NUR 631 Topic 8 Midterm Topics to Review
(Midterm Topics)
Action potential
Membrane Action Potential à Resting Neuron = – 70 MV/ (Threshold for action potential is -55) Action potential happens when internal cell reaches about -55mv/ all or nothing phenomena/ Strength of action potential is always same what changes is the frequency and conduction speed ( conduction speed is slower to glands, blood vessels. (Axon with large diameter increased conduction due to less resistance, PNS myelin sheaths are formed by Schwann cells wrapping themselves around the axon. These cell don’t touch each other and creates a gap called NODES OF RANVIER that makes salutary (Leap) conduction making current to run through axon faster. CNS oligodendrocytes wrap around the axons and lacks nodes of Ranvier. )
- Resting neuron are in – negative charge inside the cell and + charge extracellular
- Sodium is in extracellular with + charge and potassium is intracellular bonded d with negative protein with + charge
- Electrochemical gradient is … by Sodium Potassium pumps creating negative charge inside the cells and positive charge in extracellular. Sodium potassium pumps are all along the axons that exchanges 3 sodium in the cell for 2 potassium outside the cell.
- Ion channels: – most are voltage-gated channels that open … and reopens to changes in membrane potentials. Sodium channel opens @ -55 MV
- Ligand-Gated Channels: – opens with neurotransmitter latched on to receptors like hormones or serotonin
- Mechanical gated channels: – opens in response to the physical stretching of the membrane and Sodium gets in the cell.
- Action potential depolarization: – All ions channels are … at resting membrane voltage – 70mv. Depolarization of neuron has to happen for those voltage channels to open. An environmental stimulus opens mechanical channels which makes Sodium (NA+) to get in the cell changing charge inside the cell increases from -70. Threshold for action potential is -55mv. It is all or nothing phenomena. Stimulus that causes <-55 of depolarization is false alarms nothing happens.
- @-55mv gated sodium channel opens which rushes plenty of sodium on the cell causing depolarization which activates the sodium get next to it conducting this current in axon. Cell massive depolarization can go all the way up to +40 mv (which stays same for each action potential). This is action potential in action. This change in current kicks biological change down the axon. As soon as depolarization under way the process repolarization occurs where voltage gated potassium ions open letting K+ ( potassium ) flow out in extracellular space. This can cause membrane to first go hyperpolarized at about -75 before voltage channel closes and sodium potassium pumps take over.
- When the Ion channels are open in membrane it cannot respond to any other stimulus. Does not matter how strong of stimulus it is. This is called Refractory Period.
- Refractory period: – The first phase of this period from depolarization to repolarization is called absolute refractory period and it makes sure each action potential is unique in its own and all or nothing event. The second phase immediately follows the first one that spans from repolarization and back to … the relative refractory period
Atrophy (p. 50) – decrease or shrinkage in cellular size, can lead to the entire organ shrinking and atrophying – can affect any organ (most common in skeletal, heart, secondary sex and brain).
Physiologic atrophy – with early development – thymus gland undergoes physiological atrophy during childhood
Pathologic atrophy – results of decreased workload, use, pressure, blood supply, nutrition, hormonal simulation, and nervous stimulation. Examples are individuals not moving in bed, resulting in skeletal muscle atrophy (disuse atrophy)
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