Ch 9: Conduction

potassium (K+)

The concentration of what ion determines the resting membrane potential of all excitable cells?

2 physical parameters influence speed of conduction: diameter of axon resistance of axon membrane to ion leakage out of the cell *larger axon diameter or more leak-resistant membrane = faster action potential*

Why do larger neurons conduct action potential faster?

potassium level above the upper limits of normal *too much K+ in ECF*, less K+ inside cell shifts RMP *closer to threshold* & causes cells to fire *action potentials* in *respond* to smaller, *graded potentials*

Define hyperkalemia

deficiency of potassium in the bloodstream. *too little K+ in ECF*, more K+ inside cell RMP of cells *hyperpolarizes*, moving *further* from *threshold*, making it *difficult* to generate *action potentials*

Define hypokalemia

stimulus is strong enough (reach threshold -55 mv) depolarization causes membrane polarity to be reversely completely & AP is initiated

Describe the stage of "depolarization & generation of action potential"

depolarization of 1st membrane patch causes permeability changes in adjacent membrane Na+ diffuse rapidly into cell; this changes membrane's polarity inside = more positive, outside = more negative

Describe the stage of "propagation of action potential"

K+ ions diffuse out of cell as membrane permeability changes again restoring negative inside & positive outside repolarization occurs the same direction as depolarization

Describe the stage of "repolarization" (last pic)

outside slightly positive; inside slightly negative sodium (Na+) outside/extracellular; potassium (K+) inside/intracellular membrane relatively *impermeable* on both ions

Describe the stage of "resting membrane electrical conditions"

stimulus changes membrane patch's permeability Na+ diffuse rapidly *into* cell; this changes membrane's polarity inside = more positive, outside = more negative

Describe the stage of "stimulus initiating local depolarization"

sodium-potassium pump; sodium; potassium

Resting membrane potential's ionic conditions are restored by __________ pump. 3 _________ gets ejected for every 2 ______ carried in.

b. False

*QUIZ* During the absolute refractory period, a second action potential can be generate if a stronger stimulus is applied. a. True b. False

c. Serve the same function as oligodendrocytes Both cells myelinate axons. They differ in their location and number of axons they myelinate.

*QUIZ* Schwann cells _______. a. Are located in the CNS b. Myelinate multiple axons c. Serve the same function as oligodendrocytes d. None of the choices are correct

c. nodes of Ranvier

*QUIZ* The gaps in the myelin sheath are called ________. a. ion channels b. gap junctions c. nodes of Ranvier d. tight junctions

a. True

*QUIZ* The smaller the axon diameter, the slower the propagation of action potentials. a. True b. False

c. Hypokalemia

*QUIZ* __________ can lead to hyperpolarization of the neuron cell membrane moving the cell further from threshold and making it more difficult for an action potential to be generated a. Hypernatremia b. Hyperkalemia c. Hypokalemia d. both hypernatremia and hyperkalemia

*Oligodendrocytes (CNS)*: one cell forms several myelin sheaths *Schwann cells (PNS)*: once cell forms myelin sheath, myelinating one section of an axon

What are the 2 types of myelin forming cell, and where are they found?

1. resting membrane electrical conditions 2. stimulus initiates local depolarization 3. depolarization & generation of action potential 4. propagation of action potential 5. repolarization

What are the 5 stages of a nerve impulse?

any chemical that binds to *sodium (Na+), potassium (K+), or calcium (Ca+)* has potential to alter action potential conduction alternations of ECF concentration of *K+ and Ca+* are associated with abnormal electrical activity

What chemical factors alter neuron's electrical activity?

*period of time following an action potential* marked by decreased excitability

What is a refractory period?

*intensity of stimulus is directly related to AP frequently* greater stimulus strength applied to neuron = AP produced more frequently (more per sec)

What is frequency coding?

a demyelinating disease: *loss of myelin* from *vertebrate neurons* can have devastating effects on neural signaling

What is multiple sclerosis?

action potential form at each node & jump along length of axon saltatory condition is the apparent *jump of action potential* from *node to node* impulse conduction is *fast* (up to 120 meters/sec)

What is saltatory conduction?

if stimulus *exceeds threshold* (-55 mv) potential, nerve or muscle fiber will give *complete response*; otherwise no response

What is the All-or-None principle?

both happen shortly after the firing of a nerve fiber absolute refractory period: there is a *total inability* to *respond* no matter how great a stimulus is applied relative refractory period: there is a *2nd response* to a very *large stimuli*

What is the difference between absolute and relative refractory periods?

*serious consequences* to body as a whole due to the relationship between the RMP & nervous/muscle tissue excitability relies on K+ concentration *messes up the ability to communicate*

What is the significance of high and low concentrations of potassium?