L4 Neuroanatomy 3

Question 1

What are the two major descending pathways in the motor cortex?

Answer 1

pyramidal and extrapyramidal systems

Question 2

What are the differences between the pyramidal and extrapyramidal systems?

Answer 2

• pyramidal:
  
  • voluntary movement
  • direct pathway to influence lower MNs
• extrapyramidal:
  
  • control and refinement of movements (e.g. regulation of antagonistic muscles)
  • involuntary movements (posture and support)
  • indirect pathway to influence lower MNs
  • tracts mostly found in pons and medulla
  • involves: basal ganglia, midbrain nuclei and cerebellum

Question 3

What are the tracts of the extrapyramidal system?

Answer 3

• rubrospinal
• reticulospinal
• vestibulospinal
• tectospinal

Question 4

rubrospinal tract

Answer 4

• originates from red nucleus of midbrain to spinal cord
• travels in lateral funiculus (mainly in cervical spinal segments)
• upper limb control

Question 5

reticulospinal

Answer 5

• originates from reticular formation of pons and medulla
• travels in lateral (medulla) and anterior (pons) funiculus
• automatic movements and posture

Question 6

vestibulospinal tract

Answer 6

• originates from the vestibular nuclei (medulla and pons)
• travels in anterior funiculus
• control of lower limb muscle tone for upright posture and balance

Question 7

tectospinal tract

Answer 7

• “tecto” = midbrain
• originates from midbrain colliculi (back of brainstem)
• travels in anterior funiculus (cervical)
• automatic postural movements of head in response to visual and auditory stimuli

Question 8

components of the basal ganglia control system

Answer 8

• cerebral nuclei:
  
  • corpus striatum:
    
    • globus pallidus
    • putamen
    • caudate nucleus
    • (thalamus)
• midbrain nuclei:
  
  • substantia nigra
  • subthalamic nucelus (caudal diencephalon)
• cerebellum: feedback loops to cerebral and midbrain nuclei

Question 9

Spacially, how are the nuclei of the basal ganglia related?

Answer 9

they are very close together due to their shared functionality and their need to share information between each other

Question 10

What are the parts of the corpus striatum?

Answer 10

• putamen
• globus pallidus
• caudate
• thalamus

Question 11

subthalamic nucleus

Answer 11

• located in the diencephalon
• functionally part of basal ganglia
• mostly glutamatergic neurons - i.e. excitatory
• reciprocal connections with basal ganglia (esp. globus pallidus)
• site for deep brain stimulation in Parkinson’s patients

Question 12

substantia nigra

Answer 12

• “black substance” visually looks black due to neuromelanin located in midbrain
• dopaminergic neurons (is lost in parkinson’s) degenerates in parkinson’s disease

Question 13

Describe the direct pathway of basal ganglia loops

Answer 13

FACILITATES MOVEMENT

1. glutamate neurons from UMNs (in the cerebral cortex) goes through corticostriatal fibres into the putamen
2. GABA neurons connects to another GABA neuron in the globus pallidus that connects to a glutamate neuron in the thalamus
3. the glutamate neuron sends signals back to the UMNs in the cerebral cortex via the thalamocortical fibres

Question 14

Draw the indirect pathway of basal ganglia loops

Answer 14

Question 15

Draw the interaction of the substantia nigra with the basal ganglia loops

Answer 15

Question 16

role of cerebellum in the basal ganglia

Answer 16

• fine movement, coordination, precision and timing
• involved in motor learning
• compares motor plan, motor action and sensory feedback to refine movement
• inputs to thalamus (feedback loop)

Question 17

ataxia

Answer 17

• cerebellar damage
• lack of voluntary coordination (w/o feedback, therefore movements are not smooth and unrefined)

Question 18

treatments for Parkinson’s that deal with the degenerative changes in S Nigra

Answer 18

admn of L-Dopa, surgical destruction of GP (surgical lesion will stop too much inhibition), deep brain stimulation

Question 19

DBS for Parkinson’s disease

Answer 19

high frequency impulses that are likely to inhibit subthalamic nucleus

Question 20

why is parkinson’s a “hypokinetic disease”?

Answer 20

• loss of dopaminergic neurons
• increases indirect pathway signalling → inhibition of slow movement