functional hierarchy of motor system

Question 1

what type of neurones is voluntary brain control of muscles via

Answer 1

alpha-motoneurones in the spinal cord

Question 2

which 4 systems control movement

Answer 2

descending control pathways
basal ganglia
cerebellum
local spinal cord/brain stem circuits

Question 3

spinal cord spatial map of body musculature

Answer 3

medio-laterally (applies to arms and legs)

proximal shoulder muscles are mapped to medial motoneurones
distal finger muscles map to more lateral motoneurones

Question 4

what levels does sensory input enter

Answer 4

spinal cord: proprioceptors, touch, pain etc
brainstem: vestibular info about balance
cortical level: movements in response to visual, olfactory, auditory, emotional, intellectual cues

Question 5

stretch reflex

Answer 5

sharp tap on inelastic tendon
force transmitted to muscle fibres which stretch
stretch activates sensory nerves in muscle spindle: this increases number of APs in afferent nerves projecting through dorsal horn into spinal cord

Question 6

stretch reflex: spindle sensory afferents divide and make 3 types of connections…

Answer 6

1. activate a-motoneurones to sretched muscle causing rapid contraction of agonist muscle
2. sensory fibres from stretched muscle contatc antagonist muscle, causing it to relax (stretch)
3. spindle afferent info ascends in dorsal column and makes connections in somatosensory cortex to tell brain about muscle lengths

Question 7

golgi-tenson organ/clasp knife reflex

Answer 7

caused by afferent nerves from Golgi Tendon Organs which monior muscle tension

muscle contracts and shortens - this pulls strongly on the tendon and 1b sensory nerves from the GTOs inc APs

Question 8

what does golgi-tendon organ reflex cause

Answer 8

1. activation inhibitory interneurones to agonist muscle and decrease in contraction strenght
2. activation of excitatory interneurones to antagonist muscles
3. info about muscle tension ascends in dorsal columns to the somatosensory cortex

Question 9

how is GTO reflex protective

Answer 9

it prevents muscles contracting so hard that the tenon insertion is torn away from bone

Question 10

flexor//withdrawal reflex

Answer 10

use info from pain receptors in skin, muscles, joints

polysynaptic and protective

withdraw part of body away from painful stimulus and in towards the boy - so they flex the affected part

Question 11

how does flexor withdrawal reflex work

Answer 11

inc sensory APs from pain receptors cause

1. inc activity flexor muscles
2. anagonistic extensors inhibited
3. contraleterol extensors excited
4. contralateral flexors inhibited
5. sensory info ascends to the brain in contralatteral spinothalamic tracts