TBL2 - Spinal Cord Flashcards
What makes up the white and gray matter in the spinal cord?
1) The anterior (ventral) and posterior (dorsal) horns constitute gray matter of the spinal cord
2) Anterior and posterior roots of the spinal nerves contribute to the surrounding white matter
3) Nerve cells reside in gray matter
What types of spinal neurons are found in the anterior and posterior horns of gray matter?
1) Motor axons from neurons in the anterior horn constitute the anterior roots of the spinal nerves, while posterior roots of the spinal nerves contain sensory axons from neurons in the spinal ganglion. Sensory axons of the posterior roots synapse with neurons in the posterior horn
2) The spinal nerves are formed by union of the anterior roots with sensory axons from the spinal ganglion; thus, all spinal nerves contain both sensory and motor axons
How many spinal nerves are there?
All spinal nerves are bilateral (31 pairs total):
1) Cervical: 8 pairs
2) Thoracic: 12 pairs
3) Lumbar: 5 pairs
4) Sacral: 5 pairs
5) Coccygeal nerve: 1 pair
What is the conus medullaris and how does it change over time?
1) The tapering inferior end of the spinal cord below the lumbar enlargement is called the conus medullaris, positioned between vertebrae L1 and L2 in adults
2) After the spinal cord tapers out, the spinal nerves continue to branch out diagonally, forming the cauda equina
3) At birth, it is positioned between vertebrae L3 and L4 and with vertebral column elongation and the onset of erect posture, the conus medullaris ascends to the adult level by age five
What is the cauda equina?
1) The long roots of the lumbar and sacral spinal nerves collectively constitute the cauda equina
2) The length of the roots results from elongation of the spine and erect posture
What is the arachnoid mater?
1) The arachnoid mater is one of the three meninges, the protective membranes that cover the brain and spinal cord
2) It (more loose connective tissue) is interposed between the two other meninges, the more superficial and much thicker dura mater (more dense connective tissue) and the deeper pia mater, from which it is separated by the subarachnoid space
3) CSF circulates in the subarachnoid space (between arachnoid and pia mater) and presses the arachnoid against the inner surface of the dura
4) In the cervical region, observe the arachnoid lines the dural sac, which ends in the sacral region at vertebra S2
Why is lumbar spinal puncture an important diagnostic tool? Why would different vertebral levels be used in newborn infants and adults?
1) Lumbar puncture (LP, spinal tap), the withdrawal of CSF from the lumbar cistern, is an important diagnostic tool for evaluating a variety of central nervous system (CNS) disorders. Meningitis and diseases of the CNS may alter the cells in the CSF or change the concentration of its chemical constituents. Examination of CSF can also determine if blood is present
2) The location of vertebrae in relation to the spine is different in newborn infants than it in in adults. Remember the spine elongates in adults due to secondary curvature
What is the pia mater?
1) The spinal pia mater, the innermost covering membrane of the spinal cord, is thin (2-3 cell layers separated by loose connective tissue) and transparent, and closely follows all the surface features of the spinal cord. The spinal pia also directly covers the roots of the spinal nerves and the spinal blood vessels. Inferior to the conus medullaris, the spinal pia continues as the filum terminale
2) Pia mater follows the surface contours of the spinal cord
What is the filum terminale? (What is the point of the filum terminale?
1) The filum terminale, an extension of the pia, pierces the terminal end of the dural sac and anchors the sac to the coccyx
2) The filum terminale is the vestigial remnant of the caudal part of the spinal cord that was in the tail-like caudal eminence of the embryo. Its proximal end (the filum terminale internum, or pial part of the terminal filum) consists of vestiges of neural tissue, connective tissue, and neuroglial tissue covered by pia mater
3) The filum terminale perforates the inferior end of the dural sac, gaining a layer of dura and continuing through the sacral hiatus as the filum terminale externum (or dural part of the terminal filum, also known as the coccygeal ligament) to attach to the dorsum of the coccyx
4) The filum terminale is an anchor for the inferior end of the spinal cord and spinal meninges
Which blood vessels nourish the spinal cord?
1) The anterior spinal artery, two posterior spinal arteries, and the anterior and posterior segmental medullary arteries supply the spinal cord
2) The anterior and posterior spinal arteries only supply the superior part of the spinal cord; thus, most of the spinal cord is supplied by the anterior and posterior segmental medullary arteries
3) The segmental medullary arteries arise from arteries adjacent to the vertebral column and enter the spine via the intervertebral foramina
4) The great anterior segmental medullary artery (of Adamkiewicz), the largest segmental medullary artery, supplies about two thirds of the spinal cord
Why is obstructive disease of the great anterior segmental artery (of Adamkiewicz) associated with spinal cord ischemia and what is the clinical consequence?
1) The segmental reinforcements of the blood supply to the spinal cord from the segmental medullary arteries are important in supplying blood to the anterior and posterior spinal arteries. Fractures, dislocations, and fracture–dislocations may interfere with the blood supply to the spinal cord from the spinal and medullary arteries
2) Deficient blood supply (ischemia) of the spinal cord affects its function and can lead to muscle weakness and paralysis. The spinal cord may also suffer circulatory impairment if the segmental medullary arteries, particularly the great anterior segmental medullary artery (of Adamkiewicz), are narrowed by obstructive arterial disease
Where does venous blood empty into in the spinal cord?
1) Veins of the spinal cord drain into the internal vertebral venous plexus that resides in the epidural space between the dura and periosteum of the vertebral canal
2) Small branches from the venous plexus traverse the intervertebral foramina and empty into veins of the trunk and neck
