Pathways

Question 1

What do descending pathways transmit?

Answer 1

motor commands (feedforward) to the spinal cord circuitry and also transmit the results of supraspinal processing of sensory afferent (feedback) information to the spinal cord

Question 2

Which pathways go through the brainstem into distal muscles?

Answer 2

Rubrospinal and corticospinal

Question 3

Rubrospinal tract

Answer 3

Originates in magnocellular portion of red nucleus in midbrain -> descend through medulla to dorsal part of lateral column SC

Question 4

Corticobulbar fibres

Answer 4

Motor nuclei in brain stem -> facial muscles

Question 5

What does the reticulospinal tract do?

Answer 5

Reticulospinal (medullary/lateral part) under cortical control inhibits spinal MNs and pontine (medial)part facilitates stretch reflexes. Innervate motoneurone pools of proximal and axial muscles: important for postural control

Question 6

What do ascending sensory pathways do?

Answer 6

Ascending sensory pathways feedback information to the spinal cord and the brain about ongoing motor control and for future task performance.

Question 7

Supraspinal motor control systems includes

Answer 7

motor cortex, cerebellum, basal ganglia, brain stem

Question 8

Supraspinal motor control systems require

Answer 8

proprioceptive and other sensory feedback to maintain accurate control and for the learning of new skills.

Question 9

Three main systems of ascending sensory pathways:

Answer 9

1) Dorsal columns: to sensory cortex
2) Spinothalamic tracts: to sensory cortex (Antero-lateral)
3) Spinocerebellar tracts: to cerebellum (Ventral and dorsal)

Question 10

Dorsal columns: to sensory cortex

Answer 10

– Large diameter afferents therefore fast conduction velocity
– Intensity and localisation of mechanical stimulus (light touch / pressure; movement against skin; position sense)
– High degree of discrimination

Question 11

Spinothalamic tracts: to sensory cortex (Antero-lateral)

Answer 11

– Smaller diameter afferents, therefore slower conduction velocity
– Touch and pressure but less localised, thus poor stimulus discrimination
– Temperature and noxious information

Question 12

Spinocerebellar tracts: to cerebellum (Ventral and dorsal)

Answer 12

• Signal: proprioception, Light and strong touch, Nociception, temperature

Question 13

How do the different locations of white matter tracts relate to their function?

Answer 13

Dorsal = sensory to BS
Ventral = descending axons
lateral = sensory, motor and autonomic + sensory to brain

Question 14

Where does the corticospinal tract originate?

Answer 14

Layer 5

Question 15

Medial corticospinal tract innervates…

Answer 15

Innervates proximal and axial muscles bilaterally

Question 16

Lateral corticospinal tract innervates…. and is important for…

Answer 16

Innervates predominately distal muscles but has a small ipsilateral projection; crosses at the pyramids of the medulla
fractionated movements eg. Relatively independent finger movements, and other selective movements

Question 17

Where do most CST neurones synapse?

Answer 17

Interneurones of spinal cord intermediate zone

Question 18

What happens during a stroke?

Answer 18

Direct CST damage -> loss of selected /fractionated movements

Question 19

CST roles

Answer 19

1. descending control of afferent inputs, including nociception
2. selection, gating, and gain control of spinal reflexes
3. direct and indirect excitation of motoneurones
4. Facilitates Ia inhibition via innervation of the 1a inhibitory interneuron in the spinal cord
5. Particularly important for dextrous movements