Descending Pathways

Question 1

What are the classes of movement?

Answer 1

• Voluntary:

• complex actions e.g. reading and writing
• purposeful, goal directed
• learned
• Reflexes
• Rhythmic motor patterns
• combines voluntary and reflexive acts
• initiation and termination is voluntary
• once initiated, repetitive and reflexive

Question 2

What are the functions of motor control systems?

Answer 2

• Posture and balance
• Goal directed movements
• Communication

Question 3

What areas of the brain give rise to descending tracts?

Answer 3

• Corticospinal tract from cerebral cortex
From brainstem and medulla:
• Reticulospinal 
• Vestibulospinal 
• Rubrospinal 
• Tectospinal

Question 4

Where does the corticospinal tract originate?

Answer 4

2/3 originate in the motor cortex

Question 5

Where do the fibres of the corticospinal tract cross?

Answer 5

• Lateral corticospinal crosses at the medulla (pyramidal decussation)
• Anterior corticospinal remains ipsilaterally to cervical and upper thoracic segments

Question 6

What is the function of the lateral corticospinal tract

Answer 6

• Runs the length of the spinal cord

* Control voluntary fine movements of distal muscles, particularly flexors

Question 7

What is the function of the anterior corticospinal tract?

Answer 7

Control axial muscles

Question 8

What does Jacksonian epilepsy highlight?

Answer 8

• Twitching begins at the extremities then movement of the hand and then of the arm
• Reflects the spread of excitation over the cortex from epileptic focus
• Shows the somatotropic arrangement

Question 9

What is the difference in which muscles can be controlled by the primary and secondary motor cortices?

Answer 9

• Primary controls muscles of opposite side of the body

* Secondary controls muscles on both sides

Question 10

Where does the rubrospinal tract originate?

Answer 10

In the red nucleus in the midbrain

Question 11

Where do the fibres of the rubrospinal tract cross?

Answer 11

Midbrain - ventral tegmental decussation

Question 12

Where do the fibres of the rubrospinal tract terminate?

Answer 12

On interneurones of ventral (motor) horn in the contralateral spinal cord

Question 13

What is the function of the rubrospinal tract?

Answer 13

Facilitates flexor motor neurones and inhibits extensor motor muscles

Question 14

Where does the tectospinal tract originate?

Answer 14

In the superior colliculus

Question 15

Where do the fibres in the tectospinal tract terminate?

Answer 15

In interneurones in the contralateral cervical region of the spinal cord

Question 16

What is the function of the tectospinal tract?

Answer 16

Controls head movements in response to visual and auditory input

Question 17

Where does the vestibulospinal tract originate?

Answer 17

In vestibular nuclei

Question 18

What inputs does the vestibulospinal tract receive?

Answer 18

• Inhibitory input from the cerebellum

* Excitatory from the vestibular apparatus

Question 19

Lateral vestibulospinal tract

Answer 19

• Fibres don’t cross, terminate on interneurones in ipsilateral spinal cord
• Control extensor muscle motor tone of the proximal limbs
• Maintenance of erect posture

Question 20

Medial vestibulospinal tract

Answer 20

• Bilateral
• Terminate on interneurones in the cervical region
• control the neck muscles
• Keep head upright when body moves

Question 21

Where does the reticulospinal tract originate?

Answer 21

Pontine reticular formation

Question 22

Where do the fibres of the reticulospinal tract terminate?

Answer 22

Largely uncrossed, terminate on interneurons within the spinal cord

Question 23

What is the function of the reticulospinal tract?

Answer 23

Control muscles of the trunk and proximal limbs
• Medullary (lateral) tracts inhibit extensor spinal reflex activity and facilitates flexor activity
• Medial (pontine) tracts facilitate
• Maintenance of posture and startle reactions

Question 24

What may be caused by damage to the reticulospinal tract?

Answer 24

Spasticity

Question 25

Muscle motor pathway lesion

Answer 25

* Myositis, muscular dystrophy * Normal reflexes * Weakness/ wasting

Question 26

Neuomuscular junciton motor pathway lesion

Answer 26

* Myasthenia gravis * Fatigueable weakness * Normal reflexes * Normal muscle bulk

Question 27

Motor neurone motor pathway lesion

Answer 27

* UMN: CVA, spinal cord trauma | * LMN: motor neurone disease, neuropathy

Question 28

Cerebellum motor pathway lesion

Answer 28

* Incoordinaiton, multiple sclerosis * Normal reflexes and strength * Slight change in tone

Question 29

Basal ganglia motor pathway leison

Answer 29

* Parkinsons, Huntington's | * Movement changes

Question 30

Describe upper motor neurones

Answer 30

* Cell bodies are in the brain or brainstem and do not project outside of the CNS * orchestrate complex directed movements

Question 31

Describe lower motor neurones

Answer 31

* Cell bodies are in the brainstem or spinal cord and project outside the CNS to muscle * Single muscle innervation, cell bodies in the ventral horn of the spinal cord or motor nuclei of the brainstem

Question 32

Muscle bulk in UMN vs LMN lesion

Answer 32

* UMN - normal | * LMN - decreased

Question 33

Reflexes in UMN lesion vs LMN lesion

Answer 33

* UMN - increased | * LMN- absent

Question 34

Tone in UMN lesion vs LMN lesion

Answer 34

* UMN - increased | * LMN - decreased

Question 35

Power in UMN lesion vs LMN lesion

Answer 35

* UMN - Reduced extensors in arm, flexors in leg | * LMN - decreased

Question 36

Co-ordination in UMN vs LMN lesion

Answer 36

* UMN - normal | * LMN - normal

Question 37

Plantar response in UMN lesion vs LMN lesion

Answer 37

* UMN - extensor (normal is a flexed response) | * LMN - absent if leg/foot involved in lesion

Question 38

What is a normal plantar response - Babinski

Answer 38

Toes go down (flexion)

Question 39

Lamina I-VI

Answer 39

Terminations for primary afferent sensory neurones and neurones of reflex circuits

Question 40

Lamina VI

Answer 40

Sensory input from joints and muscles

Question 41

Lamina VII and IX

Answer 41

Cell bodies of motor neurones

Question 42

Describe the location of motor neurones supplying the trunk vs those supplying distal muscles

Answer 42

* Those supplying the trunk are situated medially | * Those supplying the distal muscles are situated laterally

Question 43

Describe the location of motor neurones that flex the limbs vs those that extend the limbs

Answer 43

Motor neurones that flex the limbs lie dorsal to those that extend the limbs

Question 44

What are Renshaw cells and what do they do?

Answer 44

* Interneurones | * Suppresses weakly firing motor neurones and dampens strongly firing ones to produce economical movement

Question 45

What reflects the importance of Renshaw cells?

Answer 45

* Strychnine poisoning * Disables Renshaw cells * Leads to convulsions

Question 46

Describe the Myotatic reflex (knee jerk)

Answer 46

* Monosynaptic stretch reflex * Tap of the patellar tenon stretches the quadriceps muscle * Stimualtes nuclear bag receptors of the muscle spindle * Increases the rate of firing of group IA afferent fibres leading to the contraction of the quadriceps muscle * The IA fibres also stimulate inhibitory interneurones which inhibit antagonistic (flexor) muscles of the knee joint

Question 47

When is the knee jerk reflex lost?

Answer 47

If there is damage to the lower lumbar dorsal roots of the spinal cord

Question 48

What is the step cycle

Answer 48

• Stance phase: - foot touching the ground, flexion of the knee and ankle - finishes with extension about all joints for forward movement • Swing phase: - bending (flexion) of hip, knee and ankle followed by knee and ankle straightening (extension) • Alternates between the swing and stance phase

Question 49

What is the central pattern generator

Answer 49

* Located in the spinal cord * Capable of autonomous signals * Modulated by proprioception input * Thought to be initiated by mesencephalic locomotor region - output thought to be through reticular nuclei and reticulospinal tracts