7d Descending Tracts (Motor Pathways) - Coggle Diagram
Descending Tracts (Motor Pathways)
The descending (motor) pathways alter the balance of excitatory and inhibitory input that converge upon the ex-motor neurons by three
by synapsing directly upon the α-motor neurons; this pathway has the
advantage of speed and specificity;
by synapsing directly on the γ-motor neurons which precisely control
the stretch reflex;
by synapsing on interneurons which act as switches that enable a
movement to be turned ‘on’ or ‘off’ under the demand of the higher motor centers.
directly on α-motor neurons- speed/specificity
directly on the γ-motor neurons- control the stretch reflex
synaps on interneurons- act as switches/
movement can be turned ‘on’ or ‘off’ by higher motor centers.
pyramidal tract fibers to
the spinal ventral horn cells
pyramidal tracts to
the motor cranial nuclei
begins in the cerebral
cortex and ends in the brain stem
is the longest tract
starts from the motor cortex
up to the last segment of the SC.
It's present only in higher animals and man
where cerebrum has developed.
is a slowly conducting pathway
and 50% of the fibers are unmyelinated.
Corticospinal & Corticobulbar Tracts
30% - from the motor cortex, area 4 in precentral gyrus,
30% - from the premotor cortex, area 6,
& the remaining
40% - from the somatosensory areas I and II,
adjacent parietal lobe association cortex.
The pyramidal tract fibers which arise
from the cerebral cortex converge towards the brain stem as a radiating
mass of fibers known as Corona Radiata
to reach the internal capsule.
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.
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.
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.
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
The pyramidal tract were so
called because of their shape as they pass along the surface of the medulla.
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