Histology of Nervous Tissue L7 PDF

HISTOLOGY OF NERVOUS TISSUES Dr Nurul Raudzah Adib Ridzuan General Module MED101 Session 2023/2024 24th October 2023 Specific learning outcomes From this lecture, the students should be able to understand and: 1. Describe the classifi...

HISTOLOGY OF NERVOUS TISSUES Dr Nurul Raudzah Adib Ridzuan General Module MED101 Session 2023/2024 24th October 2023 Specific learning outcomes From this lecture, the students should be able to understand and: 1. Describe the classification of the nerve tissue 2. Describe the general structure and different types of neuron 3. Describe the structure and different types of supporting cells (glia) 4. Describe the classification of receptors 2  Introduction: TISSUES OF THE BODY 3 BASIC TISSUES  Nervous tissues Receive stimuli from both the internal and external environments which are then analysed & integrated to produce appropriate, coordinated responses in various effector organs NEURONES NEUROGLIAL CELLS Functional unit of the Supporting cells of the nervous system nervous system 4  NEURONES NEUROGLIAL CELLS Functional unit of the nervous Supporting cells of the nervous system system 5 6  Neurone ~ characteristics Possesses many processes Excitability / conductivity Reception of stimuli Conduction of impulses The nerve impulse ~ ‘The electrical changes’ occurring in a neuron when it is stimulated that can spread and conduct along the neurites 7 NEURONE ~ CHARACTERISTICS Reaction to injury Neurons are completely incapable of cell division and replacement in the event of cell death DO NOT undergo mitosis Axons (when severed) can regenerate 8 9 Structure of a Neurone 2 1 1 Cell body / perikaryon 2 (cytoplasm) / soma Part of the neuron that contain the nucleus, nucleolus, organelles (highly metabolically active) 2 Neurites / Processes 3 Dendrites Axons 3 Terminal button Small swellings 10 11  Cell body of a neurone Trophic centre; metabolic site Receptive to stimuli Nissl bodies (clumps of RER + ribosomes) 12  CELL BODY OF A NEURONE - of all neurons are located in the CNS, except: Cell bodies of primary sensory neurons Terminal effector neurons of ANS → Ganglia 13  Neuron ~ DENDRITES Short extensions of cell body Highly branched, tapering processes which either end in specialised sensory receptors (as in primary sensory neurones) or form synapses with neighbouring neurones from which they receive stimuli Multiple afferent processes Becomes thinner as they extend from cell body Contain Nissl substances (RER) 14 NEURON ~ AXON Single efferent process Transmit impulses (away from cell body) → target cells Arising from cone-shaped portion of cell body (axon hillock) (no Nissl granules); tubular; uniform diameter diameter : rate of impulse conduction Conduction is away from cell body 15  Classifications of neurones A: Configuration of neurites (number of processes) B: Functional role C: Cell size D: Neurotransmitter released 16 A: Configuration of neurites (number of processes) 17 a)Bipolar neurons Special sensory function One axon and one single dendrite Act as receptor neurones (smell, sight, balance) Eg: cochlea, vestibular ganglia, retina, olfactory mucosa 18 b) Pseudo-unipolar neurones General sensory function A single process that divides into 2 branches Eg: dorsal root ganglia 19 c)Multipolar neurones Most abundant More than TWO cell processes, one process being the axon and the other dendrites Ex: motor neurones of grey matter of spinal cord, pyramidal cells of cerebral cortex, Purkinje cells of cerebellar cortex 20 21 B: Functional role 22 C: Cell size ▪ Golgi type I Large soma & long axon Ex: motor neurones of spinal cord, pyramidal cells, Purkinje cells ▪ Golgi type II Small soma & short axon Ex: interneurones of spinal cord, cerebral & cerebellar cortex 23 D: Neurotransmitter released - chemical messengers - cholinergic, adrenergic, noradrenergic, GABAergic, dopaminergic, serotonergic, glycinergic 24  D: Neurotransmitter released TYPES & DESCRIPTION EXAMPLES Cholinergic: release acetylcholine Most somatic motor neurons & parasympathetic motor neurones Adrenergic & noradrenergic: release Most postganglionic sympathetic motor adrenaline & noradrenaline neurones GABAergic: release gamma- Some neurons of cerebellum, cerebral aminobutyric acid cortex & hippocampus Dopaminergic: release dopamine Some neurones of hypothalamus Seronergic: release serotonin Parasympathetic neurones Glycinergic: release glycine Some neurones of spinal cord & brain stem 25  Neuroglia / glia cells Glial (Gr. glia, glue)cells – play important supporting role Non-excitable Smaller than neurons but more abundant (x10) Furnish microenvironment suitable for neuronal activity 26  Function: Structural & nutritional support Electrical insulation Enhancement of impulse conduction velocity 27  Neuroglia / glia cells Varieties: Astrocytes Oligodendrocytes Microglia cells Ependymal cells Satellite cells Schwann cells 28 29 30 31  Astrocytes Largest, star-shaped cells Most numerous glial cells Highly branched cells Pack the interstices between the neurons, their processes and oligodendrocytes Bind neurones to capillaries & pia mater 32  Astrocytes Give mechanical support, metabolites exchange (nutrition), form blood-brain barrier, form scar tissues (gliosis) Play important role in repair of CNS after injury or damage by disease 33  Oligodendrocytes CNS equivalent of Schwann cells of PNS Responsible for myelination of axons in CNS 34 Microglia cells Small elongated irregular nuclei Little cytoplasm with fine, highly branched processes Equivalent of monocyte-macrophage system Defence and immunological function Secrets cytokines and growth factors 35 Ependymal cells Specialized epithelium lining the ventricles of brain and central canal of spinal cord Cuboidal – low columnar epithelium (ciliated) Do not lie on a basal membrane 36  Nerve fibers Two types: Myelinated fibres: large diameter fibres, wrapped by Scchwann cell plasma membrane → myelin sheath Unmyelinated fibres: small diameter axon enveloped by cytoplasm of Schwann cells Axons enveloped by Oligodendrocytes (CNS) Schwann cells (PNS) 37 38 Nerve – bundles of nerve fibers Epineurium: surrounds whole nerve Perineurium: surrounds nerve fibres fascicle Endoneurium: surrounds individual nerve fibres 39 40  Synapse Formed by interaction of axon terminal and cell membrane of target cell Release neurotransmitter at the axon terminal Site of functional contact Neurone – neurone Neurone – effector cells (muscle & gland) 41 https://youtu.be/xF2UFV6EKt0?si=aHPDIMwWJywEv3Je  Sensory receptor endings Specialized endings of afferent neurones or separate cells that signal the afferent neurone Nerve endings or specialized cells → transduce stimuli from external/internal environments into afferent nerve impulses → pass into CNS to initiate appropriate voluntary/involuntary responses 42  Exteroceptors Respond to stimuli from outside the body Touch, light pressure, pain, temperature (general sensation) Smell, taste, sight & hearing (special senses) Proprioceptors Provide information about orientation, skeletal position, tension & movement Interoceptors Respond to stimuli from viscera 43 44  Free nerve endings ▪ Simplest form of sensory receptors, consists of numerous small terminal branches of afferent nerve fibres ▪ Temperature, touch, pain 45  Meissner’s corpuscle ▪ Small, encapsulated ▪ Found in the dermis of skin – fingertips, soles of feet ▪ Reception of light discriminatory touch ▪ Oval in shape ▪ Located in dermal papillae 46  Clinical application Reaction of neurones to injury Dead neurones are removed by macrophages Hyperplasia, hypertrophy of astrocytes, later become fibrous ‘gliosis’ Damage to axon - Regeneration can occur in axons injured far from cell bodies Neoplasms Gliomas – very invasive (incomplete removal, recurrence, not interfere with nearby neuronal function) 47  REFERENCES B Young & JW Heath. Wheather’s Functional Histology: a text and colour atlas. Churchill Livingston MH Ross & W Pawlina. Histology: A text and atlas 6th Ed. Lippincott Williams & Wilkins JF Ash, DA Morton, SA Scott. The Big Picture: Histology. McGraw Hill Junqueira & Carneiro. Basic Histology text & atlas 11th edition, McGraw Hill 48 49