3.1 Spinal Cord
What is a spinal segment?
A section of the spinal cord that has a pair of nerves exiting
Which spinal cord regions are enlarged?
Cervical region, lumbo-sacral region are enlarged because they control the head/neck and the lower half of the body
What regions on the spinal cord are intervertebral foramen founds?
Cervical, thoracic, and lumbar vertebra all have intervertebral foramens
Name the major tract in the Dorsal Column [white matter], what type of tract it is, and what it senses.
Dorsal column-medial lemniscus system · Ascending axons (afferent) · Touch and joint position (proprioception) -sensory
What is the cauda equina?
collection of nerve roots from L1-C0 into a "horse tail" or nerves that extends beyond the spinal cord
Where do spinal nerves exit the spinal column?
intervertebral foramen
What are laminae and what do they do?
laminae describe the functional organization of the grey matter. they are collections of cell bodies that are organized based on function
Name the subdivisions of white matter in the spinal cord, as well as where they are.
o Anterior median fissure -Separates right and left halves of the spinal cord in the anterior portion o Posterior median sulcus -Divides the cord in half the posterior o Anterolateral sulcus -> At the ventral horn, is the exit point for the anterior (motor) root o Posterolateral sulcus -at the dorsal horn -entry point of the posterior (sensory) root
What are the spinal cord meninges?
o Dura Mater -thick, fibrous outer layer -dura sac extends beyond the spinal cord o Arachnoid Mater -weblike intermediate layer -thin, somewhat transparent o Pia Mater -thin layer that adheres to spinal cord; -deepest layer
Axons are arranged ____________ in spinal cord tracts
somatopically "somatotopy" refers to a correspondence between -the ordering of the fibers in a tract and -the rostral-caudal ordering of their receptive field (sensory) or muscle innervated (motor)
Grey and white rami are ____________
sympathetic
What are nerve filaments/rootlets, roots, and nerve? What is rami?
-Coming off each ventral/dorsal horn are rootlets/filaments -These rootlets converge as they extend laterally to make roots -Roots are functionally separated -ventral root => motor -dorsal root => sensory -Ventral and dorsal root converge to make spinal nerves - spinal nerves and their branches have both sensory and motor components (rami)
What is grey and white matter? How are they organized in the spinal cord?
-Grey matter contains cell bodies and relatively few myelinated axons -white matter contains few cell bodies and is composed chiefly of long-range myelinated axon tracts. -In the spinal cord, grey matter exists as an H on the inside and is surrounded by white matter
Grey matter in spinal cord can be divided into 3 horns. Describe where they are and what they do
-Pair of dorsal horns · This is where all the sensory input enters the cord -Pair of ventral horns · Where all the motor outputs exist - Lateral horn · Relates to visceral motor system (autonomic nervous system)
What is the relationship between spinal cord and vertebral column? When do they stop matching?
-Spinal cord is shorter than vertebral column -spinal nerves C1-C7 exit above the vertebra with the same number; -C8 exits below C7 -> all remaining spinal nerves exit below the vertebra with the corresponding number
Clinical application for short spinal cord in relation to vertebral column
-Spinal tap to obtain cerebrospinal fluid (CSF) or for spinal nerve block: -A needle can be inserted into the subarachnoid space at the L3-4 or L4-5 level without risk of damaging the spinal cord
What is the dorsal root ganglion?
-The dorsal root ganglion is where the majority of sensory neurons cell bodies reside. -DRG has the cell bodies for primary sensory neurons -Sensory signal from finger -> spinal nerve -> dorsal root ganglia -> dorsal horn -> CNS
Describe how grey matter is organized via Autonomic/Visceral motor cell bodies (think spinal cord origins)
-Two parts to Autonomic/Visceral System: · Sympathetic and Parasympathetic system T1-L2 = sympathetic cell bodies · (thoracolumbar) · Presynaptic motor fibers here S2-S4 = parasympathetic cell bodies · (sacral part of craniosacral)
What does descending pathway mean?
-motor system -efferent neurons -bringing information from CNS to periphery
What does ascending system mean?
-sensory system -afferent neurons -bring information from the periphery to the CNS
What is the conus medullaris?
-tapering end of the spinal cord. -It occurs near lumbar vertebral levels 1 (L1) and 2 (L2), [remember, this is the end of the spinal cord] -After the spinal cord tapers out, the spinal nerves continue to branch out diagonally, forming the cauda equina.
What is the filum terminale?
A pia mater extension that tethers the tip of the conus medullaris to the end of the vertebral sacrum, around S2. Anchors spinal cord to the skeleton. -Internum = pia -Externum = dura
How many segments are in the spinal cord? Describe each region in order.
Divided into 31 segments within 5 regions: Cervical → 8 nerves (C1-C8) *note: there are only 7 cervical vertebrae-between C7 and T1 Thoracic → 12 nerves (T1-T12) Lumbar → 5 nerves (L1-L5) Sacral → 5 nerves (S1-S5) Coccygeal → 1 nerve (C0)
What happens during a herniated disk?
Existing spinal nerves get compressed
What is a myotome?
Group of muscles innervated by a single spinal nerve or spinal segment
Name the major tract in the Lateral Column [white matter], what type of tract it is, and what it senses.
Lateral corticospinal tract · Descending axons (Efferent) · Motor control role
What are the two sets of arteries that supply blood to the spinal cord? Where are they/what do they do?
Longitudinal Spinal Arteries -Runs the length of the spinal cord -from vertebral arteries Segmental Spinal Arteries -at each segment, traveling with each nerve is a segmental spinal artery -from regional branches
The segmental spinal arteries split into what two branches? What is the main segmental spinal artery
Segmental Spinal Arteries= posterior intercostal artery Medullary branches -feed blood to longitudinal spinal arteries ·Radicular branches o follow and supply spinal roots o supply roots and rootlets o Each segmental artery splits into anterior and posterior branches which, in turn, give off medullary and radicular arteries.
Name the major tract in the Ventral Column [white matter], what type of tract it is, and what it senses.
Spinothalamic / Anterolateral System · Ascending axons (afferent) · Pain and temperature -Ventral column is sensory but ventral horn is motor
What is the epidural space and where is it?
The epidural space is between the dura mater and the vertebral column (its surrounds the spinal cord). It is occupied by fat and blood vessels/
What and where is the subarachnoid space?
The subarachnoid space is a substantial space between the arachnoid and the pia mater, it contains the cerebrospinal fluid (CSF)
What and where is the subdural space?
The subdural space is a potential intracranial space situated between the arachnoid and dura. It is only a real space is something is wrong -> Fluid can collect in the subdural space and in the subarachnoid space.
What is the dorsal ramus? Ventral ramus?
This is a branch of the spinal cord that delivers sensory and motor fibers to the dorsal body wall and to skeletal muscles. The dorsal ramus is the dorsal branch of a spinal nerve that forms from the dorsal root of the nerve after it emerges from the spinal cord. The spinal nerve is formed from the dorsal and ventral rami. The ventral ramus delivers information to most of the body
Main difference between arteries and veins in spinal cord? How do they relate
Veins form internal/external plexuses Veins parallel the arteries in most cases (i.e. reticular vein parallels reticular artery)
What is a dermatome?
an area of skin supplied by a single spinal nerve or spinal segment
What arteries make up the longitudinal spinal arteries?
§ Anterior Spinal Artery - runs down the middle of cord § Posterior Spinal Arteries (2) -Runs the length of spinal cord on either side Two in the back, one in the front
White matter is spinal cord can be divided into 3 columns. What are they?
§ Dorsal column § Lateral column § Ventral column § All these columns are bilateral, they are just labeled on one side
What are the 4 components of a spinal nerve/peripheral nerve?
· 2 somatic components -What we control voluntarily -motor and sensory 1) General Sensory Afferent (GSA) Sensory (touch, pain, temp) 2) General Somatic Efferent (GSE) motor to skeletal muscles (somatic) · 2 visceral components 1) General Visceral Afferent (GVA) sensation from the viscera 2) General Visceral Efferent (GVE) -automatic/visceral motor -motor to visera
Where does the spinal cord end in relation to vertebral column?
· Spinal cord ends at vertebral level L1-L2
Dorsal column is organized into two what?
· organized into two separate fasciculi related to location of receptors o Fasciculus gracilis -Carries info from lower limb -sensory from lower limb -below T6 o Fasciculus cuneatus -Carries info from upper limb -sensory from upper limbs -above T6