33-3 The Senses

33-3 The Senses Bio 30 - NWRC

Taste

Taste • Taste is one of the five senses through which all animals interpret the world around them. Specifically, taste is the sense for determining the flavour of food and other substances. It is one of the two chemical senses (the other being smell) and it is stimulated when taste buds on the tongue come in

Taste • Clusters of small organs called taste buds are located in the mouth, mainly on the surface of the tongue. Taste buds (named so because under the microscope they look similar to plant buds) lie in small projections called papillae and contain taste receptors that bind to food molecules broken down by saliva. These receptors send messages along nerves to the brain, which interprets the flavor as sweet, sour, salty, or bitter.

Smell • Smell depends on sensory receptors that respond to airborne chemicals. In humans, these chemoreceptors are located in the olfactory epithelium — a patch of tissue about the size of a postage stamp located high in the nasal cavity.

Sight • Light enters the front of the eye through the pupil and is focused by the lens onto the retina. Rods and cone cells on the retina respond to the light and send a message through the optic nerve fiber to the brain.

Sight • The rods are more numerous, some 120 million, and are more light sensitive than the cones. However, they are not sensitive to colour. The 6 to 7 million cones provide the eye's colour sensitivity Cones function in light and are most sensitive to colours

Sight • The retina is a multi-layered sensory tissue that lines the back of the eye. It contains millions of photoreceptors (rods and cones)that capture light rays and convert them into electrical impulses. These impulses travel along the optic nerve to the brain where they are turned into images. • Watch Cow Eye Dissection

Hearing and Balance

Hearing and Balance 3 regions: outer ear or pinna (collects and directs sound waves), middle ear (transfers and amplifies the sound waves), and the inner ear (senses pitch/frequency, intensity/loudness, and quality/timbre). A snaillike structure called the cochlea is the sensory element of the inner ear.

Hearing and Balance The cochlea is a fluid-filled chamber whose fluid is set into motion by movement of the oval window between middle and inner ears.

Hearing and Balance The cochlea contains the basilar membrane that varies in stiffness along its length. High frequencies deflect the basilar membrane nearer to the oval window and low frequencies farther from the window. This deflection activate receptors, called the hair cells which trigger nerve impulses. The sensory input travels along the cranial nerve to the brain

Hearing and Balance 3 fluid-filled semicircular canals, arranged at right angles to one another Fluid movement occurring within the canals due to head movement causes nerve impulses to be sent to the brain regarding head position and movement. These structures sense head position and acceleration.

Touch

Touch

The sense of touch is the name given to a network of nerve endings that reach just about every part of our body. These sensory nerve endings are located just below the skin and register light and heavy pressure on the skin and also differences in temperature. These nerve endings gather information and send it to the brain

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1. 1. Sound, which is transmitted as sound waves (vibration of the air), enters the ear canal and reaches the eardrum. 2. The sound waves lead to the vibration of the eardrum, which also vibrates the small bones behind the ear drum. 3. The vibration motion of the bones makes the fluid in the inner ear or cochlea to vibrate. 4. The vibration waves in the inner ear fluid causes the sensory (hair) cells in the inner ear (cochlea) to bend. The hair cells change the movement into electrical signals. 5. These electrical signals are transmitted through the hearing (auditory) nerve and up to the brain, where they are interpreted.

Assessment • 2. If the cornea was damaged light might be distorted as it entered the eye causing the image in the brain to be distorted

Assessment • 3. The variety of receptors are important because the fingers encounter many different types of stimuli (pressure, pain, etc.)

Assessment • 4. The sense of taste comes from the receptors in the mouth and nasal cavity. If the nasal cavity is blocked the brain does not get all necessary information to identify a particular taste.