Development and Plasticity 1 Development of the Nervous System a Starts at the embryonic age of 2 weeks b Occurs around the neural tube i These become the ventricles and central canal c Differentiation the process that makes one neuron different from another neuron begins as the neuron is migrating but depends on the environment of the target destination d Proliferation cells lining the ventricles divide daughter cells are primitive neurons and glia e Migration proliferating cells begin to migrate toward their eventual destination in the CNS migration is guided by immunoglobins and chemokines f Myelination production of myelin sheaths around axons first in the spinal cord then hindbrain midbrain and forebrain g Synaptogenesis formation of new synapses formation and removal occurs throughout life h Axons grow before dendrites during migration i Dendritic growth happens once the neuron reaches its destination i Axons are guided to their targets by following gradients of guidance molecules found on the surface of cells 2 Neurotrophins chemicals that promote neuron growth and survival a Early in development they promote survival and growth of selected neurons i Neurons that don t get enough don t survive b Promote the regrowth of injured axons 3 Apoptosis programmed cell death a Axons that do not receive enough neurotrophins degenerate and the cell body dies i This happens by a certain age of the neuron 4 Postnatal Development a CNS development continues after birth b Generally neurons cannot be replaced exceptions hippocampus and cortex c Postnatal development plays a role in learning 5 Recovery function after Nervous System Damage a Behavioral Compensation subjects learn to be able to use the remaining portions of the nervous system to compensate i b Neural Response to Injury Involves the development of new strategies to achieve tasks i Axons in the peripheral nerves can regenerate 1 More likely after being crushed rather than cut 2 The larger the gap the less likely the axon will be repaired ii Axons in the CNS cannot regenerate iii Axons can respond to neurotrophins released by cells in the vicinity of their terminals by sprouting collateral axon terminals that can fill synapses vacated by degenerating axons 1 This is the nervous system s way of making due 2 This does not give the neuron back 6 Reorganizational Events other parts of the body a The cortex reorganizes itself after the amputation of a body part by becoming responsive to b Original axons degenerate leaving vacant synapses into which other axons sprout c Phantom Limb the continuation of sensation of an amputated body part and reflects this process 7 Denervation or Disuse Supersensitivity heightened sensitivity to a neurotransmitter after the destruction of an incoming axon or of inactivity a Potential Mechanisms i Up regulation of receptor proteins ii Up regulation of following cascade component ion channels and second messengers 8 Stroke a Ischemia the most common type of stroke resulting from a blood clot of an artery neurons los their oxygen and glucose supply b Hemorrhage resulting from a ruptured artery neurons are flooded with excess calcium oxygen and other products c Stroke can cause edema the accumulation of fluid in the brain resulting in increased pressure on the brain and increasing the probability of further strokes i Disruption of the sodium potassium pump leading to the accumulation of sodium ions inside tPA breaks up the blood clots and reduces the effects of ischemic strokes i ii Cannabinoids have also been shown to potientially minimize cell loss through anti oxidant and anti inflammatory actions iii Cooling the brain has been shown to be one of the best ways to minimize the damage of a stroke 1 Slows down the metabolism of the brain thus stabilizing neurons d Treatment Vision 1 Sensory Receptors a Chemoreceptors respond to chemicals taste buds olfactory mucosa liver b Mechanoreceptors mechanical displacement of the skin skin ear muscles c Thermal Receptors respond to temperature d Pain Receptors intense versions of thermal and mechano receptors e Light Receptors basis of vision f Adequate Stimulus every sensory receptor is tuned to respond best to a certain type of stimulus energy i Other types of stimulus will cause some reaction seeing light when you rub your eyes g Generator Potential graded potential produced in some types of receptor cells h Sensory Adaptation receptors reduce their sensitivity if continuously stimulated eating something really salty and then eating something kinda salty will not taste salty at all 2 Neural Coding a Intensity strength of the stimulus represented by the rate of action potentials in a neuron i Auditon Sound pressure stimulus attribute loudness sensation ii Vision Luminance stimulus brightness sensation b Quality the type of the stimulus what makes taste smell taste different i Audition Frequency stimulus pitch sensation ii Vision Wavelength color c The Law of Specific Nerve Energies Proposed by Johannes Muller i ii Regardless of the type of stimulus activity in a nerve always leads you to the same psychological experience 1 you won t hear from your ears now and see from them later 3 Light a Photons the brightness of a light source depends on how many photons it emits b Wavelengths The color of the source depends on the wavelengths of the photons c Electromagnetic Spectrum Light is just a small portion of the electromagnetic spectrum energy spectrum There are x rays gamma rays and radio waves i Light is approx 300 750 a Choroid Coat heavily pigmented to absorb scattered light provides oxygen and nutrients for 4 Anatomy of the Eye parts of the retina b Cornea main focus for the eye c d Lens provides fine focus by changing thickess image in inverted on retina Iris radial muscle which constricts or expands the size of the pupil innervated by Cranial Nerve 3 e Humors provides structural and functional support for the eye like water balloons keeps the eye from collapsing i Aqueous humor in the anterior chamber between cornea and lens ii Vitreous humor in the posterior chamber jell like f Retina contains the photoreceptors and neurons that process and transmit visual information to the brain i Photoreceptors hyperpolarize in response to light and synapse with horizontal calls and bipolar cells 1 Rods 2 Cones ii Horizontal Cells have large dendritic trees that make inhibitory contact with many nearby photoreceptors they DO NOT have action potentials iii Bipolar Cells
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