Descending Motor Pathways Flashcards
What are the requirements for movement ?
- Goal or purpose,
- Activation of relevant movement
- Feedback of movement
- Refinement/correction of movement 5. Cessation on completion
Where in the brain is the motor cortex located ?
Anterior to central cortical sulcus, in the frontal lobe
How much of the frontal lobe does the motor cortex occupy ?
1/3 of it
What are the sub areas of the motor cortex ?
– Primary motor cortex
– Premotor area
– Supplementary motor area

What does most of the primary motor cortex control ?
> 1/2 1° motor cortex controls hands and muscles of speech
How many muscles does the excitation of a single motor neuron control ?
Excitation of a single mn ususally excites a specific movement – not one specific muscle.
I.e. A pattern of separate muscles are excited.
Which of the primary motor cortex or premotor area gives more complex patterns of movement ?
Nerve signals from premotor areas give more complex “patterns” of movement.
What is a special feature of contractions elicited by the Supplemental Motor Area ?
Contractions elicited are often bilateral eg grasping movements of both hands.
Does the Supplemental motor area work by itself ?
Usually functions together with premotor area.
What is the function of the supplemental motor area ?
Gives background movement onto which premotor and 1° motor cortex add finer control.
How do motor signals get transmitted from cortex to the spinal cord ?
Through the Corticospinal tract
What proportion of each motor area in the cortex does the Corticospinal tract originate from ?
30% 1°
30% premotor/ supplementary motor
40% somatosensory.
Describe the path of motor signals from the cortex to
Cortex –> pyramids of medulla –> (majority)cross in lower medullae –> lateral corticospinal tractse –> mainly terminate on interneurons
Those that do not cross pass ipsilaterally in ventral corticospinal tracts.
What pathways exist to transmit motor signals ? Are they for conscious or unconscious movements ?
Lateral Pathways = Conscious Movements
Ventromedial pathways = Unconscious Movements
How are the lateral, and ventromedial pathways controlled respectively ?
LATERAL PATHWAY
Principally controlled by the cerebral cortex via 2 corticospinal tracts.
VENTROMEDIAL PATHWAY
Principally controlled in the brainstem.
What do the lateral, and ventromedial pathways control respectively ?
LATERAL PATHWAY
General control of voluntary movement.
Mainly associated with control of distal muscles.
VENTROMEDIAL PATHWAY
Control of posture and rhythmic movements associated with locomotion and posture
Control axial and proximal muscles.
What is posture ?
Position of a body and its parts relative to each other. It is a compromise between balance and movement.
Which structure is involved in controlling/adjusting posture ?
-Controlled and driven by the brainstem (where the postural set is governed)
Describe the entire posture control mechanism, especially for both unexpected and expected movement.
Central command –> Limb Movement –> Postural Instability –> Postural Adjustment (FEEDBACK for unanticipated postural instability)
Central command –> Postural Adjustment (FEEDFORWARD for anticipated postural instability)
Explain how the terms postural set and compensation relate to posture.
Posture is adjusted predominantly by involuntary movement driven both predictively (postural set) and reactively (compensation).
Where is sensory information for posture control integrated from ?
- Muscle proprioceptors (detect changes in muscle length and or tension)
- Vestibular apparatus (Detect movements of the head relative to the Earths gravitational field, and give sense of balance)
- Visual inputs (detecting movements in visual field representing movement of the body)
Where is the sensory information for posture control integrated in ?
Brainstem
What are the important parts of the brainstem in the processing of information for posture control ?
- Reticular nuclei
* Vestibular nuclei (cranial nuclei for the vestibular nerve)
What are the principal effects of the Lateral vestibulospinal tract ?
- Facilitate extensor motor neurons and inhibit flexor motor neurones innervating the ipsilateral medial and axial muscles.
- Activates alpha and Gamma MNs which causes enhanced muscle spindle mediated stretch reflexes
- Overall effect is to increase the tone to the antigravity muscles
What is the principal effect of the medial vestibulospinal tract ?
Controls head and eye movements, usually in response to a moving target
What would happen to the medial vestibulospinal tract in the case of an unplanned head movement ?
Head movements activate the vestibular apparatus which projects to the medial vestibular nucleus –> Medial vestibular nucleus links this information with visual and tectal sensory information, and transmits signals to the cranial nerves controlling head, neck and eye movements –> Head and eye movement are yoked together to maintain a steady gaze regardless of body movement.
What is the principal effect of the Reticulospinal tract ?
Co-ordinates movement and posture. Specifically,
- Pontine and medullary output coordinates truncal and proximal muscle activity to orientate the body either towards or away from a stimulus – primitive response.
- Affects muscle tone in response to planned motor activity and coordinated overall distal and proximal muscle activity
Where does the reticulospinal tract obtain sensory information from ? Where is this information processed ?
- Vestibular nuclei
- Cortical areas for voluntary movement
3 .Proprioception, vision etc
This sensory info is processed in the brainstems reticular formation
Which pathway/tract are responsible for maintaining posture ?
The ventromedial pathway, through the vestibulospinal and reticulospinal tracts
Which pathway does each of the following belong to:
- Vestibulospinal tract
- Reticulospinal tract
- Corticospinal tract
ALL THREE BELONG TO THE VENTROMEDIAL PATHWAY
Where are each of Upper Motor Neurons and Lower Motor Neurons found ?
UPPER MOTOR NEURONS (UMNs)
-Found in the cortex and brainstem nuclei
LOWER MOTOR NEURONS (LMNs)
-Found in the brainstem and spinal cord
Are UMNs/LMNs restricted to the CNS ?
UMNs
-Restricted to the CNS
LMNs
-Not restricted to the CNS (their axons leave the CNS and innervate muscle)
Do UMNs/LMNs contact muscles ?
UMNs
-Do NOT contact muscles
LMNs
-DO stimulate muscles to contract
What is the function of each of UMNs and LMNs ?
UMNs:
-Transmit nerve impulse to LMNs
LMNs:
-Deliver motor functions to muscles
Are lesions of UMNs common ? Why or why not ?
Relatively common as these axons are very long (therefore vulnerable).
What do positive and negative signs mean in the context of UMN lesions ?
NEGATIVE is a loss of function,
POSITIVE is the appearance of an abnormal response.
Give two specific examples of results of an UMN lesion.
- Extensor Planter reflex (Babinski sign) is a positive sign seen following corticospinal lesions. Corticospinal lesions lead to UMN syndrome.
- Hypertonia leading to painful spasticity due to hyperexcitable spindle neurons which induce over reactive stretch responses
NO ATROPHY OR FASCICULATION
Define the Babinski reflex. What is a normal response ?
BABINSKI REFLEX
“Occurs after the sole of the foot has been firmly stroked. The big toe then moves upward or toward the top surface of the foot. The other toes fan out.”
NORMAL
All toes point down
What do lesions of the axons of the LMNs cause ?
- Muscle paralysis
- Reduced motor tone
- Reduced stretch reflex
- Fasciculation
- Atrophy
