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Area 4 of motor cortex
- Ant to cerebral sulcus on pre central gyrus
- Primary Motor Cortex or M1
- Movement of contralateral side of body
- Lowest threshold for electing movement; strong connections to spinal motor neurons
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Area 6 of motor cortex
- Just anterior to area 4
- Premotor Area (PMA; lateral)
- -Connects to reticulospinal neurons that then connect to proximal muscles = posture
- Supplementary Motor Area (SMA; medial)
- -Connects directly with distal muscles
- -Influences planning and initiation of movements on basis of past experience; anticipation of movement triggers neutral transmissions in the SMA
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Layer V in Cortex (Input-Output of M1)
- Input from
- Cortex - Areas 6 (anterior) and 3, 1, 2 (posterior)
- Project to
- SC and brain stem
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Coding of Movement in M1
- M1 neurons activate immediately before and during voluntary movement
- -Encode force and direction
- Much of motor cortex is active for every movement
- Cell activity is a "vote" for a particular direction of movement
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Posterior Parietal
- All input to Posterior Parietal Cortex
- Area 5: info from Somatosensory Cortical areas 3,1,2
- Area 7: info from Visual Cortex
- Lesion: impaired body image and perceptual-spatial
- -Severe = neglect
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Prefrontal Areas jobs
- Abstract thought
- Decision making
- Anticipating consequences of actions
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Motor Apraxia
- Unable to carry out movements despite intact sensation, movement, and cognition
- -Ex. cannot scratch nose to command but scratch it when itches
- Damage to premotor or SMA
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Ideomotor (motor apraxia)
- Unable to perform purposeful movement on command despite understanding concept
- -May perform movement automatically
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Ideational (motor apraxia)
- Loss of ability to conceptualize, plan, and execute sequences of motor actions involving use of tools or objects in everyday life
- -Unable to plan movement related to an object bcs has lost perception/lost knowledge of what object represents
- -Disturbance in sequential organization of voluntary actions
- -Ex. comb hair with wrong side or place in mouth
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Posterior Parietal role in voluntary movements
- Assesses context in which movements are being made
- -Receives somatosensory, propriocentpive, and visual inputs and uses them to determine body positions and target in space
- -Produces internal models of movement to be made prior to involvement of the premotor and motor cortices
- -Works with prefrontal area to make decision about movements to be made
- -These send info to Area 6 informing about kind of action to take
- -Area 6 determines characteristics of appropriate movement for this purpose
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Posterior Parietal and Prefrontal Areas
- Highest level of hierarchy
- Make decisions about actions to take and likely outcome of actions
- Send axons to Area 6
- -Junction where signals encoding what actions are desired are converted to signals specifying how actions will be carried out = Higher-order motor planning
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Motor cortex areas
- Primary (Area 4 = M1)
- Motor homunculus
- Area 6
- Premotor (PMA)
- Supplemental (SMA)
- Regions of input
- Post. Parietal (5&7)
- Somatosensory
- Prefrontal
- Basal ganglia
- Efferent destinations
- Spinal cord, basal ganglia, cerebellum, retic. formation, vestibular nuclei, thalamic nuclei
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Basal Ganglia
- Made up of nuclei
- -Caudate, Putamen, Globus Pallidus (output to Thalamus), Subthalamic Nucleus, Substantia Nigra
- Caudate and Putamen together = Striatum
- -Target of cortical input
- Regulates
- M. contraction
- M. force
- Multijoint movements
- Sequence of movements
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Basal Ganglia loop
- Cortex to Basal Ganglia and Thalamus (VL) back to Cortex (esp. SMA)
- Function: selection and initiation of willful movements
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Direct Path for Motor
- Cortex
- Striatum
- Globus Pallidus
- VL
- SMA and PMA
- Cortex
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Parkinson's Disease as a Basal Ganglia Disorder
- Hypokinesia = decreased movement
- -Slowness of movement = Bradykinesia
- -Difficulty initiating movement = Akinesia
- -Increased muscle tone = Rigidity
- -Tremors of hands and jaw, increased at rest
- Also cognitive deficits
- Cause = degeneration of Substantia Nigra
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Substantia Nigra Role in PD
- Degeneration =
- -Decreased input to Striatum
- -Uses Dopamine to activate Putamen
- -Which releases VL from Globus Pallidus inhibition
- -Therefore, depleted Dopamine decreases input to SMA
- Treatment
- -Administer Dopa
- -BUT doesn't alter degeneration state of S.N. or progression of the disease
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Huntington's Disease (Basal Ganglia Disorder)
- Hyperkinesia = excess movement
- Also Diskinesias, dementia, and personality, mood, & memory disorders
- Doesn't present until well into adulthood -> ppl unwittingly pass gene on to children
Chorea: spontaneous, uncontrollable, purposeless movements with rapid, irregular motions of various parts of body
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Huntington's disease cause
- Loss of neurons in Caudate Nucleus, Putamen, and Globus Pallidus as well as in Cerebral Cortex
- Damage to BG structures = loss of inhibition to Thalamus = movement disorders
- Cortical degeneration = personality changes
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Ballism (Basal Ganglia Disorder)
- Type of hyperkinesia
- Violent, flinging of extremities
- One side of body (usually) = Hemiballism
- Cause
- Damage to Subthalmic Nucleus (usually CVA)
- Role of S.Nucleus = excites neurons in Globus Pallidus that project to VL
- So damage to S. Nucleus = loss of excitation of GP = less inhibition of VL = increased SMA activity
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Basal Ganglia jobs
- Facilitates movement by focusing activity from several areas of cortex onto the SMA
- Filter - keeps inappropriate movements from being expressed
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Cerebellum
- Provides control over timing of body's movements; loop circuit connects to motor cortex and modulates signals
- Analyzes visual signals associated with movement
- -Calculates speed of movements and adjusts accordingly
- Some involvement in language, attention, memory, and emotions
- Sequences muscle contractions for movement
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Cerebellum lesions
- Lead to ataxia = uncoordinated movements
- Test: touch finger to nose, then do with eye closed
- -Cannot do with cerebellar damage
- -Move shoulder, then elbow, then wrist = dysynergia
- -Finger ends up short of or past nose = dysmetria
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Cerebellum features
- Folia: shallow ridges
- Deep cerebellar nuclei: white matter
- -Relays cerebellar cortical output to brain stem
- Vermis: bump that separates lateral Cerebellar Hemispheres
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Cerebellar Regions
- Vestibulocerebellum: equilibrium and balance = postural muscles and eye movements
- Spinocerebellum: gross limb movements
- -Controls muscle tension at all times while releasing those muscles required to execute movements
- Cerebrocerebellum: distal limb voluntary movements
- -Ensures when one set of muscles initiates, the opposing set acts as a brake, so the body part arrives at its target precisely
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Motor Loop through Lateral Cerebellum
- Instructs Primary Motor cortex regarding direction, timing, and force of movement
- For very fast movements
- -Based on predictions for outcome (too fast for feedback)
- -Based on past experiences = motor learning
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Pathology of Ataxia
- Lesions
- Unilateral cause jerky uncoordinated movements
- Vermal causes truncal instability
- Paravermal causes gait and limb ataxia
- Vistibulocerebellum causes nystagmus and difficulty maintaining balance
- Inherited disorders - Degeneration of Purkinje cells
- Purkinje neurons release NT GABA which inhibits the firing rate of neurons therefore inhibiting unwanted involuntary movements
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Primary Clinical Features of Ataxia
- Low muscle tone
- Asynergy - lack of coordination
- Dysmetria - inability to judge distance or scale
- Dysdiadochokinesia - inability to perform rapid movements
- Primary features dependent on part of the cerebellum affected
- -Vestibulocerebellum dysfunction
- --Impaired balance and control of eye movements
- --Postural instability
- -Cerebrocerebellum dysfunction
- --Appendicular Ataxia = impaired ability to perform smoothly coordinated voluntary movements
- -Spinocerebellum dysfunction
- --Wide based gait
- --Uncertain starts and stops, lateral deviations, and unequal stops
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Upper Motor Neuron Lesions
- Cerebral Palsy
- Brain injury
- MS
- Brain tumors
- CVA
- SCI
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Common characteristics of UMN Lesions
- Paresis
- Abnormal muscle activity
- -Cocontraciton or over/underactive m activity
- Abnormal cutaneous reflexes
- Hyperactive stretch reflex
- Muscle tone/spasticity = overactivity of muscles both with movement and "at rest"
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