Spinal Tracts Flashcards
Name the
ASCENDING SPINAL TRACTS?
Dorsal Columns (2)
- fasciculus gracilis*
- fasciculus cuneatus*
Spinothalmic Tract
Spinocerebellar (2)
dorsal & ventral
Definition of
ASCENDING SPINAL TRACTS?
Nerve fibers in the spinal cord carrying impulses from pain, thermal, tactile, muscle and joint receptors to the cerebral cortex (conscious) or cerebellum (subconscious).
How many neurons in an ascending spinal tract going to the cerebral cortex?
Three
- First order neurons or primary afferents
- Second order neurons
- third order neurons
Ascending Spinal Tract
First Order Neuron
enters the spinal cord through the dorsal root of a spinal nerve.
Cell body lies int eh dorsal root ganglion
Main fiber remains ipsilateral
Terminates in either the spinal grey matter or in the medulla oblongata.
Ascending Spinal Tract
Second Order neuron
has the cell body in the cord or medulla oblongata.
Axon decussates before ascending
Terminates in the Thalamus
Ascending Spinal Tract
Third Order Neuron
Cell body in the Thalamus
Axon passes to the somatosensory cortex of the parietal lobe
Which ascending spinal tracts carry information to the conscious level (Cerebral Cortex)?
Dorsal Columns (Gracilus & Cuneatus)
Spinothalamic
What are the Dorsal Columns?
Ascending spinal tracts carrying proprioceptive, discriminative touch, and vibration impulses.
Organized in the fasciculus gracilis (medial)
and fasciculus cuneatus (lateral)
Lesions (tabes dorsalis, vit B12 deficiency) lead to ataxia and loss of discriminative touch.
What is the fasciculus cuneatus?
The lateral dorsal colum ascending spinal tract.
Carries proprioception, discriminative touch and vibration first order neurons from T6 and above to the medulla oblongata.
What is the fasciculus gracilis?
The medial dorsal column ascending spinal tract.
Carries proprioception, discriminative touch and vibration first order neurons from below T6 to the medulla oblongata.
What sensations to the spinothalamic tracts carry?
Pain
Thermal Sensation
Lesions cause impairment of pain temperature
What is the neuronal pathway of the spinothalamic tract?
2nd order neurons, cell bodies in contralateral dorsal horn.
Pain & Temp decussate within one level of origin.
Touch and Pressure my ascend several levels before decussating.
Terminate in the ventral posterior nucleus of the Thalamus.
Connect with 3rd order thalamocortical neurons which terminate in the somatosensory cortex.
What is the spinoreticulothalamic tract?
An older part of the spinothalamic tract thought to transmit dull aching (slow) pain to a conscious level.
2nd order neurons ascend to the brainstem’s reticular formation.
What sensations do the spinocerebellar tracts transmit?
Spinocerebellar tracts carry unconscious sensation from:
Muscle spindles
golgi tendon organs
Tactile receptors
to the cerebellum for posture and coordination of movement.
Lesions lead to ataxia
What is the neuronal pathway of the Spinocerebellar tracts?
Only two neurons.
A 2nd order neuron with cell body in the dorsal horn.
Dorsal spinocerebellar fibers ascend ipsilaterally and enter the cerebellum via the inferior cerebellar peduncle.
Ventral spinocerebellar fibers ascend contralaterally and enter the cerebellum via the superior cerebellar peduncle.
Function of the descending spinal tracts
Control of movement
muscle tone
Spinal reflexes
spinal autonomic functions
modulation of sensory transmission to higher centers
Name the DESCENDING spinal tracts?
Corticospinal (or Pyramidal)
Rubrospinal
Tectospinal
Vestibulospinal
Reticulospinal
What is the
CORTICOSPINAL tract?
a descending spinal tract, aka Pyramidal tract
controls discrete, skilled movements, esp of distal extremities
originates from motor AND sensory cortices
Most fibers decussate in the medullary pyramid to form the lateral corticospinal tract. The remainder form the ventral corticospinal tract and decussate near their termination.
What is the
RUBROSPINAL tract?
a descending spinal tract
Controls limb flexor muscle tone.
Originates from Red Nucleus in midbrain (tegmentum).
Decussate in the midbrain tegmentum.
As the Red Nucleus receives afferent fibres from the motor cortx and the cerebellum this is a non-pyramidal route by which they both can influence spinal motor activity.
What is the
TECTOSPINAL tract?
a descending spinal tract
involved in reflex responses to visual input
Orginates from contralateral superior colliculus
Decusates in the midbrain tegmentum
What is the
VESTIBULOSPINAL tract?
a descending spinal tract
Originates in vestibular nuclei in Pons and Medulla
recieves input from the labyrinthine system via vestibular nerve and cerebellum
Mediates excitation of limb extensor muscles in the antigravity maintenance of posture.
Does not decussate
What is the
RETICULOSPINAL tract?
A descending spinal tract.
Originates in reticular formation of Pons and Medulla.
Involved in control of:
voluntary movement, reflex activity and muscle tone.
circulatory system and breathing
Pons fibers descend ipsilaterally as medial (or pontine) reticulospinal tract.
Medullary fibers descend bilaterally in the lateral (or medullary) reticulspinal tracts
