Fundamentals of the Nervous System

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Questions and Answers

What is the role of the central process in the nervous system?

To carry impulses from peripheral receptors to the CNS (correct)

To form junctions with effector cells

To extend to the peripheral receptors

To shuttle signals through the PNS

Which statement about motor neurons is correct?

They make up the majority of the neurons in the body.

Their cell bodies are primarily located in ganglia outside the CNS.

They carry impulses away from the CNS to effector organs. (correct)

They primarily shuttle signals within the CNS.

What percentage of neurons in the human body are interneurons?

99.98% (correct)

50%

1.5%

25%

What is the function of the perineurium in a nerve?

To bind groups of axons into bundles Signup and view all the answers

Which of the following correctly describes the structure of a nerve?

It is composed of axons arranged in parallel bundles. Signup and view all the answers

What is the primary function of neurofilaments in neurons?

They provide structural support against tensile forces. Signup and view all the answers

Which statement accurately describes dendrites?

They have numerous branches to increase surface area for signals. Signup and view all the answers

How do axons differ from dendrites in their function?

Axons transmit impulses away from the soma. Signup and view all the answers

What is true about the structure of the axon?

It usually has one unbranching structure per neuron. Signup and view all the answers

What arises from the axon hillock?

The axon. Signup and view all the answers

What is the role of the cell body in a neuron?

It serves as a receptive surface for incoming signals. Signup and view all the answers

What main components provide structural strength in axons?

Intermediate filaments and microtubules. Signup and view all the answers

In the CNS, what are processes of neurons referred to as?

Tracts. Signup and view all the answers

What is the primary function of astrocytes in the central nervous system?

Support and brace neurons Signup and view all the answers

Which type of neuroglial cell is responsible for monitoring the health of neurons?

Microglia Signup and view all the answers

What characteristic differentiates microglia from other neuroglial cells in the CNS?

They are derived from blood cells Signup and view all the answers

Ependymal cells are primarily involved in which function?

Line the central cavity of the spinal cord and brain Signup and view all the answers

How do astrocytes control the chemical environment around neurons?

By taking up and releasing ions Signup and view all the answers

What is the shape of astrocytes?

Star-shaped Signup and view all the answers

What is NOT a role of astrocytes?

Phagocytose cellular debris Signup and view all the answers

Which of these neuroglial cells is least abundant in the CNS?

Microglia Signup and view all the answers

Which property of ependymal cells is significant for their function?

They have a variety of shapes Signup and view all the answers

What is one of the molecules produced by astrocytes that is essential for neural growth?

Calcium signals Signup and view all the answers

What is the primary function of ependymal cells in the central nervous system?

To circulate cerebrospinal fluid Signup and view all the answers

Which of the following statements is true regarding oligodendrocytes?

They produce myelin sheaths in the brain and spinal cord Signup and view all the answers

What role do Schwann cells play in the peripheral nervous system?

They form myelin sheaths around nerve fibers Signup and view all the answers

How does gray matter in the CNS differ from white matter?

Gray matter consists mainly of neuron cell bodies, while white matter consists of myelinated fibers Signup and view all the answers

What characterizes satellite cells in the peripheral nervous system?

They surround neuron cell bodies in ganglia Signup and view all the answers

What is the role of the neurilemma in the myelin sheath?

It contains the nucleus and cytoplasm of the Schwann cell. Signup and view all the answers

How do nodes of Ranvier contribute to nerve impulse transmission?

They are gaps that assist in rapid saltatory conduction. Signup and view all the answers

Which of the following best describes myelin sheaths?

They increase the speed of nerve impulse conduction Signup and view all the answers

Which cells form the myelin sheath in the central nervous system (CNS)?

Oligodendrocytes Signup and view all the answers

What structure surrounds the central cavity of the CNS?

Gray matter Signup and view all the answers

What do oligodendrocytes and Schwann cells have in common?

They form myelin sheaths Signup and view all the answers

What is one of the primary functions of the myelin sheath?

To protect the axon and speed up impulse transmission. Signup and view all the answers

Which of the following statements is false about gray matter?

It contains large amounts of myelin Signup and view all the answers

What type of axons can a single Schwann cell partly enclose?

15 or more unmyelinated axons Signup and view all the answers

What is the significance of the spacing of nodes of Ranvier in the CNS compared to the PNS?

They are further apart in the CNS, enabling faster transmission. Signup and view all the answers

Which type of cell is responsible for the developmental formation of myelin sheaths during fetal and early postnatal life?

Schwann cells Signup and view all the answers

Which of the following is NOT a function of the myelin sheath?

Preventing the release of neurotransmitters Signup and view all the answers

What are supporting cells in the nervous system referred to as?

Neuroglia or glial cells Signup and view all the answers

What characterizes unmyelinated axons in the nervous system?

They can be found in both the autonomic nervous system and some sensory fibers. Signup and view all the answers

What is the correct spacing of the nodes of Ranvier in unmyelinated axons?

Every 1 mm Signup and view all the answers

What distinguishes unipolar neurons from other classifications of neurons?

They have a single, short process that divides. Signup and view all the answers

Which type of neuron is found in special sensory organs and consists of two processes?

Bipolar neurons Signup and view all the answers

What is the primary function of the sensory (afferent) neurons?

Transmit impulses toward the central nervous system. Signup and view all the answers

In which part of the central nervous system is gray matter typically located superficially?

Cortex Signup and view all the answers

What characterizes multipolar neurons in the nervous system?

They have a single axon and multiple dendrites. Signup and view all the answers

What is one characteristic of neurons related to their longevity?

Neurons can live for a lifetime with little to no change in function. Signup and view all the answers

Which of the following accurately describes the role of the nerve cell body?

It serves as the major biosynthetic center of the neuron. Signup and view all the answers

What is NOT a function of the plasma membrane in neurons?

Nutrient absorption Signup and view all the answers

Which of the following statements about chromatophilic bodies is false?

They are responsible for the electrical conduction of signals. Signup and view all the answers

What distinguishes neurons from other cell types concerning cell division?

Neurons do not undergo typical mitotic division. Signup and view all the answers

Which feature describes the metabolic needs of neurons?

Neurons require continuous supplies of oxygen and glucose. Signup and view all the answers

What is the significance of the axon hillock in relation to neuron function?

It is the region where signal transmission begins. Signup and view all the answers

Which statement regarding neurogenesis in mammals is correct?

Neurogenesis can happen in specific areas like the olfactory bulb. Signup and view all the answers

What is the primary function of axonal transport in neurons?

To facilitate the movement of substances to and from the soma Signup and view all the answers

What distinguishes a nerve fiber from other types of axons?

It can be extremely long, such as those extending to the foot Signup and view all the answers

Which term is used to describe the branches that extend at right angles from the axon?

Axon collaterals Signup and view all the answers

How many terminal branches does a typical neuron have at its terminus?

10,000 Signup and view all the answers

What component is formed by oligodendrocytes within the central nervous system?

Myelin sheath Signup and view all the answers

What characterizes axons that lack a myelin sheath?

They are referred to as unmyelinated axons Signup and view all the answers

What type of cells produce the myelin sheath in the peripheral nervous system?

Schwann cells Signup and view all the answers

What occurs at the axon terminals following a nerve impulse?

Neurotransmitters are released into the extracellular space Signup and view all the answers

What is one of the key functions of the myelin sheath?

To insulate thick axons and enhance impulse speed Signup and view all the answers

Which of the following statements about axonal terminals is true?

They end in structures known as axon knobs Signup and view all the answers

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

To protect the axon and facilitate regeneration Signup and view all the answers

Which of the following statements accurately describes the nodes of Ranvier?

They are formed by oligodendrocytes in the CNS Signup and view all the answers

What is a significant consequence of myelinated axons having Schwann cells that do not touch each other?

It allows for faster nerve impulse transmission Signup and view all the answers

What type of neurons primarily contain unmyelinated axons?

Sensory neurons Signup and view all the answers

What is one of the primary advantages of the myelin sheath's insulation?

It prevents leakage of electrical current from the axon Signup and view all the answers

Which supporting cells are specifically responsible for forming myelin sheaths in the central nervous system?

Oligodendrocytes Signup and view all the answers

How many unmyelinated axons can a single Schwann cell partly enclose?

15 or more Signup and view all the answers

What structural feature differentiates myelinated and unmyelinated axons in terms of Schwann cell arrangement?

Unmyelinated axons can be enclosed within tubular recesses of Schwann cells Signup and view all the answers

Which function is NOT associated with the myelin sheath?

Separation of adjacent axons Signup and view all the answers

What is the typical spacing between the nodes of Ranvier in myelinated axons?

1 mm apart Signup and view all the answers

What is the primary role of oligodendrocytes in the CNS?

They produce and maintain myelin sheaths around axons. Signup and view all the answers

Which statement accurately describes the structure of gray matter?

It contains neuronal cell bodies and unmyelinated fibers. Signup and view all the answers

What is a distinguishing feature of satellite cells in the peripheral nervous system?

They resemble small moons surrounding a planet. Signup and view all the answers

Which function is associated with Schwann cells in the PNS?

Forming the myelin sheath around peripheral nerve fibers. Signup and view all the answers

Which statement best describes the organization of white matter in the nervous system?

It contains many axons and lacks cytoplasmic soma. Signup and view all the answers

What feature of ependymal cells contributes to their role in the CNS?

They are ciliated to help circulate cerebrospinal fluid. Signup and view all the answers

Which of the following best describes the arrangement of gray matter in the spinal cord?

It is organized into paired dorsal and ventral horns. Signup and view all the answers

What is a distinguishing characteristic of the myelin sheath formed by Schwann cells compared to that formed by oligodendrocytes?

Schwann cell myelin sheaths develop primarily during postnatal life. Signup and view all the answers

How does the structure of ependymal cells facilitate their function in the CNS?

Cilia on their surface promote CSF circulation. Signup and view all the answers

What is the effect of oligodendrocytes on axons in the CNS?

They provide insulation that enhances conduction velocity. Signup and view all the answers

Study Notes

Neuron Structure

Cell Body (soma): The central region of a neuron containing the nucleus and other organelles. The plasma membrane of the soma acts as a receptive surface for signals from other neurons.
Neurofibrils: Bundles of intermediate filaments (neurofilaments) found within the soma. They provide structural support, preventing the cell from being pulled apart during tension.
Processes: Arm-like extensions that extend from the soma, responsible for receiving and transmitting signals.
- Dendrites: Short, tapering, and branched processes that are the input regions of a neuron. They receive signals from other neurons and conduct them towards the soma.
- Axons: Slender processes of uniform diameter that arise from the axon hillock. They are the impulse generators and conductors of the neuron, transmitting signals away from the soma.
  - Axon Hillock: A specialized region of the axon that initiates the nerve impulse.
  - Functions of Axons: Generate and transmit action potentials (nerve impulses); secrete neurotransmitters from the axon terminal.
  - Axon Terminals: The endings of axons, responsible for releasing neurotransmitters.
Myelin Sheath: A fatty, insulating layer surrounding the axon, increasing the speed of nerve impulse transmission and making impulse propagation more energy efficient.
- Schwann Cells: Glial cells in the PNS responsible for forming the myelin sheath. They wrap around axons in a concentric manner.
- Nodes of Ranvier: Gaps between adjacent Schwann cells, allowing saltatory conduction of nerve impulses.
- Oligodendrocytes: Glial cells in the CNS responsible for forming the myelin sheath around CNS axons.

Neuroglia (Glial Cells)

Supporting Cells: Non-neuronal cells that support and protect neurons in the nervous system.
Functions: Support and brace neurons; segregate and insulate neurons; promote health and growth of nervous tissue.
Types of Neuroglia:
- Astrocytes: Star-shaped glial cells with bulbous ends. They are the most abundant and versatile neuroglia in the CNS, providing structural support, regulating the chemical environment, and influencing synapse formation.
- Microglia: Small, elongated cells with spiny processes. They are phagocytic cells that monitor the health of neurons, removing debris and pathogens.
- Ependymal Cells: Line the central cavities of the brain and spinal cord. They form a permeable barrier between the cerebrospinal fluid and the CNS tissue.
- Oligodendrocytes: Branched cells that wrap around axons in the CNS, forming myelin sheaths.
- Schwann Cells: Surround nerve fibers in the PNS, forming the myelin sheath.
- Satellite Cells: Surround neuron cell bodies in ganglia of the PNS, providing support and insulation.

Gray Matter and White Matter

Gray Matter: Consists primarily of neuron cell bodies, dendrites, unmyelinated axons, and neuroglia. Found in the outer layer of the brain and the inner region of the spinal cord.
White Matter: Contains myelinated axons and few cell bodies. Located in the inner layer of the brain and the outer region of the spinal cord.

Neuron Types

Sensory (Afferent) Neurons: Carry impulses from sensory receptors towards the CNS.
- Peripheral Process: Extends from the sensory receptor to the CNS.
- Central Process: Extends from the peripheral process to the CNS.
Motor (Efferent) Neurons: Carry impulses from the CNS to effector organs (muscles and glands).
Interneurons (Association Neurons): Shuttle signals through CNS pathways, connecting sensory and motor neurons. They are responsible for complex information processing in the CNS.

Structure of a Nerve

Nerve: A cable-like organ in the PNS containing bundles of axons (nerve fibers) enclosed by connective tissue layers.
Endoneurium: A delicate layer of loose connective tissue that surrounds individual axons.
Perineurium: Connective tissue that wraps around groups of axons, forming nerve fascicles.
Epineurium: A tough fibrous sheath that surrounds the entire nerve.

Nervous System: Master Controller

The nervous system is the body's communication and control system.
It monitors internal and external stimuli (sensory input).
It interprets sensory information and decides on a response (integration).
It executes actions based on the interpretation (motor output).

Neuron: The Communication Unit

Neurons are the active cells that transmit electrical signals.
They are long-lived and do not divide, except in specific brain regions.
They have a high metabolic rate and require oxygen and glucose for survival.

Neuron Structure:

Cell Body (Soma): Contains the nucleus and is the center for protein synthesis.
- It's where the axon emerges from.
- It contains Chromatophilic bodies, which are clusters of rough ER and ribosomes, responsible for protein production.
Axon: The long extension that transmits nerve impulses.
- Axons can be extremely long.
- They branch less frequently than dendrites.
- They end in axon terminals, where neurotransmitters are released.
Dendrites: They receive signals from other neurons.
- They are abundant and branching, increasing the surface area for signal reception.
Myelin Sheath: Insulating fatty layer around axons.
- Formed by oligodendrocytes in the central nervous system (CNS).
- Formed by Schwann cells in the peripheral nervous system (PNS).
- Increases signal transmission speed and efficiency.
- Gaps between myelin segments are called nodes of Ranvier, where signal jumps occur.

Supporting Cells (Neuroglia)

Neuroglia provide structural support and maintain the environment for neurons.
CNS Neuroglia:
- Astrocytes: Star-shaped cells that provide structural support, regulate blood flow, and help maintain the blood-brain barrier.
- Microglia: Phagocytic cells that remove debris and pathogens.
- Ependymal cells: Line the central canal and ventricles, help circulate cerebrospinal fluid.
- Oligodendrocytes: Form myelin sheaths around axons in the CNS.
PNS Neuroglia:
- Schwann cells: Form myelin sheaths around axons in the PNS.
- Satellite cells: Surround neuron cell bodies in ganglia, providing support and protection.

The Nervous System: Organization

Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons.
- Located centrally in the spinal cord and in specific regions of the brain.
White Matter: Composed of myelinated axons.
- Located externally in the spinal cord and surrounds the gray matter in the brain.
- Allows communication between different parts of the CNS.
Tracts: Bundles of axons traveling to similar destinations within white matter.
Cortex: Outer layer of gray matter in the cerebrum and cerebellum.

Neuron Classification

Structural Classification:
- Multipolar: Most common type, having multiple dendrites and one axon.
- Bipolar: Rare, with one axon and one dendrite.
- Unipolar (Pseudounipolar): Single short process that branches, sensory neurons.
Functional Classification:
- Sensory (Afferent): Transmit signals from periphery toward the CNS.
- Motor (Efferent): Transmit signals from the CNS to muscles and glands.
- Interneurons: Connect neurons within the CNS.

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Description

Test your knowledge on the structure of neurons, including the cell body, neurofibrils, and various processes like dendrites and axons. This quiz will help you understand the functional components and the role they play in signal transmission. Perfect for students of biology or neuroscience!