Module 3 What are the Nervous System's Functional Units Flashcards
What are the Functional Units of the Nervous System?
- Cells of the nervous System
- Internal Structure of a cell
- Genes, cells, and behavior
Cells of the Nervous System
-Debate in the early 1900s
~Golgi
*The nervous system is composed of a network of INTERCONNECTED FISHERS: a “nerve net”
~Cajal
*Nervous system is made of DISCRETE CELLS
*Neuron Hypothesis
**Neurons are the units of brain function
Cells of the Nervous System
-Cajal
-Used the Golgi stain to show that the nervous system was made up of discrete cells thereby supporting the NEURON HYPOTHESIS
Cells of the Nervous System
-Brainbow
-Individual cells can be visualized offering a way to describe where each neuron sends its processes and how it interconnects with other neurons
Neurons: The Basis of Information Processing
-Human nervous system contains more than 100 billion neurons
-Examining how one cell works can be a source of insight that we can generalize to other cell types
-As you learn to recognize some of their different types, you will also see how their specialized structures contribute to their functions in your body
-Most behaviors are produced by groups of hundreds or thousands of neurons
-Neurons continuously change their shape
~Grow and shrink
-The production of new neurons does take place throughout life and some behavior depends on new neurons
-Most CNS neurons are with you for life and are never replaced
Neurons: The Basis of information Processing
-Three Basic Subdivision
- Dendrites
- Cell Body or Soma
- Axon
Dendrites
-Gather information from other neurons
Cell Body or Soma
- Core region; contains the nucleus
- Integrates the information
-Axon
-Carries information to be passed on to other cells
Neurons: The basis of Information Processing
-Basic Structure and Function
-Dendritic Spines
~Protrusion from a dendrite that greatly increases its surface area and is the usual point of contact with axons of other cells
-Axon Hillock
~Juncture of soma and axon where the action potential begins
-Axon Collaterals
~Branch of an axon
-Teleodendria
~End branches of an axon
-Terminal Button
~Knob at the tip of an axon that conveys information to other neurons; also called an END FOOT
-Synapse
~Gap between one neuron and another neuron
~Usually between a end foot of the axon of one neuron and a dendritic spine of another neuron
-Information Flow in a Neuron
~Dendrite -> Cell body -> Axon -> End Foot
Neurons: The Basis of information Processing
-Types of Neurons
-Sensory Neurons
~Bring information to the Central Nervous System
-Interneurons (aka Association Neurons)
~Associate sensory and motor activity within the Central Nervous System
-Motor Neurons
~Send signals from the brain and spinal cord to muscles
Neurons: The Basis of Information Processing
-Neural Connections
- The appearance of each neuron tells us something about the connections that it must make
- In general, neurons with large cell bodies have extensions that are very long; neurons with small cell bodies have short extensions
Neurons: The Basis of Information Processing
-The Language of Neurons: Excitation and Inhibition
- Each neuron receives thousands of excitatory and inhibitory signals every second
- Neurons “sum” these signals and respond accordingly: They become active or not
- From the simple “yes-no” language of neurons emerges enormous possibilities for behavior
Neurons: The Basis of Information Processing
-Barbara Webb’s Robot Cricket
-Robot seeks chirping male cricket using only 2 rules:
~When a microphone detects a song, sends an excitatory message to the opposite wheel’s motor
~The message send should be proportional to the intensity of the song
Cells of the Nervous System
-Five types of Glial Cells
-Ependymal Cell
~Small, ovoid; found in the walls of the ventricles
~Make and secrete Cerebrospinal Fluid (CSF)
-Hydrocephalus
~Build-up of pressure in the brain and swelling of the head caused if the flow of CFS is blocked
~Can result in retardation
-Astrocyte
~Star shaped, symmetrical; nutritive and support function
~Structural support for neurons
~Transports substance between neurons and capillaries (blood-brain barrier)
~Scar tissue formation
~Enhance brain activity by providing fuel to active brain regions
-Microglial Cell
~Small, mesodermally derived; defensive function
~Originate in the blood as offshoot of immune system
~Phagocytosis
*Scavenge debris (dead cells)
-Oligodendroglia Cell
~Asymmetrical; form myelin around CNS axons in brain and spinal cord
~Glial cell in the Central Nervous System that myelinates axons
-Schwann Cell
~Asymmetrical; wraps around peripheral nerves to form myelin
~Glial cell in the Peripheral Nervous System that myelinates axons
Myelin
-Glial coating that surrounds axons
Multiple Sclerosis (MS)
-Nervous system disorder associated with loss of myelin
Paralysis
-Loss of sensation and movement due to nervous system injury
Peripheral Nervous System
-Microglia and Schwann cells help repair neurons
Central Nervous System
-Repair does not take place, regrowth may even be inhibited
The Basics: Chemistry Review
-Elements
-Naturally occurring substance
-Three Main Ones:
~Carbon
~Oxygen
~Hydrogen
*Make up more that 90% of a cell’s composition
The Basics:
Chemistry Review
-Atoms
-Smallest quantity of an element that retains the properties of that element
-Contains a nucleus
~Neutrons
*Neutral in charge
~Protons
*Carry a positive (+) charge
~Electrons
*Carry a negative (-) charge
**Electrons orbit the nucleus
-When an atom gives up an electron, it becomes positively charged
-When an atom takes on an electron, it becomes negatively charged
The Basics:
Chemistry Review
-Ions
-A charged atom
The Basics:
Chemistry Review
-Molecules: Salt and Water
-Molecules
~Formed when atoms bind together
~Smallest units of a substance that contain all of that substance’s properties
-Salts (NaCl)
~When formed, sodium (Na+) gives up an electron to chloride (Cl-)
~Positively and negatively charged ions tightly held together by their electrical connection
-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
Cell Membrane
-Barrier and Gatekeeper
-Separates intra- and extracellular fluid
-Regulates movement of substances into and out of the cell (most cannot pass)
~Proteins embedded within membrane allow substances into and out of cell
-Made up of PHOSPHOLIPIDS
~Hydrophilic head: phosphorous
~Hydrophobic tails: lipids (fat molecules)
Nucleus:
Site of Gene Transcription
-Chromosome
-Double-helix structure that holds an organism’s entire deoxyribonucleic acid (DNA) sequence
-Four nucleotide bases
~Adenine (A), Thymine (T), Guanine (G), and Cytosine (C)
-Human somatic cells have 23 pairs
-Contains the genes
Nucleus:
Site of Gene Transcription
-Gene
-Segments of DNA that encode the synthesis of particular proteins
Nucleus:
Site of Gene Transcription
-Transcription (to copy)
-Early phase of proteins synthesis in which the DNA strands unwind and a complementary strand of MESSENGER RNA (ribonucleic acid) is created
Nucleus:
Site of Gene Transcription
-Codon
-Sequence of 3 bases on mRNA that codes for particular amino acids
Endoplasmic Reticulum (ER):
Site of RNA Synthesis
-Ribosomes
-Protein structures that act as catalysts for protein synthesis
Endoplasmic Reticulum (ER):
Site of RNA Synthesis
-Translation
- Later phase of protein synthesis in which the messenger RNA (mRNA) travels from nucleus to the ER
- mRNA is translated into a particular sequence of amino acids to form a protein
Information flow contained in genetic code
-DNA -> ~Transcription -mRNA -> ~Translation -Polypeptide Chain (Amino acid chain)
Proteins: The Cell’s Product
-Amino Acids
- Consists of a central carbon (C) atom bond to a hydrogen (H) atom, an amino group (NH3+), a carboxyl group (COO2-), and a side chain (R)
- Linked together by PEPTIDE BOND
- POLYPEPTIDE CHAIN: a series of amino acids
Proteins: The Cell’s Product
-Enzymes
-Protein catalysts that facilitate the cell’s chemical reactions
Protein Structure
- Both the shape of a protein and its ability to change shape are emergent properties of the precise sequence of amino acids that compose the protein molecule
- Some proteins change shape when chemicals bind to them
Protein Packaging and Shipment
-Golgi Bodies
-Package proteins in membranes (vesicles) and give them a “label” indicating where they are to go
Protein Packaging and Shipment
-Microtubules
-Transport the vesicles to where they need to go within the cell or outside the cell
Crossing the Cell Membrane
-Channel
-Opening in a protein embedded in the cell membrane that allows the passage of ions
Crossing the Cell Membrane
-Gate
-Protein embedded a cell membrane that allows substances to pass only when open
Crossing the Cell Membrane
-Pump
-Protein embedded in a cell membrane that actively transports a substance across the membrane
Genes, Cells, and Behavior
-Genes -> Proteins -> Cells -> Behavior
-Genotype
~Genetic make-up
-Phenotypes
~Physical and behavioral traits
Genes, Cells, and Behavior
-Genomics
- Nucleus of each human somatic cell contains 23 pairs of chromosomes, or 46 in all
- One member of each pair of chromosomes comes from mother, and the other member comes from the father
- The chromosome pairs are numbered from 1 to 23
Chromosomes and Genes
-23 pairs of Chromosomes
-Human somatic cells have 23 pairs of chromosomes
~Chromosome pair 1 through 22 are called AUTOSOMES, and that contain the genes that contribute most or the physical appearance and behavioral functions
~The 23rd pair comprises the sex chromosomes, which contribute to our physical and behavioral sexual characteristics
Chromosomes and Genes
-Allele
-A cell contains two copies of every gene, one inherited from your mother, the other from your father; matching copies are ALLELES
Chromosomes and Genes
-Homozygous
-Having two IDENTICAL ALLELES for a trait
Chromosomes and Genes
-Heterozygous
-Having two DIFFERENT ALLELES for the same trait
Chromosomes and Genes
-Wildtype
-Refers to a normal (most common in a population) phenotype or genotype
Chromosomes and Genes
-Mutation
-Alteration of an allele that yields a different version of that allele
Dominant and Recessive Alleles
-Dominant Allele
-The member of the gene pair that is routinely EXPRESSED
Dominant and Recessive Alleles
-Recessive Allele
-The member of the gene pair that is routinely UNEXPRESSED
Dominant and Recessive Alleles
-Complete Dominance
-Only the dominant allele’s trait is expressed in the phenotype
Dominant and Recessive Alleles
-Incomplete Dominance
-The phenotypic expression of the dominant alleles trait is only partial
Dominant and Recessive Alleles
-Codominance
-The traits of both alleles of a gene pair are expressed completely in the phenotype
Genetic Mutations
-Can have positive effects, neutral effects, or negative effects
-Effects may be specific or wide spread
-Most mutations have negative effects
-Example
~Sickle shape offers some protection against malaria but sickle cells also have poor oxygen-carrying capacity
Genetic Disorders
-Tay-Sachs Disease
- Inherited birth defect caused by the loss of genes that encode the enzyme necessary for breaking down certain fatty substances
- Appears 4-6 months after birth and results in retardation, physical changes, and death about age 5
- Caused by recessive allele
Genetic Disorders
-Huntington’s Chorea
- 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
Chromosome Abnormalities
-Genetic Disorders
-Involved aberrations in part of a chromosome (or the entire chromosome) rather than a single defective allele
Chromosome Abnormalities
-Down Syndrome
- Chromosomal abnormality resulting in mental retardation and other abnormalities, usually caused by an extra copy of chromosome 21 (trisomy)
- One parent (usually the mother) passes on two copies of chromosome 21 to the child, rather than the normal single chromosome
- Children with Down Syndrome can learn to compensate greatly for the brain changes that cause their mental handicaps
Genetic Engineering
-Adding or removing genes from a genome, or modification of a gene
-Approaches
~Selective breeding
~Cloning
~Transgenic Techniques
~Knockouts
Selective Breeding
- Effective way to alter gene expression
- Maintaining spontaneous mutations is one objective of selective breeding
- Selective breeding of dogs has produced breeds that can run fast, haul heavy loads, retrieve prey, dig for burring animals, etc.
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
Transgenic Techniques
-Enable scientists to introduce genes into an embryo or remove genes from it
~CHIMERIC ANIMALS have cells with genes from both parent species and behaviors that are a product of those gene combinations
~KNOCK-IN TECHNOLOGY occurs when a number of genes from one species and is expressed in subsequent generations
~KNOCKOUT TECHNOLOGY is used to inactivate a gene so that a line of mice fails to express it
Phenotypic Plasticity and Epigenetics
- The extent of out phenotypic variation, given the same genotype, can be dramatic
- Every individual has a capacity to develop into more than one phenotype
Phenotypic Plasticity and Epigenetics
-Phenotypic Plasticity
- The capacity of the genome to express a large number of phenotypes
- The absence of a corpus callosum results from an epigenetic influence on whether the trait is expressed in a particular mouse
- Lack of CONCORDANCE (incidence of similar behavior traits) is also observed in patterns of disease incidence in identical twins
Phenotypic Plasticity and Epigenetics
-Epigenetics
-The influence of environment in selecting one or another phenotype
-The environment can allow a gene to be expressed or prevent its expression
-Epigenetics is viewed as a second code
~Describes how a single genetic code produces each different somatic cell type
~Explains how a single genome can code for many different phenotypes
~Describes how cells go astray in their function to produce diseases ranging from cancer to brain dysfunction
-Epigenetic mechanisms influence protein production
~By blocking a gene so that it cannot be transcribed
~Unlocking a gene so that it can be transcribed
-An environmental influence can induce or remove one or more blocks, allowing the environment to regulate gene expression
~Histone modification
~DNA modification
~mRNA modification
Histone Modification
-DNA may unwrap or be stopped from unwrapping from the histone