Conduction In The Nervous System Flashcards
What is the plasma membrane?
A watery medium that surrounds a cell
What does the plasma membrane (cell membrane) separate?
The cytoplasm from the extra cellular fluid
What is the cytoplasm?
All materials inside the cell and outside the nucleus
The inside of the includes
Cytosol and intracellular structures collectively known as organelles
What is the cytosol?
Liquid (intracellular fluid)
A function of the plasma membrane is that it results in physical isolation
It forms a barrier
Another function of the plasma membrane is that it regulates exchange with the environment
Ions and nutrients enter
Wastes eliminated and cellular products released
Another function of the plasma membrane is that it results in sensitivity to the environment
Extra cellular fluid composition
Chemical signals
Another function of the plasma membrane is structural support
Anchors cells and tissues
The components of the plasma membrane that allow it to perform its characteristic functions are
Membrane lipids, membrane proteins and membrane carbohydrates
Membrane lipids make up
42% of its weight
Membrane lipids form
Phospholipid bilayer
The phospholipid bilayer has
Hydrophilic heads- towards watery environment
Hydrophobic fatty-acid tails- inside membrane
Barriers to ions and water-soluble compounds
Membrane proteins are
55% of its weight
Membrane proteins can be
Within the membrane-integral proteins or bound to inner or outer surface of the membrane- peripheral proteins
Examples of important types of functional proteins include the following:
- Anchoring proteins
- Recognition proteins
- Enzymes
- Receptor proteins
- Carrier proteins
- Channels
Anchoring proteins act as
Stabilisers and attach to inside or outside structures
Recognition proteins act as
Identifiers and label cells as normal or abnormal
Enzymes
Catalyse reactions
Receptor proteins bind and respond to
Ligands (ions, hormones)
Carrier proteins transport specific diluted
Through membrane
Channels
Regulate water flow and solutes through membrane
Membrane carbohydrates are
3% of its weight
Membrane carbohydrates include
Proteoglycans, glycoproteins and glycolipids
Membrane carbohydrates
Extend outside cell membrane and form sticky “sugar coat” (glycocalyx)
Functions of the glycocalyx include
- lubrication and protection
- anchoring and locomotion
- specificity in binding (receptors)
- recognition (immune response)
Transmembrane potential is
The electrical potential of the cell’s interior relative to its surrounding
The transmembrane potential charges are separated creating a
Potential difference
Unequal charge across the plasma membrane
Is transmembrane potential
Membrane potential is
Ion movements and electrical signals
All plasma (cell) membranes produce
Electrical signals by ion movements
Membrane potential is particularly important to
Neurons
The five main membrane processes in neural activities are:
Resting potential Graded potential Action potential Synaptic activity Information processing
The resting potential is the
Membrane potential of resting cell
The graded potential is the
Temporary, localised change in resting potential and is caused by stimulus
Action potential is
An electrical impulse produced by graded potential and propagates along surface of axon to synapse
Synaptic activity releases
Neurotransmitters at presynaptic membrane and produces graded potentials in postsynaptic membrane
Information processing is
Response (integration of stimuli) of postsynaptic cell
Passive forces acting across the plasma membrane are
Chemical gradients and electrical gradients
Chemical gradients are
Concentration gradients (chemical gradients) of ions (Na+, K+)
Electrical gradients
Separate charges of positive and negative ions and result in potential difference
Electrical currents and resistance include
Electrical current and resistance
Electrical current is
Movement of charges to eliminate potential difference
Resistance is the
Amount of current, ion movements, a membrane restricts
What are the two types of membrane potential?
Passive channels and active channels
Passive channels aka leak channels are
Always open and permeability changes with conditions
Active channels aka as gated channels
Open and close in response to stimuli and at resting potential, most gated channels are closed
The three states of gated channels are
- Closed, but capable of opening
- Open (activated)
- Closed, not capable of opening (inactivated)
What are the three classes of gated channels?
Chemically gated channels
Voltage gated channels
Mechanically gated channels
Chemically gated channels open in presence of
Specific chemicals (e.g ACh) at a binding site and they are found on neuron cell body and dendrites
Voltage gated channels respond to
Changes in membrane potential and have activation gated (open) and inactivation gated (close)
Voltage gated channels have characteristic of
Excitable membrane and are found in neural axons, skeletal muscle, cardiac muscle
Mechanically gated channels respond to
Membrane distortion and are found in sensory receptors (touch, pressure, vibration)
What is an action potential?
An electrical event
Action potentials are propagated by
Changes in membrane potential, that once initiated, affect an entire excitable membrane
These electrical events are also known as
Nerve impulses and link graded potentials at cell body with motor end plate actions
What are the four steps in the generation of action potentials?
Step 1: depolarisation 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
With step 2: activation of Na+ channels there is
Rapid depolarisation
Na+ ions rush into cytoplasm
Inner membrane changes from negative to positive
With step 3: inactivation of Na+ channels and activation of k+ channels
Occurs at +30mV
Inactivation gates close (Na+ channel inactivation)
K+ channel open
Repolarisation begins
With step 4: return to normal permeability
K+ channels begin to close when membrane reaches normal resting potential (-70mV)
K+ channel finish closing and membrane is hyper polarised to -90mV. Membrane potential returns to resting level and action potential is over
What is the all or none principle?
If a stimulus exceeds threshold amount:
The action potential is the same
No matter how large the stimulus
With the all or none principle, action potential is either
Triggered, or not
All stimuli that bring the membrane to threshold generate identical action potentials
Similar example to all or none principle
The speed and range of the bullet that leaves the gun do not change, regardless the force that you applied to the trigger
The refectory period is the time period between;
From beginning of action potential
To return of resting state
During which membrane will not respond normally to additional stimuli
Because all the gated voltage sodium channels either are already open or are inactivated
Similar example to the refractory period
Flushing a toilet, nothing happens while you press the handle, until the water starts to flow (threshold is reached). After that, the amount of water that is released is independent of how hard or quickly you pressed the handle (all or none principle). Finally, you cannot flush the toilet again until the tank refills (refractory period)
There are two parts the the refractory period:
Absolute refractory period which lasts 0.4-1msec and the relative refractory period
With the absolute refractory period the sodium channels
Open or inactivated and no action potential is possible
With the relative refractory period the membrane potential is
Almost normal and very large stimulus can initiate action potential
What is propagation?
Moves action potentials generated in axon hillock and along entire length of axon
What are the two methods of propagating action potentials?
- Continuous propagation (Unmyelinated axons)
2. Saltatory propagation (myelinated axons)
- Continuous propagation of action potentials along an Unmyelinated axon affects
One segment of axon at a time
Steps in propagation:
Step 1: action potential in segment 1
- depolarises membrane to +30mV
- local current
Step 2: depolarises second segment to threshold- second segment develops action potential
Step 3: first segment enters refractory period
Step 4: local current depolarises next segment
After the steps in propagation,
The cycle repeats and action potential travels in one direction (1m/sec)
What is saltatory propagation?
Action potential along myelinated axon
Saltatory propagation is faster and used
Less energy than continuous propagation
In saltatory propagation myelin,
Insulates axon, prevents continuous propagation
With saltatory propagation, local current
“Jumps” from node to node and depolarisation occurs only at nodes
What are the components of the plasma membrane that allow it to perform its characteristic functions?
Membrane lipids, membrane proteins and membrane carbohydrates
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 of the plasma membrane forms a physical barrier between the cells internal and external environments
What type of integral protein allows water and small ions to pass through the plasma membrane?
Channel proteins are integral proteins that allow water and small ions to pass through the plasma membrane
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 neurons ability to depolarise?
If the voltage gated sodium channels in a neurons plasma membrane could not open, sodium ions could not flood into the cell, and it would not be able to depolarise
An action potential is a
Propagated change in the transmembrane potential of excitable cells, 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 neuron?
If the extra cellular concentration of potassium ions decreased, more potassium would leave the cell, and the electrical gradient across the membrane (the transmembrane potential) would increase. This condition is called hyper polarisation
What does the transmission speed of the action potential depend on?
The diameter of the axon and if it is myelinated or not
