Neuroscience: Neurons and Synapses Overview

Neuron Structure and Functions

• Dendrites: Receive signals from other neurons and conduct them to the cell body.
• Cell Body (Soma): Contains the nucleus and organelles; integrates incoming signals.
• Axon: Transmits electrical impulses away from the cell body to other neurons or muscles.
• Axon Terminals: Release neurotransmitters to communicate with other neurons.

Synapse Components and Neurotransmission

• Synapse: Junction between two neurons; consists of a presynaptic terminal, synaptic cleft, and postsynaptic membrane.
• Presynaptic Terminal: Contains vesicles filled with neurotransmitters.
• Synaptic Cleft: Gap where neurotransmitters diffuse.
• Postsynaptic Membrane: Contains receptors that bind neurotransmitters.
• Neurotransmission Steps:
  • Action potential triggers neurotransmitter release.
  • Neurotransmitters cross the synaptic cleft.
  • Bind to receptors on the postsynaptic membrane, leading to a response.

Brain Structures and Functions

• Cortex: Involved in high-level functions such as perception, thought, and decision-making; divided into lobes (frontal, parietal, temporal, occipital).
• Brainstem: Controls basic life functions (breathing, heart rate); includes midbrain, pons, and medulla oblongata.
• Midbrain: Regulates visual and auditory reflexes; involved in motor control.
• Cerebellum: Coordinates movement and balance; contributes to motor learning.

Action Potential Mechanism

• Resting Membrane Potential: Neuron is at -70 mV; maintained by the sodium-potassium pump.
• Depolarization Phase: Sodium channels open, allowing Na+ ions to rush in, making the membrane more positive.
• Threshold: When depolarization reaches a critical level (~-55 mV), an action potential is triggered.
• Repolarization Phase: Potassium channels open, K+ ions flow out, restoring the negative charge.
• Hyperpolarization: Membrane becomes more negative than resting potential before stabilizing.

Propagation of Action Potential

• Saltatory Conduction: Action potentials jump between Nodes of Ranvier (gaps in the myelin sheath), speeding up transmission.
• Continuous Conduction: In unmyelinated axons, action potential moves along the entire membrane.

Action Potentials vs. Graded Potentials

• Action Potentials: All-or-nothing signals, same magnitude regardless of stimulus strength; propagate along axons.
• Graded Potentials: Variable strength signals that decrease with distance; can sum to trigger action potentials.

Sequence of Chemical Signaling Between Neurons

• Action potential reaches presynaptic terminal.
• Calcium channels open, Ca2+ enters the terminal.
• Vesicles fuse with the membrane, releasing neurotransmitters.
• Neurotransmitters bind to receptors, eliciting a response in the postsynaptic neuron.

Receptors and Neurotransmitters

• Receptors: Specific to neurotransmitters; facilitate signal transduction when bound.
• Major Neurotransmitters: Include dopamine (catecholamine), serotonin (indoleamine), GABA (amino acid), and glutamate (amino acid).

Drug Actions: Agonists vs. Antagonists

• Agonists: Mimic neurotransmitter action, activating receptors.
• Antagonists: Block neurotransmitter binding, inhibiting the receptor response.

Studies on Nervous System Structure and Function

• Techniques such as imaging (MRI, CT scans), electrophysiology (EEG), and animal models have enhanced understanding of neuronal functions and pathways.

This quiz covers the general functions of the main parts of a neuron, key components of a synapse, and the major steps in neurotransmission. It also explores the anatomical structures of the cortex, brainstem, midbrain, and cerebellum along with their functions, as well as the processes of action potentials and their propagation along axons.