PHED-2506EL Chapter Notes - Chapter 11: Skeletal Muscle, Cholecystokinin, Enkephalin
25 Jun 2018
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Chapter 11 B
(I generalized question 1 because membrane potential is from a previous chapter)
1. Explain resting membrane potential with respect to depolarization and hyperpolarization
- The potential difference across the membrane of a resting neuron, which is generated by
different concentrations of sodium, chlorine, potassium and protein anions
- Depolarization occurs when the inside of the membrane becomes less negative then the outside
(becomes a graded potential and possibly an action potential)
- Hyperpolarization occurs when the inside of the membrane becomes more negative than the
resting membrane potential
oA larger stimulus will need to occur in order to create and action potential
2. Compare and contrast graded potentials with action potentials (I added a chart from an external
cite cause I feel like it contrasts the two better than the online notes…they are the first ones
listed)
- Graded potentials
oShort-lived local change in membrane potential
oDecreases in intensity over distance – there for can only travel short distance
oCurrent quickly dissipates due to the ‘leaky’ plasma membrane
oMagnitude varies directly with stimulus strength
o Sufficiently strong graded potentials can initiate action potentials
- Action potentials
oBrief reversal of membrane potential
oOnly generated by muscle cells and neurons
oDo not decrease in strength over distance
oPrinciple means of neural communication
-Graded potentials Action
Depending on the stimulus, graded potentials can be depolarizing or
hyperpolarizing.
Action potentials always lead to de
of the membrane potential.
Amplitude is proportional to the strength of the stimulus. Amplitude is all-or-none; strength
frequency of all-or-none action pot
Amplitude is generally small (a few mV to tens of mV). Large amplitude of ~100 mV.
Duration of graded potentials may be a few milliseconds to seconds. Action potential duration is relative
Ion channels responsible for graded potentials may be ligand-gated
(extracellular ligands such as neurotransmitters), mechanosensitive, or
temperature sensitive channels, or may be channels that are gated by
cytoplasmic signaling molecules.
Voltage-gated Na+ and voltage-gat
neuronal action potential.
The ions involved are usually Na+, K+, or Cl−. The ions involved are Na+ and K+ (fo
No refractory period is associated with graded potentials. Absolute and relative refractory pe
potentials.
Graded potentials can be summed over time (temporal summation) and
across space (spatial summation).
Summation is not possible with act
nature, and the presence of refrac
find more resources at oneclass.com
find more resources at oneclass.com
Graded potentials travel by passive spread (electrotonic spread) to
neighboring membrane regions.
Action potential propagation to ne
characterized by regeneration of a
along the way.
Amplitude diminishes as graded potentials travel away from the initial site
(decremental).
Amplitude does not diminish as ac
neuronal projections (non-decrem
Graded potentials are brought about by external stimuli (in sensory
neurons) or by neurotransmitters released in synapses, where they cause
graded potentials in the post-synaptic cell.
Action potentials are triggered by m
Graded potentials are responsible
to threshold.
In principle, graded potentials can occur in any region of the cell plasma
membrane, however, in neurons, graded potentials occur in specialized
regions of synaptic contact with other cells (post-synaptic plasma
membrane in dendrites or soma), or membrane regions involved in
receiving sensory stimuli.
Occur in plasma membrane regions
K+channels are highly concentrated.
Note: The details of action potentials noted here refer to those of neuronal action potentials.
As we will see throughout our study of physiology, other action potentials (for example, in
skeletal, cardiac, and smooth myocytes, and in some endocrine cells) exhibit different features
than those mentioned here.
http://www.physiologyweb.com/lecture_notes/neuronal_action_potential/neuronal_action_p
otential_graded_potentials_versus_action_potentials.html
3. Describe the 4 stages of an action potential
- Resting state
oSodium potassium channels closed
oleakage accounts for small movements of the two
oeach sodium channel has two voltage-regulated gates
activation gates – closed at rest
inactivation gates – open at rest
- Depolarization phase
osodium permeability increases; membrane potential reverses
osodium gates are opened, potassium gates closed
othreshold – critical level of depolarization, becomes self-generating
- Repolarization phase
osodium inactivation gate close
opermeability to sodium declines to resting levels
osodium gates close, voltage-sensitive potassium gates open
opotassium exits cell and internal negativity of resting neuron is restored
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Chapter 11 b (i generalized question 1 because membrane potential is from a previous chapter: explain resting membrane potential with respect to depolarization and hyperpolarization. The potential difference across the membrane of a resting neuron, which is generated by different concentrations of sodium, chlorine, potassium and protein anions. Depolarization occurs when the inside of the membrane becomes less negative then the outside (becomes a graded potential and possibly an action potential) Action potentials: brief reversal of membrane potential, only generated by muscle cells and neurons, do not decrease in strength over distance, principle means of neural communication. Depending on the stimulus, graded potentials can be depolarizing or hyperpolarizing. Action potentials always lead to de of the membrane potential. Amplitude is proportional to the strength of the stimulus. Amplitude is all-or-none; strength frequency of all-or-none action pot. Amplitude is generally small (a few mv to tens of mv). Duration of graded potentials may be a few milliseconds to seconds.
