Nervous tissue -CNS and PNS

Ependymal cells, also named

ependymocytes, line the spinal cord and the ventricular system of the brain. These cells are involved in the creation and secretion of cerebrospinal fluid (CSF) and beat their cilia to help circulate the CSF and make up the blood-CSF barrier. They are also thought to act as neural stem cells.

Arachnoid Mater

(made up of loosely organized formed fibroblasts, collagen and elastic fibers) It has 2 layers, a flat sheet like and the trabecular layer which connects piamater which houses blood vessels and provides space for CSF to flow. The arachnoid or arachnoid mater is the middle layer of the meninges. In some areas, it projects into the sinuses formed by the dura mater. These projections are the arachnoid granulation/arachnoid villi. They transfer cerebrospinal fluid from the ventricles back into the bloodstream. The subarachanoid space lies between the arachnoid and pia mater. It is filled with cerebrospinal fluid. All blood vessels entering the brain, as well as cranial nerves pass through this space. The term arachnoid refers to the spider web like appearance of the blood vessels within the space. Pia Mater (composed flattened fibroblasts) The pia mater is the innermost layer of the meninges. Unlike the other layers, this tissue adheres closely to the brain, running down into the sulci and fissures of the cortex. It fuses with the ependyma, the membranous lining of the ventricles to form structures called the choroid plexes which produce cerebrospinal fluid.

astrocytes

Astrocytes wrap around nerve cells to protect them and keep them healthy. They participate in virtually every function or disorder of the brain. They do house-keeping function like regulating blood flow, soaking up excess neurotransmitters, provides ionic balance where it is needed and protects brain from keeping the toxic substances away (blood brain barrier). Satellite cells in ganglion do a similar function. Satellite glial cells are small cells that surround neurons in sensory, sympathetic, and parasympathetic ganglia. These cells help regulate the external chemical environment. Like astrocytes, they are interconnected by gap junctions and respond to ATP by elevating intracellular concentration of calcium ions. They are highly sensitive to injury and inflammation, and appear to contribute to pathological states, such as chronic pain.

CSF collection:

CSF is often obtained from the cerebellomedullary cistern (CMC). Additionally, CSF can be collected from the dorsal or ventral subarachnoid space at the L5-L6 intervertebral spaces. Alternatively, CSF can also be obtained from the L6-L7 intervertebral space in some patients. CSF from the CMC is obtained by inserting a needle between the occipital bone of the calvaria and the dorsal lamina of the first cervical vertebra. Landmarks for this site include the external occipital protuberance and the cranial aspect of the wings of the atlas. An imaginary line is drawn from the external occipital protuberance caudal along the midline. Similarly, a second imaginary line is drawn between the cranial aspects of the wings of the atlas. These lines bisect at approximately the level of needle insertion. The needle is inserted parallel to the surface of the table and directed perpendicular to the long axis of the vertebral column

The Choroid Plexus - Capillaries surrounded by

Ependymal Cells

The Cerebral Cortex

I molecular layer - few neurons and mainly of extensions of apical dendrites and horizontally-oriented axons. II external granular layer - small pyramidal neurons and many stellate neurons. III external pyramidal layer - mainly small and medium-size pyramidal neurons, some non-pyramidal neurons with vertically-oriented intracortical axons. IV internal granular layer - different types of stellate and pyramidal neurons. V internal pyramidal layer - large pyramidal neurons. VI multiform layer - few large pyramidal neurons and many small spindle-like pyramidal and multiform neurons.

Oligodendrocytes

are cells that coat axons in the central nervous system (CNS) with their cell membrane, forming a specialized membrane differentiation called myelin, producing the so-called myelin sheath. The myelin sheath provides insulation to the axon that allows electrical signals to propagate more efficiently. Similar in function to oligodendrocytes, Schwann cells provide myelination to axons in the peripheral nervous system (PNS). They also have phagocytotic activity and clear cellular debris that allows for regrowth of PNS neurons.

The meninges are three layers of protective tissue called the

dura mater, arachnoid mater, and pia mater that surround the neuraxis. The meninges of the brain and spinal cord are continuous, being linked through the magnum foramen.

Glia

have a role in the regulation of repair of neurons after injury. Glial cells known as astrocytes enlarge and proliferate to form a scar and produce inhibitory molecules that inhibit regrowth of a damaged or severed axon. In the peripheral nervous system (PNS), glial cells known as Schwann cells promote repair. After axonal injury, Schwann cells regress to an earlier developmental state to encourage regrowth of the axon. This process creates a myelin sheath, which not only aids in conductivity but also assists in the regeneration of damaged fibers. While glial cells in the PNS frequently assist in regeneration of lost neural functioning, loss of neurons in the CNS does not result in a similar reaction from neuroglia. In the CNS, regrowth will only happen if the trauma was mild, and not severe. When severe trauma presents itself, the survival of the remaining neurons becomes the optimal solution. However, some studies investigating the role of glial cells in Alzheimer's Disease are beginning to contradict the usefulness of this feature, and even claim it can "exacerbate" the disease. In addition to impacting the potential repair of neurons in Alzheimer's Disease, scarring and inflammation from glial cells have been further implicated in the degeneration of neurons caused by Amyotrophic lateral sclerosis. In addition to neurodegenerative diseases, a wide range of harmful exposure, such as hypoxia, or physical trauma, can lead to the end result of physical damage to the CNS. Generally, when damage occurs to the CNS, glial cells cause Apoptosis among the surrounding cellular bodies. Then, there is a large amount of microglial activity, which results in inflammation, and finally, there is a heavy release of growth inhibiting molecules.

The epidural space

is a potential space between the dura mater and the skull. If there is hemorrhaging in the brain, blood may collect here. Adults are more likely than children to bleed here as a result of closed head injury. The subdural space is another potential space. It is between the dura mater and the middle layer of the meninges, the arachnoid mater. When bleeding occurs in the cranium, blood may collect here and push down on the lower layers of the meninges. If bleeding continues, brain damage will result from this pressure. Children are especially likely to have bleeding in the subdural space in cases of head injury.

The dura mater (

made of dense connective tissue) is the most superior of the meningeal layers. Its name means "hard mother" in Latin and it is tough and inflexible. This tissue forms several structures that separate the cranial cavity into compartments and protect the brain from displacement. Cranial dura is adhered to the skull while in spinal cord it does not adhere forming a space called epidural space.