HISTO_LC14_NERVOUS TISSUE_CNS.pdf

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC14 NERVOUS TISSUE: CNS COLLEGE OF MEDICINE, BATCH 2026 Transcribers/ Editors: Guzm...

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC14 NERVOUS TISSUE: CNS COLLEGE OF MEDICINE, BATCH 2026 Transcribers/ Editors: Guzman, A.L., Maligpas, X.E., Dr. Vida Margarette D. Andal | January 2023 Matanguihan, N., Nericua, N. bodies and neurofilaments that occur singly or in NERVOUS TISSUE: CENTRAL NERVOUS SYSTEM clusters. I. NERVOUS TISSUE ○ Nissl bodies are characteristic features of a A. Neurons neuron. RER corresponds to Nissl bodies of light B. Support Cells microscopy. They extend into the dendrites but not II. STAINING METHODS III. MENINGES into the axon hillock or axon. IV. STRUCTURAL COMPONENTS ○ Neurofilaments serve as scaffolding that will help A. Brain maintain the shape of the axon and cell body B. Spinal Cord V. SPECIAL SENSES - Microtubules transport material up and down the axon. A. Gustation That being said, even if the axon is the main output B. Olfaction terminal of the perikaryon, it can also deliver some C. Vision D. Auditory Perception messages to the perikaryon. This is called the retrograde movement whereas the more common I. NERVOUS TISSUE movement that’s happening in the axon is called the anterograde movement. NEURONS ○ Slow axonal transport carry cytoskeletal elements ○ Fast axonal transport carry membrane-bound organelles like secretory vesicles Kinesin for anterograde movement (from cell body) Dynein for retrograde movement (to the cell body) Figure 1. Neuron and Its Parts The Nervous is functionally divided into two parts: Central Nervous System (CNS) when you talk about the brain and spinal cord; and Figure 2. Perikaryon Peripheral Nervous System (PNS) when you talk about nerve endings, peripheral nerves and ganglia. For the brain and spinal b. Dendrites cord, the nerve cell is called a neuron. - look like branches - Processes that receive almost all of the arriving A. Parts impulses/action potentials (receiving area) - May contain some organelles and many neurofilaments a. Perikaryon - also has nissl bodies - the cell body of a neuron; contains a nucleus, and cytoplasm which contain organelles such as ribosomes, mitochondria, etc. - Cytoplasm contains rough endoplasmic reticulum (RER) grouped to form the Nissl substance/Nissl 1 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal c. Axon Hillock Unipolar - Only one process called a - Cone-shaped portion of the cell body from which the neurite extends from the axon arises (basically just enlargement of the proximal cell body axon) - Neurite branches to form dendritic and axonal d. Axon processes - “Nerve fibers” - Only found in invertebrates - A long process that conducts impulses/action potentials away from the cell body. Pseudounipolar - Single dendrite and single - Most neurons have a single axon though some can axon arise from a common have more stem of the cell body that is - Contains organelles and neurofilaments formed by the fusion of the - has no nissl bodies first part of the dendrite - Covered in a sheath of myelin and axon of a bipolar type - Can be myelinated or unmyelinated of neuron during embryological development e. Terminal Boutons - Pattern seen in sensory - Small swellings at the terminal end of the axon which ganglia of the dorsal root of synapses with the dendrites or perikaryon of other the spinal cord and in neurons ganglia of certain cranial nerves SUPPORT CELLS Support Cells Description Oligodendrocytes - Formation of myelin sheaths in the CNS - One oligodendrocytes can myelinate up to 50 axons Figure 3. Electron micrograph of a Neuron - Predominant neuroglia in white matter B. Types - “Sunny side up egg” Types of Neuron Description Astrocytes - Highly branched cells that Multipolar - Numerous dendrites pack the interstices between project from the cell body neurons, their processes and - Pattern seen in oligodendrocytes. intermediate, integratory - Provide mechanical support and motor neurons - Mediate exchange of metabolites between neurons and the vascular system - Form part of the blood-brain Bipolar - Single dendrite arising from barrier the pole of the cell body - Play a role in repair of CNS opposite to the origin of the tissue after damage axon - Stained by Glial Fibrillary - Pattern seen in receptor Acidic Protein (GFAP) neurons for the senses of smell, sight and balance - Seen in sensory neurons Types: 2 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal Protoplasmic astrocytes II. STAINING METHODS are astrocytes in the gray matter. Have numerous Staining Method Description short, highly branched cytoplasmic processes A. H&E Staining - Hematoxylinophilic (blue): Fibrous astrocytes are nuclei, nissl bodies astrocytes in white matter. - Eosinophilic (red): Have relatively few and cytoplasm and other straight cytoplasmic cytoplasmic organelles processes rich in intermediate filaments Microglia - CNS representatives of the monocyte-macrophage B. Luxol Fast Blue - Myelin sheath stain that system stains phospholipids (main - Defense and immunologic constituent of myelin functions sheath) - Elongated nuclei and - Myelin-rich cerebral white relatively little cytoplasm matter is stained blue which forms highly branched - in demyelinating diseases processes where myelin sheath is - Become numerous during broken down, lesions can injury be clearly identified - Stained by CD68 - no staining = no myelin Ependymal - Lines ventricles and spinal C. Nissl Stain - Uses cresyl violet to stain canal Nissl substance to identify - CSF production neuronal structure in brain - Cuboidal or low columnar, and spinal cord tissue tightly bound together - presence of nissl bodies = - Microvilli presence of a perikaryon - Ependymal layer tends to - can be used to prove become incomplete with cellular loss increasing age D. Gold/Toluidine Blue - Gold stains astrocytes and neurons, intercellular junctions, motor end plates, myelinated axons, neuronal cell processes - Toluidine blue stains neurons and glia E. Immunohistochemistry Uses antibodies to check for (IHC) certain protein markers that can Figure 4. Astrocytes (A), Oligodendrocytes (O), and Neurons (N) assist classification of various pathologies - Neurons have large nuclei, prominent nucleoli, dispersed - Epithelial Membrane Antigen chromatin, extensive basophilic granular cytoplasm (EMA) : meningioma - Oligodendrocytes have small round condensed nuclei - Glial fibrillary acidic - Astrocytes are the flat-looking/ elongated structures protein(GFAP): astrocytes, glioma, PNET - S-100: glioma, PNET, 3 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal Schwannoma, neurofibroma, chordoma - Synaptophysin: neuroendocrine tumors, PNET - Ubiquitin: Alzheimer’s. Lewy bodies, ALS - Tau: Alzheimer’s, Pick’s disease - Alpha synuclein: Lewy bodies - Polyglutamine: Huntington’s chorea, Machado-Joseph disease - Beta amyloid: senile plaques IHC is very useful in confirming the type of tumor a patient has. Figure 5. Meninges. This slide shows the Dura Mater (D), Arachnoid Aside from tumors, it is also Mater (A), and Pia Mater (P). helpful in other diseases especially in neurodegenerative IV. STRUCTURAL COMPONENTS/REGIONS diseases where there is abnormal accumulation of BRAIN proteins. A. CEREBRAL CORTEX (CEREBRUM) F. Golgi-cox Method - To visualize dendritic - Grey matter branching pattern and dendritic spines CELLS Pyramidal Cells - Pyramid-shaped cell bodies with the apex directed towards the cortical surface - Dendrites, from one pole, arise from the apex - A lot of axons arises from the base and leave the cortex to enter the subcortical white matter; - Commissural fibers that form the corpus callosum - Association fibers that project to singular III. MENINGES areas in the ipsilateral cortical association areas like the optic tract Meninges are the coverings of the brain and spinal cord. - Projection fibers that project to different regions of the CNS like the thalamus, Dura mater - very fibrous and very thick outer layer spinal cord, corticospinal tract, etc. - Make up 75%, majority of the cellular component of Arachnoid mater - delicate layer with blood vessels underneath the cortex (subarachnoid mater) - Main output neurons of the cerebral cortex - Excitatory neuron Pia mater - very closely apposed against the cerebral matter and - Differ in sizes even goes down to the cerebral sulci - Betz cells - Special type of pyramidal cells - Are the largest pyramidal cells in the cerebral cortex 4 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal Figure 6. Pyramidal Cells Figure 8. Martinotti Cells Stellate (granule) Cells - Small neurons with a short vertical axon and Fusiform Cells several short dendrites, giving the cell body the - Spindle-shaped cells oriented at right angles to the shape of a star surface of the cerebral cortex - Located all over the cortex except for the - Axon arises from the side of the cell body and superficial layer passes superficially, branching into deeper and - Modulates activity of other cortical neurons more superficial layers like Martinotti cells - Spiny cells have small dendritic protrusions. Usually in layer IV. Release glutamate, excitatory Horizontal Cells of Cajal neuron - Small and spindle-shaped but oriented parallel to - Aspiny cells have no dendritic protrusions, the surface release GABA - Have one axon and one dendrite, both synapsing locally within the same layer - Least common cell type - Found in the most superficial layer where their axons pass laterally to synapse with the dendrites of the pyramidal cells Figure 7. Stellate cells Martinotti Cells - Small polygonal cells with a few short dendrites - Axon extends toward the surface and bifurcates to run horizontally along the most superficial layer - Most densely located within the deep layers - Inhibitory neuron, releases GABA Figure 9. Different Cerebral Cortex Cells 5 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal Figure 10. Layers of the Cerebral Cortex with the different cells LAYERS OF THE CEREBRAL CORTEX I. Plexiform (Molecular) - Dendrites and axons of cortical neurons; - Where horizontal cells of Cajal can be found - Superficial layer II. Outer Granular (External granular) - A lot of support cells can be found - Small pyramidal cells and a lot of stellate cells admixed with various axons and dendritic connections from deeper layer III. Pyramidal (External pyramidal) - Pyramidal cells of moderate size; Martinotti cells - Most of pyramidal cells can be found IV. Inner Granular (Internal granular) - Densely packed stellate cells (support cells) V. Ganglionic (Internal pyramidal) Figure 11. Microscopic illustration of the Layers in the Cerebral - Large pyramidal cells, Martinotti cells, Betz cells Cortex - Most of pyramidal cells can be found VI. Multiform B. MIDBRAIN - Martinotti cells, small pyramidal cells, stellate cells, fusiform cells Substantia Nigra - Deepest layer - Divides the cerebral peduncles into dorsal and - Contains white matter ventral parts - Serves as a landmark, everything in front is the dorsal part and behind it is the ventral part - Contains neurons with dark pigment (neuromelanin), contains dopamine - Parkinson’s disease is caused by loss of neuromelanin. - Neurons are multipolar Figure 12. Neuromelanin in the Substantia nigra C. PONS Superior cerebellar peduncle (SCP) - Ascending motor fibers - White matter Middle cerebellar peduncle (M) - Descending fibers 6 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal - White matter Middle lemniscus - White matter for dorsal tracts Figure 13. Pons Figure 14. Cross-sectional cuts of the Medulla D. MEDULLA Pyramids E. CEREBELLUM - Part of the corticospinal tract decussates Medial Lemniscus  Folia - Receive fibers from fasciculus gracilis and - sulci in the cerebellum due to the plant-like cuneatus to pass it up to the thalamus appearance - Receives impulses for proprioception - SNT (Spinal nucleus of CN V) - Found in lateral dorsal part HN (Hypoglossal nucleus) - Found lateral to the fourth ventricle (V) - Grey matter Olives - Have convoluted appearance and lying immediately lateral to the pyramids - associated with several smaller nuclei (D), including the dorsal accessory olivary nucleus (N) and medial accessory olivary nucleus (MO) Figure 15. Folias in the Cerebellum LAYERS: Molecular - Outer layer - Contains relatively few neurons and large numbers of unmyelinated fibers - Lots of axons and dendrites - Has very few cells (stellate cells) 7 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal Purkinje - Single layer of Purkinje cells which have large cell bodies, a relatively fine axon extending down through the granular cell layer and an extensively branching dendritic system which arborises in the molecular layer Granular - Inner layer - Contains numerous small neurons which have unmyelinated axons that pass outwards to the molecular layer where they bifurcate to run parallel to the surface to synapse with dendrites of Purkinje cells Figure 17. Microscopic Illustration of the cells in the Cerebellum SPINAL CORD -Your spinal cord is a collection of white matter and the cell bodies of your second-order neurons. A. HORNS Ventral - contain cell bodies of the large alpha lower motor neurons - very prominent because this will control your arms Dorsal - Contain cell bodies of small second-order sensory neurons. Lateral - Found in T1- L2 - Contain cell bodies of sympathetic nervous system efferent neurons - Volume of grey matter is larger in cervical and lumbar regions corresponding to the innervation of Figure 16. Layers in the Cerebellum the limbs. CELLS B. CENTRAL CANAL - Lined by ependymal cells Stellate - Star-like shape is due to dendritic processes C. VENTRAL MEDIAN FISSURE - GABAergic cells in the molecular layer Basket D. DORSOLATERAL SULCUS - GABAergic cells in the molecular layer that - Marks the line of entry of the dorsal nerve roots synapse with Purkinje cells Golgi E. DORSAL COLUMNS - GABAergic cells in the granular cell layer - Convey fibers for vibration, proprioception and fine - Golgi Type I touch → cervical region’s fasciculus gracilis - Long axons, also seen in cerebral cortex - Golgi Type II (lower limbs) and fasciculus cuneatus (upper - Short or no axons, also seen in cerebral limbs) cortex and retina 8 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal Figure 19. Microscopic Illustration of the Anatomy of a taste bud Figure 18. Graphic Illustration vs. Microscopic Illustration of the Spinal Cord (cross section) V. SPECIAL SENSES Figure 20. Microscopic Illustration of the Taste Bud showing the taste pore (P) A. GUSTATION (TASTE) CELL TYPES: a. Gustatory Cells TASTE BUDS b. Supporting or Sustentacular Cells - Human tongue has 3,000 taste buds - secrete glycoprotein substances - Mainly located in the epithelium of the Circumvallate c. Basal Cells Papillae of the tongue, faced into the deep troughs - called as such because it is found in the surrounding the papillae base; it does not even reach the apex - Also in the palate, pharynx and epiglottis - this is the reason why just by smelling, you GLANDS OF VON EBNER secrete serous fluid into the troughs somehow have an idea of how a food tastes like to act as a solvent for taste-provoking substances because you have taste buds in your pharynx - Barrel-shaped (think of it as garlic with cloves) - Opens at the surface via the taste pore B. OLFACTION (SMELL) - Each taste bud contains about 50 long, spindle-shaped - Restricted to a small area in the roof of the nasal cells which extend from the basement membrane to the cavity taste pore - Very tall, pseudostratified columnar cells - True bipolar neurons: cell bodies are in the middle stratum of the olfactory epithelium; single dendritic process extends to the free surface where it terminates as a small swelling (olfactory knob) which gives rise to about a dozen extremely long modified cilia - Contain microtubules that become thinner distally 9 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal - Non-motile and lie flattened against the epithelial surface in the surface mucous layer - Sites of interaction between odoriferous substances and receptor cells CELL TYPES: a. Olfactory Receptors - Each receptor cell gives rise to single fine non- myelinated axon which penetrates the basement membrane to join the axons of other receptor cells - Bundles of axons pass via about 20 small holes on each side of the cribriform plate of the ethmoid bone to reach the olfactory bulbs of the forebrain where they synapse with second-order sensory neurons b. Sustentacular - Elongated with their tapered bases resting on the basement membrane Figure 22. Microscopic Illustration of olfactory epithelium showing - Long microvilli extend from their luminal surface to the terminal bar (B) at the luminal surface, bundles of afferent nerve form a tangled mat with the cilia of receptor cells fibers (N), and numerous serous glands called Bowman’s Gland (G) c. Basal Epithelial - Small conical cells which appear to be stem cells BOWMAN’S GLANDS for both olfactory and sustentacular cells - they will eventually differentiate into olfactory cell or Serous glands which produce watery surface sustentacular cell secretions in which odiferous substances are dissolved, from there, it will be interpreted by olfactory cells C. VISION (SIGHT) THE EYE Layers: a. Corneo-Scleral Layer Cornea - Transparent - Has a smaller radius of curvature than the sclera - Principal refracting medium of the eye - Focuses the image onto the retina Figure 21. Graphic Illustration of the different Olfactory Receptors - Avascular (no blood vessels) - this is the reason why it does not decay Sclera - Opaque - Provides insertion for the EOM - the point of insertion of your extraocular muscles b. Uveal Layer - Middle layer; Highly vascular layer and it is mainly made up of your choroid - Pigmented; to absorb excess light that the retina was not able to absorb 10 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal Choroid - The retina overlying the lamina cribrosa called - Between the sclera and retina Optic Disc is devoid of photoreceptors and is - Provides support for the retina ad is heavily therefore a blind spot pigmented, thus absorbing the light which has passed through the retina - Merges anteriorly with the ciliary body (circumferential thickening of the uveal) - Separated from the retina by Bruch’s membrane which compose of the basement membranes of the pigmented epithelium of the retina and endothelium of the choroid capillaries plus intervening layers of collagen and elastin fibers Ciliary Body - Contains smooth muscle that controls the shape of the lens - Surrounds the coronal equator of the lens and is attached to it by suspensory ligament or zonule Iris - Gives the color of your eyes - Forms a diaphragm extending in front of the lens - Divides the eye into anterior and posterior chamber - Anterior chamber contains Aqueous Humor that circulates through the Figure 23. Graphic Illustration of the Eye posterior chamber to the pupil to drain into a canal at the angle of the anterior chamber called Canal of Schlemm - There is a clinical condition called Angle Closure Glaucoma, wherein there is a collapse of this angle which leads to the blockage of the Canal of Schlemm. There will be an accumulation of aqueous humor in the anterior chamber of your eye. - Aqueous Humor provides nutrients to the non-vascular lens and cornea. Maintains the shape of the cornea - Posterior chamber contains a transparent gel known as the Vitreous Body (gel-like) c. Retinal Layer - Inner layer Figure 24. Microscopic Illustration of the Eye showing the ciliary - Photosensitive layer bodies (CB), Iris (I), Lens (L), Cornea (C) and the Optic Nerve - This is the layer that actually receives light (O) - Terminates along a scalloped line called Ora Serrata, behind the ciliary body - Fovea: Depression in the retina; Area of the greatest visual acuity; Surrounded by a yellow- pigmented zone called Macula Lutea - Afferent nerve fibers from the retina converge to form the Optic Nerve - Optic Nerve leaves the eyes through the lamina cribrosa of the sclera → optic canal 11 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal IX. Optic Nerve Fibers - contains axons specifically called your Optic Nerve Fibers X. Inner Limiting Membrane - Separates retina from vitreous body - Basement membrane of the Muller Cell (just another support cell) Retinal Detachment - Visual loss described as “like a dark curtain falling” - The first and second layer are separate; Usually seen in the elderly but can also happen in young adults - Sometimes this is not permanent - Definite treatment is Surgical reattachment or laser Figure 25. Microscopic Illustration of the wall of the eye showing - Common detachment site is between the pigment epithelium (P), choroid (Ch), sclera (S), retina (R) and the Photoreceptor layer and the Pigment Cells Bruch’s membrane, separating the choroid and retina THE RETINA Layers: I. Pigmented Layer - Single layer of epithelial pigmented cells resting on Bruch’s Membrane which separates them from Choroid II. Photoreceptor Layer - Made up of processes of the Cones and Rods - only the dendrites of the Rods and Cones are located here III. Outer Limiting Membrane - Thin eosinophilic layer Figure 26. Layers of the Retina IV. Outer Nuclear Layer - Made up of cell bodies of Cones and Rods THREE CELL TYPES IN THE RETINA: V. Outer Plexiform Layer 1. NEURONS - Synaptic connections between short axons of a. Photoreceptor Cells (Rods and Cones) rods/cones and integrating neurons Rod Cells/ Rods VI. Inner Nuclear Layer - They are numerous, around 100 million in the eye - Cell bodies of integrating neurons - Responsible for vision at low light levels (scotopic vision), determination of light and VII. Inner Plexiform Layer dark, peripheral vision - Synaptic connections between integrating neurons - Since it is low light, we cannot see a lot of space, and dendrites of retinal ganglion cells you just know what is bright and dark. The scotopic vision is being used and that is the work of your rod VIII. Ganglion Layer cells. - Cell bodies of ganglion cells - No color vision, low spatial acuity (no details, no two-point discrimination) 12 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal - Long, slender bipolar cells with a single dendrite extending beyond the outer limiting membrane - Axons terminate in spherical processes small number of synaptic connections - Inner segment: prominent Golgi apparatus, many Mitochondria - Outer Segment: cylindrical shape containing a stack of flattened membranous discs which incorporate the pigment Rhodopsin - Interaction of light with Rhodopsin is what converts light to energy into electric impulses that your brain can understand - Interaction with light causes conformational change in rhodopsin which initiates an action potential. The action potential then passes inwards along the Figure 27. Rods and Cones in the Retina dendrite and axon to the layer of integrating b. Ganglion Cells neurons - Discs are continually shed and produced. These - Gives off unmyelinated afferent fibers that form the optic nerve discs that are being shed are the ones being eaten up by the Pigmented Cells. c. Integrating Neurons - Axons of Rod cells will end in a spherical process - Integrate information from millions of rod cells and which can only accommodate a small number of cone cells interactions as compared to cones which accommodate a larger number of interactions - Cell bodies of these integrating neurons are found in the Inner Nuclear Layer Cone Cells/ Cones Bipolar Cells - Fewer, around 6 million in the eye - Responsible for vision at high light levels - Most numerous of all integrating neurons (photopic vision), fine two-point discrimination - Makes direct connections between - Capable of color vision, high spatial acuity photoreceptors and optic tract neurons, as - Exclusively populates the Fovea (remember that well as with horizontal and amacrine cells - Their dendrites will communicate with the the Fovea is the area of the eye with the highest visual acuity so you would expect that there will be axons of your rods and cones a lot of cones) Horizontal Cells - Axons terminate in flattened pedicles hundreds - Have several short processes and one of synaptic connections long process that connect adjacent and - Outer Segment: long, conical structure, contains more distal rods and cones more flattened membranous discs that are not - Also synapse with bipolar cells shed, but are continuous with the plasma membrane. It is only the Rods that are feeding the Amacrine Cells pigmented cells. - Have numerous dendrites which make - Contains visual pigments similar to rhodopsin connections with bipolar and optic tract neurons - Makes occasional feedback connections with rods and cones - It can also talk to your bipolar cells and ganglion cells 2. PIGMENTED EPITHELIAL CELLS - Cuboidal in shape with nuclei located basally towards Bruch’s membrane - Crammed with melanin granules, numerous mitochondria 13 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal - Phagocytes discs that are shed by rods → gives off - Pia mater → Uveal tract residual product called Lipofuschin - Provide metabolic and structural support to rods and cones - Also absorb light, preventing back reflection - Purpose is to phagocytose the discs of your rod cells, after they eat the discs of your rod cells, they give off a by-product/ pigment called Lipofuschin. That is why they are called pigmented cells because of their by-product pigment - lipofuschin 3. NEURON SUPPORT CELLS Muller Cells - Analogous to the neuroglia of the CNS - Have long cytoplasmic processes which Figure 29. Illustration of the Optic Nerve embrace and encircle the retinal neurons - Provide structural support - Mediate the transfer of essential metabolites such as glucose to the retinal neurons Figure 30. Stained slide of an Optic Nerve D. AUDITORY PERCEPTION (HEARING) - Sound waves will enter your ear, from the External Auditory Canal → Eardrum or the Tympanic Membrane (Remember that your sound waves are waves and the tympanic membrane is at solid state so it will thump on the tympanic Figure 28. Location of the different cells in the retina in the retinal membrane). Behind the eardrum is the Middle chamber of layer the ear where you have three bones that will conduct the thumping and amplify it. At the end of the three bones, they THE OPTIC NERVE will again thump on two windows called the Semicircular window and Oval window. After that, you have the Inner Ear - Unmyelinated afferent fibers from the retina converge at the and there you will find your Cochlea. Where vibrations will Optic disc (medial to fovea) then penetrate the sclera be transmitted ultimately. Fluid in the Cochlea will vibrate through the lamina cribrosa to form the Optic Nerve and the movement of hair cells will be translated to - Myelination starts at the optic disc electrical impulse. - Supplied by the Central Retinal Artery (branch of the ophthalmic artery) - Invested by meninges: - Dura mater → Sclera 14 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal THE COCHLEA - Conical-spiral shaped, to conserve space it makes 2 ½ turns Scala Vestibuli - Originates near the oval window and the base of the stapes - Conducts vibrations from the cochlear apex - Lined by unspecialized squamous epithelium Vestibular Membrane/ Reissner’s Membrane - Extremely delicate fibrous tissue lined by simple squamous epithelium - Separate scala vestibuli and scala media Scala Media - Middle compartment, triangular in cross section - Apex attached to the osseous spiral lamina Figure 31. Illustration on the Parts of the Cochlea - Spiral Limbus is a thickened mass of tissue above the free edge of the osseous spiral lamina NOTE: Image (below) is flipped to coincide with stained slide - Stria Vascularis is the thickened outer wall of the scala media that is highly vascular and lined by stratified epithelium. Responsible for maintaining correct ionic composition of the endolymph (fluid inside the cochlea) Basement Membrane - Made of fibrous tissue - Separates scala media and scala tympani - Attached medially to the osseous spiral lamina and laterally to the spiral ligament - Contains the Organ of Corti (main translator of impulses that we hear) Scala Tympani - Lined by unspecialized squamous epithelium Figure 32. Graphic Illustration vs. Stained Slide of the Cochlea 15 [HISTOLOGY] 1.14 NERVOUS TISSUE: CNS – Dr. Vida Margarette D. Andal THE ORGAN OF CORTI - Convert vibrations into electrochemical energy that excites auditory sensory receptors Inner and Outer Sensory (Hair) Cells - Have long microvilli that project on their free ends that are embedded on the Tectorial Membrane - Their axons connect to the spiral ganglion - Superiorly attached to the tectorial membrane - Main cells that conduct impulses to the Cranial Nerve VIII. Are the ones that really translates vibrations into impulses Inner and Outer Pillar Cells - Single row of columnar cells that bound the Tunnel Figure 34. Stained Slide of the Organ of Corti of Corti - Contain a dense bundle of microtubules Inner and Outer Phalangeal Cells REFERENCES - Flask-shaped cells that support the inner and outer sensory cells Mescher, A. L. (2016). Junqueira’s Basic Histology Text and Atlas - Contain microtubules (Fourteenth Edition). McGraw-Hill Education - Support cells that will hoist hair cells so they can reach the tectorial membrane Powerpoint Presentation of Dr. Vida Margarette Anda-Buenol-. S.Y. 2023-2023. Central Nervous System Histology. University of *There is an Inner and Outer Cells that is just relative to the Tunnel Northern Philippines - College of Medicine of Corti but they actually have the same functions. Figure 33. Illustration on the Parts of the Organ of Corti 16