Neuroanatomy - Spinal Cord Tracts and Injury

the ascending tracts are associated with what?

sensation

what describes mechanical stimuli?

discriminative touch, pressure, vibration, proprioception

mechanical stimuli travels through what?

the posterior column-medial lemniscus (PCML) system (fasciculi gracilis and cunteatus)

what describes nociceptive stimuli?

mechanical, chemical, thermal

noxious stimuli is involved in sensation of what?

pain and temperature

nociceptive stimuli travels through what?

anterolateral system (spinothalamic tract)

unconscious proprioception travels where?

to the cerebellum via spinocerebellar tract

conscious proprioception travels through what?

PCML

nonconscious proprioceptive is involved in what?

coordination and refinement of movement

nonconscious entroceptive is involved in what?

homeostasis

conscious proprioceptive and exteroceptive is involved in what?

conscious perception/appreciation of sensory information

the posterior column medial leminscus (PCML) transmits information about what?

discriminative/fine touch, pressure, vibration, conscious proprioception

in terms of the PCML, axons enter the spinal cord from where?

the spinal ganglion and pass directly to ipsilateral posterior column

what describes the path of neurons in regards to the PCML?

1st order neurons terminate in nuclei in the caudal medulla → 2nd order neurons decussate and form medial lemniscus (near midline) → synapse with 3rd order neurons in VPL of thalamus → primary somatosensory cortex

in regards to PCML, where do neurons decussate?

in the caudal medulla

does PCML tract or spinothalamic tract have longer first order neurons?

the PCML because its first order neurons synapse in the caudal medulla while the first order neurons of the spinothalamic tract synapse in the substantia gelatinosa

posterior column lesions lead to what?

loss of proprioception and loss of the ability to distinguish the finer aspects of tactile stimuli

what is tabes dorsalis?

neurological disorder characterized by selective destruction of PCML pathway seen in neurosyphilis

• characteristic loss of discriminative touch, vibration, and conscious proprioception from entire body (except head)

the spinothalamic tract is what?

the major ascending tract that carries pain, temperature, and non-discriminative/crude touch fibers from the spinal cord to the thalamus and cortical structures

fibers carrying pain/temperature enter where and do what?

enter posterior horn and ascend/descend a few segments in Lissauer’s tract

what describes the spinothalamic tract pathway?

first order neurons enter posterior horn of spinal cord and ascend/descend 1-3 segments in Lissauer’s tract → first order neurons synapse with second-order neurons in substantia gelatinosa; second order neurons decussate in anterior white commissure and ascend as the spinothalamic tract → second order neurons synapse with third order neurons at the VPL of the thalamus → third order neurons ascend through internal capsule to terminate in primary somatosensory cortex

what describes Lissauer’s tract?

fibers of the spinothalamic tract that ascend or descend ipsilaterally 1-3 segments before synapsing with second order neurons

PCML carries what?

fine touch, proprioception, vibration, and pressure

Spinothalamic carries what?

crude touch, pain, and temperature

PCML decussates where?

at level of caudal medulla

spinothalamic decussates where?

at vertebral level after synapse with second-order neuron

PCML and spinothalamic both carry sensation where?

to the VPL of thalamus then to primary somatosensory cortex

what describes a lateral column lesion?

loss of pain and temperature sensation on the side of the body contralateral to the injury, beginning a few levels below or above the level of the injury

descending tracts are associated with what?

motor command

motor activity is controled by what?

upper motor neuron and lower motor neuron systems

descending tracts can arise from where?

the cortex (corticospinal/corticobulbar) or from the brainstem

movement can be what?

voluntary or involuntary

what describes voluntary movement?

mostly in distal muscle groups, movements that are fine-tuned and independent of opposite side of body, mediated through lateral corticospinal tract

voluntary movement is mediated through what?

the lateral corticospinal tract

what describes involuntary movement?

mainly proximal and axial muscle groups, critical for postural stability, influenced by anterior corticospinal tract

involuntary movement is mediated through what?

anterior corticospinal tract

what is the main function of corticospinal tracts?

cortical influence (UMN) on LMNs of anterior horn of spinal cord

UMN originates from the cortex, but from what areas?

• 1/3 from primary motor cortex

• remainder from motor association areas and primary sensory area

what describes the path of UMNs?

they descend through corona radiate and converge in internal capsule to descend as distinct bundles

85-90% of UMNs decussate where?

in the medulla

after 85-90% UMNs decussate, they descend as what?

lateral corticospinal tract

remaining 10-15% of UMNs descend as what?

anterior corticospinal tract

where do the remaining 10-15% UMNs decussate?

at the spinal level that they synapse with LMN

in terms of the lateral corticospinal tract, where do UMNs decussate?

near medullary pyramids

in terms of the lateral corticospinal tract, LMNs are found where?

in lateral part of anterior horn

lateral corticospinal tract innervates what?

distal muscle groups

the lateral corticospinal tract circuit innervates what?

flexor/extensor groups over several segments = cortical control of movement of entire limb

in terms of the anterior corticospinal tract, UMNs descend and decussate how?

ipsilaterally and most decussate at the same segmental level at which they terminate

in terms of the anterior corticospinal tract, LMNs control what?

trunk and proximal musculature

in terms of the anterior corticospinal tract, what kind of innervation is seen?

bilateral innervation

anterior corticospinal tract is associated with what?

postural adjustment

lateral corticospinal tract is associated with what?

skilled movement of the extremities

what are causes of spinal cord injuries?

• traumatic (motor vehicle crash, fall)

• nontraumatic (ischemic, compressive, inflammatory)

what describes the acute phase of spinal cord injuries?

known as spinal shock

• flaccid areflexic paralysis

• anesthesia below the level of injury

• autonomic dysfunction

chronic phase of spinal cord injury could be what?

complete or incomplete

what is paralysis?

severe or complete loss of muscular strength

what describes paraplegia?

partial of complete paralysis of lower extremities due to spinal cord injury

what describes tetraplegia?

partial or complete paralysis of upper and lower extremities due to spinal cord injury

complete spinal cord injury results in what?

total bilateral loss of communication between nerve fibers above and below the lesion

complete spinal cord injury involves what?

all spinal tracts at the level (complete transection)

how does complete spinal cord injury present?

as complete absence of motor, sensory, bowel, and bladder function below the level of injury, autonomic dysreflexia

what describes incomplete spinal cord injury?

affects only some parts of ascending/descending tracts at a given level

how does incomplete spinal cord injury present?

as dissociated sensory loss with preservation of some sensorimotor function below the level of injury

what describes autonomic dysreflexia?

hyperactive, unregulated autonomic response to noxious stimulus below the level of the spinal cord injury

when does autonomic dysreflexia usually occur?

in the chronic phase of SCI, more common in complete injury

autonomic dysreflexia typically occurs when damage is where?

above the T6 level

the higher the level of cord injury, the higher the risk of what?

autonomic dysreflexia

authonomic dysreflexia may result in what?

life-threatening hypertensive episode → increased risk of stroke

in terms of autonomic dysreflexia, > 80% of the noxious stimulus is what?

urological

how to do you manage autonomic dysreflexia?

remove the trigger and correct blood pressure

what are symptoms of autonomic dysreflexia?

• high BP

• low HR

• flushing

• headache

• sweating

what describes the pathway of autonomic dysreflexia?

• SNS takes over → systemic vasoconstriction = high blood pressure

• brain sends signal to heart via the CN X to bring heart rate down = bradycardia

• PNS activated above the level of the spinal cord injury

what describes the dissociated sensory loss associated with incomplete spinal cord injury?

impairment of either pain and temperature sensation (carried by the spinothalamic tracts) or light touch and proprioception (carried by the dorsal columns)

what is the most common type of incomplete spinal cord injury?

central cord syndrome

what describes central cord syndrome?

• affects central CS tracts and lateral spinothalamic tract

• typically due to hyperextension injury

• presents with partial loss of motor strength, upper > lower

what describes anterior cord syndrome?

• affects corticospinal tracts and spinothalamic tracts

• bilateral paralysis and dissociated sensory loss (pain, temperature, crude touch), and autonomic dysfunction below level of lesion

• typically due to infarction of anterior spinal artery, worst prognosis

brown-sequard syndrome includes what?

hemisection of the cord

what describes the ipsilateral presentation of brown-sequard syndrome?

• loss of proprioception, vibration, fine touch (due to posterior column being affected)

• flaccid paresis at level of lesion (lower motor neuron lesion)

• spastic paresis below level of lesion + babinski sign (upper motor neuron lesion)

what describes the contralateral presentation of brown-sequard syndrome?

loss of pain and temperature 1-2 levels below the lesion (due to lateral column lesion)