Histology Nervous System 2024 PDF

XY2141. Histology. Nervous system Dr Viktoriia Yerokhina, Lecturer in Medical Sciences [email protected]  LEARNING OUTCOMES HiST.09 Nervous tissue, nervous system (please, revise Lecture ‘Nervous tissue’ from XY1040. HIST.09.01 - Describe...

XY2141. Histology. Nervous system Dr Viktoriia Yerokhina, Lecturer in Medical Sciences [email protected]  LEARNING OUTCOMES HiST.09 Nervous tissue, nervous system (please, revise Lecture ‘Nervous tissue’ from XY1040. HIST.09.01 - Describe the anatomy of a typical neuron and a synapse HIST.09.02 - List and describe the main structural types of neurons HIST.09.03 - Explain the main differences between dendrites and axons HIST.09.04 - List and describe the anatomy and functions of the different types of glial cells HIST.09.05 - Explain the structure and function of the blood-brain diffusion barrier (BBB) HIST.09.06 - Describe how a myelin sheath is formed in the central and peripheral nervous systems and explain the function of the sheath HIST.09.07 - Describe the anatomy of a nerve, including its connective tissue components (epineurium, perineurium, endoneurium) HIST.09.08 - Describe the process of Wallerian degeneration and its functional significance HIST.09.09 - Outline the histological differences between Cerebrum, Cerebellum, and Spinal Cord. HIST.09.10 - Prepare a diagram of the organization of the meninges. HIST.09.11 - Explain the histological differences seen in dorsal root ganglia and sympathetic ganglia.  OVERVIEW Nervous system (NS) enables the body to respond to continuous changes in its external and internal environment. NS controls and integrates the functional activities of organs and organ systems. Anatomically NS is divided into: Central nervous system (CNS) - spinal cord and brain. Peripheral nervous system (PNS) - cranial, spinal peripheral nerves and ganglia. Nervous tissue (NT) is the main component of the NS, which regulates and controls body functions. NT is a specialised tissue that shows properties of irritability and conductivity. Nervous system by Leonardo da Vinci's drawing. 15 th century  CLASSIFICATION OF NERVOUS SYSTEM (NS) Flowchart: Classification of nervous system  ANATOMICAL ORGANIZATION OF THE NS Two main divisions: Central Nervous System (CNS) Consists of the brain and spinal cord with tracts and nuclei Nucleus = collection of nerve cell bodies in the CNS. Tract = bundle of nerve fibers within the CNS Peripheral Nervous System (PNS) Consists of ganglia, cranial nerves (12 pairs), spinal nerves (31 pairs) and peripheral receptors Ganglia = contain the bodies of the neurons located outside the CNS, glial cells and a fibrous capsule on the surface Nerve = made up of nerve fiber fascicles and their connective tissue sheaths.  PERIPHERAL NERVE In the PNS the nerve fibers are grouped in bundles to form the nerves. Individual nerve fibers are held together by CT organized into: Endoneurium is a thin layer of LCT, surrounding each individual nerve fiber; Perineurium surrounds each bundle of nerve fibers; Epineurium includes the irregular DCT that surrounds a peripheral nerve. Nerves establish communication between brain and spinal cord centers and the sense organs and effectors (muscles, glands, etc.). STRUCTURE OF PERIPHERAL NERVE TRANSVERSE SECTION OF A PERIPHERAL NERVE (Ladewig trichrome stain, 150x magnification)  NEURONAL PLASTICITY AND REGENERATION o After completing the maturation of the NS during childhood, the regenerative function of the NS is very limited, especially in the CNS, due to the high degree of specialization and differentiation. o Due to their very active metabolism, NS organs are highly dependent on oxidative metabolism and on the supply of oxygen and nutrients through the bloodstream. o In case of trauma or insufficient blood supply, the neurons are usually the first cells that begin to die within 4–5 minutes. o Dead neurons are generally replaced by the proliferation of glia in the CNS → glial scar. o However, if the damaged organ recovers, with sufficient stimulation and training some areas of the brain appear to have the ability to reprogram themselves, engage other circuits and networks, and replace at least part of the function of the damaged areas, which is referred to as neural plasticity. DAMAGE, REGENERATION AND DEGENERATION OF THE PERIPHERAL NERVE AXON  NEURAL INJURY CLASSIFICATION (BASED ON THE DEGREE OF AN INJURY) 1. Neurapraxia – reversible defect in neural compression – regeneration possible within hours to 2 weeks – axons are not interrupted, no Wallerian degeneration 2. Axonotmesis – axons are interrupted, but the nerve sheaths are still uninterrupted – Wallerian degeneration occurs, but the nerve regenerates spontaneously 3. Neurotmesis – anatomical interruption of the whole nerve, spontaneous – regeneration is not possible – necessary to suture the nerve neurosurgically.  GANGLIA Aggregations of cell bodies of neurons located outside the CNS. 2 types of ganglia - sensory and autonomic. Sensory ganglia present in three cranial nerves (CNV, IX and X) and the posterior roots of the spinal nerves. Autonomic ganglia – their neurons transmit visceromotor information (sympathetic and parasympathetic).  AUTONOMIC GANGLIA a) Sympathetic ganglia – are localised closely to the spinal cord as: 1. Paravertebral ganglia (sympathetic trunk ganglia) 2. Prevertebral ganglia – in front of the aorta (coeliac ganglia, aorticorenal ganglia, superior and inferior mesenteric ganglion) 3. Neurons of the adrenal gland medulla – are also sympathetic post- ganglionic neurons adrenal medulla is developmentally a sympathetic ganglion b) Parasympathetic ganglia Location – ganglia are sometimes isolated in the vicinity of innervated organs or in the wall of organs (intramural ganglia). AUTONOMIC GANGLIA: DIFFERENCES  SENSORY GANGLIA Sensory ganglia are present just outside the CNS. Neurons of sensory ganglia carry impulses toward CNS. Examples: Dorsal root ganglia of spinal nerves Sensory ganglia of cranial nerves: trigeminal, facial, vestibulocochlear, glossopharyngeal, and vagus nerve  SENSORY GANGLIA Receive somatosensory information (proprioception, pressure, pain, temperature) and viscerosensory information (blood pressure and blood pH, internal organ tone, etc.) Sensory ganglia contain: Pseudounipolar neurons – in all sensory and in most special sensory ganglia Bipolar neurons – neurons collecting sensations from sensory cells in the cochlear and vestibular gaglion (CNVIII).  SPINAL, OR DORSAL ROOT GANGLION Each spinal ganglion has a thin СT capsule within which the nerve cells are peripherally placed. Each ganglion cell is surrounded by a single layer of satellite cells. SPINAL, OR DORSAL ROOT GANGLION  ORGANIZATION OF THE CNS CNS (brain, spinal cord) contain regions of: White matter myelinated axons and the myelin-producing oligodendrocytes. Grey matter neuronal cell bodies, dendrites, initial unmyelinated portions of axons and glial cells. Neuropil – part of the grey matter of the brain consisting of the projections of neurons and neuroglia – fills the space between the bodies of neurons and vessels Grey matter located at the surface of the cerebrum and cerebellum - cortex. Aggregates of neuronal cell bodies forming islands of grey matter - nuclei. Central canal – central spinal canal is in the middle of the grey matter.  STRUCTURE OF THE SC White matter is mainly myelinated fibers and the myelin- producing oligodendrocytes. Gray matter is cell bodies, unmyelinated axons and neuroglia. ! Spinal cord: grey matter is central white matter is peripheral.  HORNS OF SC Grey matter is subdivided into horns. Anterior (ventral) horns - short, broad, directed forwards; contain large multipolar somatomotor neurons Posterior (dorsal) horns - narrow, elongated directed backwards; contain smallmultipolar somatosensory and interneurons. Lateral horns (in T1 to L2 segments) visceromotor neurons in the segments C8-L3 and S2-S4. Nucleus = collection of nerve cell bodies in the CNS.  WHITE MATTER Divided into six columns (funiculi) containing tracts: Ascending tracts relay information from the spinal cord to the brain; Descending tracts carry information from the brain to the spinal cord.  CEREBELLUM Cerebellum (small brain, in Latin) is highly folded to accommodate millions of neurons in a small area. Cerebellar cortex is responsible for maintaining balance and equilibrium, muscle tone, and coordination of skeletal muscles. CEREBELLUM  CEREBELLUM External structure 1. Cerebellar vermis – worm, unpaired central part 2. Cerebellar hemispheres – geminate cerebellar hemispheres 2.1 Cerebellar lobes – 3 lobes 2.2 Cerebellar lobules – 10 lobules 2.3 Cerebellar folia – layers (gyri) of the cerebellar cortex 2.4 Cerebellar fissures – grooves separate the lobes and sheets  CEREBELLUM Internal structure 3. Grey matter 3.1 Cerebellar cortex – cortex of cerebellar hemispheres and vermis 3.2 Cerebellar nuclei – nuclei within the cerebellum 4. White matter 4.1 Medullar cerebellar body – cerebellar medulla consists mostly of myelinated fibers.  CEREBELLAR CORTEX Layers: 1. Outer molecular layer - surface molecular layer 2. Middle Purkinje cell layer - narrow medium layer of Purkinje cells 3. Inner granule cell layer - deepest granular layer CEREBELLUM CEREBELLUM Purkinje cells  CEREBELLAR MEDULLA Composed of: Climbing fibers, mossy fibers, Purkinje cell axons, and the deep cerebellar nuclei Mossy fibers: afferent axons from the cerebral cortex, pons, spinal cord, and vestibular nuclei to the cerebellum. Terminate on granule cells → send excitatory stimuli to the Purkinje cells. Climbing fibers: afferent axons from the inferior olivary nuclei of the medulla → terminate on Purkinje cells Four deep cerebellar nuclei (from lateral to medial): dentate, emboliform, globose, and fastigial nucleus.  CEREBELLAR GLOMERULUS Mossy fibers end as dilated terminal - rosette. This dilated terminal is surrounded by dendrites of granule cells and axons of Golgi cells. Mossy fiber terminal with surrounding dendrites and axons form light-stained areas in granular layer. These areas are called glomeruli of cerebellum.  CEREBELLAR NUCLEI Embedded within the central core of white matter there are masses of grey matter that constitute the cerebellar nuclei (dentatus, emboliformis, globosus, and fastigius). Mnemonic: Don't Eat Greasy Food (Dentate, Embolform, Globose, Fastigial)  CEREBRUM Cerebral hemispheres consist of a convoluted cortex of grey matter.  CEREBRAL CORTEX Cerebral cortex cytoarchitectonic: i. Molecular layer (horizontal cells of Cajal, their Axons of these cells form tangential plexus) ii. External granular layer (small pyramidal cells and stellate (granular) cells) iii. External pyramidal layer (medium-sized pyramidal cells) iv. Internal granular layer (densely packed stellate and pyramidal celts). v. Internal pyramidal (ganglionic) layer (large pyramidal cells, and in the motor cortex the giant pyramidal neurons of Betz). vi. Multiform layer consists of cells of various shapes. CEREBRAL CORTEX  TYPES OF CEREBRAL CORTEX In the certain areas of a cerebral cortex connected to execution of different functions, development of those or its other layers dominates. Agranular type of cerebral cortex is characterized by the greatest development of III, V and VI layer at weak development of II and IV (granular) layers (motor centers). Granular type of cerebral cortex is characterized by weak development of the layers containing pyramidal cells (III, V) at greatest development of granular (II and IV) layers (sensory centers). MENINGES  MENINGES https://next.amboss.com/us/article/WK0P2S?q=cerebrum #Xqc9CW0 MCQ FOR SELF-CONTROL https://forms.gle/fsB9t7bFL5EQfmS7A References