nervous system (BAI GIANG HE THAN KINH)

Physiology of the nervous system- Neurophysiology Objectives: Part 1: basic concepts in nerous system •The Divisions of the nervous system Central nervous system (CNS), Peripheral nervous system (PNS), sensory (afferent) nervous system, motor (efferent) nervous system, somatic nervous system, autonomic nervous system: sympathetic and parasympathetic nervous system • Neuron, the structural unit of the nervous system Types of neurons • Glial cells and their function •Resting membrane potential and action potential Role of Na+, K+ and ion channels in generating an action potential • Myelinated and unmyelinated nerve fibers thúc đẩy •Transmission of nerve impulse in myelinated and unmyelinated axons • Synapse Dẫn truyền • Synaptic transmission of nerve impulse • Excitatory postsynaptic potential (EPSP) Inhibitory postsynaptic potential (IPSP) •Spatial and temporal summation of postsynaptic potential •Neurotransmitters •Divergent and convergent pathway in the nervous system Part2: major structures of the central nervous system and their main function • Spinal cord • brain stem •Thalamus and hypothalamus •Cerebellum •Cerebrum Part 3.The autonomic nervous system Structural organization of sympathetic and parasympathetic systems and their function Specific terms and keywords • • Neuron Neuro– Neurology – Neurologist – Neuropathology/neuropathy – Neurophysiology – Neuroscience • • • • • • • Resting membrane potential Ion channels Voltage-gated ion channels Threshold Action potential/nerve signal/nerve impulse Action potential propagation/ transmission/conduction Synapse Synaptic transmission Neurons and nervous systems in different phyla • • • • Nerve net (cnidarians: jellyfish, anemones, hydra) neurons are phân tán dispersed in a thin layer Centralized and cephalized nervous system (flatworm, squid) Hạch Ganglionic central nervous system (anthropods, annelids, molluscs) Hình ống Columnar nervous system (vertebrates) – Nervous systems of all animals originate from ectoderm – Neurons of all animals are quite similar in their functional properties – Changes in evolutionary history of nervous systems: changes in the complexity of organization of neurons into systems, rather than changes in neurons themselves AHill, Wyse , Andersonn ingly Aimal physiology 2nd The divisions of the nervous system • central nervous system- CNS – Brain – Spinal cord • peripheral nervous system- PNS – Nerve fibers: 12 pairs of cranial nerves , 31 pairs of spinal nerves – Ganglion/ganglia – subdivions : • Afferent /sensory division • Efferent/motor division: – somatic motor nervous system: skeletal muscles – autonomic nervous system-ANS: smooth muscles, glands, heart muscle » sympathetic nervous system » parasympathetic nervous system Fig.7.1 C.L Standfield.2011 Principles of Human Physiology, 4th edition Cellular components of the nervous system • Neuron • Glial cells (70-90%) Neuron • Neuron: – Cell body (soma): receive information • nucleus, rough endoplasmic reticulum, free ribosomes (Nissl bodies) golgi apparatus, • Mature neurons Trung thể lack centrioles – Dendrites Sợi nhánh, đuôi gai – Axon: send information • Some mm ->1m • Transport materials to presynaptic membrane • neural impulse transmission: – Axon hillock – Axon terminal • C.L Standfield.2011 Principles of Human Physiology, 4th edition Mature neurons can not divide Structural classification of neurons C.L Standfield.2011 Principles of Human Physiology, 4th edition Classification of neuron types • Functional classification – afferent/sensory neuron – efferent/ motor neuron – interneuron • Structural classification – unipolar neuron • one axon • sensory neuron – bipolar neuron • one axon and one axon-like dendrite • Sensory neuron in the eyes, roof of the nasal cavity, and inner ear – multipolar neuron • Many dendrites and one axon • Interneuron and motor neuron Tế bào thần kinh đệm Neuroglia (glial cells) • Rudolf Virchow (1821-1902) coined the term (1846) • Large number (75-90% cells of the CNS, >1/2 brain mass) • Functions: – – – – – – Structural/physical support to neurons Metabolic support to neurons Component of blood-brain barrier Protection of neurons from pathogens and removal of dead neurons Production of cerebrospinal fluid Formation of myelin sheath surrounding axons • Types of glial cells: + + + + + Astrocyte:CNS Ependymal: CNS: cerebrospinal fluid Microglia: macrophages differentiated in CNS, Oligodendrocyte: CNS Schwann cells: PNS Synapse • C.L Standfield.2011 Principles of Human Physiology, 4th edition A specialized site of communication btw neurons, btw a neuron and an effector, or btw a nonneural sensory cell and a neuron Types of synapses • Electrical synapses: gap junction made by protein channels bridging the gap between two cells – Transmit signals instantaneously • Chemical synapses – Ionotropic chemical synapses – Metabotropic chemical synapses Structure of a chemical synapse • Presynaptic neuron, synaptic knob • Synaptic vesicles contain neurotransmitters • Voltage-gated Ca2+ channels • Synaptic cleft • Post synaptic neuron, postsynaptic membrane • Receptors on the postsynaptic membrane Fig.8.2 C.L Standfield.2011 Principles of Human Physiology, 4th edition Chemical synaptic transmission Fig.8.2 C.L Standfield.2011 Principles of Human Physiology, 4th edition Stimulus = action potential action potential -> Ca2+ channels open, Ca2+ move into presynaptic knob Ca 2+ enters the cell and triggers the release of neurotransmitter by exocytosis Neurotransmitter diffuses across the synaptic cleft, binding to receptors on the postsynaptic membrane Cell responses Some neurotransmitter is degraded by enzymes Some neurotransmitter is taken up by the presynaptic cell Some neurotransmitter diffuses away from the synaptic cleft Ionotropic chemical synapses release neurotransmitters binding to ionotropic receptors (channel-link receptors) • The receptor is also an ion channel (ligand- gated ion channel) • Neurotransmitter binds to receptor -> ion channel opens-> ion movement through postsynaptic membrane -> postsynaptic potential (PSP) • Fast response (few msec) Fig.8.3.C.L Standfield.2011 Principles of Human Physiology, 4th edition Metabotropic chemical synapses release neurotransmitters binding to metabotropic receptor ( G-protein linked receptor) (Cellular metabolism, gene expression) Fig.8.3 C.L Standfield.2011 Principles of Human Physiology, 4th edition • G-protein-regulated ion channels respond to the binding of neurotransmitter slowly (msec-hours) • Slow response Excitatory and Inhibitory neurons - + + - • Neuron releases neurotransmitters causing depolarization of postsynaptic membrane (Na+ move into the cell) -> EPSP- excitatory postsynaptic potential) -> Excitatory neuron-> excitatory synapse • Neuron releases neurotransmitters causing hyperpolarization) of postsynaptic membrane (K+ move in or Cl- move out of the cell)- IPSP- inhibitory postsynaptic potential ->Inhibitory neuron-> inhibitory synapse Modified from: http://www.nature.com/neuro/journal/v6/n11/images/nn1103-1121-F1.jpg One neurotransmitter may mediate different postsynaptic actions through different postsynaptic receptors • Acetycholine – binds ligand-gated channels/ ionotropic receptor mediating EPSPs in skeletal muscles – binds G-protein coupled receptor/ metabotropic receptor generating IPSPs in heart muscles Neural integration: One neuron may contact many other neurons through its collaterals - divergent pathway Fig 8.7 C.L Standfield.2011 Principles of Human Physiology, 4th edition Neural integration: one neuron can receive information from many other neurons - Convergent pathway Fig.8.7 C.L Standfield.2011 Principles of Human Physiology, 4th edition Spatial and temporal summation of postsynaptic potentials • EPSPs and IPSPs are graded potentials, thus they can summate temporally and spatially • Axon hillock acts as an integrator for the summation Fig.8.8 C.L Standfield.2011 Principles of Human Physiology, 4th edition Neurotransmitters (NTs) C.L Standfield.2011 Principles of Human Physiology, 4th edition •Most synapses in the CNS use amino acid neurotransmitters Most fast EPSPs result from glutamate, most fast IPSPs from GABA or glycine •Biogenic amines are found in few neurons but these neurons have widely projecting endings Many receptors for these NTs have slow actions that modulate neuronal activities, rather than mediating fast excitation or inhibition •Peptides are present in substantial minorities of CNS neurons A neuroactive peptide may be co-released with one or more small molecule neurotransmitters and may function as a cotransmitter with slow synaptic effects Neurotransmitters (NTs) and drug’s target • chemical messenger/neurotransmitterreceptor binding: potential target for a drug: - Morphine as pain killer Glutamate: excitatory neuron Serotonin and depression Benzodiazepines (as Valium), sleeping aids (zolpidem), Alcohol and anxiety (enhance action of GABA) Fig.8.2 C.L Standfield.2011 Principles of Human Physiology, 4th edition Neurons are organized into functional circuits in the nervous systems • The functions of a nervous system depend on “wiring” – the anatomical organization by which neuron are connected into circuits • Behavioral activity is a property of the neural circuit that mediates it • Startle response in cockroach Hill.Wyse.Anderson Animal physiology.2e.Sinauer Associates, 2008 Questions: Draw a typical neuron and label the main structures, list the functions of each structure If an anion is located in greater concentration outside the cell compared to inside, would the equilibrium potential for that anion be positive, negative or zero? Explain it Explain ionic basic of an action potential Explain why myelinated axons conduct action potential faster than unmyelinated axons? Explain why the transmission of action potential in axon is not bidirectional? Draw a typical chemical synapse, label the main structures, list the functions of each structure Describe the sequence of events occuring at a chemical synapse Explain ionic basic of an EPSP Compare and contrast the events caused by the binding of neurotransmitters to ionotropic and metabotropic receptors [...]... permeability increases: K+ move out of the cell • After-hyperpolarization: permeability of K+ remains high for a brief time (5-15 msec) after the membrane potential reaches the resting membrane potential • Initiation of APs follows the all-or-none principle: whether a membrane is depolarized to threshold or above, the amplitude of the resulting action potential is the same; if the membrane is not depolarized... (relative to the outside): resting membrane potential (resting Vm) For a neuron Vm= -70mV Membrane potential is defined as the potential inside the cell relative to outside Neuron communicate by generating electrical signals in the form of changes in membrane potential Some of these changes in membrane potential trigger the release of neurotransmitters which then carries signal to another cells – –... channels when cells are at rest) • The differences in the permeability of the plasma membrane to these 2 ions • Chemical and electrical forces for moving sodium and potassium ions across the plasma membrane Establishing a steady-state resting membrane potential Fig.7.8 C.L Standfield.2011 Principles of Human Physiology, 4th edition Nernst Equation : to calculate the equilibrium potential across a cell’s... outside the cell are known • • • • C.L Standfield.2011 Principles of Human Physiology, 4th edition Ei: equilibrium potential for ion I Z: the valence of the ion (I)o: Concentration of I ion outside the cell (I)i: concentration of I ion inside the cell Goldman-Hodgkin-Katz (GHK) Equation To calculate membrane potential in case only K+ and Na+ are permeant and their concentration inside and outside the cell... causes the resting membrane potential ? What causes the membrane potential to change ? What causes the resting membrane potential? solute ICF (mM) ECF (mM) K+ 140 4.0 Na+ Cl- 15.0 4.0 145.0 115.0 • Concentration gradients (created by Na+/K+ pump) of ions (sodium and potassium ions) across the plasma membrane • The presence of ion channels (leaking channels) in the plasma membrane (mainly K+ channels when... During and immediately after an action potential (AP), the membrane is less excitable than it is at rest -> refractory period • During absolute refractory period, no second AP is generated, regardless of the strength of the second stimulus • During relative refractory period, a second AP can be generated but only when the second stimulus is stronger than needed to get threshold potential in resting conditions... lactate and glycogen - component of the blood–brain barrier - regulate the external chemical environment of neurons: removal of excess ions (K+), recycling excess neurotransmitters - Direct neuron migration, modulate the growth of dendrites and axons -Remove excess neurotransmitters Microglia Oligodendrocyte CNS Oligodendrocytes: -Forming myelin sheath surrounding axons in the CNS - Cytoplasmic processes... channels in neurons • Each region (in a neuron) has specific types of ion channels • Most of the ion channels are gated (can open or close) • The opening or closing of ion channels changes the permeability of the plasma membrane for a specific ion leading to a change in electrical properties of the cell or the release of neurotransmitters • Leak channels (none gated channels): always open, found throughout... /Cells/Cells.html Schwann cells PNS fig.cox.miami.edu/ /neuro/neurophysiology.htm • • • Forming myelin sheath surrounding axons in the PNS One Schwann cell forms one myelin sheath surrounding a small portion of an axon Myelinated axons: myelin sheath and nodes of Ranvier Unmyelinated axons • a series of Schwann cells cover the length of several axons • abutting Schwann cells are tightly joined -> no Ranvier nodes... Graded potentials are small changes in the membrane potential (Vm) in response to a stimulus Graded potential is decremental • A graded potential dissipates as it moves to adjacent areas of the plasma membrane C.L Standfield.2011 Principles of Human Physiology, 4th edition thoi gian khong gian Graded potentials can sum temporally and spatially The sum may reach the threshold for triggering an action