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Nervous System (senses (the types of receptors based on stimulus origin:
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Nervous System
senses
the types of receptors based on stimulus origin:
- exteroceptor (sensitive to stimuli outside the body, most are located at or near body surface, include receptors for touch, pressure, pain temperature in the skin, most receptors of special sense organs)
- interoceptor (receive stimuli from internal viscera such as digestive tube, bladder and lungs, different interoceptors monitor different things like changes in chemical composition or stretching out tissues and temperature )
- proprioceptors (located in musculoskeletal organs, monitor degree of stretch of these locomatory organs and send input to CNS)
the types of receptors based on stimulus type:
- thermoreceptor ( responds to temperature changes, cold or warm sensitive receptors)
- photoreceptor (responds to light, located in eye)
- chemoreceptor (responds to chemicals in solutions, molecules tased or smelled)
- Nociceptor (response to harmful stimuli that results in pain)
- mechanoreceptor (responds to mechanical forces such as force, pressure, stretch, touch, vibrations)
- baroreceptor (type of mechanoreceptor that monitors pressure).
the ear components:
- external ear (auricle- collects soundwaves, external auditory meatus - sends it to eardrum)
- middle ear (tympanic membrane- border between external and middle ear, receives vibrations and sends it to auditory ossicles; auditory ossicles- transmit vibration to a fluid in middle ear and amplifying the pressure of sound vibrations) - inner ear (cochlea- snail-shaped and filled with fluid, converts vibrations into nerve signals)
hearing pathway:
cochlear receptors- cochlear branch of CN VII vestibulocochlear nerve medulla oblongata- pons- midbrain- thalamus- primary auditory cortex
olfaction components
- olfactory bulb (located on the top of cribriform plate, bundle of nerves)
- cribriform plate with cribriform foramina (olfactory axons are going through)
- olfactory epithelium (located on the roof on nasal cavity, contains different types of receptors sensitive to one particular type of molecule)
olfactory pathway: olfactory receptors- olfactory sensory neurons- olfactory tract- limbic systems (emotional brain) or primary olfactory cortex in temporal lobe
gustation components:
- taste buds (host taste receptors, located in papillae in mucosa of mouth, tongue larynx, epiglottis; consists of basal epithelial cells, gustatory epithelial cells, gustatory hair and taste pore, surrounded on two sides by stratified squamous epithelium)
- cranial nerves that transmit taste information to CNS are
- facial nerve VII (from anterior 2/3 of brain)
- the glossopharyngeal IX (from tongue's posterior third and new bads in the pharynx)
-vagus nerve X (from few taste buds on epiglottis and lower larynx)
pathway :
taste receptors (inside taste buds) - cranial nerves VII, IX and X - medulla oblongata- pons - thalamus - gustatory cortex in insula lobe
eye components :
- three tunics
- fibrous layer (sclera- white part of eye made out of dense connective tissue, protects and gives shape; cornea - transparent, focuses light into retina)
- vascular layer (choroid- nourishes the outer layer, black, prevents light from scattering, continues with ciliary body that changes shape of lens)
- sensory layer (retina- it has receptors that allow us to see, very thin and delicate)
- rods- receptors sensitive to light
- cones- receptors sensitive to color
- lens (posterior to iris, focuses light on retina)
- iris (color part of the eye, anterior to lens, posterior to cornea, has pupil and adjust it depending on light)
- optic disc (blind spot where optic nerve enters retina)
- macula lutea (opposite to pupil, best vision)
- fovea centralis (center of macula lutea, clearest vision because of high concentration of cones)
- posterior and anterior cavities
- anterior segment (from iris to cornea, filled with aqueous humor that nourishes lens and cornea and maintains normal intraocular pressure)
- posterior cavity (from iris to retina, has vitreous humor that is gel like, keeps retina in place, supports retina and lens)
visual pathway : cornea- pupil- lens- retina- optic nerve- optic chiasm- optic tract- midbrain- thalamus- primary visual cortex in occipital lobe
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neurons
structural types of neurons:
- multipolar (many processes extend from cell body, most common in CNS)
- bipolar (two processes extend from cell body, mostly in special senses)
- unipolar (one process extend from cell body, in dorsal root ganglia of spinal cord)
major components of a neuron:
- cell body (it consist of single nucleus surrounded by cytoplasm)
- nucleus and nucleolus (nucleus is spherical and clear and contains dark nucleolus near its center, nucleolus makes incomplete ribosomes)
- chromatophilic substance (clusters of free ribosomes and Rough ER. It's in charge of renewing plasma membrane and proteins within the cytosol)
- dendrites (receiving part of neuron)
- axon hillock ( axon arises from cone shaped axon hillock)
- axon (generates and conducts impulse away from cell body, only one per neuron)
- axon collaterals (additional branches from axon)
- terminal arborization (axon spreads up at the end, tee-like shape)
- terminal boutons oir axon terminals (very end of axon)
functional types of neurons:
- motor or efferent neurons (always multipolar, carry neural impulses away from CNS to muscles and glands)
- sensory or afferent neurons (cell body located in ganglia of PNS near spinal cord, central processes terminates are in CNS, majority of general senses are unipolar, some special senses are bipolar)
- interneurons or association neurons (located between neurons of CNS, structurally multipolar, it's most abundant- 98.8% of all neurons)
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