Nervous System: Embryology, Cells, and Pathologies for Dental Students

What is the embryonic origin of neurons?

Neurons originate from the ectoderm, specifically from neuroepithelium which forms the neural plate, neural groove, and neural tube.

What are the two main subsystems of the nervous system?

The Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

What does the Central Nervous System consist of?

The brain and spinal cord.

What components make up the Peripheral Nervous System?

Cranial nerves, spinal nerves, and associated ganglia.

What are the two functional components of the nervous system?

Sensory (Afferent) component and Motor (Efferent) component.

What are the two main types of cells in nervous tissue?

Neurons and supporting cells (neuroglia).

What is the structural and functional unit of the nervous system?

The neuron.

What are the main parts of a neuron?

Cell body (soma), axon, and dendrites.

What is the role of the cell body (soma) in a neuron?

It contains the nucleus and organelles necessary for the neuron's function.

What are Nissl bodies?

Clumps of basophilic material in the cytoplasm, associated with rough endoplasmic reticulum and polyribosomes.

What is the function of the axon?

To transmit impulses away from the cell body to other neurons or effectors.

What are dendrites and their function?

Dendrites are branched processes that receive signals from other neurons.

What is the difference between multipolar, bipolar, and unipolar neurons?

Multipolar neurons have multiple dendrites and one axon; bipolar neurons have one dendrite and one axon; unipolar neurons have a single T-shaped process.

What is the function of astrocytes?

Astrocytes provide structural support, maintain the blood-brain barrier, and regulate the chemical environment around neurons.

What is the role of oligodendrocytes?

Oligodendrocytes are responsible for the formation of the myelin sheath in the Central Nervous System.

What is the difference between anterograde and retrograde transport in neurons?

Anterograde transport moves materials from the soma to the axon terminals, while retrograde transport moves materials from the axon terminals back to the soma.

What is the function of microtubules in neurons?

Microtubules provide a stationary track for the transport of organelles and materials within the neuron.

What are the two types of axonal transport?

Fast transport and slow transport.

What are the main types of neuroglia in the Central Nervous System?

Astrocytes, oligodendrocytes, microglia, and ependymal cells.

What are the functions of microglia?

Microglia act as the immune cells of the Central Nervous System, providing defense against pathogens and clearing debris.

What is the purpose of the myelin sheath?

The myelin sheath insulates axons and increases the speed of impulse conduction.

What are satellite cells?

Satellite cells are supporting cells in the Peripheral Nervous System that surround neuron cell bodies in ganglia.

What is the significance of dendritic spines?

Dendritic spines are synaptic sites that can diminish with age and poor nutrition.

What is the role of neurotransmitters in neurons?

Neurotransmitters are released by neurons to communicate with other neurons or target cells.

What types of neurons are classified by function?

Motor neurons (efferent), sensory neurons (afferent), and interneurons.

What is the function of the ependymal cells?

Ependymal cells line the ventricles of the brain and the central canal of the spinal cord, producing and circulating cerebrospinal fluid.

What is the blood-brain barrier?

The blood-brain barrier is a selective permeability barrier that protects the brain from harmful substances while allowing necessary nutrients to pass.

What are microglial cells?

The smallest and rarest glial cells in both gray and white matter, involved in phagocytosis and cytokine secretion.

What is the primary role of ependymal cells?

To form the epithelium-like lining of the ventricles of the brain and spinal cord.

What are ependymocytes?

Cuboidal to columnar cells that line the ventricles of the brain and central canal of the spinal cord, aiding in circulation and absorption of cerebrospinal fluid (CSF).

What are tanycytes?

Cells that line the floor of the 3rd ventricle, involved in the transport of CSF to the hypophyseal-portal system.

What is the function of choroidal epithelial cells?

To cover the surfaces of choroidal plexuses and produce cerebrospinal fluid (CSF).

What are Schwann cells?

Flattened cells that form myelinated and non-myelinated coverings over axons and aid in axon regrowth.

What is the Node of Ranvier?

The area where two adjacent Schwann cells terminate, exposing the plasma membrane of the axon.

What is myelination in the CNS?

Occurs by the growth of oligodendrocyte processes wrapping around axons, allowing a single oligodendrocyte to myelinate multiple axons.

What are synapses?

Specialized intercellular junctions that transmit stimuli from a presynaptic cell to a postsynaptic cell.

What are the types of synaptic contact?

Axodendritic, axoaxonic, axosomatic, and dendrodendritic.

What are ganglia?

Clusters of neuron cell bodies found outside the CNS, surrounded by satellite cells.

What is the endoneurium?

The innermost layer of connective tissue that surrounds individual nerve fibers.

What is the perineurium?

The middle layer of connective tissue that surrounds each bundle of nerve fibers (fascicle).

What is the epineurium?

The outermost layer of connective tissue that surrounds groups of fascicles.

What are mechanoreceptors?

Sensory receptors that respond to mechanical deformation.

What are nociceptors?

Sensory receptors that respond to damage to tissues, signaling pain.

What is the function of thermoreceptors?

To detect changes in temperature.

What are electromagnetic receptors?

Receptors such as rods and cones in the retina that are sensitive to changes in light intensity and wavelength.

What are free nerve endings?

Non-encapsulated mechanoreceptors found in skin, cornea, and other tissues that respond to pain, touch, and pressure.

What is the structure of Meissner's corpuscle?

An encapsulated mechanoreceptor located in the dermal papillae of skin, responsible for touch and two-point tactile discrimination.

What is the role of Pacinian corpuscles?

Encapsulated mechanoreceptors that respond to vibration and pressure, found in various tissues.

What is gray matter composed of?

Aggregates of neuronal cell bodies, dendrites, unmyelinated axons, and neuroglial cells.

What is white matter composed of?

Mostly myelinated nerve fibers, found deep in the cerebrum and cerebellum.

What are nuclei in the context of the spinal cord?

Aggregates of neuron cell bodies embedded in gray matter.

What is neuropil?

A meshwork of axonal, dendritic, and glial processes associated with gray matter.

What are the six layers of the cerebral cortex?

Molecular layer, external granular layer, external pyramidal layer, internal granular layer, internal pyramidal layer, and multiform layer.

What is the function of the cerebellar cortex?

Balance, muscle tone, and coordination of skeletal muscle.

What are the three layers of the cerebellar cortex?

Molecular layer, Purkinje cell layer, and Granular layer.

What type of cells are found in the molecular layer of the cerebellar cortex?

Stellate cells, dendrites of Purkinje cells, basket cells, and unmyelinated axons of the granular layer.

What characterizes Purkinje cells?

They are large, flask-shaped cells with numerous dendrites that branch throughout the molecular layer.

What is the role of the choroid plexus?

It produces cerebrospinal fluid (CSF) and is involved in the metabolic activity of the brain.

What happens to a neuron when its cell body is injured?

Degeneration of the entire neuron occurs.

What is Wallerian degeneration?

The process where an axon becomes swollen, breaks into fragments, and is digested by Schwann cells and macrophages after injury.

What is chromatolysis?

The characteristic change in a neuron where Nissl bodies become fine and granular after injury.

What is the significance of Schwann cells in nerve injury?

They initiate the removal of myelin debris and proliferate to form bands that guide regrowth of axons.

What is the clinical significance of Hirschsprung's disease?

It is a congenital abnormality resulting in absent peristalsis in the bowel due to the absence of ganglion cells.

What is multiple sclerosis?

A progressive disease characterized by demyelination in the brain and spinal cord, leading to axonal injury.

What is Guillain-Barre Syndrome?

An acute inflammatory demyelinating polyneuropathy characterized by symmetrical weakness and loss of tendon reflexes.

What are the hallmark features of Alzheimer's disease?

Progressive loss of cognitive function associated with neuritic plaques and neurofibrillary tangles in the brain.

What causes Parkinson's disease?

Loss of dopamine-secreting cells in the substantia nigra, leading to neuronal loss and depigmentation.

What is myasthenia gravis?

An autoimmune disorder where autoantibodies induce acetylcholine receptor deficiency at the motor end plate.

What are Betz cells?

The largest pyramidal cells found in the brain, located in the motor cortex.

What is gliosis?

The hyperplasia and hypertrophy of astrocytes in response to injury in the nervous system.

What is the role of astrocytes in the CNS?

They support neurons, maintain the blood-brain barrier, and respond to injury.

What is the dura mater?

The outermost layer of the meninges, a strong and thick layer of dense connective tissue.

What is the arachnoid mater?

The middle layer of the meninges, composed of fibroblasts and collagen fibers.

What is the pia mater?

The innermost layer of the meninges, highly vascular and in close contact with the brain and spinal cord.

What is the role of macrophages in nerve injury?

They remove debris after nerve injury and facilitate the healing process.

What is the significance of neuroglial cells?

They support and protect neurons, and play a role in the response to injury.

What is the function of the granular layer in the cerebellar cortex?

It contains closely packed small granule cells and glomeruli where synapses occur.

What is synaptic stripping?

The withdrawal of synaptic terminals from the surface of an injured cell body.

What is the purpose of the bands of Bungner?

They bridge a newly formed scar and direct the growth of new nerve processes after injury.