Cell Communication

Multicellular Organisms Signal transduction pathways coordinate the activities within individual cells that support the function of the organism as a whole

Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling

Another form of short distance signaling Messages sent between neurons in Nervous system

Neurons (Nerves) Specialized cells to transmit nerve impulses from one part of body to another 3 main parts Dendrite (signal receiving end) Cell body Axon (signal sending end)

Many axons have a myelin sheath that acts as an electrical insulator. Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron

Synapses junction between two neurons where messages are passed on by neurotransmitters

Resting neuron structure Contain potassium (K+) ions inside neuron Sodium (Na+) ions are outside plasma membrane and don’t normally pass inward

Polarized neuron Inactive (not sending an impulse) Inside of neuron negatively charged to compared to outside

Stimulated neuron- Depolarization Na+ gates in membrane open and Na+ rushes into cell causing inside to be more positive than outside of cell which activates neuron to transmit an action potential

Action potential nerve impulse which causes the axon to release a neurotransmitter into synapse that binds to next neuron stimulating it

Cell Repolarization After action potential K+ rushes out of cell causing the inside to become negative again Must occur before neuron can send another nerve impulse

After repolarization Na+/K+ pump Pumps K+ into cell and Na+ out to restore cell to make it polarized again

Transmission of information via neurotransmitters between neurons occur across synapses and result in responses Responses can be stimulatory or inhibitory Epinephrine Acetylcholine Norepinephrine Dopamine Serotonin GABA

YOUTUBE Video

Long distance signaling in Humans Requires cardiovascular system to transport hormones (chemical messages = ligands) to cells in other areas of body

Endocrine signals (hormones) are produced by endocrine cells that release signaling molecules, which are specific and can travel long distances through the blood to reach all parts of the body Examples: Insulin Human growth hormone Thyroid hormone Testerone Estrogen

Insulin