Brainstem - Gross Anatomy of Medulla Oblongata, Pons and Midbrain

BRAINSTEM: GENERAL CONSIDERATIONS

Components:

The brainstem consists of (from above downward):

Midbrain (continuous with the cerebral hemisphere above)

Pons

Medulla (continuous with the spinal cord below)

Location:

The brainstem is located in posterior cranial fossa

Gross Anatomy and Blood Supply of Spinal Cord

Spinal cord is the part of the nervous system houses inside the vertebral column. It serves as a very important conduit for the passage of various ascending and descending nervous pathways to and from the higher centers.

Cerebellum: Gross anatomy and main connections

This note describes the gross features of cerebellum and its main connections.

Developmental source: It develops from the metencephalon division of rhombelcephalon (hind brain).

Basal Nuclei: Types, main features and connections

This note briefly describes the gross features of basal nuclei and their main connections.

Basal nuclei represent a collection of masses of gray matter situated within each cerebral hemisphere.

They are

o   the caudate nucleus

o   the lentiform nucleus

consists of globus pallidus medially and putamen laterally

o   the amygdaloid nucleus, and

o   the claustrum

Thalamus: location, relations, parts, nuclei and main connections

The Diencephalon: General Overview

Diencephalon is part of the prosencephalon (forebrain).

It corresponds largely to the structures that develop lateral to the third ventricles.

The lateral walls of the diencephalon form the epithalamus most superiorly,

the thalamus (dorsal thalamus) centrally and

the subthalamus (Ventral Thalamus) and 
the hypothalamus  most inferiorly.

The epithalamus:

anterior and posterior paraventricular nuclei,

the medial and lateral habenular nuclei,

the stria medullaris thalami and

the pineal gland

Cerebrum: Gross features and Blood Supply

Gross Anatomy of the Cerebral Hemispheres

The cerebral hemispheres make up the largest portion of the brain and are separated by a deep midline sagittal fissure called the longitudinal cerebral fissure.

The surface of each cerebral hemisphere is thrown into folds or gyri (sing: gyrus) which are separated from each other by sulci (sing: sulcus) or deeper fissures.

For descriptive purpose, the cerebral hemisphere is divided into lobes which are named according to the overlying cranial bones.

Main Sulci & Fissures

The surfaces of the cerebral hemispheres contain many fissures and sulci.

1. Central sulcus
2. Lateral sulcus
3. Parieto-occipital sulcus
4. Calcarine sulcus

These four sulci separates the cerebral lobes from each other.

White Matter of Cerebrum : Projection, Commissural and Association fibers

WHITE MATTER OF CEREBRUM

The white matter of the cerebral hemisphere basically contains two components

• myelinated nerve fibers of many sizes*
•  neuroglia (mostly oligodendrocytes)

*This note only describes different types of myelinated nerve fibers.

The white matter of the cerebral hemisphere are of three types:

1. commissural fibers
2. association fibers
3. projection fibers

FUNCTIONAL AREAS OF CEREBRAL CORTEX

Cerebral cortex presents functionally specialized areas. For the descriptive purpose, these areas can be located on different lobes of cerebral hemisphere as given below:

Frontal lobe

1.      Motor area or Primary motor area 

Broadmann’s area 4

-         Precentral gyrus and anterior part of paracentral lobule

-         Produce isolated movements on the opposite side of the body

-         Somatotopic representation

o   Inverted and disproportionate to the size of the body part

o   lips, tongue, face, and hands are represented in order on the lower lateral surface

o   arm, trunk, and hip in order on the upper lateral surface

o  foot, lower leg and anal and genital region on paracentral lobule on medial surface

MICROSCOPIC STRUCTURE OF CEREBRAL CORTEX

The cerebral cortex contains three main types of neurons arranged in a layered structure:

1. Pyramidal cells (shaped like a tepee, with an apical dendrite reaching from the upper end toward the cortical surface, and basilar dendrites extending horizontally from the cell body);

2. Stellate neurons (star shaped, with dendrites extending in all directions); and

3. Fusiform neurons (found in deeper layers, with a large dendrite that ascends toward the surface of the cortex).

In addition, following two types of cells are also present: