conduction of the nerve impulse Flashcards
What are graded potentials?
Temporary changes in the membrane voltage that vary in size
Graded potentials do not typically involve voltage-gated Na+ channels and can be polarizing or hyperpolarizing.
How does the amplitude of graded potentials relate to the stimulus strength?
Amplitude is proportional to the stimulus strength
Graded potentials can vary in size based on the strength of the stimulus.
What is the conduction type of graded potentials?
Conducted decrementally
Graded potentials lose their strength as they move through the cell due to leakage of charge across the membrane.
What are the types of synaptic potentials?
- Postsynaptic (synaptic) potentials (neuron -> neuron)
- End plate potentials (neurons -> muscle cell)
- Receptor potentials (sensory cells)
Synaptic potentials are caused by opening ligand-gated channels in the dendrites or soma.
What are excitatory and inhibitory postsynaptic potentials?
- Excitatory postsynaptic potentials (EPSPs) = depolarization
- Inhibitory postsynaptic potentials (IPSPs) = hyperpolarization
These potentials result from the opening of ligand-gated channels.
What is the function of the axon hillock?
Specialized region of the cell body from which the axon arises
It is the trigger zone where synaptic potentials are summed to initiate an action potential.
What is spatial summation?
Summation of graded potentials generated in different regions of the neuron
This occurs at the axon hillock.
What is temporal summation?
Summation of graded potentials over time
This occurs when multiple signals are received in rapid succession.
What factors affect nerve impulse conduction?
- Diameter of the axon
- Presence of myelin
Larger diameter axons provide lower resistance to current flow, speeding up conduction.
What is membrane capacitance (Cm)?
The ability to store charge
Higher capacitance means more charge is needed to change the membrane potential.
What is the length constant?
The distance it takes for the potential to fall to 37% of its original value
- not a physical property of the membrane
A longer length constant allows graded potentials to travel further.
What is the time constant?
The time it takes for the potential to fall to 37% of Vmax
A larger time constant means a slower change in potential in response to a stimulus.
How does membrane capacitance affect propagation velocity?
Higher capacitance slows down propagation velocity
It takes longer for the membrane potential to change in response to a given current.
What is captive current?
Some electrical current in a cell membrane is temporarily stored as charge on the membrane capacitance
This reduces the immediate contribution to the propagation of the signal.
What is the effect of myelination on conduction velocity?
Myelination increases conduction velocity
It reduces membrane capacitance and increases membrane resistance, thereby speeding up signal propagation.
What is saltatory conduction?
Propagation of action potentials along myelinated axons
Action potentials ‘leap’ from node to node, where ion channels are concentrated.
What are some pathologies affecting conduction of the action potential?
- Multiple sclerosis (MS)
- Devics disease
- Landry-Guillain-barre syndrome (GBS)
- Charcot-Marie-Tooth disease
These diseases result from breakdown or damage to the myelin sheath.
What is demyelination?
Slows down or stops conduction of the action potential
It leads to electrical current leak out of the axonal membrane.
What is the relationship between membrane resistance (Rm) and ion availability for depolarization?
↑ Rm = more ions stay inside the cell
More ions available to depolarize the cell.
What is the relationship between internal resistance (Ri) and ion propagation?
↓ Ri = ions/current propagate more freely
Lower internal resistance allows for faster conduction.
Fill in the blank: The _______ is the distance it takes for the graded potential to fall to 37% of its original value.
length constant
True or False: Graded potentials are always depolarizing.
False
Graded potentials can be polarizing or hyperpolarizing.
