Descending motor pathways

Question 1

Where is the motor cortex?

Answer 1

• Anterior to the central cortical sulcus

* Occupies ~1/3 of the frontal lobe

Question 2

What are the 3 subareas of the motor cortex?

Answer 2

• Primary motor cortex
• Premotor area
• Supplementary motor area

Question 3

What proportion of the motor cortex control hands of the muscles and muscles of the speech?

Answer 3

More than half

Question 4

What does the excitation of a single motor neurone do?

Answer 4

• Excites a specific movement (not one specific muscle)

* A pattern of separate muscles are excited

Question 5

Describe the action of the premotor area

Answer 5

• More complex patterns of movement
• most anterior part develops an image for total muscle movement
• Posterior excitation of the specific muscle acitvity that is required
• Sends signals to the primary motor cortex so the specific muscles are excited

Question 6

Describe the supplemental motor area

Answer 6

• Contractions are ofter bilateral e.g. grasping movement of both hands
• Usually functions together with the premotor area

Question 7

how have the specialised areas of motor control been identified?

Answer 7

• Electrical stimulation or observation of loss of motor function with destructive lesions

Question 8

What is Broca’s area

Answer 8

Motor speech area

Question 9

What is the role of the corticospinal tract?

Answer 9

• Carries signals direct from the cortex to the spinal cord

Question 10

Where does the corticospinal tract originate from ?

Answer 10

• 30% from the primary motor cortex
• 30% premotor
• 40% somatosensory

Question 11

Describe the pathway of the corticospinal tract

Answer 11

• Cortex
• Medulla
• Majority cross in the lower medulla
• Lateral corticospinal tracts
• Mainly terminate of interneurones

Question 12

What happens to the fibres in the corticospinal tract that do not cross in the lower medulla?

Answer 12

They pass ipsilaterally in the ventral corticospinal tracts

Question 13

Which pathway is conscious movement associated with

Answer 13

Lateral pathways

Question 14

Which pathway is unconscious movement associated with?

Answer 14

Ventromedial pathways

Question 15

Describe the lateral pathway

Answer 15

• Principally controlled bu the cerebral cortex via 2 corticospinal tracts
• General control of voluntary moments
• Mainly associated with control of distal muscles

Question 16

Describe the Ventromedial pathways

Answer 16

• Principally controlled in the brainstem
• Control of posture and rhythmic movements associated with locomotion
• control axial and proximal muscles

Question 17

What does the brain stem contain?

Answer 17

• Motor and sensory nuclei

Question 18

What special control functions does the brain stem control?

Answer 18

• Respiration
• Partial control of GI function
• Control of many stereotyped body movements, equilibrium, eye movements

Question 19

What is the brainstem made up of?

Answer 19

• Medulla
• Pons
• midbrain

Question 20

What is posture?

Answer 20

Portion of body and its parts relative to each other. Compromise between balance and movement

Question 21

How to we maintain balance?

Answer 21

Posture is adjusted predominantly by involuntary movement driven both predictably and reactively

Question 22

What is posture controlled by?

Answer 22

The brainstem

Question 23

What is the mechanism for unexpected movement?

Answer 23

• Feedback

Question 24

What is the mechanism for expected movement?

Answer 24

• Feedforward mechanism

Question 25

How is sensory information integrated in regard to posture control?

Answer 25

1. Muscle proprioceptors detect changes in muscle length and/or tension
2. Sense of balance derived from movements of the head relative to the Earth’s gravitational field (vestibular apparatus)
3. Visual inputs detect movements in visual field representing body movement

Question 26

Where is sensory information regarding balance and posture predominantly integrated?

Answer 26

In the brainstem

Question 27

What are the nuclei in the brianstem?

Answer 27

• Reticular nuclei
- pontine and medullary
• Vestibular nuclei

Question 28

What do the pontine nuclei do?

Answer 28

Excite antigravity muscles

Question 29

What do the medullary nuclei do

Answer 29

Relax antigravity muscles (works antagonistically to the pontine)

Question 30

Describe the Pontine Reticular system

Answer 30

• Nuclei transmit signals into the cord via pontine reticulospinal tract
• Fibres terminate on the medial anterior motor neurones that excite axial muscles which support the body against gravity
• When the pontine reticular excretory system is unopposed by the medullary reticular system, there is a powerful excitation of antigravity muscles throughout the body

Question 31

Where is the pontine reticulospinal tract?

Answer 31

In the anterior of the cord

Question 32

Describe the excitability of the pontine reticular system

Answer 32

• High degree of natural excitability

* Receive strong signals from the vestibular nuclei and from the deep nuclei of the cerebellum

Question 33

Describe the medullary reticular system

Answer 33

• Nuclei transmit inhibitory signals to antigravity anterior motor neurones via the medullary reticulospinal tract

Question 34

Where is the medullary reticulospinal tract?

Answer 34

In the lateral column of the cord

Question 35

Where do the medullary reticular nuclei receive strong input collaterals from?

Answer 35

1. Corticospinal tract
2. Rubrospinal tract
3. Other motor pathways

Question 36

When is the medullary reticular system activated?

Answer 36

• Activated to counterbalance pontine reticular system

Question 37

How is standing caused?

Answer 37

Some signals from higher areas of the brain can disinhibit the medullary system to excite the pontine system

Question 38

What is the specific role of the Vestibular nuclei?

Answer 38

Selectively control the excitatory signals to the different antigravity muscles depending on the particular posture
• Activated to counterbalance pontine reticular system Equilibrium in repose to signals from the vestibular apparatus

Question 39

How do the vestibular nuclei transmit signals?

Answer 39

• Transmits strong excitatory signals to antigravity muscles via lateral and medial vestibulospinal tracts in the anterior columns of the spinal cord

Question 40

What are upper motor neurones?

Answer 40

• in cortex and brainstem nuclei
• Restricted to the CNS and don’t contact muscle
• Executive function for lower motor neurones and circuits controlled LMNs
• Long

Question 41

What are the lower motor neurones?

Answer 41

• Found in the brainstem and spinal cord
• Not restricted to the CNS and stimulate the muscle to contract
• motor function to muscles
• True alpha motor neuornes

Question 42

Describe lesions in the upper motor neurones

Answer 42

• Relatively common as long axons
• Signs of lesion war positive or negative signs
- negative is a loss of function
- positive is the appearance of an abnormal response
• Babinski sign (extensor planter relflex) is a positive sign

Question 43

What do corticospinal lesions give rise to?

Answer 43

Upper motor neurone syndrome

Question 44

babinski sign

Answer 44

In response to movement of the foot, the toes curl up rather than down (pressure on heel e.g. using a pen)

Question 45

Describe lower motor neurone lesions

Answer 45

• No atrophy or fasciculations
• Muscle paralysis
• Reduced motor tone
• Reduced stretch reflex
• Fasiculation
• Atrophy

Question 46

Describe the location of the lower motor neurone

Answer 46

Axon leaves the CNS and innervate muscle

Question 47

What is hypertonia caused by?

Answer 47

Hyperexcitable spindle neurones which induce over reactive stretch responses