Motor control

Question 1

simple reflexes

Answer 1

local circuit control of spinal motor neurons by spinal sensory neurons
all movements produced by skeletal muscles are initiated by lower motor neurons

Question 2

Spinal cord contains central pattern generators, what do they do?

Answer 2

they can generate complex behaviours without input from the brain
-however, subsystems in the brain can influence these behaviours

Question 3

how do we know subsystems in the brain influence behaviours generated by central pattern generators?
Fitsch and Hitzig found?

Answer 3

stimulation of motor cortex elicits muscle movement

• demonstrated electrical stimulation of part of the cortex elicits contraction of contralateral body muscles(in dogs)
• region known as motor cortex// primary motor cortex

Question 4

What are neurons called that control motor function?

Answer 4

upper motor neurons

Question 5

Motor cortex = somatopically mapped

Sherrington and Penfield?

Answer 5

correlated the site of stimulation with location of muscle contraction and demonstrated a topographic map similar to that of the somatosensory system
(proportions reflect density of innervation and behavioural signficance)

Question 6

Somatotopy in motor cortex reflects topological organisation of spinal motor neurons

Answer 6

-each lower motor neuron innervates the fibres of just one muscle

Question 7

What is ‘motor pool’?

Answer 7

all motor neurons innervating a muscle

they’re grouped in rod-shaped clusters within the spinal cord extending over several vertebral segments

Question 8

Innervation for each muscle and its postiion?

Answer 8

Innervation for each muscle occupies a distinct mediolateral and rostrocaudal position within the ventral horn of the spinal cord

Question 9

How are motor pools organised?

Answer 9

somatotopically

=theres a map of the bodys musculature in the spinal cord

Question 10

Different upper motor neurons control different functions.
Motor cortex?
Brainstem?
Somatosensory cortex?

Answer 10

motor cortex = fine control of more distal structures
brainstem = project to medial motor pools = primarily concerned with postural movements
Somatosensoy cortex:
upper body inputs go lateral
lower body inputs go medial

Question 11

Axons of layer V cortical neurons (Betz cells)

Answer 11

-project in cortical tract
-cross midline at pyrimidial decussation in medulla
-synapse on more lateral lower motor neuron circuits in spinal cord (controlling distal muscles)
=LATERAL PATHWAY

Question 12

Axons from brainstem project ipsilaterally in several tracts

Answer 12

-synapse on more medially located lower motor neuron circuits (MNs or interneurons in spinal cord controlling more axial muscles)
=VENTROMEDIAL PATHWAYS

Question 13

Cortical layers:
main inputs?
main outputs?
axons?

Answer 13

• 90% of cortex is 6 layered structure
• main inputs = to stellate cells in layer IV
• main outputs = from layers: III, V, VI
• axons of corticospinal tract derive from large pyramidial or Betz cells in layer V

Question 14

Upper motor neuron control
Motor cortex
 - contralateral or ipsi?
- via which tract?
Brain stem
-function?
-contralateral or ipsi?
-control which muscles?

UMN synapse on what?
LMN synapse on what?

Answer 14

motor cortex = initiate voluntary movements

• project mainly contralaterally via the corticospinal tract (to muscles involved in precise limb movement)
• also project to corticobulbar tract to the hypoglossal nucleus in brainstem

brainstem =maintenance of posture, located in several nuclei including: vestibular nucleus, reticular formation, superior colliculus
-project ipsilaterally to lower motor neurons controlling axial muscles (for maintaining posture)

UMN - synapse on lower motor neurons
LMN- synapse on muscle fibres

Question 15

Integration of postural control with voluntary movements
study lifting lever after tone - which muscle contracted first?
‘feed forward’ mechanism?

Answer 15

in study leg muscle contracted first = anticipatory ‘feed forward’ mechanism that pre-adjusts body posture to compensate for forces generated when lifting lever

Question 16

Indirect and direct route of control of lower motor neurons

Answer 16

feed forward mechanisms make sense when you realise MNs in the cortex influence spinal cord circuits by 2 routes (AREA4 and AREA6)
planning and initiation in primary and premotor corticles, then either:
1 route: anticipated indirect projection via reticular formation to muscles –uses the corticoreticulospinal tract)
2 route: activation of voluntary movement direct to spinal cord via corticospinal tract

Question 17

Which circuit does this ‘anticipation’ mechanism use?

Answer 17

The motor cortex UMNs( = fine control of distal structures) sends info to anticipate movements to the brainstem UMNs (=to medial motor pools concerned with posture)
(Motor cortex innervates both the brain stem and spinal cord)

Question 18

Motor Neuron Disease (Amyotrophic lateral sclerosis)
define
what does it affect?
2 types?

Answer 18

a degenerative disease of motor neurons
-can affect upper or lower motor neurons
Lower motor neuron disease:
paralysis, loss of muscle tone, muscle atrophy, usually die from lung dysfunction
Upper motor neuron disease:
muscle weakness, increase muscle tone, hyperactive reflexes, loss of fine voluntary movement

Question 19

Basal Ganglia and Cerebellum
roles?
influence?

Answer 19

BG = gating proper initiation of movement
C = sensory motor coordination
these structures influence movement indirectly by regulating the function of upper motor neurons

Question 20

Role of Motor loop?
Explain Motor loop involving:
Basal ganglia
premotor area
thalamus

Answer 20

motor cortex connects to it, which feedback to the premotor area (area6) via the ventrolateral complex of the thalamus (VLo) to control initiation of movement.
This is known as the motor loop

Question 21

Basal Ganglia in the initiation of movement

Huntingdons disease caused by? leads to?

Answer 21

With no initiating cortical input Globus Pallidus tonically inhibits the VLo due to tonic activation from the caudate/ putamen (striatum)
input from many cortical regions converges on striatum
When activated by this input, the striatum inhibits the inhibitory activity of the GP, relaxing the VLo to activate Area6 and initiate movement!!
(In huntingtons disease = degeneration of striatum = reduced tonic inhibition and increase in initiation of hypokinesia)

Question 22

Difference between hyperkinesia and hypokinesia?

Answer 22

hyperkinesia = muscle spasm 
hypokinesia = loss of muscle movement

Question 23

Parkinsons disease leads to hypokinesis - how?

Answer 23

Substantia nigra degeneration = hypokinesis

Question 24

Basal ganglia composed of:

Answer 24

caudate, putamen and globus pallidus

Question 25

Cerebellum - required for?
receieves many inputs from?
projects back to? via the?
primary functions?
Lesions?

Answer 25

• required for the proper execution of planned, voluntary, multijoint movements
• cerebellum forms loop with motor cortex and receives massive input from many areas of cortex, corticopontocerebellar projection and sensory info from spinal cord and vestibular system
• projects back to the motor cortex via the thalamus but it has no direct output to spinal cord
• primary functions: to detect and correct difference between the intended movement and actual movement = motor error
• lesions to the cerebellum = cerebellar ataxia (poorly integrated movement)
• cerebellum - major target in BSE - characterised by cerebellar ataxia (BSE = bovine spongiform encephalitis = caused by neuronal degeneration cause by self-replicating protein)