Nervous System. Brain Teaser. IntroducGon. Which number comes next in the sequence? 4,7,10 or 12? Dr. Dinithi Peiris Dept.

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1 Nervous System Dr. Dinithi Peiris Dept. of Zoology Brain Teaser Which number comes next in the sequence? 4,7,10 or 12? 3 IntroducGon For survival, animal must respond to the outside environment External Internal To detect changes animals have Receptors 4 1

2 IntroducGon To response animals have Effectors Lower forms- receptor & effectors are the same cell In higher form they are interconnected via Nervous system Endocrine system Circulatory system 5 IntroducGon FuncGon smoothly Nervous system is rapid, fast & do not last long Endocrine system is slow & prolong Nervous & endocrine systems act independently or together. 6 Development of Nervous tissue NS develops from the ectoderm Ectoderm along mid- dorsal side of the embryo thickness to from the neural plate Cells of neural tube give rise to engre CNS 7 2

3 Introduc:on 3 structural elements Nerve cells or neurons SupporGng cells ConnecGve Gssues (join nerve cells and supporgng cells) 8 Nervous tissue Two types of neural cells in the nervous system: Neurons / Nerve cells - For processing, transfer, and storage of informagon (nerve impulses) Neuroglia Associate with neurons. For support, regulagon & protecgon of neurons 9 Nervous tissue Two Anatomical Divisions Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) All the neural Gssue outside CNS Afferent (sensory input) Efferent (motor output) SomaGc nervous system Autonomic nervous system 10 3

4 Nervous tissue CNS PNS Brain Spinal cord Sensory Motor Visceral sensory Somatic sensory Visceral motor Somatic motor Sympathetic Parasympathetic 11 Neurons : microscopic nerve cells that make up the brain, spinal cord, and nerves Neurons - 30,000 neurons can fit on a pinhead 12 Nerve cell Very specialized to conduct messages Cannot divide Damages are irreversible Metabolism is very simple and will die within 5-6 min without oxygen Extremely delicate 13 4

5 Neuron Consists of 3 parts Cell body Cell processes DendriGe Axon Distal porgon of the axon is branched. 14 Nerve cell what is the main defining characteristic of neurons? have the property of electrical excitability - ability to produce action potentials or impulses in response to stimuli 15 Each neuron contains: - Cell body with nucleus - Processes Nerve cell 1 Dendrites : fibers that receive messages from other neurons 2. Axons : fibers that send messages to other neurons 16 5

6 Cell body Ovoid or irregular structure Size varies from 4-5 μm up to 150 μm Nucleus & nucleoli large The center is called Trophic center & involve in metabolism Nissal granules can be seen. Large neurons more Nissal granules than small neurons 17 Cell body Nissal granules increases when nerves used for a long Gme During an injury granules reduces. 18 In Greek large branching. Dendrites Project from the cell body & are branched Diameter is not uniform increases when go out from the cell wall 19 6

7 Dendrites All organelles are present except nucleus & Golgi bodies No sheath around as found in axon. Always conduct impulses towards the cell body 20 Axon Thin & extremely long (may exceed 100m) Diameter is constant In vertebrates axon is surrounded by a sheath. Found in blocks In between the blocks, plasma membrane is exposed Nodes of Ranvier One neuron one axon 21 Axon At terminal end branches out Branches end in a terminal bueon Contains vesicles with neurotransmieers Ach Cholinergic neuron Adrenaline or nor- adrenaline adrenergic neurons Serotonin Seratonergic neurons 22 7

8 Axon Axoplasm Axolemma Schwann cell nucleus Neurilemma Myelin sheath 23 Axon Neurons do NOT touch; there is a gap between them called a synapse Messages are sent across the synapses by special chemicals called neurotransmieers 24 Structural ClassificaGon of Neurons Mul:polar neuron most common Bipolar neuron one dendrite/one axon Unipolar neuron Ex. sensory from skin to spinal cord directly Anaxonic neuron many dendrites/no axon Ex. help in visual processes 25 8

9 A Structural ClassificaGon of Neurons 26 Figure 12.4 Func:onal Classifica:on of Neurons Sensory neurons: Most unipolar, few bipolar Transmit sensory informagon from receptors of PNS towards CNS Motoneurons : Mul:polar transmit motor informagon from the CNS to effectors (muscles/glands/adipose Gssue) in the periphery of the body. Internurons: Mul:polar transmit informagon between neurons within the CNS; analyze inputs, coordinate outputs Most common type of neuron (20 billion) 27 Comparison of Neurons 28 9

10 Comparison of Neurons 29 Neuroglia (glial cells) Neurons are out numbered by neuroglia (1:50) CNS neuroglia Astrocytes Oligodendrocytes Microglia Ependymal cells PNS neuroglia. Schwann cells Satellite cells 30 most abundant glial cells Astrocytes (CNS) Provide structural support for neurons Largest & star shape, project from the cell body Astrocytes with few long processes Fibrous ast. Found in white maeer Ast. With many short branched processes in grey maeer Protoplasmic ast. Help & maintain BBB 31 10

11 Ependymal cells Neuroglia Cells (CNS) Low columnar or cuboidal cells Apical ends of some cells have cilia to facilitate the movement of CSF No basal lamina. Instead the basal ends are elongated & extended branch processes 32 Neuroglia Cells (CNS) Oligodendrocytes Create myelin sheath around axons of neurons in the CNS. Myelinated axons transmit impulses faster than unmyelinated axons Most common Form a supporgve networmk Microglia Brain macrophages Phagocyte cellular wastes & pathogens 33 Myelin Sheath WhiGsh, faey (protein- lipid), segmented sheath around most long axons FuncGon: ProtecGon of the axon Electrically insulagng fibers from one another Increase the speed of nerve impulse transmission 34 11

12 Schwann cells Neuroglia Cells (PNS) Surround all axons of neurons in the PNS creagng a neurilemma around them. Neurilemma allows for potengal regeneragon of damaged axons creates myelin sheath around most axons of PNS Satellite cells Support groups of cell bodies of neurons within ganglia of the PNS 35 Myelin Sheath Myelin sheath of CNS Myelin sheath of PNS 36 CNS 3 regions Cerebrum Cerebellum Spinal cord Show regions of grey & white maeer Cerebral cortex has 3 layers Molecular layer: outer layer Purkinje cells: very large neurons Granule layer: inner layer 37 12

13 CNS 38 Blood Brain Barrier Main structural component is capillary endothelium Cells are Gghtly sealed together Basal lamina of capillaries are enveloped by preivascular feet of astrocytes. BBB allows stable composigon & constant balance of ions and fluid 39 PNS 3 components Nerves: bundles of nerve fibers surrounded by glial cells and CT Ganglia Nerve endings 40 13

14 Nerve Fibers Consist of axons enclosed within a sheath. P. nerves contains groups of nerve fibers; where axons are sheathed by Schwann cells. Axons of small diameter are unmyelinated nerve fibers. Thicker axons are sheathed by numerous concentric wrappings of enveloping cells forming myelin sheath. 41 Nerves Nerve fibers are grouped into bundles to form nerves. Axon & Schwann cells are enclosed within concentric layers of nerve fibers. Consists of 3 layers Epineruium: dense fibrous coat Perineurium: surrounds each nerve fiber bundle Endoneurium: consists of spare layer of loose CT 42 Ganglia Ovoid structures containing neural cell bodies & glial cells supported by CT 2 types Sensory ganglia Receive afferent impulses Associated with dorsal root of the spinal & cranial nerves Autonomic ganglia Effects the acgvity of skeletal muscles 43 14

15 ClassificaGon of synapses CNS - Nerve & nerve only PNS Excitatory Inhibitory Nerve & muscles (Smooth, skeletal, cardiac) Nerve & nerve (Autonomic ganglia) Nerve & receptors (e.g. rods & bipolar nerve cells in the eye) 44 15