Histology of the nervous system for neuroscience Spring 2011 sv

Histology of the nervous system for neuroscience Spring 2011 sv

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Unformatted text preview: LEARNING OBJECTIVES Upon completion of this lecture, the student Upon should be able to: should • Describe and identify the basic cellular components of the Describe nervous system. nervous • Differentiate morphologically and functionally between Differentiate dendrite and axons. dendrite • Classify the basic types of neurons by their morphological Classify characteristics. characteristics. • Illustrate the cellular events which take place during Illustrate synaptic transmission. synaptic LEARNING OBJECTIVES Upon completion of this lecture, the student Upon should be able to: should • Describe the different functions of and identify the types of Describe supporting (glial) cells found in the nervous system. supporting • Diagram the basic process of myelin production and the Diagram significance of myelin. significance • Distinguish between gray matter and white matter and Distinguish describe their respective histological composition. describe LEARNING OBJECTIVES Upon completion of this lecture, the student Upon should be able to: should • Describe the LM appearance of nerves and ganglia of the Describe peripheral nervous system. peripheral • Describe the general organization of nerve fibers and cell Describe bodies in the CNS and PNS. bodies • Describe the organization and function of the choroid Describe plexus. plexus. Suggested Readings Junqueira’s Basic Histology: Text & Atlas 12th edition * Text Chapter 9: Pages 140 - 166 Pages Nervous Tissue The Neuron: The The neuron is the principle The principle cell of nervous tissue. cell Neurons are highly Neurons specialized to carry information, in the form of electrical signals, form one electrical form point to another. The Neuron The Perikaryon: also called The the soma or cell body is the soma portion of the neuron that contains the nucleus. nucleus It is the metabolic center of the neuron. * the The nucleus of neurons is The nucleus usually filled with euchromatin and typically euchromatin contains a prominent prominent nucleolus. nucleolus The Perikaryon The The cytoplasm of the The cytoplasm perikaryon contains characteristic regions having high concentrations of rER rER and free ribosomes. free These areas therefore stain with basic dyes (basophilic) basic and are called Nissl material, Nissl after their discoverer. Cell Processes Cell The processes are of two types: 1). Dendrites 2). Axons 2). Cell Processes Dendrites may be large or small diameter processes, Dendrites containing some Nissl material, microtubules, Nissl microtubules neurofilaments and mitochondria. * neurofilaments mitochondria Neurons may have one or more Neurons one more dendrites. * dendrites. As a general rule, dendrites receive As receive information from other cells or neurons and transport impulses toward the cell body. toward Cell Processes Cell Axons are processes involved in conveying information away from the cell body. * the Typically, axons are longer than Typically, dendrites (microns to more than a meter).* meter).* Only one axon originates from each Only one neuron (usually at a special region of the perikaryon known as the axon hillock). hillock). Cell Processes Cell Axons characteristically contain microtubules, neurofilaments, microtubules neurofilaments microfilaments, mitochondria, but microfilaments mitochondria but lack Nissl material and Golgi lack Nissl Golgi complexes. Axon Axon • Transport Transport • anterograde axonal transport transports molecules (nutrients, neurotransmitters) and organelles (mitochondria, neurofilaments) from cell body to distal end of axon cell Axon Axon •Transport • retrograde axonal transport occurs from distal end of axon to cell body returns used or worn out materials to cell body for restoration materials transports materials taken up by endocytosis (including toxins, viruses and markers used in neuroscience research) research) Injury to Neural Tissue Injury Neuron Classification Neuron classification is based partly upon the shape shape of the perikaryon and partly on the number and number orientation of cell processes. cell Note that cell processes also affect the shape of the perikaryon. perikaryon. Neuron Classification Pseudounipolar neurons re the principle a cell found in sensory ganglia. sensory Such a cell has one process emanating one process from the cell body that bifurcates bifurcates forming a T-shape. T-shape One of the branches extends into the One CNS and the other extends out to CNS other peripheral receptors. peripheral Pseudounipolar neurons are located in Pseudounipolar sensory ganglia of spinal nerves and of some cranial nerves some Neuron Classification Bipolar neurons have two processes two extending from each perikaryon. perikaryon Usually a dendrites extends from one dendrites end of the cell body and an axon end axon extends from the other. other Bipolar neurons are located in the Bipolar retina, olfactory epithelium and form the ganglia of vestibulocochlear nerve the Neuron Classification Multipolar neurons cells are the Multipolar most common type of neuron. most These have one axon and multiple one axon multiple dendrites extending from the cell dendrites body. Functional Classification of Neurons Functional • afferent (sensory): carry information from peripheral receptors to the CNS receptors Functional Classification of Neurons Functional • efferent (motor): carry impulses from the CNS to efferent peripheral effectors (muscle, glands) peripheral Functional Classification of Neurons Functional • interneurons: interneurons: • reside entirely within the CNS reside Functional Classification of Neurons Functional • interneurons: interneurons: • establish neuronal circuits between sensory and motor establish neurons and other interneurons neurons Synapses and Impulse Transmission Synapses Synapses are special regions of close apposition Synapses close between a neuron and its target cell (which may be neuron target another neuron, a muscle cell, or gland). neuron muscle or gland). Target cell Synapses and Impulse Transmission Synapses They act to transduce the electrical signal travelling They transduce in a process so that the target cell is also electrically excited. Synapses and Impulse Transmission Synapses Synapses therefore have pre-synaptic and Synapses pre-synaptic post-synaptic elements. post-synaptic Synapses occur between: Synapses axons and dendrites (axo-dendritic), ), axons and perikarya (axo-somatic), axons ), axons and axons (axo-axonic) and, rarely, between axons and, dendrites and dendrites (dendro-dendritic). dendrites Mechanism of Synaptic Transmission (very general) (very Mechanism of Synaptic Transmission Investing and Supporting Cells of Nerve Tissues Investing In the CNS and PNS neurons are supported and CNS PNS supported segregated into functional units by cells called glia. segregated glia The central nervous system has no connective tissue The central no connective components other than those immediately surrounding blood vessels. Supporting Cells of the Nervous System (Neuroglia or Glial Cells) (Neuroglia • ependymal • microglial • astrocytes • oligodendrocytes • Schwann cells • capsular (satellite) cells In the CNS, glial cells are divided into four In categories: categories: Astroglia Microglia Oligodendrocytes Ependymal cells Astroglia Astroglia There are two types of astroglial cells There two 1) protoplasmic astrocytes found mostly in the gray matter and matter Astroglia Astroglia There are two types of astroglial cells 2) fibrous astrocytes found mostly in the white 2) fibrous matter. matter Astroglia Astroglia Both types have extensive star-like radiating star-like processes. processes These cells are involved in selectively isolating specialized areas of synaptic exchange between nerve cells. Astroglia Astroglia They also have supportive, nutritive and reparative supportive nutritive reparative roles. Astroglia Astrocyte processes terminate as "end-feet" near Astrocyte near blood vessels and blood at the external surfaces of the surfaces CNS. CNS Astrocytes Astrocytes • astrocytic processes reach the surface of the brain and astrocytic spinal cord to form a protective covering (external limiting spinal external membrane or glial membrane) membrane Astrocytes Astrocytes • astrocytic processes surround capillaries and form part of astrocytic the blood-brain barrier (regulates the passage of materials blood-brain from blood to CNS)* from Astrocytes Astrocytes • electrolyte balance of the CNS electrolyte • remove neurotransmitters from synaptic clefts remove • produce trophic factors necessary for neuronal survival trophic • form scars after CNS injury scars Injury to Neural Tissue Injury Astroglia and the Blood-Brain Barrier Astroglia Astroglia and the Blood-Brain Barrier Astroglia Microglia Microglia These are cells probably of mesodermal origin These mesodermal involved in phagocytic activity within the CNS. phagocytic CNS Oligodendrocytes Oligodendrocytes • involved in formation and maintenance of myelin in involved myelin the CNS CNS Ependymal Cells Ependymal These cells (derived from cells lining the neural tube) These neural form an epithelial sheet which covers the internal form epithelial cavities (ventricular system) of the brain and spinal cavities brain cord. cord Ependymal cells: line the ventricles of the brain and Ependymal the central canal of the spinal cord the Choroid plexus Choroid Invaginated folds of ependymal-like epithelial cells Invaginated folds ependymal-like responsible for the production of cerebrospinal fluid production cerebrospinal (CSF). Choroid plexus Choroid Choroid plexus Choroid Choroid plexus Choroid Myelin Production Myelin Myelin is a lipoprotein material which encases many Myelin lipoprotein high speed axons in both the CNS and PNS. high axons CNS PNS In the CNS, myelin is produced as an elaboration of In CNS myelin oligodendrocyte plasmalemma; oligodendrocyte In the PNS, the Schwann cell produces myelin. PNS the Schwann myelin Myelin Production Myelin In either case, portions of the ensheathing cell In surround the axon to be myelinated, and wrap surround axon wrap successively around the axon, forming multiple layers multiple of membrane and cytoplasm. membrane Subsequently, the cytoplasm is "squeezed" out of the cytoplasm out concentric layers, and the inner aspects of the plasmalemma come together and fuse. plasmalemma Myelin Production Myelin Myelin Production Myelin In the CNS, oligodendrocytes send out many processes In CNS oligodendrocytes many from the cell body, each of which is capable of each forming one segment of myelin one around an axon. around A Schwann cell only associates Schwann with one axon one a single oligodendrocyte single typically associates with many axons. axons * one oligodendrocyte forms myelin around a variable number number of axons (up to 40 or 50) axons Organization of Neural Tissue Organization CNS: Nerve cell bodies are found principally in the Nerve "gray" areas of the brain and spinal cord, areas Gray Matter Gray • contains cell bodies, dendrites contains and axons (mainly unmyelinated)* unmyelinated)* • neuronal cell bodies with similar neuronal anatomical connections and functions tend to be located together in groups nuclei (s. nuclei nucleus)* nucleus)* • neuronal cell bodies are also neuronal arranged in layers on the surface of cerebral hemispheres surface and cerebellum cerebral and cortex, cerebellar cortex cortex cerebellar cortex Organization of Neural Tissue Organization i.e., in the central gray regions i.e., of the spinal cord and medulla, spinal and in the cortical gray of the cerebellum cerebellum and telencephalic hemispheres and (the cerebral cortex). * cerebral ). Isolated functional groupings Isolated of nerve cell bodies in the CNS are called "nuclei." are ." Cerebral Cortex * Cerebral 1: molecular layer 2: external granular layer 3: external pyramidal layer 4: internal granular layer 5: internal pyramidal layer 6: multiform layer Cerebellar Cortex * Cerebellar molecular layer Purkinje cell layer granular layer Cerebellar Cortex Cerebellar Organization of Neural Tissue Organization PNS: Outside the brain & spinal cord, nerve cell bodies nerve are grouped into ganglia, i.e., ganglia i.e., dorsal root ganglia (sensory dorsal neurons) and sympathetic chain ganglia of the autonomic chain system. Organization of Neural Tissue Organization In the PNS, autonomic ganglia are also found In dispersed in visceral organs. dispersed visceral Ganglia may contain a few to over 50,000 cells. Organization of Neural Tissue Organization Large regions containing primarily myelinated axons Large myelinated are called "white matter" because of their glistening are because white appearance in fresh tissue. Organization of Neural Tissue Organization The white matter also The contains many cell bodies of oligodendroglia and astrocytes. astrocytes. White Matter White • arranged in tracts (fasciculi, arranged tracts lemnisci)* lemnisci • tract group of axons that have similar origin, termination and course and transmit the same information transmit Pathway Pathway A series of neurons designed to carry a specific type of series information from one site to another * information (e.g. from peripheral receptors to cerebral cortex, from (e.g. peripheral receptors to cerebellum) peripheral Decussation Decussation Each cerebral hemisphere perceives sensations from, Each and controls the movements of the contralateral side of the body major ascending (sensory) and descending (motor) pathways cross to opposite side within CNS (motor) thoracic -level thoracic Closed medulla Closed Open Medulla Open Caudal Pons Caudal Midbrain Midbrain Rostral midbrain midbrain ...
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This note was uploaded on 08/10/2011 for the course MED 102 taught by Professor Prof.smith during the Spring '11 term at Harvard.

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