2.1.9 Neurotransmission Notes

Neurons Communicate by Transmitting Signals Across Synapses Using Neurotransmitters

1. Neurotransmission is the process by which neurons communicate with each other across small gaps called synapses.
2. This process involves the release of neurotransmitters, which are chemical messengers that transmit signals from one neuron to another.

The Process of Neurotransmission

Step 1: Electrical Impulse Travels Down the Axon

1. When a neuron is activated, an electrical impulse called an action potential travels down the axon toward the axon terminal.
2. This impulse is generated by the movement of ions (charged particles) across the neuron's membrane, creating a temporary change in electrical charge.

Step 2: Neurotransmitters Are Released into the Synapse

1. When the action potential reaches the axon terminal , it triggers the release of neurotransmitters stored in small sacs called vesicles.
2. These neurotransmitters are released into the synaptic gap (the small space between the sending and receiving neurons).

Step 3: Neurotransmitters Bind to Receptors

1. The neurotransmitters travel across the synaptic gap and bind to receptor sites on the postsynaptic neuron (the receiving neuron).
2. Each neurotransmitter fits into specific receptors, much like a key fits into a lock.

Step 4: Signal Is Transmitted to the Next Neuron

1. Once the neurotransmitter binds to the receptor, it triggers a response in the postsynaptic neuron.
2. This response can be excitatory (increasing the likelihood that the neuron will fire an action potential) or inhibitory (decreasing the likelihood of firing).

Step 5: Neurotransmitters Are Removed

1. After the signal is transmitted, the neurotransmitters are removed from the synaptic gap through processes such as reuptake (where they are taken back into the sending neuron) or enzymatic breakdown (where they are broken down by enzymes).

Key Neurotransmitters and Their Functions

Acetylcholine (ACh)

1. Function: Involved in muscle contraction, memory formation, and learning.
2. Example: Low levels of acetylcholine are associated with Alzheimer's disease, while high levels can lead to muscle spasms.

Dopamine

1. Function: Plays a role in reward, motivation, and motor control.
2. Example: Imbalances in dopamine levels are linked to conditions such as Parkinson's disease (low dopamine) and schizophrenia (high dopamine).

Serotonin

1. Function: Regulates mood, sleep, and appetite.
2. Example: Low levels of serotonin are associated with depression, while selective serotonin reuptake inhibitors (SSRIs) are used to treat depression by increasing serotonin levels.

Glutamate

1. Function: The primary excitatory neurotransmitter, involved in learning and memory.
2. Example: Excessive glutamate activity can lead to excitotoxicity, which damages neurons and is linked to conditions like epilepsy.

GABA (Gamma-Aminobutyric Acid)

1. Function: The primary inhibitory neurotransmitter, helps reduce neuronal excitability.
2. Example: Low levels of GABA are associated with anxiety disorders.