1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 13 The Peripheral Nervous System and Reflex Activity: Part A

2. Copyright © 2010 Pearson Education, Inc. Peripheral Nervous System (PNS) All neural structures outside the CNS Sensory receptors Peripheral nerves and associated ganglia Motor endings

3. Copyright © 2010 Pearson Education, Inc. Sensory Receptors Specialized to respond to changes in their environment (stimuli) Activation results in graded potentials that trigger nerve impulses Sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus) occur in the brain

4. Copyright © 2010 Pearson Education, Inc. Classification of Receptors Based on: Stimulus type Location Structural complexity

5. Copyright © 2010 Pearson Education, Inc. Classification by Stimulus Type Mechanoreceptors — respond to touch, pressure, vibration, stretch, and itch Thermoreceptors — sensitive to changes in temperature Photoreceptors — respond to light energy (e.g., retina) Chemoreceptors — respond to chemicals (e.g., smell, taste, changes in blood chemistry) Nociceptors — sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals)

6. Copyright © 2010 Pearson Education, Inc. Classification by Location 1.Exteroceptors Respond to stimuli arising outside the body Receptors in the skin for touch, pressure, pain, and temperature Most special sense organs 2.Interoceptors (visceroceptors) Respond to stimuli arising in internal viscera and blood vessels Sensitive to chemical changes, tissue stretch, and temperature changes

7. Copyright © 2010 Pearson Education, Inc. Classification by Location 3.Proprioceptors Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles Inform the brain of one’s movements

8. Copyright © 2010 Pearson Education, Inc. Classification by Structural Complexity 1.Complex receptors (special sense organs) Vision, hearing, equilibrium, smell, and taste (Chapter 15) 2.Simple receptors for general senses: Tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense Unencapsulated (free) or encapsulated dendritic endings

9. Copyright © 2010 Pearson Education, Inc. From Sensation to Perception Survival depends upon sensation and perception Sensation: the awareness of changes in the internal and external environment Perception: the conscious interpretation of those stimuli

10. Copyright © 2010 Pearson Education, Inc. Sensory Integration Levels of neural integration in sensory systems: 1.Receptor level — the sensor receptors 2.Circuit level — ascending pathways 3.Perceptual level — neuronal circuits in the cerebral cortex

11. Copyright © 2010 Pearson Education, Inc. Processing at the Receptor Level The receptor must have specificity for the stimulus energy The receptor’s receptive field must be stimulated The smaller the receptive field the greater the ability of the brain to localize the site Stimulus energy must be converted into a graded potential also called receptor potential or transduction A generator potential is a depolarization that leads to action potential in the afferent fibers Associated sensory neuron (neuron of first order close to the receptor) must reach threshold Information is encoded in the frequency of the stimuli – the greater the frequency, the stronger is the stimulus.

12. Copyright © 2010 Pearson Education, Inc. Adaptation of Sensory Receptors Adaptation is the change in sensitivity in the presence of constant stimulus Adaptation occurs when Receptor membranes become less responsive, or Receptor potentials decline in frequency or stop Receptors responding to pressure, touch, and smell adapt quickly Receptors responding slowly include Merkel’s discs, Ruffini’s corpuscles (light and deep pressure respectively) Pain receptors and proprioceptors do not exhibit adaptation (WHY?)

13. Copyright © 2010 Pearson Education, Inc. Processing at the circuit Level The circuit level role is to deliver the impulses to the appropriate region in the cerebral cortex. The ascending tract typically consists of 3 neurons First order neurons cell bodies in a ganglion (dorsal or cranial) Impulses from skin and proprioceptors to spinal cord or brain stem to a 2 nd order neuron Second order neuron In the dorsal horn of the spinal cord or in the medulary nuclei Transmit impulses to thalamus or cerebellum Third order neurons Cell bodies in the thalamus (no 3 rd -order neurons in the cerebellum) Transmit signals to the somatosensory cortex of the cerebrum

14. Copyright © 2010 Pearson Education, Inc. Processing at the circuit Level Impulses ascend in : Non specific pathway that in general transmit pain, temperature and touch Give branches to reticular formation and thalamus on the way up Sends general information that is also involved in emotional aspects of perception Specific ascending pathways involve in more precise aspect of sensation

15. Copyright © 2010 Pearson Education, Inc. Processing at the Perceptual Level Interpretation of sensory input occurs in the cerebral cortex The ability to identify the sensation depends on the specific location of the target neurons in the sensory cortex not on the nature of the message (all messages are action potentials)

16. Copyright © 2010 Pearson Education, Inc. Main Aspects of Sensory Perception Perceptual detection – detecting that a stimulus has occurred and requires summation Magnitude estimation – the ability to detect how intense the stimulus is Spatial discrimination – identifying the site or pattern of the stimulus Feature abstraction – used to identify a substance that has specific texture or shape Quality discrimination – the ability to identify submodalities of a sensation (e.g., sweet or sour tastes) Pattern recognition – ability to recognize patterns in stimuli (e.g., melody, familiar face)

17. Copyright © 2010 Pearson Education, Inc. Motor ending and motor activity Motor ending are the PNS elements that activate effectors by releasing neurotransmitters Innervation of skeletal muscle Somatic motor fibers innervate voluntary muscles and form neuromuscular junction. At this junction the NT that is released is the Ach Innervation of visceral muscle and glands Junctions between autonomic motor endings and their effectors – smooth and cardiac muscles and glands Acetylcholine and norepinephrine are used as neurotransmitters Tend to response slower than the somatic motor endings

18. Copyright © 2010 Pearson Education, Inc. Levels of Motor Control The three levels of motor control are Segmental level Projection level Precommand level

19. Copyright © 2010 Pearson Education, Inc. Segmental Level The segmental level is the lowest level of motor hierarchy It consists of segmental circuits of the spinal cord A segmental circuit activates network of ventral horn neurons in a certain segment causing the activation of a specific group of muscles These circuits are called central pattern generators (CPGs) A central pattern generator is a network of neurons which is able to exhibit rhythmic behavior in the absence of sensory input. locomotion, breathing, chewing

20. Copyright © 2010 Pearson Education, Inc. Projection Level The projection level controls the spinal cord and consists of: Upper motor neurons - Cortical motor areas that produce the direct (pyramidal) system Voluntary movements of skeletal muscles Brain stem motor areas that oversee the indirect system Control reflex and CPG-controlled motor actions Pass on information to lower motor neurons and send a copy of this information to higher command levels

21. Copyright © 2010 Pearson Education, Inc. Precommand Level The cerebral cortex is the highest level of conscious motor pathway but it is not the ultimate planner and coordinator of complex motor activities Cerebellum Acts on motor pathways through projection areas of the brain stem Acts on the motor cortex via the thalamus Basal nuclei Inhibit various motor centers under resting conditions

22. Copyright © 2010 Pearson Education, Inc. Structure of a Nerve Nerve – cordlike organ of the PNS consisting 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

23. Copyright © 2010 Pearson Education, Inc. Classification of Nerves Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers Pure sensory (afferent) or motor (efferent) nerves are rare Types of fibers in mixed nerves: Somatic afferent and somatic efferent Visceral afferent and visceral efferent Peripheral nerves classified as cranial or spinal nerves

24. Copyright © 2010 Pearson Education, Inc. Ganglia Contain neuron cell bodies associated with nerves Dorsal root ganglia (sensory, somatic) (Chapter 12) Autonomic ganglia (motor, visceral) (Chapter 14)

25. Copyright © 2010 Pearson Education, Inc. Cranial Nerve I: Olfactory Arises from the olfactory epithelium Passes through the cribriform plate of the ethmoid bone The axons will synapse on the olfactory bulb. From the olfactory bulbs, Olfactory nerve continues through the olfactory tracts and can synapse on the 1. Olfactory cortex (Rhinencephalon) for conscious interpretation 2. Hypothalamus (Limbic system) for emotional response 3. Autonomic Nervous System for other responses (digestive system) Functions solely by carrying afferent impulses for the sense of smell

26. Copyright © 2010 Pearson Education, Inc. Cranial Nerve II: Optic Arises from the retina of the eye Optic nerves pass through the optic canals and converge at the optic chiasm They continue to the thalamus where they synapse From there, the optic radiation fibers run to the visual cortex Functions solely by carrying afferent impulses for vision

27. Copyright © 2010 Pearson Education, Inc. Cranial Nerve III: Oculomotor Fibers extend from the ventral midbrain, pass through the superior orbital fissure, and go to the extrinsic eye muscles Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape

28. Copyright © 2010 Pearson Education, Inc. Cranial Nerve IV: Trochlear Fibers emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures; innervate the superior oblique muscle A motor nerve that directs the eyeball

29. Copyright © 2010 Pearson Education, Inc. Cranial Nerve V: Trigeminal Fibers run from the face to the pons, to the thalamus and to the primary somatosensory cortex Three divisions: ophthalmic (V 1 ), sensory from face maxillary (V 2 ), mandibular (V 3 ) supplies motor fibers (V 3 ) for mastication

30. Copyright © 2010 Pearson Education, Inc. Cranial Nerve V: Trigeminal Figure V from Table 13.2

31. Copyright © 2010 Pearson Education, Inc. Cranial Nerve VI: Abdcuens Fibers leave the inferior pons and enter the orbit via the superior orbital fissure Primarily a motor nerve innervating the lateral rectus muscle Figure VI from Table 13.2

32. Copyright © 2010 Pearson Education, Inc. http://www.neuroanatomy.wisc.edu/virtualbrain/Images/13N.jpg Cranial Nerve III, IV and VI: extrinsic eye muscles control

33. Copyright © 2010 Pearson Education, Inc. Cranial Nerve VII: Facial Fibers leave the pons to the lateral aspect of the face Mixed nerve with five major branches Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands (subconscious) Sensory function is taste from the anterior two-thirds of the tongue (taste buds to pons, to the thalamus, to the insula and parietal cortex for taste perception)

34. Copyright © 2010 Pearson Education, Inc. Cranial Nerve VIII: Vestibulocochlear Fibers arise from the hearing and equilibrium apparatus of the inner ear to enter the brainstem at the pons-medulla border Two divisions – cochlear (hearing) and vestibular (balance) Functions are solely sensory – equilibrium and hearing

35. Copyright © 2010 Pearson Education, Inc. Cranial Nerve IX: Glossopharyngeal Fibers emerge from the medulla and run to the throat Nerve IX is a mixed nerve Motor – innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland (autonomic) Sensory – fibers conduct taste and general sensory impulses from the tongue and pharynx

36. Copyright © 2010 Pearson Education, Inc. Cranial Nerve X: Vagus The only cranial nerve that extends beyond the head and neck Fibers emerge from the medulla The vagus is a mixed nerve Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs Its sensory function is in taste

37. Copyright © 2010 Pearson Education, Inc. Cranial Nerve XI: Accessory Formed from a cranial root emerging from the medulla and a spinal root arising from the superior region of the spinal cord A motor nerve Supplies fibers to the larynx, pharynx, and soft palate Innervates the trapezius and sternocleidomastoid, which move the head and neck

38. Copyright © 2010 Pearson Education, Inc. Cranial Nerve XII: Hypoglossal Fibers arise from the medulla Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech

39. Copyright © 2010 Pearson Education, Inc. Spinal Nerves: Rami The short spinal nerves branch into three or four mixed, distal rami Small dorsal ramus Larger ventral ramus Tiny meningeal branch – innervate the meninges and blood vessels within the vertebral canal Rami communicantes at the base of the ventral rami in the thoracic region that contain autonomic nerve fibers

40. Copyright © 2010 Pearson Education, Inc. Nerve Plexuses All ventral rami except T 2 -T 12 form nerve networks called plexuses Plexuses are found in the cervical, brachial, lumbar, and sacral regions Each resulting branch of a plexus contains fibers from several spinal nerves Fibers travel to the periphery via several different routes Each muscle receives a nerve supply from more than one spinal nerve Damage to one spinal segment cannot completely paralyze a muscle

41. Copyright © 2010 Pearson Education, Inc. PlexusMain spinal nervesRegions innervatedMajor nerves CervicalC1-C5Skin and muscles of head & neck. Superior chest and shoulder Phrenic (diaphragm) BrachialC5-C8, T1Shoulder and upper limbsAxillary Musculocutaneous Radial Median Ulnar LumbarL1-L4Antero-lateral abdominal wall, external genitalia, part of lower limbs Femoral SacralL4-L5, S1-S4Buttocks, perineum, lower limbs Sciatic

42. Copyright © 2010 Pearson Education, Inc. Dermatomes A dermatome is the area of skin innervated by the cutaneous branches of a single spinal nerve All spinal nerves except C 1 participate in dermatomes

43. Copyright © 2010 Pearson Education, Inc. Reflexes A reflex is a rapid, predictable motor response to a stimulus Reflexes may be: inborn (intrinsic)/basic: breathing. Putting a hand on a hot stove and quickly removing it, learned (acquired) Pavlov's dogs, every time Pavlov would feed the dogs he would ring a bell, before long even if there was no food if he rang the bell the dogs began to salivate. Example: driving skills Reflexes may Involve only peripheral nerves and the spinal cord Involve higher brain centers as well

44. Copyright © 2010 Pearson Education, Inc.

45. Reflex Arc There are five components of a reflex arc Receptor – site of stimulus Sensory neuron – transmits the afferent impulse to the CNS Integration center – either monosynaptic or polysynaptic region within the CNS Motor neuron – conducts efferent impulses from the integration center to an effector Effector – muscle fiber or gland that responds to the efferent impulse

46. Copyright © 2010 Pearson Education, Inc. Spinal Reflexes Spinal somatic reflexes Integration center is in the spinal cord Effectors are skeletal muscle Testing of somatic reflexes is important clinically to assess the condition of the nervous system

47. Copyright © 2010 Pearson Education, Inc. Stretch and Golgi Tendon Reflexes For skeletal muscle activity to be smoothly coordinated, proprioceptor input is necessary Muscle spindles inform the nervous system of the length of the muscle Golgi tendon organs inform the brain as to the amount of tension in the muscle and tendons

48. Copyright © 2010 Pearson Education, Inc. Stretch Reflexes Maintain muscle tone in large postural muscles Cause muscle contraction in response to increased muscle length (stretch)