Introduction to Neurotransmitters

Overview

• Neurotransmitters are chemicals produced and released by neurons.
• They can have excitatory or inhibitory effects.
• Released into the synapse (gap between neurons).
• Bind to neurons or other tissues (muscles, cells, glands).
• Over 100 types in the body; key types discussed in this lecture.

Key Neurotransmitters Covered

1. Acetylcholine (ACh)
2. Catecholamines (Noradrenaline, Adrenaline, Dopamine)
3. Serotonin
4. GABA (Gamma-Aminobutyric Acid)
5. Glutamate
6. Substance P

Acetylcholine (ACh)

• Receptors: Nicotinic and Muscarinic.
  • Peripheral Nervous System: Skeletal muscle contraction (via Muscarinic receptors).
  • Autonomic Nervous System: Parasympathetic (rest and digest) and sympathetic (fight or flight) systems both use ACh.
  • Central Nervous System: Important for memory, cognition (implicated in Parkinson's and Alzheimer's diseases).

Catecholamines

Noradrenaline & Adrenaline

• Produced by the amino acid tyrosine.
• Receptors: Alpha 1, Alpha 2, Beta 1, Beta 2.
  • Alpha 1 & Beta 1: Excitatory; found on blood vessels (constricts, increases BP) and heart (increases HR and contraction).
  • Alpha 2 & Beta 2: Inhibitory; found on postsynaptic neurons (auto-regulate sympathetic NS) and lungs (opens airways).
• Central Nervous System: Important for opioid release (endorphin system).
• Peripheral Nervous System: Primary neurotransmitters for sympathetic NS.

Dopamine

• Known as a "reward" molecule.
• Receptors: Dopamine 1 (excitatory), Dopamine 2 (inhibitory).
• Central Nervous System:
  • Motivation, reward, motor control (found in basal ganglia).
  • Implicated in Parkinson's disease (motor issues due to neuron death).
• Peripheral Nervous System: Blood vessel diameter, GI motility, kidney function.

Serotonin (5-HT)

• Receptors: Inhibitory (1, 5), Excitatory (2, 3, 4, 6, 7).
• Central Nervous System: Sleep, mood.
• Peripheral Nervous System: GI tract contractions, bone remodeling.

GABA (Gamma-Aminobutyric Acid)

• Receptors: GABA A, GABA B.
• Main inhibitory neurotransmitter.
• Clinical Relevance: Epilepsy, seizure management (stimulate GABA to inhibit neuron firing).

Glutamate

• Most abundant excitatory neurotransmitter.
• Receptors: NMDA, AMPA (excitatory).
• Clinical Relevance: Too much can cause glutamate toxicity (implicated in dementia, Alzheimer’s disease).

Substance P

• Role: Associated with pain (P for Pain).
• Receptors: NK 1 (excitatory).
• Released during painful stimuli (both emotional and physical).
• Clinical Relevance: Target for pain management drugs.

Summary

• Covered the major neurotransmitters and their roles in different systems (CNS and PNS).
• Highlighted receptors and their effects (excitatory or inhibitory).
• Discussed clinical implications related to neurotransmitter dysfunctions.