Histology LC15 Nervous Tissue PNS PDF

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC15 NERVOUS TISSUE: PNS COLLEGE OF MEDICINE, BATCH 2026 Transcribers...

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC15 NERVOUS TISSUE: PNS COLLEGE OF MEDICINE, BATCH 2026 Transcribers and Editors: Flores, Gallego, Gutierrez, Dr. Vida Margarette D. Andal | January 2023 Labingdalawa, Malonzo Editors: Gadut, Gadaza, Maligpas PERIPHERAL NERVOUS SYSTEM II. NEUROMUSCULAR SPINDLE I. SENSORY RECEPTORS Regulates muscle tone via the spinal stretch reflex II. NEUROMUSCULAR SPINDLE Encapsulated fusiform structures up to 6mm long, intrafusal muscle is stretched -> Figure 1. Nervous System annulospiral and flower spray endings are stimulated -> extrafusal muscle contracts I. SENSORY RECEPTORS Nerve endings or specialized cells that convert stimuli from the III. SKIN RECEPTORS environment into afferent nerve impulses Special senses: eye, ear, organ of Corti, taste buds Exteroreceptors: receptors for touch, pressure, cutaneous pain, temperature Proprioceptors: muscle spindles, Golgi apparatus Chemoreceptors Baroreceptors Interoreceptors: receptors for distention of hollow viscera (ex. Urinary bladder) Figure 3. Tactile receptors Page 1 of 6 [HISTOLOGY] 1.15 NERVOUS TISSUE: PNS – Dr. Vida Margarette D. Andal A. MEISSNER CORPUSCLE Small encapsulated receptors found in the papillary dermis of fingertips, soles of the feet, nipples, eyelids, lips, and genitalia. Fast-adapting mechanoreceptors which detect changes in texture and vibration (10-50 Hz) Ovoid in shape with a delicate collagenous tissue capsule surrounding a mass of plump oval cells arranged transversely (there’s a single orientation of these cells) Figure 6. Free nerve ending D. PACINIAN CORPUSCLE Large, encapsulated sensory receptors responsive to pressure, coarse touch and rapid vibration (200-300 Hz) Rapidly adapting Found in the deeper layers of the skin (in the base of the epidermis), ligaments and joint capsules, some serous membranes, mesenteries, viscera 1-4mm in length, appearance of an onion because of many concentric lamellae of flattened cells (likely Schwann) separated by interstitial fluid and collagen fibers. They are found among adipose tissue deep in the reticular dermis or in the subcutaneous tissue Figure 4. Meissner corpuscles are partially surrounded by epidermis. They are elliptical with an outer capsule (from the perineurium) and thin, stacked inner layers of modified Schwann cells, around which course nerve fibers B. MERKEL CELLS Located in the basal layers of the epidermis Slow-adapting mechanoreceptors that detect sustained/prolonged touch and pressure Densely staining Resemble the surrounding cells but with few, if any, melanosomes. They are abundant in highly sensitive skin like that of fingertips and at the bases of some hair follicles. Figure 7. Lamellated (Pacinian) corpuscle E. RUFFINI CORPUSCLE Slow-adapting receptors for pressure that results in stretching of the skin, low-frequency vibration, and pressure Found in superficial dermis of both hairy and glabrous skin Have collagenous, fusiform capsules anchored firmly to the surrounding connective tissue, with sensory axons stimulated by stretch (tension) or twisting (torque) in the skin Figure 5. Merkel cells or epithelial tactile cells C. FREE NERVE ENDINGS Are like naked tapering axons Most numerous among all exteroreceptors Found in the epidermis General light touch, temperature, and pain Responsible for telling you harmful stimuli (e.g., when you are touching a hot stove, you can immediately remove your hand) Figure 8. Ruffini corpuscle Page 2 of 6 [HISTOLOGY] 1.15 NERVOUS TISSUE: PNS – Dr. Vida Margarette D. Andal F. KRAUSE END BULBS 2. MYELINATED Laminated capsule of connective tissue enclosing the terminal, Mesaxon rotates around the axon thereby enveloping the axon in branched, convoluted ending of an afferent nerve fiber concentric layers of Schwann cell cytoplasm and fused plasma Basically, just a covering of a free nerve membrane called myelin sheath Seen in dermis, mucosa of oral cavity, conjunctiva Large-diameter fibers Touch and pressure As axons of large diameter grow in the PNS, they are engulfed along their length by a series of differentiating neurolemmocytes (what Schwann cells are sometimes called) and become myelinated nerve fibers. You want to myelinate large-diameter fibers in order to facilitate saltatory conduction. 1 axon: many Schwann cells 1 Schwann cell: (can only myelinate) 1 axon segment 1 oligodendrocyte: ≥ 50 axons (can myelinate several segments of a single axon while also myelinating multiple segments of another axon) Figure 9. Krause end bulb IV. PERIPHERAL NERVE A. NERVE FIBERS 1. NON-MYELINATED Axons are enveloped by the cytoplasm of Schwan cells (only one layer) Small diameter axons like those of the autonomic NS and pain fibers Their impulse conduction is not saltatory and is much slower than that of myelinated axons. In non-myelinated axons, the Schwann cells still hugs the axons once and Figure 12. Myelinated axon. Schwann cells will hug it over and over again the area where the arms of cytoplasm will meet is called your Mesaxon. forming concentric layers of cytoplasm and you end up with your myelin sheath and that’s how you myelinate your axon. Figure 10. Cross section of an axon Mesaxon Zone of apposition of Schwann cell membrane Figure 13. Electron micrograph of a myelinated axon. You can see dense layers of concentric cytoplasm of Schwann cell. It hugged the axon several times hence this very densely staining matter. Single segment of myelin produced by each Schwann cell is called internode “gaps” are called node of Ranvier (or nodal gaps) At these nodes the axolemma is exposed to ions in the interstitial fluid and has a much higher concentration of voltage-gated Na+ channels, which renew the action potential and produce saltatory conduction (L. saltare, to jump) of nerve impulses, their rapid Figure 11. Electron micrograph of a non-myelinated axon showing the movement from node to node. mesaxon Page 3 of 6 [HISTOLOGY] 1.15 NERVOUS TISSUE: PNS – Dr. Vida Margarette D. Andal Figure 14. Node of Ranvier Figure 16. Nerve organization Figure 17. In light microscopy, you can easily identify fascicles (F) containing a lot of individual nerve fibers/axons. Perineurium (P) surrounds your Figure 15. In light microscopy, you can see one axon segment, fascicle. There are also blood vessels (V) which you know because this there is a disconnect and that is your node of Ranvier (R). (slide) is smooth muscle and there are RBCs inside. You can also identify fat. Then they’re enclosed here by a unit called epineurium (E). V. SPINAL GANGLION A. GANGLION aggregation of cell bodies located outside the CNS Large nuclei, prominent nucleoli, extensive basophilic cytoplasm. Spinal ganglia are located on the posterior nerve roots. They contain cell bodies of primary sensory neurons that are pseudo-unipolar in form. surrounded by satellite cells that provide structural and metabolic support. encapsulated by supporting tissue which is continuous with the Figure 16. You see here a nucleus (N) perineural and epineural sheaths of the associated peripheral nerve. that is most likely a nucleus of your Schwann cell. B. NERVE ORGANIZATION 1. Endoneurium (your axon myelinated by Schwann cell will be enclosed with a) Loose vascular tissue that surrounds individual nerve fiber/axon A bundle of nerve fibers is called a (nerve) fascicle 2. Perineurium Condensed layer of robust collagenous tissue invested by a layer of flat epithelial cells that surround a fascicle From two to six layers of these unique connective tissue cells regulate diffusion into the fascicle and make up the blood-nerve barrier that helps maintain the fibers’ microenvironment. Figure 18. Ganglion (left); Pseudo-unipolar neuron (right). In the case of a 3. Epineurium pseudo-unipolar neuron, they will travel towards the ganglion (pointed in Cylindrical sheath made up of loose collagenous tissue that figure) (ganglion: general term for collection of cell bodies outside the CNS). encloses more than one nerve fascicle, blood vessels (arteries and If you look at it closely, these are groups of perikaryons (cell bodies). veins) and adipose tissue (fat). Epineurium will include some fat, arteries, and veins that will nourish your vesicles. Page 4 of 6 [HISTOLOGY] 1.15 NERVOUS TISSUE: PNS – Dr. Vida Margarette D. Andal Figure 19. Ganglion in H&E stain; Outside, there are support cells called satellite cells (Sa). B. SYNAPSE Figure 22. This one is oriented correctly. Terminal Boutons (TB). Vesicles (V). You can see mitochondria (M) because your axon can have mitochondria. You can also see your synaptic cleft and presynaptic neuron. C. MOTOR END PLATE Motor end plate is just like your synapse but specific for your muscles. Figure 20. This is an example of how your nerve interacts with your target organs or with another neuron. This is your synaptic unit. You have an axon. You have a terminal bouton where you see your vesicles being accumulated so they can expel neurotransmitters into the synaptic cleft which will be received by your postsynaptic neuron. Figure 23. Here, you can see synaptic vesicles and that the synaptic cleft is serrated. The purpose is to increase the surface area so that there are more points of contact. Figure 21. In election microscope, they look like this but here, the orientation is the other way around. Presynaptic neuron (P). Dendrite (D) of the postsynaptic neuron. Terminal boutons (TB) with a lot of vesicles (V) inside. You have a synaptic cleft (the empty space) and the dendrite (D) Figure 24. This is your axon with terminal boutons trying to target your that’s ready to receive neurotransmitters. Notice there's a rough myofibrils. endoplasmic reticulum (rER) in the dendrite since you can find Nissl bodies in the dendrites but not in the axons. Page 5 of 6 [HISTOLOGY] 1.15 NERVOUS TISSUE: PNS – Dr. Vida Margarette D. Andal e. The thickest sheath of connective tissue in the nerve 6. Schwann cells are found in the peripheral nervous system while oligodendrocytes are found in the central nervous system. Myelin produced by a single Schwann cell wraps around one axonal segment multiple times while myelin produced by a single oligodendrocyte wraps around multiple segments of a single axon. a. Both statements are true. b. Both statements are false. c. Only the first statement is true. d. Only the second statement is true. 7. A 22-year-old man receives a severe, traumatic compression injury to his radial nerve during a motorcycle crash. He shows an advancing Tinel sign. Which one of the following characterizes regeneration of axons after this nerve injury? a. It occurs in the absence of motor nerve action potentials. Figure 25. Terminal bouton (TB) in cross-section. Vesicles (V), Clefts of b. It occurs at a rate of about 100 mm/d. your motor end plate (C), Myofibrils (Mf) c. It occurs in the segment distal to the site of axon damage. VI. REFERENCES d. It occurs by a process that involves Schwann cell Mescher, A. L. (2016). Junqueira’s Basic Histology Text and Atlas (15th proliferation. ed.). Mcgraw Hill Education. e. It occurs in conjunction with degeneration and phagocytosis of the endoneurium. TEST YOURSELF 8. A 2-year-old boy presents with hearing impairment, poliosis 1. It is a skin receptor that can be found in the base of the dermis (a white shock of hair), complete heterochromia and sectoral responsible for course touch, pressure, and rapid vibration. heterochromia, hypertelorism, a low hairline with eyebrows that a. Ruffini corpuscle touch in the middle, white pigmentation of the skin, and b. Free nerve ending suspected neurologic deficits. He is diagnosed with Waardenburg c. Lamellated corpuscle syndrome with a mutation in the PAX-3 gene that affects neural d. Meissner corpuscle crest differentiation. Which of the following structures would most likely also be affected in this patient? 2. TRUE or FALSE. Skin contains several types of sensory receptors, a. Purkinje cells with or without capsules of collagen and modified Schwann cells. b. Pyramidal neurons c. Ventral horns of the spinal cord 3. This part is serrated to increase the surface area and maximize the d. Astrocytes point of contact in a synapse. e. Neurons and satellite cells of the spinal ganglion a. Terminal Bouton b. Perikaryons 9. Which of the following best describes a neuromuscular spindle? c. Synaptic Cleft a. Regulates skeletal tone via the spinal stretch reflex d. Myofibrils b. Contains 2-10 modified skeletal muscle fibers called intrafusal fibers 4. These are cells that surround the ganglia and provide its structural c. Encapsulated fusiform structures up to 6mm long, and metabolic support.