tre of Mark Louie D. Lop

Transcription

1 NERVE PHYSIOLOGY Mark Louie D. Lopez College of Science Polytechnic University of the Philippines

2 FUNCTIONS OF NERVOUS SYSTEM Sensory input or detection Integration processing transmission of information perception of sensory information learning and memory thought processes and conscious awareness planning and implementation of motor commands Expression of behavior - responses to environment

3 CELLS OF NERVOUS SYSTEM

4 NEURONS NEURON VS GLIAL CELLS electrically excitable cell th at processes and transmits information through electrical and chemical signals. NERVOUS SYSTEM To surround neurons and hold them in place, Supply nutrients and oxyg en to neurons, To insulate one neuron from another, To destroy pathogens and remove dead neurons. NEUROGLIA

5 TYPES OF GLIAL CELLS Microglia act as the first and main form of active immune defense in the central nervous system Oligodendrocytes provide support and to insulate the axons in the central nervous system Astroglia perform many functions, including biochemical support of endothelial cells that form the blood brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, and a role in the repair and scarring process of the brain and spinal cord following traumatic injuries Ependymal cells are a type of Glial cell and are also CSF producing cells.

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7 FUNCTIONAL ORGANIZATION OF NEURONS Receptive segment: Dendrites Integration segment: Soma Initial segment: Action Potential Conductive segment: Axon Transmissive segment: Axon Terminals

8 NEURONS ACCORDING TO FUNCTION Afferent/Sensory Neuron receives and transmits impulses to the CNS for processing Efferent/Motor Neuron originates in the CNS and transmits impulses to effector organs throughout the body Interneuron only in CNS; integrators

9 NEURONS ACCORDING TO FUNCTION Afferent Neuron Efferent Neuron Interneurons

10 NEURONS ACCORDING TO MORPHOLOGY Unipolar one process from cell body Bipolar 2 processes from the cell body and the presence of axon hillock opposite the body Multipolar - 1 axon, several dendrites; presence of axon hillock continuous to the initial segment

11 NEURONS ACCORDING TO MORPHOLOGY

12 NEURONS ACCORDING TO MORPHOLOGY

13 POTENTIAL DIFFERENCE Separated electric charges of opposite sign have the potential of doing work if they are allowed to come together. This potential is called an electric potential or, because it is determined by the difference in the amount of charge between two points, a potential difference Positively Charged Negatively Charged

14 RESTING MEMBRANE POTENTIAL All cells under resting conditions have a potential difference across their plasma membranes oriented with the inside of the cell negatively charged with respect to the outside. This potential is the resting membrane potential.

15 Concentration gradient Membrane permeability K + > Na + Negatively charged protein A -

16 Non-gated ion channels

17 IONS INVOLVED IN MEMBRANE POTENTIAL Potassium (K+) Located inside the membrane Diffuses outside and at a faster rate since the membrane is more permeable to K+ than to Na+ the diffusion of K+ out makes the membrane negative, resulting to RMP (-70mV) o Sodium (Na+) Located outside the membrane and moves inwards. Na-K Pump: restores the balance of ions and maintains the -70mV RMP

18 IONS INVOLVED IN MEMBRANE POTENTIAL

19 CHANGES IN MEMBRANE POTENTIAL Graded potential Action potential

20 ACTION POTENTIAL Transient changes in the membrane potential from its resting level produce electric signals. Such changes are the most important way that nerve cells process and transmit information.

21 ACTION POTENTIAL Action potential - reversal of polarity normal polarity: negative inside, positive outside reversed: positive inside, negative outside Initiated when threshold potential is with explosive opening of the remaining voltage-gated Na+ channels Opening voltage-gated ion channels Na+ and K + successively Electrical signal that propagate along a long distance

22 ACTION POTENTIAL

23 MEMBRANE ION CHANNELS a. Leak Channels responsible for the mov t of ions non gated ion channels - the resting potential of the axon is -70mV b. Gated Ion Channels/Voltage-Gated Channels sensitive to voltage difference across the membrane closed at resting state

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25 MEMBRANE ION CHANNELS Na Channel 2 gates - Activation Gate (M Gate) close at rest - Inactivation Gate (H Gate) open at rest K Channel (N Gate) - closing gate

26 THRESHOLD POTENTIAL Critical membrane potential o a change of at least 15mV will elicit an action potential. Otherwise, a local event is produced. And once the threshold is reached, more explosive depolarization occurs (reversal of polarity, turned to positive 70mV to -55mV: caused by the influx of Na+, hence the membrane potential will lose its positivity resulting to depolarization

27 ACTION POTENTIAL

28 DEPOLARIZATION Voltage gated Na+ ions open (M, H gates) Membrane suddenly becomes permeable to sodium ions. o The rapid influx of Na+ ions causes the membrane potential to become less negative.

29 ACTION POTENTIAL

30 OVERSHOOT Inactivation gate (H) will close, no entry of Na+ The rapid influx of Na+ ions causes the membrane potential to become too positive o more than 0mV Reversal of polarity

31 ACTION POTENTIAL

32 REPOLARIZATION The Na+ channels become inactivated, while voltage-gated K+ channels open. The efflux of K+ ions gradually restores the negative membrane potential

33 ACTION POTENTIAL

34 HYPERPOLARIZATION More negative point than the normal RMP due to the slow closing of K+ channels and an excess if K+ ions go out of the cell. After hyperpolarization, the polarity of the membrane returns to the resting potential due to the Na-K electrogenic pump

35 ACTION POTENTIAL

36 ACTION POTENTIAL

37 CONDUCTION OF IMPULSES

38 CONDUCTION OF IMPULSES

39 REFRACTORY PERIODS

40 REFRACTORY PERIODS Absolute Refractory Period - the period during which a second action potential cannot be elicited even with a strong stimulus (because the iongated channels are closed). no second response no matter how strong the second stimulus is. after depolarization, absolute since Na channel is closed

41 REFRACTORY PERIODS Relative Refractory Period - The period wherein a response may be elicited provided that the second stimulus is greater than the threshold. Na+ is slowly returning to resting, from closed H gate it will open, activation gate will slowly close, inactivation gate closed Technically open Na channel (M closing, H open) o if the Na gate is open -> returning to resting

42 GRADED VS ACTION POTENTIAL

43 NEUROTOXINS Toxin Source Effects Tetrodotoxin Puffer fish Blocks voltage gated Na + Saxitoxin Marine dinoflag-gelates, Fresh water cyanobacterium channels Blocks voltage gated Na + channels Apamin Honeybee Blocks voltage gated K + channels Batrachotoxin Poison arrow frog Keeps Na + channel from closing Calciseptin Black mamba Blocks Ca ++ channels Iberiotoxin Indian red scorpion Blocks K + channels Phoneutriatoxin Banana spider Slows closing of Na + channel Stichodactylatoxin Sea anemone Blocks voltage gated K + channels

44 3 rd review Prepare a powerpoint presentation of the review Limit your presentation to 10 slides Must be presentable within 15 minutes given time

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