Chapter 14: Brain Control of Movement Flashcards
The Major Tracts
Describe the characteristics of the corticospinal tract
- Decussation in medullary pyramids; Contralateral motor control
- Pathway carrying motor info from primary to secondary motor cortices to the brain stem and spinal cord
- One of the largest and longest axon tract in the CNS
The Major Tracts
What are the two major pathways and what are the functions?
- Lateral Pathway - voluntary movement of distal musculature
- Ventromedial pathways - control of posture and locomotion; upper motor neurons are in brainstem
The Major Tracts
Describe the characteristics of the Rubrospinal tract
- Originates in the red nucelus of the midbrain
- **Receives input from frontal regions that contribute to corticospinal tract **
- Axons decussate in pons
- Runs parallel to corticospinal tract
- Function is largely reduced in humans
The Major Tracts
What is the Babinki sign and what does it test?
- Easy test for motor tract damage
- If the toes curl in adults then ur fine but if it doesnt then ur not okay
- This tests the cortiospinal tract
The Major Tracts
What are the four ventomedial pathways?
They all originate in the brain stem
1. Vestibulospinal tract
2. Tectospinal trat
3. Pontine Reticulospinal tract
4. Medullary reticulospinal tract
The Major Tracts
Describe the Tectospinal tract
- Originates in the superior colliculus (optic tectum) of midbrain
- Recieves direct projections from retina
- Orienting response to project image on the fovea
- Axons decussate after immediately leaving superior colliculus
Motor Cortex
What is area 4?
The primary motor cortex (M1)
* Stimulation leads to muscle twitches on contralateral side
Motor Cortex
What is area 6?
Higher Motor area (Penfield)
- Stimulation leads to more complex movement
- There are two parts
1. Lateral region: premotor area (PMA)
2. Medial Region: Supplementory area (SMA)
Motor Cortex
What are mirror neurons?
Some neurons in BA6 (PMA) respond when watching another monkey making the same movements
The basal ganglia
What are the characteristics of the basal ganglia?
- Globus pallidus (internal & external )
- Subthalamic nucleaus
- Caudate nucleaus + Putamen = Striatum
- Striatum is the target of cortical input to the bg
- GP is the source of output to the thalamus
- Substantia nigra sends DA input to striatum and the process starts over.
The basal ganglia
What does the basal ganglia do?
- Projects to the ventrl lateral (VLo) nucleus of thalamus
- Provides major input to BA6
The basal ganglia
Describe the motor loop
Cortex
* Projects back to basal ganglia
* Froms a loop. Cotical-striatal-thalamo-cortical (CSTC)
* Invovled in the selection and initiation of willed moevements
* Cortex—>Basal ganglia—>VLo—>Cortex
The basal ganglia
Describe the characteristics of the basal ganglia’s direct pathway
Selects appropriate motor actions
Cortical Activation:
* Excites putamen
* Inhibits internal globus pallidus (Gpi–spontaneously active at rest)
* Releases VLo from Gpi
* Acivity in VLo increases activity in BA6
The basal ganglia
Describe the characteristics of the basal ganglia’s indirect pathway
- Antagonizes motor functions of the direct pathway
* Suppresses competing and innapropriate motor programs - Includes the GPe and Subthalamic nucleus (STN)
- cortex activates striatum
- Striatum inhibits GPe
- Lead to release of inhibition of GPi and STN
- Activation by cortex inhibits the thalamus
The basal ganglia
Summarize the basla ganglia all together
- Info flows parallel
- Regulates motor thalamus
- Direct pathway: selects appropriate motor actions
- Indirect pathway: suppresses competing and innapropriate motor programs.
Basal ganglia disorders
What are major disorders and describe them
- Parkinsons Disease and Huntington’s Disease
- Neurodegenerative diseases
Chracterized by:
* Hypokineasia - paucity of movement ( parkinson’s disease)
* Hyperkineasia - excess of movement (huntington’s disease)
Basal ganglia disorders
Go more in-depth about Parkinson’s disease
- Trouble initiating willed movements
- Symptoms: Hypokinesia Bradykinesia (slowness of movement), rigidity, temors of hand and jaw
- Lack of DA input to striatum
- Increased inhibition of the thalamus by basal ganglia
- Sustained tonic inhibition from GPi to thalamus
- Thalamus is less likely to excite motor neurons
- Inhibition wins
Basal ganglia disorders
Go more in-depth about Huntington’s Disease
- Polyglutamine disease
- Symptoms: Chorea, hyperkineasia, dyskinesias, dementia, personality changes
- Loss of neurons in caudate nucleus, putamen, globus pallidus
- consequent loss of inhibitory input to the thalamus
*Excitation wins
Basal ganglia disorders
desribe huntington’s disease BG circuit
- Projection from striatu to GPe is diminished
- Increases inhibition to STN & GPi
- Thalamic excitation is increased
- Excitation wins
Control of Movement in Primary Motor Cortex
Why is broadman’s area 4 designated as PMC or Primary Motor Cortex?
It has the lowest threshold for eliciting movements from electrical stimulation.
Control of Movement in Primary Motor Cortex
What happens in Cortical layer V?
It is the pathway where motor neurons activate LMNs.
Betz Cells
* Largest pyramidal cells
* Projects to pools of LMNs (lower motor neurons) and excites them
* Branches and excites local inhibitory interneurons
* Provides reciprocal inhibition or flexors qand extensors of the muscle/joints.
Control of Movement in Primary Motor Cortex
How are the commands to perform precise movements encoded in the activity of the upper motor neurons?
- We record pyramidal cells during visually guided reaching movements then observe a burst of activity immediately before and during voluntary movement.
- Encodes both force and direction
- **Movement direction tuning of individual M1 neurons is broadly tuned so cells can respond best to a particular direction of motion. **
Control of Movement in Primary Motor Cortex
What encoded movement of direction?
- Collective Activity of neurons -** Population coding **
- Motor cortex: most cells active for every movement
* Activity of each cell represents a “vote” and the direction of movement is determined by an average of all votes by each cell in the population - the larger the population of neurons representing a type of movement, the finer the potential control.
Control of Movement in Primary Motor Cortex
Can M1 cells switch from participating in one type of task to another?
Yes!
**Plasticity ** in the adult motor cortex
* For example, if we cut a mouse whisker then the there would still be microstimulation that causes eye or forelimb movements.
The Cerebelllum
What is the anatomy of the Cerebellum?
- Folia and lobules which serve to increase surface area
- Deep cerebellar nuclei which relays cerebellar cortical output to brain stem structures
- Vermis: midline ‘bump’
- axial musculature
- contributes to ventromedial pathways
- Cerebellar hemispheres: limb movements
- Contributes to lateral pathways
The Cerebelllum
What is the function of the cerebellum?
- Coordinate a detailed sequence of muscle contractions
- maintains fluidity of muscles
The Cerebelllum
What are the three cerebellar lesions?
- Ataxia: uncoordinated and inaccurate movements (Looks like u drunk)
- Dyssynergia: Decomposition of synergistic multi-joint movement (move like a lil barbie)
- Dysmetria: Overshoot or undershoot target
- Dyssynergia and dysmetria are characteristic of alcohol intoxication.
The Cerebelllum
Describe granule cells
- Tiny excitatory neurons
*dominate cells in cerebellum
The Cerebelllum
What are purkinje cells?
- Largest neurons in the cerebellum
*** Recieves excitatory input from granule cells in the moleculr layers - Sends inhibitory axon to deep cerebellar nuclei. **
The Cerebelllum
Describe the motor loop through the lateral cerebellum
Input to pontine nuclei
* Axons from layer V pyramidal cells in the sensorimotor cortex send massive projections to pons which then go to the cerebellum for processing called the corticopontocerebellar projection
* The cerebellum then projects back to the motor cortex via deep cerebellar nuclei and VL thalamus and then projects back to mtor cortex.
The Cerebelllum
Why is the cerebellum a sit of motor learning?
- Instructs the primary motor coretx
- Uses past experience to make predictions about outcome
