L17 Sensory and Motor Pathways

Question 1

Three areas of the cerebral cortex

Answer 1

Motor areas, sensory areas, and association areas; receives and processes sensory information and integrates motor functions.

Question 2

Ventral ramus vs dorsal ramus

Answer 2

Limbs and ventral trunk vs dorsal trunk

Question 3

Cervical enlargement vs lumbosacral enlargement

Answer 3

arms vs legs

Question 4

Somatosensory pathway, neurons

Answer 4

DCML system and A/ST system;

1st order neuron: the primary afferent
2nd: in spinal cord
(anterolateral system) or in the brain stem (dorsal column system); decussation
3rd: in the somatosensory
nuclei of the thalamus
4th: in the
somatosensory cortex

Question 5

Dorsal column medial lemniscus system function

Answer 5

fine touch, pressure,
vibration, and two-point
discrimination

Question 6

Anterolateral (spinothalamic)
system function

Answer 6

pain, temperature, and
crude touch

Question 7

Spinocerebellar Pathways, function and inclusions

Answer 7

Carry proprioceptive information to the cerebellum for motor coordination
- Dorsal/posterior spinocerebellar tract
- Ventral/anterior spinocerebellar tract
- Cuneocerebellar tract
- Rostral spinocerebellar tract

Question 8

Dorsal/posterior spinocerebellar tract function

Answer 8

carries proprioceptive information from the lower limbs and trunk to the ipsilateral cerebellum; no decussation.

Question 9

Ventral/anterior spinocerebellar tract

Answer 9

carries proprioceptive information from the lower limbs to the ipsilateral cerebellum; double decussation.

Question 10

Cuneocerebellar tract

Answer 10

carries proprioceptive
information from the upper limbs to the ipsilateral cerebellum; no decussation.

Question 11

Rostral spinocerebellar tract

Answer 11

carries proprioceptive information from the upper limbs to the ipsilateral cerebellum.

Question 12

Dorsal column pathways (nerve types, 2nd neuron site/desuccation, 3rd neuron, function)

Answer 12

• Large myelinated axons (G I/II or Aa/Ab)
• Medulla, contralateral
• Ventral posterior lateral nucleus of the thalamus
• Fine-touch, pressure, vibrations

Question 13

Anterolateral pathways (nerve types, 2nd neuron site/desuccation, 3rd neuron, function)

Answer 13

• Lightly myelinated/unmyelinated small axons (Group III/IV, Ad/c)
• Spinal cord, contralateral
• Ventral posteroinferior nucleus
• pain , temp, crude touch

Question 14

Spinocerebellar pathways (nerve types, 2nd neuron site/desuccation, 3rd neuron, function)

Answer 14

• Large myelinated axons (group I/II, Aa/Ab)
• No decussations (spinal cord/cerebellum), ipsilateral
• no 3rd order neuron
• Movement coordination, balance

Question 15

Somatomotor cortex and areas

Answer 15

One motor areas, supplemental motor areas and premotor cortex. Functions for planning, control and execution of voluntary movements.

Question 16

Lower motoneurons

Answer 16

Lies in the nucleus of the brain stem as it relates to cranial nerves, or in the spinal cord for peripheral nerves.

Question 17

Upper Motoneurons

Answer 17

Lie in the cerebrum and brain stem and synapse on the lower motoneuron that inner gates a single motor unit in skeletal muscle.

Question 18

Lateral Motor Pathways

Answer 18

• Lateral corticospinal tracts
• Rubrospinal tracts

Question 19

Medial motor pathways

Answer 19

• Ventral corticospinal tract (or anterior/medial corticospinal tract)
• Pontine and medullary reticulospinal tracts
• Lateral and medial vestibulospinal tracts
• Tectospinal tracts
• Corticobulbar tracts: controls brainstem nuclei that innervate cranial muscle

Question 20

Lateral corticospinal tracts (pathway, functions)

Answer 20

Originate in primary motor cortex and other areas.
• The upper motoneurons/Betz cells in the motor cortex → the internal capsule → the cerebral
peduncle → the basilar pons → the pyramids → 90% of the fibers decussate and enter the lateral white matter columns of the spinal cord → lower motoneurons in the lateral portions of the spinal cord.
(10% form the Ventral/Anterior Corticospinal Tract)
• Function: provide voluntary control over skeletal muscles of the limbs.

Question 21

Rubrospinal tracts (pathway, functions)

Answer 21

Begin in the red nucleus of midbrain, where fibres immediately decussate and descend through the pons and medulla into the spinal cord.
• Regulation of limb muscle movement after corticospinal tract injury.

Question 22

Medial pathways that originate in the motor cortex

Answer 22

Ventral corticospinal tracts
Corticobular tracts

Question 23

Originate in the brain stem

Answer 23

Pontine and medullary reticulospinal tracts
Vestibulospinal tracts
Tectospinal tracts

Question 24

Ventral corticospinal tracts (pathway and function)

Answer 24

10% of the fibers that travel in the corticospinal tract
Dessucate at the spinal cord only
Control movement of axial muscles in the trunk

Question 25

Corticobulbar tracts (pathway and function)

Answer 25

Terminate on motoneurons in the brain stem
50% dessuctae above relevant motor nuclei in the brain stem
Supply the head and neck muscles

Question 26

Pontine and medullary Reticulospinal tracts (pathway and function)

Answer 26

Arise from the pons and medulla respectively, do not cross.
Involved in locomotion and postural control

Question 27

Lateral and medial vestibulospinal tracts (pathway and function)

Answer 27

Originate in the lateral and medial vestibular nucleus in pons and the medulla, do not cross.
Positioning of the head and neck (medial) and balance (lateral)

Question 28

Tectospinal tracts (pathway and function)

Answer 28

Originate in the midbrain, cross contralaterally.
Coordinate head and eye movements.

Question 29

Pyramidal tract syndrome/upper motoneuron disease (mechanism, causes, symptoms)

Answer 29

Interruption of the cerebral cortical efferent fibers in the internal capsule, damage to corticospinal tracts.
Stroke, brain or spinal injury, cerebral palsy, MS, ALS.
Hyperreflexia, hypertonia, muscle weakness, clonus, Babinski sign.