In anterolateral system, signals ascend the spinal cord via the anterior and lateral spinothalamic tract. Contrast facial sensation from the head and somatic sensation from the body. Somatic sensory input comes from the receptors of the eyes, ears, nose, tongue, and skin. stream This complex system of sensory neurons, and neural pathways responds to changes at the surface of, or inside, the body. •The spinocerebellar tract. central adaptation-occurs along sensory pathways in the CNS and involves inhibition of the nuclei on this pathway. Pathways go up the spinal cord to: Brain Stem Medulla – decussation occurs here Thalamus (VP nucleus) Primary somatosensory cortex (S1) Importance of Axon Diameter Different types of sensory information is carried by axons of different diameters. endstream The somatic nervous system has sensory and motor pathways, whereas the autonomic nervous system only has motor pathways. � 2.receptive field size. several types of encapsulated mechanoreceptors detect sensations of touch, pressure and vibration. Sensory Pathways. Physiologically, the function of pain is critical for survival and has a major evolutionary advantage. Does Hermione die in Harry Potter and the cursed child? An example of sensory integration is: Baby smelling food as they bring it to their mouth; Tasting the food; Feeling the texture of the food This book is primarily designed for undergraduate medical and dental students. This book is an attempt to provide a systematic account of the way in which this somatosensory system works. D) vibration. %PDF-1.5 The first is a somatic NS pathway and the second is a central NS pathway. Chapter 15 Sensory Pathways and the Somatic Nervous System. This book constitutes the proceedings of a NATO Advanced Research Workshop held at Chateau de Bonas (France) from 10-15 July 1990 on the Midbrain Periaqueductal Gray Matter (PAG). An Introduction to Sensory Pathways and the Somatic Nervous System Learning Outcomes 15-4 Identify the major sensory pathways, and explain how it is possible to distinguish among sensations that originate in different areas of the body. The cell bodies of the three neurons in a typical somatosensory pathway are located in the dorsal root ganglion, the spinal cord, and the thalamus. Then the second order neuron ends at thalamus which then relays with third order neuron ending at the cerebral cortex. Trigeminal pathway -Carries somatosensory information from the face, head, mouth, and nasal cavity -Axons enter the brain stem at the pons 15. Each of these modalities is detected by distinct types of primary sensory neurons and is processed by different central pathways. (#��$i��2:(OH�(@����I Acetylcholinesterase. endobj stream 2. 6 0 obj Name the three major somatic sensory pathways and the types of sensory information carried along each pathway. A simple case is a reflex caused by a synapse between a dorsal sensory neuron axon and a motor neuron in the ventral horn. Sensory Pathways Sensory receptors synapse on dorsal root ganglia in the spinal cord. A somatosensory pathway will typically have three neurons: primary, secondary, and tertiary. endobj Which are examples of somatosensory senses? x��U�n�0��?� The vertebrate somatic sensory system transmits to the brain information about physical stimuli that the body experiences. Try drawing this on the Haines atlas diagram at the end of the lecture. The somatosensory receptors can be activated by these different stimuli that act on mechanoreceptors (including proprioception), nociceptors, thermoreceptors and chemoreceptors. An Introduction to Sensory Pathways and the Somatic Nervous System An Introduction to: Sensory receptors Sensory processing Conscious and subconscious motor functions Focusing on the �general senses� 15-1 Sensory Information Afferent Division of the Nervous System Receptors Sensory neurons Sensory pathways Efferent Division of the Nervous System Nuclei Motor tracts Motor neurons 15-1 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 15-1 Sensory Information Sensory Pathways Deliver somatic and visceral sensory information to their final destinations inside the CNS using: Nerves Nuclei Tracts 15-1 Sensory Information Somatic Motor Portion of the Efferent Division Controls peripheral effectors Somatic Motor Commands Travel from motor centers in the brain along somatic motor pathways of: Motor nuclei Tracts Nerves 15-1 Sensory Information Somatic Nervous System (SNS) Motor neurons and pathways that control skeletal muscles 15-2 Sensory Receptors General Senses Describe our sensitivity to: Temperature Pain Touch Pressure Vibration Proprioception 15-2 Sensory Receptors Sensation The arriving information from these senses Perception Conscious awareness of a sensation 15-2 Sensory Receptors Special Senses Olfaction (smell) Vision (sight) Gustation (taste) Equilibrium (balance) Hearing 15-2 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 15-2 Sensory Receptors The Detection of Stimuli Receptor specificity 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 15-2 Sensory Receptors The Interpretation of Sensory Information Arriving stimulus reaches cortical neurons via labeled line Takes many forms (modalities) Physical force (such as pressure) Dissolved chemical Sound Light 15-2 Sensory Receptors The Interpretation of Sensory Information Sensations Taste, hearing, equilibrium, and vision provided by specialized receptor cells Communicate with sensory neurons across chemical synapses 15-2 Sensory Receptors Adaptation Reduction in sensitivity of a constant stimulus Your nervous system quickly adapts to stimuli that are painless and constant 15-2 Sensory Receptors Adaptation 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 15-2 Sensory Receptors Adaptation 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 15-2 Sensory Receptors Adaptation 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 15-3 Classifying Sensory Receptors Classifying Sensory Receptors Exteroceptors provide information about the external environment Proprioceptors report the positions of skeletal muscles and joints Interoceptors monitor visceral organs and functions 15-3 Classifying Sensory Receptors Proprioceptors 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 15-3 Classifying Sensory Receptors General Sensory Receptors Are divided into four types by the nature of the stimulus that excites them Nociceptors (pain) Thermoreceptors (temperature) Mechanoreceptors (physical distortion) Chemoreceptors (chemical concentration) 15-3 Classifying Sensory Receptors Nociceptors (Pain Receptors) Are common In the superficial portions of the skin In joint capsules Within the periostea of bones Around the walls of blood vessels 15-3 Classifying Sensory Receptors Nociceptors May be sensitive to: Temperature extremes Mechanical damage Dissolved chemicals, such as chemicals released by injured cells 15-3 Classifying Sensory Receptors Nociceptors 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 15-3 Classifying Sensory Receptors 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 15-3 Classifying Sensory Receptors Nociceptors 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 15-3 Classifying Sensory Receptors Thermoreceptors Also called temperature receptors Are free nerve endings located in: The dermis Skeletal muscles The liver The hypothalamus 15-3 Classifying Sensory Receptors Thermoreceptors 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) 15-3 Classifying Sensory Receptors 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 15-3 Classifying Sensory Receptors Three Classes of Mechanoreceptors 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 15-3 Classifying Sensory Receptors Three Classes of Mechanoreceptors Baroreceptors Detect pressure changes in the walls of blood vessels and in portions of the digestive, reproductive, and urinary tracts 15-3 Classifying Sensory Receptors Three Classes of Mechanoreceptors Proprioceptors Monitor the positions of joints and muscles The most structurally and functionally complex of general sensory receptors 15-3 Classifying Sensory Receptors 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 15-3 Classifying Sensory Receptors Tactile Receptors Crude touch and pressure receptors Have relatively large receptive fields Provide poor localization Give little information about the stimulus 15-3 Classifying Sensory Receptors Six Types of Tactile Receptors in the Skin 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 15-3 Classifying Sensory Receptors Six Types of Tactile Receptors in the Skin 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 15-3 Classifying Sensory Receptors Six Types of Tactile Receptors in the Skin Tactile discs Also called Merkel discs Fine touch and pressure receptors Extremely sensitive to tonic receptors Have very small receptive fields 15-3 Classifying Sensory Receptors Six Types of Tactile Receptors in the Skin Tactile corpuscles Also called Meissner�s 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 15-3 Classifying Sensory Receptors Six Types of Tactile Receptors in the Skin Lamellated corpuscles Also called Pacinian corpuscles Sensitive to deep pressure Fast-adapting receptors Most sensitive to pulsing or high-frequency vibrating stimuli 15-3 Classifying Sensory Receptors Six Types of Tactile Receptors in the Skin 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 15-3 Classifying Sensory Receptors 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 15-3 Classifying Sensory Receptors Proprioceptors Monitor: Position of joints Tension in tendons and ligaments State of muscular contraction 15-3 Classifying Sensory Receptors Three Major Groups of Proprioceptors Muscle spindles Golgi tendon organs Receptors in joint capsules 15-3 Classifying Sensory Receptors 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 15-3 Classifying Sensory Receptors Receptors in Joint Capsules Free nerve endings detect pressure, tension, movement at the joint 15-3 Classifying Sensory Receptors 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 15-3 Classifying Sensory Receptors Chemoreceptors Receptors that monitor pH, carbon dioxide, and oxygen levels in arterial blood are located in: 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 15-4 Sensory Pathways First-Order Neuron Sensory neuron delivers sensations to the CNS Cell body of a first-order general sensory neuron is located in dorsal root ganglion or cranial nerve ganglion Second-Order Neuron Axon of the sensory neuron synapses on an interneuron in the CNS May be located in the spinal cord or brain stem 15-4 Sensory Pathways Third-Order Neuron If the sensation is to reach our awareness, the second-order neuron synapses On a third-order neuron in the thalamus 15-4 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 The spinothalamic pathway The posterior column pathway The spinocerebellar pathway 15-4 Sensory Pathways The Spinothalamic Pathway Provides conscious sensations of poorly localized (�crude�) touch, pressure, pain, and temperature First-order neurons Axons of first-order sensory neurons enter spinal cord And synapse on second-order neurons within posterior gray horns 15-4 Sensory Pathways The Spinothalamic Pathway Second-order neurons Cross to the opposite side of the spinal cord before ascending Ascend within the anterior or lateral spinothalamic tracts The anterior tracts carry crude touch and pressure sensations The lateral tracts carry pain and temperature sensations 15-4 Sensory Pathways The Spinothalamic Pathway Third-order neurons Synapse in ventral nucleus group of the thalamus After the sensations have been sorted and processed, they are relayed to primary sensory cortex 15-4 Sensory Pathways 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 15-4 Sensory Pathways 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 15-4 Sensory Pathways 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 15-4 Sensory Pathways Posterior Column Pathway Axons synapse On third-order neurons in one of the ventral nuclei of the thalamus Nuclei sort the arriving information according to: The nature of the stimulus The region of the body involved 15-4 Sensory Pathways 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 15-4 Sensory Pathways Posterior Column Pathway 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 15-4 Sensory Pathways 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 15-4 Sensory Pathways The Spinocerebellar Pathway Cerebellum receives proprioceptive information about position of: Skeletal muscles Tendons Joints 15-4 Sensory Pathways The Spinocerebellar Tracts The posterior spinocerebellar tracts Contain second-order axons that do not cross over to the opposite side of the spinal cord Axons reach cerebellar cortex via inferior cerebellar peduncle of that side 15-4 Sensory Pathways The Spinocerebellar Tracts The anterior spinocerebellar tracts Dominated by second-order axons that have crossed over to opposite side of spinal cord 15-4 Sensory Pathways The Spinocerebellar Tracts The anterior spinocerebellar tracts Contain a significant number of uncrossed axons as well Sensations reach the cerebellar cortex via superior cerebellar peduncle Many axons that cross over and ascend to cerebellum then cross over again within cerebellum, synapsing on same side as original stimulus 15-4 Sensory Pathways Sensory Information Most somatic sensory information Is relayed to the thalamus for processing A small fraction of the arriving information Is projected to the cerebral cortex and reaches our awareness 15-4 Sensory Pathways Visceral Sensory Pathways Collected by interoceptors monitoring visceral tissues and organs, primarily within the thoracic and abdominopelvic cavities These interoceptors are not as numerous as in somatic tissues 15-4 Sensory Pathways Visceral Sensory Pathways Interoceptors include: Nociceptors Thermoreceptors Tactile receptors Baroreceptors Chemoreceptors 15-4 Sensory Pathways Visceral Sensory Pathways Cranial Nerves V, VII, IX, and X Carry visceral sensory information from mouth, palate, pharynx, larynx, trachea, esophagus, and associated vessels and glands 15-4 Sensory Pathways Visceral Sensory Pathways Solitary nucleus Large nucleus in the medulla oblongata Major processing and sorting center for visceral sensory information Extensive connections with the various cardiovascular and respiratory centers, reticular formation 15-5 Somatic Motor Pathways The Somatic Nervous System (SNS) Also called the somatic motor system Controls contractions of skeletal muscles (discussed next) The Autonomic Nervous System (ANS) Also called the visceral motor system Controls visceral effectors, such as smooth muscle, cardiac muscle, and glands (Ch. stream julia_domicoli. �ۏhr�U�6���{��H�G2�ΊuYQRS��W��DF��8Zi�\t�~Ŏ�������� In view of the discussed data, during facial transplantation, it is important to consider different mechanisms of restoration of facial sensation. ! The ventral spinocerebellar tract will cross to the opposite side of the body then cross again to end in the cerebellum (referred to as a double cross). The ventral spinocerebellar tract will cross to the opposite side of the body then cross again to end in the cerebellum (referred to as a double cross). At the point of the first synapse event, different receptors target distinct points of the gray matter of the spinal cord (a part of the “butterfly” or “H” shape in the center of the spinal cord) called the dorsal horn. CLEAR, CONCISE, AND MEMORABLE Clinical Neuroanatomy has helped students grasp the essential aspects of neuroanatomy and its functional and clinical correlations since the first edition of this book was published by Jack Lange in 1938. Carry sensory information from the skin and musculature of the body wall, head, neck, and limbs. In a generalized pathway, the afferent neuron of the sensory unit is the first in a chain of neurons that relays information to the CNS (spinal cord and brain).The afferent neuron is the first order neuron.It synapses with a second order neuron that synapses in turn with a third order neuron in the thalamus.The third order neuron guides the impulse to the sensory cortex where it is perceived. include touch, pressure, vibration, itch and tickle. Corticobulbar tracts 2. The Senses: The Somatosensory System. Posterior Column Pathway • Fasciculus gracilis • Fasciculus cuneatus • Carries sensations of highly localized (“fine”) touch, pressure, vibration, and proprioception Figure 15–5a. 5 0 obj Identify the different somatosensory pathways and which modalities are carried by each. - Unit 3 Sensory systems (weeks 5-7). In this section on pathways, we will cover the important pathways that make up the central nervous system. The spinocerebellar pathway. This is because behaviours which cause pain are often dangerous and harmful, therefore they are generally not reinforced and are unlikely to be repeated. What should I comment on someone singing? • Mapped sensory input from different parts of the body – Spatial organization – Density of receptors in region Cortical Mapping (graphic) Somatic Motor Pathways • Descending • Primary motor area (4) and in part the premotor area (6) and somatosensory area contribute to motor neurons Study Sensory Pathways and the Somatic Nervous System- Ch 15 flashcards from Nicole Krausse's class online, or in Brainscape's iPhone or Android app. https://www.verywellmind.com/what-is-the-somatic-nervous-system-2795866 (������qIR@@I~�TG@I~�TG@��OJ��(@����� (�I��(@����I C) touch. 15-5 Describe the components, processes, and functions of the somatic motor pathways, and the levels of information processing involved in motor control. What is Somatic Nervous System.

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