lecture 19 - stuart baker

Question 1

golgi tendon organ

Answer 1

sensing the force that a muscle is exerting
connects to interneuron which is inhibitory and inhibits motor neurone

Question 2

1b inhibitory tendon reflex can become

Answer 2

excitatory
they can change depending on the state
feedback control loop during locomotion (movement)

Question 3

cutaneous reflexes

Answer 3

• skin is covered in cutaneous receptors
• important for control of movement
• electrodes on the finger stimulate the digital nerves that run along the finger
• recording the activity of the muscle in the hand shows triphasic reflex
• early excitatory component, middle latency inhibitory component, late excitatory component
• E1 (spinal) , I1 and E2 (cortical) reflexes
• the electrically stimulated reflexes are weak

Question 4

people asked to grasp and lift an object
if the object slips from the grasp it stimulates to cutaneous receptors in the fingers
this caused a reflex increase in grip force
and this reflex was really powerful

Answer 4

natural stimulus causes strong reflex

Question 5

pathway of cutaneous reflex

Answer 5

• lab used genetic techniques to identify a particular class of interneurons in the spinal cord of a mouse called dI3 interneurons
• showed that the dI3 interneurons receive input from cutaneous receptors and they project to motor neurons and they’re excitatory
• they’re able to create a KO strain of the mice that lack the interneurons
• when the KO mice are put in a cage and turned upside down they cannot grip and therefore fall out the cage

Question 6

in the intermediate zone of the spinal cord there are corticospinal terminals which is where all the interneurons are
so all the spinal interneurons that are involved in controlling movement have input from the..

Answer 6

cortex
so theyre not just involved in reflexes theyre also involved in voluntary movements

Question 7

we have a monosynaptic stetch reflex from muscle spindles which goes straight to a motor neurone and back to the same muscle
we also have a di synaptic inhibitory reflex which goes an inhibitory interneuon then motor neuron to the antagonist muscle and stops it contracting at the same time.
that inhibitory interneuron also gets input from the..

Answer 7

CS tract

Question 8

interneurons are there to join the voluntary command with sensory inputs (reflexes) and give a coherent output

Question 9

the cortex has multiple ways of sending information down to interneurons

Answer 9

can come via the brain stem
can come via propriospinal interneurons (C3-C4)
can come via segmental interneurons (C6-T1)
or via direct connections to motor neurones

Question 10

C4-C5 CS lesion causes loss of direct connections but monkey can still do fine finger movement, suggest that…

Answer 10

interneurons can mediate fine finger movement

Question 11

C2 corticospinal lesions causes the monkey not to be able to move fingers separately therefore…

Answer 11

brain stem pathways cannot mediate fine finger movements but to some extent the propriospinal interneurons can

Question 12

spinal control of locomotion:
cat can speed up walking when treadmill pace increases even though it has a complete spinal section
therefore…

Answer 12

spinal cord is capable of driving a locomotion pattern (alternation between flexion and extension in a normal gait pattern that alternates between the two limbs) it can also integrate sensory input to adapt the gait without any connection to the cortex
(central pattern generator)

Question 13

evidence that there is a central pattern generator in humans
electrodes are implanted into people that have a spinal cord injury
implanted over the spinal cord and boosted the activation of the spinal cord in a constant way and this caused production locomotor activity in the leg

Question 14

the cerebellum:

Answer 14

small structure at the base of the brain in terms of volume but has large number of neurones

Question 15

effects of cerebellar lesion

Answer 15

tremor and hypermetria (overreaching)
dysdiadochokinesia (inability to make rapid movements)
ataxic gait (walking looks like theyre drunk)

Question 16

cerebellar anatomy

Answer 16

cortex (outer part)
inside the cerebellum are the deep cerebellar nuclei
there are different sections divided into the lateral part, the intermediate part and the medial part

Question 17

the sections of the cortex communicate down to the corresponding deep cellular nuclei:
the lateral part of the cortex connects to the…

Answer 17

dentate nucleus

Question 18

the intermediate part of the cortex connects to the…

Answer 18

interposed nuclei

Question 19

the medial part (also called the vermis) connects to the…

Answer 19

fastigial nucleus

Question 20

the lateral part of the cerebellum (aka the cerebrocerebellum) gets inputs from the…

Answer 20

cerebral cortex

Question 21

the cerebral cortex projects to the pontine nuclei which then projects to the cerebellum cortex which projects to the dentate nucleus which then projects to the thalamus and then back up to the cerebral cortex

Question 22

the intermediate and medial parts of the cerebellum are often called the…

Answer 22

spinocerebellum

Question 23

they get inputs from…

Answer 23

parts of the cerebral cortex involved in somatic sensation but mainly from the spinocerebellar tract (sensory pathway from the periphery coming up the spinal cord to the cerebellum) projects to the intermediate and medial parts which projects down to the deep cerebellar nuclei (interposed and fastigial) and then that projects to the red nucleus and the reticular nuclei and then back to the spinal cord (it can also go up to the cerebral cortex as well)

Question 24

vestibulocerebellum which involes a small part of the cerebellum called the…

Answer 24

flocculonodular lobe

Question 25

input comes from the vestibular nuclei (about balance), projects to the cerebellar to the cortex and then back to the vestibular nuclei

Answer 25

cerebellar input/output circuits very often loop back

Question 26

cerebellar cortex microcircuit layers

Answer 26

top --> bottom molecular layer purkinje cells layer granular layer white matter layer

Question 27

what are the only output cells of the cerebellar cortex

Answer 27

purkinje cells (they project into the deep cerebellar nuclei)

Question 28

purkinje cells are GABAergic meaning they can only...

Answer 28

inhibit

Question 29

purkinje cells get input from...

Answer 29

climbing fibres (1:1 relationship, comes up the dendritic tree of the purkinje cell and winds around the dendrites and makes many synapses. they come from the inferior olive) and parallel fibres (originate in the granular layer at the granule cells, they send an axon up to the molecular layer where in bifurcates and then the parallel fibres cross the dendritic tree of the purkinje fibres and right angles and then make synapses)

Question 30

the granule cells get their input from mossy fibres which come from pontine nuclei which get activated cerebral cortex or from the spinocerebellar tract

Question 31

there are inhibitory interneurons in the layers:

Answer 31

golgi cell - gets input from the parallel fibres and projects back to the granule cells. so the granule cells gets input from the mossy fibre and get inhibited by the golgi cell to keep activity at the right level stellate and basket cells - get input from the parallel fibres and inhibit the purkinje cells

Question 32

purkinje cells have two different sorts of action potentials

Answer 32

1. simple spike - normal APs, caused by activation of many parallel fibres adding up by temporal summation 2. complex spike - come from the climbing fibres which cause massive depolarisation to the purkinje cells and that triggers a calcium spike which then causes a long lasting depolarisation and on top of that there is little bursts of sodium spikes. this doesn't happen very often

Question 33

Marr and Albus: - voluntary movement is produced by your voluntary intent from the cerebral cortex - the voluntary activation of climbing fibres activates the purkinje cells - the activity in the purkinje cells some how produces the movement - some of the parallel fibres are active because of the sensory context - the synapses between the parallel fibres and the purkinje cells will strengthen whenever theres paired activation of the parallel fibres and the purkinje cells (i.e when the purkinje cells are already active due to the climbing fibres) - if the same sensory context happens again now because the parallel fibres are being activated and the synapses have been strengthened those parallel fibres could now automatically activate the purkinje cells (no need for climbing fibres) - this is a way we can learn a movement (e.g driving a car, after time it becomes an automatic movement)

Question 34

evidence for this idea

Answer 34

they recorded from a purkinje cell and activate two parallel fibres (PF) that were connected to that purkinje cell they activate PF1 and 2 separately and see EPSPs they activated PF1 at the same time as activating the climbing fibre that goes to that purkinje cell (they do this a number of times) then they go back and record the response to PF1 on its own and PF2 on its own and the EPSP gets smaller in PF1 so the one that was paired with activation of the climbing fibre changes the EPSP evidence that cerebellar learning is happening

Question 35

evidence that this may occur in voluntary movements

Answer 35

trained a monkey to do a wrist movement recorded from purkinje cells when the monkey did the wrist movement there was activation of the purkinje cell when there was weight added to the handle the monkey was moving so the monkey had to adapt to the fact that the handle was heavier when they first recorded the purkinje cell started firing complex spikes around the time of the movement after the monkey got used to the fact that the handle was not weight the activity in the complex spikes decreased but also the firing rate of simple spikes had reduced they thought that during the adaptation to the load the complex spikes served as some sort of training signal which caused a reduction in the firing rate of the simple spikes because it changes the synaptic weighting of the parallel fibre synapses and that lead to the monkey being able to do the monkey with a new load