Descending Neural Pathways

Question 1

What are the two decending motor pathways?

Answer 1

Lateral and ventromedial pathways

Question 2

What modality travels in the lateral pathway?

Answer 2

Control of voluntary movements, control of mainly distal muscles. This is controlled by the cerebral cortex via corticospinal tracts

Question 3

What modality travels in the ventromedial pathway?

Answer 3

mainly the control of muscles for posture and locomotion. Controls axial and proximal muscles and mainly conrolled by the brainstem

Question 4

What are features of the premotor cortex?

Answer 4

A strong stimuli is needed (indicating a less direct path) but it produces more complex movements which can be bilateral or involve more than one joint. It is involved in the plasticity of complex sequences of movements (muscle memory) The principal actions are mediated via primary motor area.

Question 5

What occurs if there is damage to the premotor area?

Answer 5

Apraxia which is where the person cannot preform tasks that involve a complex sequence of movements such as hair brushing.

Question 6

What is the role of the supplementary motor area?

Answer 6

Role is less clear but has some involvement in planning/rehearsing movements

Question 7

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

Answer 7

• Sensory receptors,
• Info from cerebellum,
• Info from basal ganglia

Question 8

Describe the movement of neuronal fibres of the corticospinal tract

Answer 8

Neurons originate in primary motor cortex, Descending fibres form corona radiata. At the junction of medulla and spinal cord most fibres decussate and form the lateral corticospinal tract. The uncrossed fibres form the anterior corticospinal tract, these terminates and decussate at cervical and upper thoracic levels.

Question 9

What is the function of the corticobulbar tracts?

Answer 9

Responsible for innervating several cranial nerves. Therefore is responsible for influencing fascial muscles and descending postural pathways of the brainstem.

Question 10

What are the extrapyramidal tracts?

Answer 10

Vestibulospinal tract, reticulospinal tract, rubrospinal tract and tectospinal pathways

Question 11

What are the functions of the extrapyramidal tracts?

Answer 11

Vestibulospinal - Balance,
Reticulospinal - muscle tone, orientation, breathing.
Rubrospinal - cerebellar influence upper limb movement,
Tectospinal pathways - head movements that follow sight.
They are responsible for involuntary muscular movments for posture, balance and locomotion

Question 12

What is the most common cause of corticospinal tract lesions?

Answer 12

Infarcts related to cerebrovascular incidents, the middle cerebral artery is particularly vulnerable

Question 13

What are the signs of an upper motor neuron lesion?

Answer 13

• Hemipariesis,
• Increased muscle tone,
• Increased stretch reflexes and,
• Abnormal reflexes such as babinski.

Question 14

What are the signs of a lower motor neuron lesion?

Answer 14

• muscle weakness,
• Muscle atrophy,
• Fasciculation,
• reduced muscle tone,
• Reduced stretch reflexes

Question 15

What is the UMNL patter of weakness?

Answer 15

• Arm flexors are stronger than extensors.

- Leg extensors are stronger than flexors

Question 16

What is the responsibility of the ventromedial pathway?

Answer 16

To maintain posture and balance. This is mainly by predictively and reflexively.

Question 17

Compensatory responses are based on information sent from??

Answer 17

1. Muscle proprioceptors,
2. Sense of balance.
3. Visual inputs. All this info converges on nuclei in the brainstem allowing for postural set to be generated