DESCENDING SPINAL TRACTS Flashcards
What are the DESCENDING SPINAL TRACTS and their functions?
- 5
- CORTICONUCLEAR TRACTS
- ANTEROIR VS LATERAL
- ORIGINATE from the CEREBRAL CORTEX
INFLUENCE LOWER MOTOR NEURONS
- RUBROSPINAL,
- ORIGINATE from BRAINSTEM,
-AND CONTROL BODY MOVEMENT AND POSTURAL STABILITY DURING VOLUNTARY MOVEMENT.
- VESTIBULOSPINAL
- LATERAL VS MEDIAL
- ORIGINATE from BRAINSTEM,
-AND CONTROL BODY MOVEMENT AND POSTURAL STABILITY DURING VOLUNTARY MOVEMENT.
- TECTOSPINAL
- ORIGINATE from BRAINSTEM,
-AND CONTROL BODY MOVEMENT AND POSTURAL STABILITY DURING VOLUNTARY MOVEMENT.
- RETICULOSPINAL
- ORIGINATE from BRAINSTEM,
-AND CONTROL BODY MOVEMENT AND POSTURAL STABILITY DURING VOLUNTARY MOVEMENT.
CORTICONUCLEAR TRACT PROPERTIES
- Corticonuclear axons terminate BILATERALLY on MOTOR NUCLEI in the BRAINSTEM
AFFECTING MOVEMENT OF THE HEAD AND FACE:
– Motor nucleus of CNV
– Motor nucleus of CNVII
– Nucleus ambiguus (CNIX, CNX) – Hypoglossal nucleus (CN XII)
- *Two exceptions: lower portion of CNVII and CNXII are CONTRALATERAL (not bilateral).
corticobulbar (or corticonuclear) tract
- leave theINTERNAL CAPSULE and
- enter the BASILAR PART OF PONS as numerous bundles
- fibres leave the CEREBRAL CRUS ADJACENT TO THE CORTICOSPINAL TRACT
The fibres can take several paths and have several different terminations:
Termine directly on alpha motor neurones or interneurones innervating alpha motorneurons in the brainstem.
These control somatic motor acitivity in the head e.g. muscles that control mastication, expression and eye movement.
Axons that innervate motor nerve cranial nuclei can decussate (cross) before they terminate, resulting in them innervating contralateral muscles.
As some decussate and some descend ipsilaterally, it results in bilateral descending control.
Directly innervate cranial nervces or through interneurones I.E. via the corticospinal tract.
Lateral cortico spinal tract: PROPERTIES - 4
– LARGEST MOTOR TRACT
– passes through posterior limb of INTERNAL CAPSULE
– DECUSSATES in the PYRAMIDS OF MEDULLA OBLONGATA of the medulla oblongata
– PRESENT AT ALL LEVELS OF SPINAL CORD
Anterior corticospinal tract: PROPERTIES - 4
– descends with lateral corticospinal but does not decussate
in pyramids
– most decussate at spinal cord level
– terminate on LMN controlling trunk & proximal musculature (postural adjustments).
– not present inferior to L2.
Lateral corticospinal pathway - 3
- Upper Motor Neuron: cell body in precentral gyrus of frontal lobe.
- Axon descends SOMATOTOPICALLY THROUGH CORONA RADIATA, POSTEROIR LIMB OF INTERNAL CAPSULE, CRUS CEREBRI OF MIDBRAIN, BASE OF PONS AND PYRAMIDS OF MEDULLA OBLONGATA p
- DECUSSATE in the PYRAMIDS, travel in LATERAL FUNICULUS of spinal cord and synapse directly onto Lower Motor Neuron cell body in anterior horn of spinal cord grey matter.
Anterior corticospinal pathway -3
- Upper Motor Neuron: cell body in precentral gyrus of frontal lobe.
- Axon descends somatotopically through corona radiata, posterior limb of internal capsule, crus cerebri of midbrain, base of pons and pyramids of medulla oblongata.
- Travel in ANTERIOR FUNICULUS and DECUSSATE IN SPINAL CORD synapse directly onto Lower Motor Neuron cell body in contralateral anterior horn of spinal cord grey matter.
Rubrospinal tract pathway - 4
- Rubrospinal tract Upper Motor Neurons arise in the red nucleus in the tegmentum of the midbrain.
- Decussate in the anterior part of the midbrain tegmentum and descend somatotopically in the lateral white column adjacent to the much larger corticospinal tract.
- Synapse in lamina V, VI and VII of spinal grey.
- Controls muscle tone of upper limb flexors evident when corticospinal tract lesioned.
Medial vestibulospinal tract - 4 PATHWAY
1 – Second-order neurons arise from medial vestibular nucleus
2 – Descend bilaterally via the medial longitudinal fasciculus
3 – Terminate in lamina VII & VIII of spinal grey.
4 – Establish monosynaptic inhibitory connections with motor neurons of neck and back muscles to provide STABILITY TO THE HEAD during movement and COORDINATES HEAD movements WITH EYE movements .
Lateral vestibulospinal tract -3 PATHWAY
– Second-order neurons arise from lateral vestibular nucleus.
– Descend somatotopically ipsilaterally in anterolateral funiculus at cervical levels and shifts to medial part of anterior funiculus at lower spinal levels.
– Synapse on lamina VII & VIII of spinal grey at ALL LEVELS OF THE SPINAL CORD TO FACILITATE EXTENSORS AND INHIBIT FLEXORS
Tectospinal tract PATHWAY -3
1 * Upper motor neurons arising from the superior colliculus of the midbrain.
2 * Decussate in posterior tegmentum of midbrain to descend contralaterally near midline adjacent to the periaqueductal grey.
3 * Join with medial longitudinal fasciculus to terminate bilaterally on Lower Motor Neurons in lamina VI & VII in the cervical spinal cord associated with head & neck movements to influence HEAD POSITION IN REGARD TO VISUAL STIMULUS
Reticulospinal tract PROPERTIES - 4
1 * Most primitive motor system.
2 * Coordinates body positioning, gross movements, integrates distal muscle actions with proximal muscle actions, initiates changes in muscle tone related to voluntary movements of limbs.
3 * Controls breathing.
4 * Emotional motor System– modulates excitability of spinal motor neurons.
Summary
- Corticospinal is newest and largest tract controlling voluntary movement.
- Rubrospinal (upper limb flexors), lateral vestibulospinal (all extensors), tectospinal/medial vestibulospinal (head & neck muscles), reticulospinal (basic survival movements), are older and smaller tracts.
- UMN lesion in CNS only: rigid muscles, increased tendon reflexes. LMN anywhere along length of nerve from CNS to PNS: flaccid muscles, decreased tendon reflexes.
UPPER MOTOR NEURON LESION VS LOWER MOTOR NEURON LESION
An upper motor neuron lesion is a lesion of the neural pathway above the anterior horn of the spinal cord or motor nuclei of the cranial nerves.
A Lower motor neuron lesion is a lesion which affects nerve fibers traveling from the anterior horn of the spinal cord to the associated muscle(s).
