KAAP220 Lecture Notes - Lecture 20: Filum Terminale, Arachnoid Mater, Dura Mater
11 May 2018
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Lecture 20
• Spinal cord, spinal nerves, and spinal reflexes
• The spinal cord can function independently from the brain
• Not all information that goes into the spinal cord has to go up into the brain to be integrated; spinal
cord can integrate and relay back to the effectors by itself
• Reflex - quick, automatic response triggered by a specific stimulus
• Spinal reflexes - only controlled by spinal cord, not brain
• Spinal cord
• 18 in in length
• 31 segments - 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
• Spinal cord itself is shorter than the spinal column - more vertebrae than cord
• Conus medullaris - end of spinal cord; tapers into a point; around L1-L2 (where the cord
terminates)
• Filum terminale - “terminal thread”; strand of fibrous tissue from tip of conus medullar is to S2;
attaches to sacrum to help stabilize the spinal cord; provides longitudinal support to spinal cord
• Cauda equina - horse’s tail; collection of spinal roots of the spinal nerves; the ones below L2;
extended anterior and posterior roots of spinal segments L2 to S5 and filum terminale; exit out
through vertebral foramena at the appropriate level
• 31 pairs of spinal nerves; named by region of spinal cord and the specific level of spinal cord; so
cervical is “C” and then whatever number it’s from, C1-C8 nerves
• 31 pairs of spinal nerves arise from 31 spinal cord segments
• Because they’re 8 cervical nerves and only 7 cervical vertebrae, 1 exits above C1 vertebrae, 2 from
C2, C8 exits below C7 and above T1; then T1 is below T1 vertebrae
• Meninges
• Coverings of the spinal cord
• Layers that are going to be surrounding and protecting the CNS; around the brain and spinal cord
• Dura mater = outermost layer
• Arachnoid mater = middle layer
• Pia mater = directly adhered to spinal cord or brain
• Help add stability, absorbs shock with CSF, carry blood supply to the CNS; CSF also provides
nutrients
• Dura mater directly = “hard/tough mother”; toughest and thickest outermost covering; made of
collagen fibers oriented vertically
• Arachnoid mater is very difficult to see; spider-webby; shiny strands covering the pia mater;
overlies the subarachnoid space; subarachnoid space = under/below the arachnoid mater,
between arachnoid and pia, and this is where CSF is found
• Pia mater - innermost; directly adhered to spinal cord and brain; follows every groove;
combination of elastic and collagen fibers so it’s not as thick; anchored to the CNS, so if you
were to try to pick it up, you would take neurons with it
• Subarachnoid space - has CSF that helps to absorb forces/shock; between arachnoid and pia mater;
absorbs shock waves; CSF supplies nutrition to CNS; blood vessels that supply the brain and
spinal cord are found here
• Epidural space - outside the dura; between the bone and dura; has some fatty tissue, some blood
vessels that supply the dura mater; mostly areolar and adipose fat
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• (superficial) epidural mater, dura mater, arachnoid mater, subarachnoid space, pia mater (deep)
• Supporting ligaments maintain position of spinal cord
• Denticulate ligaments - part of the pia mater that goes through the arachnoid mater and attaches
to the inside of the dura mater; prevents lateral movement; has tooth like appearance -
“dentic”; resists twisting in the spinal canal
• Lumbar puncture/spinal tap - removal of CSF; typically done in lumbar region; have to do it below
L2 as you don’t want to come anywhere near the spinal cord
• Usually done between L4 and L5
• Patient is flexing forward in the fetal position; stretches the ligaments in between the vertebrae;
generally the iliac crests are at about L4, so draw a line across the back and insert the needle just
below that
• Not concerned about the cauda equina
• Spinal cord structure
• Outer white matter
• Inner gray matter with central canal; makes up the inner portion butterfly
• White matter = composed of myelinated axons (white because of fatty sheath of the myelin);
primarily myelinated axons, although a few cell bodies in there
• Gray matter = dendrites, cell bodies, parts of neurons that don’t have myelin - not many axons
• White matter - superficial, mostly myelinated and few unmyelinated axons
• CSF also in the central canal
• Posterior median sulcus - divet/dip; shallow, longitudinal groove on posterior surface
• Anterior median fissure - large opening or cut; wide gap, deep cut; on anterior surface
• Posterior root has a ganglion
• Spinal nerve - axons of sensory and motor neurons; roots are anchoring the spinal nerve to the
CNS, carrying things to and from spinal cord
• Anterior root - has axons of motor neurons
• Posterior root - has axons of sensory neurons
• Posterior root ganglion (spinal ganglion) - has cell bodies of sensory neurons in posterior root;
slight dilation of the root
• Gray matter - looks like a butterfly; larger projections; sometimes there’s a tiny bump on the lateral
side; called horns
• Posterior gray horn - where our sensory neurons are coming in; receiving all the sensory
information, somatic and visceral
• Lateral gray horn - visceral motor cell bodies here; only in thoracic and lumbar segments; only
visceral
• Anterior gray horn - somatic motor cell bodies; only somatic
• White matter
• Organized in tracts
• Bundles of axons in CNS (similar to a nerve in PNS)
• Ascending tracts carry sensory= information - in posterior columns
• Descending tracts carry motor information - in anterior columns
• Spinal nerves
• All nerves have layers of tissue around it
• 3 CT layers surround spinal nerves
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