structure and function of the spinal cord Flashcards
Where does the spinal cord extend to
From the atlas to the L1 vertebrae and tapers to form the conus medullaris.
Outline the anatomy of the spinal cord
Sits protected within the vertebral column and is surrounded by meninges: pia, arachnoid, and dura
How many regions is the spinal cord divided into
cervical region (8), thoracic region(12), lumbar(5), and sacral region (5)
What is the lumbar cistern
It is the space below L1 and contains the cauda equina (lumbar and sacral dorsal and ventral roots).
What are the roles of the cervical and lumbosacral enlargement
Innervation to the upper and lower limbs respectively.
What type of nerve fibres do ventral and dorsal roots contain
efferent and afferent nerve fibres respectively.
Outline the internal anatomy of the spinal cord
Inner core, grey matter (neuronal cell bodies, H-shaped, ventral, lateral and dorsal horns)
Outer, white matter (myelinated neurons and white tracts and columns)
Outline grey matter organisation
Dorsal horn- neurons recieving sensory input
lateral horn- preganglionic sympathetic neurons
ventral horn- motor neurons
Outline white matter organisation
Contains tracts: long ascending tracts that carry afferent (sensory) impulses to centres in the brain
long descending tracts carry efferent (motor) impulses from centres within the brain
tracts to and from cerebral hemispheres are crossed.
Outline the columns in white matter
dorsal column (contains ascending tracts) lateral column ( contains descending and ascending tracts) ventral column (contains mainly descending tracts)
What are the two types of sensory information carried within the ascending tracts
propriceptive- info originating inside the body e.g. muscles, joints etc
exteroceptive- info originating outside the body e.g. body, temp and touch etc
How many neurons in a tract
3, first order (primary sensory) neuron enters spinal cord via dorsal root.
second order neurons- ascends spinal cord or brainstem
third order neuron- projects to the cerebral cortex
Outline the DCML pathway
the dorsal column-medial lemniscus pathway, carrying information conveying fine touch and vibration sense, discriminating between fine and blunt pressures.
also conveying proprioception from muscle spindles, golgi tendons and joints.
Outside the 1st order neurons of the DCML pathway
first order neurons:
enter spinal cord and ascend dorsal column on the same side.
the dorsal column can be divided into the fasiculus gracilis/cuneatus. they remain uncrossed.
Where do the first order synapse on the second order neurons and where is information carried from lower and upper limbs
In the medulla.
lower limb- fasciculus gracilis terminates in nucelus gracilis
upper limb- fasciculus cuneatus and terminates in nucleus cuneatus.
Outline the second order neurons
They cross in the medulla and ascend to the thalamus, form medial lemniscus
Outline third order neurons
project from the thalamus to somatosensory cortex.
Outline damage to the dorsal column
lesion on one side of the spinal cord e.g. MS
loss of tactile discrimination and proprioception on same side.
clinical test- rombergs sign
Outline the spinothalamic tract
information on pain, temp and crude touch.
first order neurons enter dorsal horn and form tract of lissauer and synapse in dorsal horn with second order neuron.
second order neurons cross in dorsal horn at each level, ascend in the anterlateral column to thalamus
third order neurons, project from thalamus to somatosensory cortex
Outline damage to the anterolateral column
Lesion on one side of spinal cord- leads to loss of pain, temp and crude touch on opposite sided.
outer tract injury e.g. cord compression due to herniated disk- loss of lower limb pain first
inner tract injury- loss of upper limb pain first
Outline spinocerebellar tracts
unconscious muscle proprioception- from muscle spindles, golgi tendon organs.
there are 3 main tracts, anterior, posterior and cuniocerebllar tract
terminated in the cerebellum on the same side.
What do the descending tract control
control muscular activity, many descending tracts and grouped into pyramidal and extrapyramidal.
What is the corticospinal tract
A pyramidal tract, great voluntary motor pathway, 2 neurons in the circuit: upper motor neurons and lower motor neurons.
outline the pyramidal tract
upper motor acons pass through the pyramids of the medulla, primary motor cortex, internal capsule, cerebral peduncle, pons to pyramids of medulla.
What are the pyramids of descussation
within the pyramids of the medulla, nerve fibres decussate.
What happens if the corticospinal tract is damaged
motor neurone disease, degeneration of upper motor neurons, spastic paralysis, over active tendon reflexes and no significant muscle atrophy.
lower motor neurone disease is damage to lower motor neurones : flaccid paralysis, muscle atrophy and no tendon reflexes.
