1. Chapter 10 Special Senses and Functional Aspects of the Nervous System

2. Introduction The experiences we have as we move through life are a result of sensing the world around us These experiences are called sensations, which are a state of awareness of the external or internal condition of the body Provide the brain with information necessary to maintain homeostasis

3. How do sensations help us maintain homeostasis? Hunger – get some food Cold – find a warmer place Pain – something’s wrong – FIX IT

4. Sensory Pathways All sensory pathways begin with a stimulus, or a change in the environment that is great enough to initiate a nerve impulse The stimulus is converted to a nerve impulse by a receptor, then conducted along a sensory neuron to the CNS All receptors are excitable (have the ability to generate an action potential)

5. The threshold of stimulus for each type of receptor is typically very low for one type of stimulus yet very high for all other types of stimuli For example, receptors in the eye have a low threshold of stimulus for light and will initiate a nerve impulse in response to it, but have a very high threshold to slight changes in temperature – receptors are stimulus-specific

6. In many receptors, the threshold level for a particular stimulus may rise after continuous stimulation; this is called sensory adaptation Impulses are generated at decreasing rates until they stop completely and the sensation ends This prevents the brain from being overloaded by information that is no longer important

7. Types of Receptors Mechanoreceptors – detect mechanical or physical change in the receptor or nearby cells; sensitive to touch, pressure muscle tension, hearing, equilibrium and blood pressure Thermoreceptors- detect temperature changes Nociceptors- detect pain, usually from physical or chemical damage to nearby cells

8. Photoreceptors – sensitive to changes in the amount of light (present only in retina) Chemoreceptors—detect chemicals dissolved in fluid providing smell and taste; also detect levels of oxygen and carbon dioxide in blood

9. General Sensory Pathways Conduction pathways that carry impulses from a simple receptor (found in skin, visceral organs, and muscles) to the brain are known as General sensory pathways From the receptor, impulse is conducted along three sensory neurons before in reaches its destination in the brain

10. First-order neuron—connects receptor to the spinal cord; may extend to the medulla oblongata Second-order neuron—carries the impulse toward the thalamus Third-order neuron—conducts the impulse to the cerebral cortex for processing

14. Assumptions Video In the cerebral cortex, sensations are interpreted. Interestingly, these sensations aren’t always interpreted correctly …..

15. Special Sensory Pathways Carry impulses from complex receptors like those in the ear and eye Exhibit more variation in the number of neurons than general sensory pathways Include at least 3 sensory neurons that connect to a specific region of the cerebral cortex Located in the head, travel along cranial nerves to the thalamus then to the cerebral cortex (except for smell)