Action Potentials & Synapses

The Neuron and Its Resting State

Resting State

- Neuron: cells that are part of the nervous system which are in charge of transmitting action potentials through electrical signals

- Components:

• cell body (soma):
• dendrites: this is where synapses are found, receives signals from other neurons
• axon hillock
• axons: action potentials are sent through here, where voltage-channels start to be found
• axon terminals: where the chemical messages are released from action potentials and sent onto another neuron or target tissue via the synapse

Neurons must first have a resting state

- allows the neuron to gain more energy before

it has to wind up to send electrical signals via

axons

- this is when the axolemma hasn't been

stimulated to change its electrical charge.

Electrochemical Gradient

2 components that provide energy for an action potential to be propelled:

- Diffusion: molecules moving from an area of high concentration to areas of low concentration to provide equilibrium

- Electrical force: eletrical charge from differently charged ions establish an electrical force together to provide energy for the action potential

- These 2 balance each other to

bring equilibirum to the

neuron for potassium (K)

and chloride (Cl)

- All this energy is managed by protein

channels along the axon of the neuron,

which are voltage-gated channels that

control the charge of the neuron to be

able to send action potentials

Electrochemical Gradient

Phases of

an Action Potential

3 Phases:

- Depolarization: when the electrical charge in the axolemma goes from a negative charge to a more positive charge, after voltage-gated sodium (Na+) channels open upon a signal reaching the axon hillock

• Threshold value: when the electrical charge goes from a resting value of -70mV to a value to -55mV, which is when Na+ channels are open for it to rush into the cell

- Repolarization: the membrane potential goes from positive back down to negative when Na channels are inactivated and K+ channels open up along the axons

- Hyperpolarization: when the membrane value becomes more negative than its resting membrane potential

Phases

of Action

Potential

Propagation &

the Effect of Myelination

- This is how the signal of the action potential is reproduced along the axon

2 Types:

- Passive conduction: this is how unmyelinated axons reproduce the signal.

• slower process because the action potential signal has to keep getting replicated at each axon

- Saltatory conduction:

how myelinated axons conduct action potentials

• faster process because the axons have the insulation of the myelin sheath, so signals are only replicated at the sections that are briefly unmyelinated, the Nodes of Ranvier

Propagation

Synapse

Synapses is how neurons communicate with each other, information is passed through a small gap inbetween 2 neurons. This can happen through chemical synapses and electrical synapses.

Chemical Synapses

Neurons send Ca2+ neurotransmitters through exocytosis from the pre-synaptic channel across a small 20 nanometer gaps called synaptic clefts.The neurotransmitters then bind to sodium Na+ receptors on the otherside(post-synaptic channel) and produce one of two outcomes. In the case of an excitatory postsynaptic potential (EPSP) the action potential is more likely to fire, and in the case of an inhibitory postsynaptic potential (IPSP) the action potential is less likely to fire.

Electrical Synapses

Electrical synapses are quicker than chemical synapses and they have to travel less distance as well (3.5 nanometers). The neurotransmitters are able to go through gap junction channels to communicate with the next neuron. They are used when very fast movement is needed.

Action Potential

in Psychology

Action Potential in Psychology

The concept of action potential is important when applied to a psychology course because:

• Action potential occurs when a neuron sends information away from the body using an axon
• This results in what people call a "spike" or more commonly known as an "impulse"
• The entire thing is a large amount of electical activity, exploding, caused by a depolarizing current -- explosion of electrical activity that is

Concept of Synapses in Psychology

This concept is important for this course & psychology because:

- meeting point between pre- & post-synaptic neurons

- synpases = connections; and connection turns our

structure ---> system

- "translators and messengers", ensures smooth delivery

- synapses are throughout the nervous system

- builds our understanding of how brain & body

communicates & regulates functions/movements

- root of many psychiatric disorders

- Alzheimer's/Parkinson's = loss of synapses in brain

Synapses in Psychology

Understanding synapses enriches our understanding of how signals are transmitted each other and what signals are priortized versus what are filtered out. Knowing what signals are being "snuffed" and what are being amplified gives us a better understanding of our body's autonomy.

Take a shower

When you want to take a shower, you have this idea, and your brain will send the message to your legs, your arms, your hands and feet. When it still in the resting potential, your brain don’t send this message to your body, but the neuron is ready to accept this message.

Action

potential

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Electrical synapse

Synapse