Biological Psychology (UM)
Lecturer: Dennis van ‘t Ent
Lecture 1: 01 nov 2022
Structure and Functions of Cells of the Nervous System
Elements in itself do not mean much for the body, but when they start forming bonds,
resulting in molecules, they start to mean something. Different kinds of bonds are
Ionic bond, relating to an atom or small group of atoms that has an electrical charge
because it has added or lost one or more electrons, electrostatic force
Covalent bond, the interatomic linkage that results from the sharing of an electron
pair between two atoms, the sharing of electrons from molecules
A membrane is the thin layer that forms the outer boundary of a living cell or of an internal
cell compartment, the membrane is composed of lipids, proteins and sugars
This structure is generally referred to as the phospholipid bilayer, a thin polar
membrane made of two layers of lipid molecules
Three types of lipid are phospholipids, glycolipids and sterols, they are fatty or
oily compounds that are essential to many body functions and serve as the building
blocks for all living cells
Protein is a molecule made up of amino acids, proteins are needed for the body to
function properly, the basis of body structures
The central nervous system consists of the parts that are encased by the bones of the skull
and spinal column: the brain and the spinal cord. The peripheral nervous system is found
outside these bones and consists of the nerves and most of the sensory organs.
The central nervous system communicates with the rest of the body through nerves
Nerves are bundles of thousands of individual neurons, all wrapped in a tough,
protective membrane
Information is gathered from the environment by specialized cells of the peripheral
nervous system called sensory neurons
Movements are accomplished by the contraction of muscles, which are controlled
by motor neurons, in between the sensory and the motor neurons are the
interneurons
Most neurons have, in one form or another, the
following four structures or regions: the cell body or the
soma, dendrites, an axon and terminal buttons.
The cell body contains the nucleus and much of
the machinery that provides for the life
processes of the cell
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, Dendrites receive all the messages of the communicating neurons, they function much
like antennas, that are transmitted across the synapse
The axon is a long, slender tube often covered by a myelin sheath, the outer surface
carries information from the cell body to the terminal buttons, this is the action
potential
Terminal buttons secrete chemicals called a neurotransmitters when the action
potential travelling down the axon reaches them, releasing it into the synapse
The cell membrane defines the boundary
of the neuron, it consists of a double layer
of lipid molecules. Embedded in the
membrane are a variety of protein
molecules that have special functions.
The interior of the neuron contains a
matric of strands of protein, this is called
the cytoskeleton and it gives the neuron its
shape. The cytoskeleton is made of three
kinds of protein strands (microtubules),
linked to each other and forming a cohesive mass.
Internal structures of a neuron
Cytoplasm is complex and varies across types of cells, it can be characterized as a
jellylike substance that fills the space outlined by the membrane
The nucleus of the cell is a round or oval structure found in the soma, the
nucleolus and the chromosomes reside inside the nucleus (1)
The nucleus is enclosed by the nuclear membrane, it is responsible for the
production of ribosomes, small structures that are involved in protein synthesis
The chromosomes, which consist of long strands of DNA, contain the organism’s genetic
information. When they are active, portions of the chromosomes (genes) cause production of
another complex molecule, a mRNA, which receives a copy of the information stored.
Proteins are produced in a two-step process. First information from DNA (which cannot leave
the nucleus) is transcribed into a portable form: mRNA, this is called transcription. This
mRNA takes information to the ribosomes for the second step, this is called translation.
Proteins serve as enzymes, which direct the chemical processes of a cell by controlling
chemical reactions, they cause a chemical reaction to take place without being a part of the
final product.
Cells also contain an endomembrane system, a network of internal membranes, comprised of
endoplasmic reticulum, Golgi apparatus and lysosomes
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, The endoplasmic reticulum appears in two forms, rough and smooth, both types
consist of parallel layers of the same membrane that encloses the cell, rough contains
ribosomes, smooth provides channels for the segregation of molecules, it is for
production, storage and transport proteins (2)
Golgi apparatus is a special form of smooth endoplasmic reticulum, it serves as a
packaging agent, it is a post office for packing, neurotransmitter in vesicles (3)
The Golgi apparatus also produces lysosomes, small sacs that contain enzymes that
break down substances no longer needed by the cell, these products are then recycled
or excreted from the cell, waste processing (5)
In addition there is a power plant in the cell, named the mitochondria. These are shaped like
oval beads and are formed from a double membrane. It performs a vital role in the economy
of the cell, the extraction of energy is mainly controlled by enzymes located there.
Cells provide mitochondria with nutrients and mitochondria provide cells with a special
molecule that cells use as their immediate source of energy.
When a gene is active, a copy of the information is
made onto a molecule of messenger RNA. The mRNA
leaves the nucleus and attaches to a ribosome, where
the protein is produced.
mRNA leaves the nucleus through the pores and is
read out by ribosomes (a complex of proteins) to form
a new protein.
Axoplasmic transport shows how kinesin molecules
transport cargo along the cytoskeleton from the soma to the terminal buttons, another protein,
dynein, carries cargo from the terminal buttons to the soma (so other way around)
Retrograde transport from terminal buttons to soma, dynein
Anterograde transport from the cell body or soma to the terminal buttons, kinesin
Different types of glial cells (support cells):
Microglia, the smallest of the glial cells, important for the immunological defense for
example for attacking bacteria, they support the immune system and remove dead cells
Macroglia, larger glial cells, subtypes are the oligodendrocytes, their function is to
support axons and produce the myelin sheath, which insulates most axons from one
another in the central nervous system
Macroglia, another subtype are the Schwann cells, they perform the same function as
the oligodendrocytes but in the peripheral nervous system instead of the CNS
Macroglia, third type are astrocytes, they support structure and solidity, they can
isolate synaptic clefts (contacts between neurons) and they can take out nutrients from
the bloodstream and give it to neurons
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, The difference between the two is that oligodendrocytes can make more myelin sheaths for
multiple axons, whereas the Schwann cells can only make one myelin sheath by wrapping
itself around the axon.
The blood-brain barrier (BBB) refers to the fact that substances from the blood cannot
directly enter the brain because there are no gaps in the blood vessels located in the brain.
Therefore astrocytes place themselves against the blood vessels in the brain, by that they can
extract nutrients from the blood stream to transport to the neurons. So astrocytes are in contact
with blood vessels and neurons.
Bioelectricity is any electrical phenomenon that is actively generated by cells or that is
applied to cells to affect cell phenotype. Membrane potential is caused by a balance between
two forces
Diffusion, due to random motion, particles will move from regions with high
concentration to regions with low concentration
Electrostatics, positively charged particles repel each other and negative charged
particles repel each other and oppositely charged particles attract each other
When neurons are at rest and not involved in communicating with any other neurons, the
membrane potential remains at approximately -70mV, this is called the resting potential.
The axon generates an action potential only if the resting potential crosses a threshold, the
magnitude or intensity that must be exceeded for a certain reaction or condition to occur or be
manifested
The magnitude of the action potential is always the same (+35), it is all or none
The first action potential triggers a domino effect, this is relatively slow and energy
consuming
An action potential can also be conducted passively, without new action potentials,
this is much faster but the signal decays strongly with distance
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