Motor learning and neurological symptoms Flashcards
Describe the simple motor pathway
Motor cortex in the brain
Upper motor neuron
Lower motor neuron
Muscle
Describe the motor control of hierarchy and state the structures involved
High - function: strategy - Association areas of the neocortex and basal ganglia
Middle - Function: tactics - Motor cortex and cerebellum
Low - Function: Execution - brainstem, spinal cord
What is the purpose of the decending motor pathways
These use sensory information about balance, body position and the visual environment to reflexively maintain balance and posture.
Describe the pyramidal/corticospinal tract
Pyramidal tract derives its name from decussation in
medullary pyramids
Only cortical tract to directly synapse with motor neurons
Predominantly derived from cells in layer V
(not exclusively Betz cells)
Brodmans Area 4 (and 6)
90% fibres crossed in lateral CST but individual variation
may account for different deficits in strokes
What is the rubrospinal tract used for?
Unclear to what extend this pathway is involved in humans.
Predominantly innervates the flexor muscles in the upper limbs.
Describe the vestibulospinal tract
Originate in the vestibular nuclei of the medulla which relay sensory information from the vestibular labyrinth in the inner ear.
Medial vestibulospinal pathways projects down to the spinal cord and activates the cervical spinal circuits that control neck and back muscle guides and thus guide head movements.
Therefore it helps to keeps the eyes stable as the body is moved.
Lateral vestibulospinal projects ipsilaterally as far down as the lumbar spinal cord. Helps us maintain an upright and balanced posture by facilitating the extensor motor neurons of the legs.
Describe the tectospinal tract
Originates in the superior colliculus in the midbrain which receives direct input from the retina.
The superior colliculus receives information from the retina and the visual cortex. This is used to construct a map of the world around us.
Allows us to direct the head and eyes to move so that the appropriate point of space is imaged on the fovea.
The projections decussate immediately and lie close to the midline into the cervical regions of the spinal cord where they help to control the muscles of the neck, upper trunk and shoulders.
What is the reticulospinal tract?
The pathway runs from the brainstem. The reticular formation is just under the cerebral aqueduct and fourth ventricle. It is a complex meshwork of neurons.
It descends in two separate pathways, pontine (medial) and medullary (lateral) .
Both facilitate the extension of the limbs.
Which tracts control head and neck movements?
Tectospinal and medial vestibulospinal
Which tracts activate extensor muscles in arms and legs?
Lateral vestibulospinal and reticulospinal
Which tracts Activates flexor muscles in arms.
Rubrospinal
If the lesion is above the red nucleus which posture is present?
Decorticate posturing - flexion of arm muscles
If the lesion is below the red nucleus which posture is present?
Decerebrate posturing - extension of all 4 limbs
Describe the typical posture of a patient with damage to the motor cortex and corticospinal tract
some preserved upper limb flexion and lower limb extension
Increased tone (spasticity), Brisk Reflexes,
Extensor Plantar/Babinski reflex, Clonus
But patient maintains posture
Describe loss of descending inhibition
Altered excitability of spinal inhibitory interneurons
Brisk reflexes
increased tone to rapid passive muscle stretching= spasticity
Describe the motor homunculus
The amount of brain matter devoted to any particular body part represents the amount of control that the primary motor cortex has over that body part. This disproportionate map of the body in the motor cortex is called the motor homunculus. This map may not be fixed and may be malleable.
How are parts of the body represented in the primary motor cortex arranged?
arranged somatotopically – the foot is next to the leg which is next to the trunk which is next to the arm and the hand
Describe the effect of a proximal middle cerebral artery occlusion
Proximal lesion affects internal capsule
Complete hemiparesis
Describe the effect of a distal middle cerebral artery occlusion
Distal lesion may spare leg area of motor cortex
though secondary swelling and ischaemia may compromise function
What is Abulia?
Loss or impairment of the ability
to make decisions or act independently
What does the anterior cerebral artery supply?
Supplies medial part of frontal lobes
including leg area of motor cortex
What is area 5 in the posterior parietal cortex used for?
somatosensory afferents
What is area 7 in the posterior parietal cortex used for?
visual pathway afferents
What is the function of the posterior parietal cortex?
Mental body/ environment image
Damage results in neglect
(can perceive but do not attend)
Exploratory movements
Eg turning object in hand
(looking and feeling)
What is the function of the premotor area (PMA)?
Importance in control of
Visually guided movements
What is activated in finger flexion?
M1 only
Which areas are activated in a sequence of complex finger movements?
M1 and SMA
Which areas are activated in rehearsal of finger movements?
Only SMA
What is apraxia?
Damage to wide interconnections between sensory and motor association areas
Inability to carryout purposeful movements in the absence of paralysis or paresis.
Great difficulty in the sequencing and execution of movements.
Name the types of apraxia
Ideational (parietal)
Ideomotor (SMA)
What is ideational apraxia?
unable to report the sequence
What is ideomotor apraxia?
unable to use the tool
Describe task specific dystonias?
Repeated and extended use of the hand results
in changes in the functional organisation of brain
areas related to sensory processing and motor control.
Can be altered by ‘sensory tricks’
Although the manifestation is motor, the primary
abnormality is likely to be disrupted sensory processing
probably mediated by the basal ganglia
What is a dystonia?
sustained muscle contractions, usually producing
twisting and repetitive movements or abnormal postures or positions
What is the function of the basal ganglia?
Positive feedback loop with the cortex to select wanted movements and deselect unwanted movements.
What is the function of the cerebellum?
Coordination of muscles in order to make smooth movements.
Balance
Motor learning
