lecture 19 - stuart baker Flashcards
golgi tendon organ
sensing the force that a muscle is exerting
connects to interneuron which is inhibitory and inhibits motor neurone
1b inhibitory tendon reflex can become
excitatory
they can change depending on the state
feedback control loop during locomotion (movement)
cutaneous reflexes
- 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
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
natural stimulus causes strong reflex
pathway of cutaneous reflex
- 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
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..
cortex
so theyre not just involved in reflexes theyre also involved in voluntary movements
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..
CS tract
interneurons are there to join the voluntary command with sensory inputs (reflexes) and give a coherent output
the cortex has multiple ways of sending information down to interneurons
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
C4-C5 CS lesion causes loss of direct connections but monkey can still do fine finger movement, suggest that…
interneurons can mediate fine finger movement
C2 corticospinal lesions causes the monkey not to be able to move fingers separately therefore…
brain stem pathways cannot mediate fine finger movements but to some extent the propriospinal interneurons can
spinal control of locomotion:
cat can speed up walking when treadmill pace increases even though it has a complete spinal section
therefore…
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)
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
the cerebellum:
small structure at the base of the brain in terms of volume but has large number of neurones
effects of cerebellar lesion
tremor and hypermetria (overreaching)
dysdiadochokinesia (inability to make rapid movements)
ataxic gait (walking looks like theyre drunk)