Nerve Cells & Nerve Cells & Nerve ImpulsesNerve Impulses

The Cells of the The Cells of the Nervous Nervous SystemSystem

Anatomy of Neurons & GliaTwo Types of Cells in the Nervous System

1. NeuronsReceive & transmit information to other cellsAround 100 billion to 1 trillion

2. GliaDifferent functions but don’t transmit information like neuronsAround 9x more than neurons

Glial CellsAstrocytesAbsorbs chemicals released by axonsInvolved in reuptakeRemoves waste products, especially that created after neurons die

Glial CellsOligodendrocytesBuilds myelin sheaths around certain neurons in the brain & spinal cord

Schwann CellsBuilds myelin sheaths around certain neurons in the periphery of the body

Glial CellsRadial GliaA type of astrocyte that guides the migration of neurons & growth of axons & dendrites during embryonic development

Basic Structure of the Neuron

Cellular Membrane2 layers of fat molecules which allow some small uncharged particles to flow in & out of the cell

Protein channels allow a few charged ions to cross the membrane but most chemicals are kept out

NucleusStructure containing chromosomes

Basic Structure of the Neuron

MitochondriaProvides the cell with energy

Requires fuel & oxygen to function

RibosomesSite of protein synthesis

Endoplasmic ReticulumThin tubes that transport newly synthesized proteins to locations around the cell

Proteins may have ribosomes attached

Basic Structure of the Neuron

Dendrites – Receives input & sends it to other neuronsCell Body – Process input & contains cellular organellesAxon – Sends input down & out of the neuronMyelin Sheath – Insulates & speeds Neural ImpulsePresynaptic Terminals – Releases communication chemicals

Dendritic SpinesShort outgrowths found on some dendritic branchesChanges in dendritic spine density underlie many brain functions, including motivation, learning, and memory.

Long-term memory is mediated in part by the growth of new

dendritic spines

Other NeuronsAfferent NeuronsBrings information into a structure

Efferent NeuronsSends information away from a structure

InterneuronsLocated entirely within a single structure of the nervous system

The Blood-Brain BarrierKeeps Most Chemicals Out of the BrainBrain doesn’t have an immune system

Endothelial CellsLine the walls of the capillaries in a tight formation in the brain

Active Transport SystemPumps the necessary chemicals (e.g. glucose) through the barrier

The Neural ImpulseImportant Terms

Electrical Gradient – the difference in the electrical charge inside & outside of the cellPolarization – difference between an electrical charge between 2 locationsResting Potential – when the electrical voltage is negatively higher inside relative to the outsideSelective Permeability – a cellular membrane that allows some, not all, molecules to pass freelySodium-Potassium Pump – a protein complex on the neural membrane that transports 3 sodium ions

outside of the cell while drawing 2 potassium ions into the cell in active transportConcentration Gradient – the difference in the distribution of ions between the inside & outside of the

membraneHyperpolarization – when the negative charge inside of the axon increasesDepolarization – when the negative charge inside of the axon decreasesThreshold of Excitation – the level that a depolarization must reach for an action potential to occurAction Potential – when depolarization meets or goes beyond the threshold of excitationAll-or-none Law – a neuron must have enough stimulation of a certain type to fire or it will not fireRefractory Period – period immediately after an action potential when the neuron will resist another

action potential

The Action Potential

Axon HillockWhere the Action Potential begins

Action PotentialRegenerated due to Sodium Ions moving down the Axon, Depolarizing adjacent areas of the MembraneMoves down the axon by regenerating itself as successive points on the axon

Refractory PeriodPrevent Action Potentials from moving in the opposite direction

The Myelin Sheath

Myelin SheathMyelinated Axons: axons covered with a myelin sheath

Nodes of Ranvier: short unmyelinated sections an a myelinated axon

Saltatory ConductionThe “jumping” of the action potential from node to node

Multiple Sclerosis: disease where the axon loses myelin

Local NeuronsSmall Neurons with Short Dendrites & Short or non-existent axons