Question

Unipolar, bipolar, and multipolar neurons are best described by a. Unipolar neuron has a single neurite with different segments that function as superficial receptors or terminals b. Multipolar neurons are most common in the nervous system of invertebrates c. Neurons can never contain a single axon and dendrite at opposite poles of the cell body d. Unipolar neurons make up a major part of the blood brain barrier e. All of the above

Short answer

Answer: A. Unipolar neuron has a single neurite with different segments that function as superficial receptors or terminals.

Step-by-step solution

Statement A: Unipolar Neuron Description

Statement A describes that a unipolar neuron has a single neurite with different segments that function as superficial receptors or terminals. This statement is accurate. Unipolar neurons do have a single process, called a neurite, which branches into multiple segments acting as the receptors or terminals.

Statement B: Multipolar Neuron Description

Statement B claims that multipolar neurons are most common in the nervous system of invertebrates. This statement is inaccurate. Multipolar neurons are common in both the nervous system of invertebrates and vertebrates, not just invertebrates. They have one axon and several dendrites, allowing for complex integration and processing of information.

Statement C: Neurons with Single Axon and Dendrite

Statement C states that neurons can never contain a single axon and dendrite at opposite poles of the cell body. This statement is incorrect. Bipolar neurons are characterized by having one axon and one dendrite at opposite ends of the cell body. They are commonly found in the retina, olfactory epithelium, and inner ear.

Statement D: Unipolar Neurons and Blood Brain Barrier

Statement D asserts that unipolar neurons make up a major part of the blood brain barrier. This is inaccurate. The blood brain barrier is made up of specialized endothelial cells, astrocytes, and pericytes, not unipolar neurons.

Statement E: All of the above

Statement E claims that all of the above statements are true. Based on our analysis, we can conclude that statement E is incorrect, as statements B, C, and D have been shown to be false. With this analysis, we can conclude that the correct answer to the question "Unipolar, bipolar, and multipolar neurons are best described by" is: a. Unipolar neuron has a single neurite with different segments that function as superficial receptors or terminals.

Key concepts

Neuronal Classification

Neurons can be classified based on their structure and function. Understanding their classification helps us identify their roles within the nervous system. The primary structural types are:

• Unipolar Neurons: These neurons have a single neurite (a projection) which branches into peripheral and central axons. They are mainly found in invertebrates and sensory pathways, transmitting signals from the body periphery to the central nervous system.
• Bipolar Neurons: As the name suggests, bipolar neurons possess one axon and one dendrite extending from opposite ends of the cell body. They are typically found in sensory organs, including the retina of the eye, the olfactory epithelium, and the inner ear.
• Multipolar Neurons: This is the most common type within vertebrates. Multipolar neurons have one axon and multiple dendrites, which allow them to integrate a high amount of information. They are prevalent throughout both the central and peripheral nervous systems.

By distinguishing between these types, researchers can better understand neural circuitry and communication pathways.

Neuron Structure

The structure of a neuron is key to its function in transmitting information throughout the nervous system. Every neuron has several parts that contribute to its role:

• Cell Body (Soma): Contains the nucleus and is responsible for maintaining the life of the neuron.
• Dendrites: Branch-like structures that receive messages from other neurons and convey this information to the cell body.
• Axon: A long fiber that transmits impulses away from the cell body to other neurons, muscles, or glands. It often ends in axon terminals where neurotransmitters are released.

The unique structure of each neuron supports its specific function within the nervous system. For example, the extensive branching of dendrites provides a large surface area for receiving signals, while the length of axons enables connections across different parts of the body.

Blood-Brain Barrier

The blood-brain barrier (BBB) is a selective permeability barrier that separates the circulating blood from the brain extracellular fluid. This separation is crucial for maintaining the brain’s stable environment:

• The BBB is primarily composed of endothelial cells tightly joined together, creating a restrictive boundary that controls which substances can enter the brain.
• Astrocytes, a type of glial cell, play a supportive role in maintaining the BBB by influencing its permeability and supporting the endothelial cells.
• Pericytes are also involved, wrapping around the endothelial cells and regulating blood flow and vessel stability.

The blood-brain barrier is essential for protecting sensitive brain tissue from toxins and pathogens while allowing necessary nutrients to pass through. By understanding the components and function of the BBB, we acknowledge its vital role in brain health and disease prevention.