Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Human Anatomy & Physiology SEVENTH EDITION Elaine N. Marieb Katja Hoehn PowerPoint ® Lecture Slides prepared by Vince Austin, Bluegrass Technical and Community College C H A P T E R 13 The Peripheral Nervous System (PNS) P A R T A

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Peripheral Nervous System (PNS)  PNS – all neural structures outside the brain and spinal cord  Includes sensory receptors, peripheral nerves, associated ganglia, and motor endings  Provides links to and from the external environment  Allows CNS to gather information and then act on it

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings PNS in the Nervous System Figure 13.1

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sensory Receptors  Structures specialized to respond to changes in their environment  stimuli  Activation of sensory receptors results in graded potentials that trigger nerve impulses to the CNS

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Receptor Classification by Stimulus Type  Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch  Deformed by a mechanical force  Thermoreceptors – sensitive to changes in temperature  Photoreceptors – respond to light energy (ex: retina)  Chemoreceptors – respond to chemicals (ex: smell, taste, changes in blood chemistry)  Nociceptors – sensitive to pain-causing stimuli (ex: searing heat, extreme cold, excessive pressure)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Receptor Class by Location: Exteroceptors  Respond to stimuli arising outside the body  Found near the body surface  Sensitive to touch, pressure, pain, and temperature  Include the special sense organs (vision, hearing, taste, smell, equilibrium)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Receptor Class by Location: Interoceptors  Respond to stimuli arising within the body  Found in internal viscera and blood vessels  Sensitive to chemical changes, stretch, and temperature changes

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Receptor Class by Location: Proprioceptors  Also respond to internal stimuli  Respond to degree of stretch of the organs they occupy  Found in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles  Constantly “advise” the brain of one’s movements

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings From Sensation to Perception  Survival depends upon sensation and perception  Sensation is the awareness of stimuli (changes in the internal and external environment)  Perception is the conscious interpretation of the meaning of those stimuli

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Example of Sensation and Perception  A pebble gets into your shoe. You sense deep pressure on your foot and in turn perceive discomfort. Perception allows your brain to act and in this case, we would remove our shoe and get rid of the pebble.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Organization of the Somatosensory System  Input comes from exteroceptors, proprioceptors, and interoceptors  The three main levels of neural integration in the somatosensory system are:  Receptor level – the sensory receptors  Circuit level – ascending pathways  Perceptual level – neuronal circuits in the cerebral cortex

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.2

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Processing at the Receptor Level  Stimulus must excite the receptor in its receptive field  The receptor must have specificity for the stimulus energy  Stimulus energy must be converted into a graded potential (receptor potential)  A graded potential in the associated sensory neuron must reach threshold  action potential

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Processing at the Circuit Level  Deliver impulse to the appropriate region of the cerebral cortex

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Processing at the Perceptual Level  The thalamus projects fibers to:  The somatosensory cortex  Sensory association areas  Ability to identify and appreciate sensation depends on the specific location of the target neurons in the cerebral cortex (message is just an action potential)  Brain interprets the activity of a specific sensory receptor as a specific sensation no matter how it was activated

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Nerve  Nerve – cordlike organ of the PNS consisting of parallel bundles of peripheral axons enclosed by connective tissue  Connective tissue coverings include:  Endoneurium – loose connective tissue that surrounds axons  Perineurium – coarse connective tissue that bundles fibers into fascicles  Epineurium – tough fibrous sheath around a nerve

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Nerve Figure 13.3b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cranial Nerves  Twelve pairs of cranial nerves arise from the brain  They have sensory, motor, or both sensory and motor functions  Each nerve is identified by a number (I through XII) and a name  First 2 pair attach to forebrain, the rest to the brain stem  Four cranial nerves carry parasympathetic fibers that serve muscles and glands

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cranial Nerves Figure 13.5a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Summary of Function of Cranial Nerves Cranial NerveSensory FunctionMotor Function I. OlfactorySmellNo II. OpticVisionNo III. OculomotorNoEyeball movement IV. TrochlearNoEyeball movement V. TrigeminalGeneral SensationChewing muscles VI. AbducensNoEyeball movement VII. FacialTasteFacial Expression VIII. VestibulocochlearHearing and BalanceSome IX. GlossopharyngealTasteTongue and Pharynx X. VagusTasteThorax and Abdomen XI. AccessoryNoNeck movement XII. HypoglossalNoTongue movement

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Nerves  31 pairs of nerves arise from the spinal cord and supply all parts of the body except the head  All have both sensory and motor functions  They are named according to their point of issue  8 cervical (C 1 -C 8 )  12 thoracic (T 1 -T 12 )  5 Lumbar (L 1 -L 5 )  5 Sacral (S 1 -S 5 )  1 Coccygeal (C 0 )

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spinal Nerves Figure 13.6

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Reflexes  A reflex is a rapid, predictable motor response to a stimulus  Reflexes may be:  Inborn (intrinsic)  Unlearned, unpremeditated, and involuntary  Built into our neural anatomy  Prevent us from having to think about all the little details of staying upright, intact, and alive  Help us maintain posture, avoid pain, and control visceral activities

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Reflexes  A reflex is a rapid, predictable motor response to a stimulus  Reflexes may be:  Learned (acquired)  Result from practice or repetition  Example: reaction when driving a car

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Reflex Arc  There are five components of a reflex arc  Receptor – site of stimulus action  Sensory neuron – transmits afferent impulse to CNS  Integration center – either a single synapse between a sensory neuron and a motor neuron or multiple synapses with chains of interneurons  Always in CNS  Motor neuron – conducts efferent impulses from the integration center to an effector  Effector – muscle fiber or gland that responds to the efferent impulse

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Reflex Arc Figure 13.14

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Reflex Classification  Somatic reflexes – involve skeletal muscles  Spinal reflexes – somatic reflexes mediated by the spinal cord without direct involvement from the brain  Example: touching a hot pan  you immediately move your hand away  Autonomic (visceral) reflexes – involve glands, smooth muscle, and cardiac muscle

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Stretch Reflex  Stretch reflex makes sure that the muscle stays at its set length  Example: the knee-jerk reflex helps keep your knee from buckling when you are standing upright. As your knees begin to buckle and the quads lengthen, the stretch reflex causes the quads to contract without you having to think about it.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Stretch Reflex Figure 13.16

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Developmental Aspects of the PNS  Sensory receptors atrophy with age and muscle tone lessens  Reflexes occur a bit more slowly during old age  Deterioration seems to reflect a general loss of neurons, fewer synapses per neuron, and a slowdown in central processing