What is the primary function of neurons?
Neurons carry out electrical signaling throughout the nervous system.
What are the major components of a typical neuron?
Cell Body
Dendrites
Axon
Synaptic Knobs/Synapse
What is the cell body
Cell Body (Soma): Contains the nucleus and organelles; carries out daily functions (metabolism) to keep the neuron alive and healthy
What is found in the cell body
Nucleus: Synthesizes neurotransmitters.
Mitochondria: Synthesizes ATP
What are dendrites?
Projections that monitor the extracellular environment and receive input signals.
What is an axon?
A long projection that transmits output signals and carries information away from the neuron.
What are synaptic knobs/Synapse?
Enlargements where the axon ends and connects with another cell (neuron, muscle, or gland).
What is the role of the Myelin Sheath and Nodes of Ranvier?
The Myelin sheath provides insulation for the axon. The action potential progresses quickly from node to node (Nodes of Ranvier), which increases conduction speed and decreases the amount of ATP the neuron needs to reset the gradients.
What are electrolytes, and how are their concentrations measured?
Electrolytes are charged ions (like Na, K, Cl, Ca, Mg) that form when salt dissolves in water and conduct an electrical charge. Concentrations are measured in milliequivalents (mEq), a measure of reactivity based on charge
Describe the chemical gradient for Na and K in a resting neuron
Sodium: Concentration is much higher in the extracellular fluid (ECF).
Potassium: Concentration is much higher in the intracellular fluid (ICF)
What is the physiological basis of the resting membrane potential?
At rest, the neuron maintains a negative charge inside the cell relative to the outside (electrical gradient) and chemical gradients that keep Na outside and K inside.
What is the role of the Sodium-Potassium ATPase pump in maintaining the resting membrane potential?
The pump uses ATP and active transport to return the membrane to its original gradient after an action potential, moving three Na ions out of the cell in exchange for two K ions
Define a Graded Potential
A graded potential is a change in the cell’s interior charge (becoming more positive) that occurs when Na enters the cell through chemically gated channels after an excitatory stimulus
Define Depolarization
Depolarization is the process where the cell’s charge becomes less polar (more positive) as Na cations enter the cell. If the depolarization reaches the threshold value, voltage-gated Na channels open, triggering an action potential.
Define Repolarization
Repolarization is the return of the cell’s interior to a negative charge (more polar) as positive K ions leave the cell through open voltage-gated K channels.
Why is Na important for nerve signals, and K important for recovery?
Na is used in nerve depolarization; its disruption impairs the ability to send signals. K is used in nerve repolarization; its disruption impairs the ability to recover from signals and reset the system.
Explain how axon diameter and myelination affect conduction velocity.
Axon Diameter: Larger diameter axons transmit action potentials more quickly because their size provides less resistance to ion flow.
Myelination: Myelinated neurons are faster because the myelin insulation allows the action potential to “jump” quickly from node to node (saltatory conduction).
The fastest neurons are those that are both large diameter and myelinated.
What differentiates the Absolute Refractory Period from the Relative Refractory Period in a neuron?
They differ in the neuron’s ability to respond to a new stimulus while resetting its ion gradients:Absolute Refractory Period: The neuron cannot respond to any stimulus, regardless of its strength. This occurs because voltage-gated Na channels are inactive, preventing any new depolarization.Relative Refractory Period: The neuron may respond to a stimulus, but only if that stimulus is suprathreshold (stronger than usual). This is because the membrane is hyperpolarized or still repolarizing, requiring a larger input to reach the threshold.
Quiz Question: Movement of sodium into a neuron through voltage regulated channels occurs during:
Depolarization
Quiz Question: true or false An action potential is not generated in a neuron until it passes threshold.
True
Quiz Question: True or false The neuron cell body receives information from its axon.
false
Quiz Question: Action potentials occur in neurons when [BLANK] gates open and the cell interior becomes [BLANK] charged.
Sodium; positively
Quiz Question: If a cell is at +30mV and voltage regulated potassium channels open, which of the following will typically occur?
Repolarization
Quiz Question: The all or none response states that:
If a neuron reaches threshold, an action potential will travel the whole length of a neuron
