Neurotransmitters Chapter 4 Study Guide

Neurotransmitters

• Neurotransmitters communicate locally across synapses, synthesized by neurons.
• Released in response to action potentials (AP) and have measurable effects on postsynaptic cells.
• Can mimic effects of drugs; mechanisms exist for their removal.

Post-Synaptic Receptors

• Ionotropic Receptors: Ligand-gated ion channels with two domains; rapid postsynaptic effects.
• Metabotropic Receptors: G protein-coupled receptors that lack ion channels, slower acting, with two binding sites.

Categories of Neurotransmitters

• Acetylcholine: Involved in neuromuscular transmission; nicotinic and muscarinic receptors associated with the autonomic nervous system and CNS functions like learning and memory.
• Monoamines:
  • Catecholamines:
    • Dopamine (DA): Synthesized from tyrosine; metabotropic receptors, involved in reward mechanisms.
    • Norepinephrine (NA): Also derived from tyrosine; involved in arousal and fight/flight responses with diffusion for receptor activation.
  • Indolamines:
    • Serotonin: Affects mood, sleep, and appetite; receptors include 5-HT-R.
    • Melatonin: Regulates sleep cycles.
• Amino Acids:
  • Glutamate: Key for memory; activates AMPA and NMDA receptors, facilitating depolarization and synaptic transmission.

Types of Psychoactive Drugs

• Depressants: Alcohol, barbiturates, benzodiazepines; induce sedation and relaxation.
• Stimulants: Caffeine, nicotine, cocaine, amphetamines; increase alertness and energy.
• Psychedelics: Marijuana, LSD, psilocybin, PCP, ecstasy; alter perception and mood.
• Opiates: Morphine, codeine, endorphins; provide pain relief and euphoria.

Drug Mechanisms

• Alcohol: Agonist for GABAa receptors, causes neural inhibition and sedation; NMDA receptor antagonist, leading to memory loss.
• Ecstasy: Inhibits reuptake of serotonin, heightening mood but may cause long-term depression and anxiety.

Neuron Structure

• Soma (Cell Body): Contains nucleus, synthesizes neurotransmitters, integrates signals.
• Dendrites: Receive input from other neurons, conduct stimulation; dendritic spines allow for synaptic transmission.
• Axon: Transmits electrical impulses away from the cell body; ends in axon terminals for communication with other neurons.
• Cytoskeleton Components: Microtubules for transport, neurofilaments provide support, and microfilaments for reorganizing branches.

Glial Cells

• Astrocytes: Provide structural and nutritional support, control synapse isolation, and maintain extracellular environment.

Resting Potential

• Neuron is -70mV, indicating a more negative charge inside the membrane compared to the outside.
• Ion concentrations maintained by diffusion and ion channels/pumps.

Action Potential Phases

• Depolarization: Sodium ions enter through voltage-gated channels.
• Repolarization: Membrane potential returns to resting state.
• Hyperpolarization: Opening of chloride channels adds negative charge.
• Action potentials follow an all-or-nothing principle, reaching +40mV if the threshold is met.

Synapse Structure and Function

• Composed of presynaptic neuron, synaptic cleft, and postsynaptic neuron.
• Electrical Synapses: Direct ion movement, rapid signal transmission.
• Chemical Synapses: Involve neurotransmitter release following action potentials.

Deactivation of Neurotransmitters

• Diffusion: Moves neurotransmitters from high to low concentration.
• Degradation: Enzymes break down neurotransmitters into inactive substances.
• Reuptake: Neurotransmitters re-enter presynaptic neuron.

Excitatory and Inhibitory Postsynaptic Potentials (EPSP/IPSP)

• EPSP: Positive ion influx causes depolarization, moving potential closer to threshold.
• IPSP: Negative ion influx results in hyperpolarization, moving potential away from threshold.

Neuromodulation

• Presynaptic Facilitation: Increased neurotransmitter release due to presynaptic input.
• Presynaptic Inhibition: Decreased neurotransmitter release from altered presynaptic influence.

Basic Anatomy of the Central Nervous System (CNS)

• Meninges: Comprises three protective layers—dura mater, arachnoid, pia mater.
• Cerebrospinal Fluid (CSF): Clear fluid providing protection, waste clearance, and intracranial pressure maintenance.
• Blood Supply: Supplied by vertebral and carotid arteries; blood-brain barrier is semipermeable to protect brain functions.

Central Nervous System Structures

• Spinal Cord: Segmented into cervical, thoracic, lumbar, sacral, and coccygeal regions.
• Brain Structures:
  • Hindbrain:
    • Medulla: Connects brain to spinal cord.
    • Pons: Relays information from cortex to cerebellum.
    • Cerebellum: Coordinate voluntary movements.
  • Midbrain:
    • Tectum: Involves auditory and visual processing.
    • Tegmentum: Homeostatic and reflexive pathways.
  • Forebrain:
    • Diencephalon: Thalamus (sensory center), hypothalamus (regulatory functions).
    • Telencephalon: Cortex (higher cognitive functions) and basal ganglia (movement planning).

This quiz covers Chapter 4 on neurotransmitters, focusing on their definition, characteristics, and the types of post-synaptic receptors. Learn about how neurotransmitters communicate across synapses, their synthesis and effects on postsynaptic cells, and the distinctions between ionotropic and metabotropic receptors.