Sensory receptors - Jocha
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Sensory receptors Are dendrites specialized to detect certain types of stimuli Exteroceptors: detect stimuli from outside the body (e.g. taste, hearing, vision) Interoceptors: receive stimuli from inside the body (e.g. change in blood pressure) Types of sensory receptors Chemoreceptors: respond to nearby chemicals (molecules) Pain receptors – Chemoreceptors that respond to chemicals released by damaged tissue Taste, Smell: Cells in the mouth with specific binding sites for particular molecules Photoreceptors – respond to light energy Vision: Changes in the flow of light energy Mechanoreceptors – respond to mechanical forces such as pressure Pressure, Position, Balance , Hearing Thermoreceptors – stimulated by temperature changes How does sensation occur? 1) Sensory receptors respond to environmental stimuli 2) Nerve impulses travel to the cerebral cortex 3) Sensation (conscious perception) of stimuli occurs 4) Sensory adaptation, decrease in stimulus response, can occur with repetitive stimuli (i.e. odor) 1 Mechanoreceptors 1: Proprioceptors Mechanoreceptors involved in reflex actions that maintain muscle tone is the continuous and passive partial contraction of the muscles. It helps maintain posture Axon terminal Muscle fiber Mechanoreceptors 2: Cutaneous receptors Receptors in the dermis (skin) that make the skin sensitive to touch, pressure, pain and temperature Pain, temperature touch touch pressure touch pressure touch Chemoreceptors 1: Taste Cells in the mouth with specific binding sites for particular molecules Sensitive to sweet, sour, salty and bitter tastes in food ~ 3,000 taste buds Sensory nerve fiber mostly on the tongue Taste cell Chemoreceptors 2: Smell Depends on 10-20 million olfactory cells (modified neurons) in the roof of the nasal cavity 80-90% of what we perceive as taste is actually due to the sense of smell Sensory nerve fiber Olfactory (smell) cell 2 Mechanoreceptors 3: Hearing Outer ear: functions in hearing; filled with air Middle ear: functions in hearing; filled with air Inner ear: functions in hearing and balance; filled with fluid Cochlea: Converts vibrations into nerve impulses Contains the organ of Corti (spiral organ) Sense organ containing hairs for hearing Nerve impulses are sent to Cochlear the cochlear nerve and then to the brain nerve Auditory canal: directs sound waves to the tympanic membrane Ossicles: (malleus, incus, stapes): 3 small bones that amplify sound waves Timpanic membrane: vibrates to carry the wave to the bones Mechanoreceptors 4: Balance The Semicircular canals detect angular movement (rotational equilibrium) Depends on hair cells at the base of each semicircular canal (ampulla) Semicircular canals: rotational (balance) equilibrium Semicircular canals are arranged in such a way that each provides a different dimension of space Hair cells with cilia embedded in a gelatinous material (cupula) 3 Mechanoreceptors 5: Position Detects movement of the head in the vertical and horizontal planes (gravitational equilibrium) Depends on hair cells in the utricle and saccule Vestibule: gravitational (position) equilibrium Vestibular nerve Æ to the brain Utricle Saccule Two membranous sacs located at the base of the semicircular canals Utricle is sensitive to horizontal (back-forth) Both have hair cells with cilia embedded in a gelatinous material That has otholits, calcium carbonate granules resting on it Saccule is sensitive to vertical (up-down) Photoreceptors: Vision 2 compartments: Anterior chamber: Changes in the flow of light energy (A) between the cornea and lens filled with a clear fluid called aqueous humor Made of 2 compartments Made of 3 layers 1-Sclera: outer layer, mostly white and fibrous except the cornea Posterior chamber: (P) most of the eye, behind the lens contains a gelatinous material called vitreous humor (P) (A) Anterior light Posterior 3-Retina: inner layer containing photoreceptors 2- Choroid: middle layer, darkly, pigmented vascular layer 4 Sclera: the white of the eye that maintains eye shape 3 layers of the eyes Cornea Transparent, important in refracting light Pupil A hole that allows light into fovea centralis the eyeball Choroid – Absorbs light rays that are not absorbed by the retina lens: Refract and focus light rays Iris: regulates the size of the pupil (and the amount of light that enters the eye) Ciliary body Contains a muscle that retina controls the shape of the lens The retina in the eyes has two types of receptors. Rods are responsible for black and white vision. Cones are more sensitive to particular wavelengths of light: color vision The fovea centralis is an area densely packed with cones where images are focused The Retina: Where light is actually sensed and the image is formed Sensory receptors Choroid from the retina form the optic nerve that takes impulses to the brain Retina: Rod and cone cells layer Rods are sensitive to light: black and white vision optic nerve Important for peripheral and night vision Vitamin A is important for proper functioning Cones are located mostly to optic nerve The blind spot is where the optic nerve attaches: no vision is possible because there are not photoreceptors there in the fovea centralis LIGHT Allow us to detect fine detail and color 3 different kinds of cones containing red, green and blue pigments 5 Abnormalities of the eye • Color blindness – genetic disease most common in males in which they usually cannot see red or green • Cataracts – lens of the eye is cloudy • Glaucoma – fluid pressure builds up in the eye • Astigmatism – condition in which the cornea or lens is uneven leading to a fuzzy image • Nearsightedness – eyeball is too long making it hard to see far away objects • Farsightedness – eyeball is too short making it hard to see near objects 6
