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7d motor pathways - Coggle Diagram

- - - - In the spinal cord the fibers form separate groups according to their site of origin.
- - - - the spinal ventral horn cells constitute the Corticospinal Tracts; and
      - the motor cranial nuclei constitute the Corticobulbar Tracts or Corticonuclear Tracts.
        This is a pathway that begins in the cerebral
        cortex and ends in the brain stem
      - Origin
        
        30% of the pyramidal tract fibers arise from the motor cortex, area 4 in precentral gyrus,
        
        30% from the premotor cortex, area 6,
        
        40% from the
        -somatosensory areas I and II, and
        -adjacent parietal lobe association cortex.
        
        Course
        
        The pyramidal tract fibers which arise
        from the cerebral cortex converge towards the
        rain stem as a radiating mass of fibers
        known as Corona Radiata
        to reach the internal capsule.
        
        1.In the internal capsule.
        
        the pyramidal tracts lie in the bend (the genu), and the anterior 2/3rd of the posterior limb;
        
        point to point discrimination in
        internal capsule substance:
        the fibers concerned with control of head, shoulder, elbow, wrist,fingers, trunk, hip, knee and toe movements are arranged from
        anterior to posterior in this sequential order named.
        
        2.In the mid brain.
        
        In the crus of the mid brain the pyramidal fibers
        lie ventral to the substantia nigra, occupying the middle 3/5th of
        this region.
        
        3.In the pons
        
        The pyramidal fibers occupy the
        most ventral aspect in of trapezium
        while passing through the pons.
        Here, the tract is
        broken up into a series of scattered bundles
        by the nuclei pontis
        and the crossing fibers of
        middle cerebellar peduncle.
        
        5.In the medulla
        
        While coming out of the pons,
        the scattered corticospinal fibers are
        reunited and enter the medulla as a thick bundle.
        It occupies the most ventral part of the medulla producing a separate bulge - the Pyramid.
        
        The pyramidal tract were so
        called because of their shape as they ass along the surface of the medulla.
        
        In the lower part of the medulla,
        80-85% fibers cross to the opposite side,
        enter the lateral white column
        and descend down as lateral corticospinal tract
        or crossed/indirect pyramidal tract.
        It extends throughout the whole cord and
        at each segment some fibers leave the tract,
        turn inwards and end round the anterior horn cells (motor neurons),
        either directly or through interneurons.
        
        About 15-20% fibers do not cross,
        enter the anterior white column near the
        median fissure and descend
        down as anterior corticospinal tract or
        uncrossed/direct pyramidal tract.
        The fibers, ultimately also end round the anterior horn cells of the same side. However, some fibers cross the midline to end round the anterior horn cells of the opposite side.
        
        Functions
        
        Functions of corticospinal tracts
        
        Lateral corticospinal tracts
        -convey motor impulses to the spinal cord for controlling the voluntary movements, specially of the distal limb muscles and are concerned with the fine, precise movements of the fingers and hands to carry out skilled work.
        
        Anterior corticospinal tracts are concerned with the control of muscles of the trunk and proximal portions of the limbs to carry out postural adjustments and gross movements.
        
        They form a part of the pathways for superficial reflexes such as cremasteric, abdominal and plantar reflexes.
        
        Some corticospinal fibers end at excitatory synapses on α and γ- motor neurons,
        whereas other end on interneurons that may
        excite or inhibit the α-motor neurons.
        Thus the effect of the corticospinal pathway on the α-motor neurons may be
        excitatory or inhibitory.
        
        Some of these fibers transmit information from the brain to ‘afferent’ neurons and so can affect afferent system; they do this by ending either:
        
        Presynaptically on the axon terminals of afferent neurons as these fibers enter the CNS; or
        
        Directly on the dendrites or cell bodies of neurons in the ascending pathways;
        
        Corticospinal fibers arising from the somatic sensory area (I and II) and parietal lobe association cortex are concerned with
        sensory-motor coordination.
        For eg, - aiming the hands towards an object n manipulating it,
        -hand-eye coordination etc.
        
        Lesion of these areas causes defects in motor performance that are characterized by inability to execute learned sequences of movements such as eating with a knife and fork.
        
        Functions of corticobulbar
        (corticonuclear) tracts.
        
        These are responsible for voluntary control of muscles of larynx, pharynx, palate, upper and lower face, jaw, eye etc.
        Pseudobulbar Palsy is a condition resulting in paralysis or weakness of the muscles which
        control swallowing, talking, tongue and lip movements due to bilateral lesion of these tracts.