Cell-to-Cell Communication

• The resting membrane potentials of most cells are -50 mV, the RMP for neurons is -70 mV, the RMP for Epithelium cells is -50 mV, and the RMP for skeletal cells is -90 mV
• The Nernst Equation defines the relation between the concentrations of ions on either side of a membrane that is perfectly selective for that ion and the potential difference (voltage) than will be measures across that membrane under equilibrium conditions
• The Nernst Potential for Na+ is +55mV, the Nernst potential for Cl- is -65-70mV, and the Nernst potential for K+ is -90mV
• when the membrane conductance increases for a particular ion, the membrane potential will move toward the Nernst potential for that ion
• hypokalemia is having low potassium serum levels which is dangerous because potassium is needed to carry electrical signals in your body
• Cytokines are a large class of regulatory proteins that are hormone-like but any cell can secrete cytokines at some point in its lifespan. They play a role in cell development, cell differentiation, and immune responses
• gap junctions form direct cytoplasmic connections between adjacent cells. Spanning proteins called connexins form the union of the membrane
• Contact-dependent signals require interaction between membrane molecules on two cells
• Paracrine signals are secreted by one cell and diffuse to adjacent cells. Limited by the distance between adjacent cells 
• Autocrine signals act on the same cell that secreted them
• hormones are a form of chemical communication that are secreted by endocrine glands or cells into the blood and distributed by circulation. Only target cells with receptors for the hormone response to the signal
• neurohormones are chemicals released by neurons into the blood for action at distance targets; for body-wide distribution but by neurons rather than the endocrine system
• Receptor channels are ligand-gated channels that open or close and alter ion flow, whereas receptor enzymes are ligand-gated channels that bind to a receptor enzyme and activate an intracellular enzyme
• G Protein-Coupled Receptors are activated by a ligand binding to the extracellular domain of the receptor which opens an ion channel or alters enzyme activity
• Integrins attach to the cytoskeleton via anchor proteins and ligands binding to the receptor causes integrins to activate intracellular enzymes
• signal transduction converts chemical or electrical signals into cellular responses. Can lead to endless possible outcomes including cytokine production, antigen presentation, survival, motility, proliferation, differentiation, angiogenesis
• amplifier enzymes turn one molecule into multiple receptor molecules to create a larger effect with a small amount of ligand
• the activated membrane receptor turns on it signal transduction proteins and starts an intracellular cascade of second messengers
• metabotropic receptors are coupled in intracellular signaling pathways through G proteins, whereas ionotropic receptors are ligand-gated ion channels that are faster and more efficient.
• calcium is not only an intracellular active molecule, but it can also be an extracellular signal molecule; too much of it can cause overreactions
• gases can cause paracrine and autocrine signaling; nitrous oxide gas causes capillaries to dilate and accept oxygen; H2S acts in the cardiovascular system to relax blood cells
• glial cells are the most abundant class of cells in the nervous system, they serve supporting roles to the neurons and they are mitotic
• astrocytes are a type of glia that makes up 20-50% of the brain; they wrap around blood vessels and neurons and every capillary entering the brain. They make up the blood-brain barrier because they are semipermeable and decide what comes into and out
• ependymal cells monitor cerebrospinal fluid and circulate it. They keep the brain buoyant, filter plasma, and allow nutrients to travel
• oligodendrocytes synthesize myelin in the CNS neurons. 1 cell is able to wrap around 50-60 axon segments
• Schwann cells synthesize myelin for PNS neurons. they cover all axons but may not secrete myelin on all. They can either wrap around all axons and not myelinate them or wrap around one axon and myelinate it
• Neurolemma is the plasma membrane of the Schwann cells that surround the myelinated nerve fibers; they are involved in protecting and regenerating nerve fibers
• the function of microglia is brain patrol; they are related to macrophages and mediate immune responses; they can move to where there are pathogens and act like a macrophage
• In the PNS, myelination occurs as a result of neuregulin 1 binding to ErbB receptors on the Schwann cell telling the myelin to wrap around
• Afferent neurons carry information from the senses into the CNS. Pseudounipolar neurons operate for the somatic senses and bipolar neurons are those for smell and vision
• interneurons live in the spinal cord and they serve as integrators. Interneurons can be anaxonic or multipolar
• Efferent motor neurons carry information away from the CNS to the muscles. Motor neurons are multipolar neurons.
• Anterograde transport uses kinesin along microtubule networks to transport vesicles
• retrograde transport uses dynein to transport microtubules back to the soma
• Growth cones are dynamic structures located at the tips of growing axons during development; they play a crucial role in guiding the axon to its target destination. Elaborate branching architecture during neuronal development requires actin-based motility and guidance signal proteins to form an axon
• Neuromas are tumor-like proliferations of neural tissue that develops after a nerve has been severed or damaged and the growth cone malfunctions
• a voltage-gated ion channel is a protein that opens and closes based on the voltage across the membrane; the cell can tell if there is a positive or negative ion around and can change shape accordingly
• At rest, the sodium channel activation gate is closed and the inactivation gate is open. In action, both the activation gate and the inactivation gate are open. When they are inactivated, the activation gate is open and the inactivation gate is closed
• the absolute refractory period is characterized by a time period that another action potential cannot occur and the Na+ channel activation gates and the voltage-gated K+ channels are still open
• the relative refractory period is characterized by the time period in which another action potential can occur but only unidirectionally because the K+ channels are still open