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Questions and Answers
What primarily composes white matter in the nervous system?
What primarily composes white matter in the nervous system?
What gives gray matter its characteristic color?
What gives gray matter its characteristic color?
Which structure protects the spinal cord from damage?
Which structure protects the spinal cord from damage?
What is the primary function of the spinal cord?
What is the primary function of the spinal cord?
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Which of the following components is part of the peripheral nervous system (PNS)?
Which of the following components is part of the peripheral nervous system (PNS)?
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What type of neurons are involved in voluntary muscle control?
What type of neurons are involved in voluntary muscle control?
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Which part of the nervous system is primarily responsible for involuntary functions such as heart rate and digestion?
Which part of the nervous system is primarily responsible for involuntary functions such as heart rate and digestion?
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Approximately how many neurons are contained in the spinal cord?
Approximately how many neurons are contained in the spinal cord?
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What is the basic functional unit of the nervous system?
What is the basic functional unit of the nervous system?
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What type of neuron carries signals away from the central nervous system?
What type of neuron carries signals away from the central nervous system?
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Which part of the neuron is responsible for receiving signals?
Which part of the neuron is responsible for receiving signals?
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Which type of neuron is primarily involved in the processing of information?
Which type of neuron is primarily involved in the processing of information?
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Which functional classification of neuron is responsible for detecting stimuli?
Which functional classification of neuron is responsible for detecting stimuli?
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The axon of a neuron primarily serves which function?
The axon of a neuron primarily serves which function?
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Which type of sensory fiber is associated with 'fast' pain and temperature sensation?
Which type of sensory fiber is associated with 'fast' pain and temperature sensation?
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What characteristic is true of myelinated motor fibers?
What characteristic is true of myelinated motor fibers?
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What is the primary characteristic of multipolar neurons?
What is the primary characteristic of multipolar neurons?
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Which neurons are primarily involved in sensory functions such as sensing chemical and temperature signals?
Which neurons are primarily involved in sensory functions such as sensing chemical and temperature signals?
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Which type of neuron has two processes extending from the cell body?
Which type of neuron has two processes extending from the cell body?
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What is one function of non-neuronal cells (glial cells)?
What is one function of non-neuronal cells (glial cells)?
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What distinguishes pseudounipolar neurons from unipolar neurons?
What distinguishes pseudounipolar neurons from unipolar neurons?
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Which neuron type constitutes around 99% of neurons in the central nervous system?
Which neuron type constitutes around 99% of neurons in the central nervous system?
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Which of the following structures can vary significantly in neurons?
Which of the following structures can vary significantly in neurons?
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What describes the purpose of axons in neurons?
What describes the purpose of axons in neurons?
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Which type of neuroglia is responsible for producing myelin in the Central Nervous System?
Which type of neuroglia is responsible for producing myelin in the Central Nervous System?
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What is the primary function of microglia in the nervous system?
What is the primary function of microglia in the nervous system?
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Which type of astrocyte is found in white matter?
Which type of astrocyte is found in white matter?
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In the Peripheral Nervous System, what role do satellite cells primarily serve?
In the Peripheral Nervous System, what role do satellite cells primarily serve?
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What is a primary characteristic of neuroglial cells compared to neurons?
What is a primary characteristic of neuroglial cells compared to neurons?
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What structure do Schwann cells form that plays a role in neural regeneration?
What structure do Schwann cells form that plays a role in neural regeneration?
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What is the primary purpose of the myelin sheath?
What is the primary purpose of the myelin sheath?
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Which of the following statements accurately describes the process of myelination in unmyelinated neurons?
Which of the following statements accurately describes the process of myelination in unmyelinated neurons?
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What is the primary role of neurofibril nodes in the nervous system?
What is the primary role of neurofibril nodes in the nervous system?
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Which demographic is more commonly affected by multiple sclerosis?
Which demographic is more commonly affected by multiple sclerosis?
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What is a primary symptom experienced by individuals with multiple sclerosis?
What is a primary symptom experienced by individuals with multiple sclerosis?
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What is the outcome of the inflammatory process in multiple sclerosis?
What is the outcome of the inflammatory process in multiple sclerosis?
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In what part of the brain is gray matter primarily found?
In what part of the brain is gray matter primarily found?
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Why does multiple sclerosis lead to periods of remission?
Why does multiple sclerosis lead to periods of remission?
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During multiple sclerosis, which part of the nervous system is primarily affected?
During multiple sclerosis, which part of the nervous system is primarily affected?
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What is a common characteristic of lesions associated with multiple sclerosis?
What is a common characteristic of lesions associated with multiple sclerosis?
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Study Notes
The Nervous System
- The nervous system is made up of the central nervous system (CNS) and the peripheral nervous system (PNS)
- The CNS consists of the brain and spinal cord.
- The brain has ~85 million neurons. The spinal cord has ~ 100 million neurons.
- The PNS consists of nerves, ganglia, enteric plexuses, sensory receptors.
The Brain
- The brain is covered by white matter over a thin shell of gray matter
- The spinal cord is a tubular structure made up of nerves extending from the brain to the lumbar vertebrae.
- The spinal cord connects sensory receptors to the brain and transmits motor signals back from the brain to the body.
The Neuron
- Neurons are specialized cells for transmitting information. They are "excitable" cells.
- They are the basic functional unit of the nervous system.
- The electrical nature of the signal in neurons is the reason they are described as “excitable” cells.
- Neuron components:
- Dendrites: Tree shaped branches that receive signals. They contain numerous receptors.
- Cell body (soma): Contains the nucleus and other components typically found inside cells. e.g. mitochondria, lysosomes, golgi complex, ribosomes, etc.
- Axon: Takes the signal away from the cell body and to another neuron, muscle fibre or a gland. The axon contains cytoplasm (axoplasm) plus other cellular components but has no ribosomes and therefore cannot produce proteins.
Neuronal Classification
- Sensory neurons: This is also known as afferent neurons: Takes signals from the body to the CNS.
- Motor neurons: This is known as efferent neurons: Takes signals from the CNS to the body.
- Interneurons: These are located in the CNS and between sensory and motor neurons.
Sensory Neuron types
- Chemoreceptors (GI tract)
- Photoreceptors light (eyes)
- Mechanoreceptors (touch skin), (blood pressure; baroreceptors in blood vessels)
Motor Neuron types
- Response -delivering actions
- Contraction/relaxation (muscle)
- Secretion (endocrine glands).
Fiber types
- Sensory fibres:
- Touch – myelinated (++) "Fast" pain, temperature – myelinated (+)
- “Slow” pain, temperature, itch – unmyelinated
- Motor fibers: myelinated (+++)
Structural Classification
- Multipolar neuron: One axon but many dendrites from the cell body - Motor neurons to muscles and glands and most (99%) of the CNS neurons.
- Unipolar neuron: Have only one axon emerging from the cell body but many dendrites from the cell body for sensing different signals e.g. chemical, sound, mechanical, temperature, light
- Bipolar neuron: Two processes extending from the cell body; (eyes, ear, nose)
- Pseudounipolar neuron: Unioplar, but axon divides in two.
Diversity in neurons
- Cell bodies can vary from 5 μm to 135 μm in size.
- Pattern of dendritic branching is varied and distinctive in different areas of the nervous system.
Neuroglia
- Also called glial cells or simply glia
- These are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons.
- They make up about half the volume of the nervous system
- They are not electrically excitable.
- They can multiply and divide.
- There are six types: four in the CNS and two in the PNS.
Neuroglia of the CNS
- Neuroglia of the CNS: Astrocytes, Oligodendrocytes, Microglia, and Ependymal cells.
- Astrocytes: Two types: Protoplasmic (grey matter) with short branches and Fibrous (white matter) with long branches.
- Oligodendrocytes: Produce myelin (proteolipid) sheath around axons for electrical insulation and fast conduction.
- Microglia: Function as phagocytes, removing debris from microbes and developing or damaged nervous tissue.
- Ependymal cells: Cuboidal or columnar cells in a single layer. Possess microvilli and line the ventricles of the spinal cord and the brain. Function to assist circulation of cerebrospinal fluid.
Myelination
- Myelin sheath is made up of multiple layers wrapped around ~1mm segments of the axon.
- The cytoplasmic material of the Schwann cell in the PNS forms the outermost layer called the neurolemma.
- In unmyelinated neurons, multiple neurons are surrounded by one Schwann cell, without the repeated spiralling of the proteolipid.
Neuroglia of the PNS
- Neuroglia of the PNS: Schwann cells and Satellite cells.
- Schwann cells: Completely surround the axon and cell body. They produce myelin.
- Satellite cells: Small, flat cells that regulate the exchange of materials between cell bodies of neurons and interstitial fluid.
Nodes of Ranvier
- Gaps between the Schwann cells along the axon create nodes of Ranvier.
- Each Schwann cell wraps around one neuron between two nodes.
Neurofibril nodes
- Regions between myelinating cells are called neurofibril nodes.
- Gaps (approx 1μm) between the myelinating cells expose the axon to extracellular space.
- Very important in neurotransmission for the propagation of action potentials, by speeding up saltatory conduction.
- They are also important in neurodegenerative diseases such as multiple sclerosis.
Multiple Sclerosis (MS)
- Autoimmune neurodegenerative disease
- More common in women than men.
- Age of onset is between 20 and 40 years old.
- Inflammatory process of MS results in the gradual destruction of myelin sheaths around myelinated axons of the brain and spinal cord (CNS).
- Symptoms include:
- Muscle weakness and paralysis
- Impaired coordination and poor balance
- Depression, impaired speech
- Memory problems
- Visual problems
- Altered sensory perception
- Pain
- Fatigue
- Other dysfunctions; e.g. bowel, bladder, and sexual dysfunctions
- Deficits in neural conduction caused by damage to myelin sheaths and underlying axons in the central nervous system often lead to these symptoms.
Gray and White Matter in the Brain
- Gray matter: Contains the cell bodies of the neurons and unmyelinated axons
- White matter: Contains myelinated axons of neurons
Multiple Sclerosis and White Matter
- MS is associated with lesions in the white matter of the brain.
- MS is associated with myelin degradation in the white matter.
- MS is an autoimmune disease - damage by T (and B) cells that cross the blood-brain barrier (BBB).
- The brain tries to repair itself by generating more myelin by oligodendrocytes. This is why there are periods of remission.
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Description
Test your knowledge on the structure and functions of the nervous system, including the central and peripheral nervous systems. Dive into the details about the brain, spinal cord, and neurons, and understand how they transmit information throughout the body.
