2.2 Flashcards
Association cortex
Refers to the parts of the brain that receive multiple inputs which work so that we can respond to our experience
What happens when you receive a visual signal?
Visual signal goes to the primary visual cortex –> motor association areas –> premotor cortex –> primary motor cortex –> voluntary movement
Motor cortex and movement
The motor cortex is only one of three areas of the brain controlling movement.
While the premotor cortex is planning movement, there is also input:
- basal nuclei: to initiate purposeful movement
- cerebellum: to coordinate movement
Primary motor cortex
The primary motor cortex generates motor signals.
It executes distinct, well-defined, voluntary motor activity.
- contralateral
- homunculus: illustration showing how much of your brain controls different body parts
Primary somatosensory area
Provides feedback about the movement generated by the primary motor cortex
Premotor cortical areas
Work together to plan complex movement
1. Premotor cortex
2. Supplementary motor cortex
3. Frontal eye fields
4. Cingulate motor areas
- part of the limbic lobe
- memories and emotion
- motivation
Premotor cortex
The premotor cortex appears to be involved in the selection of appropriate motor plans for voluntary movements
Postural support of axial and girdle muscles
Receives parietal lobe sensory projections
Supplementary motor cortex
Programming of elaborate movement
- often with athletes and musicians
- bilateral coordination
- trunk and girdle muscles
Frontal eye fields
Coordinates eye movement
Cingulate motor areas
Motivational, emotional aspects of movement
Posterior parietal area
Provides tactile and visual guidance by projecting to the supplementary and premotor cortices
Activated even when you aren’t moving
Dependent on proprioception
- tactile and visual guidance to support motor activity
Cell layers of the cerebral cortex
The grey matter of the cerebral cortex has 6 layers of cells, each with a specific function.
- Layer V is mot prominent in the motor cortex. The cell bodies are pyramidal shaped.
- These are the cell bodies of the upper motor neurons.
White matter paths through the cerebrum
Grey matter cells send axons down through the white matter, carrying signals to other parts of the CNS. The white matter is arranged into bundles such as tracts, peduncles, and corpus callosum.
Axons of the upper motor neurons form white matter bundles.
Corona radiata
Corticospinal tract
Originates with the motor cortex areas and descends to the spinal cord, carrying motor signals.
These are the upper motor neurons and they will synapse with one of 3 cells:
- interneurons
- alpha motor neurons
- gamma motor neurons
Corticospinal tract pathway through brain and brainstem
Axons descend: corona radiata –> internal capsule –> midbrain –> pons -> most fibers decussate in the lower medulla (pyramidal decussation) –> spinal cord
Another view:
Lateral corticospinal tract
Mediates the execution of rapid, skilled voluntary movements of the distal musculature of the upper and lower limbs, especially the intrinsic muscles of the hand.
Anterior corticospinal tract
Postural muscles
The fibers influence the neurons that innervate the axial and proximal limb (girdle) musculature.
Cross section of corticospinal tract
R anterior corticospinal tract caries signals from the R hemisphere
R lateral corticospinal tract carries signals from L hemisphere.
Corticonuclear tract
Similar to corticospinal tract but terminates in the head and neck, synapsing on:
- cranial nerve nuclei
- brachiomotor nuclei: skeletal mm of head and neck
Pyramidal tract
The pyramidal tracts are part of the upper motor neuron system and are a system of efferent nerve fibers that carry signals from the cerebral cortex to either the brainstem or the spinal cord.
It divides into two tracts: the corticospinal tract and the corticonuclear tract.
It terminates on interneurons, alpha motor neurons, and gamma motor neurons.
Motor tract termination
CST and CNT terminate on
- interneurons
- alpha motor neurons
- gamma motor neurons
Interneurons
connect 2 neurons, facilitating or inhibiting signals
Alpha motor neurons
Synapse on muscle fibers causing skeletal muscle contraction
Lower motor neurons
They carry signals to the muscle which cause the muscle to contract.
Gamma motor neurons
synapse on muscle spindles allowing sensory feedback regarding muscle action
Muscle spindles
Provide sensory feedback regarding muscle movement
Extrafusal muscle fibers
Make up the bulk of the muscle and cause muscular contraction leading to movement
- innervated by alpha motor neuron
They contract to generate movement.
Intrafusal muscle fibers
Make up the muscle spindles and provide feedback regarding muscular contraction
Innervated by gamma motor neurons as well as sensory fibers
Alpha-gamma coactivation
Alpha motor neurons cause contraction of extarfusal muscle fibers, and gamma motor neurons keep the intrafusal muscle fibers in place so that the sensory neurons can do their job.
UMN vs LMN damage
LMN carries the signal that commands contraction.
- flaccid
UMN command contraction and keep spinal reflexes under control. When UMN are damages, spinal reflexes are unleashed.
- spasticity, increased tone
Upper motor neuron damage symptoms
More muscle contractions
- spastic
More muscle tone
- hypertonic
More muscle reflexes
- hyperreflexic
More disuse atrophy
Toes point up
- positive babinsky
Lower motor neuron damage symptoms
Less muscle contractions
- flaccid
Less muscle tone
- hypotonic
Less muscle reflexes
- hyporeflexic
Less muscle innervation
- denervation atrophy
Toes point down
- negative babinsky
Amyotrophic lateral sclorosis
Most common neurodegenerative disease
Affect only the motor system
Both UMN and LMN are affected
Associated with genetic mutations
Starting with desire, how does the brain generate movement?
The desire to move originates somewhere in the association cortex in response to something that one sees, hears, smells, tastes, feels, or thinks about.
The association cortex relays this information to the premotor cortical areas where impending voluntary movement is planned and a design of the plan is generated.
Signals of the plan are relayed to the primary motor cortex where execution of the voluntary movement is initiated.
The primary motor cortex and premotor cortical areas contain the cell bodies of upper motor neurons whose axons descend along with axons from the primary somatosensory cortex as the corticonuclear tract to the brainstem and the corticospinal tract to the spinal cord, sending signals about voluntary movement of the head and body, respectively.
The upper motor neurons influence lower motor neurons located in the cranial nerve motor nuclei (except the oculomotor, trochlear, and abducens nuclei) and the ventral horn of the spinal cord.
The axons of the lower motor neurons form bundles (peripheral nerves, i.e., cranial nerves and spinal nerves) that stimulate skeletal muscle cells and cause them to contract to produce movement.
What are the 3 major regions of the brain that control movement?
Motor activity is controlled by intricate interactions of three major regions of the brain: the cerebral cortex, the basal nuclei, and the cerebellum.
Cerebellar cortex
the ultimate command center of the nervous system, is involved in the planning and execution of complex voluntary motor activities
Basal nuclei
functions in the initiation of movement, and modulation of the motor cortex
Cerebellum
receives information from the cerebral cortex, as well as the visual, auditory, vestibular, and somatosensory systems, which it integrates and utilizes to plan, modify, and coordinate movement
Briefly summarize the role of the primary motor cortex
The primary motor cortex functions in the execution of distinct, well-defined, voluntary motor activity of the contralateral side of the body.
Briefly summarize the role of the premotor cortical areas
The premotor cortical areas function in the programming of complex motor activity, which is then relayed to the primary motor cortex where the execution of motor activity is initiated.
Which cells are the primary output neurons of the cortical descending motor pathways?
Pyramidal cells
Where do the corticospinal and nuclear pathways terminate?
spinal cord and brainstem
What is the neurotransmitter of the pyramidal cells?
Glutamate – an excitatory neurotransmitter that stimulates excitatory or inhibitory interneurons or sometimes lower motor neurons
Which descending tracts originate in the sensorimotor cortex?
Lateral and anterior corticospinal tracts and the corticonuclear tracts
What tracts originate in the brainstem?
Tectospinal, rubrospinal, reticulospinal, and vestibulospinal tracts
Where do all the descending tracts terminate?
All of the descending tracts terminate in the spinal cord with the exception of the corticonuclear tract, which terminates in the brainstem.
What percentage of the corticospinal tract fibers decussate at the pyramidal decussation?
85-90%
Pyramidal cells are which: upper or lower motor neurons?
upper
What percentage of CST fibers terminate at each level of the spinal cord?
55% at cervical to influence upper limb musculature, especially hand
20% thoracic
25% lumbar and sacral
Where are the cell bodies of the lower motor neurons?
Anterior (motor) horns of the spinal cord
- The cell bodies of the lower motor neurons serving the trunk muscles occupy the medial aspect of the ventral horns of the spinal cord
- The cell bodies of the lower motor neurons serving the upper and lower limb muscles reside in the lateral aspect of the ventral horns of the spinal cord and are concentrated at cord levels that are the sites of origin of the brachial plexus and lumbosacral plexus, structures that innervate the upper and lower limbs
Corticotectal and tectospinal tracts
The tectospinal tract is involved in the coordination of head movements with eye movements elicited by visual, auditory, and vestibular stimuli.
Corticorubral, rubrobulbar, and rubrospinal tracts
The rubrospinal tract (and all the corticospinal tract) functions in controlling the movement of the hand and digits, by facilitating flexor muscle tone and inhibition the extensor musculature of the upper limb.
Corticoreticular fibers and reticulospinal tracts
The reticulospinal tracts influence the motor control of axial (trunk) and proximal limb musculature and are involved in posture maintenance and orientation of the limbs in an intended direction.
Vestibulospinal tracts
The lateral vestibulospinal tract is involved in the maintenance of posture and balance; the medial vestibulospinal tract mediates head movement while maintaining gaze fixation on an object.
Corona radiata
white matter projections from the cerebral cortex coalesce to form the internal capsule, a bundle of fibers that feeds into the motor tracts.
