Chapter 7 (Electrical Signals) Flashcards
electrical gradient vs. concentration gradient
- electrical gradient: # of charges
- concentration gradient: # of a certain ion
signal integration occurs at the ___
axon hillock
signal transmission occurs at the ___
axon terminal
Schwann cells
- form myelin sheath
- type of glial cell
- associated with motor neurons and many sensory neurons
- only in PNS
- wrap around a single neuron
oligodendrocytes
- form myelin sheath
- only in CNS
- protection and support
- may wrap around axons of many neurons
astrocytes
- large, stellate (star-shaped)
- shortcuts between neurons and blood vessels
- in CNS
- transport nutrients, support, development, debris removal
microglia
- macrophages of CNS
- maintenance
ependymal cell
- line fluid filled cavities of CNS
- have cilia that circulate cerebrospinal fluid
depolarization
- membrane potential becomes more positive
- opening of Na+ channels causes Na+ inflow
hyperpolarization
- membrane potential becomes more negative
- opening of K+ channels causes K+ outflow
repolarization
any change that returns membrane potential to normal resting potential (-70 mV)
What determines the strength of a graded potential?
stronger stimulus = higher concentration of neurotransmitter = more ion channel opening = larger change in membrane potential = larger magnitude of graded potential
subthreshold potential
- graded potential that is not large enough to produce an action potential
- less than +15 mV
supratheshold potential
- graded potential that is larger than what is required to trigger an action potential
- greater than +15 mV
threshold potential of most neurons is __
-55 mV
temporal summation
- two subthreshold potentials building on each other
- can trigger action potential if subthreshold depolarization occur at slightly different times and combine to reach threshold potential
Describe the phases of action potentials: depolarization phase, repolarization phase, absolute refractory period, and relative refractory period.
- depolarization phase: membrane potential at axon hillock reaches threshold potential and adjacent part of membrane rapidly depolarizes (+30mV)
- repolarization phase: rapid return to resting membrane potential (hyperpolarization phase follows, becomes more negative)
- absolute refractory period: axon incapable of generating new AP
- relative refractory period: new AP can be generated only if stimulus very large
spatial summation
- subthreshold potential occurs in different dendrites
- they combine at axon hillock to produce suprathreshold potential
Hodgkin cycle
- Na+ influx from first depolarization triggers further opening of Na+ channels
- positive feedback loop
- accounts for rapid membrane depolarization
How does the action potential only travel in one direction?
the previous segment is in refractory period; its voltage gated Na+ channels are inactivated
Exposed portions of axons of myelinated neurons are called ___ and myelinated regions are called ___
nodes of Ranvier; internodes
How do myelinated axons propagate action potentials faster than nonmyelinated?
- voltage gated Na+ channels only occur at nodes of Ranvier; depolarization can only occur at these nodes
- myelination prevents ions from leaking out so spread of charge through internodes is very fast
synaptic transmission
relaying of info from one neuron cell to another via synapse (junction between cells)
electrical vs chemical synaptic transmission
- electrical: direct flow of electric current from one cell to another via gap junctions (rare)
- chemical: secretion of neurotransmitter molecules that bind to and activate receptors
Describe the synthesis and recycling of acetylcholine.
- Acetyl CoA synthesized in mitochondria
- Acetyl CoA and choline converted to ACh, catalyzed by choline acetyl transferase
- ACh packaged into synaptic vessicles
- ACh released into synapse
- ACh binds to postsynaptic cell receptors
- Acetylcholinesterase (AChE) breaks down ACh into choline and acetate (signal terminates)
- choline taken back up into presynaptic neuron and acetate diffuses out of synapse
function of acetylcholine (ACh)
primary neurotransmitter at vertebrate neuromuscular junction
Describe the events of signal transmission at a chemical synapse.
- AP arrives at axon terminal
- voltage gated Ca2+ channels open and Ca2+ enters cell
- Ca2+ triggers vesicle movement to membrane; vesicles fuse with membrane and release neurotransmitter by exocytosis
- neurotransmitter diffuses across synaptic cleft and binds to receptors, activating signal transduction pathway
ionotropic neurotransmitter receptors vs. metabotropic receptors
- ionotropic: ligand gated ion channels; rapid change
- metabotropic: signal sent via second messenger; slower
- both operate via conformational change caused by binding of neurotransmitter
