Nervous System

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Support cells

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Nonexcitable cells that provide structural support of that serve important physiological and immunological functions in the nervous system. Also called Glial cells.

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ion

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An atom or small molecule with a positive or negative electrical charge

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Central Nervous System

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The brain and spinal cord.

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Peripheral nervous system

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That portion of the nervous system that lies outside the brain and spinal cord; includes nerves and ganglia.

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excitable

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Refers to a cell that responds to stimuli by generating an electrical signal at the cell membrane. Neurons and muscle cells are excitable.

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Target cell

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a cell that receives signals from a neuron or a hormone.

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Multipolar neuron

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a neuron with a central cell body that gives rise to multiple dendrites and a single axon. The most common type of neuron in humans.

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Cell body

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the portion of the neuron containing the nucleus and organelles; also called the soma. Main nutritutional and metabolic region of the neuron. Receives information and sends them to the axon.

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Dendrites

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A cytoplasmic process that extends from a neuron's cell body. Neurons typically have many dendrites, which are usually shorter and thicker than axons and highly branched. Dendrites receive signals from other neurons and send them towards the axon.

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Axon

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A long, thin cytoplasmic process that extends fro ma neuron's cell body. The axon may be insulated with myelin. Each neuron has a single axon, which transmits action potentials.

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Action Potential

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A long-distance regenerative electrical signal transmitted along an axon. The action potential is an all-or-none event. Also called a nerve impulse, spike, or discharge.

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Nerve Impulse

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Another term for action potential.

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Synapses

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A junction between a neuron and its target cell (another neuron, muscle, gland). Signals between neurons and other cells are communicated across synapses.

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Axon Hillock

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The first portion, or initial segment of the axon. Where the action potential is generated.

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Axon Collaterals

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A branch of an axon.

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Axon terminals

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The bulbous ending of a branch of an axon. Also called synaptic ending or synaptic bouton.

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Myelin

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The insulation surrounding axons. The myelin sheath is formed by support cells that wrap repeatedly around an axon, forming a thick layer of insulation. It is produced by support cells

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Schwann cell

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One type of support cell in the nervous system. Found in the peripheral nervous system, Schwann cells form myelin sheaths around axons.

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myelination

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the insulation of an axon with myelin.

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nodes of Ranvier

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Tiny areas of bare axon between neighboring segments of myelin sheath. In a myelinated axon, charge flows across the membrane only at the nodes of Ranvier so the action potential appears to jump along the axon. The nodes are essential for conduction of the action potential

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Integral proteins

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Proteins that are embedded in the lipid bilayer of the cell membrane.

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Ion Channels

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Integral Proteins containing watery pores through which ions pass to cross the cell membrane.

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Ion channels are selective. They select for:

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charge on the ion, the size of the ion, and on how much water the ion attracts and holds around it.

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Gated Channels

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Ion channels that are opened or closed by gates. The gates may be controlled by chemicals or by membrane voltage.

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Nongated Channels

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Ion channels that are always open. Also called leakage channels.

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Voltage-gated channels

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Ion channels with gates that are opened or closed by changes in membrane voltage. Located on the axon hillock, unmyelinated axons and at the nodes of ranvier. Function: responsible for generation and propagation of the action potential.

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Membrane potential

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The electrical potential, or voltage, across a cell membrane that results from the seperation of charged particles across the membrane. When the neuron is at rest it is -70mV.

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K+ Channel opens and...

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Potassium ions run out the cell creating a more negative inside of the cell and hyperpolarizing the cell after an action potential.

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Na+ channels open and...

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Sodium rushes in creating a less negative membrane potential(depolarization) creating an action potential.

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Neurotransmitters

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a chemical that is released at synapses

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GABA

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Gamma-aminobutyric acid, a neurotransmitter. Allows Chloride into the cell by opening chemically-gated channels.

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Chemically-gated channels

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Ion channels with gates that open or close when a neurotransmitter binds to them. Located on dendrites and cell body of the neuron. Function: Responsible for synaptic potentials.

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Acetylcholine(ACh)

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A neurotransmitter that opens chemically gated channels to allow sodium to rush in and potassium to rush out of the cell.

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Resting membrane potential

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The membrane potential when a cell is at rest. It is usually -70mV with the negative side inside the cell.

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Synaptic Potentials

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A short-distance electrical signal that can vary in amplitude. Synaptic potentials are the incoming signals o neurons.

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diffusion

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The movement of molecules from one location to another because of random thermal motion. Net movement is from a region of higher concentration to a region of lower concentration.

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Anion

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A negatively charged ion.

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Cation

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A postively charged ion.

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Extracellular Fluid (ECF)

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Located outside cells, the ECF includes interstitual fluid and plasma.

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selective permeability

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The characteristics of a cell membrane that permits some particles to cross it, but prevents other particles from crossing.

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Excitable cells are very permeable to ____ and slightly permeable to ____.

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K+ and Na+

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permeability

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The characteristic of a cell membrane that permits particles such as ions to pass from one side of the membrane to the other.

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concentration gradient

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The difference in the concentration of a particular substance between two adjacent areas.

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electrical potential

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an electrical force across a cell membrane that results from the separation of charged particles across that membrane.

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Voltage

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Another term for electrical potential. A force capable of moving charged particles toward regions having an opposite charge and away from regions having a like charge.

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Electrical potential and K+

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Since opposite charges attract each other, the developing electrical potential begins to pull potassium into the cell. The electrical potential, or voltage, acts as a force that opposes the diffusion of K+ out of the cell. The width of the arrow represents the relative strength of the electrical force.

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The equilibrium potential for K+

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A simple nonexcitable cell has a concentration of 150mM K+ inside and 5mM K+ outside. At these concentrations, the chemical and electrical forces on K+ are equal and opposite when the membrane potential is -90mV

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Equilibrium potential

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For a given ion, the membrane potential at which the electrical and chemical forces that drive that ion across the cell membrane are equal and opposite.

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Resting Neurons

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When neurons are not generating electrical signals they are at rest. Rsting neurons are very permeable to K+ and only slightly permeable to Na+. They are also permeable to Cl-, but since it contributes little to the resting membrane potential

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If a neuron were permeable to K+ its resting potential would be ____. Resting neurons are also slightly permeable to Na+ which causes the membrane potential to be _____.

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-90mV, -70mV

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There is a force pushing potassium out of the cell because...

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The cell membrane potential is not equal to the potassium membrane potential.

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Na+-K+ pump

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Transport proteins in plasma membrane that move three sodium ions out of the cell and two potassium ions into the cell, using energy from hydrolysis of ATP.

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Electrochemical gradient

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The combined electrical and chemical forces on an ion. The force determines the net movement of charged particles.