Upper Motor Neurons (Glendinning) Flashcards
Identify and describe the function of the premotor cortical regions and posterior parietal cortex.
IDEAS about voluntary movement originate in FRONTAL LOBE.
PLANNING (organization of movement) then occurs in premotor cortical areas (SUPPLEMENTARY AND PREMOTOR CORTICES).
Posterior parietal cortex: spatial relationships (where is the body? where are objects in the environment?)
Define apraxia and how to test for it.
Lesions to premotor cortex or posterior parietal cortex -> contralateral apraxia (difficulty in using body part to perform complex voluntary actions)
planning of skilled movement affected
How to test?
Show me how to pour water into a cup, or brush your teeth, or light a match without those objects being there
- test even though there is no obvious weakness, paralysis or altered tone
Define UMN and distinguish it from LMN.
UMN: descending motor neurons from 1) cerebral cortex and 2) brainstem
LMN:
- in medial ventral horn: axial and proximal limb muscles (posture and balance)
- in lateral ventral horn: distal limb muscles (skilled movements)
Distinguish between function and anatomy of the medial and lateral spinal cord motor systems.
medial pathways of ventral horn -> proximal motor neurons
- stays ipsilateral (medial groove insertion)
- projects bilaterally
lateral pathways of ventral horn -> distal motor neurons
- projects directly and indirectly
Describe the functions of the corticospinal, corticobulbar, and descending brainstem pathways.
descending pathways - project to SC and brainstem alpha-motor neurons and interneurons (reflexes)
Locate the corticospinal and corticobulbar tracts as they descend through the neuraxis. Describe the anatomical location of their crossings.
Corticospinal tract = primary white matter pathway for goal-directed movements
- originates in primary motor cortex as well as premotor and somatosensory cortex
- only descending pathway to project DIRECTLY to alpha motor neurons of distal muscles
- only pathway that generates FINE MOVEMENTS of the finger
- decussates in MEDULLARY PYRAMID
- motor cortex does not “code” for specific muscles; codes for MOVEMENTS… so motor cortex lesions affect SEVERAL muscles
Describe the somatotopy of the corticospinal tract in the cortex, brainstem, and spinal cord.
Cortex: homunculus
Brainstem:
- LL is more posterior in internal capsule
- LL is more distal in midbrain
Spinal cord:
- Lateral in corticospinal tract
Compare UMN and LMN syndromes.
UMN lesions - initial shut-down of spinal circuits that lasts several days (most extreme and longest lasting is spinal shock after spinal cord injury)
Followed by:
- Weakness for voluntary movements (paresis)
- Due to loss of voluntary drive to motor neurons - Increased reflexes (hyper-reflexia)
- Due to a change in the descending influences and neuroplastic changes vs HYPOFLEXIA for LMN lesions - Hypertonia
- Due to hyper-reflexia - Posturing
- Due to imbalanced activity in muscle groups
Define hyperreflexia, clonus, spasticity clinically and physiologically.
- UMN damage disturbs the balanced modulation of spinal cord interneurons and motor neurons by descending pathways (+ and -) -> removing any of these inputs changes the balance of excitability of motor neurons and reflexes
- Loss of inputs to motor neurons produces NEUROPLASTIC CHANGES in motor neurons: denervation super sensitivity and sprouting from local interneurons
- Reduced muscle extensibility due to muscle contracture -> increased muscle spindle activation
Differentiate between the effects of Bell’s palsy and a corticobulbar tract lesion.
Bell’s Palsy: Right cranial nerve VII lesion causes LMN paralysis of 1/2 the fact; Both upper and lower face affected on right or left
Which side of the body is affected with CST lesions?
Lesions above spinal cord -> contralateral deficits
Lesions of the spinal cord -> same side lesions
Deficits are always below the level of the lesion
Recognize decorticate and decerebrate rigidity.
Posturing in spasticity
Decorticate posture in lesions ABOVE midbrain:
- Upper limb: Flexors > extensors
- Lower limb: Extensors > flexors
Decerebrate posture in lesions BELOW midbrain:
- All limbs extended
What are the lateral and medial vestibulospinal tracts?
Where do they project?
What do they contribute to?
Elaborate sensory system in inner ear with specialized receptors that monitor head position, movement, and acceleration
Both pathways project to medial ventral horn
Lateral vestibulospinal tract:
- to entire SC
- projects ipsilaterally to medial LMNs to proximal muscles
- Facilitates extensor muscles in response to changes from stable balance and upright balance
Medial vestibulospinal tract:
- only to cervical
- projects bilaterally to control (restore) head position in response to accelerations
- “vestibulocervical reflex”
What are the lateral and medial vestibulospinal tracts?
Where do they project?
What do they contribute to?
Elaborate sensory system in inner ear with specialized receptors that monitor head position, movement, and acceleration
Both pathways project to medial ventral horn
Lateral vestibulospinal tract:
- to entire SC
- projects ipsilaterally to medial LMNs to proximal muscles
- Facilitates extensor muscles in response to changes from stable balance and upright balance
Medial vestibulospinal tract:
- only to cervical
- projects bilaterally to control (restore) head position in response to accelerations
- “vestibulocervical reflex”
What is the tectospinal tract?
Where does it project?
What does it contribute to?
- Originates in the superior colliculus in midbrain and crosses in midbrain
- In in the medial motor system (only goes to cervical region)
- Generates orienting movements of the head to visual or auditory stimuli
- Helps to coordinate the eye and head
