Neuron Anatomy and Function Overview

Neuron Anatomy

• Cell Body (Soma): The central part of the neuron that contains the nucleus and organelles.
• Dendrites: Numerous branched projections that receive signals from other neurons.
• Axon: Typically a single long fiber that conducts nerve impulses away from the cell body to other neurons or effector organs.

Neuron Function

• Sensory (Afferent) Neurons: Conduct impulses from sensory receptors (e.g., skin, eyes) to the Central Nervous System (CNS).
• Association Neurons: Also known as interneurons, these transmit impulses between neurons within the CNS, facilitating communication and processing.
• Motor (Efferent) Neurons: Carry impulses away from the CNS to effectors (e.g., muscles and glands) to initiate a response.

Action Potential

• Definition: An action potential (AP) is a transient electrical signal that travels along the axon, allowing for communication between neurons and effectors.
• Mechanism:
  • The impulse travels point to point along the neuron membrane.
  • Mineral channels (ion channels) open in a specific sequence, which results in:
  • Depolarization: The membrane potential becomes less negative, moving toward a positive value.
  • Repolarization: The membrane potential returns to its resting state after depolarization.

Characteristics of Action Potentials

• All-or-None Principle: If an AP is generated, it occurs at constant, maximum strength regardless of the stimulus intensity.
• Impulse Speed: Depends on:
  • Diameter of the Axon: Larger diameters increase conduction speed.
  • Myelination: Myelinated axons conduct impulses faster due to saltatory conduction, where the impulse jumps between Nodes of Ranvier.

Neurotransmitters

• Definition: Chemical messengers found in both the Peripheral Nervous System (PNS) and CNS that transmit signals across a synapse from one neuron to another.
• Release Mechanism: Neurotransmitters are stored in the axon terminal and released in response to a nerve impulse.
• Response Variability: The effect of a neurotransmitter depends on the type and function of the receptors it binds to.
• Common Neurotransmitters:
  • Acetylcholine: Involved in muscle activation and memory.
  • Epinephrine: Associated with the fight-or-flight response.
  • Dopamine: Plays roles in mood, behavior, and cognition.