Spinal Cord & Tracts Flashcards
What muscles are activated during a reflex motion?
Ipsilateral synergists are activated and antagonists are inactivated to prevent opposition to the flexor motion
What is the function of lamina VII-IX?
Motor
What stimuli is transmitted via the spinocerebellar tract?
Proprioception
What stimuli is transmitted via the anterior spinothamalic tract?
Crude touch
UMNs for what tract are found in the superior colliculus?
Tectospinal tract
What is the function of lamina X?
Visceral touch, pain, temperature
What are the three types of nerve fibers in white matter of the spinal cord?
Long, ascending fibers
Long, descending fibers
Short, propriospinal fibers
This group of axons is located only in the cervical spinal cord and transmits stimuli from the upper body.
Fasciculus cuneatus
Where does crossing over of information take place in the spinal cord?
Anterior white commissure
What stimuli is detected by Meissner’s corpuscles?
Fine and discriminative touch
The dorsal horn houses what types of neurons?
Sensory
The C7 spinal nerve is associated with what reflex?
Triceps reflex
What is the conus medularis?
The end of the spinal cord at L1/L2
What stimuli are carried by the medial lumniscus tract?
Fine/discriminative touch, pressure and touch, vibration, proprioception, muscle stretch
What group of axons transmits stimuli from the lower body?
Fasciculus gracilis
True/False. Damage to an upper motor neuron will cause the muscle to atrophy.
False. The muscle may become more diffuse, but it will not atrophy due to increased reflex arc. LMN damage will cause muscle atrophy.
C fibers transmit dull, non-localized pain. What are the primary stimuli for these fibers?
Chemical stimuli (H+, K+, bradykinin)
Describe the somatotrophic arrangement of the internal capsule.
In the internal capsule, axons of neurons associated with the lower limbs are more lateral, while axons of the upper limbs and head are more medial. This arrangement is opposite that of homunculus where the lower limbs are found medially within the longitudinal fissure and the head is more medial near the lateral fissure.
What spinal cord nerve is associated with the achilles reflex?
S1
What is the Tract of Lissauer?
Axons of the spinothalamic tract in the lateral white column ascend/descend 2-3 spinal levels before crossing over and continuing on the tract
Briefly describe the pathway of the corticospinal tract.
Axons from the corona radiate funnel through the posterior limb of the internal capsule and enter the brainstem via the crus cerbri of the cerebral peduncles. Fibers move through the pontine nuclei and pass through the pyramids of the medulla. Contralateral fibers of the lateral tract will cross at the pyramidal decussation and continue descending. Ipsilateral fibers of the anterior tract will descend and cross in the anterior white commissure at the level of their target.
Describe the dorsal spinocerebellar tract.
First-order neurons are located in the DRG between T1-L2 and synapse on Clarke’s nuclei in the dorsal root. The axon ascends ipsilaterally via the dorsal aspect of the lateral white column and exits the spinal cord at the inferior peduncles to enter the cerebellum.
What receptor detects fine touch and superficial pressure?
Merkel’s discs
What test can be used to assess for UMN damage?
Babinski’s sign - stimulation to the sole of the foot causes the big toes to rise. A positive test is only normal in infant.
The lateral horn is only found between what spinal levels?
T1-L2
Where does the spinal cord end?
L1/L2
What is the difference between the ipsilateral and contralateral pathways?
The ipsilateral pathway crosses over in the brain, white the contralateral pathway crosses over in the spinal cord
The C6 spinal nerve is associated with what reflex?
Brachioradialis
What types of neurons synapse on extrafusal muscle fibers?
Alpha motor neurons
Proprioceptive stimuli from what parts of the body is transmitted via the cuneocerebellar tract?
Head, neck, upper limbs
Describe the lateral spinothamalic tract.
First-order neurons are located int he DRG and synapse on a second-order neurons in the dorsal root. Prior to synapsing on the second-order neuron, axons from the first-order neuron may ascend/descend the spinal cord via the Tract of Lissauer. The axons then cross over in the anterior white commissure. Most C fibers terminate in the reticular formation, with the rest ascending to the intralaminar nuclei of the thalamus. Most A-delta fibers ascend to the ventroposterior lateral and ventroposterior infection nuclei of the thalamus. Fourth-order neurons for C and A-delta fibers are in the post-central gyrus.
How many neurons are involved in the corticospinal tract?
Two
What are the two tracts of the reticulospinal tract?
Pontine/Medial Tract
Lateral/Medullar Tract
UMNs for each tract originate in the Pons and Medulla reticular formations, respectively.
Motor neurons are located in what horn of the spinal cord?
Ventral horn
This receptor is responsible for detecting stretch and vibration.
Ruffini corpuscles
Describe the anterior spinothamalic tract.
First-order neurons are located int he DRG and synapse on a second-order neurons in the dorsal root. Axons cross over in the anterior white commissure and ascend via the anterior white column to third-order neurons in the ventroposterior lateral and ventroposterior infection nuclei in the thalamus. Fourth-order neurons are located in the post-central gyrus.
The anterior corticospinal tract is responsible for what types of movements?
Gross, large muscle movement
What is the second-order neuron of the dorsal spinocerebellar tract?
Clarke’s nucleus
What structure of the brain modifies and fine-tunes motor information before being sent down the spinal cord?
Basal nuclei
Describe the medial lemniscus pathway.
Peripheral receptors send signals to a first order neuron located in the dorsal root ganglion. Axons merge to form the fasciculus gracilis/cuneatus and travel up the spinal cord to the second order neuron (nucleus gracilis/cuneatus) in the medulla. The information crosses over at the internal arcuate fibers on the way to the third-order neuron in the ventral posterior lateral nucleus. From there, information passes through the posterior limb of the internal capsule to primary and secondary somatosensory complexes.
What fibers are responsible for transmitting hot temperature stimuli?
C Fibers
What is the function of the cerebellum in motor tracts?
Integrates sensory information to inform motor functions
Where do contralateral fibers of the lateral corticiospinal tract cross?
Pyramidal decussation
The anterior corticospinal tract is responsible for what types of movements?
Gross and large muscle movements
Pain, temperature, and chemical stimuli are transmitted via which division of the spinothamalic tract?
Lateral spinothamalic tract
The dorsal spinocerebellar tract is present at what spinal levels?
T1-L2
What are the two divisions of the spinothalamic tract and their associated stimuli?
Anterior: Crude touch & superficial pressure
Lateral: Pain & temperature
What receptor detects the bending of hair of the skin?
Peritrichial nerve endings
What tract is responsible for stabilizing the head position?
Medial vestibulospinal tract
What is the primary function of the vestibulospinal tracts?
Maintain balance
What is the difference between the anterior and lateral corticospinal tracts?
In the lateral tract, axons cross over after the pontine nucleus and enter the lateral white column. In the anterior tract, axons remain ipsilateral and enter the anterior white column. They cross over at the anterior white commissure at the level of their target muscle.
How many pairs of spinal nerves are in the body?
31 pairs - 8 cervical, 12 thoracic, 5 lumbar, 4 sacral, 1 coccyxgeal
How many neurons are part of the medial lemniscus pathway?
Four
What tract plays a role in reflexive turning of the head in response to visual stimuli?
Tectospinal tract
What lamina are responsible for processing pain?
Lamina I-IV
What receptor senses touch and prevents muscle from ripping from the bone?
Golgi tendon organ
What are the two tracts of the vestibulospinal tract?
Lateral - postural changes to compensate for tilts and body movement
Medial - stabilizes head
What term describes total paralysis to one side?
Hemiplegia
How do the initiations of stretch and flexor reflexes differ?
Stretch reflexes are initiated by muscle or tendon receptors. Flexor reflexes are initiated by cutaneous receptors and involve an entire limb.
Where do gamma motor neurons synapse?
Interfusal muscle fibers
True/False. All reflexes involve one or more interneurons.
False. The stretch reflex (deep tendon reflex) involves no interneurons.
Where do UMN for the rubrospinal tract originate?
Red Nucleus
What ascending motor pathway is responsible for gross and large muscle movements?
The anterior corticospinal tract
What are the primary functions of the vestibulospinal tract?
Mediates postural adjustments and head movements
What spinal nerve is associated with the biceps brachii reflex?
C5
Fine and precise motor movements of the limbs are carried by what descending tract?
Lateral corticospinal tract
What stimuli is detected by Pacinian corpuscles?
Deep pressure and vibration
What fibers (contralateral/ipsilateral) of the corticospial tract are carried down the anterior white commissure?
Ipsilatreal fibers - they cross in the anterior white commissure at the level of their target muscle
What tract is responsible for exciting flexor muscles and inhibiting extensor muscles in voluntary movement?
Rubrospinal tract
The reticulospinal tract serves as an alternative tract for voluntary movement. What is the primary function of this tract?
Regulate sensitivity of the flexor reflex to ensure only noxious stimuli elicit a response
Where do the contralateral fibers of the corticospinal pathway travel down the spinal cord?
Lateral white columns via the lateral corticospinal tract
What fibers are responsible for transmitting cold temperature and pain?
A-delta fibers
Where are UMNs for the vestibulospinal tract found?
Vestibular nucleus
Describe the cuneocerebellar tract.
First-order neurons are located in the DRG and ascend ipsilaterally to the medulla. Second-order neurons are in the accessory cuneate nucleus in the medulla. Axons from the accessory cuneate nucleus form the external arcuate fibers and exit the medullar via the inferior cerebellar peduncles.
The patellar reflex involves what spinal nerve and muscle?
L4, quadriceps femoris
These lamina are responsible for crude touch.
Lamina V-VII
What is the primary tract that controls voluntary movement?
Corticospinal tract
What are the intrafusal fibers?
Nuclear chain and nuclear bag
