Neuroscience: Neuron Types and Characteristics

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Questions and Answers

What is a characteristic of pseudo-unipolar neurons?

They contain several spines for synaptic interactions.

They possess a T-shaped process emerging from the cell body. (correct)

They have multiple appendages for synaptic contacts.

They are primarily located in the brain.

Which of the following describes a bipolarly structured neuron?

It has one axon and several spines.

It is elongated and does not connect to the spinal cord.

It has both a dendrite and an axon. (correct)

It contains a large number of Nissl granules.

Which type of neuron controls effector organs such as muscles and glands?

Sensory neurons.

Interneurons.

Pseudo-unipolar neurons.

Motor neurons. (correct)

Golgi type I neurons are characterized by what feature?

They leave grey matter and enter white matter. Signup and view all the answers

What is true regarding unmyelinated nerve fibers?

They lack a myelin sheath altogether. Signup and view all the answers

What type of neuron connects other neurons as seen in the retina and spinal cord?

Interneurons. Signup and view all the answers

What distinguishes Golgi type II neurons from Golgi type I neurons?

Golgi type II neurons remain within the grey matter. Signup and view all the answers

Which neurons are primarily found in the cochlear and vestibular ganglia?

Bipolar neurons. Signup and view all the answers

Which of the following statements about neuron cell bodies is true?

The neuron cell body is typically larger in motor neurons compared to granular cells. Signup and view all the answers

What characterizes the cytoplasm of a neuron cell body?

It has highly developed rough endoplasmic reticulum and Nissl bodies. Signup and view all the answers

Which type of neuron has a cell body shape that is typically described as fusiform?

Bipolar neuron Signup and view all the answers

What feature differentiates dendrites from axons?

Dendrites are shorter and thicker than axons. Signup and view all the answers

Which of the following is true regarding neuroglial cells?

They help in the maintenance and protection of neurons. Signup and view all the answers

What is the primary function of microtubules in neuronal processes?

To aid in the axonal transport of substances. Signup and view all the answers

What is the significance of lipofuscin pigment in neurons?

It is a byproduct of active metabolism, increasing with age. Signup and view all the answers

Which statement correctly describes the organization of neurofilaments in a neuron?

They are abundant in the perikaryon and neuronal processes. Signup and view all the answers

Which characteristic defines the structure of myelin sheath?

Formed of many layers of modified cell membranes with higher lipids. Signup and view all the answers

What role do nodes of Ranvier play in myelinated nerve fibers?

They are gaps between adjacent sheath cells that facilitate impulse speed. Signup and view all the answers

What does the endoneurium consist of in peripheral nerve organization?

Reticular fibers formed by Schwann cells and flattened epithelial-like cells. Signup and view all the answers

What is NOT a function of the Schwann cells?

Regenerating nerve fibers without any guidance. Signup and view all the answers

Which statement about myelinated nerve fibers is correct?

They are classified based on the presence of Schwann cell sheaths. Signup and view all the answers

What type of nerve cell is characterized by a rounded cell body and a single divided process?

Pseudo-unipolar. Signup and view all the answers

What is the primary function of the lipoproteins in the myelin sheath?

To conduct electrical impulses faster. Signup and view all the answers

In the organization of peripheral nerves, what does perineurium do?

It wraps around bundles of nerve fibers. Signup and view all the answers

Study Notes

Nervous Tissue (Part 1)

Nervous tissue is fundamental in the human body for communication.
It includes neurons and neuroglial cells.
Neurons are classified according to the number of processes and function.
Neurons have a cell body (perikaryon), dendrites (multiple processes), and an axon (single process).
The cell body is rounded in pseudo-unipolar neurons, fusiform in bipolar neurons, and stellate, pyramidal, or pyriform in multipolar neurons.
Neuron size varies depending on location, ranging from 4 μm to 100 μm. For instance, granular cells in the cerebellar cortex are smaller than motor neurons.
The cell body contains a large, euchromatic nucleus with a prominent nucleolus, characteristic of an active cell.
The cytoplasm includes a well-developed rough endoplasmic reticulum (rER) and numerous polyribosomes. These structures, appearing as basophilic granular areas called Nissl bodies, are variable according to the neuronal function.
Golgi complexes are centrally located around the nucleus.
Mitochondria are dispersed throughout the cytoplasm.
Neurofilaments (intermediate filaments) are prevalent in the perikaryon (cell bodies) and processes, visible through light microscopy (LM) stained with silver. These filaments provide structural support.
Microtubules are arranged in parallel bundles within the perikaryon and processes, and are critical for axonal transport of neurotransmitter substances and enzymes.
Centrioles are absent in neurons since neurons do not exhibit cell division.
Inclusions present in neurons include lipofuscin pigment. It is a residue of undigested material from lysosomes, increasing with aging. Melanin, a dark brown or black pigment, is found in substantia nigra neurons and may be a byproduct of abnormal metabolism.
Lipid droplets are found in the cytoplasm of neurons and represent stored energy.

Classification of Neurons

Pseudo-unipolar: The cell body is rounded, and the single process splits into peripheral and central branches shortly after leaving the perikaryon (cell body). The peripheral branch functions as a dendrite, and the central branch acts as an axon. Found in dorsal root ganglia & mesencephalic nucleus of the trigeminal nerve.
Bipolar: possess a single dendrite and single axon. Present in the cochlea and vestibular ganglia of the inner ear, and in the retina and olfactory mucosa.
Multipolar: have one axon and many dendrites. They appear as stellate (star-shaped) cells in the anterior horn of the spinal cord; pyramidal in the cerebral cortex; and pyriform in the cerebellar cortex (Purkinje cells).

Classifications of Neurons based on Function

Sensory (Afferent): Receive sensory stimuli and transmit them to the spinal cord & brain via the dorsal root ganglion.
Motor (Efferent): Transmit impulses from the central nervous system to muscles and glands, such as those in the anterior horn of the spinal cord.
Interneurons: Connect neurons within the central nervous system. They are abundant in the brain and spinal cord and also in the retina.

Classification Based on Axon Length

Golgi type I: neurons possess long axons extending beyond the grey matter into white matter. Examples include motor neurons in the spinal cord, pyramidal cells in the cerebral cortex, and Purkinje cells in the cerebellar cortex.
Golgi type II: neurons possess short axons remaining confined within the grey matter. Examples include the vast majority of interneurons in the brain and cerebellum.

Nerve Fiber

A nerve fiber is an axon (the projection of the neuron) surrounded by myelin and Schwann cells.
The axon is encased by an axolemma, containing axoplasm, which is the cytoplasm within the axon.
The axon emerges from the axon hillock, which is a conical extension from the cell body.

Types of Nerve Fibers

Unmyelinated: Lack a myelin sheath and are subdivided into (a) naked fibers, present in gray matter; and (b) fibers with a Schwann cell sheath, prevalent in sympathetic postganglionic fibers.
Myelinated: Possess a myelin sheath and are subdivided into (a) fibers without a Schwann cell sheath, found in white matter; and (b) fibers with a Schwann cell sheath, found in peripheral nerves.

The Schwann Cell Sheath

The Schwann cell sheath consists of flattened cells with flattened nuclei that enwrap the myelin of the nerve fiber.
Functions: Formation of the myelin sheath in the peripheral nervous system; insulation to speed up the nerve impulse; allowing for regeneration.

Myelin Sheath

The myelin sheath is constructed from many modified cell membranes of Schwann cells.
It possesses higher lipid content compared to cell membranes.
Under the light microscope (LM), it appears as a dark structure stained by osmic acid.
Under the electron microscope (EM), it's evident as fused spiral laminae of the plasmalemma.
The myelin sheath is interrupted by Nodes of Ranvier, gaps between Schwann cells.
The space between nodes are called inter-nodal segments.

Peripheral Nervous System

Consists of nerves, ganglia (clusters of neuron cell bodies), and nerve endings.
The components involved in the nervous system are also well organized into bundles that are structurally supported.
Components of the bundles include, but are not limited to: epineurium, perineurium, and endoneurium.

Peripheral Nerve Structure

The whole nerve is covered by a dense connective tissue sheath called the epineurium.
Nerve fibers are organized into bundles, each surrounded by perineurium.
The endoneurium, a connective tissue layer, surrounds individual nerve fibers.

Test Yourself Questions

Question 1: Nerve fibers are the axon covered by the myelin and Schwann cells sheath.
Question 2: Pseudo-unipolar neurons have rounded cell bodies and a single divided process.

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Description

This quiz focuses on distinguishing between various types of neurons, their structures, and functions. Test your knowledge on characteristics of pseudo-unipolar, bipolar, and other neuron types as well as their roles in the nervous system. Ideal for students studying neuroscience or related fields.