HBS 2.1.5-2.1.7

How Neurotransmitters (Messengers) Affect Neurons

• Excitatory Transmitters: These promote the continuation of the action potential. They bind to receptors on the postsynaptic cell, causing positive ions to flow into the cell, which keeps the internal charge positive and supports the transmission of the signal.

• Inhibitory Transmitters: These reduce the likelihood of an action potential. They bind to receptors on the postsynaptic cell and cause negative ions to flow into the cell, making the internal charge more negative and preventing the signal from continuing.

• Neuromodulators: These are chemicals that influence how neurons communicate but are not neurotransmitters. They do not directly trigger or inhibit an action potential; instead, they modulate the effectiveness of neurotransmitters.

Drug Action Mechanisms

• Agonist: A drug that binds to a receptor on a cell and activates it, mimicking the action of the natural neurotransmitter (same action).
  Example: Morphine.

• Inverse Agonist: A drug that binds to the same receptor as an agonist but produces the opposite effect of the natural neurotransmitter (opposite reaction).
  Example: Diphenhydramine.

• Antagonist: A drug that binds to a receptor but does not activate it, blocking the natural action (no action).
  Example: Caffeine.

• Reuptake Inhibitor: A drug that blocks the reabsorption (reuptake) of neurotransmitters, allowing them to remain in the synaptic gap longer.
  Example: Cocaine.

Note: Neurons transmit signals both electrically and chemically.

Mechanism of a neurotransmitter page

Reflexes and Reactions

• Reflex: An automatic response to a stimulus that does not involve conscious thought (no thinking required).

• Reaction: A deliberate response to external stimuli, where the brain processes the nerve impulse before taking action.

• Complex Brain Processes: Most actions, except for simple reflexes, involve significant brain activity and processing.

Reflex Arc of the Knee

1. The patellar tendon is tapped.

2. The tap causes a slight stretch in the quadriceps, activating the receptor.

3. The nerve impulse travels to the spinal cord.

4. The motor neurons are activated (no brain involvement).

5. The motor neurons carry the signal back to the muscle, causing it to contract and produce a reflexive movement.

Neurotransmitters

Dopamine- motivation, behavior, learning, sleep, mood, focus, attention, immune health, movement, memory, pleasure

Gaba- Low levels lead to restlessness anxiety and irritability, inhibitory neurotransmitter normal brain function

Glutamate- Cognition, learning memory, excitatory neurotransmitter 90% of all brain synapses

Serotonin- Mood, depression, anxiety, sleep, emotions, appetite, digestion, temperature

Acetylcholine- Triggers muscle contraction, controls heartbeat, stimulates hormones, learning and memory

Norepinephrine- provides accurate assessment of danger or stressful situations (negative)

Epinephrine- metabolism, attention, focus, stress, fear, anger, panic, excitement (positive)