Nervous System Sept 2024 Part 1 PDF

Can you see the 3 faces? How many legs do this elephant have? 1  RNB10603 BASIC ANATMOY & PHYSIOLOGY 1 TOPIC 5: NERVOUS SYSTEM (Part I) Pek Y.S. 2  LEARNING OUTCOMES At...

Can you see the 3 faces? How many legs do this elephant have? 1  RNB10603 BASIC ANATMOY & PHYSIOLOGY 1 TOPIC 5: NERVOUS SYSTEM (Part I) Pek Y.S. 2  LEARNING OUTCOMES At the end of the session, students will be able to: 1. state the basic functions of the nervous system 2. outline the division/organization of the nervous system 3. name two types of cells in the nerve tissue 4. describe the basic structure and characteristics of neurons 5. state the types of neuroglial cells and their function 6. explain nerve physiology: i. Generation of nerve impulse ii. Conduction of nerve impulse iii. Synaptic transmission 3  INTRODUCTION The nervous system (NS) is the coordinator and controller of all systems. When several systems are working towards a common goal, they need to be able to communicate and exchange information. The nervous system operates on two levels - the unconscious and automatic level, e.g., breathing and digestion of food - The conscious level, e.g., speaking, reading, playing games The nervous system is divided into four functional systems i. Sensory receptors ii. Nerves iii. Spinal cord iv. Brain 4  INTRODUCTION NS detects and responds to changes inside and outside the body. Together with the endocrine system, it controls many vital aspects of body function and maintains homeostasis. NS also responsible for our perceptions, behaviors and memories. NS consist of: i. Brain ii. Spinal cord iii. Peripheral nerves 5 INTRODUCTION 6 FUNCTIONS OF NERVOUS SYSTEM Maintaining homeostasis Receiving sensory input Integrating information Controlling muscles & glands Establishing & maintaining mental activity 7 FUNCTIONS OF NERVOUS SYSTEM 8  DIVISIONS OF NERVOUS SYSTEM Central Nervous System Peripheral (CNS) Nervous System (PNS) 9 DIVISIONS OF NERVOUS SYSTEM 10 DIVISIONS OF NERVOUS SYSTEM 11  DIVISIONS OF NERVOUS SYSTEM Central nervous system (CNS) structures: - Brain - Spinal cord Peripheral nervous system (PNS) structures: - Cranial nerves and branches - Spinal nerves and branches - Ganglia - Sensory receptors 12  DIVISIONS OF NERVOUS SYSTEM Peripheral Nervous System 1. Somatic (SNS) Sensory neurons from the head, body wall, limbs, and special sense organs Motor neurons to skeletal muscle: voluntary 2. Autonomic (ANS) nervous systems Sensory neurons from viscera Motor neurons to viscera (cardiac muscle, smooth muscle, glands): involuntary - Sympathetic: “fight-or-flight” - Parasympathetic: “rest-and-digest” 13  DIVISIONS OF NERVOUS SYSTEM Peripheral Nervous System 3. Enteric nervous system (ENS) “Brain of the Gut” Involuntary Sensory neurons monitor chemical changes and stretching of the GI wall Motor neurons regulate contractions, secretions and endocrine secretions (involuntary) 14  Peripheral Nervous System (PNS) Efferent (Motor) division Afferent (sensory) division Transmit impulse from Transmit impulse from CNS to peripheral organs peripheral organs to CNS Somatic Autonomic Somatic Visceral Voluntary Involuntary Receive sensory Receive Skeletal muscles Cardiac muscle, input from skin, sensory Smooth muscle, joints, muscles, input from Gland special senses the visceral Sympathetic & 15 Parasympathetic DIVISIONS OF NERVOUS SYSTEM 16  CELLS OF NERVOUS TISSUE Thenervous system is made of neuron cells (or neurons) and neuroglial cells. a) Neurons The functional cells Can respond to stimuli and convert stimuli to electrical signals (nerve impulses) that travel along neurons b) Neuroglia cells The supporting cells nourish and protect neurons Neuroglia critical for homeostasis of interstitial fluid around neurons 17 a) NEURONS 18 a) NEURONS Structural and functional units of the NS. It is the “conducting” cell that transmits impulses. Highly specialized. If the neuron is destroyed, it cannot be replaced because neurons do not undergo mitosis. Each neuron has 3 basic parts: i. Cell body ii. One or more dendrites iii. A single axon 19 Structures of Neuron 20 a) NEURONS – Cell Body Has nucleus, cytoplasm with typical organelles & Nissl substance Vary in size & shape Form the grey matter of the nervous system Found at the periphery of the brain and in the centre of the spinal cord Cluster of cell bodies: - Nuclei in the CNS - Ganglion in the PNS 21 Nissl substance play important role in transmission of impulses from the cell body 22 Nissl bodies seen under the electron microscopy a) NEURONS – Dendrites These are short processes and highly branched structures. Receive & carry incoming impulses towards the cell body. Dendrites form part of synapses in motor neurons & form the sensory receptors that respond to specific stimuli in sensory neurons. 23 a) NEURONS - Axon Begins at a tapered area of the cell body – axon hillock. Conducts impulses away from the cell body toward another neuron. Axon terminals: contain synaptic vesicles that can release neurotransmitters Bundles of axons: - Nerve (in PNS) - Tract (in CNS) 24 a) NEURONS - Axon Axolemma: the membrane of the axon. Large axons and those of peripheral nerves are surrounded by a myelin sheath. This consists of a series of Schwann cells arranged along the length of the axon. The outermost layer of the Schwann cell plasma membrane is the neurilemma. 25 a) NEURONS - Myelination Axons covered with a myelin sheath - Many layers of lipid & protein insulates neurons - Increasesspeed of nerve conduction - Appears white (in white matter) Nodes of Ranvier: gaps in the myelin - Nodes are important for rapid signal conduction in myelinated neurons Non-myelinated neurons - Postganglionic fibres and some small fibres in the CNS are non-myelinated - The speed of transmission of nerve impulses is significantly slower 26 27  Clinical Application Some diseases destroy myelin such as Multiple sclerosis 28 a) NEURONS 29 30 a) NEURONS 31 a) NEURONS 32  CHARACTERISTICS OF NEURON 1. Irritability The ability to start nerves impulses due to stimuli External stimuli: touch, light waves Internal body stimuli: changes in carbon dioxide concentration in the blood will alter the respiration rate 2. Conductivity The ability to transmit impulses 33 b) Neuroglia 34 b) Neuroglia 35  Clinical Application The blood-brain barrier (BBB) Astrocyte wall plus the blood vessel wall forms the BBB Water, oxygen, CO2, alcohol, and a few other substances can pass through this barrier and move between the blood and brain tissue Other substances such as toxins, pathogens and certain drugs, cannot pass through this barrier It has clinical significance because drugs, such as Penicillin, that may be used to treat disorders in other parts of the body have no effect on the brain because they do not cross the BBB 36 ORGANIZATION OF NERVOUS TISSUE 37 Organization of Nervous Tissue 38 Recap… Organization of the Nervous System 39  Name the following structures Cell body Neurolemma Dendrites Myelin Axon Axon Node of Ranvier 40 Neuroglial cells 41  LEARNING OUTCOMES At the end of the session, students will be able to: 1. state the basic functions of the nervous system 2. outline the division/organization of the nervous system 3. name two types of cells in the nerve tissue 4. describe the basic structure and characteristics of neurons 5. state the types of neuroglial cells and their function 6. explain nerve physiology: i. Generation of nerve impulse ii. Conduction of nerve impulse iii. Synaptic transmission 42  Nerve Physiology ⚫ Generation of nerve impulse ⚫ Conduction of nerve impulse ⚫ Transmission of impulse at the synapse 43  i) Generation of Nerve Impulse ⚫ Excitability refers to the property of the nerve fiber to respond and generate a nerve signal when stimulated by a stimulus. ⚫ Resting membrane potential - The resting state of a cell - A steady potential difference of Recording of resting -70 mV (inside negative) membrane potential - State of polarization 44  i) Generation of Nerve Impulse Action potential ⚫ Brief sequence of changes which occur to the membrane potential when stimulated by a threshold stimulus ⚫ Interior of the nerve becomes positive (+35 mV) ⚫ This state is known as the depolarization phase ⚫ Repolarization, or reversal to nearly original potential, occurs rapidly after depolarization ⚫ Action potential is caused by changes in membrane permeability to Na+ and K+ 45 Resting Potential 46 Action Potential 47  ii) Conduction of Nerve Impulse ⚫ Takes place in the form of a wave of depolarization through the nerve fiber ⚫ In one direction only ⚫ Along an unmyelinated nerve fiber by electrotonic conduction ⚫ Along a myelinated nerve fiber by saltatory conduction 48  ii) Conduction of Nerve Impulse ⚫ Nerve impulse conduction (propagation) - Each section triggers the next locally as even more Na+ channels are opened ⚫ Types of conduction - Continuous conduction ⚫ In unmyelinated fibers; slower form of conduction - Saltatory conduction ⚫ In myelinated fibers; faster as impulses “leap” between nodes of Ranvier ⚫ Factors that increase rate of conduction ⚫ Myelin, large diameter and warm nerve fibers 49 50  iii) SYNAPSE ⚫ Synapse - anatomic site where nerve impulses pass from one neuron to another adjacent to it ⚫ Can be found between axon–dendrites, axon–cell body and axon–axon ⚫ The functional junction between two neurons ⚫ Can be classified as: - Chemical synapses, where transmission is carried out by neurotransmitters - Electrical synapses, where transmission occurs through gap junctions - Conjoint synapses, where both chemical and electrical transmissions coexist 51 Synapse 52 Synapse ⚫ Consists of 3 parts: a) Synaptic knob b) Synaptic cleft c) Synaptic vesicle ⚫ Pre-synaptic neuron ⚫ Neuron that transmitting impulse towards synapse ⚫ Post-synaptic neuron ⚫ Neuron that receiving impulses via synapse 53 54 55 Signal Transmission at the Chemical Synapse 56 56 Synaptic Transmission 57 58 59 60