FORM & FUNCTION (Graded Potential) Flashcards
Action potential (AP) strength:
-always the same amplitude
-“all or nothing”
-stimulus strength effects the frequency
>stronger stimuli lead to more FREQUENT APs
Sustained threshold stimulus:
-generate a train of Aps with an interval including the ARP and the RRP
Sustained supra-threshold stimulus:
-generate a train of Aps within an interval including only the ARP
Which part of the neurone will AP be initiated?
-axon hillock
Types of electrical signals in excitable cells:
- Action potential
- Graded potential
Graded potential:
-local signal proportional to the stimulus
-sub-threshold changes in membrane potential
-occurs primarily in dendrites and cell body
Characteristics of graded potential:
-vary in amplitude based on duration and strength of the stimulus
-decremental nature
Decremental nature of graded potentials:
-diminishes in strength over distance
Role of graded potential in neural communication:
-serve as initial response to external changes
Types of graded potential:
- Receptor potential/generator potential
- Postsynaptic potential
- Endplate potential
Receptor potential/generator potential:
-GP generated by sensory receptors at the nerve endings of the sensory neuron
Postsynaptic potential:
-GP generated by NT binding to its receptor on the postsynaptic neuron
Endplate potential:
-GP generated by NT binding to its receptor on the skeletal muscle fiber
GP hyperpolarizing or depolarizing:
- Excitatory postsynaptic potential (EPSP)
- Inhibitory postsynaptic potential (IPSP)
EPSP:
-depolarization
-Na+ channels on postsynaptic neurons are opened and Na+ enters the cell
IPSP:
-hyperpolarization
-Cl- channels on postsynaptic neuron are opened and Cl- enters the cell
GP: summation
- Temporal summation
- Spatial summation
*AP can NOT be summated
Temporal summation:
-successive, rapid input from a SINGLE pre-synaptic neuron is electrically summed
Spatial summation:
-simultaneous input from more than one pre-synaptic neuron is electrically summed
Propagation of electrical signals within a neuron:
- Passive spreading
- Active spreading
Passive spreading:
-slow and small amplitude
-localized
-signal dies off with distance (stays within cell body)
Active spreading:
-fast and large amplitude
-travel far
-signal is self-regenerated
-requires VG Na+ and K+ channels to be positioned along the path of propagation (can go down axon)
Steps of AP propagation:
- enters cell
- Current flows through activated patch membrane, depolarizes adjacent patch
- Adjacent path reaches threshold, current flows, depolarizes adjacent patch
- Continues in one direction as repolarized patch is refractory
*after refractory period, the channel is ready to be activated again
Distribution of Na+ and K+ channels in a neuron:
-soma: 50-75
-axon hillock: 350-500
-myelinated regions: <25
-nodes of Ranvier: 2000-12000
-axon terminal: 20-75
Myelination:
-effectively reduces the distance an AP needs to travel
-allows for ‘saltatory conduction’ (node to node conduction)
-AP jumps from node to node
Factors effecting conduction speed in neurons:
- Myelination
- Axon diameter
Unmyelinated neurons:
-continuous
-slower propagation of AP
Larger diameter:
-faster conduction due to decreased resistance to the flow of electric current
Smaller diameter:
-slower conduction
Nerve fiber classification:
-A fibers
-B fibers
-C fibers
A fibers:
-myelinated with large diameter
-fast conduction speed
-4 sub-classes
Ex. somatic motor, touch pressure
B fibers;
-myelinated
-slightly smaller than A fibers
-medium conduction speed
Ex. visceral motor (preganglionic)
C fibers:
-unmyelinated
-small
-slowest conduction speed
Ex. visceral motor (postganglionic), slow pain, temperature
GP vs. AP amplitude:
GP: proportional to strength of stimulus, small (10mV), decremental
AP: strength coded in frequency, large (100mV), non-decremental
GP vs. AP duration:
-GP: few ms to s
-AP: very short, 3-5ms
GP vs. AP channels:
-GP: ion channels (ligand gated, mechanosensitive, temperature gated)
-AP: VG Na+ and K+ channels
GP vs AP spread:
-GP: passive
-AP: active
GP vs. AP triggers:
-GP: external stimuli or NT release
-AP: membrane depolarization to threshold (due to GP)
GP vs. AP location:
-GP: any region of the membrane
-AP: only in membrane with high concentration of VG Na+ and K+ channels
