Neurobiology Synaptic Transmission Quiz

Neurobiology

• Deals with the structure and function of the nervous system.

Nervous System

• Central nervous system (CNS): Brain and spinal cord.
• Peripheral nervous system (PNS): All nerves and sensory structures outside the CNS; connects the CNS to the rest of the body (organs, limbs, skin).
  • Somatic: Voluntary control of skeletal muscle.
  • Autonomic: Involuntary control of glands and smooth muscle.
    • Sympathetic: Fight or flight.
    • Parasympathetic: Rest and digest.

Evolution and Diversity of Nervous Systems

• Basic Nervous System: Early systems in simple organisms (like cnidarians) are decentralized, with nerve nets spread throughout the body. More complex organisms have centralized systems for better coordination and processing.
• Centralization: Evolutionary trend where nerve cells (neurons) concentrate in specific regions (like a brain or spinal cord), leading to more efficient nervous function. This enables better coordination and faster responses to stimuli.
• Cephalization: Evolutionary trend where sensory organs and neurons concentrate at the front of the organism (head). This forms a distinct head region, including a brain or central ganglia and sensory structures. This process enables more efficient processing of information concerning the environment and is more prominent in higher animals (especially vertebrates).
• Evolutionary Trends: The progression from diffuse nerve networks to centralized, cephalized systems correlates with increased behavioral complexity and environmental adaptations. Vertebrates exhibit advanced cephalization, with significant development of the forebrain impacting cognition and sensory integration. Insects have a centralized brain, segmental ganglia, and moderate cephalization.

The Principle of Stimulus and Reaction

• Stimuli: Changes in the environment (e.g., light, sound, pressure, heat, chemicals) are processed by specialized sensory receptors in sense organs.
• Sensory Receptors: Convert stimuli into electrical signals.
• Sensory Neurons: Carry electrical signals from sensory organs to the CNS (Brain and Spinal Cord).
• Central Nervous System (CNS): processes electrical signals received from sensory neurons, determining what response is needed.
• Motor Neurons: Carry electrical signals from the CNS to effectors (muscles or glands), causing a response.
• Effectors: Muscles or glands that carry out responses. In essence it is what responds to the instructions of the CNS.

Structure of a Neuron

• Cell Body: Nucleus and organelles, metabolic center.
• Mitochondria: Powerhouse of the cell, responsible for cellular respiration.
• Axon Hillock: Connects the cell body to the axon; the first region of the axon to produce an action potential.
• Dendrites: Receive signals from other neurons.
• Cell Membrane: Provides a selectively permeable barrier.
• Myelin Sheath: Insulation, increases conduction speed. Made from Schwann Cells.
• Nodes of Ranvier: Gaps in the myelin sheath, crucial in saltatory conduction.
• Schwann Cells: Glial cells that produce the myelin sheath.
• Action Terminal: End of the axon, triggers neurotransmitter release.
• Synapse: Junction where neurons communicate.

Resting Membrane Potential

• Electrical charge: Measurement of voltage inside a neuron relative to the outside, approximately -70mV.
• Ion gradients: Concentration differences of ions (e.g., K+, Na+, Cl-) across the membrane.
• Concentration gradient: Drives passive movement of ions.
• Electrical Gradient: Charges drive passive movement of ions.
• Semipermeable membrane: Allows some ions to pass while others cannot.
• Sodium-Potassium Pump (Na+/K+-ATPase): Maintains ion gradients, actively transports 3 Na+ ions out and 2 K+ ions in, generating a negative interior.

Action Potential

• Depolarization: Membrane potential becomes less negative, usually initiated by stimuli.
• Sodium Channels: Open during depolarization, allowing Na+ influx.
• Reaching Threshold: Triggering a positive feedback cycle leading to rapid depolarization.
• Peak: Membrane potential reaches a maximum.
• Repolarization: Na+ channels close, K+ channels open, allowing K+ efflux, returning potential to negative values.
• Hyperpolarization (Undershoot): Briefly more negative than the resting potential.
• Voltage-gated Channels: Channels that open and close in response to changes in membrane potential.
• All-or-None Law: Action potentials occur fully or not at all, determined by threshold.

Speed of Conduction

• Myelinated axons (saltatory conduction): Faster, due to insulation, action potential "jumps" between nodes of Ranvier. Myelin sheath and nodes speed conduction. Larger axons also have less internal resistance allowing action potentials to travel faster.
• Non-myelinated axons (continuous conduction): Slower, action potentials spread down the entire axon. Fewer voltage gated channels are involved in myelinated axons than non-myelinated, thus fewer "gaps" lead to quicker and more efficient signal transmission.

Synaptic Transmission

• Neurotransmitters: Chemical messengers that transmit signals across synapses.
• Presynaptic Neuron: Releases neurotransmitters.
• Postsynaptic Neuron: Receives neurotransmitters.
• Synaptic Cleft: Space between presynaptic and postsynaptic neurons.
• Action Potential: Arriving at the end of the axon triggers neurotransmitter release.
• Neurotransmitter Binding: Receptors on the postsynaptic membrane bind to released neurotransmitters, triggering graded potentials.
• Graded Potentials: Proportional to stimulus, determine whether a threshold is reached to enable action potentials, leading to either a depolarizing (exciratory) or a hyperpolarizing (inhibitory) effect.
• Synaptic Integration: Summation of EPSPs and IPSPs to determine whether an action potential is generated in the postsynaptic neuron.
• Summation: Combining of excitatory and inhibitory postsynaptic potentials to determine whether an action potential is generated in the postsynaptic neuron.
• Neurotransmitter Breakdown/Reuptake: Keeps neurotransmitters from continuously stimulating postsynaptic cells. This is carried out by enzymes or specific cell uptake mechanisms.
• Receptor Types: Diverse effects from different neurotransmitter binding types.

Disruption of Synaptic Transmission

• Neurotoxins: Substances that disrupt synaptic transmission, often impacting neurotransmitters.
• Mimicking: Substances that mimic neurotransmitters causing receptor activation (agonists).
• Blocking: Substances that bind to receptors, preventing activation (antagonists). These substances have different effects depending on the system they act upon.

Test your understanding of synaptic transmission and the role of the myelin sheath in saltatory conduction. This quiz covers the mechanisms of neurotransmitter release, the importance of calcium ions, and the processes involved in neuronal signaling. Perfect for students studying neurobiology or related fields.