Structure and function of cells of the nervous system Flashcards
What cell is the main cell of the nervous system?
Neuron
Type of cell that makes up the nervous system and supports cognitive function
This is known as…?
Neuron
Define a neuron
Type of cell that makes up the nervous system and supports cognitive function
What are the 5 components of a neuron?
- Soma (main cell body)
- Dendrites
- Myelin sheath
- Axon
- Terminal buttons
In a neuron, what components are labelled as “branch-like structures”?
Dendrites
In a neuron, what component contains the nucleus and machinery that provides for the cell’s life processes?
Soma
In a neuron, what component is a long and slender tube, often covered by myelin sheath, and carries information (action potential) from the soma to terminal buttons?
Axon
In a neuron, what components act as recipients of messages between neurons?
Dendrites
A long and slender tube, often covered by myelin sheath, and carries information (action potential) from the soma to terminal buttons
What component of a neuron is this?
Axon
Contains the nucleus and machinery that provides for the cell’s life processes
What component of a neuron is this?
Soma
Wraps around axon some segments of the axon
What component of a neuron is this?
Myelin Sheath
There are 3 ways to divide neurons based on their functions. What are they?
1) Sensory neurons
2) Motor neurons
3) Interneurons
Describe sensory neurons
Detect changes in the external and internal environment (CNS and PNS, light, sound, odours, touch…)
Describe motor neurons
Controls muscle contraction and also gland secretion (CNS and PNS)
Describe interneurons
Lie entirely within the CNS and are involved in cognition (i.e., perceiving, learning, remembering and executive functioning such as decision making)
Lie entirely within the CNS and are involved in cognition (i.e.,perceiving, learning, remembering and executive functioning such as decision making)
What type of neuron is this?
Interneurons
Controls muscle contraction and also gland secretion (CNS and PNS)
What type of neuron is this?
Motor neurons
Detect changes in the external and internal environment (CNS and PNS, light, sound, odours, touch…)
What type of neuron is this?
Sensory neurons
There are 3 ways to divide neurons based on their structure. What are they?
1) Multipolar neuron
2) Bipolar Neuron
3) Unipolar Neuron
Neuron with one axon and many dendrites attached to its soma
What neuron is this?
Multipolar neuron
Neuron with one axon and one dendrite attached it its soma
What neuron is this?
Bipolar neuron
Neuron with one axon attached to its soma; the axon divides, with one branch receiving sensory information and the other sending the information into the central nervous system.
What neuron is this?
Unipolar neuron
Describe multipolar neuron
Neuron with one axon and many dendrites attached to its soma
Describe Bipolar neuron
Neuron with one axon and one dendrite attached it its soma
Describe unipolar neuron
Neuron with one axon attached to its soma; the axon divides, with one branch receiving sensory information and the other sending the information into the central nervous system
Which neuron is usually sensory?
1) Multipolar neuron
2) Bipolar Neuron
3) Unipolar Neuron
2) Bipolar Neuron
Which neuron has dendrites that detect events occurring in the environment and communicate the information about these events to the CNS?
1) Multipolar neuron
2) Bipolar Neuron
3) Unipolar Neuron
2) Bipolar Neuron
Which neurons transmit sensory information from the environment to the CNS?
1) Multipolar neuron
2) Bipolar Neuron
3) Unipolar Neuron
2) Bipolar Neuron
3) Unipolar Neuron
Which neuron has dendrites that detect touch, temperature changes and other sensory events that affect the skin?
1) Multipolar neuron
2) Bipolar Neuron
3) Unipolar Neuron
3) Unipolar Neuron
What happens when an action potential travels down the axon and reaches the terminal buttons?
Terminal buttons secrete a chemical called neurotransmitters
What component of a neuron secretes a chemical called neurotransmitters?
Terminal buttons
In bipolar neurons, which of these are sensitive to physical stimuli?
a) Cilia
b) Dendrites
a) Cilia
In unipolar neurons, which of these are sensitive to physical stimuli?
a) Cilia
b) Dendrites
b) Dendrites
Which early anatomist stained cells in the CNS and drew them?
Ramon y Cajal
What cell is a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala?
Pyramidal cell
Define pyramidal cell
Pyramidal cells are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala
Define supporting cells
- Glue/glial cells
- Surround neurons and hold them in place
- Control the supply of nutrients and some of the chemicals they need to exchange messages with other neurons
- Surround neurons and hold them in place
- Control the supply of nutrients and some of the chemicals they need to exchange messages with other neurons
What type of cell is this?
Glial cells
Where are glial cells found?
CNS
Glial cells make up…..% of cells in the brain
85%
Glial cells found in the CNS contain 4 cells. What are they?
1) Oligodendrocytes
2) Astrocytes
3) Microglia
4) Ependymal cells
Astrocytes are specialised glial cells. What are they shaped like?
Stars
Astrocytes are specialised glial cells. What are the 4 main purposes of astrocytes?
1) Provide physical support to neurons
2) Provide nourishment to neurons (they receive nutrients from capillaries, store them and release them to the neurons when needed)
3) When neurons die, they clean up debris by eating up dead cells and forming scar tissue
4) They control the chemical composition of fluid surrounding neurons
How do astrocytes provide nourishment to neurons?
- Neurons only consume glucose/sugar
- Astrocytes receive glucose from the blood supply and break down the sugar into simpler elements for the neurons to consume
1) Provide physical support to neurons
2) Provide nourishment to neurons (they receive nutrients from capillaries, store them and release them to the neurons when needed)
3) When neurons die, they clean up debris by eating up dead cells and forming scar tissue
4) They control the chemical composition of fluid surrounding neurons
Is this…?
a. Oligodendrocytes
b. Astrocytes
c. Microglia
d. Ependymal cells
b. Astrocytes
Which specialised glial cell supports axons and produces the myelin sheath?
Oligodendrocytes
What is myelin sheath?
- Insulation; prevents messages from spreading between axons
- 80% lipid, 20% protein
- Wraps around some segments of an axon
The bare portion of an axon is known as…?
Nodes of Ranvier
What do Oligodendrocytes do in the CNS?
- Oligodendrocytes support axons and produce myelin sheath
- Grow multiple paddle-shaped extensions that wrap around multiple adjacent axons
What do Oligodendrocytes do in the PNS?
- Schwann cells provide myelin sheath for only one axon and the entires cell surrounds the axon
- Schwann cells tightly wrap themselves several times around a single axon
Which cell provides myelin sheath for only one axon and the entire cell surrounds the axon?
Schwann cells
Which cell myelinates a single axon?
Schwann cells
Which cell myelinates multiple axons?
Oligodendrocytes
Which cells grow multiple paddle-shaped extensions that wrap around multiple adjacent axons?
Oligodendrocytes
Schwann cell can myelinate multiple axons per cell
True or False?
False
Schwann cells can only myelinate one axon per cell
The physical barrier between blood and fluid that surrounds the cells of the brain
This is known?
The Blood-Brain Barrier
The Blood-Brain Barrier is produced by…?
Cells in the walls of the brain’s capillaries
The Blood-Brain Barrier has a …….. membrane
a. Semi-permeable
b. Non-permeable
c. Completely permeable
a. Semi-permeable
A semipermeable barrier between the CNS and circulatory system, which helps to regulate the flow of nutrient-rich fluid into the brain
This is known as…?
The Blood-Brain Barrier
Why is the Blood-Brain Barrier semi-permeable?
To protect the cells as only certain substances and chemicals can pass through the barrier (filter)
What are the chemicals that can pass through the Blood-Brain Barrier?
- Oxygen
- CO2
- Water
A region of the medulla where the blood-brain barrier is weak.
This allows toxins in the blood to stimulate this area, which initiates vomiting – poison expelled from the body
What is this called?
Area Postrema
Define Area Postrema
A region of the medulla (most bottom part of the brain) where the blood barrier is weak
To permit neurons to detect the presence of toxins and later stimulate and initiate vomiting
Only Oxygen, CO2 and Water can pass through the blood barrier. Where do other substances go?
They must be actively transported through capillary walls by special proteins
What is the main difference in appearance/structure between capillaries in the CNS/brain and capillaries in all parts of the body except the brain?
Capillaries in all parts of the body except the brain have gaps/holes that allow substances to go into and out of the blood
Capillaries in the CNS/brain don’t have gaps and walls are tightly joined
Capillaries in the CNS/brain don’t have gaps and walls are tightly joined
What effect does this have on the CNS/brain?
- Lack of free exchange of most substances
- In CNS, many substances cannot leave the blood
Why do we need the blood-brain barrier? List 2 reasons
- Makes it easier to regulate the composition of extracellular fluid as fluids can move in and out of the blood
- If the composition of fluid changes, the transmission of messages from one place to another in the brain will be disrupted (disrupt brain functioning)
What are the 2 ways neurons can produce useful behaviour?
1) Withdrawal reflex
2) Inhibition
Behaviour that does not require a lot of cognitive effort is known as…?
Withdrawal reflex
Describe the 8 steps of the withdrawal reflex
1) Sensory neurons (dendrites) detect painful stimuli
2) Dendrites of SN are stimulated by noxious stimuli (e.g. contact with a hot object)
3) Dendrites send messages down the axon to the terminal buttons
4) Terminal buttons of SN release neurotransmitters which excites interneuron
5) Interneurons send messages down their axon to the terminal button
6) Terminal button of interneurons releases neurotransmitters which excite motor neurons
7) Motor neurons send messages down their axon and the axon of MN joins a nerve and travels to a muscle
8) Terminal buttons in the motor neuron release neurotransmitters, making muscle contract (e.g. hand moves away from hot object)
Explain how inhibition counteracts withdrawal reflex
e.g. You hold a pot of hot stew and feel the pain yet you still don’t pull away to avoid making a mess/dropping the pot
The brain contains neural circuits that recognise what a disaster it would be if you dropped the pot
These neural circuits send information to the spinal cord that prevents the withdrawal reflex from making you drop the pot
How do you measure the electrical charges of an axon?
Electrodes
- 1st electrode = simple wire placed in external environment of axon
- 2nd electrode = microelectrode wire that records the message of axon
Inside the axon is…
a. Negatively charged
b. Positively charged
a. Negatively charged
Outside the axon is…
a. Negatively charged
b. Positively charged
b. Positively charged
The difference in electrical charge/potential inside and outside the cell is known as…?
Membrane potential
What is potential?
Stored up source of electrical energy
Membrane potential of a neuron when it is not being altered by excitatory or inhibitory postsynaptic potentials, normally about -70 mV.
This is known as…?
Resting potential
Define resting potential
When the membrane potential of a neuron is not being altered by excitatory or inhibitory postsynaptic potentials
Normally about -70 mV
Why does resting potential happen?
- Depolarisation
- When a sufficient positive charge is applied to the inside of a cell, which is initially negative, the cell becomes positive
What is depolarisation?
A sudden change in membrane potential from a negative internal charge to a positive internal charge
What is used to measure membrane potential?
Microelectrode
What is used to measure resting potential?
Oscilloscope
What happens when a neuron is at rest?
1) Potassium ions and organic anions are more prevalent inside the cell
2) Thus, inside the cell is more negatively charged than the outside
3) This causes the membrane potential of an average neuron to be -70Mv
What does the sodium-potassium pump in a neuron do during resting potential?
- Helps maintain potential at -70Mv
- Pumps 3 sodium ions out of the cell and 2 potassium ions into the cell
- Because more positive ions are being pumped out of the cell, it helps keep the MP negatively charged
What are the 2 mechanisms in a neuron that helps ions move in and out of the cell?
1) Sodium-potassium pump
2) Ion channels
The reduction of negative charge (toward zero) of the membrane potential when we stimulate neuron
This is known as?
Depolarisation
At rest, the neuron is negatively charged. When stimulated, the neuron becomes more positively charged. What is this occurrence called?
Depolarisation
The brief electrical impulse that provides the basis for the conduction of information along an axon
This is known as…?
Action potential
The value of the membrane potential that must be reached to produce an action potential
This is known as…?
Threshold of Excitation
The increase in the membrane potential of a cell (membrane potential overshoots and becomes more negative)
Hyperpolarisation
A rapid reversal of membrane potential, so that the inside of the cell becomes positive and the outside becomes negative
This is known as…?
Action potential
An electrical charge is caused by a balance between 2 opposing forces. What are they?
1) Diffusion
2) Electrostatic pressure
The movement of molecules from areas of high concentration to areas of low concentration (salt in a cup)
This is known as…?
Diffusion
Define hyperpolarisation
The increase in the membrane potential of a cell (membrane potential overshoots and becomes more negative)
Define threshold of excitation
The value of the membrane potential that must be reached to produce an action potential
Define action potential
The brief electrical impulse that provides the basis for the conduction of information along an axon
Define diffusion
The movement of molecules from areas of high concentration to areas of low concentration (salt in a cup)
Define electrostatic pressure
When substances dissolve in water, they split into 2 parts with opposing electrical charges
Ions of the same charge repel, ions of opposing charges attract
e.g. When salt dissolves in water, molecules split into 2 parts; sodium cations (Na+) and chloride anions (Cl-)
Na+ in the same region as other Na+ ions repel, but Na+ in the same region as Cl-attract
The force created by the attraction of oppositely-charged ions and the repulsion of same-charged ions is known as…?
Electrostatic pressure
When substances dissolve in water, they split into 2 parts with opposing electrical charges
Ions of the same charge repel, ions of opposing charges attract
This is known as?
Electrostatic pressure
The fluid contained within cells is known as?
Intracellular fluid
The body fluids located outside cells are known as?
Extracellular fluid
Define Extracellular fluid
The body fluids located outside cells
Define Intracellular fluid
The fluid contained within cells
Are chloride ions more prevalent outside or inside the cell when the neuron is at rest?
Outside
Are sodium ions more prevalent outside or inside the cell when the neuron is at rest?
Outside
Are potassium ions more prevalent outside or inside the cell when the neuron is at rest?
Inside
How does diffusion affect chloride ions, which affects the membrane potential?
Chloride ions are highly concentrated outside the cell
So they diffuse into the cell to a less concentrated region
How does diffusion affect sodium ions, which affects the membrane potential?
Sodium ions are highly concentrated outside the cell
So they diffuse inside the cell to a less concentrated region
How does diffusion affect potassium ions, which affects the membrane potential?
Potassium ions are highly concentrated inside the cell
So they diffuse outside the cell to a less concentrated region
How does electrostatic pressure affect potassium ions, which affects the membrane potential?
After diffusion, potassium ions are positively charged and the region outside the cell is also positively charged
So they repel and potassium ions return to the inside of the cell
How does electrostatic pressure affect chloride ions, which affects the membrane potential?
After diffusion, chloride ions are negatively charged and the region inside the cell is also negatively charged
So they repel and chloride ions return to the outside of the cell
How does electrostatic pressure affect sodium ions, which affects the membrane potential?
After diffusion, sodium ions are positively charged and the region inside the cell is negatively charged
So they attract and sodium ions remain inside the cell
How can Na+ be found outside of the cell, when both forces (diffusion and electrostatic pressure tend to push it inside?
Sodium-potassium pump
What does the sodium-potassium pump do?
It is a protein in the membrane that pushes 3 Na+ ions out of the cells and brings 2 K+ into the cell
It is a protein in the membrane that pushes 3 Na+ ions out of the cells and brings 2 K+ into the cell
What is this?
Sodium-potassium pump
Proteins that open and close, thus allowing ions to pass through the cell wall
This is known as…?
Ion channels
What determines the permeability of a membrane to a particular ion at a given moment?
The number of ion channels that are open
Describe the 7 stages of action potential
1) Depolariation is repeated until it exceeds the threshold of excitation
2) Sodium channels open and Na+ ions move into the cell, making the internal cell more positive (-70 to +40mV)
3) Potassium channel opens after a slight delay
4) Sodium channel closes when the action potential reaches its peak (+40mV) and no more Na+ enters the cell
5) K+ ions move out of the cell, bringing the membrane potential back to its resting potential
6) Potassium channels close once equilibrium is reached and sodium channels reset
7) Membrane potential overshoots its resting potential (hyperpolarisation) but later returns to its resting potential
Why does hyperpolarisation occur?
An extra K+ ion outside of the axon and/or an extra Na+ ion inside the axon
How does action potential recover from hyperpolarisation to resting potential?
The sodium-potassium transporters remove the extra Na+ ions that leaked in and retrieve the K+ ions that leaked out
The movement of the message down an axon is called…?
Conduction of the Action Potential
What are the 2 laws that can explain the conduction of the action potential?
1) All or none law
2) Rate law
Once the action potential begins, it proceeds without decrement to the terminal buttons (it either occurs, or it doesn’t occur)
What is this known as?
All or none law
What does the all or none law explain?
Action potential either occurs or does not occur at all
Minimises possibility that information would be lost along the way
Is this all or none law or rate law?
Firing a gun
All or none law
Because the gun is only fired if there’s adequate pressure put on the trigger
The speed and force of the bullet are not affected by how hard you pull the trigger; gun either fires or does not
True or False?
Action potential changes size when travelling down the axon
False
AP remains the same size
When AP reaches a point where the axon branches, it splits but does not diminish in size
Variations in the intensity of a stimulus are represented by variations in the rate at which that axon fires
This is known as?
Rate Law
Which law explains how changes in the intensity of stimuli presented can affect the rate of reaction?
Rate Law
What does the rate law explain?
How changes in the intensity of stimuli presented can affect the rate of reaction
The more intense the stimulus, the (slower/faster) the neuron will fire
Faster
The weaker the stimulus, the (slower/faster) the neuron will fire
Slower
When electrical impulse/action potential skips from one node of Ranvier to another node down the full length of an axon
This is known as…?
Saltatory conduction
Explain saltatory conduction (3 points)
1) Due to myelination of neurons, action potential can only occur at the nodes of Ranvier
2) As depolarisation cannot occur in myelinated regions of the axion, the wave of depolarisation occurs between nodes
3) AP jumps from one node to another when travelling down an axon
What are the 2 advantages of saltatory conduction?
1) Economic: Less energy is used by the sodium-potassium pump
- Because Na+ can enter myelinated axons only at the nodes of Ranvier, much less Na+ gets in
- Thus, less Na+ has to be pumped out by the sodium-potassium pump
2) Speed: Conduction of action potential is faster in a myelinated axon
- Transmission between nodes is very fast
- Allows us to think and react faster
What is a synapse?
The junction between 2 neurons
It is the primary means of communication between 2 cells
The junction between 2 neurons
It is the primary means of communication between 2 cells
What is this?
Synapse
Define synaptic cleft
Space between presynaptic and postsynaptic membrane
Space between presynaptic and postsynaptic membrane
What is this?
Synaptic cleft
A synapse is a very narrow gap between 2 neurons called the synaptic cleft. How big is the gap?
20nm
True or False?
An action potential can easily cross the synaptic cleft
False
An action potential cannot cross the synaptic cleft, so nerve impulses are carried by chemicals called neurotransmitters
A neuron-sending impulse is known as…?
Pre-synaptic neuron
A neuron-receiving impulse is known as…?
Post-synaptic neuron
What are neurotransmitters made by? And where are they stored?
Made = Pre-synaptic neuron
Stored = Synaptic vesicles at the end of the axon
What carries action potential past the synaptic cleft?
Neurotransmitters
Define synaptic vesicles
Small, hollow, bead-like structure found in terminal buttons
Contains molecules of neurotransmitters
Small, hollow, bead-like structure found in terminal buttons
Contains molecules of neurotransmitters
This is known as…?
Synaptic vesicles
How do neurotransmitter-dependent ion channels open?
The membrane of the post-synaptic neuron has chemical-gated ion channels called neuroreceptors
These have specific binding sites for neurotransmitters
The chemical messenger fits the binding site like a lock and key
Direct opening of the ion channel is known as…?
Ionotropic receptor
Indirect opening of the ion channel is known as…?
Metabotropic receptor
Which opening of transmitter-dependent ion channels is similar to opening a locked door with a key from the outside?
Ionotropic receptor
Which opening of transmitter-dependent ion channels is similar to ringing a doorbell and having someone open the locked door from the inside?
Metabotropic receptor
Explain how ionotropic receptors open ion channels
When a molecule of the appropriate neurotransmitter attaches to the ion channel that is equipped with its own binding sight, the ion channel opens
Explain how metabotropic receptors open ion channels
- Some receptors do not open ion channels directly but start a chain of chemical events (metabotropic receptors)
- MRs are located close to G protein
- When the molecule of neurotransmitters binds with the MR, the MR activates the G protein
- G protein activates the enzyme that stimulates the production of a chemical (second messenger)
- Molecules of SM travel through cytoplasm and attach themselves to nearby ion channels, which causes them to open
Which opening of ion channels results in postsynaptic potential taking longer to begin and lasting longer?
Metabotropic receptor
A receptor that contains a binding site for a neurotransmitter; activates an enzyme that begins a series of events that opens an ion channel elsewhere in the cell’s membrane when a molecule of the neurotransmitter attaches to the binding site
This is known as…?
Metabotropic receptor
What are the 2 main mechanisms that get rid of neurotransmitters from the synaptic cleft?
1) Enzyme mechanism
2) Reuptake (different transporters)
Explain the enzyme mechanism to get rid of neurotransmitters in synaptic cleft
Enzyme destroys molecules of neurotransmitters
Explain the reuptake (different transporters) mechanism to get rid of neurotransmitters in synaptic cleft
Transporters “vacuum” or suck up all the neurotransmitters near the presynaptic cell
Transporters return neurotransmitters back to presynaptic cells where they will get back to their vesicles and wait for the next action potential
Transporters return neurotransmitters back to presynaptic cells where they will get back to their vesicles and wait for the next action potential
This is known as…?
Reuptake (different transporters) mechanism
Excitatory depolarization of the postsynaptic membrane is known as…?
Excitatory Postsynaptic Potential (EPSP)
Inhibitory hyperpolarization of the postsynaptic membrane is known as…?
Inhibitory Postsynaptic Potential (IPSP)
What are the 2 types of postsynaptic potentials?
- Excitatory Postsynaptic Potential (EPSP)
- Inhibitory Postsynaptic Potential (IPSP)
The nature of PSP is determined by …?
Postsynaptic receptors (which ion channels they open)
What are the 3 major types of ion channels?
Na+, K+ and Cl-
In terms of PSP, what happens when sodium enters the postsynaptic cell?
- Neurotransmitters bind to the postsynaptic neuron
- Ion channels open, and sodium ions enter the postsynaptic cell
- Sodium is positively charged; inside the cell is negatively charged
- Inside the cell becomes more positively charged because of the increase in + ions
- Depolarisation; excitatory postsynaptic potential
In terms of PSP, what happens when chloride enters the postsynaptic cell?
- Neurotransmitters bind to the postsynaptic neuron
- Ion channels open, and chloride ions enter the postsynaptic cell
- Chloride is negatively charged; inside the cell is also negatively charged
- Inside the cell becomes more negatively charged because of the increase in - ions
- Hyperpolarisation; inhibitory postsynaptic potential
In terms of PSP, what happens when potassium enters the postsynaptic cell?
- Neurotransmitters bind to the postsynaptic neuron
- Ion channels open, and potassium ions exit the postsynaptic cell
- Potassium is positively charged; outside the cell is also positively charged
- Inside the cell becomes more negatively charged because of the decrease in + ions
- Hyperpolarisation; inhibitory postsynaptic potential
The process by which inhibitory and excitatory postsynaptic potentials summate and control the rate of firing of a neuron.
This is known as…?
Neuronal integration
Define neuronal integration
The process by which inhibitory and excitatory postsynaptic potentials summate and control the rate of firing of a neuron.
Describe neuronal integration when there is excitatory PSP
- All inputs to a single cell are integrated with a soma/cell body
- If we have a more excitatory PSP overall, the soma will decide to fire from a region called the axon hillock if the threshold of excitation is reached
- Action potential is triggered in the axon
Describe neuronal integration when there is excitatory PSP and inhibitory PSP
- All inputs to a single cell are integrated with a soma/cell body
- If we have some excitatory PSP and some inhibitory PSP overall, they will cancel each other out and soma will decide not to fire the neuron
- Action potential is not triggered in the axon
What are the 2 summations of neuronal integration?
1) Temporal
2) Spatial
What happens in temporal neuronal integration?
- The 1st excitatory presynaptic input causes depolarisation but it is not enough to surpass the threshold of excitation
- 2nd excitatory presynaptic input comes closely after the 1st and goes over the threshold
- Action potential occurs
What happens in spatial neuronal integration?
- 2 excitatory presynaptic inputs from 2 different neurons
- When the inputs summit/come together, they will cause spatial summation
- Action potential occurs only when both inputs cause depolarisation together (closer in space) to reach the threshold of excitation
What happens in EPSP-IPSP cancellation neuronal integration?
- When there is 1 excitatory presynaptic input and 1 inhibitory presynaptic input
- Excitatory PS input = causes depolarisation
- Inhibitory PS input = causes hyperpolarisation
- No action potential occurs because both PSPs cancel each other out
