Unit One Animal Physiology

Membrane Physiology

The structure and composition of cell membranes, including epithelia and transport mechanisms.

Phospholipids

Molecules with a polar head (phosphate group) and nonpolar tails (fatty acid chains) arranged in a bilayer to form the basic structure of cell membranes.

Chemical diversity of membrane phospholipids

Saturation, fatty acid chain length and head group.

Membrane Fluidity

The ability of membrane lipids to change phase (solid to liquid).

Homeoviscous Adaptation

The maintenance of relatively constant membrane fluidity regardless of tissue temperature.

Epithelia

Specialized cells forming a covering or lining of an organ, including squamous, cuboidal, and columnar types.

Transcellular Path

Transport of molecules across an epithelium from the apical to basolateral side or vice versa.

Paracellular Path

Movement of molecules through the spaces between epithelial cells.

Simple Diffusion

The movement of solutes from an area of high concentration to an area of low concentration.

Osmosis

The net diffusion of water across a membrane that is selectively permeable.

Carrier-Mediated Transport

A transport mechanism involving a protein that binds a solute and facilitates its movement across a membrane.

Facilitated Diffusion

A form of carrier-mediated transport that moves molecules down their concentration gradient with the help of a carrier protein.

Electrochemical Gradient

The combined effect of both concentration gradient and electrical potential on the movement of an ion.

Active Transport

A transport process where energy is used to move molecules or ions against their concentration gradients.

Primary Active Transport

Active transport that directly uses ATP to transport molecules against their concentration gradient.

Secondary Active Transport

Active transport that uses the energy of an electrochemical gradient to drive the transport of a different molecule against its concentration gradient.

Vesicular (Bulk) Transport

The bulk transport of substances into or out of the cell via vesicle formation.

Endocytosis

The process by which cells take in substances from outside by engulfing them in a vesicle.

Exocytosis

The process by which cells release substances to the outside world by fusing a vesicle with the plasma membrane.

Membrane Potential

The difference in electrical potential between the inside and outside of a cell.

Nernst Equation

An equation used to determine a membrane's equilibrium potential for a specific ion.

Goldman Equation

An equation used to predict membrane potential, taking into account the permeability of multiple ions.

Resting Potential

Basic polarization of a neuron, typically around -70mV.

Depolarization

Decrease in membrane potential, making it less negative.

Repolarization

Return of membrane potential to its resting value.

Hyperpolarization

Increase in membrane potential, making it more negative than resting potential.

Graded Potential

Change in membrane potential relative to resting potential; varies in strength with stimulus.

Action Potential

A rapid, self-propagating electrical signal in a neuron.

Threshold Potential

The membrane potential that must be reached to trigger an action potential.

Voltage-Gated Sodium Channel

A membrane protein that selectively allows sodium ions to pass through the channel and is opened by a change in membrane potential.

Voltage-Gated Potassium Channel

A membrane protein that selectively allows potassium ions to pass through the channel and is opened by a change in membrane potential.

Tetrodotoxin

A potent neurotoxin that blocks sodium channels, preventing action potentials.

Axon Hillock

The trigger zone of the neuron.

Refractory Period

The time in which a new action potential cannot be initiated in a region that just underwent an action potential.

Absolute Refractory Period

Membrane region that has just undergone an action potential cannot be stimulated to fire again, no matter how strong the stimulus.

Relative Refractory Period

Membrane region that has just undergone an action potential can fire another action potential, but only with a very strong stimulus.

Myelin Sheath

Layers of glial cell membranes which wrap axons, increasing conduction velocity.

Nodes of Ranvier

Unmyelinated regions of axon where myelin sheath is discontinuous.

Saltatory Conduction

Action potentials appear to jump from one node of Ranvier to another.

Synapse

Specialized site of communication between a neuron and a target cell.

Presynaptic Neuron

Neuron that transmits a signal at a synapse.

Postsynaptic Neuron

Neuron or other cell that receives a signal at a synapse.

Electrical Synapse

Gap junctions between pre- and postsynaptic membranes permit current to flow passively through intercellular channels.

Chemical Synapse

Synaptic current flows across the postsynaptic membrane in response to the secretion of neurotransmitters.

EPSP

Excitatory post-synaptic potential; depolarizes post-synaptic cell, making it more likely to fire an action potential.

IPSP

Inhibitory post-synaptic potential; hyperpolarizes post-synaptic cell, making it less likely to fire an action potential.

GPSP

Grand post-synaptic potential; sum of all inputs to the post-synaptic potential.

Reuptake

Termination of neurotransmitter action by reabsorption.