Motor

• Motor tracts transmit information from the brain to muscles
• The cerebellum is important for the smooth coordination of movements, rapid movements that must be planned with little chance for feedback, and the learning of motor skills.It is thought to create a forward model that helps to predict the sensory consequences of a motor plan.
• Via its connections through a series of loops through the thalamus and up into the cortex, the basal ganglia can modulate the initiation and cessation of movements. They also play a role in motor planning and learning.
• Primary motor cortex generates movement most likely by controlling the force or other parameters of muscle movement. The supplementary motor complex is thought to be involved in specifying, preparing, and initiating a motor plan for an action, which is an abstract representation of an intended movement that is preprogrammed before the motor act is initiated.
• Premotor regions are thought to specify the type of motor action (such as a grasp) that is necessary to perform a task A portion of the premotor area, known as the frontal eye field, programs voluntary eye movements such as those involved in scanning visual space.
• The anterior cingulate cortex plays an important role in the selection of motor responses, especially when they are novel or atypical. It also plays a role in the evaluation of the outcome of such movements, such as wirether or not they lead to an error.
• The right inferior frontal cortex has been suggested to play a specific role in the inhibition of motor responses.
• The parietal lobe links movements with sensory information, including visual, proprioceptive, and kinesthetic information. It is thought to estimate what motor actions are required to meet a particular end state, and can aid in the online modulation of actions. It is also important for linking motoric actions to their conceptual significance, such as occurs when saluting or making the sign of the cross.
• Complex action requires the coordinated effort of all these regions in an integrated manner.
• Subcortical motor disorders affect the form and timing of movements, whereas cortical motor disorders affect the conceptual clarity of motor acts, either by disrupting the sequencing of complex motor acts or by disrupting the ability to have a motor act represent a concept.
• Parkinson's disease, which occurs because the putamen does not receive dopaminergic input due to the death of cells in the substantia nigra, results in an inability to initiate (akinesia) or slowness of spontacous movement (bradykinesia), rhythmic oscillating movements (tremors), rigidity of movement (cogwheel rigidity), and disturbances of posture.
• Huntington's disease, which occurs because of damage to the striatum, results in involuntary, undesired jerking and writhing movements. Tourette's syndrome, a rare disorder that manifests itself in childhood, is characterized in less severe cases by ties and twitching of the face, the limbs, and other regions of the body. In more severe cases, the patient makes vocalizations such as cries, grunts, and curses.
• Apraxia is a disorder that typically results from left inferior parietal lesions or left frontal lesions and prevents the individual from performing sequential skilled motor acts.
• There are many competing classifications of apraxic disorders. Some emphasize the body part that is affected, others emphasize the difference between movements required to use objects as compared with those that have symbolic significance, and still others emphasize whether the idea of movement is lost or whether such ideas are intact but disconnected from the movements required to implement them.
• There are other disorders that interfere with movements but that are not true apraxias because they mainly involve deficits in visuospatial processing. In constructional apraxia items cannot be correctly manipulated with regard to their spatial relations; while in dressing apraxia, the limbs and clothes cannot be manipulated so as to dress.
• Callosal apraxia is a disconnection syndrome characterized by an ability to perform movements or manipulate objects with the left hand in response to verbal commands due to a lesion of the corpus callosum.
• Motor unit

  A motor neuron and the muscle fibers it innervates
• Motor unit

  • Acts on contralateral muscles
  • Speech is highly depended on muscle coordination (1,400 motor commands per second)
• Describes the relationship between a motor neuron and muscle fibers that it innervates. Innervates means "to supply with nerves."
• Muscles are composed of muscle fibers that are either contracted or uncontracted. This contraction is caused by electrical impulse from a motor neuron (located in ventral portion of spinal cord). One motor neuron innervates a number of muscle fibers.
• Motor unit

  • Fine motor control/ skills
• Motor plan

  Also called a plan of action is an abstract representation of intended movement. Includes general information about the goal that a series of movements is intended to achieve and also information about the neuromuscular control that will allow the goal to be reached.
• Neuromuscular junction

  The synapse between a neuron and muscle fibers are LARGER and has more specialized structure than a typical synapse
• For muscles to move, info must be relayed from the NS to the muscles across the neuromuscular junction.
• When neuromuscular junction is interrupted, paralysis. Where in the spinal cord the Damage occurs results in how much of the body is paralyzed and how much sensation is lost.
• Pattern repeats at each level of the spinal cord but for different areas of the body.
• Spinal column

  The bony structure housing the spinal cord is composed of many sections called vertebrae. There is one nerve cell located dorsally (toward back) receives sensory information. Cells in ventral region (towards stomach) convey MOTOR commands to muscles, receives input from brain and other regions of spinal cord.
• Motor Tracts

  How information gets from the brain to the muscles. How information reaches the target muscles to execute movements from the planned movements in the brain.
• However, subcortical and cortical regions determine the form, sequencing, and planning of these movements whereas the motor tracts are just the messengers.
• 2 major sets of pathways link brain to muscles

  • Lateral pathway also known as the lateral corticospinal tract
  • Medial Pathway
• Lateral pathway

  • Cell bodies are located mainly in the PRIMARY MOTOR CORTEX
  • This tract crosses entirely from one side of the brain to the opposite side of the body in the medulla
  • Responsible for the fine movement of distal limb muscles (arms, hands, fingers, lower leg, foot)
  • Damage to these cell bodies in this tract (motor cortex) results in deficits in movement on the opposite side of the body. Can also disrupt the ability to reach, grasp, and manipulate objects.
• Medial Pathway

  • Involved in control of movements of the trunk and proximal limb muscles
  • Projects contralateral and ipsilateral and is mainly involved in the control of posture, bilateral movements such as standing, bending, turning, and walking.
• Cerebellum

  A subcortical region involved in motor control. Posterior to the brain. Divided into three main divisions.
• Cerebellum

  • Role in coordination of muscle movement timing, the planning of movements, and the learning of motor skills
  • Plays critical role in sensorimotor learning because it promotes understanding of the nature of the temporal relationships between events
  • Organized in three main division, each receive a distinctive type of information and then in turn send their output to distinct portions of the NS.
• Spinocerebellum

  Medial regions of the cerebellar hemispheres.
• Spinocerebellum

  • Receives somatosensory and Kinesthetic information (info about body movements derived from the muscles, skin, and joints). From the sponal cord and projects back to the spinal cord
  • Damage here could result in difficulty with the smooth control of movement
  • Medial areas: involved in movement of proximal muscles, such as coordinating the trunk and leg muscles for walking
  • Lateral areas: involve moving distal muscles (arm muscles). Ability to position arms, regulation of agonist and antagonistic muscles in sequence is disrupted (also known as the antagonistic pairs).
• Cerebrocerebellum

  Receives input from diff. regions of the cortex (motor and association cortices).
• Cerebrocerebellum

  • Regulation of highly skilled movement that requires complex spatial and temporal sequences involving sensorimotor learning.
• Vestibulocerebellum

  Phylogenetically oldest part of the cerebellum
• Vestibulocerebellum

  • Receives input from the vestibular nuclei in the brainstem and then projects back to this region
  • Damage here leads to difficulty with balance and to postural instability