Lec 3-Histophysiology of the Nervous System

Question 1

How are neuroglia functionally defined in the nervous system?

Answer 1

Neuroglia are functionally defined as homeostasis-preserving and defensive cells of the nervous system.

Question 2

What are the two distinct types of astrocytes found in the CNS, and where are they primarily located?

Answer 2

There are two primary types of astrocytes in the CNS: fibrous astrocytes found in white matter and protoplasmic astrocytes found in grey matter.

Question 3

What specialized astrocytes primarily present during development?

Answer 3

Radial glial cells are primarily present in the CNS during development.

Question 4

Functions of Astrocytes (7)

Answer 4

1)Provide structural support to neurons and act as a physical scaffold for neuron growth.

2) Form glial scars in damaged neural tissue and support axon regeneration during repair processes.

3) Act as glucose detectors and can speed up gastric emptying when glucose levels are low.

4) Regulation of synapses and participate in neurotransmitter uptake and release at synapses (e.g., glutamate, ATP, GABA, serotonin).

5) Regulate sodium (Na+) and potassium (K+) ion concentrations in the extracellular space.

6) Modulate synaptic transmission through rapid morphological changes that alter synaptic properties.

7) Promote the myelinating activity of oligodendroglia, often in response to ATP released by neurons,

Question 5

Potential consequences and associations related to astrocyte function:

Answer 5

1) Failures of ion regulation can lead to excess of K+, common cause of
epileptic seizures
2) Astrocytomas are tumors that originate from unchecked astrocytic growth.
3) Both astrocytosis (scar formation) and astrocytomas are involved in many neurological disorders,
4) Many neurodevelopment disorders (autism, schizophrenia)

Question 6

What is the primary function of oligodendrocytes?

Answer 6

Create and maintain myelin sheaths around axons.

Question 7

Where are internodes typically found in relation to the nodes of Ranvier?

Answer 7

Internodes are segments of axons located between the nodes of Ranvier, and they are wrapped in myelin produced by oligodendrocytes.

Question 8

In which regions of the nervous system are oligodendrocytes found in the highest concentrations?

Answer 8

Oligodendrocytes are most concentrated in white matter regions of the nervous system.

Question 9

Are oligodendrocytes found in grey matter, and if so, what is their role there?

Answer 9

Oligodendrocytes are also found in grey matter, but they do not typically produce myelin in this region. Instead, they may serve as satellite cells unattached to neurons.

Question 10

What other roles do Oligodendrocytes have?

Answer 10

1) regulating extracellular fluid,
2) May promote new myelin after injury

Question 11

What happens when oligodendrocytes are destroyed or their activity is interfered with?

Answer 11

Leads to the demyelination of white matter in the nervous system.

Question 12

What is the most common pathology associated with demyelination of white matter?

Answer 12

The most common pathology associated with white matter demyelination is multiple sclerosis

Question 13

What is a notable characteristic of microglia?

Answer 13

Microglia are extremely plastic, meaning they can change their shape and function in response to various stimuli and conditions

Question 14

What is the primary role of microglia in the nervous system?

Answer 14

Microglia serve as the primary immune cells of the nervous system.

Question 15

What role do microglia play in synaptic pruning, and when does this occur?

Answer 15

Microglia are involved in synaptic pruning, a process that occurs during both development and later stages of life. They help refine and eliminate excess or unnecessary synapses in the nervous system.

Question 16

How do microglia function as phagocytes?

Answer 16

Microglia can surround and engulf various materials, serving as phagocytes. In a non-inflamed state, they clear debris and dead cells.

Question 17

How do microglia contribute to the immune response in the CNS?

Answer 17

Microglia can activate T-cells, a type of immune cell, to initiate further immune responses in the central nervous system.

Question 18

Question: What do microglia do in an inflamed state, and what do they attack?

Answer 18

In an inflamed state, microglia actively attack bacteria, viruses, and other pathogens to protect the nervous system

Question 19

What is the primary function of ependymal cells in the central nervous system?

Answer 19

Ependymal cells line the walls of ventricles and the central canal and are responsible for circulating cerebrospinal fluid (CSF).

Question 20

How do ependymal cells assist in the circulation of CSF?

Answer 20

Ependymal cells are covered in cilia that wave to help circulate cerebrospinal fluid (CSF) within the central nervous system.

Question 21

What is the role of microvilli on ependymal cells?

Answer 21

Microvilli on ependymal cells are responsible for absorbing cerebrospinal fluid (CSF), contributing to its regulation.

Question 22

Where is cerebrospinal fluid (CSF) produced in the central nervous system?

Answer 22

CSF is primarily manufactured by the choroid plexus, which consists of modified ependymal cells and capillaries.

Question 23

What is the primary function of Schwann cells in the PNS?

Answer 23

Schwann cells myelinate axons in a manner similar to oligodendrocytes, providing insulation and facilitating faster nerve impulse conduction.

Question 24

How do Schwann cells differ from oligodendrocytes in terms of myelination?

Answer 24

Schwann cells myelinate only one axon each, while oligodendrocytes can myelinate multiple axons simultaneously.

Question 25

Components of Neurons

Answer 25

1) Cell body
2) Membrane
3) Dendrites
4) Axons

Question 26

What is the primary function of dendrites in a neuron?

Answer 26

Dendrites receive inputs from other neurons through synapses and transmit these signals toward the neuron’s cell body (soma).

Question 27

How do dendritic spines contribute to dendrite function?

Answer 27

Dendritic spines are small protrusions on dendrites that increase the surface area and provide locations for synapses, allowing for efficient reception of signals from other neurons.

Question 28

What are the primary functions of axons in neurons?

Answer 28

Axons are long processes that transmit action potentials away from the neuron’s cell body (soma) to communicate with other neurons, muscles, or glands.

Question 29

What are the main segments of an axon?

Answer 29

The axon consists of three main segments: the initial segment, the axon proper, and the axon terminals.

Question 30

What is the significance of myelin sheathing on axons?
.

Answer 30

Myelin sheathing, which consists of internodes and nodes of Ranvier, speeds up the conduction of action potentials along the axon

Question 31

How does axonal transport contribute to neuron function?

Answer 31

Axonal transport involves the movement of various materials (anterograde for away from soma and retrograde towards soma) within the axon, ensuring the neuron’s survival and functionality.

Question 32

What are the two types of cells responsible for producing myelin in the nervous system?

Answer 32

Myelin is produced by oligodendrocytes in the Central Nervous System (CNS) and by Schwann cells in the Peripheral Nervous System (PNS).

Question 33

How do oligodendrocyte soma and Schwann cells differ in their relationship to myelin?

Answer 33

Oligodendrocyte soma are located outside the myelin and can contact numerous axons, while Schwann cells incorporate their own soma into the myelin sheath around a single axon.

Question 34

What is the unique characteristic of the outer surfaces of Schwann cells in relation to their myelin sheath?

Answer 34

The outer surfaces of Schwann cells do not contact each other, creating tiny intraperiod gaps that lead from the outer to the inner mesaxon. This feature may allow small molecules to slowly reach the axon membrane, which is otherwise insulated by myelin.

Question 35

Four Types of Neurons

Answer 35

1) Unipolar (axon only)
2) Bipolar (axon & dendrite)
3) Pseudounipolar (start out as bipolar, then fuse the axon and dendrite into one process, then
this splits again later)
4) Multipolar (many dendrites, one axon)

Question 36

Which type of neurons make up the majority of neurons in the CNS?

Answer 36

Multipolar neurons, characterized by having many dendrites and one axon, make up the majority of neurons in the Central Nervous System (CNS).

Question 37

Where are pseudounipolar neurons commonly found? where are they found?

Answer 37

They are commonly found in PNS ganglia.

Question 38

Electrical Synapse

Answer 38

Involve short gap junctions that allow direct exchange of impulses between the cytoplasm of two neurons.

Question 39

Chemical Synapse

Answer 39

Specialized junction that allows one nerve cell to send signals to another nerve cell or target cell using chemical messengers called neurotransmitters.

Question 40

Axoaxonic

Answer 40

An axon terminal of one neuron forms a synapse with another neuron’s axon.

Question 41

What are the three main components of a synapse?

Answer 41

A synapse consists of the presynaptic membrane, the synaptic cleft (the gap), and the postsynaptic membrane.

Question 42

What are the filaments found on synaptic membranes, and what are they called?

Answer 42

Filaments on synaptic membranes are known as the presynaptic density and postsynaptic density.

Question 43

Where are ligands such as neurotransmitters and neuromodulators typically stored in a neuron?

Answer 43

Ligands are housed in synaptic vesicles located within the axon terminal of a neuron.

Question 44

How is the presynaptic density organized in a synapse?

Answer 44

The presynaptic density is arranged in a docking complex within the axon terminal.

Question 45

What is “kiss and run fusion” in synaptic vesicle release?

Answer 45

The vesicle releases some ligands but retains others before returning to the active docking area after release.

Question 46

What is “collapse fusion” in synaptic vesicle release?

Answer 46

The vesicle empties its contents and is absorbed into the presynaptic membrane. Excess vesicles are captured by clathrin-coated pits and may travel back, likely along microtubules, for recycling.

Question 47

What happens when Ca2+ ions enter the axoplasm during synaptic transmission?

Answer 47

The entry of Ca2+ ions into the axoplasm causes both the docking complex and synaptic vesicle to move.

Question 48

What is a Type II synapse, and what effect does it have on the postsynaptic membrane?

Answer 48

Type II synapses open Cl- ion channels in the postsynaptic membrane, leading to hyperpolarization, which makes it more difficult to open Ca2+ channels and inhibits transmission.

Question 49

How does hyperpolarization affect the postsynaptic membrane?

Answer 49

Hyperpolarization makes the postsynaptic membrane more negatively charged, making it harder to generate an action potential and thus inhibiting the transmission of signals.

Question 50

What characterizes ionotropic receptors?

Answer 50

Ionotropic receptors are ligand-gated ion channels that allow ions to cross the postsynaptic membrane when their gates open upon binding of neurotransmitters.

Question 51

What is the direct outcome of ionotropic receptor activation?

Answer 51

Activation of ionotropic receptors leads to direct and rapid effects on the postsynaptic cell.

Question 52

What are the ligands that activate ionotropic receptors typically called?

Answer 52

The ligands that activate ionotropic receptors are known as neurotransmitters.

Question 53

What characterizes metabotropic receptors?

Answer 53

Metabotropic receptors are receptor molecules that are triggered by ligands to interact with various protein complexes, modulating the metabolic activity of the postsynaptic cell.

Question 54

What is the nature of the effects produced by metabotropic receptors?

Answer 54

Activation of metabotropic receptors leads to indirect and slower effects on the postsynaptic cell.

Question 55

What are the ligands that activate metabotropic receptors typically called?

Answer 55

The ligands that activate metabotropic receptors are known as neuromodulators or neurohormones.