lecture The Nervous System: Neurons and Synapses

Flashcards covering the structure, function, and supporting cells of the nervous system, including neurotransmission and clinical correlations, based on Dr. R. Ahangari's lecture notes.

What are the two main cell types of nervous tissue?

Neurons and Neuroglial cells (support cells)

What is the primary function of neurons?

To transmit electrical signals

What are the key characteristics of neurons regarding their lifespan and division ability?

They have longevity (can live and function for a lifetime) and generally do not divide (fetal neurons lose ability to undergo mitosis).

What are Nissl bodies and where are they found within a neuron?

Nissl bodies are rough Endoplasmic Reticulum (rER) and are found in the cell body and the basal parts of dendrites, but not in the axon.

Which part of a neuron transmits impulses away from the cell body?

The axon

What is the initial segment of an axon known for?

It is the most excitable site, where the action potential originates.

What is the function of dendrites?

They increase the neuron's receptive area and transmit impulses towards the neuron.

What are the two types of supporting cells found in the Peripheral Nervous System (PNS) and their main functions?

Schwann cells (form myelin sheaths around peripheral axons) and Satellite cells (support neuron cell bodies within ganglia of the PNS).

Name the four types of neuroglial cells in the Central Nervous System (CNS) and their primary functions.

Oligodendrocytes (form myelin sheaths), Microglia (phagocytose foreign/degenerated material), Astrocytes (regulate external environment), and Ependymal cells (line ventricles and central canal).

What is a key difference between oligodendrocytes and Schwann cells regarding myelination?

One oligodendrocyte can myelinate many fibers (axons) in the CNS, whereas a Schwann cell forms a myelin sheath around only one axon in the PNS.

What happens to microglia in the event of inflammation or degeneration in the CNS?

They proliferate and become active and phagocytic.

What are two critical functions of astrocytes related to the blood-brain barrier and synaptic contacts?

Astrocytes induce the formation of the blood-brain barrier and cover synaptic contacts to insulate axon terminals from influencing neighboring neurons.

How do astrocytes help maintain a proper ionic environment for neurons?

They absorb excess K+ from the extracellular fluid, which diffuses out of neurons during nerve impulse production.

What is 'gliosis' and what typically causes it?

Gliosis is hyperplasia and hypertrophy of astrocytes that occurs in reaction to CNS injury.

What is Multiple Sclerosis (MS) characterized by?

Demyelination in the CNS, usually starting with the optic nerve, spinal cord, and cerebellum, leading to axonal degeneration.

Which cells form the myelin sheaths in the CNS and what color does this tissue appear?

Oligodendrocytes form myelin sheaths in the CNS, and areas with high concentrations of myelinated axons form the white matter, appearing white.

Why is axon regeneration more limited in the CNS compared to the PNS?

It is limited due to the absence of a continuous neurilemma and the presence of inhibitory molecules produced by oligodendrocytes and astrocytes in the injured CNS.

Name two examples of neurotrophins that promote neuron growth in a developing fetal brain.

Nerve growth factor (NGF) and Brain-derived neurotrophic factor (BDNF).

What are the components that form the blood-brain barrier (BBB)?

The endothelial cells of the cerebral capillaries and the choroid plexus epithelium.

Why can L-DOPA be used to treat Parkinson's disease, but dopamine cannot?

L-DOPA, the precursor to dopamine, can cross the blood-brain barrier, whereas dopamine itself cannot.

How do protein and cholesterol levels in CSF compare to blood concentrations?

Protein and cholesterol are excluded from the CSF due to their large molecular size, resulting in CSF levels being lower than blood.

What are synapses?

Synapses are the sites where two neurons come into close proximity, allowing them to communicate.

What are the two main types of synapses?

Chemical synapses (most common) and Electrical synapses.

In a chemical synapse, where are neurotransmitters stored before release?

They are stored in vesicles within the presynaptic cytoplasm.

Name three common neurotransmitters.

Acetylcholine (Ach), Norepinephrine, Dopamine, Glycine, Serotonin, GABA, Glutamic acid (any three).

What ionic event directly causes the release of neurotransmitters into the synaptic cleft?

An influx of Ca++ ions into the presynaptic part causes synaptic vesicles to fuse with the presynaptic membrane.

What is generally the short-term fate of neurotransmitters after they have acted on the postsynaptic membrane?

Neurotransmitters are either destructed in the synaptic cleft (e.g., Ach by Acetylcholinesterase) or reabsorbed by the presynaptic part (e.g., Catecholamines).

What is the structural basis of electrical synapses?

Electrical synapses are Gap junctions, formed by specialized channels called Connexons, which allow direct flow of ionic current between cells.

What is a main function of serotonin in the central nervous system?

It plays an important role in the regulation of anger, aggression, body temperature, mood, sleep, vomiting, sexuality, and appetite.

In the brain, what are two key functions of dopamine?

Dopamine functions in the pleasure system of the brain and its insufficient biosynthesis can cause Parkinson's disease.

Beyond its role as a neurotransmitter, what is norepinephrine's function as a stress hormone?

As a stress hormone, it underlies the fight-or-flight response, directly increasing heart rate, triggering glucose release, and increasing skeletal muscle readiness.

What is the main excitatory amino acid neurotransmitter in the CNS?

Glutamate

What are the two most common inhibitory neurotransmitters in the nervous system?

GABA (gamma-aminobutyric acid) and Glycine

What are some physiological processes Neuropeptide Y (NPY) is associated with in the brain?

Regulation of energy balance, memory and learning, and epilepsy.

Which gaseous signaling molecule, synthesized from arginine and oxygen, plays a key role in blood vessel dilation?

Nitric oxide (NO)