones

Question 15

how are alpha and gamma MNs activated and deactivated so that the central portion of the intrafusal fibres are unaffected by movement

Answer 15

they are activated and deactivated simulataneously

Question 16

what do muscle spindles also ensure

Answer 16

accuracy of movements

Question 17

what will inhibition of the MN pool causes

Answer 17

decrease contraction of the muscle as a whole

Question 18

whats involved when the muscle stretches as part of a voluntary movement

Answer 18

the descending control systems activate inhibitory interneurons that dampen down activity - so muscle doesn’t resist stretching

Question 19

what do muscle spindle fibres do in unintentional movement

Answer 19

if you have unintended stretch of the muscle it will reflexly contract

Question 20

what is reciprocal inhibition

Answer 20

e.g. contraction of biceps and so you get inhibition of stretch from gamma neurones for triceps so they relax

Question 21

properties of interneurons

Answer 21

glycinergic
inotropic receptors (LGICR)
allow cl- in for example - hyper polarising it

Question 22

what are GABAb receptors

Answer 22

metabatropic

Question 23

what does flaccid paralysis cause

Answer 23

weakness
wasting
loss of reflexes
fasciculation’s

Question 24

where do upper motor neurone have their cell bodies?

Answer 24

in the brain

Question 25

what does a lesion in the upper motor neurone mean

Answer 25

lost ability to control the motor circuits at that level of the spinal cord

they also control gamma MNs so will get uncontrolled reflexes because centre of intrafusal fibres will keep stretching

increased tone and reflexes even on voluntary movement

spasticity

no wasting

Question 26

what does spasticity mean

Answer 26

velocity dependant increase in muscle tone

Question 27

what are type Ia afferents associated with

Answer 27

nuclear bag fibres

Question 28

what are type II afferents associated with

Answer 28

nuclear chain fibres

Question 29

what are group II afferents encoding

Answer 29

different lengths of muscle

relationship between muscle length and firing (slow changes in position)

Question 30

what are the properties of group II afferents

Answer 30

thinner
slower axons
form mainly indirect connections with a neurones. (synapse onto interneurons first)

Question 31

what does a loss of upper MN input to group II reflexes cause

Answer 31

hypertonia

Question 32

how can hypertonia be treated

Answer 32

by suppressing group II reflexes 
a2 agonists (e.g. tizanidine)

Question 33

what does type Ia respond to

Answer 33

proportion to the velocity of the muscle stretch - change in length to a certain extent - tendon hammer test

Question 34

properties of type 1a fibres

Answer 34

thicker, faster axons that make monosynaptic connections to a MNs

Question 35

what does a loss of upper MN input to group Ia cause

Answer 35

spasticity

Question 36

how can spasticity be treated and what is the problem with this

Answer 36

boost effectiveness of GABAa receptors - benzodiazepines - but can end up hyperpolarising a MN so they don’t fire.

or by mimicking the effect of presynaptic inhibition and activate GABAb receptors

Question 37

what type of sensory afferent is wrapped around collagen fibres in tendons

Answer 37

type 1b sensory afferent endings

Question 38

what do Golgi tendon organs do

Answer 38

measure tension generated by active muscle contraction
if contraction is too high the Golgi tendon organ will dampen it down almost like a negative feedback - inhibitory pathway is activated

Question 39

what decides which two pathways are active for GTO afferents

Answer 39

upper motor neurones or descending pathways

Question 40

what does a loss of GTO inhibition cause

Answer 40

hypertonia in states situations

Question 41

what does a loss of GTO excitation cause

Answer 41

weakness in dynamic situations (weak walking)