1.4 Early Development of the Nervous System

entoderm

The innermost layer, the _______, gives rise to the gastrointestinal tract, the lungs, and the liver.

mesoderm

gives rise to the muscle, connective tissues, and the vascular system

ectoderm

The third and outermost layer, the ______, formed of columnar epithelium, gives rise to the entire nervous system.

neural plate

During the third week of development, the ectoderm on the dorsal surface of the embryo between the primitive knot and the buccopharyngeal membrane thickens to form the ______

neural groove

The plate, which is pear shaped and wider cranially, develops a longitudinal _____.

neural folds

The groove now deepens so that it is bounded on either side by _______

neural tube

With further development, the neural folds fuse, converting the neural groove into a _________

28

The neural tube closure is complete within ___ days

Cervical disc herniations

The discs most susceptible are those between the 5th and 6th and the 6th and 7th cervical vertebrae.

Lumbar disc herniations

The discs usually affected are those between the 4th and 5th lumbar vertebrae and between the 5th lumbar vertebra and the sacrum.

Sciatica

The sensory posterior roots most commonly pressed on are the 5th lumbar and 1st sacral, pain is usually felt down the back and lateral side of the leg, radiating to the sole of the foot, a condition known as _______

Spinal tap (lumbar puncture)

____________ may be performed to withdraw a sample of CSF for microscopic or bacteriologic examination or to inject drugs to combat infection or induce anesthesia.

60 to 150 mm of water

When the patient is in the recumbent position, the normal pressure is about____________. The pressure shows oscillations corresponding to the movements of respiration and the arterial pulse.

Caudal Anesthesia

Anesthetic solutions may be injected into the sacral canal through the sacral hiatus. The solutions pass upward in the loose connective tissue and bathe the spinal nerves as they emerge from the dural sheath

pond

The young child’s skull resembles a ping-pong ball, because a localized blow produces a depression without splintering. This common type of circumscribed lesion is known as a “____” fracture.

contrecoup injury

sudden severe blow to the head, as in an automobile accident, may result in damage to the brain at two sites

Epidural (extradural) hemorrhage

results from injuries to the meningeal arteries (commonly the anterior division of the middle meningeal artery) or veins

1.5 in (4 cm)

To stop epidural hemorrhage, the torn artery must be ligated or plugged. The burr hole through the skull wall should be placed about _______ above the midpoint of the zygomatic arch.

Subdural hemorrhage

Results from tearing of the superior cerebral veins where they enter the superior sagittal sinus . The cause is usually a blow to the front or back of the head resulting in excessive anteroposterior displacement of the brain within the skull.

Subarachnoid hemorrhage

results from nontraumatic leakage or rupture of a congenital aneurysm on the cerebral arterial circle (circle of Willis) or, less commonly, from an arteriovenous malformation.

cerebral hemorrhage, spontaneous intracerebral hemorrhage

is most common in patients with hypertension. It is generally due to rupture of the thin- walled lenticulostriate artery

hydrogen nucleus

MRI uses the magnetic properties of the ________ excited by radiofrequency radiation transmitted by a coil surrounding the head.

MRI

It is the best imaging method for detecting low-contrast lesions such as brain tumors or small multiple sclerosis plaques. It is also capable of showing clear images of the brainstem, cerebellum, and the pituitary fossa, which, in the case of a CT scan, are overshadowed by the dense bones of the base of the skull