Ascending and Descending Tracts Flashcards
Define tract
A bundle of axons with the same origin and termination
What are the two types of pathways that bring afferent sensory info to the brain
Conscious Relay Pathways
Divergent Pathways
What is a conscious relay pathway
An afferent pathway that brings info about location and type of stimulus to the cerebral cortex
Discriminative touch & proprioception IPSI
Discrimitive pain & temp CL
What is a divergent pathway
An afferent sensory pathway that transmits sensory info to many locations in the BS and cortex - both conscious and unconscious
Ie - aching pain
What are unconscious relay pathways
Bring afferent unconscious proprioception and other movement related information to the cerebellum
What does the DCML transmit?
Discriminative
Proprioception
Vibration
Light moving touch
What do the anterolateral tracts transmit?
Course/crude touch Pain Temperature Sharp/dull Tickle and itch Sexual sensations
Receptors & pathway:
Discriminative touch
PCML
A delta, myelinated
Receptors & pathway:
Proprioception
PCML
Ia, Ib, II
Receptors & pathway:
Vibration
DCML
Pacinian corpuscles, Ia, Ib, II
Receptors & pathway:
Light moving tough
PCML
superficial mechanoreceptors
Receptors & pathway:
Course/crude touch
Anterolateral
C-fiber, unmyelinated
Receptors & pathway:
Pain
Anterolateral
Fast - A delta
Slow - C-fiber
Receptors & pathway:
Temperature
Anterolateral
Free nerve endings
myelinated and unmyelinated axons
Receptors & pathway:
Sharp/dull
Anterolateral
Receptors & pathway:
Tickle and itch
Superficial mechanoreceptors
Receptors & pathway:
Sexual sensations
Superficial mechanoreceptors
Lateral to medial organization of the lateral spinothalamic tract
Sacral
Lumbar
Thoracic
Cervical
Lateral to medial organization of the Lateral corticospinal tract
Sacral
Lumbar
Thoracic
Cervical
Lateral to medial organization of the DCML/PCML
Cuneate fasciculus (Cervical) Gracile fasciculus (Thoracic, Lumbar, Sacral)
What tracts comprise the ALS system?
Spinothalamic tract
Spinoreticular tract
Spinomesencephalic tract
PCML/DCML pathway - 1st order neurons
1st order neurons: (Receptors Ia phasic & tonics, Ibs) ascend IPSI and terminate at the nucleus gracile and cuneate of the lower medulla
PCML/DCML pathway - 2nd order neurons
2nd order neurons: Begin in caudal medulla - nucleus gracile and cuneate, decussate forming the ML, which ascends to the CL BS to project to the VPL nucleus of the thalamus
PCML/DCML pathway - 3rd order neurons
Begin in the Ventral Posterolateral nucleus of the thalamus to then send axons through the posterior limb of the internal capsule to the somatosensory cortex - broadman areas 3,1,2
Spinothalamic pathway - 1st order neurons
A delta & C fibers synapse on 2nd order neurons in the substantia gelatinosa or nucleus proprius
What are “tract cells”
Travel 1-2 vertetbrae levels higher than the point of entry at the Lissauer’s tract - the substantia gelatinosa or nucleus proprius are examples
Spinothalamic pathway - 2nd order neurons
Begin at the substantia gelatinosa or nucleus proprius and decussate in the anterior commisure, then ascend contralaterally in the anterolateral spinal cord to the rostral venterolateral medulla
Spinothalamic pathway - Lateral spinothalamic tract
Ascends through the medulla and joins w/anterior spinothalamic tract to form the spinal lemniscus > midbrain ? thalamic nuclei (VPL, VPM, & medial doral)
Spinothalamic pathway - 3rdorder neurons
Pass through the posterior limb of the internal capsule > corona radiate ? primary sensory cortex (Broadmann areas 3, 1, 2)
Which broadman areas are associated with….
a) DCML
b) ALS
a) Broadman area 3
b) Broadman areas 1,2
List the conscious pathways to the cerebral cortex
PCML
ALS (spinothalamic tract, Spinoreticular tract, Spinomesencephalic tract)
Purpose of spinoreticular tract
Brings sensory info to the reticular formation - Arousal, attention, and sleep/waking cycles
Spinoreticular tract
Enters the SC similar to spinothalamic tract & projects to the reticular formation
Reticular formation axons project to midline and to the intralainar nuclei of the thalamus
Then to many areas of the brain
Purpose of the spinomesencephalic tract
Carries pain or nocicpetive sensory info to two areas in the brain and activates descending tracts to help control the pain
Spinomesencephalic tract
Enters the SC similar to spinothalamic tract, projects to the superior colliculi (to turn eyes and head towards stimulus) and projects to periqeuductral gray matter around the cerebral aqueduct (activate descending tracts)
List the Unconscious pathways to the Cerebellum
High fidelity tracts: Posterior spinocerebellar tract & Cuneocerebellar tract
Internal feedbacck tracts:
Anterior spinocerebellar tract & Rostrospinocerebellar tract
What does the unconscious pathways to the cerebellum do?
Carry sensory afferent info to the cerebellum so we can quickly assign to perkinje cells of the cerebellum
List the Descending spinal cord tracts
Lateral corticospinal tract (CST) Anterior CST Rubrospinal tract Reticulospinal tract (RST) Medial and lateral vestibular spinal tracts (VST) Tectospinal tracts
What does the lateral CST do?
Controls voluntary movement, primarily of the distal hands and feet, but also all parts of the body
Lateral CST
Begins in primary motor cortex > internal capsule > cerebral peduncles > anterior pons > pyramids of the medulla > lateral SC > alpha and gamma motor neurons
What percentage of Lateral CST neurons cross?
88-90% cross in the lower medulla
What does the anterior/medial CST do?
Controls voluntary movement, primarily of the head, neck & trunk, proximal joints (pelvis and scapula)
What happens to the CST neurons that do not cross?
The 10-12% stay ipsilateral and descend in the ventral funiculus and then project to the alpha and gamma motor neurons of the ipsilateral, contralateral, and bilateral spinal cord
T or F: The Rubrospinal tract is the same in cats and humans
False -
Cats: projects to UE and LE
Humans: UEs only
Rubrospinal tract
Projects from frontal lobe and cerebellum, originatting in red nucleus > bentral horn alpha and gamma motor neurons & interneurons of cervical SC
What does the rubrospinal neurons project to?
Shoulder, elbow & wrist mm (NOT DISTAL INTRINSIC HAND MM)
Purpose of Reticulospinal tract (RST)
Facilitate bilateral LMN innervating postrual and gross motor movement throughout the entire body
Medial Reticulospinal tract (RST)
Begins in reticular formation (pons and medulla)
Travoes length of SC to multiple neural segments bilaterally
Proximal axial & limb mm & to commissural interneurons for both sides of body
Lateral Reticulospinal tract (RST)
Begins in reticular formation (pons and medulla)
More limited than Medial RST, travel at only a few neural levels on the IPSI side
What is thought to be responsible for flexor withdrawl and crossed extension responses
Medial Reticulospinal tract (RST)
What is thought to be responsible for CPG for locomtion
Lateral Reticulospinal tract (RST)
What does the Medial Vestibulospinal tract project to?
Bilaterally project in the cervical and upper thoracic spinal segments & then to the proximal head and neck mm
Medial vestibulospinal tract (inputs & origin)
Originates in medial vestibular nucleus and gets inputs from the emdial vestibular nucleus to the semicircular canals, utricle, and saccule
What does the Lateral Vestibulospinal tract project to?
The alpha and gamma motor neurons throughout the length of the SC so influences mm throughout the body, facilitating the extensor mm and inhibiting the flexor mm
Medial vestibulospinal tract (inputs & origin)
Originates in the lateral vestibular nucleus with inputs projecting mainly the utricle and saccule
What is the tectospinal tract
A descending tract that coordinates head and eye movements
Tectospinal tract pathway
Crude visual info projects to the superior colliculus and auditory to the inferior colliculus > CL and IPSI alpha motor neurons of the head/neck mm, oculomotor & throchlear nuclei & abducens nucleus
