Neuronal Communication and Action Potential

Neuronal Communication and Action Potential

• The lecture covers neuronal communication and the action potential.

Internal Structure of a Neuron

• A neuron has internal structures including the membrane, organelles and nucleus

Membrane

• It separates intracellular and extracellular environments.
• Both environments contain water, salts, and other elements forming the cytoplasm.
• Significant water loss causes the cell to fold.
• The membrane regulates the substance passage between environments.
• An imbalance in the distribution of chemicals can harm membrane function.
• The membrane is composed of four components: phospholipides, cholesterol, proteins and carbohydrates.

Proteins

• Proteins are complex elements whose morphology induces the protein's function.
• It is composed of amino acids.
• Amino acids share a basic structure, but are different by the radical R.
• The peptide chain is the primary structure.
• It undergoes morphological and spatial transformations and becomes the secondary structure.
• The tertiary structure is obtained by folding in on itself.
• When two or more tertiary structures associate, they form a quaternary structure.

Protein Roles

• Proteins are found in cells within the cell membrane.
• Act as enzymes to induce chemical reactions.
• Are used for excretion such as hormones or neurotransmitters.
• The proteins facilitate exchanges between the internal and external environments.
• Proteins can change conformation when a molecule binds to it.
• Proteins contains a receptor site that captures the molecule and induces a shape change.

Membrane Crossing Mechanisms

• There are three mechanisms: channels, gated channels and pumps.
• Channels passively transport ions based on the concentration gradient.
• Gated channels open through the binding of a molecule to a receptor.
• Pumps actively transport ions via a change in configuration.

Organelles

• The organelles are:
  • Endoplasmic reticulum (ER)
  • Ribosomes
  • Golgi apparatus
  • Cytoskeleton that includes: microtubules, microfilaments and neurofilaments
  • Mitochondria
  • Lysosomes

Nucleus

• The nucleus contains all the genetic information of an individual (chromosomes, DNA, gene).
• Genetic code is found in the nucleus.
• Genetic code translates the information from DNA or RNA into proteins.
• Proteins largely define the function and structure of neurons.
• The neuron's function depends on its genetic code, which is the nature versus nurture debate.
• The nucleus of neurons contains chromosomes.
• Chromosomes are made of DNA in a double helix (2 strands).
• A gene is a segment of DNA and its main function is to manufacture proteins.
• DNA has four nucleic bases that pair; A with T and C with G.

Synthésizing Proteins

• Information from DNA requires a transcription and translation before its used.
• Transcription involves coding DNA into mRNA.
• Translation involves coding mRNA into proteins.
• Uracil (U) is found in mRNA instead of thymine (T).

Transcription and Translation

• Transcription (DNA => mRNA)
  • A (DNA) -> U (RNA)
  • C (DNA) -> G (RNA)
  • G (DNA) -> C (RNA)
  • T (DNA) -> U (RNA)
• Translation (mRNA => proteins)
• Translation usually starts with the codon AUG which codes for methionine.
• The codons UAA, UAG and UGA stop the translation when they are reached

Gene

• Genes are the manufacturing plan for proteins.
• Proteins are the essence of cellular function and play an important role in behavior.
• A gene's letter combination gives the sequence of amino acids in the protein.
• A protein's specificity is the order in which the amino acids are arranged.
• 20 amino acids provide several combinations.
• There are 20,000 to 25,000 genes equals over 2 million different proteins.
• The objective is to understand the connection between genes, proteins and cells to comprehend behaviour.
• The current challenge is comprehending a gene and its gene interactions.
• A gene can have 1000 nucleotides.
• Estimations of genes in humans: 100,000 (1990) -> 30,000 (2001) -> 25,000 (2004).
• 50% of genes are related to brain construction.
• Gene Mapping = human genome, and the challenge is comprehending the functions of each gene.
• Each cell contains about 2 meters of DNA.

Genetic Anomalies

• Major variations of DNA include duplications, chromosomal rearrangements and insertions.
• Subtle variations include mutations, insertions, deletions caused by polymerase errors or mutagenic agents.
• Mechanisms repair DNA, but some errors persist.
• Genetic abnormalities can alter the structure and functioning of the brain, influencing behaviour.
• Over 2,000 of such anomalies are known but are not all detectable.

Genome vs Chromosomes

• The genetic information in each cell contains the chromosomes.
• Humans have 46 chromosomes (23 pairs).
• Every pair of chromosomes are similar but not identical.
• Identical alleles mean homozygote.
• Different alleles mean heterozygote.
• The most frequent allele is wild type.
• An allele different from the wild type is a mutation.
• Mutant genes can cause genetic diseases.

Genotype vs Phenotype

• The genotype corresponds to an individual's set of genes.
• The phenotype represents observable characteristics.
• Similar alleles produce the equal protein.
• Different alleles produce differential proteins.
• Dominant alleles are more expressive than recessive.

Mendel's Laws

• Law of segregation: two alleles per trait; one allele per gamete during formation.
• Law of independent assortment: alleles of different traits separate independently, unless they are linked.
• Law of dominance: leading alleles mask receding alleles.
• Trait expressions include:
  • Dominance: dominant is more expressive than recessive
  • Semi-dominance: dominant and recessive co-expression -Co-dominance: dominant and recessive combined expression

Other Trait Aspects

• Environment and epigenetic interactions plays a role.
• Phenotypic plasticity may be present.

Pleiotropy and Gene Editing

• A gene can influence several traits; this is pleiotropy.
• A unique protein can intervene in differentiated chemical reactions
• Gene editing is possible

Chromosomal abnormalities.

• A specific allele causes diseases.
• Section of or additional chromosome may be present.

Anomalies

• An example of an anomaly is Down syndrome (trisomy 21)

Mutations and potential outcome

• Gene mutations in animal models can be expressed as knock out or knock in. They offer insights into future research.

Action Potential

• Electricity is the life force.
• Neurons transmit electrical signals.
• Neurons contain resting potential, which is when the neuron's interior is negative compared to the outside environment.
• Neurons contain graded potential, which is when there is temporary entry of ions through the neuron membrane.
• Neurons contain action potential, which is when flux of ions through the neuron membrane.
• Selective permeability of the membrane is crucial for the construction of skills.

Discovery And Conditions

• Action Potential had an initial study of squid and lobster.
• Diffusion is a passive phenomenon allowing ions to move toward areas of concentration and to achieve a equilibrium and solution homogenisation on each side of the membrane.
• Electric activity involves measuring and stimulating activity with micro-electrodes that record activity level in cellular or axonial membrane.
• Currents are made by the movement of + charged cations and - charged anions which are proteins with a - charge.
• This generates a electrical potential as the difference of charge across a membrane drives ion movement in a set electric direction.

Potential and Ions

• Potential has a gradient from ions and other interactions.
• Cl ions passing in a + charge attract Na ions to have a feedback.
• The results indicate higher Cl concentration in origin as differences are determined by membrane proprieties and their ion channels.

Resting Potential

• Resting potential describes how outside and inside cell differences are measured.
• The mean interior is at -70 in mV with variance from -50 to -90.
• By convention the exterior is 0 mV.
• 4 Main charged particles influence the resting potential: Na, K, CL and A ions.
• The extracellular medium is mainly Sodium and Clorine, with higher positive ions.
• This allows cellular stability by driving out - Potassium and pulling in Sodium ions to stabilize the negative potential across proteins.
• The interior of the positive has more proteins.
• Potassium helps negative stability.
• Sodium-potassium expulsion and retention of potassium help create the stabilizing gradient.

Potential Expressions

• Graded expressions influence electricity with static propagation.
• This happens when Na+ causes a -70 to -65 micro-volts depolarization and negative current of Cl or Potassium causes a hyperpolarization due to equilibration.
• Action potential has fast and reversible electric change.
• It is initiated after stimulation when the binary signal surpasses.
• This can be triggered by a flux of inbound Na and outbound K ions using some voltage dependant nodes.
• During Absolute refractory period there no electrical signals may occur, and the relative refractory period has signals can only occur if over stimulation. Signals should be over 5 ms apart or 200 Max per second.

Nerve Impulses

• They requires 20 mV for -70 or -50 depolarization.
• In the nerve impulse is when the Axon has a serial PA with signal distribution and it moves along axon during this uni-directional movement.
• All signals have equal amplitude or signal value during its ""All or Nothing"" function.

Signal Control

• Small stimulus create small effect.
• A large effect is achieved by signal superposition in the spatial or temporal space.
• Large Neurons transport information faster, even if mammalian have small axon diameters needing fast transmission.
• Axon transport is optimized via surrounding sheath which envelopes all Ranvier nodes.
• The sheath lacks ionization allowing for more effective and rapid transit for signal transfer on long neurons from node jumping with 120 m/s rate or 30 Without.

Signal degradation

• May happen with long amyelinated regions which require a closer position to the points of signal depolarization
• Signals May be degraded by myelinated fibre which skips in jumping the nodes.

Multiple Sclerosis

• This happens as a result of the degradation of myelin around neurons causing movement alteration
• During this process Neuron signal is changed between presynaptique to post-synaptique with 2 signal types, Excitation or Inhibition.

Potential Modification

• Post Synaptic may have excitation and inhibition potentials during neurone action
• Manual stimulation creates an activity based on polarizations or hyper-polarizations by sodium or chlorium/potassium, which is depend from stimulus value
• The neuron action is always at the core with multiple PPSE travelling among neurones, until a critical point voltage triggers core events.

Data Transmission

• Data can be transmitted via spatial or temporal domain on neuronal system
• Neurons have a threshold which depends on a decision.
• Stimulation can be applied depending on dendrite location