Introduction to the Nervous System

Question 1

From which germ layer is most of the nervous system derived?

Answer 1

Ectoderm

Question 2

What is primary neuralation and when does it occur?

Answer 2

• Formation of the neural tube, caudal portion.
• 3rd-4th week of gestation.

Question 3

What is secondary neuralation and when does it occur?

Answer 3

• Neural tube formation, sacral portion and coccyx of the spinal column.
• 4th-5th week of gestation.

Question 4

What is prosencephalon development and when does it occur?

Answer 4

• Neural tube ventral induction, face and cerebral hemispheres formation.
• 2nd-3rd month of gestation.

Question 5

What is proliferation and neuronal migration and when do they occur?

Answer 5

• Proliferation
  
  • Neuronal proliferation, of radial glial cells and glia.
  • 3rd-4th month of gestation.
• Neuronal migration
  
  • Dislocation of neuronal cells from the germinal matrix to the cerebral cortex.
  • 3rd-5th month of gestation.

Question 6

What is the organisation stage of neural development and when does it occur?

Answer 6

• Neuron differentiation (alignment, formation of cortical layers), synapse development (axonal and dendritic branching), apoptosis, proliferation and differentiation of glia.
• 5th month of development and postnatal.

Question 7

What is myelination and when does it occur?

Answer 7

• Acquisition of the myelin sheath that will cover the axons.
• Birth and postnatal.

Question 8

What are the adult derivatives of the brain vesicles?

Answer 8

Question 9

Describe the progression from progenitor cells into differentiated neural cells.

Answer 9

Question 10

What is the role of Schwann cell?

Answer 10

Schwann cells myelinate axons in the peripheral nervous system. Each schwann cell makes 1 myelin.

Question 11

Describe the assessment of the working order of the frontal lobe.

Answer 11

• Sequencing and fluency
• Luria hand sequencing task.
• Verbal fluency 1 minute word F, A, S, animals.

Question 12

Describe the assessment of the working order of the temporal lobes.

Answer 12

• Memory and speech
• Address test
• Object recall
• Serial 7s

Question 13

Describe the assessment of the working order of the parietal lobes.

Answer 13

• Spatial awareness (R), language (L)
• Clock face
• Naming objects
• Drawing cube, interlocking infinity
• Agnosia

Question 14

Give each visual field disturbance based on the site of each lesion.

Answer 14

Question 15

Describe the different parts of the brainstem.

Answer 15

• Posterior cranial fossa
• 3 parts:
  
  • Link
    
    • ​Cerebellum
    • Spinal cord
    • Cerebral hemisphere
  • Nuclei
    
    • ​Motor coordination
    • Reticular formation
    • Vital and non-vital centres
    • Cranial nerves
  • Function
    
    • ​Dependent on location

Question 16

What is the difference between the central grey matter in the spinal cord and in the brainstem.

Answer 16

• Central grey matter more vertical in the spinal cord.
• Central grey matter more horizontal in the brainstem.

Question 17

Give an overview of the origin of cranial nerves.

Answer 17

Question 18

Describe the most likely cranial nerve defect associated with a brainstem lesion.

Answer 18

A brainstem lesion will usually produce ipsilateral cranial nerve defects.

Question 19

What are the nucleus ambiguous and nucleus solitarius responsible for?

Answer 19

• aMbiguous = Motir (somatic motor: speech, swallowing).
• Solitarius = Sensory (visceral sensory: taste, gag, involuntary reflexes).

Question 20

Describe the sympathetic output from the hypothalamus.

Answer 20

• Facial sweating, eyelid elevation, vasomotor and pupil dilation.
• Descends mainly uncrossed.
• A brainstem lesion will produce an ipsilateral Horner’s syndrome.

Question 21

Describe Horner’s syndrome.

Answer 21

Question 22

Describe the different modalities of clinical sensory testing.

Answer 22

Question 23

Summarise the dorsal column medial leminiscal pathway.

Answer 23

Question 24

Give examples of conditions that may affect the dorsal spinal cord.

Answer 24

• Vitamin B12 deficiency (SCDC)
• HIV myelopathy
• Tabes dorsalis (syphilis)
• Multiple sclerosis

Question 25

Describe the arrangement of the primary somtosensory cortex.

Answer 25

Question 26

Where do spinothalamic tract fibres cross?

Why is this clinically important.

Answer 26

• Spinothalamic tract fibres cross early.
• This makes them susceptible to central cord pathology.

Question 27

Summarise which tracts carry which types of sensation to the central nervous system.

Answer 27

Question 28

Describe the structure of a voluntary movement.

Use drinking a glass of wine as an example.

Answer 28

• Sensory intergation
  
  • ​Target identification; glass of wine needs to be identified as such and its location understood.
• Planning
  
  • ​Movements required to bring glass of wine to mouth must be ascertained. Relative positions of wine and mouth need to be computed so movement can be planned.
• Execution
  
  • ​Commands from cortical and brainstem centres need to be ordered and initiated in order to provide the correct strength grip and to smoothly move the glass from the table to the mouth.
• Each phase involved the involvement of distinct areas of the cerebral cortex as well as feedback from basal ganglia and cerebellum.

Question 29

Describe the motor connections of the supplementary and premotor areas.

Answer 29

• If primary motor area is destroyed, initially electrical stimulation of either premotor areas has no effect.
  
  • Therefore, their principal actions are mediated through the primary motor cortex.
• Damage to the premotor areas produces more complex deficits:
  
  • Apraxia - cannot perform tasks that involve a complex sequence of movements like brushing one’s hair or drawing a quick sketch.
  • Role has been investigated by measuring cerebral blood flow (fMRI).

Question 30

Describe the parietal cortex.

Answer 30

• The role of the parietal cortex (as most association areas) is multifaceted.
• It receives signals from a number of sources but is primcipally involved with spatial processing of visual stimuli.
• This information can be integrated in the planning of a sequence of motor outputs.
  
  • Somatic sensory area (about limb position).
  • Vestibular system (about head position).
  • Premotor areas (about motor plans).
  • Visual system.
  • Limbic cortex (about motivational state).
• The motor system as a whole integrates information from these modalities to focus attention on relevant target and / or upon the spatial relationships of objects of interest.
• Some neurons in this area are context-specific and are only active when the hand is exploring an object of interest.

Question 31

Where are the primary spinal motor control routes?

Answer 31

Corticospinal tracts

Question 32

Describe the corticospinal tracts.

Answer 32

• Contain about 1,0000,000 nerve fibres, about 1/3 of which come from the primary motor cortex.
• Most of the remainder come from pre-motor areas and association areas.
• Most axons in the corticospinal tract decussate at the ventral pyramids in the brainstem (pyramidal or lateral corticospinal tract).
• 10% remain ipsilateral until they finally innervate bilaterally at the level of their ventral root (anterior / medial corticospinal).
• The axons in the lateral tract are excitatory and control distal muscle (for example, the digits).

Question 33

What are the inputs to the corticospinal output that fine tune movement?

Question 34

Summarise the neural elements controlling movement.

Answer 34

Question 35

What are the 2 major systems of descending pathway from the brain to motor centres?

Answer 35

• Lateral pathways
  
  • ​Control voluntary movements
  • Control distal muscles
  • Mainly controlled by cerebral cortex (via the corticospinal tracts)
• Ventromedial (medial) pathways
  
  • ​Mainly control posture and locomotion
  • Control the axial and proximal muscles
  • Mainly controlled by the brainstem
  • Mainly uncrossed

Question 36

What are the signs of upper and lower motor neuron lesions?

Answer 36

Question 37

Describe upper motor neuron pattern weakness.

Answer 37

• Arm extensors weaker than felexors (flexors are stronger).
• Leg flexors are weaker than extensors (extensors are stronger).

Question 38

What is polymyalgia rheumatica?

Answer 38

A condition in the elderly which comes in association with temporal arteritis - patients wake up with pain particularly around the shoulders and neck. Responds very well to steroids.

Question 39

What is scotoma?

Answer 39

A blank spot in the visual field.