Chapter 14 - The Brain and Cranial Nerves - CHAPTER 14 |...

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14|THE BRAIN ANDCRANIAL NERVESFigure 14.1 Too Hot to TouchWhen high temperature is sensed in the skin, a reflexive withdrawal is initiated by themuscles of the arm. Sensory neurons are activated by a stimulus, which is sent to the central nervous system, and amotor response is sent out to the skeletal muscles that control this movement.IntroductionChapter ObjectivesAfter studying this chapter, you will be able to:Describe the components of the somatic nervous systemName the modalities and submodalities of the sensory systemsDistinguish between general and special sensesDescribe regions of the central nervous system that contribute to somatic functionsExplain the stimulus-response motor pathwayThe somatic nervous system is traditionally considered a division within the peripheral nervous system. However, thismisses an important point: somatic refers to a functional division, whereas peripheral refers to an anatomic division. Thesomatic nervous system is responsible for our conscious perception of the environment and for our voluntary responsesCHAPTER 14 | THE BRAIN AND CRANIAL NERVES561Download for free at ."The Brain and Cranial Nerves" fromAnatomy and Physiologyby OpenStax College is available under aCreative Commons Attribution 3.0 Unportedlicense. © 2013, Rice University.
to that perception by means of skeletal muscles. Peripheral sensory neurons receive input from environmental stimuli, butthe neurons that produce motor responses originate in the central nervous system. The distinction between the structures(i.e., anatomy) of the peripheral and central nervous systems and functions (i.e., physiology) of the somatic and autonomicsystems can most easily be demonstrated through a simple reflex action. When you touch a hot stove, you pull your handaway. Sensory receptors in the skin sense extreme temperature and the early signs of tissue damage. This triggers an actionpotential, which travels along the sensory fiber from the skin, through the dorsal spinal root to the spinal cord, and directlyactivates a ventral horn motor neuron. That neuron sends a signal along its axon to excite the biceps brachii, causingcontraction of the muscle and flexion of the forearm at the elbow to withdraw the hand from the hot stove. The withdrawalreflex has more components, such as inhibiting the opposing muscle and balancing posture while the arm is forcefullywithdrawn, which will be further explored at the end of this chapter.The basic withdrawal reflex explained above includes sensory input (the painful stimulus), central processing (thesynapse in the spinal cord), and motor output (activation of a ventral motor neuron that causes contraction of the bicepsbrachii). Expanding the explanation of the withdrawal reflex can include inhibition of the opposing muscle, or crossextension, either of which increase the complexity of the example by involving more central neurons. A collateral branch

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Term
Fall
Professor
N/A
Tags
Physiology, Anatomy, sensory receptor, Olfactory receptor neuron

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