Histology Level 1, Semester 1 PDF

Histology lectures (11 & 12) Nervous system Histology 1. Brain. 1. Peripheral nerves: cranial or spinal nerves. 2. Spinal cord. 2. Ganglia: spinal or autonomic ganglia.  Receive changes (Stimuli...

Histology lectures (11 & 12) Nervous system Histology 1. Brain. 1. Peripheral nerves: cranial or spinal nerves. 2. Spinal cord. 2. Ganglia: spinal or autonomic ganglia.  Receive changes (Stimuli) occurring inside and outside the body.  N.S. is able to integrate and interpret this sensory information.  Then decide if action is needed  A response to the integrated stimuli.  The response activates muscles or glands Histology Specialized cells that function to transmit electrical impulses within nervous system. The basic (structural& functional) units of the nervous system which carry the impulses. The nervous system converts sensory information into electrical impulses in order to rapidly respond to stimuli  Contains : 1. Nucleus: Large, rounded, central and vesicular 2. Cytoplasm contain organelles (Nissl granules, Golgi apparatus & Mitochondria) where essential metabolic processes occur to maintain cell survival.  Axon.  Dendrites.  Basophilic granules scattered in cytoplasm.  All over the neuron except in: a. Around nucleus. b. Axon  Basic stain: Hx & Toluidine blue.  Synthesis of protein. Histology  Many dendrites are extended from  Single a single cell body  short branched extended from  long thread nerve cell  Uniform diameter  Tapering ends  Do not contain Nissl’s granules  Contain Nissl’s granules.  Highly branched to increases the  Branched at their terminal ends surface area that can receive only (terminal arborization). impulse  Carry nerve impulses away from  Carry nerve impulses to the cell the cell body (Centrifugal). body (Centripetal). Histology  The nerve cells are rounded.  Mesencephalic nucleus of  Has only one process. trigeminal nerve  The nerve cells are rounded.  Sensory ganglia or spinal  Has single process which divides in ganglia inverted T-shaped manner into 2 branches, a dendrite and an axon.  The cells are fusiform.  Bipolar neurons of retina  Has 2 processes, dendrite & axon.  Olfactory epithelium  The cells have star-shaped body.  Neurons in sympathetic  Have many dendrites and one axon. ganglia Anterior horn cells of spinal Neurons of reflex arc in spinal Cells of spinal ganglia cord. cord. Histology  It is the axon of the nerve cell with its surrounding membranes.  The axon membrane →axolemma  the cytoplasm → axoplasm.  Have no Nissl granules.  It may be Naked or ensheathed (with myelin sheath, neurolemma or both). A. Naked Fibers: (Non-myelinated without neurolemma) e.g. nerve fibers in gray matter (Termination of peripheral nerves). B. Ensheathed fibers: 1. Myelinated with neurolemma: peripheral nerves. 2. Myelinated without neurolemma: nerve fibers in white matter. 3. Non-myelinated with neurolemma: sympathetic nerve fibers. Histology  White tubular covering of the axon  Interrupted at intervals called “nodes of Ranvier”  Segment between two successive nodes → “internodal segment”.  Appears in the form of concentric layers derived mainly from the cell membrane of Schwann cell  Insulation of the nerve impulses.  Chain of cells forming a tube around myelin sheath  Each cell has a flat oval nucleus  Corresponds to an internodal segment 1. Insulation in nonmyelinated nerve fibers. 2. Regeneration of peripheral nerve after injury. 3. Myelin formation Histology  Groups of nerve fibers (myelinated with neurolemma) arranged in bundles. It is a dense C. T. surrounds the whole nerve trunk. It is a dense C. T. divide the trunk into bundles. It is a delicate loose C. T. lie between the individual nerve fibers.  Histology It is a point at which a nervous impulse (signal) passes from one neuron to another (Between the axon of one neuron and the body or dendrites of another neuron).  Formed by terminal button (expanded end of an axon) that delivers impulses to the synapse.  It contains mitochondria and neurovesicles contain neurotransmitters (acetylcholine or dopamine).  Composed of a segment of dendrite or cell body of the other (target) neuron that receives impulses.  It is a thin space between presynaptic and postsynaptic terminals.  It is about 20-30nm wide -  Electrical impulse (stimuli) in presynaptic  The two neurons are connected by gap neuron activates the release of junctions. neurotransmitters (acetylcholine or  This synapse allows electrical signals to dopamine) from neurovesicles. travel quickly from the presynaptic cell to  Then these chemical messengers the postsynaptic cell (rapidly speeding of (neurotransmitters) cross synaptic cleft and the transfer of signals). connect with receptor sites in next nerve cell.  Most synapses are of this type. Histology According to type of cellular structures serving as the pre- and post-synaptic components:  Where axon of one neuron ends with dendrites of next neuron.  Where axon of one neuron end around body of next neuron.  Where axon of one neuron ends with the initial segments of the axon of the next neuron. Histology It is the interstitial supporting tissue of the nervous system, Non-neuronal cells present in central nervous system and peripheral nervous system. 1. Astrocytes 1. Satellite cells 2. Oligodendroglia 2. Schwann cells 3. Microglia 4. Ependymal cells Histology  Nutrition by connecting neurons to blood vessels  Star-shaped branching  Regulate external chemical environment cells of neurons by removing excess ions during synaptic transmission.  Can transform into a macrophage that  Small cells having spiny can clear up the neuronal debris. processes  Detect injuries to neuron.  Formation of myelin sheath of nerve  Cells have few processes fiber In CNS.  Cells line spinal cord and ventricular system of  Secretion of cerebrospinal fluid (CSF). brain  Small cells that surround neurons in sensory,  Highly sensitive to injury and sympathetic & inflammation parasympathetic ganglia  Flat cells forming a tube  Formation of myelin sheath of nerve around myelin sheath of fiber in PNS. nerve fiber  In CNS: oligodendrocyte form myelin sheath by: These cells have processes that wrap around the axons. One oligodendrocyte forms myelin sheath for several neurons (from 3 to 50 neurons).  In PNS: Schwann cell form myelin sheath by: One Schwann cell provide myelination for one axon (only segment of one axon). Histology Collection of nerve cells and nerve fibers, covered by a C. T. capsule, outside CNS. Nerve cells. Nerve fibers. Covered by C.T. capsule. 1- Spinal. 2- Autonomic: Sympathetic & Parasympathetic. Dorsal roots of spinal nerves. Sympathetic chain Thick and usually present. Thin and may be absent Pseudounipolar Multipolar Mostly of the small uniform size (30 Large or small (20-120 μm). μm) Central Eccentric Numerous and form complete Few and form incomplete capsule. capsule In groups or rows parallel to Scattered irregularly. capsule. Few Numerous  Thickly myelinated.  Thinly or non myelinated  Widely separated  Close to each other.  Parallel to the capsule.  Irregularly distributed.  Synapse: absent (as the fibers  Present (fibers synapse with enter the C.N.S) ganglion cells Poor Rich  Acts as relay for different  Acts as relay for different motor sensations before their functions arising from the spinal entrance into the spinal cord cord Histology