Histology of the Central Nervous System

Pseudounipolar neurons are primarily sensory neurons near the Central Nervous System (CNS).

Brain and spinal cord are covered by three protective membranes called meninges.

The brain and spinal cord are made up of gray matter and white matter.

Gray matter (pia mater) is a thin layer with abundant nerve fibers, glia, and blood vessels.

White matter (dura mater and arachnoid layer) is a protective layer made of fibrous tissue and collagen.

Cerebrospinal fluid (CSF) fills the brain ventricles and spinal cord, providing mechanical and immunological protection.

Lumbar puncture is a medical procedure to collect CSF for diagnostic testing.

Astrocytes are the largest neuroglial cells, helping neurons by maintaining tight junctions and metabolic support.

Oligodendrocytes produce myelin, and one cell myelinates many axons.

Microglia are phagocytic cells, protecting the brain from infection and injury.

Ependymal cells line the ventricles and produce CSF.

Blood-brain barrier (BBB) is a functional barrier that tightly controls the passage of substances into the CNS.

Choroid plexus in the ventricles produces CSF and removes water from blood.

The cerebrum consists of white matter and gray matter, with the cortex being highly convoluted.

The cerebral cortex contains various neuronal and glial cells, including Betz's pyramidal cells, capillaries, oligodendrocytes, astrocytes, and microglia.

The cerebellum's white matter forms a branched tree-like structure.

The Purkinje layer is an intermediate layer in the cerebellum with large Purkinje cells and tree-like dendritic arborizations.

The spinal cord consists of several structures, including the conus medullaris, cauda equina, filum terminale, and spinal meninges.

The conus medullaris is a medullary cone located at the end of the spinal cord, while the cauda equina is a collection of nerve roots that continue beyond the termination of the spinal cord.

The filum terminale is a long, thin tissue that extends from the conus medullaris to the coccyx and serves to anchor the spinal cord to the end of the dural sac.

The spinal cord is surrounded and protected by three connective tissue coverings: the dura mater, arachnoid mater, and pia mater.

The dura mater is the thickest and strongest of the three layers, serving as a durable protective covering for the spinal cord. It is continuous with the cranial dura mater at the cranial end and joins the filum terminale at the caudal end.

The arachnoid mater is a thin, transparent layer that forms a spider-web like structure around the spinal cord. It carries blood vessels and separates the spinal cord from the dura mater.

The pia mater is the innermost layer of the spinal meninges, which adheres closely to the surface of the spinal cord. It terminates at the inferior limit of the spinal cord and contains the central canal, which is filled with cerebrospinal fluid (CSF) and extends throughout the length of the cord.

The epidural space is a potential space located between the outermost layer of the spinal meninges (dura mater) and the walls of the vertebral canal. It contains loose connective and adipose tissue and serves as a site for anesthetic injections.

The denticulate ligaments are double folds of pia mater that extend from the lateral aspects of the cord, penetrate the arachnoid, and attach to the inner surface of the dura. They allow the cord to "float" in the spinal canal and alternate with the points of exit of nerve roots.

The central canal, also known as the ependymal canal, is a continuous structure filled with CSF that extends throughout the length of the spinal cord. It helps transport nutrients to the cord and protects it by cushioning against impact.

The spinal cord contains several fissures and sulci that divide it into right and left halves. The anterior median fissure is a deep longitudinal fissure, while the posterior median sulcus is a shallow furrow. The spinal cord is joined by a commissural band of tissue that contains the central canal.

The posteriorolateral sulcus is a sulcus that runs laterally from the posterior median sulcus on each side of the spinal cord.

The size and shape of the central canal varies along the length of the spinal cord, with it being situated nearer the anterior aspect at the cervical and thoracic segments and in the center at the lumbar segments. In the conus medullaris, it is located in the posterior third and is lined by ciliated, columnar epithelium.

The central canal, also known as the terminal ventricle or the ampulla caudalis, is a structure located at the transition from the tip of the conus medullaris to the origin of the filum terminale. It is a fusiform, widest part of the central canal that is visible in newborns and up to 5 years of age, but regresses during the first weeks after birth.

The spinal cord contains several fissures and sulci that divide it into right and left halves. The anterior median fissure is a deep longitudinal fissure, while the posterior median sulcus is a shallow furrow. The spinal cord is joined by a commissural band of tissue which contains the central canal. The posteriorolateral sulcus is a sulcus that runs laterally from the posterior median sulcus on each side of the spinal cord.

The Spinal Cord: Gross Anatomy

31 pairs of spinal nerves attached

Dorsal roots enter the spinal cord in the cervical and upper thoracic segments only

Spinal nerves attach to the spinal cord with anterior (motor) roots and posterior (sensory) roots

Each root is attached by series of rootlets, each posterior nerve root has a posterior root ganglion (dorsal root ganglion)

Spinal nerves are united as ventral and dorsal roots, attached to the sides of the spinal cord

Spinal ganglia are large groups of neurones on the dorsal spinal roots

Spinal nerves penetrate the dura at the intervertebral foramen, and the sleeve of dura becomes continuous with the epineurium of the peripheral nerves

The Spinal Cord: Gross Anatomy & Internal Structure

Spinal cord has a central core of grey matter surrounded by an outer covering of white matter

Grey matter is configured in a characteristic H or butterfly shape

Amount of grey matter present at any given level is related to amount of muscle innervated at that level

Spinal cord is differentiated into ventral & dorsal columns, or horns

White matter surrounds the central core of grey matter, composed mainly of myelinated fibres with neuroglia & blood vessels

White matter is divided into anterior, posterior & lateral funiculi (white columns)

Rostral regions of the spinal cord have more white matter due to accumulated ascending fibers and fewer descending fibers

Grey matter and white matter are continuous across the midline through the grey and white commissure

Cervical sections are wide and flat with large ventral horn enlargements, while sacral sections have almost no white matter

The Spinal Cord: Gross Anatomy & Blood Supply

Blood supply comes from 2 sources: longitudinal vessels and segmental (radicular) spinal arteries

Longitudinal vessels arise superior to the cervical portion of the cord and descend on its surface

Ant. spinal artery: a single artery from vertebral arteries, runs parallel to the anterior median fissure

Post. spinal arteries: paired arteries that originate from the terminal branch of each vertebral artery and descend along the posterolateral sulcus

Segmental (radicular) spinal arteries: branches of the vertebral arteries that enter the spinal cord via the intervertebral foramina and anastomose with the anterior spinal artery.