Overview of Central Sensory and Motor Pathways

Question 1

Which area of the central nervous system represents the
highest centre for processing of
sensory information and for
commanding of motor commands?

Answer 1

The cerebral cortex.

Question 2

Where in the cerebral cortex is sensory information represented?

Answer 2

In the primary sensory cortex.

Question 3

Where in the cerebral cortex are motor commands represented?

Answer 3

In the primary motor cortex.

Question 4

What separates the primary motor cortex from the primary sensory cortex?

Answer 4

The central sulcus of the cerebral cortex.

Question 5

What is an ascending tract?

Answer 5

Any fibre tract of the sensory system by which sensory information is conveyed to the brain.

Question 6

What are the 3 categories of ascending tracts?

Answer 6

• Dorsal spinocerebellar tract
• Ventral spinocerebellar tract
• Spinothalamic tract

Question 7

What is conscious sensation?

Answer 7

Sensation is said to be conscious sensation if we are directly
aware of the information.

Question 8

What is the significance of categorising sensation into conscious and unconscious sensation?

Answer 8

Sensations giving rise to conscious sensation are conveyed

differently from those not giving rise to conscious sensation.

Question 9

How do primary sensory neurones divide upon reaching the spinal cord?

Answer 9

• Into 3 branches:
• 1 axonal process terminates in the dorsal
  horn of its respective spinal segment and synapses with its respective secondary sensory neurone.
• Another axonal process is sent to the
  dorsal horn of the spinal segment above.
• Another axonal process is sent to the
  dorsal horn of the spinal segment below.

Question 10

In which anatomical entity are axonal segments travelling to the spinal segments above and below the level of origin carried in?

Answer 10

The posterolateral tract of Lissauer.

Question 11

Where in the dorsal horn do sensory fibres conveying pain terminate and synapse with the secondary sensory neurone? What is this area known as?

Answer 11

In laminae 3 and 4.

Known as nucleus proprius.

Question 12

What is the path taken by a secondary sensory neurone conveying pain and temperature information?

Answer 12

• First travels towards the midline and towards the central canal of the spinal cord.
• Then dives under the central canal.
• Then crosses the midline to emerge on the opposite side.
• Then into the white matter of the opposite side.
• Then into the lateral funiculus, joining the fibres of the lateral spino-thalamic tract.
• Then to the ventral posterolateral nucleus of the thalamus that is opposite to that on which the sensory signal arose.

Question 13

What is spinal decussation?

Answer 13

The crossing of secondary sensory neurones conveying pain and temperature information over the midline.

Question 14

What are fibres that comprise spinal decussation known as?

Answer 14

Anterior commissures or spinal arcuate fibres.

Question 15

What structures in the brain do secondary sensory neurones of the spinothalamic tract ascend?

Answer 15

The medulla, pons, midbrain and end in the ventral posterolateral nucleus of the thalamus.

Question 16

Where do secondary sensory neurones synapse with tertiary sensory neurones?

Answer 16

In the ventral posterolateral nucleus of the thalamus.

Question 17

Where do axons of tertiary sensory neurones terminate?

Answer 17

In the post-central gyrus of the cerebral cortex.

Question 18

What do axons of tertiary sensory neurones travel through?

Answer 18

The internal capsule.

Question 19

Why is the spinothalamic tract said to be somatotopically organised throughout its full extent?

Answer 19

Because the spatial mapping of the body’s surface is preserved within the tract.

Question 20

Fibres arising from which part of the body ascend dorsolaterally within the spinothalamic tract?

Answer 20

Fibres arising from the lowest part of the body.

Question 21

Fibres arising from which part of the body ascend ventromedially within the spinothalamic tract?

Answer 21

Fibres arising from the cervical cord.

Question 22

What is syringomyelia?

Answer 22

A disorder in which a cyst forms in the spinal cord.

Question 23

How is the way in which proprioceptive and tactile information is carried different from the way in which pain and temperature information is carried?

Answer 23

• Proprioceptive & Tactile
  information is carried on the
  same side of the spinal cord as
  its origin.

- Pain and Temperature
information crosses the
midline at the same
neural level as its
respective dermatome.

Question 24

Does proprioceptive and tactile information remain ipsilateral throughout its extent of transmission?

Answer 24

No. Only ipsilateral until the medulla, where it decussates.

Question 25

Where is the motor strip located?

Answer 25

In the precentral gyrus.

Question 26

What does the motor strip control?

Answer 26

Somatic / skeletal muscles of the body.

Question 27

How are neurones of the motor strip grouped?

Answer 27

According to the skeletal muscles they command.

Question 28

Are the brains motor commands of muscles decussated?

Answer 28

Yes.

Question 29

Where are the cell bodies of the neurones whose axons comprise descending tracts found?

Answer 29

In motor areas of the cerebral cortex such as the motor strip in the pre-central gyrus / frontal cortex.
- Form cortical descending tracts.

or

In sub-cortical areas of the brain such as the midbrain, brainstem, pons and medulla.
-Form non-cortical descending tracts.

Question 30

What are the two classes of descending tracts?

Answer 30

Cortical and non-cortical descending tracts.

Question 31

Where are the cell bodies of upper motoneurones found?

Answer 31

In the brain.

Question 32

Where are the cell bodies of lower motoneurones found?

Answer 32

In the spinal cord.

Question 33

What are the two classes of upper motoneurones?

Answer 33

Cortical efferents or pyramidal upper motoneurones.

and

Brainstem efferents or extra-pyramidal upper motoneurones

Question 34

Where can cell bodies of lower motoneurones be found outside of the ventral horn of the spinal cord?

Answer 34

In the motor nuclei of the cranial nerves in the brainstem.