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Flashcards in Motor control Deck (25)
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1
Q

simple reflexes

A

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

2
Q

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

A

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

3
Q

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

A

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
4
Q

What are neurons called that control motor function?

A

upper motor neurons

5
Q

Motor cortex = somatopically mapped

Sherrington and Penfield?

A

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)

6
Q

Somatotopy in motor cortex reflects topological organisation of spinal motor neurons

A

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

7
Q

What is ‘motor pool’?

A

all motor neurons innervating a muscle

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

8
Q

Innervation for each muscle and its postiion?

A

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

9
Q

How are motor pools organised?

A

somatotopically

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

10
Q

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

A

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

11
Q

Axons of layer V cortical neurons (Betz cells)

A

-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

12
Q

Axons from brainstem project ipsilaterally in several tracts

A

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

13
Q

Cortical layers:
main inputs?
main outputs?
axons?

A
  • 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
14
Q
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?

A

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

15
Q

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

A

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

16
Q

Indirect and direct route of control of lower motor neurons

A

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

17
Q

Which circuit does this ‘anticipation’ mechanism use?

A

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)

18
Q

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

A

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

19
Q

Basal Ganglia and Cerebellum
roles?
influence?

A

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

20
Q
Role of Motor loop?
Explain Motor loop involving:
Basal ganglia
premotor area
thalamus
A

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

21
Q

Basal Ganglia in the initiation of movement

Huntingdons disease caused by? leads to?

A

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)

22
Q

Difference between hyperkinesia and hypokinesia?

A
hyperkinesia = muscle spasm 
hypokinesia = loss of muscle movement
23
Q

Parkinsons disease leads to hypokinesis - how?

A

Substantia nigra degeneration = hypokinesis

24
Q

Basal ganglia composed of:

A

caudate, putamen and globus pallidus

25
Q
Cerebellum - required for?
receieves many inputs from?
projects back to? via the?
primary functions?
Lesions?
A
  • 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)