ACTION POTENTIALS Chapter 11 Part 2 HONORS ANATOMY & PHYSIOLOGY

Key terms action potential: A short-term change in the electrical potential that travels along a cell (such as a nerve or muscle fiber); the basis of neural communication. neural impulse: The signal transmitted along a nerve fiber, either in response to a stimulus (such as touch, pain or heat), or as an instruction from the brain (such as causing a muscle to contract). Plasticity: The ability to change and adapt over time. Polarity: The spatial differences in the shape, structure, and function of cells.Almost all cell types exhibit some sort of polarity, which enables them to carry out specialized functions. Free to share, print, make copies and changes. Get yours at The Brain and Behavior

Reuptake: The reabsorption of a neurotransmitter by a neuron after the transmission of a neural impulse across a synapse. Depolarization: the act of depriving of polarity, or the result of such action; reduction to an unpolarized condition resting potential: The membrane potential of inactive cells. The voltage that exists across plasma membranes during the resting state of excitable cells; ranging from: -90 to -20 millivolts Free to share, print, make copies and changes. Get yours at The Brain and Behavior

Neurons  use pulses of electrical current to receive transmit regulate the flow of information over long distances w/in the body

Neuron Organization

Types of Neurons  Sensory Neurons  transmit information (senses) from body  brain  are afferent  specialized dendrites that initiate action potential when stimulated

Types of Neurons 2. Motor Neurons  transmit signals to muscle fibers & glands  are efferent

ACTION POTENTIALS nerve impulses occur in neurons only neurons are electrically excitable  communicate with one another using 2 types of electrical signals: 1. graded potentials (short distances only) 2. action potentials (short or long distances)

Synapse  junction between axon terminal & next cell (another neuron, muscle fiber, gland cell)  neurotransmitters are chemical messengers most synapses that pass action potential to receiving cell

Synapse  presynaptic cell: cell releasing neurotransmitter & passing on action potential  postsynaptic cell: receiving neurotransmitter  synaptic cleft: physical space between the 2; neurotransmitter released into this space & diffuses across it  attaching to receptors on postsynaptic cell

Synapse

Ion Pumps  ions unequally distributed across plasma membrane  inside of cell slightly (-) compared to outside cell  source of potential nrg  called the membrane potential  resting potential : the membrane potential of rest =  -60 to –80 mV

Resting Potential

Formation of Resting Potential  Na+/K+ pump generates & maintains the ionic gradients of membrane potential  1 turn of pump  1 ATP  3 Na+ out  2 K+ in

Membrane Potential

Ion Channels  pores that span the membrane allowing ions to diffuse across (in or out)  membranes are selectively permeable and variations in how easily any particular ion can cross a membrane depends on the # of channels & how often they are open

Types of Ion Channels

Action Potentials  neurons have gated ion channels that open or close in response to stimuli  open/close changes permeability for that ion  neurons have K+ channels  when open K+ diffuses out of cell  changes resting potential from: -60 mV to -90 mV

Hyperpolarization  when K+ channels open & resting potential decreases to -90 mV inside of cell becoming more (-) than normal resting potential called: hyperpolarization

K+ Ion Channels in Neurons

Depolarization  when Na+ ion channels open Na+ diffuse into cell making inside less (-) compared to outside cell  membrane potential shifts toward (+) mv  this reduction in magnitude of membrane potential called depolarization

Graded Potentials  any shift in membrane potential  magnitude of shift varies with strength of stimulus  induce a small electrical current that flows along the membrane leaking out of the cell  so only lasts short distance from source

Action Potential  electrical signal that propagates along the membrane of a neuron as a nongraded (all or nothing) depolarization  have a constant magnitude & can regenerate in adjacent regions of the membrane  travel long distances

Voltage-Gated Ion Channels  ion channels that open/close based on membrane potential passing a particular level  Na+ channels in neurons are voltage gated: open when depolarization occurs  Na+ diffuses into cell  becomes more depolarized  more Na+ channels open (+ feedback)

Threshold  Action potentials occur when a depolarization increases the membrane voltage to a particular value (the threshold)  for mammals the threshold is a membrane potential ~ -55mV  once started the action potential has a magnitude independent of the strength of triggering stimulus

 + feedback loop of depolarization & channel opening triggers an action potential whenever the membrane potential reached the threshold  membrane depolarization opens both Na+ & K+ channels but Na+ opens faster initiating the action potential  Na+ channels become inactivated as action potential proceeds (gates close) & remain so until after membrane returns to resting potential

Refractory Period  (-) membrane potential restored by inactivation of Na+ channels, which increases K+ outflow  This is followed by a refractory period:  no matter how strong the stimulus to initiate next action potential is cannot initiate one during refractory period

Conduction of Action Potentials

Action Potentials  An electrical impulse travels along the axon via depolarized voltage-gated ion channels in the membrane, and can either "jump" along a myelinated area or travel continuously along an unmyelinated area.

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