General senses Flashcards
Sensory receptors
- adaptation: magnitude of response decreases over time in response to continuous stimulus
- perception: remaining aware of sensation over time and interpreting what that sensation means in larger context
General senses
Microscopic receptors widely distributed in the skin, mucosa, connective tissues, mm, tendons, joints, and viscera
- somatic and visceral senses
Special senses
Localized receptors for
- smell
- taste
- vision
- hearing/equilibrium
Stimulation of the sensory receptor
Selectivity: a given receptor responds vigorously to one particular kind of stimulus (weakly or not at all to other stimuli) in its receptive field
Transduction of the stimulus
Converts energy in stimulus into graded potential
Generation of nerve impulses
Graded potential reaches threshold and triggers propagation toward CNS
Integration of sensory input
Regions of CNS and post central gyrus receive and integrate impulses
Classification of receptors
- Location
- exteroceptors - visceroceptors (interceptors) - proprioceptors - Stimulus
- mechanoreceptors - chemoreceptors - thermoreceptors - nociceptors - photoreceptors - osmoreceptors - Structure
- free nerve endings - encapsulated nerve endings
Exteroceptors
- located on or very near the body surface
- respond most frequently to stimuli that arise external to the body itself
- sometimes called cutaneous receptors (detect pressure, touch, pain, and temperature)
Visceroeptors (interoceptors)
Located internally
- primarily in blood vessels and viscera
- provide info regarding internal environment (usually not consciously perceived, if stimuli is strong may be perceived as pain or pressure)
- activated by pressure, stretching, and chemical changes
- involved in mediating sensations such as hunger, thirst, BP, full bladder
Proprioceptors
- Special type of visceroceptor
- less numerous and more specialized than other visceroceptors - Located in skeletal mm, joint capsules, and tendons
- Provide information regarding
- body movement
- orientation in space
- mm stretch
Two types:
- Tonic: provides information while the body is at rest, non-adapting
- Phasic: provides information during movement. Rapidly adapting and triggered only when there is a change in position
Mechanoreceptors
- detect mechanical stimuli that deform or change position of the receptor
- ex: pressure to skin, blood vessels, that results in stretch or pressure in mm, tendon, or lung tissue
Chemoreceptors
- detect chemicals in the mouth, nose, and body fluids
- activated by either the amount or the changing concentration of certain chemicals
- ex: sense of taste, smell, pH homeostasis
Thermoreceptors
Activated by changes in temperature
Nociceptors
- activated by intense stimulu that could result in tissue damage
- chemical
- intense light
- sound
- pressure
- heat - The sensation produced is pain
Photoreceptors
- found only in the eyes
- detect light that strikes the retina
Osmoreceptors
- concentrated in the hypothalamus
- sense levels of osmotic pressure in body fluids
- activated by changes in concentration of electrolytes in extracellular fluids
- stimulate the hypothalamic thirst center
Free nerve endings
- bare dendrites
- the simplest, most common, and most widely distributed sensory receptors
- include both exteroceptors and interoceptors
Encapsulated nerve endings
have some type of connective tissue capsule that surrounds the terminal end or dendritic end
- usually mechanoreceptors (activated by mechanical or deforming stimulus)
- major types:
- Tactile/meissners corpuscle
- Lamellar/pacinian corpuscle
- Bulbous/ruffini cells
- Bulboid/Krause corpuscle
Pic
Pic
Sense of pain
Nociceptors-FREE nerve endings
- primary sensory receptors for pain
- 2 types: acute/fast pain and chronic/slow pain
Pain A delta fibers
- concentrated in the skin, mucous membranes, and other superficial areas
- sharp, intense, localized fast/somatic pain
- “fast pain” travels over myelinated fibers (250 ft/sec)
- associated with superficial injury or trauma
Pain C delta fibers
- originates in deeper/visceral regions (thoracic and abdominal regions)
- intense or less sever, but persistent, dull aching pain
- develops more slowly over time
- “slow pain” travels over unmyelinated fibers (3.5 ft/sec)
Sense of temperature
- FREE nerve endings
- mediate sense of heat and cold
- called thermoreceptors - Warm receptors
- located in dermis
- activated in temperature range of 77-114 degree F
- >118 degrees = burning - Cold receptors
- located in deepest layer of epidermis
- activated in temperature range of 50-104 degrees F
- <50 dramatic decrease in firing rate but activates nociceptors (freezing pain)
Sense of touch
- Types of touch sensations
- skin movement
- itch
- tickles
- light touch
- deep touch - Free and encapsulated endings
Touch-skin movement
Root hair plexuses - FREE nerve endings
- activated with very slight movement on or in the skin
- bends or deforms a hair follicle or shaft
Touch - Itch
Free nerve endings
- activated by chemical irritation
- inflammatory chemicals (bradykinin or histamine)
Touch - Tickle
Free nerve endings
- activated by touch from an outside source
- involves both thalamus and cerebellum before reaching the cerebral cortex
Light/discriminative touch
Mediated by a variation of a FREE nerve ending
- tactile or nerves disk: transmits compression of the outer layer of skin to the tactile disk neuron (mechanoreceptors)
- detects discriminative touch and surface form and contours
Deep touch
Encapsulated nerve endings
- tactile/meissner corpuscles
- enmeshed in connective tissue
- located close to the dermal papillae in hairless skin areas like fingertips, lips, nipples, and genitals - Mediate light touch, textural sensations, and low frequency vibration
Anatomical variants of meissner corpuscles
- Bulboid/Krause corpuscle
- more numerous in mucous membranes - Bulbous/ruffini corpuscle
- crude, heavy, and persistnat touch - Lamellar/Pacini corpuscles
- deep pressure, high frequency vibration, and stretch
Sense of proprioception
- tells us level of contraction and stretch in each of our skeletal muscles
- proprioceptors (muscle spindles and Golgi tendon receptors)
Muscle spindles
Encapsulated nerve endings
- discrete grouping of 5-10 modified mm fibers called intrafusal fibers surrounded by sensory nerve fibers
- respond to mm stretch (stretch reflex and subconscious postural adjustments)
Golgi tendon organ
Encapsulated nerve endings
- located at the junction between mm tissue and tendon
- stimulated by excessive stretch of a tendon (when pulling too great a load for the muscles to bear—tension)
- protects mm from tearing
