What is the estimated total number of neurons in the human brain?
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86 billion.
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What is the estimated total number of neurons in the human brain?
86 billion.
On average, how many synapses does each neuron have?
Approximately 7000.
Are there neurons with more than 7000 synapses?
Yes, some neurons have considerably higher synapse counts.
What is an example of a reflex arc?
Stretch reflex.
What is the first step in the stretch reflex?
Extension of muscle sensed by receptors in the thigh.
What are the meninges?
Connective tissue coverings that protect the brain and spinal cord.
What is the clinical implication of the highly metabolic state of neurons?
Neurons are highly sensitive to deprivation.
How do sensory neurons contribute to the reflex arc?
They transmit information to motor neurons in the ventral horn of the spinal cord through synaptic connections.
Why do we have unmyelinated axons?
To allow some signals to be slow and sustained rather than fast and transient.
What is the primary function of the meninges?
To provide protection for the brain and spinal cord.
What are the characteristic features of Alzheimer's disease?
The presence of amyloid plaques and neurofibrillary tangles.
What initiates the contraction of the flexor muscles in the stretch reflex?
Action potential at the neuromuscular junction.
What is a key reason for regeneration failure in the CNS?
Failure of oligodendrocytes to remove degenerating myelin.
What type of signals are typically transmitted by unmyelinated axons?
Signals related to pain.
What is the major cell type involved in neuroinflammation?
Microglia.
What are the beneficial aspects of transient, low levels of neuroinflammation?
They can aid in repair after injury.
What is a characteristic of the direct connection in the reflex arc?
It is fast.
What is a characteristic of the cell bodies in autonomic ganglia?
They are small.
What are plaques in Alzheimer's disease primarily made of?
Pieces of the protein Beta-amyloid that clump together.
What do oligodendrocytes fail to form that impacts regeneration?
Tubes.
What is the ultimate effect of amyloid plaques and neurofibrillary tangles in Alzheimer's disease?
They kill neurons in specific places.
What morphological change occurs in microglia during neuroinflammation?
They can change to an amoeboid shape.
What are the detrimental effects of high levels or chronic neuroinflammation?
They can have harmful effects on the nervous system.
Where are the nuclei located in autonomic ganglia?
Eccentric.
What happens to injured axons in the PNS?
Sprouts appear from the end of the injured axons.
What structure is formed by astrocytes that hinders regeneration in the CNS?
Glial scar.
Where are plaques found in relation to neurons?
Outside the neuron.
Which other immune cells can infiltrate the area of a lesion during neuroinflammation?
Lymphocytes.
What role does neuroinflammation play after an injury?
It is involved in the repair process.
How do nerve fibers behave in autonomic ganglia?
They do not tend to form bundles.
What role do Schwann cells play in axon regeneration?
They dedifferentiate, proliferate, form tubes, and release substances to guide re-growing axons.
What type of inhibitory molecules are increased due to glial scar formation?
Chondroitin sulfate proteoglycan.
What type of axons are found in the PNS?
Both myelinated and unmyelinated axons.
What is one effect of plaques in Alzheimer's disease?
They block other processes.
What role do other glial cell types play in neuroinflammation?
They contribute alongside microglia.
What is notable about the number of satellite cells in autonomic ganglia?
They are fewer in number.
What is the function of the endoneurium in the PNS?
It surrounds individual axons.
What trophic support do microglia provide under normal conditions?
Secretion of factors.
What causes Chronic Traumatic Encephalopathy (CTE)?
Repeated blows to the head.
What is the final outcome of axon regeneration in the PNS?
Axons regrow and reach target cells again.
What is a characteristic of the cell body in dorsal root ganglia?
It is large.
What occurs in a normal PNS condition?
The axon contacts muscle or another cell type.
What is the connective tissue that is continuous with the dura mater in the PNS?
Epineurium (dense irregular connective tissue).
What is the unique feature of neuronal morphology?
Neuronal processes.
What covers unmyelinated axons in the PNS?
Schwann cell cytoplasm.
What is the most common demyelinating disease in the CNS?
Multiple Sclerosis.
What does the perineurium encase?
Bundles of axons, known as fascicles.
How can CTE be definitively diagnosed?
Only at autopsy.
What is one of the key functions of microglia related to synapses?
Synaptic pruning.
What does 'A' represent in the organization of peripheral nerves?
Axon (pink thread-like structure).
Where is the nucleus located in the dorsal root ganglia cell body?
In the center.
Which connective tissue is continuous with the arachnoid in the PNS?
Perineurium.
How does regeneration in the CNS compare to the PNS?
There is little regeneration in the CNS compared to the PNS.
What is Multiple Sclerosis thought to be?
An autoimmune disease.
What is Wallerian degeneration?
A process that occurs after an axon is damaged, leading to degeneration of the axon distal to the injury.
What is the primary function of a Schwann cell?
To myelinate a short portion of an axon (up to 0.1 mm).
What do axons do?
Carry information AWAY from the soma.
What is the role of the epineurium?
It surrounds the whole nerve and the spaces between fascicles.
What is indicated by 'NR' in peripheral nerve organization?
Node of Ranvier.
What are the main components of a peripheral nerve?
Axons and Schwann cells.
What are the criteria for diagnosing CTE?
Evidence of neuronal degeneration and an abnormal pattern of the microtubule-associated protein, Tau.
Why are microglia important during development?
They play a crucial role in the development of the nervous system.
What is the connective tissue associated with the pia mater in the PNS?
Endoneurium.
What happens to myelin in Multiple Sclerosis?
It is destroyed in focal lesions.
How can axonal transport be clinically significant?
It can be hijacked to transport substances into the CNS that shouldn't be transported.
Why is there limited regeneration in the CNS?
Due to differences in both glia and axonal response.
How do nerve fibers pass through the dorsal root ganglion?
They form bundles.
Where are astrocytes found?
In the central nervous system (CNS).
What is the unmyelinated region between adjacent Schwann cells called?
Node of Ranvier.
What is a synapse?
A site of communication between the axon and the next cell.
What is the neuromuscular junction?
The connection between the axon of a motor neuron and a muscle cell.
What is a ganglion in the peripheral nervous system?
A region with neuronal soma, dendrites, and some axons.
What is a characteristic feature of Schwann cells in peripheral nerves?
They have a membrane that surrounds the axons.
What is the first step in Schwann cell myelination?
The axon invaginates into the Schwann cell.
What does 'M' stand for in the context of peripheral nerves?
Myelin (space showing granularity).
What are dendritic spines?
Protrusions that serve as sites of contact for synaptic communication.
Where do the lesions in Multiple Sclerosis typically radiate from?
From the ventricles (periventricular).
What are reactive astrocytes?
Astrocytes that respond following injury or in disease states.
What happens if an axon in the PNS is damaged but the cell body remains intact?
Recovery can occur proximal to the site of injury while the distal part degenerates and then regenerates.
What happens to neurons in the CNS when they die?
They are gone because few neurons undergo mitosis.
Where is the axon open to the environment?
At the Nodes of Ranvier.
What type of cells are present around the neuronal cell body in dorsal root ganglia?
Satellite cells.
What are the processes of astrocytes that contact blood vessels called?
End feet.
What is the function of dendrites?
Carry information TOWARDS the soma.
What is Wallerian degeneration?
A process that occurs when a nerve fiber is cut or crushed, leading to the degeneration of the part of the axon distal to the injury.
Which virus is known to utilize axonal transport to enter the CNS?
Rabies virus.
What are supporting cells in the nervous system primarily classified as?
Glial cells or neuroglia.
Where are synapses found?
At the distal end of the axon.
What is the primary function of myelinated axons?
To increase the speed of conduction up to 30 times.
What is typically the antigen in Multiple Sclerosis?
One of the myelin-associated proteins.
What happens to myelin during processing of peripheral nerves?
Myelin is removed, revealing spaces.
What are microglia?
Tiny cells found in the central nervous system (CNS).
What diseases are neuroinflammation linked to?
Most neurodegenerative diseases like Alzheimer’s and Parkinson’s.
What does 'N' represent in the organization of peripheral nerves?
Nucleus of Schwann cell.
What elements are important in dendritic spines?
Cytoskeletal elements and synaptic receptors.
What is the blood-brain barrier?
A theoretical barrier that selectively lets certain substances through while blocking others.
Which neurotransmitter is used at the neuromuscular junction?
Acetylcholine.
What is the approximate rate of nerve regeneration in the PNS?
Approximately 1 inch per month.
What happens after the axon invaginates into the Schwann cell?
The Schwann cell membrane wraps concentrically around the axon.
What role do specific proteins in neuronal cilia play?
They can contribute to obesity.
How does regeneration in the PNS differ from the CNS?
In the PNS, regeneration is more effective due to the presence of Schwann cells, which promote axonal growth, while in the CNS, regeneration is limited due to inhibitory factors and the absence of supportive cells.
What happens to the axon between the Nodes of Ranvier?
It is otherwise isolated.
What structures can astrocytes contact?
Neuronal soma and myelin.
What is an example of a ganglion?
Dorsal Root Ganglion (DRG).
What type of neuron is found in the dorsal root ganglia?
Pseudounipolar neuron.
What morphological changes occur in reactive astrocytes?
Increase in size and branch thickness.
What types of glial cells are found in the Central Nervous System (CNS)?
Oligodendrocytes, astrocytes, and microglia.
What are the meninges?
Several layers that protect the brain and spinal cord.
What factors influence the speed of conduction in myelinated axons?
The diameter of the axon and the thickness of the myelin.
What was the initial belief about how West Nile Virus enters the CNS?
It was originally thought to work the same way as rabies virus.
Which neuropsychiatric diseases are associated with neuroinflammation?
Schizophrenia, Autism, and Depression.
From what do microglia develop?
From the same precursors as other macrophages.
What are neurodegenerative disorders characterized by?
Numerous different characteristics.
What types of cells can communicate at a synapse?
Another neuron or another type of cell, such as muscle or blood vessel.
What are the gaps in the myelin sheath of peripheral nerves called?
Nodes of Ranvier.
What does 'NF' denote in the context of peripheral nerves?
Nerve fiber, which includes axon and its myelin sheath.
What is the primary function of autonomic ganglia?
They are involved in the autonomic nervous system, controlling involuntary functions.
How do astrocytes interact with neurons?
They communicate with neurons.
What role do Schwann cells play in the PNS?
They support the regeneration of damaged axons by forming a regeneration tube and secreting growth factors.
What factors can influence the speed of nerve regeneration?
Age, health, and other factors.
What does the blood-brain barrier regulate?
The passage from the vascular system to the nervous system.
What does dendritic tree variability refer to?
The amazing range of variability in the structure of dendritic trees among different types of neurons.
What is the initial segment of the axon?
The part of the axon that is myelinated by Schwann cells.
What are the main components of the cytoskeleton in both axons and dendrites?
Microtubules and microfilaments.
How do dendritic spines vary?
They come in different shapes.
What types of glial cells are found in the Peripheral Nervous System (PNS)?
Schwann cells and satellite cells in the dorsal root ganglia (DRG).
What can reactive astrocytes form?
A scar.
What are the Nodes of Ranvier?
Gaps in the myelin sheath that allow for saltatory conduction.
Is neuroinflammation linked to COVID-19?
Yes, it is being studied in relation to COVID-19.
Which pathway is implicated in the connection between neuronal cilia and obesity?
The leptin pathway.
What is the outermost layer of the meninges?
Dura mater.
What constitutes a nerve in the peripheral nervous system?
Regions with only axons and their glial cells, without soma or dendrites.
How many neurons innervate each muscle fiber?
Each muscle fiber is innervated by 1 neuron.
What occurs to the Schwann cell cytoplasm and nucleus during myelination?
They are pushed to the edge and remain around the axon.
What type of neurons are found in dorsal root ganglia?
Sensory neurons that transmit sensory information to the central nervous system.
When do microglia enter the brain?
Very early in brain development.
What are neurofibrillary tangles?
They occur when microtubules are disrupted in Alzheimer's disease.
What specific intermediate filament protein is associated with astrocytes?
Glial fibrillary acidic protein (GFAP).
What inhibits regeneration in the CNS?
The presence of myelin-associated inhibitors and the formation of a glial scar.
What primarily forms the blood-brain barrier?
Complex tight junctions (TJ) between endothelial cells of capillaries.
What do we now understand about the mechanism of West Nile Virus entry into the CNS?
It involves a combination of axonal transport and other mechanisms.
What is the specific process called that occurs during degeneration of the distal axon?
Wallerian degeneration.
What can be observed in neurodegenerative disorders?
Neuronal loss.
What is the role of ependymal cells?
Ependymal cells line the ventricles of the brain and the central canal of the spinal cord, but their importance is sometimes questioned.
Is neuroinflammation a cause or a consequence of diseases?
It is still under investigation whether it is a cause or a consequence.
What is the significance of the Nodes of Ranvier in neuronal function?
They facilitate faster nerve impulse conduction through saltatory conduction.
What gases can penetrate the blood-brain barrier?
Oxygen (O2) and carbon dioxide (CO2).
What is the dura mater?
The thick outer layer of the spinal cord meninges.
Which meningeal layer is the thickest?
Dura mater.
Where are autonomic ganglia located?
Near or within the organs they innervate.
What is the outcome of Wallerian degeneration in the PNS?
It often leads to successful regeneration of the nerve fiber.
What happens to microtubules if the neuron survives after injury?
They can fail to assemble in a linear manner.
What occurs to the distal part of a damaged axon in the PNS?
It degenerates and then regenerates.
What role do microglia play in the CNS?
They function as resident macrophages.
How is the cytoskeleton organized in dendrites compared to axons?
The cytoskeleton in dendrites is less organized and more associated with branching.
What happens to the protein Tau in neurofibrillary tangles?
Tau becomes dissociated from the microtubule and clumps together.
What role do astrocytes play in the blood-brain barrier?
They play a significant role in the functioning of tight junctions of endothelial cells.
What is the primary function of dendrites?
To carry information towards the soma.
How do the shapes of dendritic spines change?
They change over development.
What is an axosomatic synapse?
A synapse where an axon connects to the cell body of another neuron.
What is the significance of MC4R and ADCY3 in the context of obesity?
Their subcellular localization at neuronal primary cilia underlies a common pathway for genetic predisposition to obesity.
What is the function of excitatory neurotransmitters?
They facilitate the firing of an action potential in the connected cell.
What defines regions of the CNS at a gross level?
Regions defined based on neuronal soma, not glia.
What is a characteristic feature of each type of neuron?
Each type of neuron has its own characteristic dendritic tree.
What is observed in the center of the Nodes of Ranvier?
The axon, represented as a dark line.
Where are satellite cells located?
In the peripheral nervous system (PNS).
What is a potential approach to managing neuroinflammation?
Various treatments are being explored.
What is often required to visualize many features of neurodegenerative disorders?
Special stains.
Why were supporting cells originally not viewed as important?
They were not considered particularly important for nervous system functioning.
Which substances are transported across the blood-brain barrier by carrier proteins?
Glucose, amino acids (aa), and vitamins.
What is axonal transport?
A bidirectional process for transporting materials along the axon.
What is the location of dorsal root ganglia?
Adjacent to the spinal cord, along the dorsal roots of spinal nerves.
What is the function of the arachnoid layer?
It has projections (trabeculae) that extend inward.
Where is the arachnoid layer located?
Between the red and black lines in the spinal cord meninges.
What happens to the neuronal cell body during Wallerian degeneration?
It undergoes changes such as chromatolysis, which is the breakdown of the cell's Nissl bodies.
What occurs at the end of the axon that prevents growth?
A mass of structures forms due to continued axonal transport.
Why are microglia important in the CNS?
Because the CNS is protected from the immune system.
What are pericytes' role in the blood-brain barrier?
They also have a significant role in the barrier's functioning.
How is the cytoskeleton arranged in axons?
It is more polarized and arranged in bundles for transport.
What does the white space at the Nodes of Ranvier indicate?
The absence of myelin due to processing.
What is the typical size of satellite cells?
They are small cells.
What happens to bigger molecules at the blood-brain barrier?
They are often blocked.
What constitutes gray matter in the CNS?
Regions with neuronal soma, dendrites, and some axons.
Where do the original branches of dendrites arise from?
From the soma.
What is the effect of neurofibrillary tangles on axonal transport?
They block axonal transport.
What do inhibitory neurotransmitters do?
They prevent the firing of an action potential in the connected cell.
What is an axodendritic synapse?
A synapse where an axon connects to a dendrite, typical and most common in the CNS.
What does the subarachnoid space contain?
Cerebrospinal fluid (CSF) and blood vessels.
What type of neurons are primarily found in autonomic ganglia?
Postganglionic neurons that innervate target organs.
How does the number of branches in a dendritic tree affect a neuron?
More branches mean more opportunity for input.
What is retrograde transport?
Transport towards the soma and away from the synapse at the end of the axon.
What underlies the formation of retraction bulbs in axonal regeneration?
Disorganized microtubules.
What causes some neurodegenerative disorders?
Aggregation of abnormal proteins.
What is found in the subarachnoid space?
Dorsal and ventral roots.
What is the role of microglia in neuroinflammation?
They are part of the neuroinflammatory response.
What are dendritic branches classified based on?
Their origin and structure.
Where are satellite cells commonly found?
In ganglia, often close to the neuronal soma.
What is the role of the Schwann cell sheath in relation to the Nodes of Ranvier?
It curves around the axon, contributing to the formation of the myelin sheath.
Are drugs able to cross the blood-brain barrier?
Many drugs are blocked by the barrier.
Where is most protein made in a neuron?
In the soma.
