✅Conduction Of The Nervous System Flashcards
What is a plasma membrane?
A watery medium that surrounds a cell
What does plasma membrane separate?
cytoplasm from the
extracellular fluid
What is cytoplasm?
All materials inside the cell and outside the nucleus
What is cytosol?
Liquid ( intracellular fluid)
What are organelles?
Intracellular structures
What are the four functions of the plasma membrane?
Physical isolation
Regulation of exchange with environment
Sensitivity to the environment
Structural support
How does the plasma membrane act as physical isolation?
Act as barrier
How does the plasma membrane controls regulation of exchange its the environment?
• Ions and nutrients enter
• Wastes eliminated and cellular products released
How does the plasma control sensitivity to the environment?
• Extracellular fluid composition
• Chemical signals
How does the plasma membrane act as structural support?
Anchors cells and tissues
What components of the plasma membrane all it to perform its characteristic functions?
membrane lipids, membrane proteins, and membrane carbohydrates.
How much of the plasma membranes weight is membrane lipids?
42%
What are the three sections of phospholipid bilayer in membrane lipids?
Hydrophilic heads
Hydrophobic fatty-acid tails
Barrier to ions and water
Where do you find hydrophilic heads?
Toward watery environment, both sides
Where do you find hydrophobic fatty-acid tails?
Inside membrane
Where do you find the barrier to ions and water?
Soluble compounds
How much of the plasma membranes weight is membrane proteins?
55%
Where do you find integral proteins?
Within the membrane
Where do you find peripheral proteins?
Bound to inner or outer surface of the membrane
What do anchoring proteins do? (Stabilisers)
Attach to inside or outside structures
What do recognition proteins do? (Identifiers)
Label cells as normal or abnormal
What do enzymes do?
Catalyse reactions
What do receptor proteins do?
Bind and respond to ligand ( ions, hormones)
What do carrier proteins do?
Transport specific salutes through membrane
What do channels do?
Regulate water flow and salutes through membrane
How much of the plasma membranes weight is membrane carbohydrates?
3%
Describe Proteoglycans, glycoproteins, and glycolipids
• Extend outside cell membrane
• Form sticky “sugar coat” (glycocalyx)
What are the functions of the glycocalyx?
- Lubrication and Protection
• Anchoring and Locomotion
• Specificity in Binding (receptors) - Recognition (immune response)
What is transmembrane potential?
The electrical potential of the cell’s interior relative to its surrounding
In transmembrane potential what is created when charges separate?
Potential difference
What is unequal charge across the plasma membrane?
Transmembrane potential
What is membrane potential?
Ion movements and electrical signals
How do all cell membranes produce electrical signals?
By ion movements
What is membrane potential particularly important to?
Neurons
What are the five main membrane processes in neural activities ?
Resting potential Graded potential Action potential Synaptic activity Information processing
What is resting potential?
The membrane potential of resting cell
What is graded potential?
Temporary, localised charge in resting potential
How us graded potential caused?
By Stimulus
What is action potential?
An electrical impulse
How is action potential produced?
By graded potential
What does action potential propagate along?
Surface of axon to synapse
What does synaptic activity release?
Neurotransmitters at presynaptic membrane
What does synaptic activity produce?
Graded potentials in postsynaptic membrane
What is information processing?
Response ( integration of stimuli) of postsynaptic cell
What are the two passive forces acting across the plasma membrane?
Chemical gradients
Electrical gradients
What are chemical gradients?
Concentration gradients (chemical gradient) of ions (Na+, K+)
What do electrical gradients separate?
Charges of positive and negative ions
What does electrical gradients result in?
Potential difference
What is electrical current?
Movement of charges to eliminate potential difference
What is resistance?
The amount of current, ion movements, a membrane restricts
In passive chemical gradients what do ions do as a result of potassium ions (k+) being relatively high?
They moves out of the cell through potassium leak channels.
What do sodium ions do because the extracellular concentration of sodium ions (Na+) is relatively high?
Move into the cell through sodium leak channels.
What are the movements of potassium and sodium ions driven by?
Concentration gradient, or chemical gradient
What do Sodium–potassium
++
(Na /K ) exchange
pumps maintain ?
the concentration of sodium and potassium ions across the plasma membrane.
Why do Potassium ions leave the cytosol
more rapidly than sodium ions enter?
because the plasma membrane is
much more permeable to potassium
than to sodium
What is the result of Potassium ions leave the cytosol
more rapidly than sodium ions enter?
there are
more positive charges outside the plasma membrane
Negatively + charged protein molecules within the – cytosol cannot cross the plasma
membrane what does this lead to?
more
negative charges on the cytosol side
of the plasma membrane
What is the result of more
negative charges on the cytosol side
of the plasma membrane?
an electrical
gradient across the plasma + membrane.
What happens when positive and negative ions are held apart?
A potential difference arises
What do we measure potential difference in?
mV
What is The resting membrane potential for most neurons?
About -70 mV
What does the minus sign show in -70mV?
the inner surface of the plasma membrane is negatively charged with respect to the exterior.
What does Potassium permeability 100x more than?
Sodium permeability
What maintains the concentration of sodium and potassium ions across the plasma membrane?
The sodium-potassium exchange pumps
The intercellular concentration of potassium ions (K+) is relatively what?
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 what?
Low
Do sodium ions move in or out of 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 chemical gradient)
Potassium leave what quicker than sodium ions enter?
Cytosol
Why do potassium ions leave cytosol quicker 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
What kind of charges are there more of 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 this result in?
An electrical gradient across the plasma membrane
What is the equilibrium potentiometer for K+
-90mV
The plasma membrane is highly permeable to what kind of ions?
K+
The electrochemical gradient for sodium ions is large but the membranes permeability for sodium is very what?
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 changed with the conditions
What are passive channels also known as?
Leak channels
When do active channels open/close?
Active channels open and close in responsive to stimuli
What are active channels also know as?
Gated channels
What channels are closed at tasting potential?
Gated (active)
What are the 3 states of gated channels?
Closed but capable of opening
Open (activated)
Closed but not capable of opening (inactive)
Name the 3 classes of gated channels
Chemically gated channels
Voltage gated channels
Mechanically gated channels
What channel is being described:
Open in presence of specific chemicals (ACh) at a binding site
Found on Neuton cell body and dendrites
Chemically gated channels
What channel
Responds to changes in the membrane potential
Has activation gates and inactivation gates
Characteristics 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)
What kind of event is action potential?
Electrical
Name this:
Propagated changes in membrane potential?m, that once initiated, affect and entire excitable membrane
Action potential
Electrics events are also known as what?
Nerve impulses
The axolemma contains both what?
Voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential
What is the axolemma?
The plasma membrane of an axon and
Name the four steps in the generation of action potentials
1- depolarisation to threshold
2- activation of NA+ channels
3- inactivation of NA+ channels and activation of K+ channels
4- return to normal permeability
What happens at the depolarisation to threshold?
The stimulus that initiates an action potential is a grades depolarisation 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 what?
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 depolarisation 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 depolarisation
What happens at stage 3 (+30mV) of generating action potential?
- NA+ channels are inactivated
- K+ channels are activated (opened)
- repolarisation begins
Describe stage 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
Until all the potassium channels have closed, potassium ions continue to leave the cell, what does this produce?
This produces brief hyperpolarisation
Explain the “all or none principle”
If a stimulus exceeds threshold amount, the action potential is the same, no matter how large the stimulus
According THE the all or none principle the action potential is either what?
Triggered or not
All stimuli that bring the membrane to threshold generate what?
Identical action potentials
Relate a gun to the all or none principle
The speed a and range of the bullet that leaves the gun do not change, regardless the forces that you applied to the trigger
What is the refractory period?
The time period from beginning of and 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?
Once you flush the toilet, the amount of water that is released is independent of how hard or quickly you presses the handle
The all or none principle
What does this example refer to?
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?
0.4-1msec
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 what type of axons?
Unmyelinated
Saltatory propagation is the propagation of what kind of axons?
Myelinated
What does continuous propagation affect?
It affects one segment of axon at a time
What are the 4 steps in continuous propagation?
Step 1- action potential in segment 1
Step 2- depolarises second segment to threshold
Step 3- firs segment enters refractory period
Step 4- the local current from segment 2 depolarises next segment
Then the cycle repeats
How many directions does action potential travel in in continuous propagation?
1
Name the action potential along a myelinated axon
Saltatory propagation
What does myelin do?
It insulated the axon
What propagation does myelin prevent?
Continuous propagation
How does the local current travel in saltatory propagation?
The local current ‘jumps’ from node to node
In saltatory propagation where can depolarisation only occur?
At nodes
Which component of the plasma membrane is primarily responsible for the membranes ability to form a physical barrier between the cells 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 abnormal cell under homeostatic conditions
What effect would a chemical that blocks the voltage gated sodium channels in neutron plasma membranes have on a neuron’s ability to depolarise
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 depolarise
Define action potential
An action potential is 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 extra cellular potassium ions have on the transmembrane potential of a neutron?
-more potassium would leave the cell
-the electrical gradient across the membrane would increase
This condition is called hyperpolarisation
What does the transmission speed of the action potential depend on?
The diameter of the axon and if it’s myelinated or not
