QUIZ #4

Name the parts of the neuron

• dendrites— receive signals from other cells

• Cell body— organizes & keeps the cell functional

• Nucleus— controls entire neuron

• Cell membrane— protects cell

• Axon hillock— generates impulse in neuron

• Axon— transfers signals to other cells & organs

• Node of ranvier— allow diffusion of ions

• Myelin sheath— increases the speed of signal

• Schwann cell— produces the myelin sheath

• Axon terminal— forms junctions w/ other cells

Id the phases of an action potential

• resting state (polarization): -70mV/ sodium potassium pump maintains high sodium outside & high potassium inside/ voltage gates channels are closed

• Depolarization (rising phase): -55mV/ voltage gated channels open/ sodium rushes in cell/ inside becomes +

• Repolarization (falling phase): sodium channels close at peak/ voltage gated potassium channels open allow K+ to go out/ lowers internal voltage back toward negative state

• Hyperpolarization: potassium channels close slowly causing excess overload of K+ ions

• Return to resting: K+ channels close/ sodium potassium pump restores og ion concentrations/ reestablishing resting potential

Describe the ionic basis of an action potential

• relies on rapid sequential changes in membrane permeability to sodium (Na+) & potassium (K+) ions through voltage gated ion channels

Describe the chemical & electrical driving forces acting on sodium (Na+)

• chem force- so fun has high concentration outside of cell & low concentration Inside

  • chem force (concentration gradient) constantly pushes sodium into cell

• electrical force- @ rest, inside of cell is negative relative to outside (-70mV) bc sodium is + charged cation neg interior of cell attracts it

  • Elec force also pulls sodium into cell

• Work in same direction creating strong net driving force pulling sodium inward

Discuss the chemical & electrical driving forces acting on potassium (K+)

• chem force- K+ has high concentration inside cell & low concentration outside

  • Chem concentration gradient pushes K+out of cell

• Elec force- negative interior of cell attracts + charged K+ ion pulling it into cell which opposes chem force

• This oppose each other

What is the importance of a sodium/potassium pump?

• vital protein in cell membrane that actively moves 3 sodium ion s out of the cell & 2 potassium ions into cel using energy from ATP

• Maintains resting potential

• Powers secondary active transport

• Enables nerve signaling

• Drives muscle contraction

What is graded potential?

• located in soma & dendrites

• Signal strength varies (proportional to stimulus size)

• Travels short distance/ fades out quickly

• Uses Chemically gated (ligand) or mechanically gated ion channels

• Can be depolarizing or hyperpolarizing

• Can add together (summate)

• No threshold required (caused directly by stimulus)

• No refractory period

What is action potential?

• located in axon & axon hillock

• Signal strength is constant/uniform (all or None)

• Travels long distance/ travels down the entire axon

• Uses voltage gated ion channels

• Always depolarizing & reversing

• Can’t sum together

• Requires threshold

• Has refractory period (to prevent backward firing)

Define depolarization

• inside of cell becomes less negative

  • Happens when positively charged Na+ ions rush into cell

Define hyperpolarization

• inside of cell becomes more negative than the normal resting state bc K+ channels stay open too long

Define Repolarization

• inside of cell returns to normal negative charge

  • Happens when K+ ions flow out of cell

What is the difference btwn btwn absolute & relative refractory periods

absolute refractory period—is a phase during action potential when no stimulus can trigger another signal

Relative refractory period— is the following phases when a stronger than normal stimulus can trigger a new action potential