ASD 3003 Human Physiology L4 Nervous System PDF

ASD 3003 Human Physiology L4 Nervous System / 1 Function of Nervous system To sense感覺 changes within the body and the external environment To interpret 解釋 the changes To respond 回應 to the changes by initiating responses To assimilate experiences...

ASD 3003 Human Physiology L4 Nervous System / 1 Function of Nervous system To sense感覺 changes within the body and the external environment To interpret 解釋 the changes To respond 回應 to the changes by initiating responses To assimilate experiences 吸收經驗 for memory, learning and intelligence 2 Neurons (神經單位(細胞)/神經元) Basic unit (cell) of nervous system Structure of neurons Cell body (細胞體) A mass of cytoplasm with a nucleus inside Dendrites (樹突) Receive stimuli Axons 軸突 (nerve fiber) – Conducts nerve impulses away from the cell body Wrapped with myelin sheath 髓鞘 Node of Ranvier 節點– gap between segments of myelin 3  3. Types of Neurons Afferent neurons / sensory neurons (感覺神經元) Conduct signal from sensory receptors into the CNS Efferent neurons / motor neurons (運動神經元) Conduct signal out of the CNS to effector organs (muscle and glands) Interneurons (聯合神經元) Lie within CNS Connect afferent and efferent neurons Afferent neuron/ CNS Sensory neuron Receptors 感覺受體 Interneurons Efferent neuron/ Motor neuron Effectors 效應器 4 Neuroglia (神經膠質細胞) Supporting cells in nervous system function in assisting neurons’ function Physically support neurons Form myelin sheaths (髓鞘) Increases speed of conduction of the action potential Help to regulate the extracellular fluid composition 5 Different types of neuroglia Schwann cells 施旺细胞 Form myelin sheaths covering PNS axon Oligodendrocytes 少突细胞 Form myelin sheaths covering CNS axon Astrocytes 星形细胞 Help the formation of blood- brain barrier Microglia 小神經膠質 Phagocytic cells for defence 6  Nervous System Central nervous system (CNS) (中樞神經系統) Brain and spinal cord脊髓 Inside the skull and vertebral column脊柱 (For protection) Responsible for integration Peripheral nervous system (PNS) (外周神經系統) Nerves extending from CNS to muscles, glands and sense organs Cranial nerves顱神經& spinal nerves脊神經 7 Spinal cord, spinal nerve and spinal reflex (背根) carries sensory nerve fibres into the spinal cord 腹根 carries motor nerve fibres away from the spinal cord to the effectors Functions of spinal cord  To provide many reflex centers which control involuntary reflex actions不自覺反射  To provide pathway for transmitting nerve impulses to and from the brain which controls voluntary actions 8  Brain Forebrain前腦 Cerebrum大腦 Diencephalon間腦 Brainstem腦幹 Midbrain中腦 Pons腦橋 Medulla oblongata延髓 Cerebellum小腦 9 Brainstem Midbrain, pons, medulla oblongata Control of involuntary movements不自主運動 Integrating centers for cardiovascular and respiratory activity Medulla Oblongata The place where the spinal cord arises Functions: Cardiac center to control the rate and force of heart rate, cardiac activity Respiratory center to control the rate and depth of breathing Vasomotor center to control the caliber口徑 of the blood vessels Autonomic reflex center to induce vomiting, cough and sneezing 10 Cerebellum Posture, balance and skeletal muscle functions Participate in some forms of learning 11 Forebrain Cerebrum Right and left cerebral hemispheres Diencephalon Thalamus丘腦 Hypothalamus下丘腦 12 Cerebrum Right and left cerebral hemispheres Cerebral cortex (大腦皮層) 4 lobes Frontal 額葉, parietal 頂葉, occipital 枕葉and temporal 顳葉 13 Cerebrum Highest sensory and motor center High level of brain functions Memory, learning, language, planning, decision making, etc. 14 Motor and sensory areas of the cerebral cortex 15 Diencephalon Thalamus Integrating centers for sensory inputs Hypothalamus Regulate pituitary hormone secretion Homeostatic regulation穩態調節, e.g. water balance, body temperature 16 Peripheral Nervous System (PNS) Afferent neuron/ Sensory neuron CNS Receptors Interneurons Effectors Efferent neuron/ Motor neuron 17 Peripheral Nervous System Sensory (afferent) division Carries impulses from the receptors to the CNS Somatic 軀體 - stimuli comes from the skin and skeletal muscles Visceral 內臟- stimuli comes from the internal organs Motor (efferent) division Carries impulses from the CNS to effectors Somatic - voluntary control自願控制 of skeletal muscles Autonomic自主 - involuntary control 不自覺控制 of cardiac, smooth muscles and glands腺體 Sympathetic nervous system交感神經系統 Parasympathetic nervous system副交感神經系統 18  Efferent Division of PNS Somatic nervous Autonomic nervous system (ANS) system Involuntary control of internal Voluntary control of organs (cardiac muscles, skeletal muscles smooth muscles and glands) Fig. 9-1 19 Autonomic Nervous System Part of the peripheral nervous system Consists of sympathetic nerves + parasympathetic nerves They act antagonistically 對立 to each other The balance between the two sets of nerves results in coordinated regulation of organs and glands 20 Sympathetic nervous system ~ “fight or flight” action 戰鬥或逃跑行動 To cope with challenges from the environment outside, Nerves are utilized in situations of stress or strong emotions Functions: Increase heart rate Dilates bronchi 擴張支氣管 Dilates arteries to muscle 擴張動脈至肌肉 Constrict arteries to gut 收縮動脈到腸道 Convert glycogen to glucose Increase secretion of epinephrine腎上腺素 21 Parasympathetic nervous system ~ conservation Effects opposite to sympathetic system Concerned with body conservation for the body’s well-being in quiet state 22 Antagonistic characters 23 The autonomic nervous system Sympathetic: Red Parasympathetic: Blue 24 How does a neuron function? ? 25 Resting Membrane Potential (RMP)靜息膜電位 Contraction gradient is established Selective permeability of resting cell and maintained by Na+/K+ ATPase membrane Resting membrane is [K+] is higher inside the cell more permeable to K+ than to Na+ [Na+] is higher outside the cell Resting cell K+ moves across the resting membrane approaching the K+ equilibrium potential (-90 mV) Slight inward diffusion of Na+ occurs Resting membrane potential = -70 mV 26 Na+/K+ -ATPase Pump Maintains and establishes the concentration gradient of Na+ and K+ across cell membrane. Fig. 6-26 27  Action Potential (AP) 動作電位 Transmission of electrochemical signal 電化學信號 along the cell membrane Produced in excitable cells e.g. neuron, muscle cell and sensory cell Dramatic change in RMP to produce electrical signals Involves localized inversion of the resting membrane potential to +40 mV followed by a return to the resting membrane potential of -70 mV Long-distance transmission Conduct signal for long distance without decrease All-or-none response Action potentials either occur maximally or they do not occur at all 28 Action Potential (AP) Consists of 3 distinct electrochemical events Depolarization去極化 Inversion of resting membrane potential (-70 to +40 mV) Occurs due to Na+ flooding into cell by diffusion (through voltage- gated* Na+ channel) Repolarization 復極化 Restoration of resting membrane potential (+40 to -70 mV) Occurs due to K+ flooding out of cell by diffusion (through voltage-gated* K+ channel) *voltage-gated ion channels are cell membrane proteins which open and close in response to changes in membrane potential Hyperpolarization 超極化 An overshoot of resting membrane potential -90 mV 29 30  Synapse 突觸 The functional connection between a neuron (end of an axon) and another neuron, muscle or gland cells Presynaptic neuron Conduct signal toward a synapse Postsynaptic neuron Conduct signal away from synapse Synaptic knob 旋鈕 Terminal of presynaptic neuron Synaptic cleft 裂口 The narrow gap between pre- and postsynaptic neuron 31 Synapse Electrical synapse Directly pass the action potential to the postsynaptic neuron via gap junctions Chemical synapse Transmit signals by releasing neurotransmitters 神經遞質 from presynaptic neuron endings to postsynaptic neuron 32 Mechanism of Neurotransmitter Released in Chemical Synapse 1. Arrival of presynaptic AP 2. Opening of Ca2+ channels and Ca2+ influx 3. Release of neurotransmitter e.g. acetylcholine from vesicle into synaptic cleft 4. Diffusion of neurotransmitter across synaptic cleft to postsynaptic membrane 5. Binding of neurotransmitter on the receptors of postsynaptic membrane 6. Activation of ion channels of postsynaptic membrane and generation of postsynaptic potential 7. Generation of postsynaptic AP 8. Removal of neurotransmitter from synapse 33 Fig. 7-22 The release of neurotransmitter at a chemical synapse 34 Synaptic Potentials Depolarization or hyperpolarization of the inside of the postsynaptic neuron after the binding of the neurotransmitters secreted from the presynaptic neurons Excitatory postsynaptic potential (EPSP) Depolarization on postsynaptic membrane Inhibitory postsynaptic potential (IPSP) Hyperpolarization on the postsynaptic membrane 35  Presynaptic AP conducted by axon toward terminal neuron Axon Opens voltage-gated Ca2+ channels  release of neurotransmitters into synaptic cleft Postsynaptic Neurotransmitters bind to the ligand- neuron gated channels on postsynaptic membrane Dendrite Inward diffusion of Na+  depolarization  EPSP EPSP exceeds threshold potential Initial Open voltage-gated Na+ channel and segment then K+ channel  AP Axon AP conducted along axon Fig. 7-25 The sequence of events in synaptic transmission 36  When a threshold level of depolarization is produced, action potentials are generated in the axon Stimuli of increasing strength produce increasing amounts of depolarization Fig. 7-29 The graded nature of excitatory postsynaptic potential (EPSPs) 37 When only one presynaptic neuron releases excitatory neurotransmitter, the EPSP When more than one produced may not be presynaptic neuron sufficiently strong to stimulate produces EPSP at the same action potentials in the time. However, the EPSP Postsynaptic neuron can summate at the axon hillock to produce action potential Fig. 7-33 Spatial summation of EPSPs 38 Neurotransmitters Classes of neurotransmitters 1. Acetylcholine (ACh) 2. Biogenic amines: e.g. norepinephrine (NE), epinephrine, serotonin 3. Amino acids e.g. glutamic acid, gamma-aminobutyric acid (GABA) 4. Neuropeptide, etc 39 Acetylcholine (ACh) Common neurotransmitter in neuromuscular junction of PNS Cholinergic fibers Nerve fibers release ACh Acetylcholinesterase Enzyme rapidly destroys ACh for the clearance of neurotransmitters in synaptic cleft Two types of ACh receptors (cholinergic receptors): Nicotinic ACh receptors Muscarinic ACh receptors 40 Acetylcholine (ACh) Nicotinic receptors enclose membrane channels and open when Ach binds to the receptor. This causes a depolarization called an excitatory postsynaptic potential (EPSP) The binding of Ach to muscarinic receptors open ion channels indirectly, through the action of G-proteins. This can cause either an EPSP or a hyperpolarization called an inhibitory postsynaptic potential (IPSP) After Ach acts at the synapse, it is inactivated by the enzyme acetylcholinesterase (AChE) 41 Nicotinic acetylcholine (ACh) receptors also function as ion channels 42 Muscarinic ACh receptors require the mediation of G-proteins 43  The AChE in the postsynaptic cell membrane inactivates the Ach released into the synaptic cleft. This prevents continued stimulation of the postsynaptic cell unless more Ach is released by the axon. The acetate and choline are taken back into the presynaptic axon and used to resynthesize acetylcholine. The action of acetylcholinesterase (AChE) 44  Thinking… Alzheimer’s disease Alzheimer’s disease is a brain disease that usually begins in middle age and produces progressive mental deterioration. This is caused by degeneration of cholinergic neurons with unknown reason, resulting a decreased amount of ACh in certain part of the brain. 45 Important words Neuron Afferent neuron Efferent neuron Interneuron Sensory neuron Motor neuron Central nervous system (CNS) Peripheral nervous system (PNS) Somatic nervous system Autonomic nervous system Sympathetic nervous system Parasympathetic nervous system Resting membrane potential Action potential 46