Lecturer Prof. Dr. Ali K. Al-Shalchy MBChB/ FIBMS/ MRCS/ FRCS 2014
Dorsal root: The dorsal root carries both myelinated and unmyelinated afferent fibers to the spinal cord. Posterior gray column: Long and narrow column of gray matter reaches almost to the surface of the spinal cord. Primarily concerned with sensory input. Anterior gray column: Short and broad column of gray matter. Concerned with motor function. Both posterior and anterior gray columns are sites where sensory and motor cell bodies, respectively, are found. Ventral root: Bundle of somatic motor fibers. Constitute the efferent outflow of the spinal cord.
Anterior median fissure: About 3 mm deep. Contains blood vessels (anterior spinal artery) supplying the anterior two thirds of the cord. Anterior funiculus: Between the anterior median fissure and anterolateral sulcus (ventral root). Merges with the lateral funiculus. Contains ascending and descending tracts. Lateral funiculus: Between the dorsal and ventral roots. Merges with the anterior funiculus. Contains ascending and descending tracts. Posterior lateral sulcus: Site of entry of dorsal root. Posterior funiculus: Between posterior median sulcus and dorsal root. Contains ascending tracts.
The spinal cord tracts can be divided into ascending (sensory or afferent) and descending (motor or efferent) tracts. The sensory tracts include dorsal column/medial lemniscus system, anterolateral system, and spinocerebellar tracts ; while the motor tracts include the pyramidal and extrapyramidal tracts.
In the dorsal column-medial lemniscus tract, a primary neuron's axon enters the spinal cord and then enters the dorsal column. If the primary axon enters below spinal level T6, the axon travels in the fasciculus gracilis, the medial part of the column. If the axon enters above level T6, then it travels in the fasciculus cuneatus, which is lateral to the fasciculus gracilis. Either way, the primary axon ascends to the lower medulla, where it leaves its fasciculus and synapses with a secondary neuron in one of the dorsal column nuclei: either the nucleus gracilis or the nucleus cuneatus.
At this point, the secondary axon leaves its nucleus and passes anteriorly and medially. The collection of secondary axons that do this are known as internal arcuate fibers. The internal arcuate fibers decussate and continue ascending as the contralateral medial lemniscus. Secondary axons from the medial lemniscus finally terminate in the ventral posterolateral nucleus (VPL) of the thalamus, where they synapse with tertiary neurons. From there, tertiary neurons ascend via the posterior limb of the internal capsule and end in the primary sensory cortex. This system transmits touch, proprioception and vibration modalities of sensations.
The anterolateral system works somewhat differently. Its primary neurons axons enter the spinal cord and then ascend one to two levels before synapsing in the substantia gelatinosa. The tract that ascends before synapsing is known as Lissauer's tract. After synapsing, secondary axons decussate and ascend in the anterior lateral portion of the spinal cord as the spinothalamic tract. This tract ascends all the way to the VPL, where it synapses on tertiary neurons. Tertiary neuronal axons then travel to the primary sensory cortex via the posterior limb of the internal capsule. This system transmits pain and temperature modalities of sensations.
Proprioceptive information in the body travels up the spinal cord via three tracts. Below L2, the proprioceptive information travels up the spinal cord in the ventral spinocerebellar tract. Also known as the anterior spinocerebellar tract, sensory receptors take in the information and travel into the spinal cord. The cell bodies of these primary neurons are located in the dorsal root ganglia. In the spinal cord, the axons synapse and the secondary neuronal axons decussates and then travel up to the superior cerebellar peduncle where they decussate again. From here, the information is brought to deep nuclei of the cerebellum including the fastigial and interposed nuclei.
From the levels of L2 to T1, proprioceptive information enters the spinal cord and ascends ipsilaterally, where it synapses in Clarke's nucleus. The secondary neuronal axons continue to ascend ipsilaterally and then pass into the cerebellum via the inferior cerebellar peduncle. This tract is known as the posterior spinocerebellar tract. From above T1, proprioceptive primary axons enter the spinal cord and ascend ipsilaterally until reaching the accessory cuneate nucleus, where they synapse. The secondary axons pass into the cerebellum via the inferior cerebellar peduncle where again, these axons synapse on cerebellar deep nuclei. This tract is known as the cuneocerebellar tract.
The corticospinal tract serves as the motor pathway for upper motor neuronal signals coming from the cerebral cortex and from primitive brainstem motor nuclei. Cortical upper motor neurons originate from Brodmann areas 1, 2, 3, 4, and 6 and then descend in the posterior limb of the internal capsule, through the crus cerebri, down through the pons, and to the medullary pyramids, where about 90% of the axons cross to the contralateral side at the decussation of the pyramids.
They then descend as the lateral corticospinal tract. These axons synapse with lower motor neurons in the ventral horns of all levels of the spinal cord. The remaining 10% of axons descend on the ipsilateral side as the ventral corticospinal tract. These axons also synapse with lower motor neurons in the ventral horns. Most of them will cross to the contralateral side of the cord (via the anterior white commissure) right before synapsing.
They are called so because they don t reach their targets by traveling through the "pyramids of medulla". Pyramidal tracts go through the pyramids of medulla. Extrapyramidal tracts indirectly control the anterior horn cells (for modulation and regulation). Extrapyramidal system is responsible for gross, synergic movements which require the activity of large groups of muscles
Radiculopathy Nerve root impingement with typical pain radiation and/or motor or sensory impairment leading to nerve root dysfunction. Typical Findings: weakness of the index muscle mainly innervated by that nerve, diminished reflexes of the same muscle and dermatomal sensory disturbance. The most common distribution of radiculopathy is the lumbar spine followed by the cervical spine. Radiculopathy is less common in the thoracic spine. Pain usually exacerbated with coughing, sneezing or during defecation.
Myelopathy Compression or stretching of the spinal cord can cause myelopathy, which is more common in the cervical rather than the thoracic spine. Hyperreflexia and positive Babinski sign are common. Sensory deficits include impaired sensory level, dermatomal sensory disturbance in the arms, glove-distribution sensory loss in the hands and posterior column dysfunction. Motor deficits with arm weakness and wasting of hand muscles are encountered and paraparesis can occur. However, hemi- or tetraparesis are less frequent. Spasticity and sphincter distubances occur also.
Localized demyelination of the spinal cord. Is caused by an immune process resulting in small vessel vasculopathy, ischemia, and demyelination. Symptoms: Clinical picture is identical to cord transection occurring over hours to a few days. Most common in the thoracic cord. Band-like chest pain mimicking acute myocardial infarction may occur before the onset of flaccid paralysis, sensory level, and urinary retention. Progressive rise in the sensory level may occur. Treatment: High-dose intravenous steroids
Definition: The procedure of taking CSF from the spine in the lower back through a hollow needle, usually done for diagnostic purposes (e.g. meningitis).
The patient should lie flat on his side with the back at the edge of the bed. Flexion of hips and knees is done. Introduction of 20- to 22-gauge needle in between 2 spinous processes (either,commonly L3-L4, or L4-L5) exactly in the midline. By pushing the needle pointing slightly towards the patient s head, piercing the dura is performed at 5-6 cm. Collect the CSF and send it to analysis.