Anatomy Block 1-Deep Back/Spinal Cord
The spinal cord is segmented like the vertebral column, but in contrast to the vertebrae, there are only _____ cord segments
31 There are 31 segments of the spinal cord and 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal, for a total of 31. There are 33 vertebrae arranged in 5 regions: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal. Motion only occurs among 24 vertebrae: the 7 cervical, 12 thoracic, and 5 lumbar. (The sacral and coccygeal vertebrae are usually fused.)
Prostate cancer is diagnosed in an 82 year old male. Thereafter a malignant brain tumor of prostatic origin is found. He subsequently dies. An autopsy reveals tumor sites in the prostate, vertebral column, and brain, but no other organs. By what vascular pathway did the cancerous cells get to the brain:
A valveless venous system, the internal vertebral venous plexus is clinically significant because it can transmit cancer metastases to distant locations. The anterior spinal artery and vertebral arteries would not be the route for cancer cells to reach the brain. The azygos system contains valves and would carry blood toward the heart and lungs, not toward the brain. Finally, the thoracic duct is a major channel for lymph flow to reenter the circulation. Although cancer cells may be carried by lymphatics, the thoracic duct would not direct cancer to the brain.
Which is a source of axons found in the dorsal primary ramus of the 4th thoracic spinal nerve?
Afferent neurons arising from the skin overlying the trapezius muscle Dorsal primary rami innervate the true back muscles (like erector spinae) and the skin overlying the back. So, they would contain afferent neurons arising from the skin overlying the trapezius muscle. The rhomboid muscles and levator scapulae are not true back muscles. This means that they are innervated by the ventral primary rami of spinal nerves, not the dorsal primary rami. The trapezius receives motor innervation from the accessory nerve--CN XI; it does not receive motor fibers from any spinal nerve.
In an adult, the conus medullaris of the spinal cord is normally positioned at which vertebral body levels:
B. T12-L2
Kyphosis is an accentuated or abnormal curvature of which region of the spine?
B. Thoracic Lordosis = lumbar spine Scoliosis = lateral curvature
In the lumbar spine, the L4 nerve root sleeve exits:
Below the pedicle of L4 and at the top of the intervertebral foramen Remember, in the lumbar region, spinal nerves exit below the vertebra with the same number. So, the L4 nerve exits below the L4 vertebra. The spinal nerves also exit at the top of the intervertebral foramen.
A football player suffers a herniated (ruptured) intervertebral disk in his neck. The disk compresses the spinal nerve exiting through the intevertebral foramen between the 5th and 6th cervical vertebrae. Which spinal nerve is affected?
C. C-6
A man has a herniated intervertebral disk between the fourth and fifth lumbar vertebrae. If this disk compresses the spinal nerve in the intervertebral foramen immediately posterior to this disk, which spinal nerve would be affected?
C. L-5
Both the dural sac and the subarachnoid space end at which vertebral level?
C. S-2
The subtrapezial plexus of nerves includes:
C3-C4, and spinal accessory (CNXI)
The number of vertebrae and number of spinal cord segments are the same in each region except:
Cervical
Inserting a spinal tap needle in the lumbar region, in the midline, you hear and feel a 'pop' at the needle tip. What structure was perforated to cause the 'pop?'
D. Dura mater
Because of their structure and interconnections, which veins are especially important in the metastatic spread of cancer?
D. Internal vertebral venous plexus
It is decided to image the spinal cord and spinal nerve rootlets by doing a myelogram (injection of a radio-opaque dye into the subarachnoid space followed by a radiograph). In order to inject the dye without injury to the spinal cord, the injection is usually done below what vertebral level?
D. L-4
Which structure does NOT contain efferent autonomic nerve fibers?
Dorsal root of T6 The dorsal root of a spinal nerve contains afferent sensory nerve fibers and no efferent autonomic nerve fibers. The efferent autonomic nerve fibers, which originate in the lateral horn of the spinal nerve, travel out of the spinal cord through the ventral root of the spinal nerve. As the ventral and dorsal roots join to form the spinal nerve, the fibers from both roots intermingle, and the dorsal and ventral primary rami take a mix of fibers, including afferent sensory fibers from the dorsal root, and efferent motorfibers from the ventral root. Postganglionic sympathetic efferent fibers join each spinal nerve via a gray ramus communicans. So, all of the other nerves listed do contain efferent autonomic fibers.
In the final stages of labor a caudal anesthetic is sometimes given via a needle inserted into the sacral hiatus. The anesthetic is thus placed around the outside of the sacral spinal nerve roots and into the:
Epidural space A caudal anesthesia is administered by a catheter inserted through the sacral hiatus. Anesthetic is placed in the catheter, and the anesthetic bathes the sacral nerve roots. The catheter is in the epidural space, and this is where the anesthesia is placed. The central canal of the spinal cord is a space in the spinal cord through which CSF circulates. The dural sinuses are venous sinuses found in the brain--this is where blood drains from the brain. The subarachnoid space is found under the arachnoid mater; this is the space where the cerebrospinal fluid circulates around the spinal cord. Finally, the subdural space is a space between the dura and arachnoid mater--this is a potential space only!
Which muscle is innervated by posterior primary rami?
Erector spinae because it is a true back muscle
A patient is diagnosed as having a venous anomaly of the posterior spinal veins which have enlarged, putting pressure on the spinal cord. In order to expose the veins, the surgeon will have to pass through the skin, subcutaneous tissue, deep back muscles and then, in order, the:
Laminae and ligamenta flava, epidural space, dura, subdural space, arachnoid, subarachnoid space, pia. The surgeon needs to remove all the coverings of the spinal cord to reach the veins on the posterior surface of the cord. So, the surgeon would remove the lamina, a broad, flat plate of bone located between the transverse process and the spinous process of the vertebra . The surgeon would NOT remove the pedicles, which are short strong processes that extend posteriorly from the posterolateral surface of the vertebral body to connect the body with the transverse processes. The pedicles are far too deep in the back to be removed! The surgeon would now pass through the ligamenta flava, which is an elastic ligament which joins the laminae of adjacent vertebrae. Then, the surgeon would cross through the coverings of the spinal cord and associated spaces, starting with the epidural space, continuing with the dura mater, subdural space, arachnoid mater, subarachnoid space, and finishing with the pia mater. Remember--the posterior longitudinal ligament extends over the posterior side of the vertebral bodies--it does not need to be penetrated to reach the spinal cord!
In order to expose the spinal cord from the posterior side, it is necessary to remove the:
Laminae, spinous processes, and ligamenta flavum This is straight from lab: To expose the spinal cord, it was necessary to remove the laminae, spinous processes, and ligamenta flavum. The supraspinous ligament and the interspinous ligament also needed to be removed.
The myelogram also revealed that the dorsal and ventral rootlets of the 5th and 6th cervical nerves had been avulsed (torn or pulled out) from the spinal cord on the right side. Which nerve fibers would not be damaged by the avulsion?
Post or Pre-ganglionic Somatic afferent neurons originate from the dorsal root and dorsal rootlets. If dorsal rootlets were avulsed, somatic afferent nerve fibers would be damaged. Somatic efferent neurons originate from the ventral root and ventral rootlets. If ventral rootlets were avulsed, somatic efferent nerve fibers would be damaged. Preganglionic (presynaptic) sympathetic neurons originate from the lateral horn of the spinal cord between the levels of T1 and L2. They exit the spinal cord through the ventral rootlets and eventually synapse at sympathetic ganglia. Since they travel through the ventral rootlets, the preganglionic sympathetic neurons would be damaged by the avulsion of ventral rootlets between T1 and L2, but not in cervical regions. The postganglionic sympathetic fibers would not be disrupted by avulsing the dorsal and ventral rootlets in any region. They orginate in the sympathetic ganglia which are not a part of the spinal cord. (There will be much more to come on ganglia later on--stay tuned!)
Quasimoto, the "Hunchback of Notre Dame," suffered from an abnormal thoracic curvature called kyphosis. In this condition the accentuated convexity of the curvature is:
Posterior
A neuron with a cell body in the dorsal root ganglia could convey what type of fibers?
Sensory from the skin overlying the trapezius The dorsal root ganglia is the location of the cell bodies of somatic sensory neurons. Cells from the dorsal root ganglia transmit somatic sensation from areas like the skin to the central nervous system. A neuron with a cell body in the dorsal root ganglia might be involved in conveying sensory information from the skin overlying the trapezius. Motor neurons have their cell bodies in the ventral horn of the spinal cord. They leave the spinal nerve through the ventral root, join a spinal nerve, and then divide into the ventral and dorsal primary rami. The dorsal primary rami innervate the deep back muscles, while the ventral primary rami innervate other muscles, including pectoralis major (which is innervated via the brachial plexus). The cell bodies of preganglionic sympathetic fibers are found in the lateral horn of the spinal cord. Finally, visceral afferent sensation is not carried on somatic sensory neurons--instead, the sensation from the stomach is carried on special visceral afferent nerves which accompany sympathetic nerves.
As the spinal needle in the above question is being inserted, which ligament would it pass through on its way to the subarachnoid space?
Supraspinous
It was noted that after the injury the patient's face on the right side was flushed due to dilation of the blood vessels. The lack of vasoconstriction was due to interruption of what fibers somewhere along their course?
Sympathetic The sympathetic nervous system is responsible for the vasoconstriction of peripheral vasculature. If the sympathetic nervous system was damaged, peripheral vessels would no longer be able to constrict. The resultant vasodilation would cause flushing. Somatic afferent, efferent, and parasympathetic fibers are not involved with the innervation of the vasculature. Disrupting any of these other fibers would not cause these symptoms.
A patient is suspected of having bacterial meningitis. A lumbar puncture is performed to remove cerebrospinal fluid (CSF) for analysis. If done properly, the needle used for the tap would penetrate all layers except:
The pia mater is the innermost covering of the spinal cord which is closely applied to the entire spinal cord. It does not need to be pierced to retrieve CSF. This fluid is found in the subarachnoid space, outside of the pia mater. The needle must pass through the following layers during a lumbar puncture: skin, fat, supraspinous ligament, interspinous ligament, between or through the ligamenta flava, epidural fat and veins, dura, subdural space, and arachnoid.
The myelogram revealed that the dye had leaked out along the spinal nerves in the mid cervical region on the right side. For the dye to leak out, what layer must have been torn or ruptured?
The previous question stated that a myelogram is a radiograph taken following injection of a radio-opaque dye into the subarachnoid space. So, it should make sense that the arachnoid must be ruptured for the dye to leak out following this procedure. Denticulate ligaments are specializations of the pia mater that form a longitudinal shelf separating the dorsal and ventral rootlets. They suspend the spinal cord in the subarachnoid space. These ligaments would not be disturbed during a myelogram. Periostium is a fibrous connective tissue that invests bones, and perineurium is a connective tissue covering that encloses a fasicle of peripheral nerve fibers. The pia mater is the innermost covering of the spinal cord. It closely follows the entire spinal cord and is not penetrated during a myelogram
A 45-year-old man complained to his physician that the muscles of his upper limb were weak and he felt clumsy while walking. Tests revealed that he had amyotrophic lateral sclerosis (Lou Gehrig's disease), a disease which attacks the neurons of the voluntary motor system. Where would one expect to see atrophic or degenerated nerve cell bodies?
Ventral horn
If in the process of doing a lumbar puncture a spinal needle was inserted posteriorly in the midline until it had just penetrated the posterior longitudinal ligament, would the needle have entered the subarachnoid space?
Yes, because the PLL is right before the subarachnoid space
The intervertebral disk
adds about 1/4 the entire length to the vertebral column. The interveterbral discs, consisting of an outer anulus fibrosus and an inner nucleus pulposis, add about 1/4 the length to the vertebral column. They act as shock absorbers between the vertebral bodies. The discs are not found between all adjacent vertebrae. There is no disc between the C1 and C2 vertebrae, and the most inferior disc is between L5 and S1. Discs are not synovial joints--they are cartilagenous joints (symphyses) designed to bear weight. The center of the disc, the nucleus pulposis, is highly elastic and compressible, but it is a cartilaginous structure, not liquid. Finally, the intervertebral disc is not penetrated to form a spinal tap. The needle only needs to penetrate the subarachnoid space to retrieve CSF.
A patient is suspected of having bacterial meningitis. As part of the diagnostic procedure, a lumbar puncture is to be performed. The attending physician asks you where she should insert the spinal needle to withdraw CSF. You answer, "just below the spine of the 4th lumbar vertebra." What reference point would you use to identify the spine?
crest of the ilium
The part of a spinal nerve that supplies the true back muscles and the skin overlying them is the
dorsal primary ramus The dorsal primary ramus supplies sensory innervation to the skin of the back and motor innervation to the true back muscles. Ventral primary rami supply sensory innervation to the skin of the anterior trunk and limbs and motor innervation to the skeletal muscles of the neck, trunk, and extremities. The ventral and dorsal roots of a spinal nerve are made of the ventral and dorsal rootlets, which come from the spinal cord. The ventral root contains efferent motor fibers, while the dorsal root contains afferent sensory fibers. The two roots eventually fuse to form a spinal nerve which gives off the dorsal and ventral primary rami.
The conus medullaris
gives origin to most of the cauda equina Located at L2, the conus medullarus is the tapered termination of the spinal cord proper. Most of the cauda equina originate from the conus medullaris and then travel to the vertebral foramina inferior. Although the spinal cord exhibits both a cervical and a lumbar enlargement, the conus medullaris refers to the termination of the spinal cord, not the entire spinal cord. There is no modified neural tissue extending from the termination of the conus medullaris to the coccygeal ligament. Instead, the filum terminal internum, which is a thread-like extension of the pia mater, extends from the conus medullaris. Eventually, this filum terminal internum becomes enclosed in the filum terminale externum, which is a thread-like extension of the dura mater extending below the end of the dural sac (at the S2 level). The filum terminal externum is what attaches to the coccyx, forming the coccygeal ligament. The conus medullaris is located at L2, at the termination of the spinal cord. The dural sac, however, continues to the S2 level. (These are important levels to keep in mind!) Finally, the conus medularis is not anesthetized to perform a spinal tap--hopefully, the needle used for a spinal tap won't even touch the conus medullaris!
While moving into a new apartment a student lifting a heavy box of books experiences a sharp pain in his back, radiating down the anterior thigh and medial side of his leg. After several days of misery, he finally goes for treatment and is told that he has a herniated intervertebral disk at the L 4 level which is compressing a spinal nerve where it exits the vertebral column. The point of compression is the:
intervertebral foramen A "slipped disk" is the herniation of the nucleus pulposis through the anulus fibrosis. This usually happens in a posterolateral direction. Once a disk herniates, it commonly puts pressure on the nerve roots or the dorsal root ganglion exiting the intervertebral foramen at or below its level. The vertebral canal or vertebral foramen is the opening formed by the combination of the body and vertebral arch. This is not the location where the disk is compressing nerves. The foramen magnum is an opening in the occipital part of the skull that transmits the spinal cord. The hiatus of the sacral canal is a normal feature that results from the failure of fusion of the laminae of the fifth sacral segment (and sometimes the fourth) during development.
The denticulate
is a modification of the pia mater. The denticulate ligaments are specializations of the pia mater that extend from the lateral surface of the pia, helping to suspend the spinal cord in the subarachnoid space. These ligaments form longitudinal shelves that separate the dorsal and ventral rootlets. There are only 21 pairs of denticulations, so they are not found between all dorsal and ventral rootlets. These ligaments are not continuously attached to the dural sac; instead, they appear between the dorsal and ventral rootlets. Radicular arteries arise as multiple branches of several vessels (vertebral, posterior intercostal, lumbar, and lateral sacral arteries) and accompany the ventral rootlets to reach the spinal cord. They do not have a special relationship with the denticulate ligaments.
If one does a laminectomy (removing the laminae of two adjacent vertebrae) to expose the spinal cord, which ligament must be removed?
ligamentum flavum
A patient is suspected of having bacterial meningitis. A lumbar puncture is performed to remove cerebrospinal fluid (CSF) for analysis. The fluid would be removed from the:
subarachnoid space There are 2 issues to think about here. First, from what compartment is the CSF removed? Second, at what level should the needle be inserted in a spinal tap? CSF is removed from the subarachnoid space. The epidural space contains epidural fat, and the subdural space is a potential space only. Also, remember that a lumbar puncture should be performed at the level of L4. Because the spinal cord ends at the bottom of L1 or the top of L2, L4 is a safe level for inserting a needle.
