Resting Membrane Potential Nervous System Part 1 Organization Resting Membrane Potential Signaling Graded Potentials Action Potentials

Organization Control System that receives info about internal and external environment, integrates, and directs activities to respond. Divided into the CNS and the PNS.

Organization Consists of 2 classes of cells: Neurons (20%) – communication Neuroglia (80%) – many fnctns: structurally supporting, nurturing, insulating, & protecting neutons Nerves – Bundles of neurons in the PNS

Organization 3 types on neurons: Afferent (sensory) neurons Interneurons Efferent (motor) neurons

Organization Main parts of a neuron:

Resting Membrane Potential A charge difference across the membrane of -70mV at rest. Has the potential to do work. K+ and Na + leak channels in the cell membranes establish electrochemical gradients.

Resting Membrane Potential

Resting Membrane Potential If the cell only had K + channels the equilibrium potential of the cell would be –90mV.

Resting Membrane Potential If the cell only had Na+ channels the equilibrium potential of the cell would be 60mV.

Resting Membrane Potential There are more K+ leak channels so Vm is closer to EK than ENa.

Resting Membrane Potential Active transport Na+/K+ pumps maintain the ion concentrations as seen in table 6-2.

Signaling Changes in a cell’s membrane potential produce electrical signals. Graded potentials – signaling over short distances. Action potentials – signaling over long distances Terms for the direction of changes relative to resting potential are seen to the right.

Graded Potentials Changes in membrane potential confined to a small region of a neuron. They are graded, meaning they can vary in magnitude.

Action Potentials If the minimum threshold voltage is reached, a graded potential becomes an action potential.

Action Potentials Voltage-gated sodium and potassium channels are responsible for the depolarization and repolarization of the membrane.

Action Potentials

Action Potentials Always an all-or-nothing event. Propagates away from a neuron’s trigger zone.

Nervous System Part 1 (cont.) Action Potentials Review Synapse

Action Potentials Review ‘http://outreach.mcb.harvard.edu/animations/actionpotential.swf

Action Potentials Review A typical neuron would have a resting membrane potential of about (A) +70 mV (B) +70 V (C) -70 mV (D) -70 V (E) All of the above are observed at rest.

Action Potentials Review At the peak of the action potential, the membrane potential is: (A) exactly at the Na+ equilibrium potential (B) close to but more positive than the Na+ equilibrium potential (C) close to but less positive than the Na+ equilibrium potential (D) exactly at 0 mV (E) the same as the resting membrane potential

Action Potentials Review True or False: Threshold voltage for opening is approximately the same for voltage-gated Na+ and K+ channels. Voltage-gated Na+ and K+ channels open at the approximately the same threshold voltage… K+ channels are just much more slower at opening wide and closing completely than Na+ channels.

Action Potentials Review Schwann cells are glia cells that that for the myelin sheath. They insulate the axons of neurons and increase the rate of action potential propagation.

Synapse Synapse: the narrow gap b/w 1 neuron & the next. Neurotransmitter: the chemicals that cross the synapse

Synapse

Synapse Response by postsynaptic cell depends on: Type of neurotransmitter Conc. of neurotransmitter Type of receptor Number of receptors Responsiveness of the receptors

Synapse Many axon terminals synapse onto one neuron. Excitatory and inhibitory signals are integrated All synaptic potentials are graded potentials

Synapse EPSP: excitatory post-synaptic potentials; depolarization IPSP: inhibitory post-synaptic potentials; hyperpolarizing When threshold is reached an action potential is fired down the post-synaptic neuron.

Synapse Neurotransmitters need to be removed ASAP after signal is complete. Many helpers: Diffusion Enzymes Protein pumps