Introduction to NeurobiologyDauphin Island Sea LabJuly 20-August 8, 2015

Animal cells and their components 1

http://micro.magnet.fsu.edu/cells/animalcell.htmlNervous systems are made up of neurons and glia. Both have the same components as other cells including intracellular structures called organelles.Nucleus: The nucleus has two major functions: it stores the cell's hereditary material, or DNA, and it coordinates growth, intermediary metabolism, protein synthesis, and reproduction (cell division).Centrioles: Centrioles are self-replicating organelles made up of nine bundles of microtubules and are found only in animal cells. They appear to help in organizing cell division, but aren't essential to the process.Endoplasmic Reticulum: The endoplasmic reticulum is a network of sacs that manufactures, processes, and transports chemical compounds for use inside and outside of the cell. It is connected to the double-layered nuclear envelope, providing a connection between the nucleus and the cytoplasm.

Animal cells and their components 2

Endosomes and Endocytosis: Endosomes are membrane-bound vesicles, formed via processes collectively known as endocytosis, and are found in the cytoplasm of virtually every animal cell. It involves the invagination (folding inward) of a cell's plasma membrane to surround macromolecules or other matter in the extracellular fluid.

Ribosomes: All living cells contain ribosomes which create proteins from amino acids through the action of mRNA and tRNA. The amino acids are attached to transfer RNA (tRNA) molecules, which enter one part of the ribosome and bind to the messenger RNA sequence. The attached amino acids are then joined together by another part of the ribosome. The ribosome moves along the mRNA, "reading" its sequence and producing a chain of amino acids.

Golgi Apparatus: The Golgi apparatus modifies proteins and fats synthesized in the endoplasmic reticulum and prepares them for transport within the cell or exocytosis.

Intermediate Filaments: These are fibrous proteins that play roles as both structural and functional elements of the cytoskeleton. They function as tension-bearing elements to help maintain cell shape and rigidity.

Animal cells and their components 3

Microfilaments: Rods made of globular proteins called actin (6 nm in diameter). They are primarily structural in function and are an important component of the cytoskeleton.

Microtubules: Straight, hollow cylinders (25nm diameter) found throughout the cytoplasm of all eukaryotic cells and their functions range from transport to structural support.

Lysosomes: Their main function is digestion. The lysosomes break down cellular waste products and debris from outside the cell into simple compounds, which are transferred to the cytoplasm as new cell-building materials.

Cilia and Flagella: Cilia and flagella are essential for the locomotion of some types of individual organisms. In multicellular organisms, cilia function to move fluid or materials past an immobile cell as well as moving a cell or group of cells.

Mitochondria: Mitochondria are oblong shaped organelles that are the main power generators, converting oxygen and nutrients into energy.

The cell membrane

Plasma Membrane: All living cells have a plasma membrane that encloses their contents. It protects the contents, and also regulates the passage of molecules in and out of the cells. The plasma membrane is a lipid bilayer, with the nonpolar hydrophobic tails pointing toward the inside of the membrane and the polar hydrophilic heads forming the inner and outer surfaces of the membrane.

The membrane is very selective about what it allows to pass through; this characteristic is referred to as "selective permeability." For example, it allows oxygen and nutrients to enter the cell while keeping toxins and waste products out. Only small, uncharged polar molecules can pass freely across the membrane. Other molecules need the help of membrane proteins to get across. Proteins and cholesterol molecules are scattered throughout the flexible phospholipid membrane.

The cell membrane

There are a variety of membrane proteins that serve various functions: Some proteins attach loosely to the inner or outer surface of the plasma membrane. Integral proteins extend across the membrane, from inside to outside. Proteins are scattered throughout the flexible matrix of phospholipid molecules, somewhat like icebergs floating in the ocean, and this is termed the fluid mosaic model of the cell membrane.Channel proteins: Proteins that provide passageways through the membranes for certain hydrophilic or water-soluble substances such as polar and charged molecules. No energy is used during transport, hence this type of movement is called facilitated diffusion.Transport proteins: Proteins that spend energy (ATP) to transfer materials across the membrane. When energy is used to provide passageway for materials, the process is called active transport.Adhesion proteins: Proteins that attach cells to neighboring cells or provide anchors for the internal filaments and tubules that give stability to the cell.Receptor proteins: Proteins that initiate specific cell responses once hormones or other trigger molecules bind to them

Back to mitochondria: They are 0.5 to 1.0 um in diameter. They have their own DNA and in humans they are inherited from the mother. They can divide, change shape and ruse with other mitochondria.

Cytoskeleton

The cytoskeleton of cellsis comprised of actin filaments,Intermediate filaments, and microtubules. The cytoskeleton helps to maintain the shape ofcells, but is very dynamic, andcytoskeletal remodeling is the reason that cells can migrate. It isalso critical in neuronal development.

Introduction: Why are cells of the nervous system not something else?

Genes encode proteins. Each human cell has roughly 20-25,000 protein-encoding genes in its nucleus. But each cell uses only a subset of those genes and they turn on and off as the cell progresses through its life. What differentiates one cell type from another is differential gene expression. That is, what genes are expressed, what genes are not expressed and when all of this happens. More of the genome is expressed in the nervous system than in any other organ system of the body.

In addition to the protein-encoding region of the gene, there are regulatory sequences called promoters and enhancers, that are necessary for controlling when and in what cells a gene is transcribed. A promoter is the site where RNA polymerase binds to the DNA to initiate transcription of a gene. An enhancer is a DNA sequence that that controls the efficiency and rate of transcription of a specific promoter.

Other proteins, called transcription factors, bind to the promoter or enhancer regions and interact to activate or repress the transcription of a particular gene.

Transcription factors often directly regulate not just one but often a large number of downstream target genes.

Examples of transcription factors: Microphthalmia (MITF) The microphthalmia transcription factor is active in the ear and pigment forming cells of the eye and skin. Humans heterozygous for a mutation in the gene that encodes MITF are deaf, have small eyes and multi- colored irises, and a white forelock in their hair. This is called Waardenburg syndrome.

Pax 6: This transcription factor is needed for the development of the mammalian eye, nervous system, and pancreas. Homozygous Pax 6 mutant rats and mice lack eyes and a nose. People who are heterozygous for a mutant form of Pax 6 or who lack one copy of the gene have little or no iris (aniridia).

Nervous systems are made up of neurons and glia: there are an estimated 100,000,000,000 neurons in the brain

Clusters of functionally related neurons in the brain form nuclei. Hence the neurons of the lateral geniculate nucleus receive input from retinal ganglion cells. In animals without backbones, these clusters are often clled ganglia.

Examples of the rich variety of nerve cell morphologies found in humans.

Examples of the rich variety of nerve cell morphologies found in humans.

Examples of the rich variety of nerve cell morphologies found in humans.

Glia: There are an estimated 100,000,000,000 neurons in the brain, and there are many times that number of another cell type, glia. Glia are also very complex but for today, there are 3 basic types. Glia have a variety of important functions. They help to form the blood-brain barrier, they serve to provide myelin sheaths around axons that increase the speed of action potential conduction, they play a nutritive role, and they help to recycle neurotransmitters.

Some glia also express neurotransmitter receptors and can respond to transmitters released from neurons. Some glia can also release neurotransmitters and other neuroactive substances themselves that affect the activity of neurons.

Blood brain barrier

This image shows the blood vessels in a human from just above the knees to the head. Blood vessels in the brain are different than in other parts of the body. This was first observed in the mid 1800s by a bacteriologist named Paul Ehrlich and his student, Edwin Goldman.

The ability of substances to move from the vasculature into the brain is controlled by the blood brain barrier. It is the result of tight junctions between neighboring vascular endothelial cells. In addition, the outside of the capillary is surrounded by the end feet of astrocytes. So molecules that move from the blood into the brain have to pass through the endothelial cells and traverse the astrocyte end feet.

Electrical signals

Terms in electrophysiology

Ion: An atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. Examples include Na+, K+, Cl-, and Ca2+.

Current: A flow of electric charge through a medium. For this course, we will often use this in the context of the charge is carried by ions in a solution. Units: amperes

Voltage: the voltage between two points is the total energy required to move a small electric charge along that path. Units: volts

Resistance: The opposition to the passage of an electric current. Units: ohms

Ohm’s Law: V=IRVoltage=current x resistance

Neuronal signals

2.2 Recording passive and active electrical signals in a nerve cell. (Part 1)

2.2 Recording passive and active electrical signals in a nerve cell. (Part 2)

2.4 Electrochemical equilibrium. (Part 1)

Membrane potentials

The equilibrium potential (sometimes called the Nernst potential) can be predicted by a simple equation-the Nernst equation. (Walter Nernst, electrochemist; won the Nobel prize in 1920)

Ex= RT/ZF ln([X]o/[X]i

If z=1 (Na+, K+) then Ex=58 log [X]o/[X]I

• R (Gas Constant) = 8.314472 (J/K·mol)• T (Absolute Temperature) = t °C + 273.15 (°K)• F (Faraday's Constant) = 9.6485309×104 (C/mol)

2.4 Electrochemical equilibrium. (Part 2)

2.5 Membrane potential influences ion fluxes. (Part 1)

2.5 Membrane potential influences ion fluxes. (Part 2)

Box A The Remarkable Giant Nerve Cells of a Squid

2.7 Evidence that the resting potential is determined by K+ concentration gradient. (Part 1)

2.7 Evidence that the resting potential is determined by K+ concentration gradient. (Part 2)

The problem is that in real cells there are several ions in solution, not just one.These include Na+, K+, Cl-, etc. The Nernst equation is not applicable in these cases.

There is an equation that allows us to calculate the resting membrane potential of a neuron.

It’s called the Goldman Hodgkin Katz equation, or GHK for short.

R (Gas Constant) = 8.314472 (J/K·mol)T (Absolute Temperature) = t °C + 273.15 (°K)F (Faraday's Constant) = 9.6485309×104 (C/mol)

Things to discuss:•Permeability•Cl-

•What about Ca2+

2.6 Resting and action potentials entail permeabilities to different ions.

2.8 The role of sodium in the generation of an action potential. (Part 1)

2.8 The role of sodium in the generation of an action potential. (Part 2)

Box B Action Potential Form and Nomenclature

2.3 Ion transporters and channels are responsible for ionic movements across membranes.