Conduction in the Nervous System Flashcards
Name the watery medium that surrounds a cell.
Plasma Membrane
The _____ _____ separates the cytoplasm from the extracellular fluid.
plasma membrane
______: all materials inside the cell and outside the nucleus.
cytoplasm
Intracellular fluid (making up the cytoplasm) is known as ________.
cytosol
Intracellular structures are collectively known as ___________.
organelles
What is the cytoskeleton made of?
Proteins organised in fine filaments or slender tubes.
What are the functions of the cytoskeleton?
To provide strength and support
Movement of cellular structures and materials
The plasma membrane consists of a _____ bilayer, steroids, _______ and __________.
phospholipid, proteins, carbohydrates
Name the 4 functions of the plasma membrane.
Physical Isolation
Regulation of Exchange with the Environment
Sensitivity to the Environment
Structural Support
One of the plasma membrane’s roles is physical isolation, what does it act as?
Acts as a barrier
The plasma membrane allows ____ and _____ to enter.
ions, nutrients
What does the plasma membrane allow to be eliminated and released by the cell?
Waste is eliminated and cellular products are released
The plasma membrane can respond to _____ signals.
chemical
How does the plasma membrane structurally support the cell?
It anchors cells and tissues
Name the components of the plasma membrane that allow it to perform its characteristic functions.
Lipids, Proteins and Carbohydrates :)
How are membrane lipids arranged?
In a phospholipid bilayer.
The lipid heads are ______.
hydrophilic
The plasma membranes contain hydrophilic heads, define what is meant by hydrophilic.
They like water- so will face a watery environment.
The lipid tails are _____.
hydrophobic
Where are hydrophobic tails found?
INSIDE the plasma membrane
What can the phospholipid bilayer act as?
It acts as a barrier :)
Name the 2 types of membrane proteins.
Integral and Peripheral
Where are integral proteins found?
WITHIN the membrane
Where are peripheral proteins found?
Bound to the inner or outer surface of the membrane
Anchoring Proteins, Recognition Proteins, Enzymes, Receptor Proteins, Carrier Proteins and Channels are all examples of _____ proteins found in the ______ _______.
functional, plasma membrane
What functional proteins attach to inside or outside structures?
Anchoring Proteins
What type of protein can label cells as normal or abnormal?
Recognition Proteins
What do enzymes do?
Catalyse reactions
Receptor proteins bind and respond to ______.
ligands
Give 2 examples of ligands.
ions and hormones
_____ proteins transport specific solutes through the membrane and _____ regulate water flow and solutes through the membrane.
carrier
channels
Membrane _____ make up 3% of the plasma membrane’s weight.
carbohydrates
Proteoglycans, glycoproteins and glycolipids are all examples of what?
Membrane Carbohydrates
Proteoglycans, glycoproteins and glycolipids extend _______ the cell membrane. What do they form?
outside
They form a sticky sugar coat called glycocalyx.
Name the sticky sugar coat extending from the cell membrane, made from membrane carbohydrates.
Glycocalyx
What are the functions of Glycocalyx?
- Lubrication and Protection
- Anchoring and Locomotion
- Specificity in binding (receptors)
- Recognition (immune response)
Define Transmembrane Potential.
The electrical potential of the cell’s interior relative to its surroundings.
Name this:
The electrical potential of the cell’s interior relative to its surroundings
Transmembrane Potential
Charges in a cell are separated, what does this create?
This creates a potential difference.
Unequal Charge across the membrane is ________ __________.
Transmembrane potential.
What does membrane potential involve?
Ion Movement (this sends Electrical Signals.)
All plasma membranes produce _____ _____by _____ _______.
Electrical signals, ion movement.
What is membrane potential particularly important to?
Neurons.
Name the 5 Main Membrane Processes in Neural Activities.
1-Resting Potential 2-Graded Potential 3-Action Potential 4-Synaptic Activity 5-Information Processing
What is Resting Potential?
The membrane potential of a resting cell.
What is Graded Potential
Graded Potential is a temporary, localised change in the resting potential caused by a stimulus.
Define Action Potential.
Action Potential is an electrical impulse produced by graded potential.
In Action Potential, what happens?
An electrical impulse propagates along the surface of the axon to the synapse.
What 2 things does synaptic activity do?
- It releases neurotransmitters at presynaptic membrane
- It produces graded potentials at postsynaptic membrane
What is the final stage of Neural Activities?
Information Processing
What happens at the final information processing stage of neural activities?
Response (integration of stimuli) of postsynaptic cell.
Chemical gradients and Electrical gradients are _____ forces acting across the membrane.
Passive
What is meant by “Chemical Gradients”?
The concentration gradients of ions eg. sodium (Na) and potassium (K).
Electrical Gradients _____ charges of _____ and ______ ions which result in a _______ ________.
Separate, positive, negative, potential difference.
What is the movement of charges in order to eliminate a potential difference known as?
Electrical Current
The amount of current, ion movements, a membrane restricts is called _______.
Resistance
What maintains the concentration of sodium and potassium ions across the plasma membrane?
The Sodium-Potassium Exchange Pumps
The intracellular concentration of potassium ions (K+) is relatively _______.
High
In what direction do potassium ions (K+) tend to move?
They tend to move out of the cell (through potassium leak channels).
The intracellular concentration of sodium ions (Na+) is relatively _______.
Low.
Sodium ions move _____ the cell through sodium leak channels.
into
What is sodium moving into the cell and potassium moving out of the cell driven by?
A concentration gradient (aka. A Chemical Gradient.)
Potassium ions leave the ______ more rapidly than sodium ions enter.
Cytosol.
Why do potassium ions leave the cytosol more rapidly than sodium ions enter?
The plasma membrane is much more permeable to potassium than to sodium.
Because Potassium leaves the cytosol faster than Sodium ions entering, what does this result in?
More positive charges outside the plasma membrane.
There are more ________ charges on the cytosol side of the plasma membrane
negative
With the outside of the plasma membrane being more positive and the inside of the plasma membrane being more negative, what does result in?
An electrical gradient across the plasma membrane.
What is the resting membrane potential for most neurons?
-70mV
The inner surface of the plasma membrane is _______ charged with respect to the exterior.
negatively
-90mV is the equilibrium potential for _____.
K+
The plasma membrane is highly permeable to ________ions.
potassium
The electrochemical gradient for sodium ions is very _______ but the membrane’s permeability for sodium is very _______.
large, low.
Name the ratio of sodium that goes out and potassium that goes into the cell by the action the sodium-potassium pump.
3:2
What type of channels are always open?
Passive Channels.
In passive channels, when does permeability change?
It changes with the conditions.
What are passive channels also known as?
Leak Channels
When do active channels open/close?
Active channels open and close in response to stimuli.
At resting potential most ____ channels are closed.
Gated (active)
What are active channels also called?
Gated channels
What are the 3 states of gated channels?
- Closed but capable of opening
- Open (activated)
- Closed, not capable of opening (inactivated)
Name the 3 classes of gated channels.
- Chemically Gated channels
- Voltage-Gated channels
- Mechanically Gated channels
Name the channel:
• Open in presence of specific chemicals (e.g., ACh) at a binding site
• Found on neuron cell body and dendrites
Chemically Gated channels
Name the channel:
• Respond to changes in membrane potential
• Have activation gates (open) and inactivation gates (close)
• Characteristic of excitable membrane
• Found in neural axons, skeletal muscle , cardiac muscle
Voltage Gated Channels
What do Mechanically Gated Channels respond to and where are they found?
They respond to membrane distortion
Found in Sensory Receptors (touch,pressure, vibration)
An action potential is an ______ event.
electrical
Name this:
Propagated changes in membrane potential, that once initiated, affect an entire excitable membrane.
Action Potential
Electrical events are also known as _____ _______.
Nerve Impulses.
The ______ contains both voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential.
axolemma
What is the axolemma?
The plasma membrane of an axon.
Name the 4 steps in the Generation of Action Potentials.
Step 1: Depolarization to threshold
Step 2: Activation of Na+ channels
Step 3: Inactivation of Na+ channels and activation of K+ channels
Step 4: Return to normal permeability
What happens at the depolarization to threshold?
- The stimulus that initiates an action potential is a graded depolarization large enough to open voltage gated sodium channels
- The opening of the channels occurs at the membrane potential known as the threshold.
When the sodium channel activation gates open, the plasma membrane becomes much more permeable to _______.
Na+ (sodium)
During stage 2 of generating Action Potential, what happens.
- Driven by the large electrochemical gradient, sodium ions rush into the cytoplasm, and rapid depolarization occurs.
- The inner membrane is now more positive than the outside of the membrane (+10mV)
Name stage 2 of generating an action potential.
Activation of Sodium Channels and Rapid Depolarization
What happens at Stage 3 (+30mV) of generating an Action Potential?
- Na+ channels are inactivated
- K+ channels are activated (are opened)
- Repolarization begins.
Describe step 4- Return to Permeability.
- K+ channels begin to close when the membrane reaches normal resting potential (-70mV)
- K+ channels finish closing, membrane is hyperpolarised to -90mV.
- Membrane potential returns to resting level
- Action potential is over.
Until all the potassium channels have closed, potassium ions continue to leave the cell, what does this produce?
This produces a brief hyperpolarization.
Explain the “All or None Principle”.
If a stimulus exceeds threshold amount, the action potential is the same, no matter how large the stimulus.
Action potential is either _____ or not according to the ____ __ _______ principle.
Triggered, All or None principle.
All _____ that bring the membrane to _____, generate ____ action ______.
Stimuli, threshold, identical, potentials.
“The speed and range of the bullet that leaves the gun do not change, regardless the force that you applied to the trigger.”
What principle does this refer to?
The All or None principle.
What is the refractory period?
The time period from beginning of an action potential to return to resting state.
During the refractory period, what will the membrane not respond to?
Additional Stimuli.
Why will the membrane not respond to additional stimuli during the refractory period?
Because all the gated voltage sodium channels either are already open or inactivated.
What does this example refer to?- think Action Potential
Flushing a toilet, nothing happens while you press the handle, until the water starts to flow.
Threshold is reached.
What does this example refer to?- think Action Potential
Once you flush the toilet, the amount of water that is released is independent of how hard or quickly you pressed the handle.
The All or None Principle
What does this example refer to?- think Action Potential
Finally, you cannot flush the toilet again until the tank refills.
The Refractory Period.
What are the 2 parts of the refractory period?
Absolute Refractory Period
Relative refractory period
How long does the absolute refractory period last for?
0.4-1 msec
Name the type of refractory period:
- Sodium channels open or inactivated
- no action potential possible
Absolute Refractory Period
Name the type of refractory period:
- membrane potential almost normal
- very large stimulus can initiate action potential
Relative Refractory Period
What is being described here?
• Moves action potentials generated in axon hillock
• Along entire length of axon
Propagation
Name the 2 methods of propagating action potentials.
- Continuous Propagation
- Saltatory Propagation
Continuous propagation is the propagation of _______ axons.
unmyelinated
Saltatory propagation is the propagation of _____ axons.
myelinated
What does continuous propagation affect?
It affects one segment of axon at a time.
The steps in continuous propagation are as follows:
Step 1- _____ _____ in segment 1
Step 2- _______ second segment to _______.
Step 3- First segment enters ______ period
Step 4- The _____ ______ from segment 2 depolarizes next segment.
This cycle then _____.
action potential Depolarizes, threshold refractory local current repeats
In continuous propagation, action potential travels in _______ direction/s (1m/sec).
one
Name the action potential along a myelinated axon.
Saltatory Propagation
Saltatory propagation is ______ and uses less ______ than continuous propagation..
faster, less
What does myelin do?
It insulates the axon.
What propagation does myelin prevent?
It prevents continuous propagation.
How does the local current travel in saltatory propagation?
The local current “jumps” from node to node.
In saltatory propagation where can depolarization only occur?
It can only occur at nodes.
Which component of the plasma membrane is primarily responsible for the membrane’s ability to form a physical barrier between the cell’s internal and external environments?
The phospholipid bilayer
Which type of integral protein allows water and small ions to pass through the plasma membrane?
Channel Proteins
Define the resting potential.
The resting potential is the transmembrane potential of a normal cell under homeostatic conditions.
What effect would a chemical that blocks the voltage gated sodium channels in neuron plasma membranes have on a neuron’s ability to depolarize?
The voltage-gated sodium channels couldn’t open so the sodium ions could not flood into the cell, and it would not be able to depolarize.
Define action potential.
An action potential is a propagated change in the transmembrane potential of excitable cells.
What is action potential often initiated by?
It is initiated by a change in the membrane permeability to sodium ions.
What effect would decreasing the concentration of extracellular potassium ions have on the transmembrane potential of a neuron?
- More potassium would leave the cell
- The electrical gradient across the membrane (the transmembrane potential) would increase.
- This condition is called hyperpolarization.
The four steps involved in the generation of action potentials are:
(1) _________ to threshold;
(2) activation of ______ channels and rapid depolarization;
(3) _________ of sodium channels and activation of _______ channels;
(4) return to normal _______.
Depolarization
Sodium, Depolarization
Inactivation, potassium
permeability
What does the transmission speed of the action potential depend on?
The diameter of the axon and if it’s myelinated or not.
