NUR1019_L5_L6_Nervous System AY2425S1 PDF

Nervous System (神經系統) Dr. Sarwat Fatima 1 Learning Outcomes 1. What is the nervous system? 2. How do nerves conduct signal? 3. What is the central nervous system? 4. What is the peripheral nervous system? 5. Division of the peripheral nervous system. 6. What is effe...

Nervous System (神經系統) Dr. Sarwat Fatima 1 Learning Outcomes 1. What is the nervous system? 2. How do nerves conduct signal? 3. What is the central nervous system? 4. What is the peripheral nervous system? 5. Division of the peripheral nervous system. 6. What is effect of aging on nervous system? 7. How does the nervous system play a role in homeostasis? 2 1. What is the Nervous System A complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body. It uses electrical and chemical means to help all parts of the body to communicate with each other. The brain has approximately 100 billion neurons. In contrast, the spinal cord only has roughly 13.5 million neurons throughout its length. Neurons can’t divide or replace themselves. This means that nerve damage is often permanent. 3 Neuron: Basic building blocks of the nervous system A bundle of neurons wrapped in connective tissues= nerve A neuron is a specialized cell that collect and send information (to and form sensory organs, muscle, glands, and other neurons) *Myelin sheath is produced by: Schwann cells in peripheral nervous system or 4 Oligodendrocytes in central nervous system https://opentextbc.ca/introductiontopsychology/chapter/3-1-the-neuron-is-the-building-block-of-the-nervous-system/ Functions of nervous system * Sensory input - Monitors changes inside and outside the body and sends signals from sense organs to the brain * Integration - Interpret signals received from sensory input to form an appropriate response * Motor output - Gives a response by activating muscles and glands 5 Different types of neurons 感覺神經元 運動神經元 中間神經元 6  2. How do nerves conduct signals? * Neurons communicate with each other by sending messages using a form of electricity. * In neurons, this electricity is created by the flow of charged particles called ions that move across the outer membrane of the cell * Nerve signal is called action potential, conducted by axon. * Nerve cell at rest, is not excited, has a voltage across its Na+ Na+ Na+ Na+ membrane called resting potential. Na+ Na+ outside cell membrane Na+ Na+ Inside cell membrane 7 The charge of this membrane can change in response to neurotransmitter molecules released from other neurons and environmental stimuli. Any voltage is a difference in electric potential between two points. 8  Why inside of cell is negative compared to outside? Two main factors 1. Slow leakage of potassium ions (K+) ions outside the cells and more sodium ions (Na+) outside cell. 2. Presence of large proteins that cannot diffuse outside the cell Na+ Na+ Na+ Na+ Na+ But in action potential, this Na+ Na+ Na+ Na+ polarity of the cell will change 9 Resting neuron (resting potential) * When a neuron is resting (not transmitting signal), outside of the cell has a next positive charge, Inside of cell has a net negative charge Concentration gradients Concentration gradients are key behind how action potentials work. In terms of action potentials, a concentration gradient is the difference in ion concentrations between the inside of the neuron and the outside of the neuron (called extracellular fluid). 10 What is an action potential? 11 Generation of resting potential - Inside cell membrane= higher concentration of K+ - Outside cell membrane= higher concentration of Na+ - Membrane not permeable to charged proteins More K+ leak channels than Na+ leak channels K+ and Na+ leak channels are always open -allow movement of ions across their concentration gradient Sodium-potassium pump is driven by ATP hydrolysis Maintains differential level of Na+ and K+ by pumping 3 Na+ out of cell in exchange for 2 K+ into cell A neuron at rest is negatively charged because the inside of a cell is approximately 70 millivolts more negative than the outside (−70 mV) 12 Generation of action potential Resting potential Na+ and K+ leak channels are open Na+ and K+ voltage gated channels are closed -70mV Depolarization +35 - Na+ voltage gated channels open - Na+ move inside the cell membrane - Inside of cell become +ve relative to outside of cell - depolarization continues until intracellular voltage reaches approximately +35mV 13  Generation of Action potential cont’d Repolarization +35 - Na+ voltage gated channels close - K+ voltage gate channels open - K+ leave the cell - Inside of cell becomes negative again Hyperpolarization Hyperpolarization K+ voltage gate channels stay open a little longer than needed - Eventually, the voltage-gated potassium to bring the membrane back to its resting potential. The channels close and the membrane potential membrane potential briefly dips lower (more negative) than stabilizes at resting potential. its resting potential. Na+ voltage gated channels remain closed 14 Summary: action potential Na+/K+ leak channels Na+/K+ voltage gate channels Sodium/Potassium pump membrane potential time (milliseconds) RMP: resting membrane potential https://quizlet.com/265919934/action-potential-diagram/ 15 Action potential travels along the entire length of axon * An action potential is generated in the body of the neuron and Direction of travel of action potential propagated through Cell body its axon. * Action potential always propagates forward, never backwards * *Refractory period - Interval of time during which another action potential CANNOT be generated - Na+ voltage gated channels closed - cannot respond to another stimulus until the gates are reset. 16 https://cnx.org/contents/[email protected]:cs_Pb-GW@5/How-Neurons-Communicate Action potential travels along the entire length of axon https://content.byui.edu/file/a236934c-3c60-4fe9-90aa-d343b3e3a640/1/module5/readings/refractory_periods.html 17  Speed of action potential along an axon Myelinated axon -conduction of nerve impulses is faster in myelinated axons. -myelin covers the axon in a way that "insulates" the axon from depolarization waves. In this way, a depolarization even will occur only at the "Nodes of Ranvier“ -Nodes contain voltage-gated K+ and Na+ channels. Action potentials travel down the axon by jumping from one node to the next (saltatory conduction) Unmyelinated axon - conduction of nerve impulse is slower in unmyelinated axons. -since Na+ and K+ channels have to continuously regenerate action potentials at every point along the https://vivadifferences.com/myelinated-vs-unmyelinated-neurons/ axon instead of at specific points 18  Speed of action potential along an axon Speed of action potential along an axon Node of Ranvier https://content.byui.edu/file/a236934c-3c60-4fe9-90aa-d343b3e3a640/1/module5/readings/refractory_periods.html 19 Speed of action potential along an axon 20 Resting potential vs action potential 21  Summary: How do nerves conduct signals? Summary Direction of travel of action potential Cell body 22 Summary: How do nerves conduct signals? Summary cont’d Covered in Myelin sheath Saltatory conduction action potentials conducted faster NOT covered in Myelin sheath action potentials conducted slower 23  Transmission of signal between neurons Synaptic cleft: Gap between pre-synaptic and post-synaptic neurons Axon terminals Transmitting neuron Receiving neuron Synaptic (postsynaptic membrane) (presynaptic cleft membrane) Synapse: site of functional contact between two neurons where an electrical impulse is transmitted between pre-synaptic and post-synaptic neurons. 24  Neurotransmitters (神經傳導物質) Neurotransmitters are chemical messengers that transmit signals from a neuron to a target cell across a synapse. Important for rapid communication in synapse. Neurotransmitters are packed in synaptic vesicles in axon terminals. Bind to respective receptors at postsynaptic neurons 3 types of neurotransmitters Mechanisms exist for inactivation and termination of their activity. 25 26 Transmission of signal between neurons a. Action potential reaches axon terminal. b. Ca2+ channels open and Ca2+ enters axon terminals. c. Synaptic vesicles (enclosed with neurotransmitters) fuse with plasma membrane of presynaptic neuron. d. Neurotransmitters released into synaptic cleft and bind to receptors on membrane of postsynaptic neuron. e. Na+ chemically gated channels open, Na+ enter and depolarize the postsynaptic membrane. Spreading of depolarization fires an action potential in postsynaptic neuron. - ligand-regulated gates ONLY open when a neurotransmitter binds to it….similar to lock and key effect (different from voltage-gated channels) f. Released neurotransmitters are deactivated. 27 Neurotransmitters (神經傳導物質) How are neurotransmitters regulated? i. Enzymes in postsynaptic membrane inactivate the neurotransmitters ii. Presynaptic membranes reabsorbs neurotransmitters by packaging into vesicles - This prevents continuous stimulation or inhibition of postsynaptic membranes There are many drugs that acts an inhibitory or excitatory neurotransmitters Neurotransmitters and diseases Alternations in levels of neurotransmitters can lead to several health disorder e.g. Alzheimer's, Depression, Anxiety 28 Type of neurotransmitters What body functions do nerves and neurotransmitters help control? Heartbeat and blood pressure. Breathing. Muscle movements. Thoughts, memory, learning and feelings. Sleep, healing and aging. Stress response. Hormone regulation. Excitatory neurotransmitters: promote generation of action potential in the Digestion, sense of hunger and thirst. receiving neuron Inhibitory neurotransmitters: Senses (response to what you see, hear, feel, touch and taste). inhibit action potential in the receiving neuron 29 Summary * sending neuron (prestsynaptic neuron) * receiving neuron (postsynaptic neuron) * synaptic cleft * Ca2+ ions *neurotransmitters * Na+ ion channels https://www.physio-pedia.com/Neurotransmitters?veaction=edit#:~:text=Alterations%20in%20the%20levels%20of,%2C%20depression%2C%20and%20Alzheimer%20disease. 30 Learning Outcomes 1. What is the nervous system?  2. How do nerves conduct signal?  3. What is the central nervous system? 4. What is the peripheral nervous system? 5. Divisions of peripheral nervous system 6. What is effect of aging on nervous system? 7. How does the nervous system play a role in homeostasis? 31 3. What is the Central Nervous System (CNS) 32  3. Central nervous system vs Peripheral nervous system? CNS PNS Function: CNS receives sensory Function: information and the PNS is involved in sending processed information is information to the CNS and sent into effector organs sending responses from as the response the CNS into the effector organs. https://ib.bioninja.com.au/standard-level/topic-6-human-physiology/65-neurons-and-synapses/nervous-system.html 33 Neuron regeneration (再生) CNS vs PNS PNS CNS Incapable of regeneration Most nerves can regenerate 34 3. What is the CNS? Our body cannot operate without the CNS Brain = CPU of It is like the CPU of a computer computer The three broad functions of the CNS are (i) to take in sensory information, (ii) process information, Spinal cord= central cable (iii) send out motor signals. that carries messages to and from the computer The CNS receives sensory information from the nervous system and controls functions of the body including awareness, movement, thinking, speech, and Nerves= carry message the 5 senses of seeing, hearing, feeling, tasting and to every party of body smelling and also back to the brain 35 Central Nervous System (CNS) Brain and Spinal Cord share 3 characteristics 1. Gray matter & White matter (灰質& 白質) 2. Meninges (腦膜) 3. Cerebrospinal fluid (腦脊髓液) 36 2. White vs gray matter Neurons arrange themselves in very distinct ways within the CNS, which makes the brain and spinal cord appear as areas of either gray or white color https://www.simplypsychology.org/what-is- grey-matter-in-the-brain.html White matter Gray matter  Tissue of brain and spinal cord that contains  Tissue of brain and spinal cord composed of myelinated axons. neuronal cell bodies and dendrites.  Transmit signals to other regions of the brain,  Receives information and regulates outgoing spinal cord, and body. information. Brain: Outer portion of cerebrum Spinal cord: grey matter lies in the inner contains grey matter while the inner side and the white matter is on the portion contains white matter outside 37 https://www.hopkinsmedicine.org/health/conditions-and-diseases/anatomy-of-the-brain  meninges of brain 2. Meninges * Spinal cord and brain are wrapped in protective 3 layers of membranes called meninges. Function of meninges 1. Protect your CNS (central nervous system) from trauma injury to your brain such as blow to your head by acting as a shock absorber. meninges of spine 2. Contains blood vessels that deliver blood to the CNS tissues, nerves. 3. Provides space for flow of cerebrospinal fluid. 38  2. Meninges 39 https://www.bodycentricwellness.co.uk/key-to-health/  meninges of brain Meninges i. dura mater= outer part - tough, fibrous connective tissue, white - closest to skull - contains a drainage system, called the dural venous sinuses, which allows blood to leave your brain and allows cerebrospinal fluid to re-enter the circulation. ii. arachnoid mater= middle layer - thin layer between dura mater and pia mater - does not contain blood vessels - has a spiderweb-like appearance because it has connective tissue projections that attach to mater meninges of spine iii. pia mater= deepest layer - closest to brain tissue/spine - Thin layer, tightly held together - Contains blood vessels - subarachnoid space between arachnoid mater and pia mater. It’s filled with cerebrospinal fluid which cushions and protects brain and spinal cord. 40 https://teachmeanatomy.info/neuroanatomy/structures/meninges/ 3. Cerebrospinal fluid (CSF) Colorless liquid that protects the brain and spinal cord from physical and chemical damage. Produced by choroid plexus of ventricles. It circulates through the ventricles of the brain, subarachnoid space, and central canal of spinal cord. Contents Lymphocytes (protection against pathogens) Glucose Lactic acid Na+, K+, Ca2+, Urea Proteins https://en.wikipedia.org/wiki/Cerebrospinal_fluid#/media/File:Blausen_ 41 0216_CerebrospinalSystem.png CSF Functions Provides chemical environment to support neuronal signaling. A balance of different ions helps generation of action potential. Protects brain and spinal cord from sudden impact or injury. Exchange of nutrients between blood and nerve tissues. Prevents the brain from compressing blood vessels against the internal surface of bones of skull. Hydrocephalus: accumulation of CSF in the ventricles - Enlarged skull - Brain tissue between ventricles and skull will be compressed leading to brain damage https://www.choc.org/neuroscience/hydrocephalus/ 42 References 1. https://my.clevelandclinic.org/health/body 2. https://www.britannica.com 3. Longbaker, Susannah Nelson. (2017). Mader's understanding human anatomy physiology. New York: McGraw Hill. 89