Chemical Signals and Hormones
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Chemical Signals and Hormones

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Questions and Answers

What is the primary role of neurotransmitters in the nervous system?

  • To stabilize cell membranes
  • To act as chemical signals for local cell communication (correct)
  • To provide energy for nerve impulse conduction
  • To serve as long-distance hormonal signals

    • Which of the following correctly lists a characteristic of steroid hormones?

  • They act only inside the cell nucleus.
  • They can cross the plasma membrane. (correct)
  • They are derived from proteins.
  • They are quickly broken down in the bloodstream.

    • Which neurotransmitter is primarily associated with pain signaling?

  • Serotonin
  • GABA
  • Substance P (correct)
  • Endorphin

    • What distinguishes catecholamines from other biogenic amines?

    <p>They are synthesized from tyrosine.</p> Signup and view all the answers

    Which of the following hormones is an amino acid-derived hormone?

    <p>Thyroxine</p> Signup and view all the answers

    In terms of signal transduction, what is the role of agonists and antagonists in drug design?

    <p>Agonists enhance signal reception, antagonists block it.</p> Signup and view all the answers

    What type of neurotransmitter is primarily responsible for muscle contraction at the neuromuscular junction?

    <p>Acetylcholine</p> Signup and view all the answers

    Which of the following best describes peptide hormones?

    <p>They are composed of short chains of amino acids.</p> Signup and view all the answers

    What is the primary role of voltage-gated calcium channels in muscle contraction?

    <p>They facilitate the influx of calcium ions.</p> Signup and view all the answers

    How do muscarinic receptors differ from ion channel receptors?

    <p>Muscarinic receptors do not contain an ion channel.</p> Signup and view all the answers

    What is a characteristic of the G-protein-coupled receptors that affects cell function?

    <p>They modulate downstream signaling pathways.</p> Signup and view all the answers

    What happens at the axon hillock when dendritic depolarizations reach the threshold?

    <p>An action potential is triggered.</p> Signup and view all the answers

    Why are ion channel-mediated signaling pathways considered faster than others?

    <p>They allow immediate ion flow during signaling.</p> Signup and view all the answers

    What is a common difference between nicotine and muscarine in pharmacology?

    <p>Nicotine activates ion channels while muscarine does not.</p> Signup and view all the answers

    What role does GTP play in the function of G-proteins?

    <p>It is critical for the activation and inactivation of G-proteins.</p> Signup and view all the answers

    Which characteristic distinguishes the muscarinic receptor's response to acetylcholine?

    <p>It generates a more subtle and varied cellular response.</p> Signup and view all the answers

    What initiates the release of acetylcholine at the motor end plate?

    <p>Fusion of vesicles with the pre-synaptic membrane</p> Signup and view all the answers

    Which of the following best describes the role of acetylcholinesterase at the synaptic cleft?

    <p>It breaks down acetylcholine to terminate its action</p> Signup and view all the answers

    How does binding of acetylcholine to its receptor influence the muscle cell?

    <p>It causes an influx of sodium ions into the muscle cell</p> Signup and view all the answers

    What is the effect of neurotoxins that inhibit acetylcholinesterase?

    <p>They promote continuous activation of acetylcholine receptors</p> Signup and view all the answers

    Which structure is primarily responsible for synthesizing and storing acetylcholine?

    <p>Intracellular vesicles</p> Signup and view all the answers

    What type of receptor is the nicotinic acetylcholine receptor classified as?

    <p>Ionotropic receptor</p> Signup and view all the answers

    In what way does the synaptic cleft contribute to neuronal signaling?

    <p>It allows diffusion of signaling molecules between neurons</p> Signup and view all the answers

    Which component of the neuromuscular junction is primarily responsible for forming the synaptic cleft?

    <p>Muscle cell membrane</p> Signup and view all the answers

    Study Notes

    Chemical Signals

    • Defects in secretion and signalling can lead to disease.
    • Drugs often work by mimicking chemical signals, acting as agonists or antagonists.
    • Neurotransmitters:
      • Amino acids: GABA, glutamine, glycine
      • Acetylcholine
      • Small molecules: serotonin, histamine, dopamine (biogenic amines)
      • Catecholamines: noradrenaline and adrenaline (derived from tyrosine)
      • Purinergic neurotransmitters: ATP and adenosine
    • Neuropeptides: endorphin, enkephalins, substance P (pain), neuropeptide Y (eating)
    • Many neurotransmitters have other functions in the body.

    Hormones

    • Lipid-soluble hormones: derived from cholesterol (steroid hormones)
      • Can diffuse across cell membranes.
      • Examples: oestradiol, testosterone, aldosterone, cortisol
      • Bound to proteins for blood transport, long half-life (60-90 minutes).
    • Amino-acid derived hormones:
      • Adrenaline and noradrenaline: derived from tyrosine in the adrenal gland, short half-life (about 1 minute).
      • Thyroxine: produced in the thyroid gland from tyrosine and iodine.
      • Melatonin: produced in the pineal gland from tryptophan.

    Peptide hormones

    • Short peptides: ADH (antidiuretic hormone) and oxytocin, produced in the brain and released by the posterior pituitary gland (9 amino acids).
    • Small proteins: growth hormone (191 amino acids).
    • Glycoproteins: FSH (follicle-stimulating hormone) (96 amino acids).
    • Insulin: composed of α-chain (21 amino acids) and β-chain (30 amino acids) bridged by disulfide bonds.

    Faster Signalling: Action Potentials

    • Calcium ion influx through voltage-gated channels activates contraction in muscle cells.
    • In nerve cells, dendritic depolarizations summate at the axon hillock, triggering an action potential if a threshold is reached.
    • Action potentials are the fastest type of signal transduction.

    Slower Signalling: Muscarinic Acetylcholine Receptors

    • Muscarinic acetylcholine receptors are G-protein-coupled receptors that mediate acetylcholine responses from parasympathetic nerves.
    • They do not have an ion channel, so they trigger different responses (and have different pharmacology) than nicotinic acetylcholine receptors.
    • Acetylcholine binds to the receptor's extracellular side, causing a structural change on the inner side and affecting the interaction with the G-protein complex.
    • G-proteins are GTP-coupled protein complexes and are essential for many cell functions.

    The Motor End Plate

    • The motor end plate is the synapse between a motor neuron and a muscle cell.
    • When a nerve impulse reaches the motor end plate, acetylcholine-filled vesicles fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft.
    • Acetylcholine binds to acetylcholine receptors (AChR) on the muscle cell membrane.

    Post-Synaptic Events

    • Acetylcholinesterase rapidly breaks down acetylcholine in the synaptic cleft.
    • Some acetylcholine is also taken back up by the presynaptic membrane.
    • Neurotoxins and insecticides can inhibit acetylcholinesterase, leading to paralysis.
    • Presynaptic vesicles can release multiple bioactive substances.
    • The nicotinic acetylcholine receptor (AChR) is a pentameric protein spanning the muscle cell membrane. It has binding site(s) for acetylcholine on its extracellular face.

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    Description

    Explore the intricate world of chemical signals and hormones in this quiz. Learn about neurotransmitters, neuropeptides, and the various types of hormones, including lipid-soluble and amino-acid derived hormones. Understand their roles in disease and drug action.

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