Human Anatomy & Physiology: The Neurone & Nerve Transmission PDF

2. The Neurone & Nerve Transmission Course Human Anatomy & Physiology Status Complete Materials 3. The Neuron and Nerve Transmission - Slides Table of Contents The Neuron...

2. The Neurone & Nerve Transmission Course Human Anatomy & Physiology Status Complete Materials 3. The Neuron and Nerve Transmission - Slides Table of Contents The Neuron Neuron Classification Neuroglia Myelin Sheath Nerve Tramsmission Membrane Potential Types of Gated Ion Channels Terms used to describe changes in membrane potential Location of gated ion channels Types of Changes in Potential Graded Potential Action Potential Steps in the formation 2. The Neurone & Nerve Transmission 1  Transmission of outgoing signal Saltatory Conduction Comparison Graded Potential Action Potential Integration at Axon Hillock The Synapse Steps at the Synapse The Neuromuscular Junction The Neurotransmitter (NT) Neuron Circuits Nerve Transmission Summary The Neuron Function: receives and transmits electrical impulses Structure: cell body and processes Nissl bodies: clusters of RER Neurofibrils: cytoskeletal elements for shape Dendrites: processes that receive info Axon: process that sends info Collateral: branch off of axon Axon hillock: integration area Telodendria: branches at the distal end of axon 2. The Neurone & Nerve Transmission 2  Synaptic terminal: release neurotransmitter Neurotransmitters: chemical signals Neuron Classification Structural: number of processes on cell body Unipolar: one process Bipolar: two processes Multipolar: many processes Functional: Sensory (1): delivers information Inter or Association (2): makes a decision 2. The Neurone & Nerve Transmission 3  Motor (3): sends information to muscle Neuroglia Neuroglia: supports the Neuron In CNS: Astrocyte: provides 3-D framework & controls environment (forms the blood brain barrier) Oligodendrocyte: myelin sheath of cns Microglia: immune function In PNS: Satellite cell: same function as astrocyte 2. The Neurone & Nerve Transmission 4  Ependymal: Schwann cell: myelin sheath of PNS epithelial-like cell that line fluid-filled canals and cavities and produces cerebrospinal fluid (CSF) Myelin Sheath Structure: Multiple membrane layers that wrap around the axon CNS: Oligodendrocyte PNS: Schwann cell Function: 1. Protect and insulate 2. Increase speed of nerve transmission Node of Ranvier: gaps along the myelin sheath 1. Where collaterals arise 2. Nerve impulse is transmitted Peripheral nerve cross-section 2. The Neurone & Nerve Transmission 5  Satellite cells wrap unipolar cell bodies (PNS) Nerve Tramsmission Membrane Potential Membrane Potential: the unequal charge difference across a membrane The resting membrane potential for most cells is -70mV 2. The Neurone & Nerve Transmission 6  A membrane potential occurs because: Membranes are barriers to charges (ions) Sodium potassium ATPase pump establishes and maintains ion gradients resulting in: high potassium inside the cell high sodium outside the cell Negatively charged proteins inside the cell Membranes leak so pump is always on Changes in membrane potential are used to create a signal Occurs only in nerve and muscle cells Occurs when gated ion channels open or close and ions move down their gradients Only a few ions move across Rapid Ion concentration changes are corrected by sodium potassium ATPase pump 2. The Neurone & Nerve Transmission 7  Types of Gated Ion Channels Chemically regulated Voltage regulated Mechanically regulated Light regulated and many others Terms used to describe changes in membrane potential Rest or Resting state: -70mV Polarized: is the resting membrane potential (-70mV) Depolarization: potential becomes more positive (less polar) Hyperpolarization: potential becomes more negative (more polar) Repolarization: becomes more negative returning to rest Hyper-repolarization: becomes more negative than -70mV 2. The Neurone & Nerve Transmission 8  Location of gated ion channels Chemically gated Na+ or K+: cell body & dendrites Voltage gated Na+ and K+: axon Voltage gated Ca2+: axon terminal Types of Changes in Potential Graded Potential: due to chemical gates occurs along cell body and dendrites Action potential: due to voltage gates, occurs along the axon Graded Potential Can vary in magnitude Can be a depolarization or hyperpolarization event 2. The Neurone & Nerve Transmission 9  Graded potentials are either IPSP or EPSP: IPSP: Inhibitory post synaptic EPSP: Excitatory post synaptic potential potential NT binds to and opens NT binds to and opens sodium potassium channels channels Potassium moves out resulting Sodium moves in resulting in in hyperpolarization depolarization Action Potential Action Potential: All or none response resulting in depolarization and repolarization Note the following parts of the Threshold graph: Depolarization Repolarization Absolute refractory period Resting membrane potential Relative refractory period Stimulus 2. The Neurone & Nerve Transmission 10  Refractory Period: period in repolarization where the axon can not respond to a second stimulus ion channels are open or just closing and membrane can not respond further i.e. is already depolarized Ensures that each action potential is a separate, all or none event and that transmission is one way Absolute Refractory: opening and closing of voltage gated sodium channels Relative refractory period: sodium gates are closed and membranes are repolarizing and a strong stimulus will reopen sodium channels Steps in the formation 1. Stimulus brings membrane to threshold which opens sodium voltage gated ion channels 2. Sodium moves in bringing membrane to +30 mV (depolarization) 3. At +30mV, potassium voltage gated channels open and sodium voltage gated ion channels close 4. Potassium ion moves out (repolarization) 2. The Neurone & Nerve Transmission 11  5. Overshoot (hyperpolarization) is corrected by Na+ - K+ ATPase pump (returns to rest) 6. Overtime, Na+ - K+ ATPase pump restores intracellular ion levels Transmission of outgoing signal Occurs by propagation Events creating the change in potential are repeated along the axon Steps: 1. graded potential of + 30mV forms in axon hillock region 2. Local current depolarizes adjacent segment bringing sodium voltage gates to threshold 3. Action potential forms while hillock region enters refractory period 4. Cycle repeats until reaching axon terminal Saltatory Conduction Saltatory Conduction: occurs in myelinated axons Myelin resists flow of ions 2. The Neurone & Nerve Transmission 12  Propagation: occurs from node to node faster and uses less energy Speed of Action Potential increased by myelination & larger diameter axons Transmission is unidirectional because: Axon hillock region cannot form an action potential Previous segment enters into refractory period Comparison Graded Potential Action Potential Magnitude varies Same magnitude Depolarize or hyperpolarize Depolarizes and repolarizes Signal fades Signal is propagated Found in cell body & dendrites Found in axon and axon terminal Chemically gated ion channels Voltage gated ion channels Neurotransmitter driven Threshold driven Integration at Axon Hillock Result of the summation of graded potentials 2. The Neurone & Nerve Transmission 13  The Synapse Consists of three components 1. Axon terminal: filled with vesicles containing neurotransmitter 2. Synaptic cleft: extracellular space between 3. Motor end plate (or post neuron cell body & dendrite): contains receptors for neurotransmitters or chemically gated ion channels 2. The Neurone & Nerve Transmission 14  Steps at the Synapse 1. Action potential arrives 2. Voltage calcium gates open and calcium ion moves in 3. Calcium in the cytoplasm triggers fusion of vesicle with the cell membrane releasing neurotransmitter into the synaptic cleft. For neuromuscular junction the NT is Ach 4. Neurotransmitter binds to receptors on the post synaptic neuron or muscle (motor end plate) opening gated ion channels, forming a EPSP or IPSP 5. Depolarization (graded potential or EPSP) may or may not create an action potential in post synaptic neuron or muscle The Neuromuscular Junction 2. The Neurone & Nerve Transmission 15  Three parts: 1. axon terminal containing NT 2. Synaptic cleft or space between 3. Skeletal muscle effector containing receptor for NT Axon terminal releases neurotransmitter or acetyl choline (Ach) into synaptic cleft. NT diffuses and binds to receptors on skeletal muscle opening sodium channels (depolarization). Acetyl choline esterase is in synaptic cleft and removes Ach. The Neurotransmitter 50 -100 different types of (NT) neurotransmitters Lock and key interaction 2. The Neurone & Nerve Transmission 16  each neuron is exposed to a variety of NT effects are stimulatory or inhibitory response depends on receptor Neuron Circuits Serial Nerve Transmission Summary 2. The Neurone & Nerve Transmission 17  Sensory or incoming signal IPSP and EPSP graded potentials occur in cell body and dendrites Integration Graded potentials are summed (temporal or spatial) in the axon hillock region Motor or outgoing signal If threshold is reached in axon hillock region then an action potential forms in the axon Action potential is propagated the length of the axon Action potential opens calcium channels in axon terminal and Calcium triggers vesicle fusion. Transmitter is released. NT binds to post synaptic neuron or muscle forming a graded potential 2. The Neurone & Nerve Transmission 18