Motor pathways

Question 1

Give 2 properties of motor control.

Answer 1

• Functional segregation:
• Hierarchical organisation: high order areas of hierarchy are involved in more complex tasks (programme and decide on movements, coordinate muscle activity) lower level areas of hierarchy perform lower level tasks (execution of movement)

Question 2

Fill in the table of motor system hierarchy

Answer 2

table

Question 3

LO 35 Describe the location, function and organisation of Primary motor cortex

Answer 3

• Location: precentral gyrus, anterior to the central sulcus
• Function: control fine, discrete, precise voluntary movement Provide descending signals to execute movement
• Somatotopic organisation: Penfield’s motor homunculus

Question 4

LO 36 Name and describe the 2 descending motor pathways (which muscles do they supply): Corticobulbar pathways

Answer 4

• The Lateral Corticospinal tract: to skeletal muscles in the distal parts of the limbs
• The Anterior Corticospinal tract: to skeletal muscles in the trunk and proximal parts of the limbs
• Corticobulbar pathway: motor cortex neuron -> synapse in hypoglossal nucleus in medulla-> hypoglossal nerve -> geniohyoid and genioglossus muscles

Question 5

LO 35 Describe the location, function and organisation of premotor cortex.

Answer 5

• Location: frontal lobe anterior to M1
• Function: planning of movements, Regulates externally cued movements

Question 6

LO 35 Describe the location, function and organisation of supplementary motor area.

Answer 6

• Location: frontal lobe anterior to M1, medially
• Function: planning complex movements; programming sequencing of movements, Regulates internally driven movements (e.g. speech) SMA becomes active when thinking about a movement before executing that movement

Question 7

Define : lower motor neuron upper motor neurone Pyramidal Extrapyramidal

Answer 7

• Lower motor neuron: Spinal cord, brainstem
• Upper motor neuron: Corticospinal, corticobulbar
• Pyramidal: Lateral corticospinal tract
• Extrapyramidal: Basal ganglia, cerebellum

Question 8

Name and describe the 2 association cortex

Answer 8

• Posterior parietal cortex:ensures movements are targeted accurately to objects in external space
• Prefrontal cortex:involved in selection of appropriate movements for a particular course of action

Question 9

LO 37 Give the features of upper motor neuron lesion

Answer 9

• Loss of function (negative signs):
  
  • Paresis: graded weakness of movements
  • Paralysis (plegia): complete loss of muscle activity
• Increased abnormal motor function (positive signs) due to loss of inhibitory descending inputs:
  
  • Spasticity: increased muscle tone
  • Hyper-reflexia: exaggerated reflexes
  • Clonus: abnormal oscillatory muscle contraction
• Babinski’s sign

Question 10

Give the features of Apraxia

Answer 10

lost information about how to perform skilled movements Lesion of inferior parietal lobe, the frontal lobe (premotor cortex, supplementary motor area)

Question 11

Give the features of Lower motor neuron lesion

Answer 11

• Weakness Hypotonia (reduced muscle tone)
• Hyporeflexia (reduced reflexes)
• Muscle atrophy
• Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch
• Fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination

Question 12

LO 38 Give the features of Motor neuron disease (MND)

Answer 12

Progressive neurodegenerative disorder of the motor system Presents as a spectrum of disorders eg Amyotrophic Lateral Sclerosis (ALS) Upper motor neuron signs Increased muscle tone (spasticity of limbs and tongue) Brisk limbs and jaw reflexes Babinski’s sign Loss of dexterity Dysarthria Dysphagia Lower motor neuron signs Weakness Muscle wasting Tongue fasciculations and wasting Nasal speech Dysphagia