Chapter 2: COMMUNICATION WITHIN A NEURON Flashcards
How do neurons conduct signals?
-With electrical signals sweeping across axons
What happens when someone touches a hot stove?
- Dendrites of sensory neurons detect painful stimuli
- The interneuron excites a motor neuron causing muscular contraction
- The muscle contraction causes withdrawal from source of pain
What happens when someone is holding a warm, but not too hot cup of tea?
- Dendrites of sensory neuron detect temperature stimuli
- An interneuron excites a motor neuron
- Another interneuron inhibits the motor neuron preventing muscular contraction
- The person doesn’t drop the cup
What is a membrane potential?
Any difference in electrical charge (positive or negative) between the inside and the outside of a membrane.
Potential=stored up source of energy
What is the membrane’s resting potential?
When the neuron is at rest and not involved with communicating with any other neurons, the membrane’s resting potential is -60 to -70 mV.
Astrocytes resting potential?
-80 to -90 mV
Skeletal muscle resting potential?
-95 mV
Smooth muscle resting potential?
-60 mV
What are the three ways you can measure electrical potential of axons?
- electrode: apply electrical stimulation or record electrical potentials
- microelectrode: record activity of individual neurons
- membrane potential: electrical charge across cell membrane
What are the 3 key players for maintaining resting potential?
- neuronal membrane
- fluid
- ion channels (protein) in the neuronal membrane
What are the functions of the neuronal membrane?
- enclose cytoplasm and cytosol
- establish the electrical potential of the cell
- control the flow of ions into and out of the cell
- conduction of nerve impulse
- sense neurotransmitters
cytosol vs cytoplasm?
- cytosol is the fluid present inside the cell membrane
- cytoplasm is a cell component present outside the cell membrane
What are cytosol and extracellular fluid composed of ?
-Water and electrically charged ions (cations +, anions -)
What are the properties of the water that composes the cytosol and extracellular fluid?
- Key ingredient: polar molecule that make water an effective solvent for charged or polar molecules
- spheres of hydration: clouds formed around ions because they attract water molecules, which insulates the ions from one another
What are the properties of the neuronal membrane, knowing that it is a “sheet” of phospholipids?
- hydrophobic: does not dissolve in water due to even electrical charge, because lipid are hydrophobic
- also hydrophilic (neuronal membrane is semipermeable because permeable to certain ions and also depending on if it is depolarized or not)
- Lipids contribute to resting and action potential
What are ion channels composed of ?
- Channel proteins: pore formed by 4 to 6 membrane-spanning proteins. Each structure is called a subunits.
- Each subunit: has hydrophilic and hydrophobic regions, determines properties of ion channels
On what factors can ion channels be selective?
- charge
- size (diameter of the pore)
- gating: channels can open or close based upon local microenvironments.
What are ion pumps and what do they do?
- ion pumps are also situated on the axon, and are active.
- They use ATP (adenosine triphosphate) to pump ions in and out of the cell.
What does the force of diffusion do?
- distribute the molecules evenly throughout the medium in which they are dissolved.
- molecules ultimately attain balance
What does the force of electrostatic pressure do?
-Pulls ions of opposite charges together and pushes ions with the same charges apart.
What are the 2 factors electrostatic force is determined by?
-electrical potential (voltage): force exerted on charged particle, difference in charge between anode and cathode
-electrical conductance (g):
R is electrical conductance, R= 1/g, relative inability of an electrical charge to migrate
What is the movement of electrically charged ion determined by?
- concentration gradient
- difference in electrical potential across the membrane
What is osmosis?
The diffusion of water from a hypotonic solution to a hypertonic solution across a semipermeable membrane.
What is osmotic balance?
It ensures optimal concentration of ions in intracellular and extracellular fluids.
Balance reached when electrical force pulling an ion in/out is equal to diffusion force pushing an ion in/out
What would the RMP equal to if it depended only on K+ or Na+?
- K+= -80mV
- Na+= 62 mV
Why is an ion not easily maintained at its equilibrium potential?
- Membranes are leaky
- K+ always leaking out and Na+ always leaking in
- This interferes with concentration gradient required to maintain RMP
What is the solution to the leaky membrane?
The sodium-potassium pump
What does the sodium-potassium pump do ?
- It is made of sodium-potassium transporters that exchanges 3 Na+ (push them out) for 2 K+ (take them in)
- So it keeps the concentration of Na+ low in side the membrane by increasing the concentration of K+ by a little bit
How is the membrane with regards to potassium (K+)?
Very permeable to K+ (very leaky to K+)
Small change in extracellular= big change in intracellular
What is depolarization?
A change in membrane potential from a resting value to a less negative value
What are the two mechanisms that regulate the external concentration of potassium?
- blood-brain barrier
- Potassium spatial buffering by astrocytes
How does the blood-brain barrier regulate external concentration of potassium?
-astrocytes take up K+ when extracellular levels are high (K+ pumps)
