Hierarchy of nervous system

Question 1

Voluntary control of muscles is by what

Answer 1

alpha motoneurones in the spinal cord “final common path”

Question 2

Reflex control of muscles is by what

Answer 2

Autonomous wired into motoneurone circuits at each segmental spinal level BUT brainstem nuclei exert control over spinal reflexes and integrate them into higher order reflexes controlling posture and balance

Question 3

Example of overiding

Answer 3

descending inputs from vestibulospinal and reticulospinal tracts regulate trunk and limb muscle reflexes

Question 4

Four systems controlling movement

Answer 4

Four systems control movement

1) descending control pathways, 2) basal ganglia, 3) cerebellum and 4) local spinal cord/brain stem circuits

Question 5

Where does sensory input come from

Answer 5

spinal cord
brainstem
cortical level

Question 6

examples of sensory input from the spine

Answer 6

proprioceptors, touch and pain

Question 7

examples of sensory input from brainstem

Answer 7

vestibular system for balance

Question 8

what happens if sensory input is damaged from the spinal level.

Answer 8

paralyses if the motor neurones themselves are damaged

Question 9

what happens in stretch reflex

Answer 9

• tap to elastic tendon
• force is transmitted to muscle fibres which are more elastic so can stretch more
• MORE APS IN AFFERENT NERVES PROJECTING THROUGH DORSAL HORN INTO SPINAL CORD
• spindle sensory afferents divide and make three connections

Question 10

3 Types of afferent connections in stretch reflex

Answer 10

• Direct activation of alpha motor neurones to streched muscle
• Indirect influence of antagonist
• Afferent information ascending to dorsal column

Question 11

What happens in direct activation of alpha motor neurones

Answer 11

it causes rapid contraction of the agonist muscle

MONOSYNAPTIC REFLEX, as NO INTERNEURONS

Question 12

What happens in indirect influence of antagonists muscle.

Answer 12

agonist contraction causes antagonist to relax

DUE TO ACTIVATION OF INHIBATORY NEURONES which reduce alpha motor neurones in the antaganist muscle causing it to relax.

Question 13

What happens when afferent info ascends up the dorsal column

Answer 13

make connections in somatsensory cortex to tell brain about brain muscle length

Question 14

Explain how stretch reflex is a classic negative feedback system

Answer 14

Muscle stretch - stimulates muscle spindles - cause reflex muscle contraction- muscles shorten to previous length

Question 15

Explain the inverse stretch reflex (clasp knife or golgitendon )

Answer 15

Caused by afferent nerves from the golgi tendon organs that minitor muscle tension.

Muscle contracts and shortens. this pulls on the tendon causing GTOs to fire more APs

Question 16

What does the inverse stretch reflex cause.

Answer 16

• Activates inhibitory interneurones to agonist muscle= reduces contraction strength.
• Activates excitory interneurones to antagonist muscles
• information about muscle tension goes up dorsal columns to somatosensory cortex

Question 17

Purpose of GTO reflex

Answer 17

Its protective and is polysynaptic to ensure muscles dont contract to hard that they tear the tendon

Question 18

Describe the Flexor withdrawal Reflex

Answer 18

polysynaptic and protective
and use pain receptors
in skin (ipsilateral response to pain)

one leg flexes to withdraw from the painful stimulus (on left)

the other extends to maintain balance because of shifted weight

Question 19

Steps of Flexor reflex

Answer 19

• activity in the flexor muscles of the affected part via a number of excitatory interneurones.
• At the same time, via a number of excitatory and inhibitory interneurones, the antagonistic extensors are inhibited.
• Several excitatory interneurones which cross the spinal cord excite the contralateral extensors
• At the same time, via several interneurones, there is inhibition of the contralateral flexors

this helps to maintain an upright posture by extending the limb to bear the body weight.
5. Sensory information ascends to the brain in the contralateral spinothalamic tract.

Question 20

Cab GTO be overridden?

Answer 20

Yes by cns
you wouldnt drop a child if it was suddenly heavy no?
: descending cortical excitatory and inhibitory signals : so continual integration of EPSPs and IPSPs
So when holding something heavy but very important, descending voluntary excitation of  motoneurones can override the inhibition from the GTOs and maintain contraction.

Question 21

Can stretch reflex be over ridden?

Answer 21

Yeaaaa,

strong descending inhibition hyperpolarizes α-motoneurones and the stretch reflex can not be evoked.
so when testing reflexes, subjects may need to be distracted to prevent voluntary effects on the reflex responses.
So the absence of stretch reflex responses in an uncooperative patient may not be evidence of peripheral nerve damage