Chapter 2: Neurons and Glia

Transcription

The process whereby the genes encoded by the genomic DNA are converted to messenger RNA (mRNA)

• occurs in the cellular nucleus

Transcription is the process of converting the genetic template in DNA to messenger RNA.

True or False

True

Neurons are similar to other cells

Neuron cells also have

• Organelles

• Cell membranes

• Cytoplasm

• Genetic material

• Basic functions like metabolism, protein synthesis

What do all cells including neurons derive from?

Stem Cells and Precursor cells

Stem cells

cells that are able to produce cells identical to themselves (self-renew) and may produce daughter cells that differentiate into a more mature cell type

During development

• Each cell starts as an egg that has been fertilized

• then divides and forms a group of identical embryonic stem cells

• form an inner mass of cells in a developing zygote that are totipotent or capable of forming any type of cell in the human body

Neural Stem cells

cellular source of the central nervous system (CNS) and peripheral nervous system (PNS).

Neural Restricted Progenitors

NRP

can differentiate into a limited range of neuron types

Totipotent

Embryonic stem cells form an inner mass of cells in a developing zygote

• capable of forming any type of cell in the human body

• Early-stage embryo

How important are neurons for normal human functioning?

They control most of our major functions, including regulating systems that are integral to life like heart rate and respiration

also provide a means for us to experience our world through sensory systems (somatosensory and special senses) and allow us to move through and manipulate our environment through motor systems

Neurons are polarized

meaning that the different ends of a neuron are specialized to perform certain functions. The functional poles of a neuron include the dendritic trees and axons.

Soma

The cell body

• generally lies between the dendrites and the axon and contains the nucleus and all the major cell organelles

• functions as the organizing center for the neuron

Dendrites

are the receiving end of a neuron

• They receive messages from other neurons on specialized structures called dendritic spines.

Axon

Each neuron has one, and only one

the sending end of the neurons and the site of action potential propagation

• may extend for long distances, making neurons the largest cells in the body

• may be myelinated, which speeds up action potential propagation

Cytoskeleton

The unique shape of neurons is provided for by the neuronal..

Neurons need to generate significant amounts of cellular energy

so they have many mitochondria

Nucleus

Located in the soma, contains the cell’s DNA,
involved in gene expression

Myelin Sheath

A fatty, insulating layer that wraps around the
axon

Node of Ranvier

Gaps in myelin sheath that allow for rapid,
saltatory conduction of action potentials

Axon terminal

Transmits signals to other neurons or the target
cells, contain synaptic vesicles that store
neurotransmitters

Synapses

Essential for the transmission of neuronal
impulses from one neuron to the next

Difference between Grey matter and White Matter

Grey Matter→unmyelinated

White Matter→ myelinated

Specialized neuron functions

• Detect environment
  ● Relay neural impulses
  ● Process neural
  information
  ● Execute response

Unipolar Neuron

Single elongated process, with the cell body located off to the side

Bipolar Neuron

Two processes separated by the cell body

• often situated within the special senses (seeing, hearing, balance, olfaction, taste), where a one-to-one correlation with incoming sensory stimuli is needed

• ex: are located in the retina, where they transfer information coming from the light-sensing rods and cones to the neurons that make up the optic nerve

Multipolar Neuron

Have more than two processes, a single axon, and multiple dendrites

• They are the most numerous type of neuron shape and many neuron subtypes

There are three types of cytoskeleton scaffolds:

microfilaments, intermediate filaments, and microtubules

Microfilaments

the smallest type of cytoskeletal elements

• 6 nanometers (nm) in diameter

• composed of polymerized filaments of the protein, actin

• function both in maintaining structures and in transporting cellular components with the cooperation of myosins

Intermediate Filaments

• 10 nm in diameter, but these filaments may be composed of different proteins.

• referred to as neurofilaments, of which there are several types (e.g., neurofilament light, medium, and heavy chains, internexins, peripherin

• proteins are specific for the type of cell where they are expressed

• only known function is to maintain structure

Microtubules

• largest cytoskeletal element, having a diameter of about 25 nm

• spiral-shaped polymers of the dimeric protein, tubulin

• are found in the shafts of axons and dendrites, where they function both in maintaining structure and in the transport of cellular components

• second function, it is important to note that microtubules are directional. They have a plus (+) end, where tubulin monomers are preferentially added during polymerization, and a minus (−) end, where tubulin monomers are preferentially removed during depolymerization.

Glia