PHYSIOLOGY NOTES Chapter 11

1. a. Cell body: contains the nucleus; control center; carries out metabolism b. Dendrite: thin branched processes that project from cell body; receives impulses from other c. hillock: narrow region where axon begins; nerve impulse originates here d. Axon and axonal terminals: axon is a long process that conducts impulses away from the cell body; axonal terminals are the enlarged ends of the axon. 2. Myelin sheath in peripheral system: from Schwann cells; leaves exposed patches (Nodes of Ranvier) Myelin in central : from oligodendrocytes (neuroglia) 3. Nodes of Ranvier: gaps in the myelin sheath; rapid ion exchange area. 4. : when cells have an electrical charge across their membrane due to negative proteins and K+ inside the cell and Na+, Ca² and Cl- outside the cell; it is about -70mv. 5. a. : when the membrane potential becomes less negative (more positive); can be caused by Na+ moving into the cell! b. Repolarization: when membrane potential moves back toward -70mv; can be caused by K+ moving out of the cell or Cl- moving in. c. Hyperpolarization: when membrane potential becomes more negative than -70mv; can be caused by K+ moving out of the cell or Cl- moving into cell 6. Gated ion Channels: found in ; open due to a certain stimulus; will stay open a fraction of a second before being blocked; there are ion channels for Na+, K+, and Cl- 7. Voltage gated: channels that open at a certain membrane potential; axon terminals have Ca+² voltage gated channels Ligand gated ion channels: open when a certain molecule binds to a receptor the membrane surface 8. : rapid changes in membrane potential across a small section of the axon membrane caused by ion movement cross the membrane 9. Na+ movement: depolarization below -50mv opens voltage gated Na+ channels to Open; Na+!the cell; membrane potential rises to +30mv and then blocks Na+ channels and Na+ movement stops. K+ movement: after Na+ channels open, gated K+ channels open letting K+ out of the cell; membrane potential drops to -90mv; 10. Na+/K+ pump: moves Na+ back out of the cell and K+ into the cell, resetting the proper ion gradient 11. Myelinated axons: the myelin sheath will not allow ions to cross the membrane; at the nodes of Ranvier, the axon is bare and here ions can cross at these areas; this is called saltatory conduction. Non-myelinated axons: have no sheath of myelin; action move down the entire length of the axon; every stretch of the axon will experience depolarization and repolarization; the action potential moves like a wave.

12. All or None Law: voltage gated channels will open all the way once the membrane potential reaches the threshold; therefore, every action potential has same strength. 13. Refractory period: time period during an action potential in which the axon cannot respond to a new change in the membrane potential. 14. Absolute refractory period: when Na+ ion channel is opened it can not respond to another depolarization until it moves from the active state to the closed state. Relative refractory period: if a 2nd depolarization occurs while the K+ channels are open , it takes a more intense depolarization to overcome the effect of the K+ leaving through the open K+ channels. 15. : junction point between two neurons or between a and an effector cell (muscle or gland). 16. : chemicals stored in vesicles in the axon terminal of the pre-synaptic cell. Function: when an action potential moves down the axon to the terminal, the membrane depolarization opens voltage gated Ca+² channels; -Ca+² enters the cell causing the vesicle to fuse with the presynaptic membrane releases neurotransmitters in the synaptic cleft - neurotransmitters cross the synaptic cleft and bind to receptors on the post-synaptic membrane. 17. Excitatory postsynaptic potential: depolarization; more neurotransmitters= more Depolarization; no refractory period; several EPSP’s can be summed to create a greater depolarization Inhibitory postsynaptic potential: hyperpolarization; lessens the chance for depolarization due to increased outward diffusion of K+ ions and > increase of positive charge outside the membrane. 18. Describe: a. Acetylcholine: excitatory in the CNS and ; can be excitatory or inhibitory b. Ligand-gated channels: nicotinic acetylcholine receptors: acetylcholine binds to receptors and opens channels that let Na+ in and K+ out; more Na+ comes in so they produce EPSPs in neuromuscular junction c. G-protein mediated channels: muscarinic acetylcholine receptors: binding of acetylcholine to these receptors activate a G-protein; one type of G protein opens K+ channels letting K+ out causing an IPSP; another type closes K+ channels causing an EPSP; therefore, two different cells can have opposite response to muscarinic stimulation. d. Acetylcholinesterase: enzyme in the synaptic cleft that degrades acetylcholine. e. Monoamines: neurotransmitters derived from amine groups; similar in action to acetylcholine f. Second messenger mediation: rather than activating ion channels directly, monoamines work through a 2nd messenger, Cyclic AMP which is the second messenger; cyclic AMP!ion channels to open g. Monoamine inactivation: monoamines are reabsorbed by the pre-synaptic cell and degraded by the enzyme monamine oxidase h. Serotonin: involved in mood, behavior, appetite, cerebral circulation. i. Dopamine: two separate systems: one involved in control of movements and one involved in behavior and reward j. Norepinephrine: involved in general arousal k. Amino acids as neurotransmitters: some create EPSP’s and others, IPSP’s by opening voltage gated Cl- channels (glycine, glutamate, GABA) l. Polypeptides: analgesics, opioids; (endorphins) m. Nitric oxide: diffuses out of pre-synaptic cell and into postsynaptic cell and causes muscle relaxation in target organ; can produce engorgement of spongy tissue with blood in males 19. Signal integration: all the EPSP’s and IPSP’s that occur on the dendrites of the post-synaptic cell will add together to alter membrane potential of axon hillock 20. Spatial summation: occurs when IPSP’s and EPSP’s from several combine to alter the membrane potential 21. Temporal summation: occurs when several EPSP’s or IPSP’s are generated from the same synapse in a very short period of time and the collected effect is added together to alter the membrane potential