Histology of the Nervous System – Part 2 Summer 2024 PDF

HISTOLOGY OF THE NERVOUS SYSTEM – PART 2 S 2024 María José Navarrete Talloni, DVM, MPVM PhD...

HISTOLOGY OF THE NERVOUS SYSTEM – PART 2 S 2024 María José Navarrete Talloni, DVM, MPVM PhD Department of Biomedical Sciences, RUSVM Disclaimer: Images and information in this presentation come from different sources including Drs. I. Irimescu, O. Illanes, M. Smith, M. Zibrin, P. Hanna and H. Bogdanovic‘s notes. Dellmann’s and Junqueira’s histology books, P. Hyttel et al. and K. Moore embryology books. This presentation is for teaching purposes only, please do not distribute. Part 2 Outline Ventricular system Choroid plexus and CSF Cerebellum structure Nuclei in CNS Spinal cord PNS – nerves & ganglia  Ventricular System Ependymal cells line the inside of a system of ventricles in the CNS, which also communicates with the subarachnoid space. Both circulate Cerebrospinal fluid (CSF).  Ependymal Cells Ependymal cells form an epithelium that lines ventricular cavities within the brain and the central canal of the spinal cord. The cells are typically cuboidal or columnar with numerous motile cilia on their apical surfaces. Central canal ependymal cells have cilia to help the circulation of the CSF. Spinal cord central canal  Ependyma has an important barrier function that protects neural tissue from potentially harmful substances by mechanisms that are still incompletely understood. Ependymal cells have only limited regenerative capacity and thus typically do not undergo mitotic proliferation. Ependymal cells (simple columnar epithelium) line the central canal of a canine spinal cord. Motile cilia projecting into the lumen of the central canal are evident (arrows). HE. Dellmann's Textbook of Veterinary Histology, 6th Edition. Cerebrospinal Fluid (CSF) Produced in the choroid plexus by specific modified ependymal cell. Produced and MUST BE drained away at constant rate. The total volume of CSF is formed and renewed 3X times a day. Can be sampled for clinical examination. Roles: Medium for filtration system facilitates the removal of metabolic waste from the brain and exchange of biomolecules into and out of the brain Helps maintain the delicate extracellular environment required by the brain to function optimally (homeostasis) Cushions the CNS in case of impacts  Choroid Plexus * CSF is formed as plasma filtered from the blood through the choroid plexus ependymal cells. Produced by a mechanism that involves active secretion of Na+ into the ventricles water follows the resulting osmotic gradient. *A plexus (from the Latin for "braid") is a branching network of the vessels or nerves.  Choroid Plexus The choroid plexus consists of a layer of cuboidal epithelial cells surrounding a core of capillaries and loose connective tissue. The epithelium specific modified ependymal cells, that have microvilli and are linked to adjacent cells by tight junctions (unlike the ependymal). These tight junctions prevent the majority of substances from crossing the cell layer into the cerebrospinal fluid (CSF) acts as a blood–CSF barrier. Choroid plexus  The choroid plexus folds into many villi around each capillary, creating frond-like processes that project into the ventricles. Choroid plexus 4th ventricle, cat (N61-13RUSVM). O.Illanes The villi, along with a brush border of microvilli, greatly increases the surface area of the choroid plexus. CSF Circulation CSF in the subarachnoid space is resorbed back into the venous circulation  Choroid Plexus There are four choroid plexuses in the brain, one in each of the ventricles It is present in all parts of the ventricular system (except cerebral aqueduct, frontal horn and occipital horn of the lateral ventricles). Horse brain. Choroid plexuses of the lateral ventricles. UCVM-Illanes  Blood-Cerebrospinal Fluid Barrier (BCSFB) A pair of membranes separate blood from CSF and CSF from brain tissue The blood–CSF boundary at the choroid plexus is a membrane composed of the ependymal cells and tight junctions that link them. (Note choroid plexus capillaries are fenestrated and have no tight junctions.) The brain–CSF boundary is the arachnoid membrane, which envelops the surface of the brain Functions: Prevents the passage of most blood-borne substances into the brain. Facilitates the transport of different substances into the brain due to the distinct structural characteristics between the two barrier systems (for a number of substances, the BCSFB is the primary site of entry into brain tissue. Facilitates the removal of brain metabolites and metabolic waste into the blood Modulates the entry of leukocytes from the blood into the central nervous system. The choroid plexus cells secrete cytokines recruit monocyte-derived macrophages, among other cells, to the brain. This cellular trafficking has implications both in normal brain homeostasis as in neuroinflammatory processes BCSFB and the brain blood barrier (BBB) have similar functions, but must NOT be confused!  Classification of capillaries A. Continuous: Most common. Found in muscle, brain, bone, lung, etc. E.g. Blood-brain and blood-testis barriers. B. Fenestrated (gaps 10-100 nm): In tissues with substantial fluid exchange, e.g.: intestinal villi, choroid plexus, ciliary process, glomerular capillaries. C. Discontinuous (Sinusoidal): Hepatic and splenic sinusoids > large molecules can exit (RBC in the spleen). CEREBELLUM Gray matter WITH ARBOR VITAE Folia Cortex cerebelli – grey matter 1. Molecular layer – basket cellsouter 3 2. Ganglionic cell layer – Purkinje 1 cells 3. Granular cell layer – granule cells 2 in stratum granulosum 4. White matter core myelinated nerve fibers Note: the Cerebral Cortex is even more complex, organized in 6 layers of grey matter. White matter Jan Evangelista (1787 –1869) was a Czech anatomist and physiologist. In 1839, he coined the term 'protoplasm' for the fluid substance of a cell. He is best known for his 1837 discovery of Purkinje cells, large neurons with many branching dendrites found in the cerebellum. He is also known for his discovery in 1839 of Purkinje fibers, the fibrous tissue that conducts electrical impulses from the atrioventricular node to all parts of the ventricles of the heart.  1 Gray matter 2 3 Cerebellum, dog, normal, OI-UCVM 1. 2. Molecular layer – basket cells Ganglionic cell layer – Purkinje cells White matter 3. Granular cell layer  CEREBELLUM 3 1. Molecular layer 2. Ganglionic cell layer 3. Granular cell layer Gray matter 1 2 Cat, cerebellar folia (N61-13). RUSVM, O. Illanes.  The fetal cerebellum and the cerebellum of the new born has an additional exterior cortical lamina (arrowed – the external granular cell layer). These cells will populate the internal granular cell layer during early postnatal development. a White matter 1. External granular cell layer am 2. Molecular layer 3. Ganglionic cell layer 4. Granular cell layer I in 11 2 3 4 am Mar 1 Nucleus in CNS A cluster of neurons in the CNS, located deep within the cerebral hemispheres and brainstem, performing a common function. Examples:  SPINAL CORD In cross sections of the spinal cord, white matter is peripheral and gray matter is central, assuming the shape of an H. In the horizontal bar of this H is an opening, the central canal, which is a remnant of the lumen of the embryonic neural tube. The central canal is lined with ependymal cells.  SPINAL CORD The gray matter of the legs of the H forms the ventral horns (anterior horns). These contain bones Dorsal Dorsalhorns motor neurons whose axons make up the ventral roots of the spinal nerves. Gray matter also forms the Is T.si arms of the H, called dorsal horns (posterior horns), which receive sensory fibers from neurons in the spinal ganglia (dorsal roots) Nerve Tissue & Nervous System Assoc. Prof Dr. Karim Al-Jashamy IMS/MSU 2010  SPINAL CORD Spinal cord neurons are large and multipolar, especially in the ventral horns (anterior horns), where large motorneurons are found. From Histology@Yale Spinal cord – Transverse section  Nervous System Nervous System Central nervous Peripheral nervous system (CNS) system (PNS) Brain Spinal cord Autonomic nervous Somatic system (ANS) nervous system Parasympathetic division Sympathetic division  PERIPHERAL NERVOUS SYSTEM (PNS) Functional PNS Divisions A. Somatic Nervous System: a one neuron system that innervates (voluntary) skeletal muscle or somatosensory receptors of the skin, muscle & joints. B. Autonomic Nervous System: a two neuron visceral efferent system, that innervates cardiac and smooth muscle and glands. It is involuntary and has two major subdivisions: 1) Sympathetic (thoracolumbar) 2) Parasympathetic (craniosacral) A. Somatic Nervous System B. Autonomic Nervous System  NERVES Collections of AXONS/DENDRITES outside CNS. Consist of axons, dendrites, blood vessels, glial cells, and connective tissue (CT) investments: Endoneurium, perineurium, epineurium Cells present in a nerve: no Endothelial cells, fibroblasts, Schwann cells. GANGLIA Collections of NEURONAL CELL BODIES and processes found outside the CNS. Cells of a ganglion: Neurons, neuroglial cells (amphicytes), Schwann cells, endothelial cells. Axons are also present. Two types of Ganglia: SENSORY (craniospinal) AUTONOMIC Nerve Structure Epineurium M m hmfyfk kmmrm x Endoneuriu Perineurium m My www.eoes tissue connective Peripheral nerve, nerve fascicle in cross section, RUSVM teaching specimen, H&E. O. Illanes  Glial cells of the PNS Schwann cells envelope nerve fibers in PNS wind repeatedly around a nerve fiber produces a myelin sheath similar to the ones produced by oligodendrocytes in CNS assist in the regeneration of damaged fibers Satellite glial cells (amphicytes) surround the neurosomas in ganglia of the PNS provide electrical insulation around the soma regulate the chemical environment of the neurons  Schwann cells Myelin sheath – an insulating layer around a nerve fiber formed by oligodendrocytes in CNS and Schwann cells in PNS consists of the plasma membrane of glial cells 20% protein and 80 % lipid Myelination – production of the myelin sheath begins the 14th week of fetal development te species proceeds rapidly during infancy depending completed in late adolescence of dietary fat is important to nervous system development Plastic embedded, TS of peripheral nerve. Osmium-fixed preparation. Note good preservation of myelin sheaths, dog – O.Illanes Normal myelinated nerve fiber: Which axonal and Schwann cell organellescan you see? Note collagen fibers in the endoneurium TEM – myelin sheath Peripheral nerve, cat F22660-99 AVC, longitudinal section, H&E, O. Illanes Normal myelinated nerve fibers HEALTHY nerve NERVE fibre myelin sheath A: Normal; B: Wallerian degeneration; C: segmental demyelination; D: Axonal degeneration with 2ry demyelination Neuronal or axonal injury Satelite cells/Amphicytes Neuronal cell body Autonomic ganglion Dorsal root ganglion Small intestines, 5x MYENTERIC PLEXUS Situated between the inner and outer longitudinal layers of the tunica muscularis This structure helps to control SM hocent peristaltic movement of the gastrointestinal tract GItruct 40x 1000x SUMMARY Different cells from the CNS