LAB EXERCISE 18 GENERAL SENSES

Sensory Information Afferent Division of the Nervous System Receptors Sensory neurons Sensory pathways Spinal cord to brain Deliver somatic and visceral sensory information to their final destinations inside the CNS using: Nerves Nuclei Sensory tracts Sensory processing centers in brain Higher-Order Functions Conscious and subconscious motor centers in brain Memory, learning, and intelligence may influence interpretation of sensory information and nature of motor activities Sensory pathways General sensory receptors

Somatic Nervous System (SNS) Sensory Information Somatic Motor Portion of the Efferent Division Controls peripheral effectors Skeletal muscle Somatic Motor Commands Travel from motor centers in the brain along somatic motor pathways of: Motor nuclei Tracts Nerves Motor pathways Somatic Nervous System (SNS) Skeletal muscles

Sensory Receptors General Senses Describe our sensitivity to: Temperature Pain Touch Pressure Vibration Proprioception

Sensory Receptors Special Senses The Special Senses Are provided by special sensory receptors Olfaction (smell) Vision (sight) Gustation (taste) Equilibrium (balance) Hearing

SENSATION VS PERCEPTION Occurs when nerve impulses arrive at the cerebral cortex From sensory neurons created by an action potential. Chemoreceptors Thermoreceptors Nociceptors Baroreceptors What we are not aware of

SESNSATION VS PERCEPTION Perception is the conscious awareness & interpretation of a sensation Occurs when the cerebral cortex interprets the meaning of sensations. We have no perception of some information because it never reaches the cortex. Blood pressure is received in the medulla

Sensory Integration Input comes from Exteroceptors Interoceptors Proprioceptors Input is relayed toward the head, and is processed along the way

Sensory Receptors Exteroceptors Respond to stimuli arising outside the body Receptors in the skin Touch Pressure Pain Temperature Most special sense organs Vision Hearing Equilibrium Taste Smell

Sensory Receptors Interoceptors **Visceroceptors Respond to stimuli arising in internal viscera and blood vessels Sensitive to Chemical changes Tissue stretch Temperature changes Pain Discomfort Hunger Thirst

Sensory Receptors Proprioceptors Provide a purely somatic sensation Respond to stretch in Skeletal muscles Tendons Joints Ligaments Connective tissue coverings of bones and muscles Inform the brain of one’s body movements 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 Sensory Receptors

Processing at the Circuit Level This level consists of pathways of three neurons conduct sensory impulses upward to the appropriate brain regions First order neurons Second order neurons Third order neurons

Processing at the Circuit Level First order neurons Conduct impulses from the receptor level to the second-order neurons in the brain stem or spinal cord

Processing at the Circuit Level Second-order neurons Transmit impulses to the Thalamus Tracts cross over

Processing at the Circuit Level Third-order neurons Conduct impulses from The thalamus to The somatosensory cortex Perceptual level

Processing at the Perceptual Level The axons of the third order continue to ascend without crossing over to the somatosensory area. As a result Left cerebral hemispheres receive info from the right side Right cerebral hemispheres receive info from the left side

Sensory Receptors Learning Outcomes 15-3 Identify the receptors for the general senses, and describe how they function.

Sensory Receptors General Sensory Receptors Are divided into four types by the nature of the stimulus that excites them Chemoreceptors **Chemical concentration Nociceptors **Pain 3. Thermoreceptors **Temperature 4. Mechanoreceptors **Physical distortion

Classifying Sensory Receptors Nociceptors (Pain Receptors) Most concentrated in the superficial portions of the skin In joint capsules Within the periostea of bones Around the walls of blood vessels

Classifying Sensory Receptors Nociceptors Are free nerve endings with large receptive fields May be sensitive to: Temperature extremes Mechanical damage Dissolved chemicals, such as chemicals released by injured cells *Associated with tissue damage Type A or Type C

Classifying Sensory Receptors Myelinated Type A Nociceptor 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

Classifying Sensory Receptors Type C Nociceptor 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

Classifying Sensory Receptors -Referred pain “Incorrect" source perceived *Pain in the forehead when eating ice cream too quick *Heartburn *Dentistry *Angina –Pain in the arm when the heart does not receive enough oxygen Classifying Sensory Receptors

Classifying Sensory Receptors Thermoreceptors Also called temperature receptors Are free nerve endings located in: The dermis Skeletal muscles The liver The hypothalamus

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

Classifying Sensory Receptors Three Classes of Mechanoreceptors Tactile receptors Provide the sensations of Touch Shape & texture Pressure Degree of distortion Vibration Pulsing or oscillating pressure

Classifying Sensory Receptors Three Classes of Mechanoreceptors Baroreceptors Detect pressure changes in Walls of blood vessels Portions of the digestive Portions of the reproductive Portions of the urinary tracts

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

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

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

Classifying Sensory Receptors Tactile Receptors Crude touch and pressure receptors Have relatively large receptive fields Provide poor localization Give little information about the stimulus

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

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

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

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

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

Meissner’s vs Pacinian If you close your eyes and have a friend place an object in the open palm of your hand, chances are good you will be able to detect the object but you will not be able to identify it. By moving the object to your finger tips where Meissner's corpuscles are abundant, you gather information about its shape, texture, and density, information your brain uses to identify the object. The Pacinian corpuscles enable you to detect the object due to its weight. Meisner’s enable you to define it by fine touch

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

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

Classifying Sensory Receptors Proprioceptors Monitor: Position of joints Tension in tendons and ligaments State of muscular contraction

Classifying Sensory Receptors Three Major Groups of Proprioceptors Muscle spindles Golgi tendon organs Receptors in joint capsules

Classifying Sensory Receptors Muscle Spindles Monitor skeletal muscle length Trigger stretch reflexes

Classifying Sensory Receptors 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

Classifying Sensory Receptors Receptors in Joint Capsules Free nerve endings detect pressure, tension, movement at the joint

Chemoreceptors Respond to small concentration changes of specific molecules (chemicals) Internal chemoreceptors monitor blood composition (e.g. Na+, pH, pCO2 ) Found within aortic and carotid bodies Very important for homeostasis

Chemoreceptors Respond to small concentration changes of specific molecules (chemicals) Internal chemoreceptors monitor blood composition (e.g. Na+, pH, pCO2 ) Found within aortic and carotid bodies Very important for homeostasis

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