Cell Signalling Notes

Cell Signalling

• Cell Signalling Overview
  • Involves communication within the body to maintain homeostasis.
  • Utilizes hormones as chemical messengers produced in one part of the body to affect different parts.

Hormones

• Types of Hormones:
  • Lipid-Based (Steroid) Hormones
  • Characteristics:
    • Small and non-polar.
    • Hydrophobic and lipid-soluble.
  • Mechanism:
    • Diffuses across cell membrane easily.
    • Binds to intracellular receptor proteins in cytoplasm and nucleus.
    • Acts as transcription factors to directly turn on genes.
  • Protein-Based Hormones
  • Characteristics:
    • Hydrophilic, not lipid-soluble.
    • Cannot diffuse across the cell membrane.
  • Mechanism:
    • Binds to receptor proteins on the cell membrane.
    • Triggers a secondary messenger to relay the signal inside the cell.
    • Activates chemical pathways involving polypeptides and glycoproteins.

Signal Transduction Pathway

• Steps in Signal Transduction:

  1. Reception of Agonist:
     • Hormone binds with receptors.
  2. Signal Transduction:
     • Secondary messengers transmit the signal into the cytoplasm or nucleus.
  3. Response:
     • Regulation of gene expression, protein activation, or metabolic processes.

• Examples:

  • Fight or Flight response when epinephrine (adrenaline) is secreted.
  • Triggers increase in glucose production, heart rate, and prepares the body for immediate energy.

Endocrine vs. Nervous System

• Endocrine System:
  • Hormonal signals travel long distances through the bloodstream.
• Nervous System:
  • Consists of neurons (nerve cells) with multiple entry points and a single path to transmit signals.
  • Structure:
  • Dendrites (signal input)
  • Cell body
  • Axon (signal output)
  • Synapses (gaps between nerve cells)

Neurotransmitters

• Function:
  • Chemical substances that transmit signals across synapses between neurons.
• Types of Neurotransmitters:
  • Epinephrine: Associated with the Fight or Flight response.
  • Dopamine: Related to feelings of reward.
  • Serotonin: Regulates sleep patterns.
  • GABA: Acts as an inhibitory neurotransmitter to reduce neuronal excitability.

Action Potential

• Process of Action Potential Generation:
  1. Resting state with sodium (Na+) channels closed.
  2. Stimulus causes depolarization:
     • Sodium channels open, sodium ions influx, and the cell becomes positively charged.
  3. Repolarization:
     • Potassium (K+) channels open, potassium ions exit, restoring the negative charge.
  4. Resetting to resting potential for another action potential signal.