Structure and function of the spinal cord Flashcards
What does the spinal cord narrow to form
- Conus medullaris
What is the terminal filum
- Is a delicate strand of tissue, about 20 cm in length, proceeding downward from the apex of the conus medullaris
What is the cauda equina
- Is a bundle of spinal nerves and spinal nerve rootlets, consisting of the second through fifth lumbar nerve pairs
What are the four divisions of the spinal cord
Cervical division - C1-C7
Thoracic division - T1-T12
Lumbar division - L1-L5
Sacral division - S1-S5
What is the conus medullaris
- The conus medullaris (Latin for “medullary cone”) or conus terminalis is the tapered, lower end of the spinal cord. It occurs near lumbar vertebral levels 1 (L1) and 2 (L2), occasionally lower. The upper end of the conus medullaris is usually not well defined.
What type of fibres do the ventral roots contain
Efferent fibres
What type of fibres do the dorsal roots contain
Afferent fibres
What does the inner core, gray matter of the spinal cord contain
- Neuronal cell bodies
- H shaped
- Ventral, lateral and dorsal horn
What does the outer, white matter of the spinal cord contain?
- Myelinated axons
- White columns/tracts or funiculi
What part of the spine are the lateral horns specific to
- Thoracic region
Where is there extra gray matter
- At levels that supply the limbs
What type of neurons are present in the dorsal horn
- Neurons receiving sensory input
What type of neurons are present in the lateral horn
- Preganglionic sympathetic neurons
What type of neurons are present in the ventral horn
- Motor neurons
What type of white matter tracts carry afferent(sensory) impulses
- Long ascending tracts carry afferent(sensory) impulses to centres within the brain
What type of white matter tracts carry efferent(motor) impulses from centres within brain
- Long descending tracts carry efferent(motor) impulses from centres within brain
What happens to tracts that go to/from cerebral hemispheres
- Cross
- ie left cerebral hemisphere controls right side of body
What column are the ascending white matter tracts located
- Dorsal column
What column are the descending white matter tracts located
- Lateral column = descending + ascending tracts
What does the ventral column contain?
- mainly descending tracts
What is proprioceptive information
- info originating from inside the body(from muscles, joints, tendons)
What is exteroceptive info
- info originating from outside the body(pain, temp, touch)
What is a first order(primary sensory) neuron
- Enters spinal cord via dorsal root
What is a second order neuron
- Ascends spinal cord or brainstem
What is a third order neuron
- Projects to the cerebral cortex
What is detected by the dorsal column-medial lemniscus pathway
- Fine touch(from cutaneous mechanoreceptors)
- Proprioception(from muscle spindles, golgi tendon organs, joints
- Provides brain with positional information
Where do first order neurons enter in the dorsal column-medial lemniscus pathway
- Enter spinal cord and ascend dorsal column on the same side within the
1) fasciculus gracilis(medial)
2) fasciculus cuneatus(lateral)
Where do first-order neurons synapse on second-order neurons in the dorsal column-medial lemniscus pathway
- In the medulla
Where does the fasciculus gracilis terminate and what limbs does it carry info from
- Terminates in nucleus gracilis(gracile)
- Info from lower limb
Where does the fasciculius cuneatus terminate and what limbs does it carry info from
- Terminates in nucleus cuneatus(cuneate)
- Info from upper limb
What is the path of the second-order neurons in the dorsal column-medial lemniscus pathway
- Cross in medulla and ascend to thalamus
- Form medial lemniscus(ribbon)
What is the path of third-order neurons in the dorsal column-medial lemniscus pathway
- Project from thalamus to somatosensory cortex
What happens when there is a lesion on one side of the spinal cord in the dorsal-column medial lemniscus pathway
- Lesion on one side of spinal cord
- eg. in multiple sclerosis
- loss of tactile discrimination + proprioception on same side
What are the symptoms of a lesion compromising the dorsal root medial lemniscus pathway
- Sensory ataxia - loss of coordination and balance without visual cues(ie no positional info)
What is romberg’s sign
- Severe swaying on standing with eyes closed/feet together
- Indicative of a lesion affecting the dorsal root-medial lemniscus pathway
What does the spinothalamic tract detect
- Pain, temp and crude touch(from nociceptors)
Path of first-order neurons in spinothalamic tracts
- Enter dorsal horn and form tract of lissauer
- Collateral branches given off at the tip of dorsal horn
- Run up or down 1-2 segments
- Synapse in dorsal horn with second-order neurons
Path of second-order neurons in the spinothalamic tracts
- Cross in dorsal horn at each level
- Ascend in anterolateral column to thalamus
- Fibres from lower limb - lateral
- Fibres from upper limb - medial
Path of third-order neurons in spinothalamic tracts
- Project from thalamus to somatosensory cortex
