Lecture 3: Nervous System 3 Cont Flashcards
More ____ is going to be going outside the cell than _____ going into the cell
K
Na
Equilibrium potential for K is
-90mV
Equilibrium potential for Na is
+60mV
At resting potential is Na or K at equilibrium?
If not, what direction do they leak?
Nope
K into the cell
Na out of the cell
What counterbalances the leakage of Na and K across the membrane?
The Na/K pump
What is responsible for the electrical property of the membrane?
The unequal distribution of a few key ions between the ICF and the ECF and their selective movement across the plasma membrane
Permeability of the axon membrane to Na and K is regulated by ____, which open in response to _______
gates
stimulation
Two stages of net diffusion of Na and K
- Na moves into the axon
2. K moves out
Ion channels are made of
integral membrane proteins
Ion channels are selective, meaning
they only permit the passage of certain ions
Ion channels are controlled by
gates which open or close the channels
Three types of gates
Voltage-gated
Ligand-gated
Modality-gated
Ligand-gated
A chemical binds to the gate, opening the channel
Voltage-gated
Controlled by changes in the membrane potential
Activation gate opened by the depolarization of nerve cell membrane
Example of a voltage-gated ion channel
Na+
Modality-gated ion channel
Specialized structures that transform the energy of a specific, local stimulus into action potentials
4 examples of modality-gated ion channels
- Mechanoreceptors
- Thermoreceptors
- Chemoreceptors
- Nociceptors
Mechanoreceptors
sensing touch, stretch, and pressure
Chemoreceptors
Sensing taste, smell, and specific chemicals such as O2 and H+
Changes in the membrane potential can take two basic forms:
Graded potentials
Action potential
Graded potentials
Local changes in resting membrane potential that travel in a decremental fashion and does not reach the initiation segment
Why are local potentials called graded potentials?
Because they vary from large to small depending on the stimulus strength or frequency
Temporal summation
Increased frequency of stimulation can cause two or more local potentials to combine
Local potentials occur most often where?
- In dendrites and cell bodies of neurons
- Near the sites where the neurons innervate muscle cells
What is the basic mechanism for transmission of information in the nervous system and in all types of muscle
Action potential
Threshold potential
When a local potential depolarizes to this point, it will cause an action potential
Polarization
The membrane has potential
There is a separation of opposite charges
Depolarization
Process of making the membrane potential less negative
Also referred to as a decrease in potential
Repolarization
Return of the membrane to resting potential after having been depolarized.
Also referred to as an increase in potential
Hyperpolarization
The process of making the membrane potential more negative than the resting potential
Refractory period
- Period during which another action potential cannot be elicited from an excitable cell. Can be absolute or relative.
- Ensures the unidirectional propagation of the action potential down the axon, away from the initial site of activation
What kind of response does an action potential have?
All or nothing
An action potential is inevitable once
the membrane is depolarized to threshold
Action potential propagation - does the original action potential travel along the membrane?
Nope, instead it triggers an identical new action potential in the adjacent area of the membrane.
It is non-decremental
Two types of action potential propagation
- Local current flow
2. Saltatory conduction
Saltatory conduction
Action potential “jumps” between the nodes of Ranvier
Nodes of Ranvier
Places in the fibers that are not covered in the myelin sheath. Sodium channels are concentrated here.
