1 / 14

Neurophysiology

Neurophysiology. Functions How a Nerve Impulse Occurs The synapse. Neurophysiology – Major functions. Irritability (or excitable) : nerve cells respond to a stimulus and convert it into a nerve impulse Conductivity : nerve cells transmit impulse to other nerves, muscles, or glands.

corby
Download Presentation

Neurophysiology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Neurophysiology Functions How a Nerve Impulse Occurs The synapse

  2. Neurophysiology – Major functions • Irritability (or excitable): nerve cells respond to a stimulus and convert it into a nerve impulse • Conductivity: nerve cells transmit impulse to other nerves, muscles, or glands

  3. How a Nervous Impulse Occurs • Resting potential of the membrane: polarized and unstimulated • POLARIZED : The electrical charge on the outside of the membrane is positive while the electrical charge on the inside of the membrane is negative. • The outside of the cell contains excess sodium ions (Na+); the inside of the cell contains excess potassium ions (K+). This arrangement of Na+ and K+ is maintained by the Sodium-Potassium Pump and protein channels in the membrane.

  4. How a Nervous Impulse Occurs • A stimulus occurs (ex. Light, sound, touch) cause depolarization • DEPOLARIZATION: The inside of the cell membrane becomes more positive • Na+ channels open and Na+ ions diffuse into the cell along the concentration gradient making the cell’s interior more positive • If enough Na+ enters the cell, then more Na+ channels open. Once the charge reversal occurs, the Na+ channels close and the K+ channels open.

  5. How a Nervous Impulse Occurs 3. K+ leaves through open K+ channels causing repolarization • REPOLARIZATION: Another change that returns the cell membrane to its resting potential – a polarized state • The K+ carries positive (+) charges out of the cell making the cell’s interior more negative (-) • Neuron can not conduct another impulse until repolarization occurs

  6. How a Nervous Impulse Occurs • Depolarization and repolarization constitutes an action potential • ACTION POTENTIAL: change in charge that is transmitted along a nerve. • To go from resting potential to action potential takes 1 or 2 milliseconds • It is an “all or nothing event”- • Stimuli/neurotransmitters arrive and open some of the chemically-gated Na+ channels • If stimuli reach the threshold level  depolarization occurs • Voltage-gated Na+ channels open • An action potential is generated • If stimuli do not reach the threshold level  nothing happens

  7. How a Nervous Impulse Occurs • Sodium-Potassium Pump restores balance of resting state. • Restores sodium and potassium by pumping 3 Na+ ions out of the cell and 2 K+ ions into the cell • concentration gradient drives Na+ to go into the cell • concentration gradient drives K+ to go out of the cell • Occurs against a concentration gradient, so ATP needed (active transport) Occurs extremely fast to allow for quick nerve impulse reactions

  8. `

  9. How a Nervous Impulse Occurs • Remember: the impulse doesn’t jump from one neuron to the next. A new impulse is started when the neurotransmitter diffuses across the synapse to the next neuron. • Saltatory Conduction: faster conduction of action potential along myelinated nerves. > Energy efficient – the membrane only has to depolarize and repolarize at the nodes > Less Na+/K+ATPase activity is required, therefore, less energy is required

  10. Saltatory Conduction • Not a continuous process of region to region depolarization • A “jumping” depolarization • Myelinated axons transmit an action potential differently • The myelin sheath acts as an insulator preventing ion flow in, and out of, the membrane • Neurofibril nodes (nodes of Ranvier) interrupt the myelin sheath and permit ion flows at the exposed locations on the axon membrane; nodes make it unnecessary for action potentials to travel the entire cell membrane.

  11. The Synapse • Function • There must be a means of communication between each neuron and the next target cell • The synapse is the connection • Organization • Presynaptic neuron • Synaptic cleft • Postsynaptic neuron

  12. Action of a Chemical Synapse • Presynaptic Events • An action potential reaches the presynaptic terminal and depolarizes the axonal terminal. • Ca2+ channels open…Ca2+ ions enter the axoplasm • Neurotransmitters are released from their vesicles by exocytosis • Neurotransmitter diffuses across the cleft and bind to specific receptor molecules on the postsynaptic membrane.

  13. Action of a Chemical Synapse • Postsynaptic Events • Ion channels (Na+, K+, or Cl-) on the postsynaptic membrane open or close as a result of the neurotransmitter binding to their specific receptors • An action potential on the postsynaptic membrane is either stimulated or inhibited. • Neurotransmitter molecules are removed quickly • degraded by enzymes in the synapse, with the products returned to the presynaptic terminal, or • diffused away from the synapse to the blood circulation

More Related