Neurophysiology 9 Flashcards
Describe the secondary motor cortices/ motor association cortex
The prefrontal areas project into the secondary motor cortices, which include thepremotor cortexand thesupplemental motor area.
These assist in planning and coordinating movements.
Are located adjacent to the primary motor cortex.
The premotor cortex is more lateral, whereas the supplemental motor area is more medial and superior.
The premotor area aids in controlling movements of the core muscles to maintain posture during movement, whereas the supplemental motor area is hypothesized to be responsible for planning and coordinating movement
The supplemental motor area also manages sequential movements that are based on prior experience (that is, learned movements).
Neurons in these areas are most active leading up to the initiation of movement.
For example, these areas might prepare the body for the movements necessary to drive a car in anticipation of a traffic light changing
Describbe the frontal eye fields
Thefrontal eye fieldswhich are responsible for moving the eyes in response to visual stimuli.
There are direct connections between the frontal eye fields and the superior colliculus
Describe Broca’s area
Broca’s area, responsible for controlling movements of the structures of speech production.
Lies anterior to the premotor and primary motor cortex
People with an underdeveloped or damaged Broca’s area cannot produce speech but they do not have impairments to understanding speech.
Describe homunculus of the primary motor cortex
Located in the precentral gyrus of the frontal lobe, arranged as a homunculus.
The neurons responsible for musculature in the feet and lower legs are in the medial wall of the precentral gyrus and the hand and face are in the lateral aspect of the gyrus.
Also, the relative space allotted for the different regions is exaggerated in muscles that have greater innervation.
More cortical space is given to muscles that perform fine, agile movements, such as the muscles of the fingers and the lower face.
Less space is occupied by the muscles that perform coarser movements, such as the buttock and back muscles.
Describe the descending pathways?
The motor output from the cortex descends into the brain stem and to the spinal cord to control the musculature through motor neurons.
These upper motor neurons send axons that synapse onto interneurons and alpha motor neurons.
Thus, neurons located in the primary motor cortex, namedBetz cells, are large cortical cells that synapse with lower motor neurons in the brain stem or in the spinal cord
Any motor command from the primary motor cortex is sent down the axons of the Betz cells to activate lower motor neurons in either the cranial motor nuclei or in the ventral horn of the spinal cord.
Give examples of and describe the descending pathways travelled by the Betz cells
The two descending pathways travelled by the axons of Betz cells are thecorticobulbar tractand thecorticospinal tract, respectively.
Thecorticobulbar systemcontrols brainstem nuclei that innervate cranial muscles.
Thecorticospinal systemcontrols interneurons and motor neurons in the spinal cord.
These two descending pathways are responsible for the voluntary (sometimes, conscious) movements of skeletal muscles
The axons of the corticobulbar tract are ipsilateral, meaning they project from the cortex to the motor nucleus on the same side of the nervous system.
Conversely, the axons of the corticospinal tract are largely contralateral, meaning that they cross the midline of the brain stem or spinal cord and synapse on the opposite side of the body
What are the medial descending spinal pathways?
Medial pathwayscontrol axial muscles and are responsible for posture, balance, and coarse control of axial and proximal muscles.
anterior corticospinal tract
vestibulospinal tracts
reticulospinal tracts
tectospinal tract
What are the lateral descending spinal pathways?
Lateral pathwayscontrol both proximal and distal muscles and are responsible for most voluntary movements of arms and legs.
lateral corticospinal tract
rubrospinal tract
Describe the corticospinal tract
Descends from the cortex through the deep white matter of the cerebrum.
Passes between the caudate nucleus and putamen of the basal nuclei as a bundle called theinternal capsule.
Then passes through the midbrain as thecerebral peduncles, after which it burrows through the pons.
Upon entering the medulla, the tracts make up the large white matter tract referred to as thepyramids
The defining landmark of the medullary-spinal border is thepyramidal decussation, which is where most of the fibres in the corticospinal tract cross over to the opposite side of the brain.
At this point, the tract separates into two parts, which have control over different domains of the musculature.
These different domains are referred to as axial and appendicular facilitated for by the anterior and lateral corticospinal tracts, respectively.
Describe the lateral corticospinal tract
Is composed of the fibres that cross the midline at the pyramidal decussation.
The axons cross over from the anterior position of the pyramids in the medulla to the lateral column of the spinal cord.
These axons are responsible for controlling appendicular muscles.
This influence over the appendicular muscles means that the lateral corticospinal tract is responsible for moving the muscles of the arms and legs
The ventral horn in both the lower cervical spinal cord and the lumbar spinal cord both have wider ventral horns, representing the greater number of muscles controlled by these motor neurons.
Thecervical enlargementis particularly large because there is greater control over the fine musculature of the upper limbs, particularly of the fingers.
Thelumbar enlargementis not as significant in appearance because there is less fine motor control of the lower limbs
Describe the anterior corticospinal tract
Is responsible for controlling the muscles of the body trunk. I. e., axial control.
These axons do not decussate in the medulla. Instead, they remain in an anterior position as they descend the brain stem and enter the spinal cord.
These axons then travel to the spinal cord level at which they synapse with a lower motor neuron.
Upon reaching the appropriate level, the axons decussate, entering the ventral horn on the opposite side of the spinal cord from which they entered
In the ventral horn, these axons synapse with their corresponding lower motor neurons.
The lower motor neurons are located in the medial regions of the ventral horn, because they control the axial muscles of the trunk.
Because movements of the body trunk involve both sides of the body, this tract is not entirely contralateral.
Some collateral branches of the tract will project into the ipsilateral ventral horn to control synergistic muscles on that side of the body, or to inhibit antagonistic muscles through interneurons within the ventral horn.
Through the influence of both sides of the body, the anterior corticospinal tract can coordinate postural muscles in broad movements of the body.
These coordinating axons in the anterior corticospinal tract are often considered bilateral, as they are both ipsilateral and contralateral.
What is the extrapyramidal system/controls?
Refers to the other descending connections between the brain and the spinal cord.
Also called the extrapyramidal system.
The name comes from the fact that this system is outside the corticospinal pathway, which includes the pyramids in the medulla.
The pathways of the extrapyramidal system are influenced by subcortical structures.
For example, the basal nuclei, which are important for regulating movement initiated by the CNS, influence this system as well as its thalamic feedback to the motor cortex
Which pathways contribute to the extrapyramidal controls?
A few pathways originating from the brain stem contribute to the extrapyramidal system.
Thevestibulospinal tractconnects the brain stem nuclei of the vestibular system with the spinal cord.
This allows posture, movement, and balance to be modulated on the basis of equilibrium information provided by the vestibular system
Thetectospinal tractprojects from the midbrain to the spinal cord and is important for postural movements that are driven by the superior colliculus.
Thereticulospinal tractconnects the reticular system, a diffuse region of grey matter in the brain stem, with the spinal cord.
This tract influences trunk and proximal limb muscles related to posture and locomotion.
Also contributes to muscle tone and influences autonomic functions.
Explain the parallel and serial processing of the motor system
Although the motor system is organized hierarchically, the hierarchy is not a simple chain of processing from higher to lower areas.
Many pathways enable the different levels of the hierarchy to influence each other.
Thus, the flow of information through the motor system has both a serial organization (communication between levels) and a parallel organization (multiple pathways between each level).
This parallel organization is critically important in understanding the various dysfunctions that can result from damage to the motor system.
If the motor hierarchy had a strictly serial organization, like a series of links on a chain, then damage to any part of the system would produce severe deficits or paralysis in almost all types of movements.
However, because of the parallel nature of processing, paralysis is actually a relatively rare outcome, produced by damage to the lowest level of the hierarchy.
Damage to higher levels results in deficits in motor planning, initiation, coordination, and so forth, but movement may still possible.
The parallel nature of organization is also important for the ability of undamaged parts of the motor system to compensate (at least partially) for injuries to other parts of the system.
Ventral horn output
