Structure and function of the spinal cord Flashcards
Where does the spinal cord extend from and to?
medulla at the cranial border of the atlas
to the first lumbar vertebra
What is the conus medullaris?
The spinal cord narrowing off at L1
What is the terminal filum?
Attaches to the coccyx
The carrying on of the pia and dura past the lumbar vertebrae
What is the cauda equina?
The bundle of spinal nerves arising from the end of the spinal cord
Contains lumbar/sacral dorsal/ventral roots
Where is the spinal cord located?
Sits within the vertebral column
Surrounded by meninges
Well protected
How is the spinal cord divided?
Into four regions corresponding to which spinal nerves form that region exit the vertebral column
What are the two points of enlargements?
Cervical enlargement
Lumbosacral enlargement
What are the vertebral divisions and how many vertebrae are in each division?
7 cervical
12 thoracic
5 lumbar
5 sacral
What are the different spinal nerves and how many are there?
C1-C8 spinal nerves
T1-T12 spinal nerves
L1-L5 spinal nerves
S1-S5 spinal nerves
What does the lumbar cistern contain?
the cauda equina (lumbar/sacral dorsal/ventral roots)
Describe the cervical enlargement
C4-T1 level, origin of the brachial plexus, innervation to upper limbs
Describe the lumbosacral enlargement
T11-L1, origin of lumbar and sacral plexi, innervation to the lower limb
What is the terminal filum made of?
Pia internally, dura externally
What are spinal nerves?
Spinal nerves connect the periphery to the spinal cord
How many spinal nerves are there?
31 pairs, each formed by a dorsal and ventral root (which sort of connect to form one thing)
What role do dorsal and ventral roots have?
Dorsal - afferent- cell bodies of primary sensory neurons (pseudounipolar)
Ventral - efferent - motor neurons
Describe the inner core of vertebrae
Grey matter - contains neuronal cell bodies. H shaped.
Ventral (front), lateral (side) and dorsal (back) horns.
Lateral horns only in thoracic spine!
Different amounts of grey matter - expanded at levels supplying the limbs e.g. cervical
Describe the outer area of a vertebra
White matter
myelinated axon
White columns/tracts or funiculi
Describe the general rules of grey matter organisation
Dorsal horn - neurons receiving sensory input
Lateral horn - preganglionic sympathetic neurons
Ventral horn - motor neurons
There are also interneurons between/within these levels
Describe white matter organisation
Contains tracts
Long ascending tracts carrying sensory/afferent information to brain centres
Long descending tracts carrying efferent/motor impulses from brain centres
Tracts to/from the cerebral hemispheres cross - their axons cross the midline i.e. left cerebral hemisphere controls right side of body
Describe the tract organisation of the spinal column
Dorsal column - ascending tracts (afferent/sensory) Lateral column (descending and ascending tracts (mixed) Ventral column (mainly descending tracts (efferent/motor)
What are the two types of sensory information carried in ascending tracts?
- Proprioceptive - information originating from within the body e.g. muscles, joints, tendons
- Exteroceptive - information originating from outside the body e.g. skin (pain, temperature, touch)
Describe the general ascending tract circuit
first order neuron (primary sensory)
- enters spinal cord via dorsal root
- brings info from the periphery into the CNA
- synapses onto second order neuron
Second order neuron
- ascends spinal cord or brainstem
- synapses onto third order neurons often in the thalamus, going up to the cerebral cortices
Third order neuron
- projects to the cerebral cortex
What does the dorsal column-medial lemiscus pathway detect?
fine touch (from cutaneous mechanoreceptors)
- tactile discrimination, vibration sense
proprioception
- from muscle spindles, golgi tendon organs, joints
provides brain with positional information§
1st order neurons of the dorsal column - medial lemniscus pathway
enter spinal cord and ascend dorsal column on same side within the fasciculus gracilis (more medial) and the fasciculus cuneatus (lateral)
Fibres ascend the dorsal column uncrossed
Longest neurons in the body
1st order neurons synapse on second order neurons in the medulla
How are the axons of the dorsal column medial lemniscus organised topographically?
Fasciculus gracilis terminates in the nucleus gracilis (gracile)
- information from lower limb
- more medial
Fasciculus cuneatus terminates in the nucleus cuneatus
- information from the upper limb
- more lateral
Describe the second order neurons of the dorsal column medial lemniscus system
Cross in the medulla and ascend to the thalamus
- form the medial lemniscus (a large ascending bundle of axons which cross in the medulla)
Where from and to do the third order neurons project?
From the thalamus to the somatosensory cortex
What does a lesion on one side of the spinal cord result in?
E.g. in multiple sclerosis
loss of tactile discrimination and proprioception on the same side of lesion
Symptoms include sensory ataxia
- loss of coordination and balance without visual cues
- clinical test: Romberg’s sign - severe swaying on standing with eyes closed/ feet together
What type of sensory innervation is the spinothalamic tract responsible for?
Pain, temperature and crude touch (from nociceptors)
Describe the first order neurons of the spinothalamic tract
Enter the dorsal horn and form the tract of Lissauer
Collateral branches given off at tip of dorsal horn and run up or down 1-2 segments
Synapse in dorsal horn with second order neurones
Describe the second order neurons of the spinothalamic tract
Cross in the dorsal horn at each level
Ascend in the anterolateral column to the thalamus
- fibres from the lower limb are lateral
-fibres from the upper limb are medial
Describe the third order neurons of the spinothalamic tract
Project from the thalamus to the somatosensory cortex
What happens if there is damage to the anterolateral column?
If there is a lesion on one side of the spinal cord, there is a loss of pain, temperature and crude touch on the opposite side
Outside compression of cord: loss of lower limb pain first (fibres sit laterally)
Inside grey matter tumour: loss of upper limb pain first (fibres sit medially)
What are spinocerebellar tracts?
Ascending tracts responsible for unconscious muscle proprioception (from muscle spindles, golgi tendon organs) - unconscious because not going to higher brain centres
Allow smooth motor coordination
