BIOL 3301 Integration of Nervous System Function Fall 2024 PDF

Integration of Nervous System Function BIOL 3301 Kristen Winter, PhD Learning Objectives List the types of somatic and visceral sensory receptors, tell where they are located, and describe how they function in sensation Describe the roles of receptor potentials and ad...

Integration of Nervous System Function BIOL 3301 Kristen Winter, PhD Learning Objectives List the types of somatic and visceral sensory receptors, tell where they are located, and describe how they function in sensation Describe the roles of receptor potentials and adaptation Differentiate between primary and secondary receptors Differentiate between tonic and phasic receptors List the major ascending sensory tracts and state a function for each Describe the sensory and association areas of the cerebral cortex and discuss their interactions  Sensation Process initiated by stimuli acting on sensory receptors Action potentials are generated by stimuli at the sensory receptor and propagate along nerves to the brain and spinal cord Perception – conscious awareness of those sensations Results when the brain interprets the sensation- generated action potentials in the cerebral cortex Not all sensory information results in perception Senses – means by which the brain receives information about the environment and body General senses Special senses  Senses General senses – receptors distributed over a large part of the body Somatic senses – sensory information from the body and environment Touch Pressure Temperature Pain Proprioception – sense of body’s position and movement Visceral senses – information from internal organs Pain Pressure Special senses – localized to specific organs with specialized receptors Smell Taste Vision Hearing Balance  Types of Sensory Receptors TABLE 14.1 Classification of the Senses Classified based Types of Sense Receptor Type Initiation of Response Specific Examples GENERAL SENSES on Somatic Touch Mechanoreceptors Compression of receptors Types of Stroking Meissner corpuscle Hair follicle receptor Texture Merkel disk stimulus they Vibration Pacinian corpuscle Skin stretch Ruffini end organ detect Itch, tickle Free nerve endings Location in the Pressure Mechanoreceptors Compression of receptors Merkel disk Proprioception Mechanoreceptors Compression of receptors Free nerve endings Pacinian corpuscle body Muscle spindle Golgi tendon organ Receptor Temperature Thermoreceptors Temperature around nerve endings Free nerve endings Cold receptors structure Pain Nociceptors Irritation of nerve endings (e.g., mechanical, Warm receptors Free nerve endings chemical, or thermal) Visceral Pain Nociceptors Irritation of nerve endings Free nerve endings Pressure Mechanoreceptors Compression of receptors Pacinian corpuscle SPECIAL SENSES Smell Chemoreceptors Binding of molecules to membrane receptors Olfactory receptor Taste Chemoreceptors Binding of molecules to membrane receptors Taste receptor Vision Photoreceptors Chemical change in receptors initiated by light Rods and cones Hearing Mechanoreceptors Bending of microvilli on receptor cells Hair cells Balance Mechanoreceptors Bending of microvilli on receptor cells Hair cells  Types of Sensory Receptors Mechanoreceptors Respond to mechanical force (compression, bending, stretching of cells) Touch, pressure, proprioception, hearing, and balance Chemoreceptors Respond to chemicals Smell and taste Thermoreceptors Respond to changes in temperatures Sense of temperature Photoreceptors Respond to light Vision Nociceptors Pain receptors Respond to extreme, mechanical, chemical, and thermal stimuli Can respond to more than one type of stimuli Types of Sensory Receptors Cutaneous receptors Associated with the skin Provide information about the external environment Visceroreceptors Associated with the viscera or organs Provide information about the internal environment Proprioceptors Associate with joints, tendons, and other connective tissue Provide information about body position, movement, and extent of stretch or force of muscular contraction Types of Sensory Receptors TABLE 14.2 Structural Classification of General Sensory Receptors Type of Receptor Structure Function Free nerve Branching, no capsule Pain, itch, tickle, temperature, joint ending movement, and proprioception Merkel Consists of flattened expansions at the end of axons; each Light touch and superficial disk expansion is associated with a Merkel cell pressure Hair follicle Wrapped around hair follicles or extending along the hair axis; Light touch; responds to very slight receptor each axon supplies several hairs, and each hair receives bending of the hair branches from several neurons, resulting in considerable overlap Pacinian Onion-shaped capsule composed of several cell layers with a Deep cutaneous pressure, vibration, corpuscle single central nerve process and proprioception Meissner Several branches of a single axon associated with Two-point discrimination corpuscle specialized Schwann cells and surrounded by a connective tissue capsule Ruffini end Branching axon with numerous small, terminal knobs Continuous touch or pressure; organ surrounded by a connective tissue capsule responds to depression or stretch of the skin Muscle Three to 10 striated muscle fibers enclosed by a loose Proprioception associated with detection of spindle connective tissue capsule, striated only at the ends, with muscle stretch; important for control of muscle sensory nerve endings in the center tone Golgi tendon Surrounds a bundle of tendon fasciculi and is enclosed by a Proprioception associated with the stretch organ delicate of a tendon; important for control of connective tissue capsule; nerve terminations are branched, muscle with small swellings applied to individual tendon fasciculi contraction  Free Nerve Endings Simplest structure Most common sensory receptor Unspecialized neuronal branches similar to dendrites Distributed throughout most parts of the body Abundant in epithelial and connective tissues Detect pain, temperature, itch, movement  Merkel (Tactile) Disks More complex than free nerve endings Consist of axonal branches that end as flattened expansions each associated with specialized epithelial cell Found in the basal layers of the epidermis and dome-shaped mounds of thickest epidermis in hairy skin Detect light touch and superficial pressure Skin displacement of less than 1 mm Hair Follicle Receptors (Hair End Organs) Respond to slight bending of the hair during light touch Very sensitive to low levels of stimulation Not well localized Dendritic tree has several hair follicle receptors Receptive fields overlap  Pacinian (Lamellated) Corpuscles Complex structure Multiple layers of tissue surrounding a single dendrite (like an onion) Compression causes an action potential Located in subcutaneous tissue Respond to deep cutaneous pressure and vibration Associated with joints Proprioceptive information Meissner (Tactile) Corpuscles Distributed throughout dermal papillae Involved in two-point discrimination Ability to detect simultaneous stimulation of Meissner corpuscles in two distinct receptor fields by touching at two points on the skin Distance between two points varies in different body regions (abundant in tongue and finger tips, less in back) Evaluates texture of objects  Ruffini End Organs Located in dermis of the skin Primarily in the fingers Respond to pressure on the skin directly superficial to receptor and stretch of adjacent skin Important for continuous touch or pressure  Muscle Spindles 3-10 specialized muscle fibers located in skeletal muscles Provide information about the length of muscle Important for control and tone of postural muscles Stretching of muscles stimulates gamma motor neurons and activates the stretch reflex to increase muscle tone Golgi Tendon Organs Proprioceptive receptors associated with a tendon near the junction between muscle and tendon Activated by increased tendon tension caused by contraction of muscle or passive stretch of the tendon  Responses of Sensory Receptors Receptor potential – graded potential created when a sensory receptor is stimulated Primary receptors – sensory receptor cells that conduct action potentials in response to the receptor potential Secondary receptors – have no axons or short, axon like projections and only produce receptor potentials  Adaptation of Sensory Receptors Adaptation – decreased sensitivity to continued stimulus Graded depolarization produced by receptor potential adapts or returns to resting level even though stimulus is still being applied Tonic receptors – generate action potentials as long as a stimulus is applied and adapt slowly Merkel disks and Ruffini end organs Phasic receptors – adapt rapidly and are sensitive to changes in stimuli Pacinian and Meissner corpuscles  Sensory Pathways Transmit information form sensory receptors to the CNS Ascending spinal pathways – sensory pathways involving the spinal cord Carry a specific modalities Names often indicate origin and termination Names may indicate location in the CNS Conscious sensory input Spinothalamic tract of the anterolateral system Dorsal-column/medial-lemniscal system Unconscious sensory input Anterolateral system (spinomesencephalic and spinoreticular tracts) Spinocerebellar tract Anterolateral System One of two major systems that convey cutaneous system information to the brain Includes three tracts Spinothalamic tract – conscious perception of pain and temperature information, light touch and pressure, tickle, and itch sensations Spinoreticular tract – carry pain and touch sensation that is not consciously perceived to other parts of the brain Spinomesencephalic tract – carry pain and touch sensation that is not consciously perceived to other parts of the brain  Spinothalamic Tract Transmits sensory signals from peripheral receptors to the cerebral cortex Three neuron chain Primary neurons – conduct action potentials from the sensory receptor to the CNS (dorsal horn of the spinal cord) Axons form dorsal root of spinal nerve with cell bodies in dorsal root ganglia Synapse on interneurons Secondary neurons – neurons in the spinal cord that relay information to the brain Axons decussate (cross) to the contralateral (opposite) side of the spinal cord Fibers enter the spinothalamic tract and ascend to the thalamus where they synapse on tertiary neurons Tertiary neurons – in the thalamus and relay information to the somatosensory cortex of the cerebrum Spinoreticular & Spinomesencephalic Tracts Ascend with the spinothalamic tract in the spinal cord Divert to the midbrain and other brainstem nuclei Some neurons of spinoreticular tracts do not cross over and ascend on the ipsilateral (same) side Spinotectal tract – portion of the spinomesencephalic tract that ends in the superior colliculi of the midbrain Transmits action potentials involved in reflexes that turn the head and eyes toward cutaneous stimulation  Dorsal-Column/Medial-Lemniscal System Consists of two pathways that carry sensations of two-point discrimination, proprioception, pressure, and vibration Travels in the dorsal column of the spinal cord and medial lemniscus of the brainstem Dorsal column is divided into Fasciculus gracilis – conveys sensation from the lower part of the body, terminates in the nucleus gracilis of medulla oblongata or with neurons of the posterior spinocerebellar tracts Fasciculus cuneatus – conveys sensation from upper part of the body, terminates in nucleus cuneatus of the medulla oblongata  Dorsal-Column/Medial-Lemniscal System Primary neurons – in the dorsal root ganglia, have largest cell bodies Some primary neurons have axons enter the spinal cord and ascend the entire length without crossing to the contralateral side and synapse with secondary neurons in the medulla oblongata Other neurons synapse in the thoracic portion of the spinal cord Secondary neurons – exit nucleus gracilis and nucleus cuneatus and cross to the opposite side of the medulla oblongata at the decussations of the medial lemniscus Ascend through medial lemniscus to synapse with tertiary neurons in the thalamus Tertiary neurons – project to the primary somatosensory cortex to the cerebrum Trigeminothalamic Tract Join the spinothalamic tract in the brainstem Primarily consists of afferent fibers from the trigeminal nerve (CN V), a few tactile afferent fibers from ear and tongue carried by CN VII, IX, and sometimes CN X Carries same information as spinothalamic tracts and dorsal- column/medial-lemniscal system from the face, nasal cavity, and oral cavity Primary neurons – synapse with secondary neurons Secondary neurons – decussate to the opposite side of the brainstem and synapse on tertiary neurons in the thalamus Tertiary neurons – project to primary somatosensory cortex of the cerebrum  Spinocerebellar Tracts Carry proprioceptive information to the cerebellum Compares information concerning actual movements can be monitored and compared with cerebral information representing intended movements Posterior spinocerebellar tract Carries information from the upper part of the body in the thoracic and upper lumber regions Contains uncrossed fibers entering the cerebellum through the inferior cerebellar peduncle Anterior spinocerebellar tract Carries information form lower trunk and lower limbs Contains both crossed and uncrossed nerve fibers that enter the cerebellum through superior cerebellar peduncle Crossed fibers recross in the cerebellum