Sensory Reception

SENSORY RECEPTORS The senses are the human brain’s connection to the outside world.

SENSORY RECEPTION AND PERCEPTION Sensation is initiated in the senses through sensory reception, but sensation and perception take place in the brain. Everyone’s perception of the world is unique.

Sensory receptors convert different forms of energy into electrochemical energy, which the nervous system interprets.

DIAGRAM OF THE EYE

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Parts of the Eye StructureFunction ScleraSupports and protects delicate photocells CorneaRefracts light toward the pupil Aqueous humourSupplies cornea with nutrients and refracts light Choroid layerContains blood vessels that nourish the retina IrisRegulates the amount of light entering the eye Vitreous humourMaintains the shape of the eyeball and permits light transmission to the retina LensFocuses the image on the retina PupilThe opening in the iris that allows light into the eye RetinaContains rods used for viewing in dim light and cones used for identifying colour Fovea centralisMost light-sensitive area of the retina –contains only cones Blind spotWhere the optic nerve attaches to the retina

PHOTORECEPTION The cornea, lens, and humours (aqueous – in front and vitreous – in behind the lens) focus light on the retina.

The pathway of light: light enters the eye through the pupil, and is gathered on the pigmented epithelium of the retina. Photoreceptors on the retina are stimulated by the light and relay the message via the bipolar cells and the ganglion cells to the optic nerve which then relays the message to the CNS. Optic nerve Thalamus Primary visual cortex Visual association cortex

ACCOMODATION The lens is flexible. Its ability to change shape in order to focus on near or far objects is called accommodation.

The ability to focus is impaired if the cornea is uneven (causes astigmatism), or if the eyeball is too long (myopia) or too short (hyperopia).  ---nearsightedness – a concave lens is used to correct vision  --farsightedness – a convex lens is used to correct vision Astigmatism - unevenly ground glasses or contacts can be used to correct vision

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BLIND SPOT Each eye has a blind spot, where the optic nerve connects to the eyeball, but each eye compensates for what the other cannot see. Binocular vision (both eyes pointing the same way) also allows us to see in three dimensions.

RODS AND CONES The retina contains the photoreceptor cells. The rods function in dim light and produce black and white images. The cones function in bright light and produce colour images.

The Chemistry of Vision: An estimated 160 million rods surround the colour-sensitive cones in the centre of the retina. The rods contain a light-sensitive pigment called rhodopsin. Rhodopsin is composed of a form of vitamin A and a large protein molecule called opsin. When a single photon strikes a rhodopsin molecule, it divides into two components: retinene, the pigment portion, and opsin, the protein protion.

This division alters the cell membrane of th rods and produces an action potential. For the rods to continue to work, rhodopsin levels must be maintained. A long term vitamin deficiency can permanently damage the rods. Extreme sensitivity of rhodopsin to light can cause rhodopsin to break down faster than it can be restored. The opsins used for colour vision are much less sensitive to light and, therefore, operate best with greater light intensity.

Colour Perception: The cones are responsible for colour vision Each cone is sensitive to one of the three primary colours of source light: red, blue and green. When combinations of cones are stimulated, the brain perceives different colours. The three types of cones firing in different combinations allow humans to see millions of different shades of colour. Colour blindness occurs when one or more types of cones are defective.

Afterimages: Positive afterimages occur after you look into a bright light and then close our eyes. Negative afterimages occur when the eye is exposed to bright light for an extended period of time.

VISUAL PROCESSING Once stimulated, the rods and cones send a neural message to the occipital lobe of the brain, which processes and integrates the information, and then perceives it as an image.

MECHANORECEPTORS - HEARING The mechanoreceptors for hearing and balance are located in the inner ear. Hair cells on the basilar membrane synapse with dendrites of the auditory nerve which transmit an electrochemical impulse to the temporal lobe of the brain.

The cochlea, semicircular canals, utricle, and saccule all contain hair cells that react to movement.  rotational equilibrium  head position and balance

HEARING AND PROPRIOCEPTION The hair cells synapse with nerve fibres, which transmit the sensory information to the nerves. The nerves then send an impulse to the brain. Proprioceptors in the muscles, joints, and tendons also inform the brain about the position of body parts.

s/ /CGY_neto_jose_110518/ ?hub=CalgaryHome s/ /CGY_neto_jose_110518/ ?hub=CalgaryHome Calgarian Jose Neto “sees” with his tongue!

Sensory receptors in the tongue (taste buds), nose (olfactory cells), and skin (temperature, pressure, and pain receptors) provide additional information to the brain.

OLFACTORY (SMELL) RECEPTORS

TASTE RECEPTORS

Chapter 12 Concept Organizer

Chapter 12 Summary Sensory reception occurs at the senses. Sensation and perception occur in the brain. Photoreceptors detect light. Chemoreceptors detect tastes, odours, and internal conditions, such as blood pH and volume. Thermoreceptors detect temperature. Mechanoreceptors function in hearing, balance, and coordination. The cornea, lens, and humours of the eye direct light on the photoreceptor cells in the retina. Rods function in dim light and produce black and white images. Cones function in bright light and produce colour images. The optic nerve transmits signals from the rods and cones to the occipital lobe of the brain, where images are perceived.

Chapter 12 Summary The outer ear transmits sound waves to the middle ear, which makes the tympanum and, in turn, the bones of the middle ear vibrate. These bones amplify and transmit the vibrations to the oval window in the inner ear. The vibrations in the oval window produce pressure waves in the fluid of the cochlea in the inner ear. The pressure waves are detected by hair cells, which relay electrochemical messages to the brain via the auditory nerve. Hearing aids that amplify sound can sometimes be used to treat conduction deafness caused by damage to the outer or middle ear. Noise-induced hearing loss, caused by destruction of the hair cells, is more difficult to treat. It results in a loss of ability to hear sounds of specific frequencies.

Chapter 12 Summary Hair cells in the semicircular canals of the inner ear allow for rotational equilibrium (balance). Hair cells in the utricle and saccule of the inner ear allow for gravitational equilibrium (balance). Proprioceptors are another type of mechanoreceptor involved in coordination. Tastes are detected by chemoreceptors in the taste buds of the tongue. Smells are detected by chemoreceptors in the nose. The skin contains receptors for light touch, pressure, pain, heat, and cold. Sensors in the nose, tongue, and skin all help the nervous system maintain homeostasis.