Brein en Cognitie
WEEK 1
Cells of the nervous system
Two views of a neuron
- Staining techniques, a technique to make neurons visible, give color to neurons. The
first person to make this technique available was Golgi with his nerve net theory. His
original idea was that there are branches that are intertwined and there is some sort
of substance going between it for communication. Cajal’s neuron theory used Golgi’s
theory, he came up with the conclusion that neurons are actually separate and not
connected with tubes.
Structure and function of a neuron
The upper part of a neuron is called dendrites. Information gets picked up in this part of the
neuron, this is information that a neuron gets from other neurons. Under the upper body is a
cell body, this is the part of the neuron where a decision is being made. Then a signal is being
sent to the axon.
Neurons are the basis of information processing
- A behavior or cognitive function cannot be assigned to a single neuron or a single
neuron type.
- Neural networks are groups of neurons that work together to produce a function.
- Most of our neurons are with us for life, but their connectivity with other neurons
changes as a function of experience. The connectivity reflects what we have learned
or experienced.
Structure and function – morphological details
- Dendrite, the dendritic area is increased by dendritic spines that are the points of
contact with other neurons. The dendritic spine has a synapse with a connection to
the end foot of an axon of another neuron
- Cell body, a dendrite is connected to the cell body, a cell body has a nucleus, DNA
etc. then there is an axon hillock, the part where a decision is being taken. Dendrites
integrate all the information and when there is enough information it is being taken
to the cell body. In the axon hillock the decision will be made, this hillock may branch
out in one or more axon collaterals.
- The end of the axon collaterals contains terminal buttons or end foots which
functionally connects (but does not touch) a dendritic spine of another cell.
Three functions/classes of neurons
- Sensory neurons, the neurons closest to the outside world. Bring information to the
central nervous system. There are bipolar neurons (retina) they are activated by light,
the upper part of this neuron is the dendrite. Another sensory neuron is a neuron of
which the dendrite is part of our skin, touch information of nerve endings can be
send to our cell bodies in our spinal cord, when activated information gets send on in
the axon.
, - Interneurons, associate sensory and motor activity in the central nervous system.
Many different types of interneurons. They are not in direct contact with the outside
world and also don’t active muscles.
- Motor neurons, send signals from the brain and spinal cord to muscles. Motor
neurons drive our muscles.
Excitation and inhibition
Sending neurons either excite or inhibit other neurons. Receiving neurons sum the excitatory
and the inhibitory input.
Glial cells
- Glial cells are the nervous system’s support cells.
- Glial cells provide support, nutrients, and protection to the neurons.
- There are five major types of glia, each with its own characteristic structure and
function.
o Ependymal cells, look like a small ovoid. Are responsible for the production of
CSF.
o Astrocyte, are stare shaped, contributes to neuronal nutrition, support, and
repair; contributes to forming blood-brain barrier and to healing scarring after
injury.
o Microglial cell, small, derived from blood, defensive function to remove dead
tissue and protect from invaders.
o Oligodendroglia cell, forms myelin around CNS axons in brain and spinal cord.
Myelination results in a faster transmission between axons.
o Schwann cell, wraps around peripheral nerves to form myelin.
Astrocytes
They help to tighten up the junctions of a blood vessel. This prevents large molecules to
enter the brain. This makes it also difficult for medicine to cross the blood-brain barrier.
Astrocytes are able to increase the amount of blood that run through vessels. They trigger
the blood vessels to dilate allowing greater oxygen- and glucose carrying blood flow.
Microglia
Originate in the blood as an offshoot of the immune system. Identify and attack foreign
tissue (phagocytosis; the process, they are eating up dead neurons). Microglia also provide
growth factors (chemicals that help the tissue to repair itself) that aid in repair.
Glial cells, disease and neuron repair
- Glial cells play a central role in some diseases such as multiple sclerosis (MS).
- Glial cells aid in peripheral nervous system repair such as after a cut of the axons. 1)
when a peripheral axon is cut, the axon dies 2) Schwann cells first shrink and then
divide, forming glial cells along the axon’s former path 3) the neuron sends out axon
sprouts, one of which finds the Schwann-cell path and becomes a new axon 4)
Schwann cells envelop the new axon, forming new myelin.
- No regrowth and repair in the central nervous system, an axon can only regrow in
this way in a peripheral nervous system.
,Internal structure of the cell
Quick overview
Cell membrane: membrane surrounding the cell, it separates the cell from its surroundings.
Forms the boundary, substances can’t just leave or enter a cell.
Intracellular fluid: most of this fluid is water. Fluid in which the cell’s internal structures are
suspended.
Nuclear membrane: membrane surrounding the nucleus
Nucleus: structure containing the chromosomes and genes
Endoplasmic reticulum: folded layers of membrane where proteins are assembled.
Golgi body: membranous structure that packages protein molecules for transport.
Tubule: give the cell its shape, tiny tube that transports molecules.
Microfilaments: little brother of the tubule, threadlike fibers making up much of the cell’s
‘skeleton’.
Mitochondrion: structure that gathers, stores, and releases energy.
Lysosomes: sacs containing enzymes that break down wastes.
Cell membrane: barrier and gatekeeper
Phospholipid bilayer, the cell membrane is a bilayer that separates extracellular fluid
(outside the cell) from intracellular fluid (inside the cell). Inner part is hydrophobic, they
have no polar regions and makes it impossible for water to pass. Hydrophilic has polar
regions (- and +) and does attract water. The phosphate groups will bind to water. Fatty acid
tails have no binding sites for water.
The nucleus and protein synthesis
Each chromosome is a double-stranded molecule of DNA. DNA has ATGC, Adenine binds
with Thymine. Guanine binds with Cytosine. 1) DNA uncoils to expose a gene, a sequence of
nucleotide bases that encodes a protein 2) one strand of the gene serves as a template for
transcribing a molecule of mRNA 3) the mRNA leaves the nucleus and comes in contact with
ribosomes in the endoplasmic reticulum 4) as a ribosome moves along the mRNA, it
translates the bases into a specific amino acid chain, which forms the protein.
The endoplasmic reticulum and protein manufacture
Thymine becomes U in the mRNA due to the transcription. The combination of letters forms
a codon, and this can be translated to an amino acid. A chain of amino acids is called a
polypeptide chain. Note: the handbook mentions UGG instead of CGG. UGG encodes the
amino acid tryptophan (Trp) instead of arginine (Arg). UUU = Phe, GGC= Gly, UCA=Ser.
Amino acid structure: the chemical composition of the R group distinguishes one amino acid
from another. The amino group and carboxyl group are the same for an amino acid. These
two molecules are what makes it a polypeptide chain. A chain of amino acids forms a
protein. There are only 20 amino acids.
DNA -> mRNA -> protein
Proteins: the cell’s product
Primary structure: amino acid chains…
Secondary structure: … form pleated sheets or helices. …
, Tertiary structure: … Sheets and helices fold to form a protein. …
Quaternary structure: … A number of proteins combine to form a more complex protein.
Golgi bodies and microtubules: protein packaging and shipment
1) Proteins formed in the ER enter the Golgi bodies, where they are wrapped in a
membrane and given a shipping address.
2) Each protein package is attached to a motor molecule and moves along a
microtubule to its destination
3) A protein may be incorporated into the membrane, …
4) …remain within the cell to act as an enzyme, …
5) …or be excreted from the cell by exocytosis.
Crossing the cell membrane: channels, gates, and pumps
- A protein’s function depends on its shape.
- A protein can change shape as a function of other chemicals, temperature, electrical
charge, …
- When the key fits in the lock, the door opens … an example: protein has a receptor
site for glucose, protein changes shape when glucose docks with the receptor.
a) Channel, ions can cross a cell membrane through the appropriately shaped channel.
b) Gated channel, a gated channel changes shape to allow the passage of substances
when gates are open and to prevent passage when one or both gates are closed.
c) Pump, a pump transporter changes shape to carry substances across a cell
membrane. Extracellular fluid comes in, intracellular fluid goes out.
Genes cells and behavior
Your genotype (genetic makeup) influences your phenotype (physical and behavioral
characteristics. The environment (i.e., experience) also influences your phenotype. The
discussion of the relative importance of the genotype and the environment is called the
nature-versus-nurture debate. Mendelian genetics studies how genes influence our
phenotype. Epigenetics studies how the environment influences gene expression.
Mendelian genetics and the genetic code
- Humans have 22+1 chromosome pairs. The last pair determines your sex, double x is
female, and x and y are male.
- Alleles are copies of a gene and their identity determines whether they are
homozygous or heterozygous.
- Wild-type allele versus a mutation, wild-type is most common among a population
and mutation is a rare type of a gene.
Dominant and recessive alleles
- if both alleles in a gene pair are heterozygous, they encode somewhat different
proteins.
- A member of a gene pair that is routinely expressed (whether it is affecting your
phenotype) as a trait is called a dominant allele; an unexpressed allele is recessive.
