motor system Flashcards
components of hierachy
- Neocortex (conscious), brainstem and spinal cord (automatic)
- Normally functions as a whole
- Hughlings-Jackson (19th Century)
- Conceived of nervous system as organized in successive layers, with higher levels controlling complex behavior by acting through lower levels
- Adapted from evolutionary theory
hierachical control of movement: steps 1 to 8
- visual info required to locate the target
- frontal-lobemotor areas plan the reach and command the movement
- spinal cord carries info to the hand
- motor neurons carry message to muscles of the hand and forearm
- sensory receptors on the fingers send message to sensory cortex saying that the item has been grasped
- spinal cord carries sensory info to the brain
- basal ganglia judge grasp forces, and cerebellum corrects movemnet errors
- sensory cortex receives message that the item has been grasped
the forebrain and initiation of movement
Frontal Lobes (Neocortex)
- Prefrontal Cortex: Planning of movements, specifying the goal (e.g. deciding to play with smartphone)
- Premotor Cortex: Organizes motor sequences (e.g. select movements appropriate to the context of the action)
- Primary Motor Cortex:
- Produces specific, skilled movements
the motor cortex; history
1870: Fritsch and Hitzig
- Electrical stimulation of a dog’s cortex produced movement of mouth, limbs, and paws
- 1930s: Wilder Penfield
- Used electrical stimulation to map the cortices of human patients who were about to undergo neurosurgery
- Confirmed the role of primary motor cortex in producing movement in humans
organisation of the motor system → the motor cortex
Homunculus (little person)
- Representation of the human body in the sensory or motor cortex
- Topographic Organization
- The parts of the motor cortex that control the hands, fingers, lips, and tongue are disproportionately larger than parts of the motor cortex that control other areas (e.g. foot)
organization of the motor system → corticospinal tracts
Corticospinal Tract (pyramidal tract)
- Bundle of nerve fibers directly connecting the cerebral cortex to the spinal cord
lateral corticospinal tracts
- Branches at the brainstem level, crossing over to the opposite side of the brain and spinal cord
- Moves the digits and limbs on the opposite side of the body
- Ventral Corticospinal Tract
- Remains on the same side of the brain and spinal cord
- Moves the muscles of the midline body (trunk) on then same side of the body
organization of the motor system → motor neurons
- Two kinds of neurons located inthe spinal column’s ventral horns
- Interneurons project to motorneurons
- Motor neurons project tomuscles of the body
- Laterally located motorneurons project to the muscles that control thefingers and hands
- Intermediately located motor neurons project to muscles that control the arms and shoulders
- The most medially located motor neurons project to muscles that control the trunk
organization of the motor system → control of muscles
- Motor neurons release acetylcholine at the neuromuscular junction and triggers muscle contraction
- Limb muscles are arranged in pairs
Extensor
- Moves (extends) the limb away from the trunk
Flexor
- Moves the limb toward the trunk
extensor
muscles
Moves (extends) the limb away from the trunk
flexor
muscles
Moves the limb toward the trunk
consequences of spinal cord damage
- Quadriplegia
- Paraplegia
what is Quadriplegia
Paralysis of the legs and arms due to spinal cord injury
what is paraplegia
Paralysis of the legs due to spinal cord injury
basal ganglia
anatomy
- Collection of subcortical (below the cortex) nuclei within the forebrain
- Striatum (caudate, putamen, accumbens), globus pallidus, substantia nigra, subthalamic nucleus
where does the basal ganglia recieve input from
- All areas of the neocortex (e.g. motor cortex) and limbic cortex (e.g. amygdala, hippocampus)
→ These areas are not part of the basal ganglia
- Project back to the motor cortex
- Allow us to adjust the force of our movements
the volume hypothesis
the basal ganglia and movement force
- The internal globus pallidus acts like a volume dial and projects to the thalamus, which projects to the motor cortex
- Two pathways within the basal ganglia
- Direct (overall excitatory, promotes movement)
- Inhibitory effect on GPi:
- Too much activity leads to overactivity in the thalamus and amplified force of movement
- Inhibitory effect on GPi:
- Direct (overall excitatory, promotes movement)
- Indirect (overall inhibitory, suppresses movement)
- Excitatory effect on GPi:
- Too much activity leads to underactivity in the thalamus and reduced force of movement
- Excitatory effect on GPi:
damage to the basal ganglia can lead to what ?
- hyperkinetic symptom
- hypokinetic symptom
what are hyperkinetic sympyom
basal ganglia
Symptom of brain damage that results in excessive involuntary movements, as seen in Huntington’s Chorea
what are hypokinetic sympyom
basal ganglia
Symptom of brain damage that results in a paucity of movement, as seen inParkinson’s disease
what is huntington’s chorea
genetic disorder, affects muscle coordination
- - atrophy of striatum [caudate nucleus and putamen] and degeneration of indirect pathway neurons while direct pathway spared
→ loss of ‘braking system’ while accelerator spared
symptoms of huntington’s chorea
excessive spontaneous movements, irregularly timed, randomly distributed, and abrupt in character
how do you treat huntington’s chorea
antipsychotics [e.gy clozapine] that block dopamine transmission
what is parkinson’s disease
- Slowly progressive disorder that affects movement, muscle control, and balance
- Loss of substantia nigra that sends dopamine projections to putamen that
controls movement and coordination.
(can be chemically induced by the toxin ‘MPTP’ - Dopamine normally increases activity
in the direct pathway (D1R expressing)
neurons, and decreases activity in the
indirect pathway (D2R expressing
neurons) - Studies from Parkinsonian (MPTP
treated) monkeys show that there is
overactivity in the indirect pathway and
underactivity in the direct pathway
symptoms of parkinson’s disease
slowness of movement,
resting tremor, stiffness of muscles,
‘gait’: small shuffling of steps
treatment for parkinson’s disease
*Treatment is L-Dopa- >dopamine precursor
* Boost dopamine levels and increase its transmission
* Loss of efficacy in many patients > 5 years
