Presentation on theme: " Located in almost all animals Carries electrical impulses on the specialized cell membrane of the nerve cells Nerve cells coordinate the opening."— Presentation transcript:
Located in almost all animals Carries electrical impulses on the specialized cell membrane of the nerve cells Nerve cells coordinate the opening and closing of ion channels in the cell membrane to create an action potential.
Made of two layers of phospholipids a.k.a. a lipid bilayer Proteins and cholesterols are embedded in the membrane
1. Passive transport Simple diffusion Facilitated diffusion 2. Active transport 3. Endocytosis and exocytosis
a) Simple diffusion Materials move from areas of high concentration to areas of low concentration Energy from the cell is not needed When concentrations are equal, molecules still move but no net change results Things like water, oxygen, and carbon dioxide move by simple diffusion The diffusion of water across a selectively permeable membrane is called osmosis
Osmotic pressure = a force driven by differences in solute concentration; can cause cells to shrink or swell
Hypertonic = “above strength,” more solute present in the solution Hypotonic = “below strength,” fewer solutes present in the solution Isotonic = “same strength,” same amount of solute in solution as in cell
b) Facilitated diffusion Channel proteins and carrier proteins help larger molecules cross the membrane Many channels are gated for regulation Carrier proteins change shape to move molecules through More specific than simple diffusion but still does not require energy Things like proteins and sugars move by facilitated diffusion
Cells sometimes need to move substances against the concentration gradient Often carrier proteins act as pumps Energy is required Supplied by ATP Amino acids, sugars, and ions are often moved by active transport
a) Sodium ions normally are in high concentration in extracellular fluid Sodium ions diffuse into cells This reduces the amount of water inside the cell As a result water diffuses into the cell This is bad Too much water means cells can swell and burst High extracellular sodium concentration is also necessary for glucose transport The solution…..
Sodium potassium pump in action Sodium potassium pump in action
1. Sodium ions flow into neuron, causing depolarization; starts at the dendrites 2. If enough Na + enters neuron (and K + moves out), the membrane reaches threshold potential 3. An action potential is initiated at the axon hillock (has higher density of Na + /K + pumps) 4. The signal passes and the membrane repolarizes 5. The signal is sent along the axon causing a nerve impulse
Myelin sheath = electrical insulator that is discontinuous along the axon of the neuron; increases capacitance Axon hillock = base of the axon; has higher density of Na+/K+ pumps so action potential is more easily initiated here Neural synapse = gap between two neurons along signal pathway
1. Electrical synapse – uses ion channels connected axon to dendrite without a gap to communicate between neurons.
1. Chemical synapse – uses vesicles to move chemicals (neurotransmitters) across a small gap between neurons
Vesicles move substances into and out of cells Substances that are big molecules Proteins and polysaccharides are moved in = ENDO Proteins and waste are moved out = EXO Exocytosis moves neurotransmitters into the synaptic cleft Summary Animation