topic 8 notes pruna

• Frontal cortex/ cerebrum/ cerebral hemispheres

  Thinking, feeling emotions, learning, memory

  
• Medulla oblongata


  Regulation of heart rate (cardiovascular control centre), breathing (ventilation centre), blood pressure
• Cerebellum


  Control of movement, control of balance, fine motor skills
• Unmyelinated neuron structure
• The action potential


  1. Stimulus

  2. Depolarisation

  3. Repolarisation

  4. Hyperpolarisation

  5. The resting potential
• Resting potential


  • 70 mV across the membrane of the neuron, maintained by Na+/K+ ATPase

  
• Myelinated neuron structure


  • Schwann cells with myelin sheaths cover the axon and provide insulation
  • At nodes of Ranvier, the axon's cell membrane is exposed and there are clusters of voltage gated sodium channels and voltage gated potassium channels that allow depolarization when impulse arrives
  • Impulse jumps to the next node of Ranvier (this is saltatory conduction)
  • Ensures faster conduction

  
• What happens when the action potential reaches the axon terminal

  1. Action potential reaches the axon terminal

  2. Voltage gated calcium channels open, Ca2+ diffuses into the neuron cell

  3. Ca2+ signal for synaptic vesicle fusion with the presynaptic membrane

  4. Neurotransmitter released through exocytosis

  5. Neurotransmitter diffuses through synaptic cleft

  6. Binds to receptor on the postsynaptic membrane, activates voltage gated sodium channels, Na+ diffuses in the cell and initiates action potential (depolarization)

  
• Rod cells


  Highly specialized cells in the retina, monochrome vision – dark/light

  
• In the dark, rod cells are depolarized


  1. Action potential reaches the presynaptic terminal

  2. Voltage gated calcium channels open, Ca2+ diffuses into rod cell

  3. Ca2+ signal for synaptic vesicles fusion with the presynaptic membrane

  4. Inhibitory neurotransmitter (glutamate) released through exocytosis

  5. Inhibitory neurotransmitter (glutamate) diffuses through synaptic cleft

  6. Binds to receptor on the postsynaptic membrane, inhibits voltage gated sodium channels, Na+ cannot diffuse in the cell to initiate action potential

  
• In the light, the rod cell is hyperpolarized

  1. Glutamate is no longer released, releasing the inhibition of bipolar neurons

  2. Bipolar neurons are depolarized, this allows an impulse to be transmitted through the optic nerve to the visual cortex

  
• Rhodopsin (pigment)


  Transmembrane protein found in outer segment of rod cells, consists of cis-retinal (prosthetic group, red) and opsin (protein, blue)
• The signalling cascade


  1. Rhodopsin absorbs light

  2. Cis-retinal converted to trans-retinal

  3. Change in shape of rhodopsin, releases opsin

  4. Signalling cascade resulting in closure of voltage gated sodium channels

  5. Hyperpolarization of the rod cell, stopping the release of inhibitory glutamate, bipolar neurons are depolarized, this allows the impulse to be transmitted through the optic nerve to the visual cortex

  
• Pupil contracting, bright light


  Circular muscle contracts, radial muscle relaxes
• Dark adaptation


  1. Trans-retinal converted back to cis-retinal

  2. Rhodopsin is reformed from opsin and retinal

  3. Na+ channel open, partial depolarization of rod cells

  4. More glutamate is released and inhibits the bipolar neurons

  
• IAA (indole acetic acid, auxin) in the phototrophic response

  • Auxin, a plant hormone, produced in the tip of the shoot
  • Auxin diffuses away from the light source and accumulates on the dark side of the shoot
  • Auxin stimulates cell elongation
  • Causing the shoot to grow towards the light source – positive phototropism

  
• Phytochrome


  A photosensitive pigment in seed germination and flowering
• Parkinson disease


  • Associated with low dopamine levels in the synaptic cleft
  • Less dopamine available to diffuse and bind to receptors on postsynaptic membrane and activate voltage gated sodium channel
  • Fewer depolarizations of the postsynaptic membrane, threshold not achieved, action potential not initiated
  • Transmission of nerve impulses is disrupted, resulting in lack of control of muscle movement/ tremors
  • Treatment: L-DOPA is a precursor of dopamine that can cross the blood brain barrier and is converted to dopamine in the brain
• Depression


  • Associated with low serotonin levels in the synaptic cleft
  • Less serotonin available to diffuse and bind to receptors on postsynaptic membrane and activate voltage gated sodium channel
  • Fewer depolarizations of the postsynaptic membrane, threshold not achieved, action potential not initiated
  • Transmission of nerve impulses is disrupted
  • Treatment: Selective Serotonin Reuptake inhibitors (SSRI) bind and inhibit the reuptake transporter in the presynaptic membrane, increased level of serotonin in the synaptic cleft
  • MDMA binds to reuptake inhibitors in the presynaptic membrane, increased level of serotonin in the synaptic cleft; however, it can leave neurons depleted of serotonin

  
• MRI, magnetic resonance imaging


  Uses magnetic field/ radio waves, higher resolution, more detail can be seen, images at one point in time, 2D and 3D, limitations: noisy, need to stay still, not indicated for people with metal implants, pacemakers, more expensive
• CT, computed tomography


  Uses X-rays, lower resolution, images at one point in time, 2D and 3D, limitations: X-rays – not as safe, risk of mutations
• fMRI – functional MRI

  Uses magnetic field/ radio waves, can allow brain activity to be seen in real time, moving image, detects changes in blood flow, increased aerobic respiration, thus increased blood flow/ oxyhaemoglobin in areas of increased brain activity, oxyhaemoglobin absorbs fewer radio waves, these areas appear as bright spots

  
• PET – Positron emission tomography

  Uses radioactive markers (radioactively labelled metabolite – glucose), detects emissions of positrons/production of gamma rays, PET scan shows area that are metabolically active/cells dividing more, 3D image
• Habituation


  1. High frequency of impulses may lead to less responsive voltage gated calcium channels in the axon terminal

  2. Fewer calcium ions diffuse into the axon terminal

  3. Fewer signals for the fusion of synaptic vesicles with the presynaptic membrane

  4. Less neurotransmitter released through exocytosis into the synaptic cleft, less neurotransmitter diffuses through the synaptic cleft

  5. And bind to receptors on the postsynaptic membrane

  6. Less depolarization/ no action potential in the postsynaptic membrane

  
• Habituation may be of benefit to a sea slug by
• Critical period is a time during early postnatal life when the development and maturation of functional properties of the brain, its "plasticity," is strongly dependent on experience or environmental influences
• Critical period for vision - the experiments of Hubel and Wiesel
• Neurotransmitters


  1. Pass through the synaptic cleft

  2. Bind to receptors on the postsynaptic membrane

  3. Cause less depolarization/no action potential in the postsynaptic membrane
• Habituation


  • Avoid wasted energy to repetitive non-threatening stimulus
  • Focus on potentially threatening stimuli
• Critical period


  A time during early postnatal life when the development and maturation of functional properties of the brain, its "plasticity," is strongly dependent on experience or environmental influences
• Critical period for vision

  1. Ocular dominance column cells develop in the visual cortex

  2. Neurons form synapses with these cells

  3. Visual stimulation required to strengthen connections with these cells

  
• Perspectives on use of animals in preclinical trials

  • Absolutists (black or white) say all use of animals is unacceptable
  • Relativists (grey) say animal welfare is important
  • Rationalists say overall good should outweigh harm done to animals
• Cloning


  1. PCR to produce multiple copies of DNA

  2. Use a restriction enzyme to cut out the gene of interest; sticky ends produced

  3. Use the same restriction enzyme to cut open the plasmid (vector); sticky ends produced

  4. Hydrogen bonds formed between nucleotides at 'sticky ends'

  5. DNA ligase catalyses formation of phosphodiester bonds to bind gene of interest to plasmid

  6. Uptake of plasmid by organism and gene expression
• Cons of genetically modified organisms (GMOs)

  • Possible gene transfer to other species, resulting in resistance to pesticide / antibiotics
  • Possible harmful effects from genes e.g. biochemical changes to substances that could act as allergens, long term effects of consuming
  • There is a risk related to use of viral vectors
• DNA sequencing


  Determining the order/sequence of nucleotides in segments of DNA
• Genome sequencing


  Determining the order/sequence of nucleotides in all of the DNA of an organism (that is, the genome)
• Benefits of the Human Genome Project (HGP)


  • Novel genes and proteins, leading to new possible drug targets
  • Genetic variations in the populations, called single nucleotide polymorphisms (SNP), explaining why some drugs are more efficient in certain groups of people and less efficient in others; this lead to the idea of personalised medicine
• Cons of personalised medicine

  • Patients may pay more for personalised medicine as more research involved – is it affordable?
  • Patients may be denied drug treatment if they possess a certain SNP
  • Patients may be charged more by an insurance company if they possess a certain SNP (if patient's genetic information passed on to insurance companies)
• Frontal cortex/ cerebrum/ cerebral hemispheres

  Region of the brain involved in thinking, feeling emotions, learning, memory

  
• Hypothalamus


  Region of the brain involved in thermoregulation