Test: Neural Cells - 1 - MCAT MCQ

Norepinephrine is a neurotransmitter that is released by postganglionic neurons of the sympathetic nervous system. These postganglionic neurons are part of the autonomic nervous system, specifically the sympathetic division. They innervate various target organs and tissues throughout the body.

In the case of norepinephrine release, the autonomic neurons innervating the heart are responsible for releasing this neurotransmitter. Norepinephrine plays a role in the sympathetic regulation of heart rate and contractility, among other cardiovascular functions.

Neurotransmitters are chemical messengers that transmit signals between neurons. When GABA is released by a presynaptic neuron, it binds to receptors on the postsynaptic neuron's dendrites. Dendrites are the branch-like structures that extend from the cell body (soma) of a neuron. They receive signals from other neurons and transmit those signals towards the soma.

By binding to GABA receptors on the dendrites, GABA inhibits the activity of the postsynaptic neuron, reducing its excitability. This inhibition helps regulate and balance neuronal activity in the brain and spinal cord.

Option A (Soma) is incorrect because GABA does not directly interact with the soma of the neuron.

Option B (Myelin sheath) is also incorrect because the myelin sheath is a fatty covering that surrounds the axon of a neuron, facilitating the efficient transmission of electrical signals. GABA does not interact with the myelin sheath.

Option C (Axon) is incorrect because GABA primarily acts on the postsynaptic neuron, specifically on the dendrites, rather than the axon.

Therefore, the correct answer is Option D: Dendrites.

Guillain-Barre syndrome (GBS) is an autoimmune disease characterized by the immune system attacking the peripheral nerves. Specifically, it targets the myelin sheath, which is the protective covering around the nerve fibers. In GBS, the immune system mistakenly recognizes gangliosides, which are molecules found on the surface of cells, including Schwann cells.

Schwann cells are responsible for producing the myelin sheath in the peripheral nervous system. They wrap around the nerve fibers, providing insulation and aiding in the conduction of nerve impulses. When Schwann cells are attacked in GBS, the myelin sheath is damaged or destroyed, leading to a slowed or blocked conduction of nerve impulses.

Astrocytes are a type of glial cell that are abundant in the brain and central nervous system (CNS). They play crucial roles in supporting and maintaining the function of neurons. Astrocytes have diverse functions, including providing structural support, regulating the extracellular environment, controlling nutrient supply to neurons, and participating in the formation and maintenance of synapses.

While neurons are highly specialized cells responsible for transmitting and processing information in the brain, they are actually outnumbered by astrocytes. The ratio of astrocytes to neurons in the brain is estimated to be around 1:1 or even higher, indicating the abundance of astrocytes in the brain.

Oligodendrocytes are another type of glial cell in the CNS that produce myelin, which insulates neuronal axons. Ependymal cells are specialized epithelial cells that line the ventricles of the brain and play a role in producing and circulating cerebrospinal fluid.

The choroid plexus is a structure found in the ventricles of the brain that produces cerebrospinal fluid (CSF). It consists of a network of capillaries covered by specialized cells called ependymal cells. These ependymal cells have cilia on their surfaces, which help move the CSF and facilitate its circulation within the ventricles.

Ependymal cells are a type of glial cell that line the ventricles of the brain and the central canal of the spinal cord. They have a role in the production and regulation of CSF, which provides cushioning and nourishment to the central nervous system.

Neurons, oligodendrocytes, and astrocytes are not typically found within the choroid plexus.

Microglia, the resident immune cells of the central nervous system (CNS), originate from the mesoderm during embryonic development. The mesoderm is one of the primary germ layers formed during gastrulation. It gives rise to various structures, including muscle, connective tissue, blood vessels, and certain immune cells.

Microglia develop from myeloid progenitor cells that arise from the yolk sac and subsequently migrate into the developing CNS. Once in the CNS, these progenitor cells differentiate into microglia and take up residence in the brain and spinal cord.

Bacterial meningitis is an infection of the meninges, the protective membranes surrounding the brain and spinal cord. During an infection, microglia, the resident immune cells of the central nervous system (CNS), respond to the presence of bacteria and increase in number as part of the inflammatory response. Microglia act as the first line of defense in the CNS against infections and play a crucial role in immune surveillance and clearance of pathogens.

Option A (Subdural hematoma) is incorrect because a subdural hematoma is a condition where blood collects between the dura mater and the arachnoid mater, usually as a result of head trauma. Microglia are not directly involved in this condition.

Option B (Multiple sclerosis) is incorrect because while microglia are involved in the inflammatory response in multiple sclerosis, an increased number of microglia alone is not specific to this condition.

Option D (Peripheral nerve damage) is incorrect because microglia primarily reside in the central nervous system (CNS) and are less prevalent in the peripheral nervous system (PNS). An increased number of microglia would not be directly indicative of peripheral nerve damage.

Neurons found in the dorsal root ganglion (DRG) are classified as pseudounipolar neurons. Pseudounipolar neurons have a single process that divides into two branches, forming a T-shape. One branch, called the central process, extends centrally towards the spinal cord, while the other branch, called the peripheral process, extends peripherally towards the sensory receptors in the body. The cell body of the pseudounipolar neuron is located in the dorsal root ganglion.

Astrocytes perform a variety of important functions in the central nervous system, but monitoring for pathogens in the interstitial fluid is not typically considered one of their primary roles.

Option A (Structural support) is correct because astrocytes play a crucial role in providing structural support to neurons. They contribute to the formation and maintenance of the blood-brain barrier, which helps regulate the exchange of substances between the bloodstream and the brain.

Option B (Hypoxia buffering) is correct because astrocytes can help buffer and regulate the levels of oxygen in the brain. They contribute to the regulation of cerebral blood flow and oxygen delivery to neurons, ensuring adequate oxygen supply during conditions such as hypoxia.

Option C (Barrier protection) is correct because astrocytes participate in the formation and maintenance of the blood-brain barrier, which serves as a protective barrier between the blood and the brain tissue. This barrier helps regulate the entry of substances into the brain and protects it from potentially harmful molecules or pathogens.

Therefore, the correct answer is Option D: Interstitial fluid monitoring for pathogens. While astrocytes can respond to inflammation and infection in the brain, their primary functions are not focused on actively monitoring the interstitial fluid for pathogens. Other immune cells, such as microglia, play a more direct role in pathogen surveillance in the central nervous system.

A local nerve block is a technique commonly used in medicine and dentistry to provide anesthesia to a specific area of the body. By injecting an anesthetic agent near a nerve or group of nerves, the nerve impulses from the sensory receptors in the target area are temporarily blocked or inhibited. This results in loss of sensation and pain relief in the specific region where the nerve block is applied.