Topic 5.1 Structure of NS PDF

(NERVOUS TISSUE) BY: Pn.Tuminah Bt Sabar 1 At the end of session, the student should be able to:  describe the organization of the nervous system  explain the three basic functions of nervous system  describe the structure and functio...

(NERVOUS TISSUE) BY: Pn.Tuminah Bt Sabar 1 At the end of session, the student should be able to:  describe the organization of the nervous system  explain the three basic functions of nervous system  describe the structure and function of neurons and neuroglia  distinguish between gray matter and white matter  explain the nerve impulses (action potential)  explain the process of synapse and neurotransmitters 2  The nervous system is the major system in controlling, regulatory, and communicating system of the body  Centre of all mental activity including thought, learning and memory  Together with the endocrine system, it is responsible for regulating and maintaining homeostasis 3 The structures make up the nervous system:  Brain  Cranial nerves & their branches  The spinal cord  Spinal nerves & their branches  Ganglia  Enteric plexuses  Sensory receptors 4 Organized into 2 main subdivision  Central nervous system (CNS)  Peripheral nervous system (PNS) 5  Consists of brain & spinal cord  Brain  located in the skull  contains 100 billion of neuron  Spinal cord  encircled by the bone of vertebral column  contain 100 millions of neuron connected to the brain  Brain & spinal cord are continuous at the foramen magnum 6 Consists of:  Cranial nerves & branches  Spinal nerves & branches  Ganglia  Enteric plexuses in small intestine  Sensory receptors in the skin 7 8  Sensory function  Sensory receptors detect internal/external stimulation – e.g. increase blood acidity (internal) & rain drop on hand (external)  Cranial & spinal nerve will carry the sensory information to the brain & spinal cord  Integrative function  The nervous system will integrates/process the information by analysing/storing/making decision for appropriate response  Motor function  Carry the response that have been processed to the effectors (muscle & gland)  Simulations to the effector caused muscle to contract & glands to secrete 9 10 2 main types of tissue  Neuron  Neuroglia/glial cell 11  Functional unit of nervous system  It is a nerve cell that conducting nerve impulse  Consists of a cell body, one axon , many dendrites & axon terminal  Required oxygen and glucose for survival  Do not undergo mitosis Supported by connective tissue – neuroglia 12 Cell body  Contains similar to other type of cell except no centrioles as no mutation occur  Form the grey matter of the nervous system  Found in the periphery of the brain and in the centre of spinal cord  Group of cell bodies are called nuclei in the CNS and ganglia in PNS 13 Axon & Dendrites  Axon & dendrites are extensions of cell bodies  Form a white matter of nervous system  Referred as nerves or nerves fiber outside the brain & spinal cord 14 Dendrites  Shorter and branching  Function – receive and carry incoming impulses towards cell body from another neuron  In motor neuron – form part of synapse  In sensory neuron – form the sensory receptors that receive impulse 15 Axon  Function - Carrying impulse away from the cell body to another neuron  Found deep in the brain  If in group – called tract at the periphery of the spinal cord  Axolemma – plasma membrane of axon  Myelin sheath – cover the axon  Nodes of Ranvier  unmyelinated region between the myelin  function - speed up the transmission 16 Axon terminal  Place where two neurons or a neuron & effector cell will communicate (synapse)  Swell into synaptic end bulb – contain synaptic vesicle (store neurotransmitter) 17 18 Sensory neuron  Carry message from the receptors to the CNS Interneurons/association neuron  Located in the CNS (brain & spinal cord)  Receive signals from many neurons and carry out integrative functions (make decisions on responses) Motor or efferent neuron Carry message from the CNS to effector (muscle & glands) 19 Central Nervous System (CNS) Peripheral Nervous System (PNS) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Association neuron (interneuron) Sensory neuron Receptors Motor neuron Skeletal muscles Motor neurons Cardiac muscle Smooth muscle Glands Autonomic ganglion Neuron can be classified according to their structure Multipolar neuron  Have several dendrites & 1 axon  Mostly located in the brain & spinal cord Bipolar neuron  Have 1 main dendrite & 1 axon  Found in the eye, ear & nose Unipolar neuron  Have 1 axon extension & the cell body is to 1 side of the axon 21 Type of neuron Function Sensory / Transmit impuls from Afferent periferal reseptor to neurones CNS Transmit impuls from Motor / Efferent CNS to effectors such as neurones muscle & lymph Integrate incoming Association information from sensory (Interneurons) neuron & transmit impulse to motor neuron 22  Also known as glia  Make up ½ the volume of CNS  Do not conduct nerve impulse  Functions:  Supply nutrient & oxygen  Surround the neuron & hold them in place  Destroy pathogens and remove dead neurons  Maintain homeostasis in the interstitial fluids  In case of injury or disease, neuroglia multiplies to fill in the spaces formerly occupied by neurons 23  Astrosytes  Microglia  Oligodendrocytes  Ependymal cells 24 Astrocytes  Cover the blood vessels  Form blood-brain barrier – protect the brain from potentially toxic substances and chemical variation Ependymal cells  Actively in formation & circulation of cerebrospinal fluid (CSF) 25 Microglia  Protect CNS cells from disease by engulfing invading microbes  Migrate to areas of injured nerve tissue where they clear away debris of dead cells Oligodendrocytes  Produce and maintain myelin sheath around axons of CNS neurons 26 27 Schwann cells  Form a myelin sheath around a axon in PNS  Active role in nerve fiber regeneration in PNS Satellite cells  Support neuron in PNS ganglia and regulate exchange of materials between neuron and interstitial fluid 28 Myelin sheath  White, fatty substance surrounded the axon  Axon with myelin sheath – myelinated  Axon without myelin sheath - unmyelinated Nodes of Ranvier  The unmyelinated region between the myelin  Function - speed the transmission of impulses 29 White Matter  Form primarily of myelinated axon  Whitish color of myelin gives white matter its name Grey matter  Contains neuronal cell bodies, dendrites, unmyelinated axon, axon terminal & neuroglia  Appear grey color 30  Consists of numerous neuron collected into bundle  Bundle of nerve fibers in CNS is called tract  Nerve covering  Endoneurium – covered each axon or nerve fibre  Perineurium – covered each bundle of fibre  Epineurium – covered the whole nerve 31 Sensory (afferent) nerve  Carry information from the body to spinal cord then pass to the brain Sensory receptors  Specialized endings of sensory neurons that respond to different stimulus inside & outside the body  Once stimulated – impulse generated & transmitted by sensory neuron into the brain & spinal cord  Sense detected;  Somatic sense – originate from skin & respond to pain, touch, heat & cold  Proprioceptor sense – originate in muscle & joint to maintain posture & balance  Special sense – sight, hearing, balance, smell & taste 32 …cont  Autonomic afferent nerves - originate in in internal organ, glands & tissues. E.g. baroreceptor control blood pressure, chemoreceptors control respiration Motor (efferent) nerve  Originate in the brain, spinal cord & autonomic ganglia  Transmit impulse to the effector organs – muscle & glands  2 types;  Somatic nerves – involve in voluntary & reflex skeletal muscle contraction  Autonomic nerve (sympathetic & parasympathetic) – involved in cardiac & smooth muscle contraction & glandular secretion Mixed nerve  Consists of both sensory & motor fibers 33 34  An impulse is initiated by stimulation of sensory nerve endings (sensory receptor)  Action potential or transmission of impulse is due to movement ions across the nerve cell membrane  2 major characteristic of neuron  Irritability - ability to initiate nerve impulses in response to stimuli from outside the body or inside the body  Conductivity - the ability to transmit an impulse to other neurons, muscles, or glands 35  Once the ions that move along an axon membrane reaches synapse, neurotransmitters will release  Allow neuron to communicate with other neuron & body cells  When neuron reaches certain level of stimulation, an electrical impulse is generated  The principle of ions involved:  Sodium -major positive ion in extracellular fluid  Potassium -major positive in intracellular fluid  Generation of action potential depends on the existence of a membrane potential & the present of voltage-gated channels for Na+ & K⁺  During action potential, voltage-gated channels for Na+ & K⁺ channel open in sequence 36  Resting membrane potential  Depolarization  Repolariztion  Refractory phase 37 Resting/polarised state  A neuron not conducting an impulse  Na+ gated channel closed completely +  K gated channel are partly open – slowly flow out +  K is higher inside the cell than outside  Na + is higher outside the cell than inside  It will remains until a stimulus comes along 38 Depolarization  Very rapid process in few milliseconds  A nerve cell is stimulated  Na+ gated channels open → more inflow of Na+ ion from extracellular fluid into neuron → membrane more positively charge than the outside  At the end of depolarization, the Na+ gates are all closed 39 Repolarization  Occur at the end of depolarization phase  K+ gates open to allow K+ leave the neuron  Following repolarization, the K+ gates closed slowly 40 Refactory period  Condition where a neuron is undergoing recovery +  Na+ channel closed & K channels open → action potentials only fire down the axon  Following action potential, a neuron is unable to conduct a nerve impulse until it has recovered because its Na+ gates closed 41   An action potential travels down the nerve axon to the terminal region  When it arrives at the terminal, the action potential causes neurotransmitter molecules to be released into the synapse  These molecules stimulate the receptors in the next cell and the action potential is transmitted 42 Signal Conduction in Nerve Fibers  Local anesthetics and certain neurotoxins prevent opening of voltage-gated Na+ channels so nerve impulses cannot pass the obstructed region 44  More than 1 neuron involved  No physical contact between these neuron  Synapse - point where the nerve impulse passes from one to another  Released chemical substance called neurotransmitter  Synapse transmission – event where neurons communicate with another neurons or effectors Presynaptic neuron - the neuron sending the signal Postsynaptic neuron - the neuron receiving the message 45  Synaptic cleft - the space between presynaptic neuron and postsynaptic neuron which filled with interstitial fluids  Synaptic knobs - end of axon which branches to many small swellings  Very close to the dendrites and cell body of the post synaptic neurone  Contain synaptic vesicles 46  Synaptic vesicles  tiny sac contain neurotransmitter  Neurotransmitter  chemical that allow transmission of signals from one neuron to the next across synapse - released in the synaptic cleft 47 48 49  Once impulse reached the presynaptic neuron, synaptic vesicles in the synaptic knobs will release neurotransmitter into synaptic cleft  Released by exocytosis  Neurotransmitter binds to specific receptor on postsynaptic neuron/effector organ such as muscle  Neurotransmitter initiate electrical response to excite or inhibit the post synaptic neuron 50  The action is short lived, because immediately after stimulated the postsynaptic neuron or effector organ, they are inactivated by enzymes or taken back into the synaptic knob 51  There are about 100 types of neurotransmitter Type of neurotransmitter:  Acetylcholine  Most common transmitter in CNS & PNS  Noradrenaline (norephinephrine)  Play roles in arousing (awakening from deep sleep), dreaming & regulating mood  Adrenaline (epinephrine)  Dopamin  Help regulate skeletal muscle tone  Serotinin  Histamine 52