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Summary of Neurology Chapter 4 - Strength and sensation
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Summary Neurology Kuks and Snoek Chapter 4 - Strength and sensation
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Chapter 4 - Strength and sensationPhysiological background
Each muscle is controlled by a peripheral nerve whose cell body lies in the anterior horn of the spinal
cord. The peripheral motor neuron does not act independently but as a component of a reflex arc in
which the peripheral motor neuron (PMN) is the output (efferent) element and a sensory nerve the input
(afferent) element.
The patellar reflex is an example of a plurisegmetal and monosynaptic reflex. Different types op spinal
reflexes:
Proprioceptive: originating from the muscle
spindles/sensors in tendons or joint capsules
(deep sensation)
Exteroceptive: originating from the body's
surface; nociceptive
Enteroceptive: originating from the organs
and viscera within the body.
Modulation of spinal reflexes (refinement) mostly
occur in the corticospinal tract, which originates in the
cerebral cortex and is part of the pyramidal tract. This
tract modulates the reflex through direct action on the
anterior horn cells and the interneurons. The
corticospinal tract contains axons of the central motor
neurons whose cell bodies are located in the motor
cortex. In the brainstem most of the pyramidal tract
crosses in the medulla oblongata. Therefore, the PMN
is controlled by the contralateral CMN.
Loss of function of the corticospinal tract causes
demodulation/disinhibition of the spinal reflex arc,
which causes hyperreflexia.
In the case of paresis due to dysfunction of the CMN
there is loss of motor function with increased reflexes; this Kuks, J. and Snoek, J., 2018. Textbook Of
is known as central paresis. In the case of dysfunction of Clinical Neurology. pp.p.26 - p.46.
the PMN there is paresis with low reflexes; this is called
peripheral paresis. In central paresis there is a Babinski sign.
Spinal shock occurs in the acute phase of central paresis;
reflexes and tonus are decreased with usually abnormal foot
responses.
Peripheral motor neurons steered by medial pathways are
situated in the medial part of the anterior horn and mainly
control the gross motor function of the trunk muscles and
proximal muscles of the limbs. The lateral pathways modulate
the peripheral motor neurons in the
Kuks, J. and Snoek, J., 2018. Textbook Of lateral parts of the anterior horn.
Clinical Neurology. pp.p.26 - p.46.
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