Histology of Nervous Tissue PDF

Histology Nervous tissue - Nervous System -tissue specialized to: 1- receive information from external and internal stimuli 2- integrating and analyzing it to prod...

Histology Nervous tissue - Nervous System -tissue specialized to: 1- receive information from external and internal stimuli 2- integrating and analyzing it to producing response - consists of two cell types: a) nerve cells (neurons ) b) glial cells (neuroglial cells) - reception of stimuli is the function of the sensory component of the peripheral nervous system (PNS) - processes of integration and analysis and response are carried by central nervous system (CNS) - transmission of the response to the effector organ is carried by the motor component of the PNS - Neurons - Structural and functional unit of nervous system - Histological structure : 2 parts: A- Cell body ( perikaryon ) size: varies from 4 µm as in cerebellar cortex to 100 µm as in motor neurons in spinal cord shape: depends on the number of cell processes: a) unipolar: globular shape b) Bipolar: fusiform shape c) multipolar: stellate, pyramidal or pyriform - The nucleus: large spherical, prominent nucleolus Dr. Kandeel  Histology Nervous tissue - The cytoplasm: 1- highly developed rER and Free polyribosomes: - synthesize both structural proteins and proteins for transport - basophilic granular areas called Nissl bodies 2- Golgi: around the nucleus 3- mitochondria: scattered in the cytoplasm 4- Neurofilaments: - intermediate filaments: abundant in perikaryon and processes - bundle together as result of the action of fixatives to form: * neurofibrils stained brown by Ag, provide structural support 5- microtubules: - arranged in parallel bundles in perikaryon and processes. - involved in axonal transport of neurotransmeitter substances, enzymes 6- centrioles: not seen as neurons cannot divide 7- inclusions: a) Lipofuscin pigment: - golden brown, residue of undigested material by lysosomes - its amount increases with aging b) melanin pigment: dark brown or black, found in neurons c) lipid droplets: in cytoplasm as energy reserve Dr. Kandeel Histology Nervous tissue B-the processes ---------------- Dendrites Axon Number numerous Single Length Short Long Thickness Thick thin Process Multiple single Branching - Branching like a tree - not branching except at its end - Branches arise at acute angle - may give collateral branches near cell body that arise at right angle Diameter Subdivided into branches: become thinner Constant diameter Impulse - receive stimuli from environment conveys information away from the cell direction - carry it to cell body body to other neurons Organelles - Contain Nissl granules, mitochondria - no nissl granules & - neurofibrils and microtubules - no golgi apparatus - but no golgi apparatus - has mitochondria, neurofilament, microtubules. Dr. Kandeel  Histology Nervous tissue * Classification of Neurons: a) acc to Number of processes -------- a) Unipolar b) Bipolar c) Multipolar Process - single process, close to perikaryon one dendrite+ one axon+ many dendrites - divided into 2 branches (T-shape): one axon * one branch to peripheral (dendrite) * other branch to CNS (axon) -stimuli are picked by dendrite travel to axon without passing perikaryon Site - spinal ganglia - Cochlear -take different forms: - mesencephalic Nucleus of - vestibular ganglia 1)stellate: - anterior horn cell in trigerminal nerve In ear spinal cord - retina in eye - sympathetic ganglia - olfactory mucosa 2)Pyramidal: cerebral cortex in nose 3)pyriform: purkinje cell in cerebellar cortex Dr. Kandeel  Histology Nervous tissue --------- B- According to function c- length of axon 1- sensory (Afferent) neurons: 1- Golgi type 1 : - receive sensory stimuli as cells - neurons have long axon that of dorsal root ganglion - leaves the grey matter and enters white matter - EX: - motor neurons in: 2- motor (efferent ) neurons: - spinal cord Str - control effector organs as muscles - pyramidal cells in cerebral cortex, and glands - purkinje cells in cerebellar cortex - as in anterior horn in spinal cord 2- Golgi type 2: 3- interneurons: - neurons have short axon - connect neurons as in retina and - does not leave the grey matter spinal cord - EX: interneurons in: - cerebral, cerebellar cortex, spinal cord Dr. Kandeel  Histology Nervous tissue - SYNAPsE - Site of contact between neurons or (neurons and effector cells) - main function: to transmit impulse from presynaptic to postsynaptic cell - Classification according to: 1- Methods of transmission of nerve impulse 2- Site of contact of axon 1- chemical: most common, impulses takes place by release of 1- Axosomatic: neurotransmitters - axon forms synapse with cell body 2- electrical : contain gap junctions that: 2- Axodendritic: 1) allow movement of ion between cells - axon forms synapse with dendrite 2) permit spread of electric current 3- Axoaxonic: - ex: cerebellum - axon forms synapse with axon Dr. Kandeel  Histology Nervous tissue - Histologically: the chemical synapse is formed of: ------- Presynaptic postsynaptic 3- synaptic cleft Name axon terminal surface of other cell intercellular space Str - Rich in mitochondria - Has receptors for chemical transmitter - which is 20-30 nm and Synaptic vesicles in width -shows continuous zone of dense cytoplasm with of chemical - shows delicate fibers filaments called synaptic web transmitter and granules -this dense area formed by interlinked proteins that: * fix neurotransmitter receptors to cell membrane * translate neurotransmitter receptor into intercellular signal. - Nerve fiber and covering - consist of axon covered by axolemma and contains axoplasm (cytoplasm) - arises from a conical extension of cell body called axon hillock Dr. Kandeel  Histology Nervous tissue - Types of nerve fibers: 1-Unmyleinated nerve fibers 2-Myelinated nerve fibers - unmyleinated without schwann cells (neurolemma): - Myleinated without schwann cells: - gray matter (naked). - in white matter - Unmyleinated with schwann cells: - myleinated with schwann cells: - sympathetic post ganglionic fibers. - in peripheral nerve fibers - sheath of schwann ( neurilemmal sheath ): - flattened cells with flattened nuclei that form a thin chain around myelin - its Function: 1- Formation of myelin sheath in peripheral nerves 2- electric insulation 3- Regeneration of axon grows from the proximal stump Dr. Kandeel  Histology Nervous tissue * MYLEIN SHEATH Definition Structure Under microscope - formed by rotation of schwann cell - many layers of modified LM: - H,E: lipoprotein dissolves (PNS) or oligodendroglia in (CNS) cell membranes with higher - stained black with osmic acid around the axon several turns lipids than other cell EM: fused spiral laminae membranes -each schwann wraps around one segment - shows nodes of ranvier: of one axon - Function: * gap between adjacent sheath cells -each oilgodendroglia cell wraps around enhances speed of nerve - sheath of myelin is divided into one or more segments of many axons impulse segments by the nodes which are called (10-60) turns internodal segments - Stages of myelination (formation of myelin sheath): 1- axon invaginates into schwann cell in PNS or oligodendroglia in CNS 2- further invagination: axon is surrounded by a single turn of cell membrane 3- many turns in a spiral form due to rotation of the sheath cell 4- cytoplasm is pushed to cell body leading to compaction of the turns 5- fusion of cell membranes form myelin sheath. Dr. Kandeel  Histology Nervous tissue - Peripheral nervous system - consists of nerves, ganglia and nerve endings - All nerve is covered by dense connective tissue called epineurium - nerve bundles are surrounded by perineurium: - flattened epithelium like cells joined by tight junctions - this forms a barrier: protect nerve fiber - Inside the bundle: each nerve fibers are connected by endoneurium: - black ring (sheath of henle): consists of reticular fibers formed by schwann cells. * Ganglia - collection of nerve cells and glial cells outside CNS, types: ------------------ Spinal Sympathetic (autonomic) Capsule Thick C.T Thin C.T Vascular Less More Cells Unipolar, larger, variable in size Stellate multipolar, smaller, uniform in size Glomeruli Present, formed by coiling of axon around Absent cell body before splitting in T form Satellite Large number Smaller number Arrangement In groups or rows of cells Scattered cells Nerve fibers Thick myelinated Thin unmyelinated synapse Absent Present Dr. Kandeel  Histology Nervous tissue - Degeneration of nerve tissue -------- retrograde ( traumatic ) degeneration Wallerian degeneration Site - in Nerve cells, proximal part of nerve fiber - in distal part of nerve fiber - chromatolysis: disappearance of nissl with - Axon: neurofibrils: beaded, then segmented, decrease in basophilia then granular and disappear - Increase in volume of perikaryon - widening of nodes of ranvier Str - loss of dendrites - inter nodal segments are termed fermentation - migration of nucleus to peripheral position chambers as fat split into fatty acids - disappearance of golgi and mitochondria - schwann cells proliferate: - fragmentation of neurofibrils - giving rise to column that act as guide - lysosomes increase for growing axons during regeneration - Stains of degeneration: 1- silver: to demonstrate golgi body and neurofibrils 2- osmic acid: to demonstrate myelin sheath 3- Basic stains: to demonstrate nissl bodies Dr. Kandeel  Histology Nervous tissue - Regeneration of Nerve Fibers - Macrophages: remove debris and secrete interleukin 1: * stimulate schwann cells to secrete substances that promote nerve growth - Regeneration is efficient when: the fibers and the columns of schwann cells are directed to correct place *Note: - When there is extensive gap between the distal and proximal segments of the axon or when the distal segment disappear as in amputation of a limb: * the newly grown nerve fibers may form a swelling or neuroma that can be source of pain - demyelinating diseases: damage to myelin sheath, loss of ability to transmit electrical impulses - most glial cells can divide, but neuron do not divide, so all tumors originate from glial cells - Neural stem cells: constitute a reserve of cells that can under correct stimulation replace lost neurons - found in certain regions of the brain - they can mature to functional neurons Dr. Kandeel  Histology Nervous tissue Neuroglia * Glial cells: - They surround cell bodies and processes, smaller than neurons * Types of glial cells: Astrocyte (macroglia) - the largest glial cells, large and pale nucleus - star shaped with multiple long processes - they have centrioles so can divide * E.M: intermediate filaments made of glial fibril acid protein (GFAP) - ectodermal in origin - Functions: 1- processes with expanded end feet capillaries, so control metabolic exchanges between nerve, blood 2- blood brain barrier 3- structural support, repair process - 2 types of astrocytes: Cytoplasmic astrocyte Fibrous astrocytes In grey matter In white matter Cytoplasm is granular Cytoplasm is fibrillary Many shorter process Fewer long process Dr. Kandeel  Histology Nervous tissue Oligodendrocyte Microglia (mesoglea) - the most numerous in white matter - smallest and rarest glial cells - have few processes - many short branches - intermediate in size between astrocytes, microglia - cell body, branches are decorated by spines - they have centrioles - oval dark nucleus - ectodermal in origin - cytoplasm is scanty - present in both grey and white matter - no centrioles - mesodermal in origin - there are 2 types: - in grey and white matter - phagocytic cells Satellite Interfasicular - stained by vital stains as trypan blue oligodendrocytes oligodendrocytes In grey matter In white matter associated with between bundles perikaryon of axons Support nerve cells Formation of myelin sheath and electric insulation Dr. Kandeel  Histology Nervous tissue *Some important notes: Glial cell type Origin Site Functions Astrocytes Ectodermal CNS 1- metabolic exchange, blood brain barrier 2- structural support, repair processes Oligodendroglia Ectodermal CNS - Myelin production - Electric insulation Microglia Mesodermal CNS - Phagocytic activity Schwann cell Ectodermal Around axons in PNS - Myelin production - Electric insulation, Regeneration Satellite cells Ectodermal Around nerve cell in Structural and metabolic support ganglia (PNS) Ependymal cells Ectodermal Simple cubical ciliated - Production and movement of CSF epithelium - Line ventricle of brain, central canal of spinal cord Dr. Kandeel  Histology Nervous tissue Nerve endings * Nerve endings in epithelium A) Receptors: -------- 1) Free nerve ending 2) merkel ending 3) peritrichial nerve 4) neuro epithelium ending ending - epidermis of skin - epidermis of - Hairy (thin) skin - taste buds in tongue - cornea of eye hairless (thick) skin around hair follicles - organ of corti in ear Site - macula utriculi, sacculi , cristae ampullaris (for equilibrium) - non encapsulated - non encapsulated - loses its myelin below - loses its myelin - non encapsulated ----------- Capsule basement membrane and sheath and form disc pass in between the like expansion under epithelial cells merkel cell near the base of the epidermis Function mechanoreceptors for pain mechanoreceptors for mechanoreceptors for - For taste temperature and touch touch touch and movement of -for hearing hair - for equilibrium Dr. Kandeel  Histology Nervous tissue B- Effectors: - autonomic nerve endings: supplying glandular epithelium as lacrimal and salivary glands - unmyelinated nerve fibers form network outside basal lamina of the epithelium, its branches penetrate lamina and end between bases of glandular cells. *Note: a) Receptors: receive external or internal stimuli and convert them to nerve impulses. - classified into: Nerve endings in connective tissue 1) exteroceptors: receive external stimuli 2) proprioreceptors: receive stimuli from the muscle 3) interceptors: receive internal stimuli b) Effectors: bring efferent nerve impulses to effectors (muscle or gland) Dr. Kandeel  Histology Nervous tissue - All are receptors: Free nerve Meissner Krause Ruffini golgi tendon Pacinian corpuscle ------ ending corpuscle end bulb corpuscle = tendon spindle - dermis of skin - dermal papillae dermis of - dermis of Tendons near - Dermis, hypodermis of - stroma of of skin skin of skin the muscle skin cornea - in palm and external -especially in insertion - periosteum of bone Site sole genitalia sole - joint capsule - C.T of some organs as pancreas wall of rectum and urinary bladder mechanoreceptor mechanoreceptor Mechano- mechanorecep Mechano- - Mechanoreceptors for Function for pain, touch, for touch receptor tor for receptors for vibration and pressure that temperature for touch stretch and compression responds to displacement of twisting of muscle tension the capsule lamellae. skin - one of the - pacinian corpuscle in joint proprioceptors capsule is one of the proprioceptors Non- Encapsulated Cap sule encapsulated Shape --------- Oval Oval Fusiform Fusiform Large, Oval Dr. Kandeel  Histology Nervous tissue - Similar to Axon lose its axon Axon enters sensory nerve - thin C.T capsule enclosing epithelial cells myelin to enter enters capsule after penetrates the 20-60 concentric lamellae corpuscle, spirals corpuscle losing myelin capsule (C.T of modified schwann cells: up between after sheath and sheath) to end * narrow spaces filled with modified losing its branches around the gel like material flattened myelin, between collagen * lamellae become closely schwann cells, branches parallel bundles packed ends at the repeatedly collagen - myelinated nerve fibers Mechanism upper pole of inside fibers. enter corpuscle at one pole. corpuscle - its schwann cell sheath becomes continuous with the capsule while the myelin sheath ends inside corpuscle - naked nerve fiber runs parallel to the longitudinal axis and ends in a small expansion Dr. Kandeel  Histology Nervous tissue Nerve endings in muscular tissue A) Receptors: Muscle spindles - site: skeletal muscles, more numerous: in fine movements muscles as muscle of hand, antigravity muscles. - Function: 1) mechanoreceptor for stretch, muscle length. 2) one of proprioceptors: regulation of the muscle tone through stretch reflex 3) keeps the CNS informed about length of muscle by indirectly control of voluntary muscle. - shape: fusiform, lie parallel to muscle fibers - structure: capsule surrounding lymph filled space that contain: * Intrafusal fibers: smaller than skeletal muscle fibers - They have central non-striated area containing the nuclei. - they are of 2 types: 1) Nuclear bag type: the central nuclear area is dilated 2) nuclear chain type: no dilatation, nuclei are in form of chain - Types of nerves: Afferent Efferent Sensory nerve that envelope intrafusal muscle fibers motor nerve innervate striated portion of intrafusal muscle fiber, extrafusal muscle fiber Dr. Kandeel  Histology Nervous tissue B) Effectors: Motor end plate (neuromuscular junction) - myelinated motor nerve branches out to several terminal branches - nerve loses its myelin sheath and forms dilated terminal that contains many mitochondria and synaptic vesicles containing acetyl choline - sits in depression on the muscle cell surface called sole plate - external lamina of schwann cells fuses with that of sarcolemma - space between the terminal swelling and the muscle fiber is called synaptic cleft - post synaptic membrane: has many deep junctional folds which provide more surface area and more acetylcholine receptors - muscle fiber cytoplasm under junctional folds contain many mitochondria, nuclei, rER and free ribosomes. - organelles are involved in synthesis of specific acetylcholine receptors in the membrane of the cleft as well as acetylcholinesterase. Dr. Kandeel