An Introduction to Brain and Behavior Chapter 3 PDF

An Introduction to Brain and Behavior CHAPTER 3 Cells of the nervous system Brain tissue consists of 2 types of nerve cells Neurons, ~86 billion Glial cells (lit. glue), ~85 billion  information processing  support cells Cells of the nervou...

An Introduction to Brain and Behavior CHAPTER 3 Cells of the nervous system Brain tissue consists of 2 types of nerve cells Neurons, ~86 billion Glial cells (lit. glue), ~85 billion  information processing  support cells Cells of the nervous system How can we count nerve cells?  ‘Brain soup’ click here for recipe Cerebral cortex (82% brain mass) ~ 16 billion neurons (19% brain neurons) ~ 61 billion glial cells Cerebellum (10% brain mass) ~ 69 billion neurons (80% brain neurons) ~ 16 billion glial cells Rest of the brain (8% brain mass ) ~ 1 billion neurons (1% brain neurons) ~ 8 billion glial cells (Azevedo et al., 2009) doi 10.1002/cne.21974 TED talk (Herculano-Houzel et al., 2014) doi 10.1002/glia.22683 Neurons – basic structure Neurons consist of 3 main parts: part no. function dendrites many collect information (input) δένδρον = tree from other neurons cell body (soma) 1 integrates information σώμα = body axon 1 sends information (output) άξων = axis branches at the end Neurons – flow of information FLOW OF INFORMATION INPUT DENDRITES INTEGRATION CELL BODY OUTPUT AXON  Neurons – three major types INPUT (AFFERENT) ASSOCIATION OUTPUT (EFFERENT) see Ch2 long dendrites short dendrites short dendrites short axon short axon long axon dendrites + cell body outside CNS dendrites, cell body, axon inside CNS dendrites + cell body inside CNS (cell body in dorsal root ganglion) (in brain + spinal cord) (in lower brainstem + spinal cord) axon inside CNS axon outside CNS NB: reality is much more complex:  some sensory neurons have short dendrites (e.g. bipolar neuron in retina)  some interneurons have long axons (e.g. pyramidal cells in cortex) Glial cells – support cells Aid neurons in processing information by providing:  physical support, protection  nutrients  increase conduction (lit. glue neurons together) NB: glial cells do not transmit information themselves Glial cells – five major types  Ependymal cells  Astrocytes  Microglia  Oligodendroglia  Schwann cells NB: memorize Table 3-1 p 82 Glial cells – Ependymal cells (CSF) Glial cells – Astrocytes  Provide structural support to the CNS (scaffold cells)  Move nutrients and chemicals between blood vessels and neurons  Enhance brain activity by contributing to increased blood flow  Stimulate repair of damaged brain tissue (scarring)  Enable tight bond between blood-vessel cells and neurons  blood-brain barrier Glial cells – Microglia  Originate in the blood as an offshoot of the immune system (type of macrophage) and migrate throughout the nervous system (all other glial cells originate in the brain)  Identify and attack foreign tissue (defense cells)  Invade areas with damaged cells and provide growth factors to aid in repair.  Consume dead and inflamed brain cells (plaques, Alzheimer) Glial cells – Oligodendroglia and Schwann cells  Myelinate neurons to enhance neural transmission speed (insulate axons) Oligodendroglia Schwann cells (inside CNS) (outside CNS) Glial cells – Neuron Repair Schwann cells (PNS) encourage neuronal repair  cells in the PNS can be repaired after damage Oligodendrocytes (CNS) do not encourage neuronal repair  cells in the CNS cannot be repaired (yet) How do we know all this? Histology ‘traditional’ staining Main disadvantage of staining  only works in fixed brain tissue (ex vivo, in vitro, post-mortem) More recent imaging techniques also work in living tissue (in vivo)  DTI: Diffusion Tensor Imaging (See Chapter 7) Clarity (makes brain tissue transparent) Brainbow (transgenic technique) Video (4 minutes) Video (4 minutes) Internal structure of a typical (nerve) cell  Cell membrane  membrane surrounding the cell  Nucleus  cell core, contains chromosomes and genes  Nuclear membrane  surrounds nucleus  Endoplasmic reticulum  assembles proteins  Golgi bodies  wraps, addresses and ships off proteins  Microtubules  form the transportation network  Microfilaments  reinforce the cell’s structure  Mitochondria  supply energy to the cell  Lysosomes  transport incoming supplies and remove and store wastes NB: names and functions of red components are required for the exam Cell Membrane Separates the intracellular and extracellular fluid Total width ~8 nm (one billionth of a meter) Consists of 2 layers of phospholipid molecules:  head: phosphate group = hydrophilic (binds to water)  tail: fatty acid (lipid) = hydrophobic (does not bind to water) Only a few small (uncharged) molecules can passively traverse the phospholipid layers (e.g. oxygen, carbon dioxide) head = hydrophilic tail = hydrophobic Cell Membrane Proteins The cell membrane is semi-permeable, i.e., only specific molecules can pass  Channel specific ions can pass  Gate ions can pass if the gate is open  Pump active transport (uses energy) some ions in, others out e.g. sodium/potassium pump (helps maintain resting state potential) See also chapter 4 (next lecture) Nucleus – core cell structure Surrounded by a nuclear membrane Inside the nucleus are the chromosomes  double-stranded DNA molecules  contain the human genome DNA (deoxyribonucleic acid) is made of chemical building blocks called nucleotides that consist of three parts:  phosphate group  sugar group  one of four types of nitrogen bases: adenine (A), cytosine (C), guanine (G), and thymine (T). Chromosomes The nucleus of each human cell contains 23 chromosome pairs for each pair: one chromosome from mother, one chromosome from father 46 chromosomes in total Pair 1-22 autosomes (matched pairs)  determine physical characteristics and behavioral function (e.g. hair color, intelligence) Pair 23 sex chromosomes: X or Y  determine gender XX (girl) or XY (boy) Genetic defects (not necessarily hereditary): e.g., Trisomy #21 = 3 chromosomes #21 (instead of 2)  Down syndrome Greek: chroma “color” + soma “body”  “colored bodies” (requires staining) Genes  Each chromosome contains thousands of genes  A gene is a segment of a DNA strand  Corresponding genes within a chromosome pair are called alleles  one allele from mother  one from father If allele sequences are the same  homozygote alleles If allele sequences are different  heterozygote alleles Most common sequences  wild-type allele Less common sequence  mutation (e.g. T base substituted by an A base = SNP) NB: mutations can be: neutral (most common)  do nothing beneficial (rare)  increased bone density, tetrachromacy harmful (rare)  sickle cell disease, cystic fibrosis Alleles – dominant vs recessive Alleles can be dominant or recessive  they lead to a certain trait or not Laws of Mendel Genes  Each chromosome contains thousands of genes  A gene is a segment of a DNA strand  Genes are the ‘blueprints’ for protein synthesis in the endoplasmic reticulum (= protein factory) 4 nucleotide bases in DNA: adenine (A) -- thymine (T) guanine (G) -- cytosine (C) The sequence of bases in a gene spells out the order in which amino acids - the constituent molecules of proteins - should be assembled to construct a particular protein The ‘bases’ of behavior: bases  amino acids  peptides  proteins  cells  behavior Amino acids  peptides  proteins Amino acids are encoded in sequences of 3 nucleotide bases (codons) on mRNA (= single-stranded) Example: DNA: Thymine, Guanine, Guanine (TGG) mRNA: Uracil, Guanine, Guanine (UGG) Amino acid: Tryptophan (Trp) = precursor of serotonin (see Chapter 6) amino acid 1 amino acid 2 peptide bond Amino acids are bound together by peptide bonds Chains of amino acids are called (poly)peptides Long peptide chains with a certain form are called proteins Protein Synthesis 1. 2. 1. 3. 2. 3. video (3 minutes) Protein Packaging and Shipment  Golgi Bodies  packaging and shipping address  Microtubules  shipment Proteins that are incorporated in cell membrane form protein channels, gates, pumps (see Chapter 4)