Neurons and Action Potentials

Functions of Glial Cells

1. support neurons 2. insulate the electrical activity moving down the axon and at the synapse 3. maintain fluid balance around neuron 4. transports nutrients 5. repair damaged axons

Saltatory Conduction

AP jumps along the axon due to myelination *only depolarizes the parts of the axon at the Nodes of Ranvier

Continuous Conduction

AP moves along entire length of axon (unmyelinated neurons)

Deploarization occurs twice. When?

Allows Na+ in, reducing the resting potential. After an Action Potential is triggered, the cell causes voltage-gated sodium channels to open on that part of the membrane, making the cell less and less negative

Depolarization begins at the ______?

Axon hillock

What are Neurons?

Building blocks of the nervous system. Information processing and signaling elements

Oligodendrocytes: PNS or CNS?

CNS

When is an action potential triggered?

Depolarization causes the cell to be less negative and resting potential drops below threshold (about -50 mV)

Neural Connective Tissue, layers of the PNS

Endoneurium, perineurium, and epineurium

Resting Potential of Neuron: Extracellular and Intracellular

Extracellular: more Na+ and Cl- Intracellular: more K+ and negatively charged molecules **This results in a negative charge

Action potentials

Information is carried as electrical signals

Diffusion of Ions at Rest

K+ ions diffuse in and out of the cell (potassium channels) In: due to attraction to protein Out: due to concentration gradient Na+ ions also move in to some extent due to concentration gradient

Neurotransmitters

Made in the neuron, released from the terminal boutons and interact with the structure on which the axon is synapsing.

What are Glial Cells?

Majority of brain cells**All neurons will have this cell whether they are myelinated or unmyelinated

What can disturb resting potential?

Mechanical stimuli (open mechanically-gated sodium channels) and Neurotransmitters (open ligand-gated sodium channels)

Depolarization

Membrane potential becomes more positive (from -70 mV to +40 mV)

Basic elements of the nervous system

Neurons and Glia

Vesicles/terminal boutons contain... what?

Neurotransmitters

Types of Glial Cells

Oligodendrocytes and Schwann Cells

Action potential is an "all-or-none" phenomenon. What does this mean?

Once depolarization reaches threshold the AP occurs.

Schwann Cells: PNS or CNS?

PNS

Resting potential

Period where neuron is reestablishing the resting potential. Means that APs are unidirectional

Which form of conduction is faster? Why?

Saltatory, jumps along the axon

How is resting membrane potential maintained?

Sodium-Potassium Pump-->pumps 2 K+ ions into cell for every 3 Na+ ions it pumps out Leaky Potassium Channel-->facilitates diffusion of K+ out of cell (Due to cell permeability)

After an action potential is triggered?

The reduced potential (at threshold) causes hundreds of voltage-gated sodium channels to open on that part of the cell membrane

What is the function of Neurons?

Transmits information

Relative Refractory Period

When neuron potential is between -50 and -70 mV. AP can be triggered by a stronger stimulus. (after start of hyperpolarization)

Myelin

White, fatty wrapping. Formed by glia. Insulate the axon and increase the speed of conduction of nerve impulses alone the axon.

Soma

cell body, has cell membrane around it. cell membrane has small pores which allow certain ions to move through the membrane.

Resting Membrane Potential

charge difference across the cell membrane when the cell is at rest. The electrical potential is -70 mV.

If diffusion at rest was allowed to continue, what would happen?

concentration would equalize across the membrane and resting potential would be 0

Synapse

connection between neurons or between a neuron and a muscle

Size (strength) of AP remains ________.

constant (like a toll booth)

Strength of stimulus is reflected in ______ of APs triggered.

frequency

Concentration gradient

ions move from areas of high concentration to areas of low concentration

Axon hillock

junction between axon and soma

Absolute Refractory Period

no AP can be triggered during this time (happens after repolarization)

Axons

projections carrying messages from the cell body

Dendrites

projections carrying messages to the cell body

Hyperpolarization

seen in the overshooting region of the action potential, when the resting potential dips even more negative than the resting potential. (more negative than -70 mV)

Electrochemical gradient

similarly charged ions repel one another, oppositely charged ions attract one another

Nodes of Ranvier

spaces between myelin

Endoneurium

surrounds Schwann cells which are wrapped around 1 or more axons

Epineurium

surrounds several neural bundles to form nerve trunks

Perineurium

surrounds several sets of neurons each covered by endoneurium to form neural bundles (fasicle)

Repolarization

the return of the membrane potential to resting potential (+40 back to -70 mV)