Excitable Cells Flashcards
What is ECF?
Extracellular fluid
What is ICF?
Intracellular fluid
What chemical is dominant in the ECF?
Na+ and Cl-
What chemical is dominant in the ICF?
K+
What are passive channels?
Channels in the cell membrane that are always open allowing ions to flow across the cell membrane freely
How does K+ move in cells?
K+ constantly leaks out of the cell via passive channels down its concentration gradient
What is the ATPase pump?
A pump that runs on ATP and moves three sodium ions out of the cell and two potassium ions in
What is the net charge of cells?
Net negative charge inside the cell and net positive charge outside the cell
What is membrane potential?
The separation of ions across a membrane causing opposite charges
What are excitable cells?
Are cells that can generate and transmit signals
What are the main types of excitable cells?
Neurons and muscle cells
What is the resting membrane potential?
The constant state of separated charges
What is the resting membrane potential in neurons?
-70mV
What is polarisation?
When the membrane potential is at resting levels
What is depolarisation?
When there is a decrease in potential hence becomes less negative
What is repolarisation?
When it is returning to resting potential after depolarisation
What is hyperpolarisation?
When the resting potential is overshot at there is an increase in potential hence becomes more negative
What triggers a change in membrane potential in neurons?
Voltage gated Na+ channels which open in response to a change in voltage
What is graded potential?
Temporary changes in the electrical charge of a cell membrane
What impacts the size of graded potential?
The size of the trigger
What is the threshold level in neurons?
-50mV - -55mV
What happens when threshold levels are met in neurons?
Lots of Na+ channels open and Na+ flows into the cell until peak polarisation is reached
What is the peak polarisation in neurons?
+30mV
What happens when Na+ channels close?
Voltage gated K+ channels open to let K+ out of the cell
What is hyperpolarisation in neurons?
-80mV
How do neurons become polarised after overcorrection?
By the continuous flow of K+ through passive channels
What are the gates of the Na+ channels?
An activation gate which is like a hinged door and an inactivation gate which is like a ball and chain
What is the gate in the K+ channel?
One gate which opens and closes
What is the all or nothing rule?
Action potentials always last for the same amount of time
Why are action potentials unidrectional?
Due to the refractory period
What is the refractory period in neurons?
Time after an action potential when a neuron is less likely to fire another action potential
What happens when action potential reaches an axon terminal?
Causes the voltage gated calcium channels to open and calcium flows into the presynaptic cell which releases acetylcholine
How does conduction occur in neurons?
The original action potential doesn’t travel but rather triggers identical events down the axon
What does acetylcholine do?
Diffuses across cleft and binds to receptors on membrane of postsynaptic cells which opens Na channels allowing the target cell to depolarise
How is action potential ended?
The synaptic cleft releases acetylcholine esterase which stops binding and recycles ACh closing the Na channels
What is the sarcolemma?
A cell membrane of a muscle fiber that conducts the stimulus throughout the muscle fiber
