Chapter 3 Flashcards
(74 cards)
How do neurons solve the problem of conducting info over long distances?
Using electrical signals that sweep along the axon.
How does electrical charge in the cytosol of the axon get carried?
- By electrically charged atoms (ions) instead of free electrons.
- This makes cytosol far less conductive than copper wire.
- Also, axon is not especially well insulated and is bathed in salty extracellular fluid which conducts electricity.
Action potential
(Nerve impulse) A special type of signal that overcomes biological constraints. They do not diminish over distance (unlike passively conducted electrical signals). They are signals of fixed size and duration.
Excitable membrane
Cells capable of generating and conducting action potentials.
What does it mean when a cell is at rest?
The cytosol along the inside surface of the membrane has a negative electrical charge compared to the outside.
What is the difference in the electrical charge across the membrane?
The membrane resting potential. In terms of the resting potential, the action potential is a brief reversal of this condition (inside is positive).
Ions
Atoms or molecules that have a net electrical charge.
Ionic bond
Electrical attraction of oppositely charged atoms.
Electrical charge of an atom depends on…
…the difference between the number of protons and electrons.
Give examples of hydrophilic substances.
Ions, polar molecules. These dissolve in water.
Give examples of hydrophobic substances.
- Hydrophobic: Any compound held together by nonpolar covalent bonds (no net electrical charge).
- Lipids (important to structure of cell membranes).
Lipids of neuronal membrane contribute to resting and action potentials by…
…forming a barrier to water soluble ions and to water itself.
Phospholipids
- The main chemical building blocks of cell membranes.
- Contain long nonpolar chains of carbon atoms bonded to hydrogen atoms, as well as a polar phosphate groups (phosphorous bonded to three oxygen atoms) attached to one end of the molecule.
How are phospholipids arranged (the head and tail)?
They have a polar head (containing phosphate) that is hydrophilic, and a nonpolar tail (containing hydrocarbon) that is hydrophobic.
Which side of the phospholipid faces the outer and inner watery environments?
Hydrophilic heads face outer and inner watery environments. Hydrophobic tails face each other.
Neuronal membrane consists of…
…a sheet of phospholipids, two molecules thick. This is the phospholipid bilayer, and it effectively isolates the cytosol of the neuron from the extracellular fluid.
Proteins provide…
…routes for ions to cross the neuronal membrane.
Describe the physical characteristics of amino acids.
- All have a central carbon atom (alpha carbon) which is covalently bonded to four molecular groups.
- A hydrogen atom, an amino group, a carboxyl group, and a variable group called the R group.
What is the difference between amino acids?
Differences between amino acids result from differences in the size and nature of R groups.
How are amino acids assembled into a chain?
They are connected by peptide bonds, which join the amino group of one acid to the carboxyl group of the next.
Polypeptides
Proteins made of a single chain of amino acids.
Regions where nonpolar R groups are exposed will be…
…hydrophobic and will tend to associate readily with lipid.
Regions with exposed polar R groups will be…
…hydrophilic and will tend to avoid a lipid environment.
Ion channels
Suspended in a phospholipid bilayer, with its hydrophobic portion inside the membrane and its hydrophilic ends exposed to the watery environments on either side.