CH. 7 Nerve Cells and Electrical Signaling Flashcards
What are the cells of the nervous system?
- neurons - excitable cells
2. glial cells - support cells
What are the 5 components of a neuron?
- soma
- dendrites
- axon
- axon hillock
- axon terminal
What is the function of the soma?
contains nucleus and most organelles
What is the function of dendrites?
reception of incoming information
What is the function of the axon?
transmits electrical impulses called action potentials
What is the function of the axon hillock?
where axon originates and action potentials are initiated
What is the function of the axon terminal?
releases neurotransmitter
What are the two types of neuron transport?
1, anterograde transport - from soma to axon terminal (A to B)
- retrograde transport - from axon to soma (B to A)
What is a synapse?
site of communication between two neurons or between a neuron and an effector organ
What is synaptic flexibility?
with continued use, synapse changes anatomically which produces a different synapse
What are the 3 ion channels of a neuron?
- leak channels
2, ligand-gated channels
- voltage-gated channels
- sodium and potassium channels
- calcium channels
What are the characteristics of leak channels?
- always open
- located throughout the neuron
- has a resting membrane potential
What are the characteristics of ligand-gated channels?
- open or close in response to ligand binding
- located on dendrites and cell body
- synaptic potentials?
What are the characteristics of voltage-gated channels?
- open or close in response to changes in membrane potential
- sodium/potassium channels are found throughout but more in the axon (action potentials)
- calcium channels found at axon terminal (releases neurotransmitter)
What are the three structural classes of neurons?
- bipolar
- pseudo-unipolar
- multipolar
What are the three functional classes of neurons?
- afferent neurons
- efferent neurons
- interneurons
What are the four types of glial cells?
- astrocytes
- microglia
- oligodendrocytes
- schwann cells
What are the characteristics of oligodendrocytes?
- located in the central nervous system
- one oligodendrocyte forms several myelin sheaths and myelinates sections of several axons
What are the characteristics of schwann cells?
- located in the peripheral nervous system
- one schwann cell forms one myelin sheath and myelinates one section of an axon
Why do resting membrane potentials exist?
there are more negative charges inside the cell and more positive charges outside the cell
What is the resting membrane potential of neurons?
-70 mV
What are the two factors that are critical in determining resting membrane potential?
- ion concentration gradients
2. membrane permeability to these ions (ion channels)
What is a graded potential?
relatively small change in the membrane potential produced by some type of stimulus that triggers the opening or closing of ion channels
What is the concentration gradient produced by the Na+/K+ pump?
high sodium outside, low inside
low potassium outside, high inside
How does electrical driving force respond when K+ diffuses out of cell that is permeable to potassium only?
wants to pull K+ back into the cell to make less negative
When is an ion at equilibrium?
when there is no net force for it to move across the membrane
i.e chemical force = negative electrical force
or
electrochemical force = 0
What is the ion permeability of neurons?
neuron is 25 times more permeable to potassium than sodium
- more potassium leaves the cell than sodium enters
- makes the inside of the cell more negative
What are the chemical driving forces of a typical neuron?
potassium out
sodium in
What is the steady state of a neuron?
inflow of sodium is balance by outflow of potassium
- creates a resting membrane potential of -70mV
What are the different types of gated channels in neurons?
- voltage gated
- ligand (chemically) gated
- mechanically gated
What are the phases of an action potential?
resting - depolarization - repolarization - hyperpolarization
What does it mean when graded potentials are decremental?
magnitude decays as it spreads
What is temporal summation?
a graded potential where the same stimulus is repeated close together in time
What is spatial summation?
a graded potential where different stimuli overlap in time
What is an action potential?
rapid large depolarization is used for communication
How do action potentials travel in neurons?
along axons from cell body to the axon terminal
- if afferent neuron, from receptor to terminal
What occurs that prevents an action potential from reaching the equilibrium constant of sodium?
the slow opening of potassium channels and the slow closing of sodium channels
What restores the resting membrane potential when an action potential has reached hyperpolarization?
sodium/potassium pump
What are the two gates associated with the voltage gated sodium channel?
activation gate and inactivation gate
What is the “all-or-nothing” principle?
a threshold depolarization needs to be met in order to induce the regenerative mechanism for the opening of sodium channels
i.e for action potential to occur
What is the refractory period?
period of time following an action potential
- absolute
- relative
How long does the absolute refractory period last?
spans all of depolarization and most of the repolarization phase
- second action potential cannot be generated
How long does the relative refractory period last?
spans the last part of the repolarization phase and hyperpolarization
- second action potential can be generated but with a stronger stimulus
What are the 3 consequences of refractory periods?
- all-or-nothing principle
- frequency coding
- unidirectional propagation of action potentials
What needs to be present for the propagation of action potentials?
myelin
