Sensation Lesson 4 PDF

Sensation The human being is made up of five senses-eye, ear, nose, skin, and tongue- which gather information about the environment. Sensation is the process by which information from our senses is received from our environment.(APA 2007). - - - For example, your eyes are watching words...

Sensation The human being is made up of five senses-eye, ear, nose, skin, and tongue- which gather information about the environment. Sensation is the process by which information from our senses is received from our environment.(APA 2007). - - - For example, your eyes are watching words on the page of your textbook. The sensory receptors in your eye are registering different patterns of light which are reflecting off the page. Your brain is interpreting the light into meaningful perception of words. Your eyes-sensory organs- are not seeing words but your brain -perceptual organ - is interpreting the lines and reflection on the page into meaningful words and concepts. Structure and Function When we see something a beam of light enters the eye through the **cornea**, a transparent or clear covering over your eye that protects the eye. The light then passes through the **pupil**, a small round opening in the center of the eye that allows light waves to pass into the eye.. The pupil is surrounded by the **iris,** the colored part of the eye that controls the amount of light that enters the eye by constricting or dilating in response to the amount of light present. For example when we enter a dark area, the muscles in the iris open the pupil (dilates) and allow more light to enter. Similarly, in bright light the iris constrict thereby allowing less light to enter the eye. Behind the pupil is the **lens**, a transparent structure whose curved surface bends and focuses the light waves into a narrow beam of light onto the retina. This process is known as **visual accommodation. Light** rays from the top of the image strike the bottom of the retina and vice versa, and rays from the left side of the image strike the right part of the retina and vice versa, causing the image on the retina to be upside down and backward. Retina, the layer of tissue located at the back of the eye that contains sensitive light cells called **photoreceptor cells**. These cells begin the process of transduction by absorbing the light waves. **Visual Pathways: Eye to Brain** **"Seeing takes place in the brain"** Light waves leave the retina and travel through the optic nerve to the occipital lobe located at the back of the brain. At back of each occipital lobe is a primary visual cortex, which transforms nerve impulses into simple visual sensations, such as texture, lines, and colors. At this point, you would report seeing only these basic sensations, not a complete item. However, to make sense of what you see, the nerve impulses must be sent from the primary visual cortex to neighboring visual association areas which add meaning to the item. **Audition** **We also hear from our brain.** Sound waves enter the outer ear (pinna) and travels through the auditory canal unto the eardrum where it strikes it causing it to vibrate. This vibration is passed on to the first of three tiny bones in the middle ear called **ossicles** better known as the **hammer, anvil and the stirrup.** **When the eardrum vibrates so does the hammer who then sends the vibration to the anvil who also sends the vibration to the stirrup which then connects to the oval window.The function of the middle ear is to pick up vibrations produced by the eardrum, amplify them and pass them on to the oval window and then to the cochlea in the inner ear.** **The cochlea (kock-lee aa)** contains receptors for hearing (called hair cells) and its function is **transduction** which is transforming vibrations into nerve impulses unto the brain for processing into auditory information. **Vestibular & Kinesthetic Senses** Vestibular senses are senses located in the inner ear which track the position of the head, keeping it upright, and help maintain balance. An infection to the vestibular sense can cause dizziness, nausea, and the inability to balance. The vestibular sense is also involved in **Motion sickness** which is feelings of discomfort, nausea, and dizziness in a moving vehicle. This happens when there is a sensory mismatch between the information from the vestibular sense---that your head is physically bouncing around---and the information reported by your eyes---that objects in the distance look fairly steady. **Kinesthetic Sense** **Kinesthetic senses** are senses which inform us about our bodies' positions and motions relative to gravity. Whenever we are moving various parts of the body, the sensory organs send information through the spinal cord and then to the brain for the coordination of motor movements. **Chemical Sense** Taste is called a chemical sense because the stimuli (anything that triggers a response) are various chemicals. The tongue has receptors, called taste buds, for the five tastes: sweet, salty, sour, bitter, and umami - a meaty-cheesy taste found in cheese, meat, pizza, and MSG. The function of taste buds is to perform **transduction**, which is transforming chemical reactions into nerve impulses. When eating something the chemicals, which are the stimuli for taste, break down into molecules and these molecules mix with saliva and run down into narrow trenches on the surface of the tongue. Once inside the trenches, the molecules stimulate the taste buds. **Taste buds** are receptors for taste.The chemicals dissolved in the saliva activate the taste buds, which then produces nerve impulses that goes to the brain's parietal lobe. The brain then transforms these nerve impulses into sensations of taste. The ability to taste something is greatly affected by our ability to smell. **Smell, or Olfaction** **Olfaction** refers to the sense of smell. The upper part of the nose is made up of a small area that contains receptor cells for olfaction. The function of the olfactory receptors is **transduction**, to transform chemical reactions into nerve impulses. **How we smell** If someone sprays perfume in the classroom, you can only smell the substance because it is **volatile**. A volatile substance is one that can release molecules into the air at room temperature. These molecules enter the nasal passages, where the olfactory receptors are located.The olfactory cells trigger the nerve impulses that travel to the brain, which interprets the impulses as different smells. **Functions of the olfactory** 1. 2. 3. 4. The sense of touch enclosed in includes pressure, temperature, and pain. Beneath the outer layer of skin are approximately half-dozen tiny sensors that act as receptors for the sense of touch. The function of the touch sensors is to change mechanical pressure or temperature variations into 4 nerve impulses that are sent to the brain for processing. **Pain** is an unpleasant sensory and emotional experience which may result from tissue damage, one's thoughts or beliefs, or environmental stressors (Plotnik & Kouyoumdjian 2014). The human body is made up of many pain receptors which send nerve impulses to the brain where these impulses are changed to pain sensations. The purpose of pain is to warn us to avoid or escape dangerous situations and to make us take time to recover from injury. Pain definition differs from other senses in three ways: - - - **Gate control theory** Have you ever realized that some headaches come and go, depending on what you are doing or what you shift your attention too? This can be explained by the **gate control theory** which states that non painful impulses (shifting attention) compete with the pain impulses (headache) in reaching the brain. This competition creates a bottleneck that hinders the amount of pain impulses reaching the brain and increases the non painful impulses to the brain. One\'s perception of pain from an injury can also be reduced when your brain secretes a pain-reducing chemicals, called **endorphins**. These endorphins are produced in situations that evoke great fear, anxiety, stress, or bodily injury, as well as after intense aerobic activity.