Neuronal Communication

NEURONS

oldest and longest cells in the body, 100 to 100 billion in nervous system

Sensory neurons

information from environment

Motor neurons

contraction of muscles

Interneurons

between sensory and motor

Soma

cell body/nucleus

Dendrites

branches that communicate with other neurons via synapse, receiving end of neurons that carry info to cell body

Axon

long slender tube covered by myelin sheath, carries information away from cell body

Multipolar neurons

most common, one axon to multiple trunks

Bipolar neurons

interneurons, one axon and one dendritic tree, soma in middle of axon

Unipolar neuron

one stalk, usually sensory

Terminal buttons

secrete neurotransmitters, can be excitatory and inhibitory

Synapse

microscopic space in between terminal button and dendrites of another neuron, where neurotransmitters pass through

Membrane

double layer of lipid molecules, proteins that can detect other substances and control access to interior, enzymes that control chemical actions

Inside cell

nucleus with chromosomes, cytoplasm, mitochondria, cytoskeleton

Cytoplasm

gel-like fluid that fills the cell, protects from damage

Mitochondria

contains own DNA and makes ATP

Cytoskeleton

microtubules and axoplasmic transport

Anterograde transport

faster transport, from soma to terminal button

Retrograde transport

from terminal button to soma

Glial cells

glue cells

Macroglia cells

astrocytes, oligodendrocytes, schwann cells

Astrocytes

support, nourish, monitor, and address critical chemical levels and clean-up/recycling, receive glucose from capillaries, reduce to lactase, pass to neurons

Oligodendrocytes

produce the myelin sheath, segments of coverage are 1 mm, nodes of ranvier in between are 1 micrometer

Myelin sheath

insulates axon to speed up action potential

Nodes of ranvier

spaces in between myelin sheath

Schwann cells

one schwann cell per one section of axon, located on myelin sheath, help dendritic growth and repair

NG2 cells

oligodendrocyte precursor cells, transform into different kind of glia and neurons

Microglia cells

immune and inflammatory responses

BLOOD BRAIN BARRIER

walls of capillaries, selectively permeable, blocks all molecules except those that can pass by lipid solubility (ex: oxygen, carbon dioxide, ethanol, vitamins A, D, E, and K) or allowed in by specific transport systems (sugars and some amino acids), glial cell management

CELLULAR COMMUNICATION

inside of cell membrane is -70 mV relative to outside of cell (resting potential)

Depolarization

take away some of electrical charge, reduce membrane potential

Threshold of excitation

-55 mV, leads to action potential

Depolarization

inside becomes more positive relative to resting state

Hyperpolarization

more negative than resting potential for nanosecond

Diffusion

molecules distribute themselves evenly, move from high concentration to low concentration

Electrostatic pressure

force of opposite ions repelling

Cations

positive charge

Anions

negative charge

Sodium potassium pump

metabolically expensive, pumps out 3 Na+ for every 2 K+ in, maintains homeostasis

Extracellular fluid

seawater, Na+Cl-

Intracellular fluid

membrane is impermeable, A- and K+ exist at resting potential inside cell membrane of -70 mV

Action potential

occurs when voltage dependent channels reach -55 mV, voltage changes from -55 mV to 30 mV as Na+ rushes into cell, sodium channels become blocked until resting potential reached again but some sodium can still get in, potassium still leaves due to electrostatic pressure because inside of cell is now positive, potassium channels close as membrane returns to resting potential

Hyperpolarization

extra potassium exists outside of membrane briefly, causing greater negative charge

All or none law

action potentials either happen or don't, can't happen halfway