Motor learning and neurological syndromes Flashcards
Consider the pyramidal/corticospinal tract.
Outline its path
Decussation?
It is the great voluntary motor pathway and itcontrols muscular activity
Derived from cells in layer 5 (Brodmann 4 and 6)
From primary motor cortex (precentral gyrus) –> posterior limb of internal capsule –> cerebral peduncle –>upper motor neurons of pons–> pyramics of medulla –> lateral and anterior cortical tracts
Lateral tract goes via ventral CST to lower motor neurons to skeletal muscles
Decussation in medullary periods
Only cortical tract to directly synapse with motor neurons. 90% of fibres crossed in lateral CST, individual variation accounts for deficits in stroke
Damage to the corticospinal tract can cause posturing.
What is this?
Types?
Posturing- preserved upper limb flexion, lower limb extension. Increased muscle tone (spasticity) and brisk reflexes, Babinski reflex (toes spaced out), clonus
Posturing in coma can be seen when delivering minimal trauma- supraorbital pressure, nail bed stimulation, sternal pressure)
Decorticate posturing - lesion above red nucleus
Decerebrate posturing - lesion below red nucleus
What happens in a loss of descending inhibition?
- Altered excitability of spinal inhibitory interneurons
- Brisk reflexes
- Increased tone to rapid passive muscle stretching =spasticity
**Different from damage to motor cortec and corticospinal tract as there is reduced tone, loss of reflexes, muscle wasting
Outline the corticobulbar pathway
A two-neuron white matter motor pathway connecting the cingulate motor cortex to the Medullary pyramids
- Intrapyramidal
- The white matter is located in the ventral portion of the cerebral peduncles, called the crus cerebri. The middle third of the crus cerebri contains the corticobulbar and corticospinal fibers.
- The corticobulbar fibers exit at the appropriate level of the brainstem to synapse on the lower motor neurons of the cranial nerves.
- Fibers of the corticobulbar tract also end in the sensory nuclei of the brainstem including gracile nucleus, cuneate nucleus, solitary nucleus, and all trigeminal nuclei.
Facial palsy can occur as a result of a stroke.
What is it?
What is Bell’s palsy?
A facial palsy is weakness or paralysis of the muscles of the face.
Bell’s Palsy, are idiopathic by definition
Consider the differential diagnosis for facial palsy
What upper motor neuron causes are there?
What lower motor neuron causes are there?
UMN causes- stroke, SDH, or tumour
Will present with forehead sparing
LMN causes
Infective -such as acute otitis media, cholesteatoma, viral infection (including HSV-1, CMV, and EBV)
Neoplasm (parotid malignancy)
Trauma or iatrogenic
Neurological (Multiple Sclerosis or Guillain-Barré syndrome)
How ca you depict where the lesion is based on the areas of the face affected in facial palsy?
Upper motor neuron lesion in the primary cortex
-Neuron from here form subnucleus for muscle of forehead and eye. Right upper quadrant affected.Left upper quadrant unaffected as recieves motor input from unaffected region as well
-Neuron from UMNL form subnucleus for muscles of lower face. Both right and left lower quadrant affected
Describe the topographical organisation in the motor cortex
What is the motor homunculus?
Every part of the body is represented in the primary motor cortex, these are arranged somatopically (foot next to leg)
Amount of brain matter correlates to the amount of control that the primary motor cortex has over body part
The disproportionate map of the body in the motor cortex. not fixed, malleable
How would a parasagittal meningioma present?
Bilateral leg weakness and spasticity as it is pressing on foot/leg area of both motor cortices
Which areas of the brain does the anterior cerebral artery supply?
If occluded (as in stroke) what would happen?
Supplies the medial and superior surfaces and frontal pole (including the leg of the primary motor cortex)
- Crural (leg) paresis > arm paresis
- frontal signs (e.g. abulia- loss/impairment of ability to make decisions/act independently)
Which areas of the brain does the middle cerebral artery supply?
If occluded (as in stroke) what would happen?
Supplies the lateral surfaces and temporal pole
- Proximal lesion affects internal capsule causing COMPLERE HEMIPARESIS
- Distal lesion may spare leg area of primary motor cortex
Where does the anterior choroidal artery supply?
Which else can supply this area?
Most middle aspect of brain (under third ventricle and around pallidum)
Middle cerebral artery -RARE
Branch of internal carotid
What is a jacksonian seiziure? (aka Seizure march)
Partial onset simple motor seizure becoming secondarily generalised
-Strongly associated with structural abnormality in or close to motor cortex
What 2 kinds of afferents are found in the posterior parietal cortex?
Brodmann 5- somatosensory afferents
Brodmann 7- visual pathway afferents
Where mental body/environment image. Damage results in neglect (can perceive but do not attend)
Exploratory movements e.g. turning object in hand (looking and feeling)
Motor planning is heteromodal. What does this mean?
Gustatory, vestibular, somatosensory, auditory and visual information is involved
Therefore perceptual motor dysfunction is hetermodal
What is the relevance of the premotor area?
What can happen in damage?
Important in control of visually guided movements e.g. orientation of hand in relation to object to be grasped (Prehension). Receives input from the cerebellum and is involved in planning movements based on external (visual) cues. Most important in control of postural and proximal limb muscles
Perseveration of motor activity despite lack of success. Lesions disrupt learned responses to visual cues
What is Rowland concept of movement?
Mental rehearsal of finger movements occurs in SMA activation
Sequence of complex finger movements activates M1 and SMA
Simple finger flexion activates only M1
Describe the connection between senses and motor action in humans
What happens in damage?
Wide connections between sensory and motor association areas
Damage leads to apraxia- inability to carry out purposeful movements in the absence of paralysis or paresis. There is great difficulty in the sequencing and execution of movements
Ideational (parietal)- unable to report the sequence (show me how to make a jam sandwich)
Ideomotor (SMA)- unable to use the tool (show me how to use and hold a pair of scissors)
Task specific dystonias are a typeof aberrant sensory processing
Define dystonia
How do they occur?
A dystonia is a sustained muscle contractions usually producing twisting and repitiitive movements or abnormal postures or position
Repeated and extended use of the hand results in changed in the functional organisation of brain areas related to sensory processing and motor control. Although the manifestation is motor, the primary abnormality is likely to be disrupted sensory processing mediated by the basal ganglia
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
Outline the rubrospinal tract
Extrapyramidal tract that goes via red nucleus
-Activates flexor muscles in arms
Outline the tectospinal tract
Superior colliculus (in midbrain) –> TST in anterior white column of spinal cord –lower motor neuron
Control head and neck movements
Outline the vestibulospinal tract
2 tracts
Lateral vestibular nucleus to lateral vestibulospinal tract
-Activates extensor muscles in arms and legs
Medial vestibular nucleus to medial VST
-Controls head and neck movements
Outline the reticulospinal tract
EXTRAPYRAMIDAL
Brainstem reticular formation –> lateral reticulospinal tract –> medial reticulospinal tract
Activates extensor muscles n arms and legs- important for posture and locomotion
- Regulates ventral horn motor activity/reflexes
- Facilitates and inhibits lower motor neurons
