The Peripheral Nervous System Section 31.3

How does the central nervous system recieve sensory information? Through the peripheral nervous system Even in our head we have cranial nerves arranged to ganglia that stimulate regions of the head and neck The peripheral nervous system can be divided in two: The sensory division and the motor division The sensory division transmits impulses from sense organs to the Central nervous system The motor division transmits impulses in the opposite direction

What constitutes a stimulus?

What is the link between the nervous system and homeostasis? The nervous system plays a key link by coordinating the activities of other systems and organs Once it has gathered and processed information, it will send commands to other parts of the body The motor division of the peripheral nervous system transmits impulses from the central nervous system to muscles or glands These messages can be relayed through either the somatic nervous system or the autonomic nervous system

What is the somatic nervous system? The somatic nervous system regulates body activities that are under conscious control, such as the movement of skeletal muscles Ordinarily you can control movement of muscles, but, when your body is in danger it can take over – the difference between voluntary control and reflex arcs Voluntary control is when you choose to move a body part, and our brains sends an impulse to the necessary muscle through the central nervous system A rapid response (reflex) is an automatic reaction to a stimulus The body reacts before a message is sent to the brain, informing it of the injury The spinal cord controls most, but not all reflexes Blinking, and sneezing are reflexes controlled by the brain

What is the autonomic nervous system? The autonomic nervous system regulates activities that are involuntary, or not under conscious control Example – when your run the autonomic nervous system speeds up your heart rate There are two important parts: The sympathetic nervous system and the parasympathetic nervous system, The two work together, but have opposite effects on organs

Key concepts What are the different roles of the sensory division and motor division Give three examples of stimuli that your sensory receptors are responding to right now Is a reflex arc part of the central nervous system, the peripheral nervous system or both? Describe a situation when you would expect your sympathetic nervous system to be more active than your parasympathetic nervous system

The Senses Section 31.4

What are the five senses?

What is the largest sense organ in the body? Your skin! Nearly all areas are sensitive to touch Different sensory receptors in the body respond to touch, temperature and pain All are found in the skin, but some in other areas as well Human skin contains at least seven types of sensory receptors, including several that respond to different levels of pressure Different parts of the body have different numbers of receptors Thermoreceptors are sensory cells that respond to heat and cold Found throughout skin, and in hypothalamus (part of brain that senses blood temperature). Pain receptors are found throughout the body. Those in the skin respond to physical injuries. Many in tissues respond to chemicals released during infection or inflammation. The brain has no pain receptors

How is the sense of smell and taste related? Both involve the ability to detect chemicals Both your nose and mouth contain chemoreceptors responsible for both of these senses, and send impulses to the brain The sense of smell is capable of producing thousands of different sensations. Much of what we “taste” is actually related to the smell Our taste buds respond to salty, bitter, sweet and sour foods Recently, a five receptor identified, responding to umami Strongly simulated by monosodium glutamate (MSG) often added to Asian food to enhance flavor Meat and cheese have a similar effect due to glutamate

How is hearing and balance related? The human ear has two sensory functions – hearing and detecting positional changes associated with movement Mechanoreceptors found in parts of the ear transmit impulses to the brain, which the brain translates into sound and information about balance The semicircular canals within the ear, alongside two tiny sacs located behind them, monitor the position of the body in relation to gravity The semicircular canals and sacs are filled with fluid and lined with hair cells. As the head changes position, the fluid in the canals changes position This causes hair on the hair cells to bend This sends impulses to the brain that enable it to determine body motion and position

How does the eye and brain produce vision? The lens focuses light onto the retina, which contains photoreceptors Photoreceptors convert light energy into nerve pulses that are carried to the brain through the optic nerve Rods are light sensitive, but do not distinguish color Cones are color sensitive, but only work well in good light. They are concentrated In the fovea Blind spot – where optic nerve joins retina The brain is able to process and interprets all of the information producing a 3-D visual image

Key Concepts What three types of sensations to receptors in the skin respond to? Which will have more sensory receptors the sole of your feet or back of your neck? Why? What are the five basic tastes detected by taste buds? Why can’t you taste food when you have a bad cold? What structures in your ear gather information about the position of your body? Why do you feel dizzy after you spin around a few times? If a person suffers from night blindness, which photoreceptor is likely not functioning properly?