Back Anatomy Flashcards
Spinal tracts
Anterior spinothalamic tract - sensation of crude touch and pressure
Lateral spinothalamic tract - sensation of pain and temperature
Corticospinal tract - voluntary control of body musculature, pyramidal tract
Dorsal columns - vibration sesnation, conscious proprioception
Spinocerebellar tracts - proprioceptive information
Rubrospinal tracts - responsible for some motor function, unclear specifically what this is
The tracts for motor function to the upper limbs are found more centrally in the cord compared those to the lower limbs. As a consequence of this “central cord syndrome” may lead to loss of motor function in the upper limbs to a greater extent than the lower limbs.
The descending tracts include the pyramidal and extrapyramidal tracts:
Pyramidal tracts – corticospinal and corticobulbar tracts
Extrapyramidal – reticulospinal, vestibulospinal, rubrospinal, tectospinal
The ascending tracts include the conscious tracts and the unconscious tracts:
Conscious tracts: dorsal column-medial lemniscal pathway and the anterolateral system (anterior and lateral spinothalamic tracts)
Unconscious tracts – spinocerebellar tracts
Lateral corticospinal – limb movement
Anterior spinothalamic – sensation of crude touch and temperature
Lateral spinothalamic - sensation of pain and temperature
Anterior spinocerebellar - proprioceptive information from the lower limbs
Posterior spinocerebellar - proprioceptive information from the lower limbs
Atlas and Axis ligaments and joint
The tectorial membrane is a projection of the posterior longitudinal ligament which attaches to the anterior foramen magnum.
The alar ligaments pass from the dens to tubercles on the medial side of the occipital condyles.
The apical ligament passes from the odontoid process of the axis to the anterior rim of the foramen magnum.
The transverse ligament passes across the ring of the atlas and contains the dens of the axis.
The anterior atlanto-occipital membrane passes between the anterior ring of the atlas and the anterior margin of the foramen magnum.
The atlanto-occpital joint is an articulation between the superior articular facets of the lateral masses of the atlas and the occipital condyles. Flexion-extension and lateral flexion can occur at this joint.
The alar ligaments pass from the sides of the dens to the lateral margins of the foramen magnum.
The atlantoaxial joint contains 3 articulations.; 2 between the superior facet of C2 and the inferior facet of the lateral mass of C1 and one between the dens and the anterior arch of the atlas. Rotation can occur here
Spinal cord syndromes
Brown-Sequard syndrome occurs following hemisection of the spinal cord. Patients exhibit the characteristic loss of proprioception on the ipsilateral side of the lesion with contralateral loss of pain and temperature.
In central cord syndrome the upper limbs are affected more than the lower limbs.
Anterior cord syndrome occurs due to ischaemia in the anterior spinal artery territory leading to loss of function of the anterior 2/3 of the spinal cord. The dorsal columns are spared and so vibration sense and conscious proprioception are preserved.
Anterior spinal cord syndrome occurs following damage to the anterior spinal artery and results in loss of function in the anterior two thirds of the spinal cord. The corticospinal tracts (motor function) and spinothalamic tracts (pain and temperature) are affected. Autonomic dysfunction may occur, however there is sparing of the dorsal columns.
Difference in vertebrae
In the thoracic region the vertebral bodies are heart shaped, the spinous processes are long and point inferiorly and the transverse processes have facets for articulation with the ribs.
In contrast the bodies of the lumbar vertebrae are larger and kidney shaped, they have short, broad spinous processes for articulation of strong lumbar musculature and the facet joints are orientated to face medially / laterally.
The cervical vertebrae have short, bifid spinous processes, smaller vertebral bodies with a relatively large canal and foramen in the transverse process for transmission of the vertebral artery.
Muscles of the back
The intrinsic muscles of the spine are formed into three layers; the superficial, intermediate and deep layers.
The superficial layer contains the spinotransversales (splenius capitis and splenius cervicis).
The intermediate layer includes the erector spinae muscles (from lateral to medial: iliocostalis, longissimus and spinalis).
Finally the deep layer is made up of the transversospinales (semispinalis, multifidus and rotatores).
Intervertebral discs
The intervertebral discs contribute 25% of the spinal column height. The discs includes an outer fibrous ring and inner gelatinous nucleus pulposus.
The outer fibrous ring - annulus fibrosus is comprised of type 1 collagen, water and proteoglycans. It has a high collagen to proteoglycan ratio. The inner nucleus pulposus is composed of type 2 collagen, water and proteoglycans. The high polysaccharide and water content in the nucleus pulposus results in a hydrated gel.
The intervertebral disc is avascular, it receives nutrients from capillaries terminating in the vertebral end plates.
In the cervical spine the nerve roots pass through the intervertebral foramen above the corresponding named vertebra. In contrast the lumbar nerve roots pass below their corresponding vertebra. The dura mater extends to the sacrum. The exact level at which it ends varies between reference material (S2-S3)
Spinal cord blood supply
The spinal cord is supplied by the anterior spinal artery and paired posterior spinal artery. Segmental medullary and radicular arteries provide a significant additional supply, these small vessels enter via the nerve roots. The anterior spinal artery supplies the anterior 2/3 of the spinal cord. The artery of Adamkiewicz is the largest anterior segmental medullary artery and arises from the inferior intercostal or upper lumbar arteries.
