BIO-203/L203: Schematics of the CNS

Lobes and folds

_{Image source}

fronal

central sulcus

parietal

occipital

temporal

transverse fissure

Anatomists who study the brain have classfied this central organ based on several aspects of its structure. The brain has two hemispheres, divided at the midline, creating a symmetry between left and right. Further, the lobes of the brain are separated based on function and location. We can also consider the insula, which is deep to the temporal lobe and the frontal lobe, as a “hidden brain lobe”.

Sulci are grooves in the brain, while gyri are elevated tissue folds. The most promiminent sulcus is the central sulcus which is located between the frontal and parietal lobes; the central sulcus also has a precentral gyrus and a postcentral gyrus.

The brain has two major fissures, the transverse cerebellar fissure separating the main lobes of the brain from the cerebellum, and the longitudinal fissure which separates the two hemispheres of the brain.

Midsagittal section

A midsagittal section of the brain cuts along the median plane of the brain to divide it into symmetrical halves. This sort of dissection reveals important structures in the brain in relative positions to each other, such as the diencephalon and the brain stem region. While the brain stem can be removed from the brain and studied in isolation, the midsagittal section reveals its proximity to other cortical regions.

_{Image source}

corpus callosum

pons

pineal gland

medulla oblongota

pituitarity gland

cerebellum

arbor vitae

interthalamic adhesion

thalamus

fornix

choroid plexus

optic chiasma

hypothalamus

Things to remember:

• The cerebellum is not necessarily a lobe in the brain, but it is separated from the rest of the brain through a transverse fissure.

• Arbor vitae codes for the “tree of life”, which is a distinct pattern of white matter branching in the cerebellum.

• The optic chiasma will be more significant when you study the special senses. Do not mix this up with the pituitary gland.

• The hypothalamus is a great control center in the brain. The epithalamus is basically just the pineal gland. The thalamus is a completely different structure. The prefix “hypo-” refers to below and “epi-” refers to outside of.

• The hypothalamus is related to the pituitary gland. This becomes more relevant when studying the endocrine system.

• The interthalamic adhesion connects the nuclei of the thalamus.

• The corpus callosum is what splits the two lobes of the brain into symmetrical halves.

• The pons is the part of the brain stem that relies cortical and cerebrals impulses.

• The medulla is the most inferior part of the brain stem and houses several necessary autonomic centers.

• The choroid plexuses produces the cerebrospinal fluid that circulates through the ventricles.

Spinal Cord

_{Image source}

dorsal horn

ventral horn

central canal

ventral root

dorsal root

dorsal root ganglion

sensory

motor

SS interneurons

VS interneurons

visceral efferents

somatic efferents

gray matter

white matter

_{Image source}

cervical plexus

thoracic plexus

lumbar plexus

sacral plexus, cauda equina

A plexus is a group of nerves. The most important plexuses in the human body are the spinal nerves, pictured above.

The orientation of gray matter and white matter in the spinal cord is the inverse of the neural arrangement in the brain. In the cortex, the gray matter covers the white matter of the brain, while in the spinal cord, the white matter is on the exterior surface surrounding the gray matter.

Meningeal Layers

_{Image source}

dura mater

arachnoid mater

pia mater

Meninges (singular: meninx) are connective tissue coverings of the central nervous system. These coverings are generalized to the brain and the spinal cord with the same sort of orientation and structure. Although it is not pictured in this diagram, the same meningeal layers are common the spinal cord, which rests in cerebrospinal fluid (hence the name “cerebro-” referring to the cerebral cortex and “-spinal” referring to the spinal cord). Cerebrospinal fluid, abbreviated as CSF, is similar to plasma with different concentrations of ions. There is a blood-brain barrier preventing non-optimal conditions of the blood from compromising the brain.

Dura mater is the thickest connective tissue layer located closest to the bone surrounding the CNS. This connective tissue is fibrous and encloses a venous sinus. Arachnoid mater is named after its spiderweb-like look and contains CSF and the largest vasculature that reaches the brain. Pia mater is the thinnest connective tissue layer that is intimately superficial to the brain and is richly vascularized with small blood vessels.

_{Copyright: Pearson Education}