Lecture 7/8 - How neurons communicate

What are the two classic experiments to determine how neurons communicate

• Galvani

• Loewi 

Luigi galvani:

• Observed WHAT hanging on a wire would WHAT during an electrical storm

• Hypothesized that sparks from the storm activated WHAT

• Applied WHAT to a dissected WHAT attached to the leg (the leg WHAT)

• Concluded that the WHAT used WHAT to communicate

Luigi galvani:

• Observed FROG LEGS hanging on a wire would TWITCH during an electrical storm

• Hypothesized that sparks from the storm activated MUSCLES

• Applied CURRENT to a dissected NERVE attached to the leg (the leg TWITCHED)

• Concluded that the NERVOUS SYSTEM used ELECTRICITY to communicate

Chemical communication: 1st evidence

• Done by Otto loewi WHAT experiment 

• Stimulated the WHAT 

• DOES WHAT TO the heart 

• The two hearts shared fluid and they exhibited the same WHAT even though the other heart was not stimulated 

• Chemical found to be WHAT 

Chemical communication: 1st evidence

• Done by Otto Loewi FROG HEART experiment 

• Stimulated the VAGUS NERVE 

• SLOWS the heart 

• The two hearts shared fluid and they exhibited the same RESPONSE even though the other heart was not stimulated 

• Chemical found to be ACETYLCHOLINE 

Movement of ions = WHAT

Movement of ions = CHARGE

Intercellular and extracellular fluid is filled with WHAT

Ions (charged particles)

What are the ions most important for neuron electrical signals

• Sodium (Na+)

• Potassium (K+) 

• Chloride (Cl-) 

• Large negatively charged proteins (A-) 

• Calcium (Ca 2+) 

What contributes to a cells electrical charge:

Outside cell:

• WHAT 

• WHAT 

• WHAT 

Inside cell (leakage channels):

• WHAT 

• WHAT 

What contributes to a cells electrical charge:

Outside:

• Lots of SODIUM (Na+)  

• Lots of CHLORIDE (Cl-)  

• Lots of CALCIUM (Ca2+)

Inside:

• Lots of POTASSIUM (K+)  

• Lots of NEGATIVE PROTEINS (A-)  

Of all these, only WHAT ions can, to some extent move freely through specific WHAT channels 

Of all these, only K (±)  ions can, to some extent move freely through specific K (±)  channels 

What are ion channels 

a HYDROPHILIC pathway that facilitates ion movement across the PLASMAMEMBRANE 

What are three features of the ion channel

1. Permeability 

2. Selectivity 

3. Gating 

No channels or closed channels means WHAT

No channels or closed channels means NO PERMEABILITY

Most channels are closed at WHAT except for some WHAT

Most channels are closed at REST except for some NON-GATED K (±) channels 

The cellular membrane potential is a function of:

• WHAT differences mainly in WHAT and WHAT on the inside and outside of the WHAT

• Combined with WHAT differences for these WHAT 

The cellular membrane potential is a function of:

• CONCENTRATION differences mainly in METAL CATIONS and LARGE ORGANIC ANIONS on the inside and outside of the PLASMAMEMBRANE

• Combined with SELECTIVE PERMEABILITY differences for these IONS 

Movement of ions: Diffusion

• All molecules WHAT and therefore will spread from areas where they are more WHAT to areas of WHAT 

• No WHAT required, due to WHAT 

• Eventually ions will be distributed WHAT in solution - called WHAT 

Movement of ions: Diffusion

• All molecules MOVE and therefore will spread from areas where they are more CONCENTRATION to areas of LOW CONCENTRATION 

• No ENERGY required, due to RANDOM MOVEMENT  

• Eventually ions will be distributed EVENLY in solution - called DYNAMIC EQUILIBRIUM  

Movement of ions: Diffusion:

• WHAT selectively restrict the free diffusion of certain molecules

Movement of ions: Diffusion:

• SEMI-PERMEABLE MEMBRANES selectively restrict the free diffusion of certain molecules

Semipermeable membrane: Concentration gradient

• What will the separation look like if the membrane is permeable to K+ and impermeable to A- 

Movement of ions: voltage gradients and electromotive forces:

• Move from areas of WHAT to areas of WHAT

• Separation of WHAT, which costs WHAT, creates an WHAT

Movement of ions: voltage gradients and electromotive forces:

• Move from areas of HIGH CHARGE to areas of LOW CHARGE

• Separation of CHARGES, which costs ENERGY, creates an ELECTROMOTIVE FORCE (EMF)

How does electrochemical equilibrium work

Positive charges flow through the semi-permeable membrane till there is an equal amount of charge between the K+ and A-, once equilibrium is reached the K+ will continue to flow back and forth between the semi-permeable to maintain the system of equilibrium 

Electrical activity of cell membranes: Resting membrane potential

• When undisturbed, there is a WHAT difference across the membrane  

• Inside the membrane is WHAT relative to WHERE 

• This voltage difference is called a WHAT “WHAT”

• Usually inside is WHAT to WHAT MORE negative than outside (so the inside = WHAT to WHAT) 

• The inside can range between WHAT and WHAT depending on cell and species 

Electrical activity of cell membranes: Resting membrane potential

• When undisturbed, there is a STABLE difference across the membrane  

• Inside the membrane is NEGATIVE relative to OUTSIDE 

• This voltage difference is called a MEMBRANE “POTENTIAL”

• Usually inside is 65mV to 70mV MORE negative than outside (so the inside = -65mV to -70mV) 

• The inside can range between -40mV and -90mV depending on cell and species 

Resting membrane potential mainly depends on the WHAT

Resting membrane potential mainly depends on the CONCENTRATION of K+ IONS

Resting membrane potential is near the WHAT at which the concentration gradient pushes WHAT out of the cell cancels out with the pulling of WHAT into the cell

Resting membrane potential is near the VOLTAGE at which the concentration gradient pushes K+ out of the cell cancels out with the pulling of K+ into the cell

Resting membrane potential varies a little depending on the cells WHAT (remember: most channels are WHAT at rest except for some WHAT channels) 

Resting membrane potential varies a little depending on the cells PERMEABILITY to other IONS (remember: most channels are CLOSED at rest except for some K (±) channels) 

Resting membrane potential to sodium (Na+):

• HOW MUCH more concentrated outside the cell 

• Membranes is not very WHAT to Na+ (but some leaks in)

• Would this slow leak eventually eliminate the charge separation: WHAT

• There is a WHAT which is a WHAT pump that reverses the WHAT 

Resting membrane potential to sodium (Na+):

• 10X more concentrated outside the cell 

• Membranes is not very PERMEABLE to Na+ (but some leaks in)

• Would this slow leak eventually eliminate the charge separation: YES

• There is a “BILGE PUMP” which is a Na+/K+  pump that reverses the SLOW LEAK 

All cells have a WHAT

All cells have a RESTING CELL MEMBRANE

Changes in the membrane WHAT are at the heart of how neurons WHAT to signals and WHAT information 

Changes in the membrane VOLTAGE are at the heart of how neurons RESPOND to signals and PROCESS information 

What are the three ways the opening state of an ion channel can be changed (change in permeability)

• Chemical 

• Mechanical 

• Electrical

How do chemicals change the permeability

Neurotranmitter receptors

How do mechanicals change the permeability

For instance, stretch receptors

How do electricals change the permeability

Some channels open when the membrane potential reaches a certain threshold (aka voltage-gated) 

What are the two types of electrical signals

1. Graded potentials

2. Action potentials 

In the three ways the opening state of an ion channel can be changed (change in permeability) which ones are graded potential and which ones are action potentials

• Chemical (graded potential)

• Mechanical (graded potential) 

• Electrical (Action potential) 

Graded potential:

• When the membrane is stimulates a change in WHAT can be produced 

• WHAT 

• WHAT 

Graded potential:

• When the membrane is stimulates a change in MEMBRANE POTENTIAL can be produced 

• DEPOLARIZATION  

• HYPERPOLARIZATION  

What is depolarization

LESS difference between the inside and outside, thus, neuron is LESS negative 

What is hyperpolarization 

LARGER difference between the inside and outside, thus, neuron is MORE negative

Basis of Graded potentials:

• Change in membrane WHAT of certain ions (ie, channels open)  

Depolarization:

• Increase influx of WHAT (or WHAT) 

Hyperpolarization:

• Increase influx of WHAT or WHAT 

Basis of Graded potentials:

• Change in membrane PERMEABILITY of certain ions (ie, channels open)  

Depolarization:

• Increase influx of Na+ (or Ca 2+) 

Hyperpolarization:

• Increase influx of K+ or Cl- 

Graded potential - Hyperpolarization:

Graded change in voltage depends on:

• WHAT 

• WHAT 

Graded potential - Hyperpolarization:

Graded change in voltage depends on:

• Stimulus strength 

• Distance  

Graded potential - Depolarization:

Graded change in voltage depends on:

• WHAT 

• WHAT 

• WHAT 

• WHAT is past threshold

Graded potential - Depolarization:

Graded change in voltage depends on:

• Stimulus strength  

• Distance  

• Threshold 

• ACTION POTENTIAL is past threshold

Action potentials are a WHAT response:

• The neuron either produces a WHAT and WHAT the electrical signal to the next neuron or no WHAT is generates ( remains “WHAT”) 

Action potentials are a ALL-OR-NONE response:

• The neuron either produces a FULL ACTION POTENTIAL and TRANSMITS the electrical signal to the next neuron or no ACTION POTENTIAL is generates ( remains “SILENT”) 

Action potentials are always the same WHAT no matter how strong the WHAT is

Action potentials are always the same SIZE no matter how strong the DEPOLARIZING STIMULUS is

Strength of stimulus is coded in the WHAT and WHAT of action potentials

Strength of stimulus is coded in the PATTERN and FREQUENCY of action potentials

ie, number of action potentials per second (Hz) (think of how many action potential go off when a feather brushes your arm vs someone pinching you) 

The Hodgkin-Huxley model:

• Hodgkin and Huxley described the ionic basis of the WHAT

• This is considered the most important single achievement in WHAT

• They derived a relatively simple but detailed mathematical and biophysical model of the WHAT

• 1980 the scientist were able to identify and record WHAT 

• 1990 cloning of WHAT (to discover their WHAT) 

• 2000 first 3-dimensional structure and function of a WHAT 

The Hodgkin-Huxley model:

• Hodgkin and Huxley described the ionic basis of the ACTION POTENTIAL

• This is considered the most important single achievement in CELLULAR NEUROPHYSIOLOGY

• They derived a relatively simple but detailed mathematical and biophysical model of the ACTION POTENTIAL

• 1980 the scientist were able to identify and record SINGLE ION CHANNELS  

• 1990 cloning of ION CHANNELS (to discover their AMINO ACID SEQUENCE) 

• 2000 first 3-dimensional structure and function of a ION CHANNEL 

All cells maintain a WHAT

Resting membrane potential

Only WHAT cell types (muscle cells and neurons) can generate WHAT 

Only EXCITABLE cell types (muscle cells and neurons) can generate ACTION POTENTIALS 

No action potential generation possible in WHAT cells 

• Graded potentials move the WHAT towards or away from the WHAT but no WHAT can be generated 

No action potential generation possible in NON-EXCITABLE cells 

• Graded potentials move the MEMBRANE POTENTIAL towards or away from the THRESHOLD but no ACTION POTENTIAL (AP) can be generated 

Action potential generation possible in WHAT cells 

• Graded potentials move the WHAT towards or away from the WHAT; WHAT can be generated 

Action potential generation possible in EXCITABLE cells 

• Graded potentials move the MEMBRANE POTENTIAL towards or away from the THRESHOLD; ACTION POTENTIAL (AP) can be generated 

Action potentials are WHAT events - their amplitudes does not depend on WHAT

Action potentials are ALL-OR-NOTHING events - their amplitudes does not depend on STIMULUS STRENGTH

Graded potentials:

• Variable WHAT and WHAT which depends on WHAT and WHAT of triggering event 

• Spread WHAT (flows with no channel opening outside the point of origin), decrementing (gradual decrease) with distance from point of WHAT 

• Travel over WHAT 

Graded potentials:

• Variable MAGNITUDE and DURATION which depends on STRENGTH and DURATION of triggering event 

• Spread PASSIVELY (flows with no channel opening outside the point of origin), decrementing (gradual decrease) with distance from point of INITIATION (the electrical signal moves through the cell membrane without requiring additional ion channel activity away from the stimulus site and loses strength, or intensity, as it spreads out from where it began)

• Travel over SHORT DISTANCES  

Action potentials:

• WHAT event triggered when membrane potential is raised above a certain WHAT 

• Spread WHAT (self-regenerating) in non-decremented fashion 

• Travel over WHAT

Action potentials:

• ALL-OR-NOTHING event triggered when membrane potential is raised above a certain THRESHOLD 

• Spread ACTIVELY (self-regenerating) in non-decremented fashion (Spread actively (self-regenerating)" = each region of the membrane actively generates the action potential anew. "Non-decremental" = the amplitude stays constant as the action potential moves down the axon, unlike graded potentials.)

• Travel over LONG DISTANCES

Action potentials in neurons:

• Signals are conveyed along the neuron’s axon by an WHAT 

• Brief but large change in WHAT of the WHAT membrane 

• Shapes and firing patterns differ widely among WHAT 

• Vary in WHAT (1ms to 15ms) 

• Voltage potential WHAT, so the inside becomes WHAT relative to the outside 

• Reverts back to WHAT just as quickly 

• So rapid taht some neurons can have HOW MANY of action potentials per second 

Action potentials in neurons:

• Signals are conveyed along the neuron’s axon by an ACTION POTENTIAL 

• Brief but large change in POLARITY of the AXON’S membrane 

• Shapes and firing patterns differ widely among DIFFERENT types of neurons 

• Vary in DURATION (1ms to 15ms) 

• Voltage potential REVERSES, so the inside becomes POSITIVE relative to the outside 

• Reverts back to NEGATIVE INTERIOR just as quickly 

• So rapid taht some neurons can have 100 of action potentials per second 

Generation of action potentials: Key steps

• Depolarizing input(s) makes resting membrane potential WHAT 

If this reaches the threshold potential:

• Initiates start of WHAT in WHAT 

• Does not require further WHAT, will continue on its own 

• Membrane potential further WHAT and subsequently the interior becomes WHAT relative to the WHAT:

• can reach WHAT

• Total change can be more than WHAT

• Membrane potential then WHAT

• Overshoots WHAT and become WHAT

• Returns to WHAT

Generation of action potentials: Key steps

• Depolarizing input(s) makes resting membrane potential LESS NEGATIVE 

If this reaches the threshold potential:

• Initiates start of ACTION POTENTIAL in AXON HILLOCK 

• Does not require further STIMULATION, will continue on its own 

• Membrane potential further DEPOLARIZES and subsequently the interior becomes POSITIVE relative to the OUTSIDE:

• can reach +40mV

• Total change can be more than 100mV

• Membrane potential then REPOLARIZES

• Overshoots RESTING POTENTIAL and become HYPERPOLARIZED

• Returns to RESTING POTENTIAL 

Action potentials: Key elements

1. Asymmetric concentration distribution of (mainly) WHAT and WHAT ions across the WHAT established by WHAT mechanisms 

2. The presence of WHAT, WHAT K+ and Na+ channels in the plasmamembrane, these channels are normally WHAT when neuron is at rest

3. When a cell depolarizes, the WHAT change causes these channels to WHAT quickley:

• Only found in WHAT and WHAT cells

• WHAT after opening 

4. Voltage gates WHAT channels open and close more slowly

1. Asymmetric concentration distribution of (mainly) K+ and Na+ ions across the PLASMAMEMBRANE established by ACTIVE TRANSPORT mechanisms 

2. The presence of ION-SELECTIVE, VOLTAGE GATED K+ and Na+ channels in the plasmamembrane, these channels are normally CLOSED when neuron is at rest

3. When a cell depolarizes, the VOLTAGE change causes these channels to OPEN quickly:

• Only found in NEURONS and MUSCLE cells

• INACTIVE after opening 

4. Voltage gates K+ channels open and close more slowly

Ionic conductance events underlying the action potential summarized

How do (voltage) gated channels work:

• Passive (non-gated) WHAT (leakage channels) have one configuration → WHAT

• All gated channels have HOW MANY (or WHAT) configurations: 

1. WHAT (resting) 

2. WHAT (inactive, mainly sodium channels) 

3. WHAT 

• Part of the protein is WHAT (protein reshapes when cell WHAT) 

How do (voltage) gated channels work:

• Passive (non-gated) K+ CHANNELS (leakage channels) have one configuration → OPEN

• All gated channels have 2 (or 3) configurations: 

1. CLOSED (resting) 

2. CLOSED (inactive, mainly sodium channels) 

3. OPEN 

• Part of the protein is CHARGED (protein reshapes when cell DEPOLARIZES) 

A refractory period is a period in which triggering another WHAT is much more difficult or even impossible

A refractory period is a period in which triggering another ACTION POTENTIAL is much more difficult or even impossible

The absolute refractory period is due to the WHAT. In this period NO new WHAT can be generated

The ABSOLUTE refractory period is due to the Na+ CHANNEL INACTIVATION GATE. In this period NO new ACTION POTENTIAL can be generated

The RELATIVE refractory period is due to the WHAT. The neuron needs a stronger WHAT input to reach threshold for an WHAT can be generated 

The RELATIVE refractory period is due to the K+ CHANNEL ACTIVATION GATE. The neuron needs a stronger DEPOLARIZING input to reach threshold for an ACTION POTENTIAL  can be generated

Refractory period diagram

Propagation of impulse diagram

Nerve impulses are WHAT 

Movement of action potential along the axon 

When a segment of an axon generates an WHAT it depolarizes the WHAT section

When a segment of an axon generates an ACTION POTENTIAL it depolarizes the ADJACENT section

An action potential represents a WHAT change in the WHAT of the membrane 

An action potential represents a -100mV change in the POTENTIAL of the membrane 

You only need about HOW MUCH change to reach WHAT

You only need about 20mV change to reach THRESHOLD

Action potential brings the WHAT section to WHAT, activating the voltage sensitive WHAT channels in the adjacent section

Action potential brings the ADJACENT section to THRESHOLD, activating the voltage sensitive Na+ channels in the adjacent section

Each action potential WHAT the next WHAT

Each action potential PROPAGATES (moves) to the next neuron

At each segment of the axon the action potential WHAT completely:

• No loss in WHAT from the start of the axon to the end

• It is the same WHAT at each stage 

At each segment of the axon the action potential REGENERATES completely:

• No loss in AMPLITUDE from the start of the axon to the end

• It is the same SIZE at each stage 

Stronger stimuli do not produce bigger WHAT, just more WHAT ones

Stronger stimuli do not produce bigger ACTION POTENTIALS, just more FREQUENT ones

Action potentials only move in WHAT

One direction

What are two solutions that speed up nerve impulses

1. Myelin 

2. Saltatory conduction 

These solutions make your axon WHAT (larger WHAT, squids and other invertebrates)

These solutions make your axon HUGE (larger DIAMETER, squids and other invertebrates)

These solutions make it really hard for WHAT to escape by insulating the axon (WHAT, vertebrates) 

These solutions make it really hard for IONS to escape by insulating the axon (MYELINATION, vertebrates) 

What is multiple sclerosis

Loss of myelin around axons

Myelination increases WHAT

Nerve conduction

Saltatory conduction:

• The action potential is WHAT fully at each WHAT 

• Action potential jumps from WHAT to WHAT 

• Moves WHAT (up to 150m/s) than opening millions of channels over a comparable portion of an WHAT neuron (0.5-10m/s)

Saltatory conduction:

• The action potential is REGENERATE fully at each NODE of RANVIER 

• Action potential jumps from NODE to NODE 

• Moves FASTER (up to 150m/s) than opening millions of channels over a comparable portion of an UNMEYLINATED neuron (0.5-10m/s)

Not all axons are WHAT

Not all axons are MYELINATED

Unmyelinated axons: Group C fibers:

• Group C fibres include WHAT in the Autonomic nervous system and nerve fibers at the WHAT roots (IV fiber) 

• Group C fibers carry WHAT information 

• Group C fibers, small in WHAT, WHAT conducting

Unmyelinated axons: Group C fibers:

• Group C fibres include POST GANGLIONIC FIBERS in the Autonomic nervous system and nerve fibers at the DORSAL roots (IV fiber) 

• Group C fibers carry SENSORY information 

• Group C fibers, small in DIAMETER, SLOW conducting

(Voltage-gates) Ion channels shape electrical behaviour of neurons

• WHAT

• WHAT of action potential 

• WHAT 

• WHAT of action potentials 

• WHAT of action potential trains 

(Voltage-gates) Ion channels shape electrical behaviour of neurons

• EXCITABILITY (how eager are they to generate an action potential) 

• SHAPE of action potential 

• RESPONSE CHARACTERISTICS 

• FREQUENCY of action potentials 

• PATTERNING of action potential trains 

Each neuron has its own characteristic action potential (AP) WHAT and activity WHAT

Each neuron has its own characteristic action potential (AP) SHAPE and activity PATTERN

Electrical activity patterns diagrams 

Since action potentials are a all-or-nothing response you can consider them as a WHAT (0 or 1) or WHAT signal 

Since action potentials are a all-or-nothing response you can consider them as a BINARY (0 or 1) or DIGITAL signal 

Sensory input is WHAT (continuous)

Sensory input is ANALOG (continuous)

The coding of these analog signals is in the WHAT (number of action potentials per second) and WHAT of action potentials

The coding of these analog signals is in the FREQUENCY (number of action potentials per second) and PATTERN of action potentials

Neurons can receive inputs from HOW MANY (sometimes HOW MANY) other neurons

Neurons can receive inputs from 1000s (sometimes 100000) other neurons

Neuron only has HOW MANY output, one WHAT

Neuron only has ONE output, one AXON

Post synaptic potentials (PSP) = WHAT

• Put a recording electrode is WHAT (cell body) post synaptic neuron 

• Tease apart incoming WHAT 

• Stimulate individual WHAT 

• Some WHAT the post synaptic neuron (WHAT) 

• Some WHAT the post synaptic neuron (WHAT) 

Post synaptic potentials (PSP) = GRADED POTENTIAL

• Put a recording electrode is SOMA (cell body) post synaptic neuron 

• Tease apart incoming SENSORY FIBERS 

• Stimulate individual FIBERS 

• Some DEPOLARIZES the post synaptic neuron (EXCITATORY) 

• Some HYPERPOLARIZE the post synaptic neuron (INHIBITORY) 

Excitatory postsynaptic potential (EPSP = WHAT graded potential)

• Brings the WHAT closer to the threshold, thus increasing the probability that the cell will fire an WHAT 

Excitatory postsynaptic potential (EPSP = DEPOLARIZING graded potential)

• Brings the POTENTIAL MEMBRANE closer to the threshold, thus increasing the probability that the cell will fire an ACTION POTENTIAL 

Inhibitory postsynaptic potential (IPSP = WHAT graded potential)

• Move the WHAT away from the threshold, thus decreasing the probability that the cell will fire an WHAT 

Inhibitory postsynaptic potential (IPSP = HYPERPOLARIZING graded potential)

• Move the POTENTIAL away from the threshold, thus decreasing the probability that the cell will fire an ACTION POTENTIAL 

Excitatory postsynaptic potential (EPSP)

• Open WHAT channels

• WHAT floes in the cell by its WHAT and WHAT 

Excitatory postsynaptic potential (EPSP)

• Open Na+ channels

• WHAT floes in the cell by its VOLTAGE and CONCENTRATION GRADIENT 

Inhibitory postsynaptic potential (IPSP)

• Opens WHAT or WHAT channels

• WHAT flows out and WHAT flows into the cell by its WHAT

Inhibitory postsynaptic potential (IPSP)

• Opens K+ or Cl- channels

• K+ flows out and Cl- flows into the cell by its CONCENTRATION GRADIENT

Inhibitory postsynaptic potential (IPSP) and Excitatory postsynaptic potential (EPSP) are proportional in WHAT to the strength of the stimulus

Inhibitory postsynaptic potential (IPSP) and Excitatory postsynaptic potential (EPSP) are proportional in SIZE to the strength of the stimulus

Neurotransmitters released by the WHAT neuron determines if the WHAT neuron will generate an WHAT or an WHAT 

Neurotransmitters released by the PRE-SYNAPTIC neuron determines if the POST-SYNAPTIC neuron will generate an EPSP (eg, NE) or an IPSP (eg, GABA)  

Neurons receive many WHAT and WHAT potentials 

Neurons receive many SIMULTANEOUS and CONSECUTIVE potentials 

These signals will have a WHAT effect and determine whether the electrical message is WHAT or if it WHAT at that point

These signals will have a SUMMATIVE effect and determine whether the electrical message is CONVEYED or if it STOPS at that point

Spatial summation:

If PSPs occur simultaneously they will WHAT 

This can occur cause either:

• WHAT

• WHAT

• WHAT  

Spatial (in space) summation:

If PSPs occur simultaneously they will SUMMATE 

This can occur cause either:

• Larger EPSP

• Larger IPSP

• Cancel each other out   

Temporal (in time) summation:

If two signals occur close enough together in WHAT, the send one has its WHAT before the first has WHAT 

Temporal (in time) summation:

If two signals occur close enough together in TIME, the send one has its EFFECT before the first has DEGRADED 

In reality there is a combination of both WHAT 

In reality there is a combination of both  SPATIAL and TEMPORAL SUMMATION 

Where does integration take place

The axon hillock

The cell body (soma) does not have WHAT channels, it cannot fire an WHAT

The cell body (soma) does not have VOLTAGE GATED channels, it cannot fire an ACTION POTENTIAL 

Only an axon can generate and conduct an WHAT

Action potential

The action potential is generated at the WHAT:

• Rich in WHAT channels 

• The WHAT of all the EPSPs and IPSPs at the axon hillock will determine if the cell will fire an WHAT 

The action potential is generated at the AXON HILLOCK:

• Rich in VOLTAGE GATED channels 

• The SUM of all the EPSPs and IPSPs at the axon hillock will determine if the cell will fire an ACTION POTENTIAL 

PSP (post synaptic potential) spreads though WHAT/WHAT:

• Loses WHAT as it spreads 

PSP (post synaptic potential) spreads though DENDRITES / CELL BODY

• Loses INTENSITY as it spreads