Functional Units of the Nervous System PDF

Functional Units of the Nervous System Austen Smith Outline 1. Cells of the nervous system Neurons Glia 2. Internal structure of a cell Chemistry review 3. Genes, cells, & behaviour 2 1. Cells of the Nervous System Neurons...

Functional Units of the Nervous System Austen Smith Outline 1. Cells of the nervous system Neurons Glia 2. Internal structure of a cell Chemistry review 3. Genes, cells, & behaviour 2 1. Cells of the Nervous System Neurons 1. Vary greatly in size & shape but have a common plan 2. Diameter of most neurons is 0.02 mm 3. ~86 billion neurons in the human nervous system Glia 1.~87 billion glial cells 3 The Neuron Theory 1. Neurons are the nervous system’s functional units 2. Interactions between neurons enables behavior 3. The more neurons an animal has, the more complex its behavior 4 The Neuron Theory Golgi stain (Camillo Golgi, 1843-1926) Silver chromate Distinct parts of neuron Santiago Ramón y Cajal: Traced connections of the brain (over 25 years!) using the Golgi stain. Golgi & Cajal were rivals but ended up sharing the Nobel Prize for Medicine in 1906 5  Neuron Structure Dendrite (Dendritic spine) Cell Body (Axon hillock) Axon – Axon collaterals – Telodendria – Terminal button Synapse 6 Neurons Flow of information 7 Neurons Three basic types of neurons: Structured to perform three functions: – Sensory neurons Carry information from the sensory receptors in or on the body to the spinal cord 8 Neurons Three basic types of neurons: Structured to perform three functions: – Interneurons (association neurons) Associate sensory and motor activity within the central nervous system 9 Neurons Three basic types of neurons: Structured to perform three functions: – Motor neurons Send signals from the brain and spinal cord to muscles 10 Neurons The three organizational aspects of neurons are also features of neuronal networks: – Input, association, output How do neurons communicate? – Excitation & Inhibition: Neurons either turn on (excite) or turn off (inhibit) other neurons. 11 Glia Forgotten but important The nervous system’s support cells Glial cells help neurons deliver messages Glue 5 major types: 12 13 Astrocytes & Blood-Brain Barrier 14 Schwann Cells & Neuron Repair 15 2. Internal Structure of the Cell Chemistry Review Element – Naturally occurring substance Atom – Smallest quantity of an element that retains the properties of that element – Contains a nucleus (Neutrons = neutral charge; Protons = positive (+) charge; Electrons orbit the nucleus and carry a negative (−) charge). 16 17 Chemistry Review Molecules: Smallest units of a substance that contain all of that substance’s properties – Formed when atoms bind together Salts (NaCl) – When NaCl is formed, sodium (Na+) gives up an electron to chloride (Cl−). – Positively and negatively charged ions tightly held together by their electrical connection 18 Chemistry Review Water (H2O) – Atoms held together by shared electrons – Polar molecule Opposite charges at opposite ends Chemical properties of water enable it to dissolve salt crystals into their component ions. 19 Internal Structure of the Cell 20 Internal Structure of the cell 21 Cell Membrane Envelops the neuron’s contents; contributes to forming the cell body, dendrites and spines, axons and terminals. – Forms a boundary around intracellular compartment Separates intracellular and extracellular fluid Regulates movement of substances into and out of the cell – Proteins embedded within membrane allow substances into and out of cell. 22 The Nucleus & Protein Synthesis The Nucleus: Stores and copies the “blueprints” for making proteins. – Blueprints = genes Gene: DNA segment that encodes the synthesis of a particular protein. – Chromosomes contain genes 23 The Nucleus & Protein Synthesis Each Chromosome contains thousands of genes. – Book of Blueprints = chromosome Human somatic (body) cell has 23 pairs, or 46 chromosomes. – (vs. a reproductive cell with only 23 chromosomes) 24  Each strand has a sequence of four nucleotide bases The sequence of ACTG base pairs spells out the order that amino acids should be assembled. – Adenine (A) – Thymine (T) – Guanine (G) – Cytosine (C) 25 DNA à mRNA à Protein 26 Protein Packaging & Shipping: Golgi Bodies & Microtubules 27 3. Genes, Cells, & Behaviour Mendelian genetics Genotype – Gregor Mendel, whose – Genetic makeup research led to the concept Phenotype of the gene – Physical and behavioral – Studies how genes influence traits our traits – Epigenetics studies how the environment influences gene expression 28 Chromosomes & Genes 29 Chromosomes & Genes Allele: The two copies of a gene Homozygous – Dominant allele: the – Having two identical member of the gene pair that alleles for a trait is routinely expressed Heterozygous – Having two different – Recessive allele: the alleles for the same member of the gene pair that trait is routinely unexpressed 30 31  Disorders Tay-Sachs disease – Caused by a recessive allele – Inherited birth defect caused by loss of genes that encode the enzyme necessary for breaking down certain fatty substances – Appears 4 to 6 months after birth; results in intellectual disability, physical changes, and death by about age 5 32  Disorders Huntington’s disease – Autosomal disorder that results in motor and cognitive disturbances – Caused by an increase in the number of CAG (cytosine-adenine- guanine) repeats on chromosome 4 – The buildup of an abnormal version of the huntingtin protein kills brain cells, especially in the basal ganglia and the cortex. 33 Chromosomal Abnormalities Genetic disorders can be caused by copy number variations (E.g. Autism, schizophrenia) Down syndrome: Usually caused by an extra copy of chromosome 21 (trisomy) which may potentially result in: intellectual impairment heart defects respiratory infections Leukemia Alzheimer’s disease 34 Genetic Engineering Modification of a gene – Adding or removing genes from a genome Approaches – Selective breeding – Cloning – Transgenic techniques 35 Selective Breeding 36 Cloning Producing an offspring that is genetically identical to another animal Clones can be used to preserve valuable traits, to study the relative influences of heredity and environment, or to produce new tissue or organs for transplant to the donor. 37 Transgenic Technique Introduction of genes into an embryo or removal of genes from it – Knock-in technology is in use when genes from one species are added to the genome of another species and expressed in subsequent generations. – Knockout technology is used to inactivate a gene so that a line of mice fails to express it. 38  CRISPR Produces an RNA sequence that identifies DNA – which can be cut, deleted, & replaced Clustered Regularly Interspaced Short Palindromic Repeat https://www.wnycstudios.org/podcasts/radiolab/articles/antibodies-part-1-crispr https://www.wnycstudios.org/podcasts/radiolab/articles/update-crispr https://www.scientificamerican.com/article/what-crispr-baby-prison-sentences-mean- for-research/ 39 Phenotypic Plasticity & Epigenetic Code The extent of phenotypic variation given the same genotype is remarkable. Phenotypic plasticity: The capacity for an individual to develop more than one phenotype due to the genome’s capacity to express many phenotypes and epigenetics. Less than perfect concordance rates between twins for diseases like Alzheimer’s, MS, cancer, Crohn’s points to epigenetics. 40