section 1, chapter 12: general senses
DESCRIPTION
general sensesTRANSCRIPT
Section 1, Chapter 12
The Senses
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Introduction
• General senses• Receptors are widely distributed throughout the body• Skin, various organs and joints• Touch, pain, temperature, pressure, ect.
• Special senses• Specialized receptors confined to structures in the head • Vision, Taste, Smell, Hearing
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Receptors, Sensation, and Perception
• Sensory receptors• Specialized cells or multicellular structures that collect
information from the environment
• Stimulate neurons to send impulses along sensory fibers to the brain
• Sensation• A feeling that occurs when brain becomes aware of
sensory impulse
• Perception• A person’s view of the stimulus; the way the brain
interprets the information
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Receptor Types
• Chemoreceptors• Respond to changes in chemical concentrations
(smell, taste, pH)
• Pain receptors (nociceptors)• Respond to tissue damage
• Thermoreceptors• Respond to changes in temperature
• Mechanoreceptors• Respond to mechanical forces• Stretch receptors, proprioceptors, baroreceptors
• Photoreceptors• Respond to light
• Projection• Process in which the brain projects the sensation back
to the apparent source• It allows a person to pinpoint the region of stimulation
Sensations and Perception
• Ability to ignore unimportant stimuli
• Involves a decreased response to a particular stimulus from the receptors (peripheral adaptation) or along the CNS pathways leading to the cerebral cortex (central adaptation)
• Sensory impulses become less frequent and may cease
• Stronger stimulus is required to trigger impulses
Sensory Adaptation
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12.3: General Senses
• Senses associated with skin, muscles, joints and viscera
• Three (3) groups:• Exteroceptive senses (exteroceptors)
• Senses associated with body surface such as touch, pressure, temperature, and pain
• Visceroceptive senses (interoceptors)• Senses associated with changes in the viscera such as blood
pressure stretching blood vessels and ingestion of a meal
• Proprioceptive senses• Senses associated with changes in muscles and tendons such
as at joints
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Touch and Pressure Senses
Free nerve endings• Common in epithelial
tissues• Simplest receptors• Sense itching
Tactile (Meissner’s) corpuscles• Abundant in hairless portions of
skin and lips• Detect fine touch; distinguish
between two points on the skin
Lamellated (Pacinian) corpuscles• Common in deeper subcutaneous
tissues, tendons and ligaments• Detect heavy pressure and vibrations
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Touch and Pressure Receptors
Epidermis
Dermis
(a)
(b)
(c)
Section ofskin
Free nerveendings
Epithelialcells
Sensorynerve fiber
Epithelialcells
Tactile (Meissner’s) corpuscle(touch receptor)
Sensory nervefiber
Lamellated(Pacinian) corpuscle(pressure receptor)
Connective tissuecells
Sensory nervefiber
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b, c: © Ed Reschke
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Temperature Senses• Warm receptors
• Sensitive to temperatures above 25oC (77o F)• Unresponsive to temperature above 45oC (113oF)
• Cold receptors• Sensitive to temperatures between 10oC (50oF) and 20oC
(68oF)
• Pain receptors• Respond to temperatures below 10oC• Respond to temperatures above 45oC
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Sense of Pain
• Free nerve endings
• Widely distributed
• Nervous tissue of brain lacks pain receptors
• Stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature
• Adapt very little, if at all
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Visceral Pain
• Pain receptors are the only receptors in viscera whose stimulation produces sensations
• Pain receptors respond differently to stimulation• Pain receptors are not well localized• Pain receptors may feel as if coming from some other part
of the body• Known as referred pain…
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Referred Pain• May occur due to sensory impulses from two regions
following a common nerve pathway to brain
Appendix
Ureter
Lung and diaphragm
Heart
Stomach
Pancreas
Colon
Kidney
Urinary bladder
Liver andgallbladder
Smallintestine
Ovary(female)
Liver andgallbladder
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Pain Nerve Pathways
• Acute pain fibers• A-delta fibers • Thin, myelinated• Conduct impulses rapidly• Associated with sharp pain• Well localized
• Chronic pain fibers• C fibers • Thin, unmyelinated• Conduct impulses more
slowly• Associated with dull, aching
pain• Difficult to pinpoint
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Regulation of Pain Impulses
• Thalamus • Allows person to be aware of pain
• Cerebral cortex • Judges intensity of pain • Locates source of pain• Produces emotional and motor responses to pain
• Pain inhibiting substances:• Enkephalins• Serotonin• Endorphins
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Proprioception
• Mechanoreceptors
• Send information to spinal cord and CNS about body position and length, and tension of muscles
• Main kinds of proprioceptors:• Pacinian corpuscles – in joints• Muscle spindles – in skeletal muscles*• Golgi tendon organs – in tendons*
*considered to be stretch receptors
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Stretch Receptors
(a)
Muscle spindleSkeletal muscle fiber
Golgi tendon organ
Tendon
(b)
Sensorynerve fiber
Sensorynerve endings
Sensorynerve fiber
Connectivetissue sheath
Intrafusalfiber
Skeletal musclefiber
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Visceral Senses
• Receptors in internal organs
• Convey information that includes the sense of fullness after eating a meal as well as the discomfort of intestinal gas and the pain that signals a heart attack
Summary of Receptors of the General Senses
End of Section 1, chapter 12