BIO2870 Chapter 15 Slides and Lecture Notes
BIO2870 Chapter 15 Slides and Lecture Notes Bio 2870
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This 47 page Class Notes was uploaded by Makenna McClellan on Sunday August 7, 2016. The Class Notes belongs to Bio 2870 at Wayne State University taught by Dr. Jyoti Nautiyal in Fall 2016. Since its upload, it has received 9 views. For similar materials see Anatomy & Physiology in Science at Wayne State University.
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Ch-15 Neural Integration 1 Oct-15-2015 Bio-2870 Anatomy and Physiology Chapter 15 Neural Integration 1: Sensory Pathways and the somatic Nervous System Ch-15 Neural Integration 1 Oct-15-2015 2 A & P Fall-2015 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Information ▯ Afferent Division of the Nervous System ▯ Receptors ▯ Sensory neurons ▯ Sensory pathways ▯ Efferent Division of the Nervous System ▯ Nuclei ▯ Motor tracts ▯ Motor neurons Figure 15–1 An Overview of Neural Integration. (ed-9) 3 Ch-15 Neural Integration 1 Oct-15-2015 Figure 15–1 An Overview of events occurring along the sensory and motor pathways A & P Fall-2015 4 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Information ▯ Sensory Receptors ▯ Specialized cells that monitor specific conditions in the body or external environment ▯ When stimulated, a receptor passes information to the CNS in the form of action potentials along the axon of a sensory neuron ▯ Sensory Pathways ▯ Deliver somatic and visceral sensory information to their final destinations inside the CNS using ▯ Nerves: PNS ▯ Nuclei: CNS ▯ Tracts: CNS ▯ Somatic Nervous System (SNS) ▯ Motor neurons and pathways that control skeletal muscles 5 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Receptors ▯ Sensation ▯ The arriving information from these senses ▯ Perception ▯ Conscious awareness of a sensation ▯ General Senses ▯ Describe our sensitivity to ▯Temperature ▯Pain ▯Touch ▯Pressure ▯Vibration ▯Proprioception 6 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Receptors ▯ The special senses are provided by special sensory receptors ▯ Special sensory receptors ▯ Are located in sense organs such as the eye or ear ▯ Are protected by surrounding tissues ▯ Special Senses ▯ Olfaction (smell) ▯ Vision (sight) ▯ Gustation (taste) ▯ Equilibrium (balance) ▯ Hearing 7 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Receptors ▯ The Detection of Stimuli ▯ Receptor sensitivity ▯ Each receptor has a characteristic sensitivity ▯ Receptive field ▯ Area is monitored by a single receptor cell ▯ The larger the receptive field, the more difficult it is to localize a stimulus Figure 15–2 Receptors and Receptive Fields 8 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Receptors ▯ The Interpretation of Sensory Information ▯ Arriving stimulus ▯ Takes many forms: • physical force (such as pressure) • dissolved chemical • sound • Light ▯ Sensations ▯ Taste, hearing, equilibrium, and vision provided by specialized receptor cells ▯ Communicate with sensory neurons across chemical synapses 9 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Receptors ▯ Adaptation ▯ Reduction in sensitivity of a constant stimulus ▯ Your nervous system quickly adapts to stimuli that are painless and constant ▯ A) Central B) peripheral 1) Tonic receptors ▯ Are always active ▯ Show little peripheral adaptation ▯ Are slow-adapting receptors ▯ Remind you of an injury long after the initial damage has occurred 2) Phasic receptors ▯ Are normally inactive ▯ Become active for a short time whenever a change occurs ▯ Provide information about the intensity and rate of change of a stimulus ▯ Are fast-adapting receptors 10 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Receptors ▯ Stimulation of a receptor produces action potentials along the axon of a sensory neuron ▯ The frequency and pattern of action potentials contain information about the strength, duration, and variation of the stimulus ▯ Your perception of the nature of that stimulus depends on the path it takes inside the CNS ▯ Exteroceptors provide information about the external environment ▯ Proprioceptors report the positions of skeletal muscles and joints ▯ Provide a purely somatic sensation ▯ No proprioceptors in the visceral organs of the thoracic and abdominopelvic cavities ▯ You cannot tell where your spleen, appendix, or pancreas is at the moment ▯ Interoceptors monitor visceral organs and functions 11 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors ▯ General sensory receptors are divided into four types by the nature of the stimulus that excites them 1) Nociceptors (pain) 2) Thermoreceptors (temperature) 3) Mechanoreceptors (physical distortion) 4) Chemoreceptors (chemical concentration) 12 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 1) Nociceptors (also called pain receptors) ▯ Are common in the superficial portions of the skin, joint capsules, within the periostea of bones, and around the walls of blood vessels ▯ May be sensitive to temperature extremes, mechanical damage, and dissolved chemicals, such as chemicals released by injured cells ▯ Are free nerve endings with large receptive fields ▯ Branching tips of dendrites ▯ Not protected by accessory structures ▯ Can be stimulated by many different stimuli ▯ Two types of axons: Type A and Type C fibers 13 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 1) Nociceptors ▯ Myelinated Type A fibers ▯ Carry sensations of fast pain, or prickling pain, such as that caused by an injection or a deep cut ▯ Sensations reach the CNS quickly and often trigger somatic reflexes ▯ Relayed to the primary sensory cortex and receive conscious attention ▯ Type C fibers ▯ Carry sensations of slow pain, or burning and aching pain ▯ Cause a generalized activation of the reticular formation and thalamus ▯ You become aware of the pain but only have a general idea of the area affected 14 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 2) Thermoreceptors ▯ Also called temperature receptors ▯ Are free nerve endings located in ▯ The dermis ▯ Skeletal muscles ▯ The liver ▯ The hypothalamus ▯ Temperature sensations ▯ Conducted along the same pathways that carry pain sensations ▯ Sent to: • the reticular formation • the thalamus • the primary sensory cortex (to a lesser extent) 15 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 3) Mechanoreceptors ▯ Sensitive to stimuli that distort their plasma membranes ▯ Contain mechanically gated ion channels whose gates open or close in response to ▯ Stretching ▯ Compression ▯ Twisting ▯ Other distortions of the membrane 16 Ch-15 Neural Integration 1 Oct-15-2015 Transmembrane Potential Figure 12–11 Gated Channels . 17 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 3) Mechanoreceptors ▯ Three Classes of Mechanoreceptors 1) Tactile receptors ▯ provide the sensations of touch, pressure, and vibration: • touch sensations provide information about shape or texture • pressure sensations indicate degree of mechanical distortion • vibration sensations indicate pulsing or oscillating pressure 2) Baroreceptors ▯ Detect pressure changes in the walls of blood vessels and in portions of the digestive, reproductive, and urinary tracts 3) Proprioceptors ▯ Monitor the positions of joints and muscles ▯ The most structurally and functionally complex of general sensory receptors 18 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 1) Mechanoreceptors: Tactile Receptors ▯ Fine touch and pressure receptors ▯ Are extremely sensitive ▯ Have a relatively narrow receptive field ▯ Provide detailed information about a source of stimulation, including: • its exact location, shape, size, texture, movement ▯ Crude touch and pressure receptors ▯ Have relatively large receptive fields ▯ Provide poor localization ▯ Give little information about the stimulus 19 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 3 4 1 2 5 6 Figure 15–2 Tactile Receptors in the Skin. 20 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 3) Mechanoreceptors : 1) Tactile Receptors Six Types of Tactile Receptors in the Skin 1) Free nerve endings ▯Sensitive to touch and pressure ▯Situated between epidermal cells ▯Free nerve endings providing touch sensations are tonic receptors with small receptive fields 2) Root hair plexus nerve endings ▯Monitor distortions and movements across the body surface wherever hairs are located ▯Adapt rapidly, so are best at detecting initial contact and subsequent movements 21 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 3) Mechanoreceptors : 1) Tactile Receptors Six Types of Tactile Receptors in the Skin 3) Tactile discs ▯ Also called Merkel discs ▯ Fine touch and pressure receptors ▯ Extremely sensitive to tonic receptors ▯ Have very small receptive fields 4) Tactile corpuscles: ▯ Also called Meissner corpuscles ▯ Perceive sensations of fine touch, pressure, and low-frequency vibration ▯ Adapt to stimulation within 1 second after contact ▯ Fairly large structures ▯ Most abundant in the eyelids, lips, fingertips, nipples, and external genitalia 22 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 3) Mechanoreceptors : 1) Tactile Receptors Six Types of Tactile Receptors in the Skin 5) Lamellated corpuscles ▯ Also called Pacinian corpuscles ▯ Sensitive to deep pressure ▯ Fast-adapting receptors ▯ Most sensitive to pulsing or high-frequency vibrating stimuli 6) Ruffini corpuscles ▯ Also sensitive to pressure and distortion of the skin ▯ Located in the reticular (deep) dermis ▯ Tonic receptors that show little if any adaptation 23 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 2) Mechanoreceptors : Baroreceptors ▯ Monitor change in pressure ▯ Consist of free nerve endings that branch within elastic tissues in wall of distensible organ (such as a blood vessel) ▯ Respond immediately to a change in pressure, but adapt rapidly 24 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 3) Mechanoreceptors: Proprioceptors ▯ Monitor Figure 13–18 A Muscle Spindle ▯ Position of joints ▯ Tension in tendons and ligaments ▯ State of muscular contraction ▯ Three Major Groups of Proprioceptors ▯ Muscle spindles ▯ Monitor skeletal muscle length ▯ Trigger stretch reflexes ▯ Golgi tendon organs ▯ Located at the junction between skeletal muscle and its tendon ▯ Stimulated by tension in tendon ▯ Monitor external tension developed during muscle contraction ▯ Receptors in joint capsules ▯ Free nerve endings detect pressure, tension, movement at the joint 25 Ch-15 Neural Integration 1 Oct-15-2015 Classifying Sensory Receptors 4) Chemoreceptors ▯ Respond only to water-soluble and lipid-soluble substances dissolved in surrounding fluid ▯ Receptors exhibit peripheral adaptation over period of seconds; central adaptation may also occur ▯ Located in the ▯ Carotid bodies: • near the origin of the internal carotid arteries on each side of the neck ▯ Aortic bodies: • between the major branches of the aortic arch ▯ Receptors monitor pH, carbon dioxide, and oxygen levels in arterial blood 26 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Pathways ▯ Somatic Sensory Pathways ▯ Carry sensory information from the skin and musculature of the body wall, head, neck, and limbs ▯ Three major somatic sensory pathways 1) The posterior column pathway 2) The spinothalamic pathway 3) The spinocerebellar pathway 27 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Pathways Fig 15–5 Sensory Pathways and Ascending Tracts in the Spinal Cord. 28 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Pathways ▯ Somatic Sensory Pathways 1) Posterior column pathway ▯ Carries sensations of highly localized (“fine”) touch, pressure, vibration, and proprioception ▯ Spinal tracts involved: ▯ left and right fasciculus gracilis ▯ left and right fasciculus cuneatus 29 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Pathways 1) Posterior Column Pathway ▯ Processing in the thalamus ▯ Determines whether you perceive a given sensation as fine touch, as pressure, or as vibration ▯ Ability to determine stimulus ▯ Precisely where on the body a specific stimulus originated depends on the projection of information from the thalamus to the primary sensory cortex ▯ Sensory information ▯ From toes arrives at one end of the primary sensory cortex ▯ From the head arrives at the other: ▯ when neurons in one portion of your primary sensory cortex are stimulated, you become aware of sensations originating at a specific location 30 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Pathways 1) Posterior Column Pathway ▯ Sensory homunculus ▯ Functional map of the primary sensory cortex ▯ Distortions occur because area of sensory cortex devoted to particular body region is not proportional to region’s size, but to number of sensory receptors it contains Figure 15–6a The Posterior Column Pathway. 31 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Pathways 2) The Spinothalamic Pathway ▯ Provides conscious sensations of poorly localized (“crude”) touch, pressure, pain, and temperature 32 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Pathways 2) The Spinothalamic Pathway ▯ Feeling Pain (Lateral Spinothalamic Tract) ▯ An individual can feel pain in an uninjured part of the body when pain actually originates at another location ▯ Strong visceral pain ▯ Sensations arriving at segment of spinal cord can stimulate interneurons that are part of spinothalamic pathway ▯ Activity in interneurons leads to stimulation of primary sensory cortex, so an individual feels pain in specific part of body surface: • also called referred pain 33 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Pathways 2) The Spinothalamic Pathway ▯ Feeling Pain (Lateral Spinothalamic Tract) ▯ Referred pain ▯ The pain of a heart attack is frequently felt in the left arm ▯ The pain of appendicitis is generally felt first in the area around the navel and then in the right, lower quadrant Figure 15–7 Referred Pain. 34 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Pathways 3) The Spinocerebellar Pathway ▯ Cerebellum receives proprioceptive information about position of skeletal muscles, tendons, and joints Figure 15–6 The Spinocerebellar Pathway 35 Ch-15 Neural Integration 1 Oct-15-2015 A & P Fall-2015 36 Ch-15 Neural Integration 1 Oct-15-2015 Sensory Information ▯ Afferent Division of the Nervous System ▯ Receptors ▯ Sensory neurons ▯ Sensory pathways ▯ Efferent Division of the Nervous System ▯ Nuclei ▯ Motor tracts ▯ Motor neurons Figure 15–1 An Overview of Neural Integration. 37 Ch-15 Neural Integration 1 Oct-15-2015 Somatic Motor Pathways ▯ SNS, or the somatic motor system, controls contractions of skeletal muscles (discussed next) ▯ ANS, or the visceral motor system, controls visceral effectors, such as smooth muscle, cardiac muscle, and glands (Ch. 16) 38 Ch-15 Neural Integration 1 Oct-15-2015 Somatic Motor Pathways Conscious & Subconscious Motor Commands ▯ Control skeletal muscles by traveling over three integrated motor pathways 1) Corticospinal pathway 2) Medial pathway 3) Lateral pathway Figure 15–8 Descending (Motor) Tracts in the Spinal Cord. 39 Ch-15 Neural Integration 1 Oct-15-2015 Somatic Motor Pathways 1) The Corticospinal Pathway Motor homunculus ▯ Primary motor cortex corresponds point by point with specific regions of the body ▯ Cortical areas have been mapped out in diagrammatic form ▯ Homunculus provides indication of degree of fine motor control available: • hands, face, and tongue, which are capable of varied and complex movements, appear very large, while trunk is relatively small • these proportions are similar to the sensory homunculus Figure 15–9 The Corticospinal Pathway. 40 Ch-15 Neural Integration 1 Oct-15-2015 Somatic Motor Pathways 2 & 3 The Medial and Lateral Pathways ▯ Several centers in cerebrum, diencephalon, and brain stem may issue somatic motor commands as result of processing performed at subconscious level ▯ These nuclei and tracts are grouped by their primary functions ▯Components of medial pathway help control gross movements of trunk and proximal limb muscles ▯Components of lateral pathway help control distal limb muscles that perform more precise movements 41 Ch-15 Neural Integration 1 Oct-15-2015 Somatic Motor Pathways 42 Ch-15 Neural Integration 1 Oct-15-2015 Somatic Motor Pathways ▯ The Basal Nuclei and Cerebellum ▯ Responsible for coordination and feedback control over muscle contractions, whether contractions are consciously or subconsciously directed ▯ Provide background patterns of movement involved in voluntary motor activities ▯ Some axons extend to the premotor cortex, the motor association area that directs activities of the primary motor cortex: • alters the pattern of instructions carried by the corticospinal tracts ▯ Other axons alter the excitatory or inhibitory output of the reticulospinal tracts 43 Ch-15 Neural Integration 1 Oct-15-2015 The Cerebrum • The Basal Nuclei – Also called cerebral nuclei – Are masses of gray matter – Are embedded in white matter of cerebrum – Direct subconscious activities 44 Ch-15 Neural Integration 1 Oct-15-2015 Somatic Motor Pathways ▯ The Basal Nuclei and Cerebellum ▯ The Cerebellum ▯ Monitors ▯Proprioceptive (position) sensations ▯Visual information from the eyes ▯Vestibular (balance) sensations from inner ear as movements are under way Figure 14–7a The Cerebellum 45 Ch-15 Neural Integration 1 Oct-15-2015 Somatic Motor Pathways The Cerebellum ▯ Levels of Processing and Motor Control ▯ All sensory and motor pathways involve a series of synapses, one after the other ▯ General pattern • Spinal and cranial reflexes provide rapid, involuntary, preprogrammed responses that preserve homeostasis over short term ▯ Cranial and spinal reflexes • Control the most basic motor activities ▯ Integrative centers in the brain • Perform more elaborate processing • As we move from medulla oblongata to cerebral cortex, motor patterns become increasingly complex and variable ▯ Primary motor cortex • Most complex and variable motor activities are directed by primary motor cortex of cerebral hemispheres 46 Ch-15 Neural Integration 1 Oct-15-2015 Somatic Motor Pathways ▯ Neurons of the primary motor cortex innervate motor neurons in the brain and spinal cord responsible for stimulating skeletal muscles ▯ Higher centers in the brain can suppress or facilitate reflex responses ▯ Reflexes can complement or increase the complexity of voluntary movements 47
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