lecture 18 - stuart baker

Question 1

direction encoding in M1

Answer 1

cells fire more in different movement directions

Question 2

population vector

Answer 2

each cell has a vector
made each cells vector point in the preferred direction (where fire cells most maximally)
measure the firing rate and use that as the magnitude
do it for all cells in the motor cortex and then add up the single cell vectors
end up with one vector which is the population vector

Question 3

cells encode muscle activation

Answer 3

a single CS axon diverges and projects to motor neurones pools controlling multiple muscles

Question 4

division of the premotor cortex

Answer 4

lateral PM cortex (down the side) and mesial supplementary motor area (down the midline)

Question 5

in the visually guided task (light flash –> press button) the monkey with the ______ lesion had high errors

Answer 5

premotor cortex

Question 6

in the internally guided task (pull, twist lift manipulandum) the monkey with the ___ lesion had more errors

Answer 6

supplementary motor area

Question 7

single cell recording
trained monkey do to visually guided task and internally triggered task

Answer 7

in the PM cortex cells fire more for the visually triggered movement
in the SMA the cells fire more for the internally guided movement

Question 8

SMA is involved in bimanual coordination

Answer 8

there are projections from SMA to SMA, SMA to pre motor and SMA to motor cortex
coordination goes via the SMA
the monkey couldn’t do different things with its hands after SMA lesion

Question 9

lateral pre motor area

Answer 9

• involved in visual guidance of movement
• control of grasp
• got monkeys to grasp different objects
• recorded from cells
• e.g cell in the lateral PM area fired for the ring grasp and sphere grasp
• lateral pre motor encodes a library of grasp patterns

Question 10

neurons showed mirror activity

Answer 10

the cell fires when a monkey makes a particular grasp of an object r
the cells also fire when the monkey watches another monkey doing the same thing
these are call mirror neurones

Question 11

spinal cord:
dorsal is towards the ____ of the spinal cord

Answer 11

back

Question 12

ventral is towards the _____ of the spinal cord

Answer 12

front

Question 13

dorsal is where the _____ axons come in

Answer 13

sensory

Question 14

ventral is where…

Answer 14

the motor neurones leave

Question 15

in the grey matter there are different divisions

Answer 15

dorsal horn (interneurons involved in sensory processing)
ventral horn (motor neurones)
bit in the middle is called the intermediate zone (interneurons that tie sensation and movement together)

Question 16

what are reflexes

Answer 16

fast stereotypes movement in response to sensory input

Question 17

muscle spindles:
modifies muscle fibres
found within spindle capsules
they have two distinct types of innovation….

Answer 17

1. sensory innovation - axons that wind around the muscle spindles and sense the stretch of the muscle spindles
2. they have a motor innovation - gamma motor neurones which cause the muscle spindles to contract

Question 18

3 different types of muscle spindles

Answer 18

1. dynamic nuclear bag
2. static nuclear bag
3. nuclear chain

Question 19

which are responsible for sensing the length of the muscle that the muscle spindle is found in

Answer 19

static nuclear bag and nuclear chain

Question 20

which a responsible for sensing the rate of change of length

Answer 20

dynamic nuclear bag

Question 21

1a sensory fibres (faster conducting) innovate all three types of muscle spindles
group II sensory fibres only innovate the

Answer 21

static nuclear bag and the nuclear chain

Question 22

meaning the group II fibres only measure…

Answer 22

lengthh

Question 23

the group 1a fibres fire in response to,..

Answer 23

length and rate of change of length

Question 24

2 types gamma motor neurones:
static gamma neurones which innovate the…

Answer 24

static nuclear bag and the nuclear chain
- controls the sensitivity of the static system

Question 25

dynamic gamma motor neurone which control the…

Answer 25

sensitivity of the dynamic system

Question 26

1a sensory fibre firing rate increases due to

Answer 26

change of length
and rate of change of length

Question 27

stimulating the static gamma motor neurones will cause

Answer 27

sensitivity to length will go up

Question 28

stimulating the dynamic gamma motor will cause

Answer 28

sensitivity to rate of change of length will go up

Question 29

monosynaptic stretch reflex

Answer 29

-1a afferents sense the length and rate of change of length
- axon comes from the muscle spindle, into the spinal cord, the axon passes through to the ventral horn and synapses on the motor neurones that project back onto the same muscle
- that gives us a fast reflex (doesnt go up to the brain and theres only one synapse involved) that responds to the stretch of a muscle by contracting that muscle

Question 30

1a inhibitory interneuron

Answer 30

• input from the muscle spindle
• goes monosynaptically to the motor neurone and back to the same muscle (e.g quadriceps)
• but the muscle spindle also activates an inhibitory interneuron that inhibits the antagonist muscle that would pull in the opposite direction (e.g hamstring)
• disynaptic inhibitory reflex

Question 31

load compensation

Answer 31

• you’re holding a cup and waiting for somebody to pour coffee into your cup
• when it starts filling the weight goes up
• becuase the weight is now exerting bigger force than the force your posing with you muscles your arm will drop
• you could adjust that force voluntarily, but that would use a lot of cognitive processing
• could we use a reflex instead
• as the coffee cup fills it drops and that leads to a stretch of the bicep muscle
• the stretch could cause a reflex increasing the activation of the biceps
• causing the muscle to contract more and bring the coffee cup back to a neutral position

Question 32

however this reflex is producing an extra force (F) which is proportional to the displacement error (X)
k = reflex gain
F=kx
problem, as if X is zero, F is also zero. this doesnt make sense as if you compensate completely there would be no error and that would mean theres no extra force which isn’t true
if the reflex gains goes to high you get oscillations

Answer 32

cant use monosynaptic stretch reflexes to do load compensation

Question 33

instead there are long latency smart reflexes

Answer 33

go via the cortex