Exam 3 -Specialized Tissues, Stem Cells and Tissue Renewal 2 Flashcards
What is sensory epithelia?
- Specialized Epithelium
- covers sensory tissue of nose , ears, and eyes
- Derived from ecto derm
- Collects signals forme xternal enviroment and delivers them to the CNS
- Sensory Cells present in the sensory epithelium are transducers
- convert enviromental signals into eletrical form that can be interpreted by the CNS
- Well conserved through evolution
What are sensory Cells and there respective examples?
- All of these are either neurons or neuron like
- At apical end
- detects the external stimulus and converts it into a change in membrane potential
- At basal end
- synapse with neurons and relays sensory inforamtio to brain
- At apical end
- Eyes = photo receptors
- Ears = auditory hair cells
- Nose = olfactory sensory neurons
What are olfactory Neurons
- Present in oflactory epithelium in the nasal cavity
- Bipolar neurons with dendrite facing the extracellular environment (interior space of nasal cavity) and an axon that travels along the olfactory nerve to olfactory bulb in the brain
- Many hair like cilia protrude from dendrtie
- Supporting cells in between neurons hold neuron in place and seperate them
- Sensory surfaces of epithelium kept moist and protect by a layer of fluid (mucus)
- Not sure but in lecture
- “basal cells in the epithelium - cells in contact with basal lamina “
What are olfactory Receptors?
- Free surfaces of cilia have odorant receptor proteins (olfactory receptors)
- A type of G protein Coupled receptor
- There are a 1000 odorant receptor genes in a dog and 350 in humans and each neuron only express one of these allows the cell to respond to only one class of ordant
- ordant - organic small molecules
- Structural features recongized by receptor
- All olfactory neurons respond by a common mechanism
How does the common mechanism for all olfactory neurons work?
- AAffinty is variable depending on how well the ligand binds to its receptors
- each receptor binds to one class of ordant molcules
- Activated olfactory receptor in turn activates intracellular G - Protein “Golf”
- activates adenylate cyclase which produces cyclic AMP
- Opens Ion channels in the plasma membrane which results in an influx of sodium and calcium into the cell
- this influx of postive ions causes neurons to depolarize generating an action potential
Where are olfactory signals sent after they reach brain ?
- The action potential relayed via axon to brain
- relay stations in brain called glomeruli
- located in olfactor bulbs on each side of brain
- 1800 glomeruli per bulb in mouse brain
- Although olfactory neurons express the same ordant receptor are located in different places on olfactory epithelium there axons converge on the same glomerulus
How does regeneration of olfactory neurons occur?
- Indivdual neurons survive for a month
- Neural stem cells residing among basal cells in the olfactory epithelium generate replacements for the lost neurons
- Basal stem cells in contact with basal lamina divide and differentiate into olfactory neurons
- Ordorant receptor protein help in axonal guidance and allow the growh cone to migrate to and establish connection with correct glomerulus in olfactory bulb
- Regeneration of olfactory receptor cells is one of the only few instances of adult neurogenesis in CNS
How does olfaction in neurodegenerative disorder?
- Reducted olfaction has been observed in aged individuals and in people with age dependent neurodegenerative disorders
- In idiopathic Parkinsons diesase reduce sense of smell precedes clinical symptoms of the disease by almost ten years
- in alzheimers disease severity of the disease correlates with the degree of the loss of olfaction
- CNS the most difficult to construct in adult life
- adult brain and spinal cord have little capacity to self repair or regenerate
where are stem cells found in the brain?
Stem cells in brain divide and produce neurons and glial cells
Prevalent only in
- Ventricles of forebrain
- Hippocampus
What are characteristics of stem cells in the ventricles ?
- Stem cells present in the region lining the brain ventricles
- continously divide and produce new stem cells
- migrate to the olfactory bulb where they differentiate into olfactory neurons
- linked to renewal of olfactory epithelium
What are stem cells in hippocampus?
Involved in learning and memory formation
Continous turnover of cells in hippocampus
Plasticity of adult brain associated with turnover of a specific subset of neurons
About 1400 fresh neurons are generated every day, givng a turnover of 1.75% of the population per year
What is the Experimental evidence for neural stem cells ?
- Cultures established from self renewing regions of brain and fetal brain tissue show neurospheres
- clusters of neural stem cells, neural cells, and glial cells
- neurospheres can be propagated through several generations
- depending upon culture conditions they can stay as stem cells, differentiate into neurons, or differentiate to produce both neurons and glial cells
What are the applications of neural stem cells?
- Neural stem cells can be grafted in adult brain
- have remarkable ability to adjust their behavior to match new location
- stem cells from hippocampus when implanted into olfactory bulb pathway give rise to neurons that become correctly incorpated into the olfactory bulb
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What are different types of neuogensis of the brain?
Neuronal activity such as that which occurs during learning the induction of long term potentiation (LTP) and in vitro depolarization , potently activates quiescent stem cell proliferation.
a different subpopulation of stem cell is activated following exposure to nonrepinephrine (NE) and it is thought that this population responds to NE mediated antidepressant treatment which can alleviate clinical depression
Electrical Simulation such as deep brain stimulation and eletroconvulsive shock which are currently used to treat many neurodegnerative and psychiatric conditions.
what an example of regerneation and repair in non-mammalian organism?
- Planaria - fresh water flatworm
- Has extra ordinary capacity to regenerate
- started it gets smaller by reducung its cell number whie maintaing body proportions (degrowth)
- Transformation common in non-mammalian species whicha re able to regenerate lost tissues and organs
- regeneration of newt limb following amputation
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- regeneration of newt limb following amputation
