neuro 14 ascending tracts student
TRANSCRIPT
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ASCENDING PATHWAYS
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Ascending Pathways
Three-neuron pathways:
Primary sensory neurons:
From external receptors
Travel through dorsal roots of spinal cord
Secondary neurons:
Make up tracts in spinal cord and brainstem
Tertiary neurons:From thalamus to primary sensory cortex
Travel through internal capsule
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Ascending Pathways
For conscious perception:
Spinothalamic system
Medial Lemniscal system
For unconscious perception:
Spinocerebellar
Spino-olivary
SpinotectalSpinoreticular
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Spinothalamic System
Lateral spinothalamic tract
Anterior spinothalamic tract
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Lateral Spinothalamic Tract
Carries pain and temperature
Primary fibers ascend or descend 1-2spinal cord segments before synapsingwith secondary fibers.
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Lateral Spinothalamic Tract
Secondary axons decussate throughanterior gray and white commissures.
Secondary axons make up the lateralspinothalamic tract traveling in the lateralcolumn of the spinal cord.
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Lateral Spinothalamic
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Lateral Spinothalamic Tract
Secondary fibers are joined in brainstemby fibers of the trigeminothalamic tract:
(Pain and temperature from face and teeth.)
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Lateral Spinothalamic Tract
Secondary fiber collaterals project toreticular formation:
Stimulate wakefulness and consciousness.
Secondary fibers project to ventralposterolateral (VPL) nucleus of thalamus.
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Lateral Spinothalamic Tract
Secondary fibers synapse with tertiaryfibers in VPL.
Tertiary fibers (corticopetal fibers) synapsein postcentral gyrus:
Somatic sensory areas 3, 1, 2
Tertiary fibers form part of internalcapsule.
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Anterior Spinothalamic Tract
Carries light touch (crude touch), pressure,tickle, itch
Primary neurons may ascend 8-10 spinal
cord segments before synapsing withsecondary neurons.
Secondary fibers decussate in anterior
gray or white commissures.
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Anterior Spinothalamic Tract
Secondary fibers ascend to synapse withtertiary fibers in VPL nucleus of thalamus.
Tertiary fibers ascend through internal
capsule to primary sensory cortex.
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Lateral Spinothalamic Tract
Red
1
Blue
2
Green
3
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Lateral Spinothalamic Tract
Red
1
Blue
2
Green
3
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Anterior Spinothalamic
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Anterior Spinothalamic Tract
Red:
1
Blue
2
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Anterior Spinothalamic Tract
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Medial Lemniscus System
Also called posterior column system.
Carries sensations for two-point sensation(fine touch), pressure, and vibration.
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Medial Lemniscus System
Primary fibers ascend entire length ofspinal cord and synapse with secondaryneurons in medulla:
Fasciculus gracilis
Fasciculus cuneatus
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Medial Lemniscus
Red:
Gracilis
Blue
cuneatus
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Medial Lemniscus System
Fibers of fasciculus gracilis synapse innucleus gracilis:
Convey sensations from below midthoracic level.
Fibers of fasciculus cuneatus synapse innucleus cuneatus:
Convey sensations from above midthoracic level.
Also conveys proprioceptive sensation from arms tocerebellum.
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Medial Lemniscus System
Secondary fibers decussate.
Secondary fibers ascend to synapse inVPL of thalamus.
Tertiary fibers ascend through internalcapsule to primary sensory cortex.
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Medial Lemniscus
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Medial Lemniscus
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Posterior Spinocerebellar Tract
Originates in thoracic and upper lumbarregions.
Consists of uncrossed fibers that entercerebellum through inferior cerebellarpeduncles.
Transmits ipsilateral proprioceptiveinformation to cerebellum.
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Anterior Spinocerebellar Tract
Originates in lower trunk and lower limbs.
Consists of crossed fibers that recross inpons and enter cerebellum throughsuperior cerebellar peduncles.
Transmits ipsilateral proprioceptiveinformation to cerebellum.
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Spinocerebellar Tracts
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Spino-Olivary Tracts
Project to accessory olivary nuclei andcerebellum.
Contribute to movement coordinationassociated primarily with balance.
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Spinotectal Tracts
Project to superior colliculi of midbrain.
Involved in reflexive turning of the headand eyes toward a point of cutaneousstimulation.
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Spinoreticular Tracts
Involved in arousing consciousness in thereticular activating system throughcutaneous stimulation.
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Stretch (myotactic) Reflex
Muscle spindle = receptor:
3-10 small, specialized intrafusal muscle fibers:
Contractile only at ends.
Non-contractile center.
Afferent neurons from center of intrafusal fiberstravel through dorsal root of spinal nerve tosynapse directly with alpha motor neurons of
extrafusal fibers in which muscle spindle isembedded.
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Stretch (myotactic) Reflex
Afferent neurons from muscle spindle alsosynapse with ascending fibers withinspinal cord.
Gamma motor neurons supply intrafusalfibers of muscle spindle:
Regulate sensitivity of intrafusal fibers.
Gamma neurons are modulated by
descending fibers within spinal cord. Refer to syllabus for specific stretch
reflexes.
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Golgi-Tendon Reflex
Golgi tendon organs:
Encapsulated nerve endings:
End with numerous terminal branches with
small swellings associated with individualtendon fascicles.
Lie within tendons near the muscle-tendon
junction.Stimulated when tendon is stretched.
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Golgi-Tendon Organs/Reflex
Afferent neurons from Golgi organs passthrough dorsal root of spinal nerve andsynapse with inhibitory association
neurons in posterior gray matter of spinalcord.
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Golgi-Tendon Organs/Reflex
Association neurons synapse with alphamotor neurons that innervate muscle fibersassociated with tendon.
Causes relaxation of associated musclesand prevents damage to the tendon due toexcessive tension.