Neurohisto

Neurohistology

1. NEURO HISTO Group 4

2. Meninges Are composed of connective tissues Has three layers: Dura mater(or Pachymeninx ) , Arachnoid and Pia mater Neurons and Macroglia – are of ectodermal origin Blood vessels of the CNS – are of mesenchymal origin Arachnoid + Pia Mater = Leptomeninges

3. Dura MAter I nner surface is lined by SQUAMOUS CELLS Connected to the spinal cord on each side by Denticulate Ligaments

4. Dura mater of the Brain has two layers closely joined in adults both consist of collagenous fibers and elongated fibroblasts NO distinct border between the two layers small blood vessels are present in both layers only some differences in organization

5. Dura mater of the brain Periosteal dura outer layer adheres loosely to the inner aspect of the skull except at Cranial Sutures where it is more firmly adherent functions as a periosteum richer in cells contain many blood vessels collagen fibers organized in distinct bundles Meningeal dura inner layer almost continuous sheet of fine fibers fibers coursing upward and backward from the frontal region fibers oriented at an angle to the outer layer fibroblasts have darker cytoplasm, elongated processes, ovoid nuclei, more condensed chromatin

6. Border cell layer internal to the inner dura modified , flattened fibroblasts w/ long sinous processes that intermingle with neighboring cells have usual organelles processes are attached at occasional desmosomes and gap junctions (are lacking on the cells of the meningeal dura ) distinctive features: dark highly branched fibroblasts, amorphous intercellular material , absence of connective tissue fibers transitional zone between the border cell layer and the meningeal dura , flocculent intercellular material is found, together with small collagen fibers

7. Intercellular spaces are occupied by flocculent material ( polysaccharide in nature)

8. Spinal dura collagenous fibers are oriented longitudinally The inner surface of the dura is lined by squamous cells is firmly connected to the spinal cord along each side by a series of denticulate ligaments fewer elastic fibers than cerebral dura

9. Inner surface of Vertebral Canal lined by its own periosteal layer of connective tissue while the

10. Spinal cord enclosed by a separate loose cylindrical dural membrane

11. Epidural Space wide space between the periosteum and the dura contains loose connective tissue, adipose cells and the EPIDURAL VENOUS PLEXUS

12. Arachnoid Arachnoid Barrier Layer layer of closely apposed cells separated by little or no extracellular space attached to one another by many desmosomes and tight junctions Arachnoid Trabecular Cells inner layer of very loosely associated cells perpendicluar to the arachnoid barrier layer traverses the subarachnoid space are modified fibroblasts w/ long processes attached to the cells of the barrier layer by desmosomes and gap junctions few collagen fibers

13. Pia Mater closely adherent to the brain and spinal cord composed of flattened modified fibroblasts that conforms to the contours of the brain may for a single layer or overlap one another resembles cells of the arachnoid trabeculae numerous blood vessels that are often surrounded by trabecular cells fine collagenous and elastic fibers are interposed in between this layer and the brain

14. macrophages are also found between the pial cells and the glial basement membrane around the pial blood vessels in humans, often contain yellow pigments that reacts positively to iron mast cells and lymphocytes (may increase in number during a pathologic condition) may be found along pial vessels melanocytes (variable in number) can be found on pia covering the ventral surface of medulla oblongata

15. Meningeal Spaces

16. Subdural Space normally no such space between dura and arachnoid when present, it is an artefact of specimen preparation subdural hematoma commonly follows head injuries is not beneath the dura but blood accumulation within the dural border cell layer, intradural (the dural border cell layer has many intercellular spaces, is a weak plane, extravagation of blood or fluids enlarges the spaces, disrupts cell junctions or tears off process creating a larger space where none normally exists)

17. Subarachnoid Space between arachnoid barrier cell layer and pia mater truly occurring, traversed by arachnoid trabeculae and normally filled with large amount of cerebrospinal fluid narrow in the convolutions of the brain, wide and deep in sulci between cerebral hemispheres wide throughout the spinal cord greatly enlarged is some places in the brain called cisternae

18. cisternae magna (largest cisternae), lies above the medulla oblongata and below the posterior border of the cerebellum. 4 th ventricle communicates with it through 3 openings in tela choroidea (1 medial foramen of Magendie and 2 lateral foramina of Luschka ) communicates with the ventricles of the brain where CSF is produced

19. Nerves of the meninges The dura and pia mater are richly supplied with nerves All vessels of the pia, and of the choroid plexus, are surrounded by extensive nerve plexuses in their adventitia The axons, belonging to the sympathetic system, originate in certain cranial nerves and in the carotid and vertebral plexuses. Non-encapsulated sensory nerve terminations, and even single nerve cells, are also present in the adventitia of the blood vessels.

20. In addition to the nerves to the vessels, the cerebral dura contains many sensory nerve endings The pia also contains extensive nerve plexuses, most abundant in the tela choroidea of the third ventricle The axons end either in large pear-shaped or bulbous expansions or in spiral convolutions like those of Meissner’s corpuscles

21. In the spinal pia, the vessels receive their nerves from the plexuses following the larger spinal blood vessels. Afferent nerve endings are also present, but these are unevenly distributed. Both myelinated and unmyelinated nerve fibers accompany the blood vessels into the substance of the spinal cord and the brain, ending on the smooth muscle cells of the vessel walls

22. innervation The dominant nerve supplying most of the supratenotrial dura is the tentorial nerve (a branch of the ophthalmic nerve (CN Va) which supplies the falx, calvarial dura and superior surface of the tentorium.

23. Anterior cranial fossa meningeal branches from the anterior and posterior ethmoidal nerves, off the  nasociliary nerve  from the ophthalmic division of the trigeminal nerve meningeal branches from the maxillary nerve (CN Vb )

24. Middle cranial fossa meningeal branches of ophthalmic, maxillary and mandibular divisions of trigeminal nerve   middle meningeal nerve (a branch off the maxillary nerve (CN Vb ) supplies the anterior parts of the fossa meningeal branch of the mandibular nerve (CN Vc ) supplies the posterior parts of the fossa

25. Posterior cranial fossa sensory meningeal branches from the vagus nerve (CN X) and glossopharyngeal nerve (CN IX) supply the inferior surface of the tentorium and dura of the posterior fossa small sensory branches of the C1 to C3 dorsal rami supply around the foramen magnum

26. Ventricles CNS develops from the embryonic neural tube Remains a hollow organ in the adult Form a continuous channel for the flow of CSF If part of this channel will be occluded by disease preventing free circulation of fluid, intracerebral pressure increases, resulting in hydrocephalus and other serious consequences Central canal of the spinal cord is minute in the adult and may be obliterated. The ventricular cavity is divided into four regions:

27. Ventricles 2 Lateral Ventricles in the medial wall of the cerebral hemispheres Third Ventricle in the roof of the diencephalon between the two thalami; caudal to the nondilated cerebral aqueduct traversing the midbrain. Fourth Ventricle Roof of the Pons and Rostral Medulla Oblongata Choroid Plexuses develop in all four regions Most of the fluids is from the blood vessels of these plexuses