Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Fundamentals of Anatomy & Physiology SIXTH EDITION Frederic H. Martini Chapter 15, part 1 Neural Integration I: Sensory Pathways and the Somatic Nervous System
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Learning Objectives Specify the components of the afferent and efferent divisions of the nervous system, and explain what is meant by the somatic nervous system. Explain why receptors respond to specific stimuli and how the organization of a receptor affects its sensitivity. Identify the major sensory pathways.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Learning Objectives Explain how we can distinguish among sensations that originate in different areas of the body. Describe the components, processes and functions of the somatic motor pathways. Describe the levels of information processing involved in motor control.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings SECTION 15-1 An Overview of Sensory Pathways and the Somatic Nervous System
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Neural pathways Afferent pathways Sensory information coming from the sensory receptors through peripheral nerves to the spinal cord and on to the brain Efferent pathways Motor commands coming from the brain and spinal cord, through peripheral nerves to effecter organs
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.1 An Overview of Neural Integration Figure 15.1
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings SECTION 15-2 Sensory Receptors and their Classification
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Specialized cell or cell process that monitors specific conditions Arriving information is a sensation Awareness of a sensation is a perception Sensory receptor
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings General senses Pain Temperature Physical distortion Chemical detection Receptors for general senses scattered throughout the body Special senses Located in specific sense organs Structurally complex Senses
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Each receptor cell monitors a specific receptive field—the larger the field, the poorer the spatial resolution Sensory receptors
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Receptive Fields
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Receptors transduce stimulus signals to neural signals Transduction A large enough stimulus changes the receptor potential, reaching generator potential
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tonic receptors Always active Slow acting receptors Phasic receptors Provide information about the intensity and rate of change of a stimulus Fast acting receptors Adaptation Reduction in sensitivity in the presence of a constant stimulus Receptors
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tonic and Phasic Responses and Adaptation
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Two Examples of Adaptation
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Three types of nociceptor Provide information on pain as related to extremes of temperature Provide information on pain as related to extremes of mechanical damage Provide information on pain as related to extremes of dissolved chemicals Myelinated type A fibers carry fast pain Slower type C fibers carry slow pain The general senses
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Myelinated sheathing and Axon diameter
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.2 Figure 15.2 Receptors and Receptive Fields
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Found in the dermis Mechaniceptors Sensitive to distortion of their membrane Tactile receptors (six types) Baroreceptors Proprioceptors (three groups) Thermoceptors and mechaniceptors
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.3 Tactile Receptors in the Skin Figure 15.3a-f
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Touch Types of classification: Capsulated/non-capsulated Fast-adapting/slow-adapting; amount of myelin Superficial/Deep layer
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Touch Receptor Cell Types Merkel cell: Slow adapting, superficial, non- capsulated Meissner cell: Fast adapting, superficial, capsulated Pacinian: Fast adapting, deep, capsulated Ruffini: Slow adapting, deep, non-capsulated
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Chemoreceptors—function is to allow for regulation of pH, PCO2, and PO2 Carotid bodies Aortic bodies Chemoreceptors
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.5 Figure 15.5 Chemoreceptors
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.4 Figure 15.4 Baroreceptors and the Regulation of Visceral Function
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Nociceptors (Pain Receptors) Useful to indicate something is amiss (adaptive advantage to know when something is hurting you) Normally produced by intense stimuli that can damage tissue BUT, hypersensitivity to pain can occur
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Hypersensitivity to Pain Hyperalgesia: Sensitization such that normal pain becomes excruciating pain Allodynia: Normal, non-pain (e.g. light touch) becomes painful How and why would hypersensitivity occur?
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Hypersensitivity to Pain Can occur due to nociceptor sensitization—may result from changes in membrane permeability, membrane receptors, post- and pre-synaptic modulation, etc. Peripheral sensitization: occurs in PNS; increased responsiveness/lower threshold to stimuli E.g. sunburn Central sensitization: occurs in CNS; increased excitability of neurons—often triggered by increase in nociceptor activity E.g. Following an injury Actually a manifestation of abnormal sensory processing within the CNS (not on the periphery) E.g. migraines, post-surgical hypersensitization, “tender” areas surrounding injury And MAYBE fibromyalgia, irritable bowel syndrome
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Silent Nociceptors Often can involve so-called “silent nociceptors”— nociceptors that normally don’t respond except under conditions of sensitization Up to 30% of nociceptors are silent May add to pain further, as the functioning density of nociceptors has essentially increased
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings SECTION 15-3 The Organization of Sensory Pathways
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings First order neurons Sensory neurons that deliver sensory information to the CNS Second order neurons First order neurons synapse on these in the brain or spinal cord Third order neurons Found in the thalamus Second order neurons synapse on these First, second, and third order neurons
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Three major pathways carry sensory information Posterior column pathway Anterolateral pathway Spinocerebellar pathway Somatic sensory pathways
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.6 Figure 15.6 Sensory Pathways and Ascending Tracts in the Spinal Cord
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Carries fine touch, pressure and proprioceptive sensations Axons ascend within the fasciculus gracilis and fasciculus cuneatus Relay information to the thalamus via the medial lemniscus Decussation—”crossing over” Posterior column pathway
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.8a, b Figure 15.8 The Posterior Column Pathway and the Spinothalamic Tracts
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Carries poorly localized sensations of touch, pressure, pain, and temperature Axons decussate in the spinal cord and ascend within the anterior and lateral spinothalamic tracts Headed toward the ventral nuclei of the thalamus Anterolateral pathway
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.8c Figure 15.8 The Posterior Column Pathway and the Spinothalamic Tracts
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Sensory Homunculi
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Posterior and Anterolateral Pathways
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Includes the posterior and anterior spinocerebellar tracts Carries sensation to the cerebellum concerning position of muscles, tendons and joints Spinocerebellar pathway
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.9 Figure 15.9 The Spinocerebellar Pathway
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Carry information collected by interoceptors Information from cranial nerves V, VII, IX and X delivered to solitary nucleus in medulla oblongata Dorsal roots of spinal nerves T1 – L2 carry visceral sensory information from organs between the diaphragm and pelvis Dorsal roots of spinal nerves S2 – S4 carry sensory information below this area Visceral sensory pathways
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings SECTION 15-4 The Somatic Nervous System
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Upper motor neuron Cell body lies in a CNS processing center Lower motor neuron Cell body located in a motor nucleus of the brain or spinal cord Somatic motor pathways
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Figure Descending (Motor) Tracts in the Spinal Cord
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Provides voluntary skeletal muscle control Corticobulbar tracts terminate at cranial nerve nuclei Corticospinal tracts synapse on motor neurons in the anterior gray horns of the spinal cord Visible along medulla as pyramids The corticospinal pathway
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Most of the axons decussate to enter the descending lateral corticospinal tracts Those that do not cross over enter the anterior corticospinal tracts Provide rapid direct method for controlling skeletal muscle Pyramids
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Figure The Corticospinal Pathway
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The medial and lateral pathways Issue motor commands as a result of subconscious processing Medial pathway Primarily controls gross movements of the trunk and proximal limbs Includes the vestibulospinal tracts, tectospinal tracts and reticulospinal tracts medial and lateral pathways
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Lateral pathway Controls muscle tone and movements of the distal muscles of the upper limbs Rubrospinal tracts lateral pathways
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Basal nuclei adjust motor commands issued in other processing centers Provide background patterns of movement involved in voluntary motor movements Cerebellum monitors proprioceptive information, visual information and vestibular sensations The basal nuclei and cerebellum
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Levels of processing and motor control Spinal and cranial reflexes provide rapid, involuntary, preprogrammed responses Voluntary responses More complex Require more time to prepare and execute control and responses
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Figure Centers of Somatic Motor Control
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Spinal and cranial reflexes are first to appear Complex reflexes develop as CNS matures and brain grows During development
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The components of the afferent and efferent divisions of the nervous system, and what is meant by the somatic nervous system. Why receptors respond to specific stimuli and how the organization of a receptor affects its sensitivity. The major sensory pathways. How we can distinguish among sensations that originate in different areas of the body. The components, processes and functions of the somatic motor pathways. The levels of information processing involved in motor control. You should now be familiar with: