11.2 Flashcards
Motor System Organization
What is a homunculus? (when talking about biopsychology)
A representation of the human body in the sensory or motor cortex; also any topographical representation of the body by a neural area
Where in the body does the right primary motor cortex control movement?
The left side of the body
How is the homunculus in the motor cortex distorted? (2 ways)
- Sizes of neural representation of different parts is disproportionate (cortical magnification)
- Motor homunculus is discontinuous - not a perfect spatial representation
What is topographic organization?
Neural spatial representation of the body or areas of the sensory world perceived by a sensory organ
Where are whole-body movements elicited in the brain?
The premotor cortex
Where are more precise movements elicited in the brain?
M1 (primary motor cortex)
What is the position-point theory?
A theory that states that the motor cortex has a map of where parts of the body can be in space so that when a part of the cortex is stimulated, the associated part of the body moves to the appropriate spatial position, regardless of its starting position
How do motor neurons increase a movement’s force?
By increasing their firing rate and its duration
What is the role(s) of motor cortex neurons?
Planning (timing and force) and initiating movements; simple coding for where we want the position to end (completing the movement)
What happens in M1 when someone imagines movement?
It displays subthreshold activity
What is subthreshold activity?
Activity that is not strong enough to produce a movement
What is constraint-induced therapy?
A procedure in which restraint of a healthy limb forces a patient to use an impaired limb to enhance recovery of function
What does constraint-induced therapy exemplify?
Plasticity in the motor cortex
What are corticospinal tracts?
The main efferent pathway from the motor cortex to the brainstem to the spinal cord
Why are corticospinal tracts also known as pyramidal tracts?
They form bumps (pyramids) on the ventral surface of the brainstem
What happens at the pyramidal protrusion?
Axons cross hemispheres of the body (80% of them)
What is the difference between the anterior corticospinal tract and the lateral corticospinal tract?
The anterior corticospinal tract is uncrossed whereas the lateral corticospinal tract is crossed.
What do the anterior corticospinal tracts do?
Moves the muscles of the midline body (trunk) on the same side of the body
What do the lateral corticospinal tracts do?
Moves the fingers and limbs on the opposite sides of the body
What are the roles of interneurons?
Immediate feedback, involved in organizing complex movements
What is the role of motor neurons?
Carrying all nervous system commands to the muscles
Where in the spinal cord are spinal cord motor neurons (interneurons included) located?
Anterior horns
What does an extensor muscle do?
Moves the limb away from the trunk
What does a flexor muscle do?
Moves the limb in towards the trunk
What is the main neurotransmitter at the neuromuscular junction?
Acetylcholine
The ________ organization of the motor cortex is represented by a(n) ________, in which parts of the body that are capable of the most skilled movements (esp. the mouth, fingers, and thumbs) are regulated by _______ cortical regions
topographic; homunculus; larger
________ theory states that the motor cortex has a map of where body parts can be in space, such that when a part of the cortex is stimulated, the associated body part moves to an appropriate special position
Position-point
Many corticospinal-tract fibers cross to the opposite side of the spinal cord to form the ________ tracts; some stay on the same side to form _______ tracts
lateral; anterior
The anterior corticospinal tracts carry instructions for ___________ movements, whereas the lateral corticospinal tracts carry instructions for ______ and ________ movements
midline; finger; arm
Motor neuron axons in the spinal cord carry instructions to ________ that are arranged in pairs. One ______ a limb; the other ______ the limb
Muscles; extends; flexes
What does the plan of movements in the motor cortex, as revealed by electrical stimulation, tell us about the brain’s representation of movement?
M1 is organized into a set of functional categories that encode a movement lexicon, or dictionary. Used in different combinations, these few movements enable more complex movements
What are the corticobulbar tracts?
Tracts responsible for head muscle movements.
Goes from motor cortex to facial muscles
