Biology Chapter 10: The Nervous System I

Neural Tissue

• Neuron: Fundamental unit of the nervous system, responsible for transmitting nerve impulses.
• Neuroglia Cells: Support cells in the nervous system that produce myelin, facilitate communication between neurons, and maintain ionic balance.

Neuron Structure

• Two types of fibers: Dendrites and axons, projecting from the neuron’s cell body.
• Dendrites: Receive nerve impulses and carry information toward the neuron body.
• Axon: Transmits nerve impulses away from the neuron body to other neurons or cells.

Axon Characteristics

• Axon Terminals: Knobbed branches at the end of an axon that transmit signals to other cells.
• Myelin Sheath: Insulating layer surrounding axons, composed of fatty material from Schwann cells; it enhances signal transmission efficiency by preventing impulse dissipation.

Nodes of Ranvier

• Definition: Gaps in the myelin sheath that allow nerve impulses to jump, increasing conduction speed.

Nerves and Synapses

• Nerves: Bundles of axons that transmit signals in the nervous system.
• Synapse: The junction between an axon terminal and another neuron or cell, critical for electrochemical communication.

Types of Synaptic Transfers

• Electrical Transfer: Direct transfer of electrical signals; prevalent in the heart and digestive system for maintaining rhythmic contractions.
• Chemical Transfer: Involves neurotransmitters released from axon terminals, transmitting signals across synapses.

Neurotransmitter Function

• Release Mechanism: Upon receptor binding, they generate a nerve impulse in the receiving cell. Following transmission, neurotransmitters are broken down or reabsorbed to terminate the signal.

Neuron Types

• Unipolar Neurons: Single process extending from the cell body; primarily located outside the brain and spinal cord.
• Bipolar Neurons: Two processes extending from each end; located in specialized sensory organs such as the eyes, ears, and nose.
• Multipolar Neurons: Multiple processes from the cell body; primarily found in the brain and spinal cord.

Functional Neuron Categories

• Sensory Neurons (Afferent): Transmit impulses from peripheral sensory receptors to the CNS; often unipolar.
• Interneurons: Found in the CNS, transmitting signals between different parts of the brain and spinal cord; typically multipolar.
• Motor Neurons (Efferent): Carry impulses from the CNS to effectors like muscles and glands; usually multipolar.