Lecture 29: Specialized Tissues, Stem cells and Renewal 2 Flashcards
Sensory epithelium
- Sensory tissue of the nose, ears, and eyes
- Derived from ectoderm
- Sensory cells present in sensory epithelium act as transducers, converting signals form the environment into an electrical form that can be interpreted by CNS
Nose has ____ sensory neurons
olfactory
Ears have ____ hair cells
auditory
eyes have ____ sensory cells
photoreceptors
Each sensory cell carries ____ at it apical end that functions to _______. At its basal end
Each sensory cell carries a specialized structure at its apical end that detects the external stimulus and converts it into a change in membrane potential. At its basal end it makes synapse with neurons that relay the sensory information to specific sites in the brain
Olfactory Neurons are present in
olfactory epithelium of nasal cavity
Structure of Olfactory Neurons
Bipolar neurons with a dendrite facing the extracellular environment (interior space of the nasal cavity) and an axon that travels along the olfactory nerve to the olfactory bulb in the brain
Olfactory Receptors
- The free surfaces of cilia have odorant receptor proteins (olfactory receptors)
- A type of G protein coupled receptor
- each neuron expresses only one of these genes/receptor and is thus responsible for only one class of odorant
- structural features of that one odorant recognized by the receptor
- Activated olfactory receptor in turn activates an intracellular G-protein
- Activates adenylate cyclase which produces cyclic AMP
- opening of ion channels in the plasma membrane results in an influx of sodium and calcium into the cell
- This influx of positive ions causes the neuron ot depolarize, generating an action potential
- this AP is realyed ia the axon to the brain relay stations (glomeruli)
- Activates adenylate cyclase which produces cyclic AMP
Glomeruli (relay stations in the brain for AP from olfactory receptors) are located in
olfactory bulbs (one on each side of the brain)
Olfactory neurons expressing the same odorant receptors may be located in different places on the olfactory epithelium, but their axons converge on
the same glomerulus
Regeneration of Olfactory Neurons
- Individual Olfactory neurons survive for only a month
- Neural stem cells generate replacement for the lost neurons
- Basal stem cells in contact with basal lamina divide and differentiate into olfacotry neurons
- Odorant receptor proteins help in axonal guidance and allow the growth cone to migrate to and establish connection with the correct glomerulus in the olfactory bulb
- Regeneration of olfactory receptor cells is one of the only few instances of adult neurogenesis in the CNS
Olfaction in Neurodegnerative Disorders
- Reduced olfaction has been observed in aged individuals and in people with age-dependent neurodegenerative disorders
- Parkinson’s disease
- reduced sense of smell almost 10 years before clinical symptoms of disease
- Alzheimer’s disesase
- severity of disease correlates with degree of loss of olfaction
Neural Stem cells are prevalent only in what parts of the brain
- Ventricles of forebrain, cells from this region migrate to the olfactory bulb
- Hippocampus: region involving learning and memory
Evidence for Neural Stem Cells
- Cultures established from dissociated brain tissue show neurospheres
- Neurospheres: are clusters of neural stem cells
- Neurospheres can be propagated through several generations
- Can differentiate to produce both neurons and glial cells
Regeneration in Non-mammalian organisms
- Regneration of newt limb following amputation
- Differentiated muscle cells in the stump reenter the cell cycle, de-differentiated and become embryonic cells and proliferate to form a limb bud similar to the embryo
- Regenerate the missing limb
