King Ch 10, Part I - Spinocerebellar pathways

Question 1

What are the two extensive ascending afferent systems in the CNS that do not reach conscious perception?

Answer 1

Spinocerebellar pathways and ascending reticular formation

Question 2

What type of information do the spinocerebellar pathways transmit?

Answer 2

Information to the cerebellar cortex from muscle proprioceptors about the activity of all skeletal muscles

Question 3

What is the dorsal spinocerebellar tract also known as?

Answer 3

Direct spinocerebellar tract

Question 4

List the three characteristics of the dorsal spinocerebellar tract.

Answer 4

• It does not decussate
• It lies close to the dorsal horn
• It enters the cerebellum by the nearest (caudal cerebellar) peduncle

Question 5

Where does neuron 1 of the dorsal spinocerebellar tract originate?

Answer 5

In the dorsal root ganglion of a spinal nerve serving a hindlimb

Question 6

What is the cell location of neuron 2 in the dorsal spinocerebellar tract?

Answer 6

Base of the dorsal horn

Question 7

What type of fibers are found in the dorsal spinocerebellar tract?

Answer 7

Very large diameter (about 20 μm) and fast conducting (about 120 m/s)

Question 8

What is the thoracic nucleus previously known as?

Answer 8

Dorsal nucleus of Clarke or Clarke’s column

Question 9

What is the ventral spinocerebellar tract also known as?

Answer 9

Indirect spinocerebellar tract

Question 10

List the two characteristics of the ventral spinocerebellar tract.

Answer 10

• It decussates twice
• It lies relatively far away from the dorsal horn

Question 11

What type of receptor does neuron 1 of the ventral spinocerebellar tract receive information from?

Answer 11

Golgi tendon organ

Question 12

Where does neuron 2 of the ventral spinocerebellar tract decussate?

Answer 12

Immediately after its cell location in the base of the dorsal horn

Question 13

What is the cell location of neuron 1 in the spinocuneocerebellar pathway?

Answer 13

Dorsal root ganglion of a spinal nerve serving the forelimb

Question 14

What is the role of the lateral cuneate nucleus in the spinocuneocerebellar pathway?

Answer 14

It is homologous to the thoracic nucleus and serves as the location for neuron 2

Question 15

What differentiates the cranial spinocerebellar tract from the ventral spinocerebellar tract?

Answer 15

• Being ipsilateral throughout
• Entering the cerebellum via the caudal and rostral cerebellar peduncles

Question 16

What is the contribution of muscle proprioceptors to the cerebral cortex?

Answer 16

General perception of the movement and position of the limbs (kinaesthesia)

Question 17

How many neurons are involved in the pathway from muscle proprioceptors of the hindlimbs to the cerebral cortex?

Answer 17

Four neurons

Question 18

What do the spinocerebellar pathways inform the cerebellum about?

Answer 18

Activities of all the skeletal musculature throughout the whole body

Question 19

What is notable about spinocerebellar tracts in ungulates?

Answer 19

Well developed dorsal and ventral spinocerebellar tracts in ungulates

Question 20

What modality do the spinocerevellar tracts transmit?

Answer 20

They
transmit the modality of muscle proprioception only

Question 21

How many neurons are in the main spinocerebellar pathways?

Answer 21

Two neuron pathways

Question 22

Name the spinocerebellar pathways from the pelvic limbs

Answer 22

Dorsal spinocerebellar tract and ventral spinocerebellar tract

Question 23

Describe the pathway of the dorsal spinocerebellar tract

Answer 23

Receptor is a muscle spindle > cell of the first neuron in the dorsal root ganglion of a PL spinal nerve > axon projects into the dorsal horn > axon does not decussate and ascends in the dorsal spinocerebellar tract in the dorsolateral region of the lateral funiculus > enters the cerebellum by the caudal cerebellar peduncle > ends somatotopically on the cerebellar cortex

Question 24

Describe the pathway of the ventral spinocerebellar tract

Answer 24

Receptor is a Golgi tendon organ > cell of the first neuron is in the dorsal root ganglion of a PL spinal nerve > axon decussates immediately > axon ascends rostrally in the ventral spinocerebellar tract, in the ventrolateral region of the lateral funiculus > ascends to the level of the rostral cerebellar peduncle > turns caudally into the rostral cerebellar peduncle > enters the cerebellum > decussates for the second time > axons therefore ends on the same side that it started

Question 25

Name the spinocerebellar pathways from the thoracic limbs

Answer 25

The spinocuneocerebellar pathway and the cranial spinocerebellar pathway

Question 26

Describe the pathway of the spinocuneocerebellar pathway

Answer 26

Receptor is a muscle spindle > cell of the first neuron in the dorsal root ganglion of a TL spinal nerve > axon enters the ipsilateral cuneate fascicle of the dorsal funiculus > synapse with the lateral cuneate nucleus of the medulla oblongata > axon travels rostrally in the cuneocerebellar tract > enters the cerebellum via the ipsilateral caudal cerebellar peduncle > ends somatotopically in the ipsilateral cerebellar cortex

Question 27

Describe the pathway of the cranial spinocerebellar pathway

Answer 27

Receptor is a golgi tendon organ > cell of the first neuron in the dorsal root ganglion of a TL spinal nerve > neuron two cell body at the dorsal horn > axon enters the ipsilateral cranial spinocerebellar tract, which lies on the medial aspect of the ventral spinocerebellar tract > axon enters the cerebellum through either the rostral or the caudal cerebellar peduncle > ends somatotopically on the ipsilateral cerebellar cortex

Question 28

What is the purpose of information from muscle proprioceptors projecting to the cerebral cortex?

Answer 28

Contributes to the general perception of the movement and position of the limbs (the sense of kinaesthesia).

Question 29

Describe the pathway of conscious perception of muscles from the pelvic limbs

Answer 29

Neuron 1 in dorsal root ganglion > neuron 2 at the base of the dorsal horn (thoracic nucleus) > axons in the dorsal spinocerebellar tract form collaterals as the tract enters the medulla oblongata > the collaterals and the tract diverge and synapse with neurons in a displaced fragment of the gracile nucleus, known as nucleus Z > axons of these neurons join the medial lemniscus > project via the ventral thalamic nuclei > to the primary somatic sensory area of the cerebral cortex ## Footnote 4 neuron pathway

Question 30

Describe the pathway of conscious perception of muscles from the thoracic limbs

Answer 30

Collaterals from the spinocuneocerebellar pathway > synapse with neurons in nucleus X which lies near the lateral cuneate nucleus > axons of these neurons join the medial lemniscus > project via the ventral thalamic nuclei > to the primary somatic sensory area of the cerebral cortex ## Footnote 4 neuron pathway

Question 31

Where do the thoracic spinocerebellar pathways come in at the spinal cord?

Answer 31

Cranial to T8