9.21.2023 - Nervous System Student (1).pptx

Nervous System ID 767 – FALL 2023 MICHAEL BROWN, PT, DPT, SCS OBJECTIVES 1. Identify the components of a neuron 2. Identify the various cells found in nervous tissue 3. Describe the function of the cells of the nervous system 4. Describe the structure of a synapse and synaptic communication 5. Ide...

Nervous System ID 767 – FALL 2023 MICHAEL BROWN, PT, DPT, SCS OBJECTIVES 1. Identify the components of a neuron 2. Identify the various cells found in nervous tissue 3. Describe the function of the cells of the nervous system 4. Describe the structure of a synapse and synaptic communication 5. Identify histological features of different regions of the nervous system Nervous Tissue 1.Elongated cells with fine processes 2.Very small amount of extracellular matrix 3.Functions to transmit nerve impulses Nervous System Cells Neurons Glial Cells Neuron Functions 1.Respond to environmental changes (stimuli) 2.Receive, process, and send information 3.Uses bioelectrical and biochemical signaling Neuron Structure 1.Cell body (Soma) – information/metabolic center 2.Dendrites – short “branches” extending from the body 3.Axon – long projection Neuron Cell Body 1. Nucleus a) Large, euchromatic with prominent nucleolus (N) 2. Cytoplasm a) Polyribosomes b) Highly developed RER (ACTIVE) c) Nissl Substance (NS) d) Golgi e) Mitochondria 3. Cytoskeletal components a) Microtubules, actin, microfilaments, intermediate filaments Nissl Substance (NS) Large masses of free polysomes and RER Indicates high protein synthesis rate Basophilic Dendrites (D) 1. Short, numerous “branches” from the cell body a) Receive information from other neurons at synapses 2. Dendritic spines (DS) a) Tiny projections b) Typical site of synapse c) Dynamic – number of synapses changing constantly d) Key in neural plasticity Axon (A) 1. Axon Hillock (AH) a) Initial component connected to the cell body b) Beginning of action potential c) Site of impulse decision – Send an action potential or not 2. Axolemma – plasma membrane of the axon 3. Axoplasm – content (cytoplasm) of the axon a) No RER nor polyribosomes b) Mitochondria, microtubules, neurofilaments, actin filaments, transport vesicles Axonal Transport 1. Bidirectional transport of molecules within axons a) Anterograde – away from the cell body towards the synaptic terminal via Kinesin. b) Retrograde – away from the synaptic terminal towards the cell body via Anterogra de Retrograd e Neuron Morphology - Multipolar 1. Has 2 or more dendrites and 1 axon 2. Most abundant/common type 3. Examples: Motor neurons, interneurons, pyramidal cells of cerebral cortex, Neuron Morphology - Bipolar 1. 1 dendrite and 1 axon 2. Examples: sensory neurons of the retina, olfactory epithelium (CN I), and inner ear (CN VII) Unipolar / Pseudounipolar Neuron 1. Single process the splits into two branches (central and peripheral) a) Peripheral – longer b)Central – shorter 2. Examples: Sensory neurons – posterior spinal cord, cranial nerve ganglia, Neuron Morphology - Anaxonic 1. Many dendrites with no axon 2. No action potential 3. Function to regulate electrical charges of nearby neurons Synapses 1. Site where nerve impulses are transmitted from one neuron to another, or from neurons and other effector cells 2. Convert electrical signal into a chemical signal using mostly neurotransmitters Synapses - Types 1. Axosomatic – connection of the axon to the cell body of another neuron 2. Axodendritic – connection of the axon to the dendrite of another neuron 3. Axoaxonic – connection of the axon to the axon of another neuron Synapse Components 1. Presynaptic axon terminal (terminal bouton) a) Mitochondria, synaptic vesicles with neurotransmitters b) Sending the information 2. Postsynaptic axon terminal a) Receptors for the neurotransmitters b) Receives the information 3. Synaptic cleft a) Intercellular space that separates both terminals Nervous Organization 1. Central Nervous System (CNS) a) Cerebrum, cerebellum, spinal cord 2. Peripheral Nervous System (PNS) a) Cranial nerves b) Spinal nerves c) Ganglia and nerve endings Glial Cells (G) 1. “Glue” cells 2. Numerous and outnumber neurons (N) 10 to 1 3. Supporting function through several types 4. Communicate via gap junctions Np = Neuropil – fibrous intercellular network of processes Astrocytes (A) CNS 1. Contact neuronal cell bodies, dendrites, axons, synapses 2. Numerous cytoplasmic processes (end feet) 3. Functions: a) Blood brain barrier* b) Structural and metabolic support c) Growth factor secretion d) Homeostasis e) Injury scarring 4. Named: a) Protoplasmic astrocytes in gray matter b) Fibrous astrocytes in white matter C= capillary Oligodendrocytes - CNS 1. Synthesizes myelin 2. Surrounds the axons with a myelin sheath a) Increases speed of signal propagation or creates a faster action potential 3. Most common glial cell in the white matter (axons) 4. Cell appearance – condensed rounded nucleus, unstained cytoplasm (Golgi) Microglia - CNS 1. Found in gray and white matter 2. Provides immune defense a) Removes microbial invaders b) Secretes cytokines 3. Phagocytosis a) Remove debris / dead cells 4. Cells are small with many long, branched processes Ependymal Cells (E) - CNS 1. Columnar or cuboidal 2. Line the fluid-filled ventricles of the brain and the central canal of the spinal cord 3. Some have cilia apically to facilitate movement of cerebrospinal fluid 4. Some have long microvilli apically to aid in absorption 5. No basal lamina C = Central Canal Schwann Cells - PNS 1. Form myelin sheaths around peripheral nerves 2. Only a portion around one axon 3. Multiple Schwann cells may create the sheath for a single axon 4. Myelinated axons lead to faster action potential propagation Satellite Cells (S) - PNS 1. Form thin layer around each large neuronal cell body (N) in the ganglion of PNS a) Ganglion – group / bundle of neuron cell bodies; Ganglia is the plural form 2. Provide support with electrical insulation, nourishment, and microenvironment regulation L = lipofuscin Peripheral Nerve 1. Nerve fibers grouped into bundles 2. Axons and Schwann cells enclosed within layers of connective tissue a) Endoneurium – around axons b) Perineurium – around fascicles (groups of axons) c) Epineurium – around nerve (groups of fascicles) Peripheral Nerve E = Epineurium, N = Nerve fibers, A = Artery, V = Vessel P = Perineurium, En = Endoneurium Nerve Conduction Nerve Conduction SC = Schwa nn Cells Nerve Conduction A longitudinally oriented nerve shows one node of Ranvier (N) with the axon visible. Collagen of the sparse endoneurium (En), blue in this trichome stain, surrounds the Schwann cells and a capillary (C). At least on Schwann cell nucleus (S) is also clearly seen.” Questions? Tissue Examples White vs. Gray Matter A = Axon; G = Glia; N = Neuronal cell bodies Cerebrum P = Pyramidal neurons; A = Astrocytes Cerebellum M = Medulla; ML = Molecular Layers; GL = Granular Layers; P = Purkinje neuron Choroid Plexus CP = Choroid plexus; V = Ventricle; C = capillaries; E = Ependymal cells Spinal Cord C = Central Canal; A = Anterior horn; P = Posterior horn Ganglion (G) G = Ganglion, F = Nerve Fibers, C = Connective tissue capsule Peripheral Nerves A = Axon; C = Capillary; P = Perineurium; S = Schwann cells; F = Fibroblasts; N = Nerve; E = Endoneurium References Felten DL, O'Banion MK, Maida MS, et al. Netter's Atlas of Neuroscience. Fourth ed. Philadelphia, PA: Elsevier; 2022. Accessed September 14, 2023. https://histologyguide.org/index.html Nerve Tissue & the Nervous System. In: Mescher AL. eds. Junqueira's Basic Histology Text and Atlas, 16e. McGraw Hill; 2021. Accessed September 14, 2023. https://accessmedicine.mhmedical.com/content.aspx?bookid=304 7&sectionid=255120935