ANAT2241 Nervous System Lecture Slides 2022 PDF

ANAT2241 Histology: Basic & Systematic Nervous System: Central Nervous System (CNS) & Peripheral Nervous System (PNS) Dr. Reza Shirazi Department of Anatomy, School of Medical Sciences Faculty of Medicine & Health, UNSW Sydney [email protected] Image by Dr John Abramyan, University of Mi...

ANAT2241 Histology: Basic & Systematic Nervous System: Central Nervous System (CNS) & Peripheral Nervous System (PNS) Dr. Reza Shirazi Department of Anatomy, School of Medical Sciences Faculty of Medicine & Health, UNSW Sydney [email protected] Image by Dr John Abramyan, University of Michigan Resources Recommended reading: Textbook chapter (Wheather's online): Nervous System Textbook chapter (Junqueira’s Basic Histology: Text and Atlas, 15e online): CNS & PNS Nervous System Online Support Page University of Michigan Histology and Virtual Microscopy Learning Resources Chapman Histology https://www.youtube.com/channel/UCvSvCkHjCbHn8aGd6OPno_A/featured Learning Objectives 1. To understand the function and location of CNS and PNS 2. To understand the basic components of CNS and PNS 3. To understand the structure of cerebral and cerebellar cortex 4. To understand the composition of white and grey matter 5. To understand the various types of ganglia Nervous Tissue and Nervous System Nervous tissue: 1- Cells: I. Nerve cells/Neurons II. Supporting cells/Neuroglial cells a. Astrocytes b. Oligodendrocytes c. Microglia d. Ependymal cells e. Schwann cells f. Satellite cells 2- Extracellular matrix (ECM) o Very small amount Nervous system: o Nervous tissue o Associated tissues (meninges, blood vessels, connective tissue, CSF, …) 1- CNS 2- PNS (X200; H&E staining) • N: neuronal cell body • G: glial cell • Np: neuropil (X200; Gold chloride and hematoxylin staining) Central Nervous System (CNS) CNS: o Brain • Cerebrum • Cerebellum • Brain stem o Spinal cord Protectors of CNS: o Skull and vertebral column o Connective tissue (Meninges) o Cerebrospinal fluid (CSF) Glial Cells Glial cells present in CNS: 1. Astrocytes 2. Oligodendrocytes 3. Microglia 4. Ependymal cells Glial cells present in PNS: 1. Schwann cells 2. Satellite cells Central Nervous System (CNS) White matter Grey matter Structural features (according to differential distribution of lipid-rich myelin): o White matter: • Myelinated axon (tracts) • Oligodendrocytes (myelin-producing cells) • Astrocytes • Microglia o Grey matter • Neuronal cell bodies • Dendrites • Astrocytes • Microglia • Where most synapses occur (X400; H&E staining; Spinal cord) • G: glial cells • N: neuronal cell bodies • A: axons White Matter vs. Grey Matter Location of white matter: o Inner part of the brain (medulla) o Outer part of spinal cord Location of grey matter / neuronal cell bodies: o Outer part of the brain (cerebral cortex) o Inner part of the spinal cord o Islands of grey matter in inner part of the brain (nuclei) o Complexes of neuronal cell bodies associated with PNS (ganglia) o o Retina Olfactory epithelium Cerebral Cortex Made up of six layers of neurons with different sizes and shapes: o Pyramidal neurons • Integration of sensory information • Initiation of voluntary motor responses (X200; H&E staining; Cerebral cortex) • P: pyramidal neurons (X200; Silver staining; Cerebral cortex) • P: pyramidal neurons • A: protoplasmic astrocytes Cerebellar Cortex (stain: Luxol fast blue, H&E; Cerebellum [cat]) Cerebellar Cortex o o Coordinates muscular activity throughout the body Organized with three layers (X6; Cresyl violet; Cerebrum) • ML: molecular layer • P: Purkinje neurons • GL: granular layer • M: medulla (X20; H&E; Cerebrum) (X40; H&E; Cerebellar cortex) (X40; Silver; Cerebellar cortex) Cerebellar Cortex (X380; Stain: double-fluorescent–labelling methods; Cerebellum) Spinal Cord (Center X5, a, b X100; All silver-stained; Spinal cord) White matter: peripheral Grey matter: deeper H-shaped mass o Anterior horns: • Cell bodies of very large motor neurons whose axons make up the ventral roots of spinal nerves • Astrocytes o Posterior horns: • Neurons which receive sensory fibers from neurons in the spinal (dorsal root) ganglia • Oligodendrocytes Grey commissure o Central canal • Lined by ependymal cells • Contains CSF White commissure (X200; H&E; Anterior horn) • N: motor neurons • P: Purkinje neurons • GL: granular (X200; H&E; White commissure) • T: tracts Meninges Three membranes of connective tissue 1- Dura mater 2- Arachnoid mater 3- Pia mater (X100; H&E; an area near the anterior median fissure of spinal cord) • D: dura mater SD: subdural space • A: arachnoid SA: subarachnoid space • T: trabeculae BV: blood vessels • P: pia mater WM: white matter Dura Mater o Dense irregular connective tissue o In brain, organized as: • Outer periosteal layer continuous with the periosteum of the skull • Inner meningeal layer (dura mater proper) ü Dural venous sinuses o In spinal cord, organized as: • One meningeal layer ü Epidural space Arachnoid (Mater) Avascular connective tissue Two components: (1) A sheet of connective tissue • In contact with the dura mater (2) A system of loosely arranged trabeculae • Composed of collagen and fibroblasts • Continuous with the underlying pia mater layer Subarachnoid space Arachnoid villi o Penetration of dura mater by arachnoid o Protrusion into blood-filled dural venous sinuses o Sites for absorption of CSF into the blood of the venous sinuses Pia mater o Consists of flattened, mesenchymally derived cells closely applied to the entire surface of the CNS tissue o Separated from the neural elements by the glial limiting membrane, or glia limitans: • Very thin superficial layer of astrocytic processes Blood-Brain Barrier (BBB) A functional barrier that allows much tighter control than that in most tissues over the passage of substances moving from blood into the CNS tissue Structural component of the BBB: 1- Capillary endothelium • Occluding junctions • Little or no transcytosis activity • Surrounded by the basement membrane 2- Limiting layer of perivascular astrocytic feet • Envelops the basement membrane of capillaries BBB absent in: 1- Hypothalamus where plasma components are monitored 2- Posterior pituitary 3- Choroid plexus Choroid Plexus Highly vascular tissue, elaborately folded and projecting into the large ventricles of the brain o Thin layer of well-vascularized pia mater covered by cuboidal ependymal cells Location of choroid plexus: o Roof of the third ventricle o Roof of fourth ventricle o Parts of the two lateral ventricular wall Function of choroid plexus: o Production of CSF Function of CSF: o Providing the ions required for CNS neuronal activity o Serving to help absorb mechanical shocks in arachnoid (X12; Kluver-Barrera stain; choroid plexus) (X150; choroid plexus) Peripheral Nervous System (PNS) Components: 1- Nerves o Cranial nerves o Spinal nerves 2- Ganglia o Sensory Ganglia o Autonomic Ganglia • Sympathetic ganglia • Parasympathetic ganglia Peripheral Nerves Bundles of nerve fibers (axons) individually surrounded by Schwann cells and connective tissue Nerve fibers: o Containing axons enclosed within sheaths of glial cells (Schwann cells/neurolemmocytes ) specialized to facilitate axonal function • Myelinated fibers • Unmyelinated fibers (X640; toluidine blue stain; peripheral nerve) • Epi: epineurium • A: axon • SL: Schmidt-Lanterman cleft • NR: node of Ranvier Myelinated Fibers Axons engulfed along their length by a series of Schwann cells/neurolemmocytes Process of myelination: o Fusion of the plasma membrane of each covering Schwann cell with itself at an area termed the mesaxon o Continuation of wide, flattened process of the cell to extend itself, moving circumferentially around the axon many times o Union of the multiple layers of Schwann cell membrane as a thick myelin sheath Function of myelin sheath: o Insulate axons o Maintain a constant ionic microenvironment most suitable for action potentials Myelinated Fibers Myelin clefts / Schmidt-Lanterman clefts: o Periodic separation of cytoplasmic surfaces of the Schwann cell membrane along the myelin sheath o Allow transient movement of cytoplasm for membrane maintenance Nodes of Ranvier / Nodal gaps o Axon is only partially covered by interdigitating Schwann cell processes Internodal segment Myelinated Fibers (X400; Mallory trichome; peripheral nerve) • N: node of Ranvier • En: endoneurium • C: capillary Unmyelinated Fibers o Only smallest diameter axons of peripheral nerves are still enveloped within simple folds of Schwann cells o Portions of many axons with small diameters enclosed by Schwann cells • No nodes of Ranvier • No saltatory conduction o No multiple wrapping to form a myelin sheath Nerve Organization (X140; H&E) Endoneurium o Immediately around the external lamina of the Schwann cells o Consisting of reticular fibers, scattered fibroblasts, and capillaries Perineurium o Groups of axons with Schwann cells and endoneurium are bundled together as fascicles by a sleeve of perineurium o Containing flat fibrocytes with their edges sealed together by tight junctions • Blood-nerve barrier Epineurium o Externally, peripheral nerves have a dense, irregular fibrous coat (X200; PT) (X450) Nerve Organization (X400; PT) (X200; H&E) (X200; H&E) (X300; H&E) (X1200) Ganglia Ovoid structures containing neuronal cell bodies and their surrounding glial satellite cells supported by delicate connective tissue and surrounded by a denser capsule Serve as relay stations to transmit nerve impulses • At least one nerve enters and another exits from each ganglion Sensory Ganglia (X56; Kluver-Barrera stain) Receive afferent impulses that go to the CNS associated with both cranial nerves (cranial ganglia) and the dorsal roots of the spinal nerves (spinal ganglia) The large neuronal cell bodies (pseudounipolar neurons) of ganglia are associated with thin, sheetlike extensions of small glial satellite cells Sensory ganglia are supported by a distinct connective tissue capsule (X400; H&E) Autonomic Ganglia Small bulbous dilations in autonomic nerves, usually with multipolar neurons (X160; silver and H&E stain; Human; sympathetic ganglion) (X500; silver and H&E stain; Human; sympathetic ganglion) Sensory G. vs Autonomic (X160; H&E stain; Cat; dorsal root ganglion) (X350; H&E stain; Cat; dorsal root ganglion) (X160; silver and H&E stain; Human; sympathetic ganglion) (X500; silver and H&E stain; Human; sympathetic ganglion)