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Lecture 1Part 1: From chemical elements to cell membrane
Element Symbol % of human body weight
Oxygen O 65
Carbon C 18
Hydrogen H 10
Nitrogen N 3
Calcium Ca 2
Phosphor P 1.1
Potassium K 0.35
Sulfur S 0.25
Sodium Na 0.15
Chloride Cl 0.15
Magnesium Mg 0.05
Bonding element
➔ Ionic bond (electrostatic force)
◆ + attract - → Na+ and Cl-
➔ Covalent bond (sharing of electrons forms molecules)
◆ eg: H2O: oxygen + hydrogen: inner shell can have 2
atoms and other shells can have 8 → oxygen has
inner 2 and outer has 6 (8 in total) → hydrogen has
only one on the inner shell → they form a bond
◆ Sometimes there are 8 around oxygen and
sometimes they go to hydrogen and then hydrogen has 2
◆ Oxygen has a stronger positive core (8 atoms) so the negative electrons are
more likely to be attracted to the oxygen core than the hydrogen core → the
oxygen core is more negative than the hydrogen
core
Carbon chains →
● Glucose is made by a covalent bonding
● Amino acid is also made by covalent bonding
○ are important in our body → key structure for making proteins
● Protein: structure of amino acids (1000 amino acids)
○ Peptides: are short protein chains (10 amino acids)
● Lipids (fat): long carbon chains by covalent bondings between carbon
● Phospholipids: carbon chains connected by an extra phosphate (P) group →
phosphate has a static negative charge (carbon chain with P element → has many
protons and so it attracts electrons → net negative charge) and is consequently
hydrophilic head
○ Tails (chain of carbon) from the phospholipids are lipids → hydrophobic
1
, ○ Double layer of phospholipids forms cell membrane (tails to the inside heads
to the outside) and for the outside of the cells in our body
Part 2: Nerve cells
Nerve cell
● = soma with extensions (dendrites) receive information from other cells
● the body than integrate the signals → can be excitatory or inhibitory
● Either action potential yes or no
● Action potential over the axon (sends signals)
○ Axon is covered in fatty layer = myelin sheath
around 100 billion neurons in the human brain = 100 hard-disks with 1TB capacity
Global structure
1. In the soma is the cell nucleus with little pores for transport of messenger mRNA
a. Nucleus contains chromosomes with genes (pieces of DNA: deoxyribonucleic
acid)
2. Endoplasmic reticulum (production, storage and transport of proteins): mRNA is read
to produce proteins → is the mRNA is produced it needs to be
read →
3. Golgi apparatus: post office for packing (neurotransmitter in
vesicles for transport)
4. Mitochondria: power plant (ATP: adenosine Tri-Phosphate →
energy of the cell)
5. Lysosomes: waste processing
6. Road system: microtubuli: road system for transportation
neurotransmitter through axon
DNA → mRNA (transcription: genes are read from the DNA and converted to messenger
RNA = mRNA) → mRNA leaves the nucleus through the pores, and is read out by
ribosomes (complex proteins), to form a new protein → need to be transported →
Axoplasmic transport
● Kinesin: anterograde transport from the cell body (soma) to
terminal buttons → walk along the microtubuli
● Dynein: retrograde transport from terminal buttons to soma
○ Pick up chemicals that are not used back to the soma
not only neurons in the brain, there are also:
Glial cells (support cells)
● Microglia: immunologic defense and removal dead cells
● Macroglia:
○ Oligodendrocytes: they form the myelin sheath in the central nervous system
(can make more myelin sheaths for more axons).
○ Schwann cells: also make myelin sheath, but in the peripheral nervous
system. One cell that wraps around an axon to form a sheet of myelin (one
sheath of myelin).
2
, ○ Astrocytes (star shape): support → structure and solidity (glia = glue), isolate
synaptic clefts, and can take out nutrients from the bloodstream and give it to
the neurons → blood cannot contact brain cells directly
■ Blood-brain barrier taken over
■ Feeding neurons by converting glucose in the blood to lactate
■ Astrocyte can also storage a little bit of nutrients
Part 3: Bioelectricity (Membrane potential)
Axon holds a charge (-90 in quids and -65 mV in humans in the cells)
Membrane potential origin
● the 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 concentrations
● Electrostatics: positively charged particles repeal each other, negatively charged
particles repel each other, but oppositely charged particles attract each other
● The membrane on nerve cells is not completely closed → they have ion channels.
the channels can be in an open or closed state.
○ To let sodium, potassium or chloride in or out
Cell at rest →
- Inside the cell many proteins (A-) are made and they attract elections
- According to law of attractions they attract positive proteins but they cannot get otu
- Inside the cell is a lot of K, but this charge does not outway the negative charge of
the proteins
- Electrostatic pressure keep K in the cell
- K can leak out, and so the inside will be more negative → more difficult for other
electrons to leave the cell → eventually K cannot leave anymore = the exact
membrane potential (-70 mV)
- on the outside is a lot of Na and Cl, and because there is pressure (abundant) they
want to move into the cell
- For chloride this is not possible → they are retained by the electrostatic force
- But Na, because of diffusion, is attracted to the inside
- Membrane will lean in some Na
- Then moved out by Na/K pump
3
, Sodium/Potassium pump maintains membrane potential
● Higher Na+ concentration outside the cell due to Na/K pump
○ 3 Na ions outward for 2 K ions inward
● The pumps require energy and are active all day
Part 4: Bioelectricity (Action potential)
Electric stimulation of the axon induces an action potential
All or none activation
● The axon generates an action potential only if the resting
potential crosses a threshold
● The magnitude of the action potential is always the same → all or none
Action potential mechanism
● Electrical stimulation causes the membrane potential to
be less negative
● If the threshold is crossed (-70 mV to -60mV) a
cascade starts:
1. More Na+ channels are opened, Na+ flows into the cell,
cell inside becomes less negative (depolarisation)
2. K+ channels open, K+ flows out the cell, will counteract
the electrical effect of the Na+ inflow
3. Na+ channels close (refractory period), Na+ inflow is
halted
4. K+ keeps flowing out, cell return to negative
(repolarization)
5. K+ channels close, Na+ channels returns to their
normal closed condition (can be opened again)
6. Following the massive outflow of K+, the membrane
temporarily has an extra negative charge
(hyperpolarization)
Part 5: Bioelectricity (Action potential conduction)
→ The first action potential triggers a dominion effect
But this type of conduction is:
1. Relatively slow → new action potentials are generated in neighboring regions
2. Energy consuming → resting potential needs to be recovered across the whole
axon, by means of the Na/K pumps
4
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