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27 Cards in this Set
- Front
- Back
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Movements can only be accomplished by means of ? |
Spinal cord or brain stem lower motor neurons, which innervate skeletal muscle (the lower motor neuron is the final pathway for movement).
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What lies anterior to the primary motor cortex on the lateral aspect of the hemisphere?
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Premotor cortex (important for sensory guidance of limb movements)
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What lies anterior to the primary motor cortex on the medial aspect of the hemisphere?
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Supplementary motor cortex (important for programming motor sequences and indirectly in preparing for motor function)
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Generally, what do the premotor and supplementary motor areas do?
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Give a higher level of control over all lower components of the motor system hierarchy
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Generally, what does the primary motor cortex area do?
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Gives a higher level of control over the brain stem motor centers and direct control over the brain stem and spinal cord lower motor neurons. Conscious movement requires activation of the primary motor cortex.
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Where is the motor cortex located?
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Anterior wall of central sulcus and the precentral gyrus
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What type of cells does the motor cortex contain?
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Large numbers of pyramidal shaped (output) cells. Some are very large and referred to as Betz cells.
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What does the somatotopic representation of the motor cortex (e.g., the motor homunculus) look like?
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Leg -- Medial/superior aspect
Arm -- Upper lateral aspect Face -- Lower lateral aspect *More cortex devoted to muscles that perform fine movements (e.g., fingers, face) than to those involved in proximal movements |
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What fibers make up the pyramidal system?
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Corticobulbar: projects to brain stem
Corticospinal: projects to spinal lower motor neurons |
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Where do the fibers of the pyramidal system arise from?
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Motor cortex: 30%
Premotor cortex: 30% Parietal lobe: 40% (mainly primary somatosensory cortex) |
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How are the pyramidal fibers arranged in the posterior limb of the internal capsule?
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Somatotopically (face-arm-leg from anterior to posterior). This arrangement continues throughout their course in the brain.
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What area of body does the corticobulbar control movement for?
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Head (specifically, mastication (V), facial expression (VII), pharynx and larynx (IX and X), neck (XI), and tongue (XII)).
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Describe the pathway of the corticobulbar tract
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Primary motor cortex, corona radiata, anterior part of the posterior limb of the internal capsule, and terminates on successive brain stem lower motor neuron nuclei that give rise to the cranial nerves V, VII, IX, X, XI, XII.
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What area does the corticospinal tract control movement for?
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The body below the head/neck
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Describe the pathway of the corticospinal tract
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Primary motor cortex, corona radiata, anterior part of the posterior limb of the internal capsule, crus cerebri of the midbrain cerebral peduncle, basilar part of the pons, and the medullary pyramid. It divides at the juncture of the medulla and spinal cord. Most of the fibers cross n the lower medulla and is called the pyramidal decussation. They cross to the contralateral lateral funiculus of the spinal cord, forming the lateral corticospinal tract that extends the length of the cord. The fibers of the lateral corticospinal tract descend to the appropriate segmental level and enter the gray matter of the anterior horn where they terminate on alpha motor neurons that innervate extremity muscles and on related interneurons. (remaining fibers descend uncrossed in the anterior funiculus as the ant. cortricospinal tract). Anterior tract controls neurons in proximal muscles, lateral tract controls neurons in distal extremity muscles.
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How is the brainstem involved in the motor system?
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Brain stem centers provide unconscious reflex control over the spinal cord component of the motor system. Alpha motor neurons inntervating muscles supplied by cranial nerves are located in the brainstem.
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Brain stem descending motor pathways: What are they called and where are they located?
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Termed descending extrapyramidal pathways because do not go through pyramids of medulla. Are called vestibulospinal tract, reticulospinal tract, tectospinal tract, and descending medial longitudinal fasciculus. Located in the ventromedial white matter of the spinal cord.
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Vestibulospinal tract
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Projects from lateral vestibular nucleus in medulla to postural muscles in trunk. Senses changes in equilibrium and is important for maintaining upright posture.
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What does the descending extrapyramidal system do?
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Establish/modulate muscle tone and body posture, provide framework on which skilled, purposeful movements take place. (Involuntary unconscious framework)
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What is the pyramidal system responsible for?
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Initiation and direction of voluntary movements. Occur on the postural framework established by the descending extrapyramidal system.
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Lower motor neuron
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Comprised of brain stem nuclear cell body or spinal cord motor neuron cell body and axon projecting peripherally to striated muscle. These execute all movements.
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What are the profuse, pedominantly ipsilateral segmental inputs to the lower motor neurons?
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Direct projections from muscle spindle afferents, indirect projections by way of interneurons from other receptors including Golgi tendon organs, inputs from other levels of the SC. These inputs permit some general coordinations of posture and extremity movements.
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Which part of the internal capsule do the pyramidal tracts travel through?
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Posterior limb (On posterior limb, from posterior side to anterior side goes leg, trunk, arm, face).
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What part of the crus cerebri of the cerebral peduncle do the corticospinal fibers travel through?
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The middle third
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What happens at the decussation of the pyramids?
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The corticospinal tracts cross to enter the contralateral side of the spinal cord. These are located in the medulla.
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What is the anterior corticospinal tract and where is this tract distributed?
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It is the motor tract that does not cross at the decussation. It is distributed in the cervical and thoracic spinal cord.
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What laminae of the spinal cord gray matter does the lateral corticospinal tract terminate? Upon what kind of neurons?
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Lamina IX (and maybe XIII). Terminates on alpha motor neurons that innervate extremity muscles and on related interneurons in gray matter of anterior (ventral) horn.
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