Photographic view with midbrain

The Parkinson's-Reversing Breakthrough

Cure for Parkinson Disease

Get Instant Access

This is another brain specimen showing the inferior surface of the brain, in which the brainstem has been sectioned through at the level of the midbrain, removing most of the brainstem and the attached cerebellum. The cut surface of the midbrain is exposed, showing a linear area of brain tissue, which is black in coloration; this elongated cluster of cells is the nucleus of the midbrain called the substantia nigra, and consists of neurons with pigment inside the cells (discussed with Figure 65). The functional role of the substantia nigra is discussed with the basal ganglia (see Figure 24 and Figure 52).

This dissection reveals the inferior surface of both the temporal and the occipital lobes. It is not possible to define the boundary between these two lobes on this view. Some of these inferior gyri are involved with the processing of visual information, including color, as well as facial recognition. The parahippocampal gyri should be noted on both sides, with the collateral sulcus demarcating the lateral border of this gyrus (seen in the previous illustration; discussed with Figure 72A and Figure 72B).

The optic nerves (cut) lead to the optic chiasm, and the regrouped visual pathway continues, now called the optic tract (see Figure 41A and Figure 41C). Behind the optic chiasm are the median eminence and then the mam-millary (nuclei) bodies, both of which belong to the hypothalamus. The median eminence (not labeled) is an elevation of tissue that contains some hypothalamic nuclei. The pituitary stalk, identified on the previous illustration, is attached to the median eminence, and this stalk connects the hypothalamus to the pituitary gland. Behind this are the paired mammillary bodies, two nuclei of the hypothalamus (which will be discussed with the limbic system, see Figure 78A).

Also visible on this specimen is the posterior thickened end of the corpus callosum (discussed with the next illustration) called the splenium (see Figure 17 and Figure 19A).

A thick sheath of dura separates the occipital lobe from the cerebellum below — the tentorium cerebelli (as it covers over the cerebellum). The cut edge of the tento-rium can be seen in Figure 17, and its location is seen in Figure 18, above the cerebellum. The tentorium divides the cranial cavity into an area above it, the supratentorial space, a term that is used often by clinicians to indicate a problem in any of the lobes of the brain. The area below the tentorium, the infratentorial space, corresponds to the posterior cranial fossa. The tentorial sheath of dura, the tentorium cerebelli, splits around the brainstem at the level of the midbrain; this split in the tentorium is called the tentorial notch (hiatus).

Clinical Aspect

The uncus has been clearly identified in the specimens, with its blunted tip pointed medially. The uncus is in fact positioned just above the free edge of the tentorium cer-ebelli. Should the volume of brain tissue increase above the tentorium, due to brain swelling, hemorrhage, or a tumor, accompanied by an increase in intracranial pressure (ICP), the hemispheres would be forced out of their suprat-entorial space. The only avenue to be displaced is in a downward direction, through the tentorial notch, and the uncus becomes the leading edge of this pathological event. The whole process is clinically referred to as "uncal her-niation."

Since the edges of the tentorium cerebelli are very rigid, the extra tissue in this small area causes a compression of the brain matter, leading to compression of the brainstem; this is followed by a progressive loss of consciousness. CN III is usually compressed as well, damaging it, and causing a fixed and dilated pupil on that side, an ominous sign in any lesion of the brain. This is a medical emergency! Continued herniation will lead to further compression of the brainstem and a loss of vital functions, followed by rapid death.

Optic tract

Uncus

Collateral sulcus

Parahippcampal gyrus

Splenium of corpus callosum

Optic tract

Splenium of corpus callosum

Medial Eminence Midbrain

Pituitary stalk Mammillary body

Cerebral peduncle

Substantia nigra

F = Frontal lobe T = Temporal lobe O = Occipital lobe Md = Midbrain (cut)

Pituitary stalk Mammillary body

Cerebral peduncle

Substantia nigra

FIGURE 15B: Cerebral Hemispheres 5 — Inferior View with Midbrain (photograph)

Was this article helpful?

+1 0
Peripheral Neuropathy Natural Treatment Options

Peripheral Neuropathy Natural Treatment Options

This guide will help millions of people understand this condition so that they can take control of their lives and make informed decisions. The ebook covers information on a vast number of different types of neuropathy. In addition, it will be a useful resource for their families, caregivers, and health care providers.

Get My Free Ebook


Post a comment