Exam 3 Part one Flashcards
Receptors are
Structures that detect stimuli. Range in complexity from simple dendritic endings to complex sensory organs. Monitors external & internal environmental conditions & conduct info about stimuli to CNS. We are aware of some specific stimuli
Receptive field is
Entire area through which the sensitive ends of the receptor cell are distributed.
Describe what is means if the receptive field is small
Precise localization & sensitivity are easily determined
Describe what it means if the receptive field is broad
Only detects general region of a stimulus
Describe why or why not it would be an advantage or disadvantage to have all receptors have small receptive fields
The number of receptors in the body would have to increase to detect environmental stimuli. The energy costs to maintain the activity would be enormous
Transducers
All receptors act as transducers. Structures that transform the energy of one system (e.g. heat) into a different form of energy (e.g. a nerve impulse)
How does the size of the receptive field influence sensitivity
If the receptive field is small we get a precise localization & sensitivity are easily determined. A broad field only detects the general region of the stimulus
Receptors can either be
Tonic or phasic
Tonic receptors
Respond continuously to stimuli at a constant rate; (e.g. balance receptors in the ear that keep the head upright)
Phasic receptors
Detect new stimulus or a change in a stimulus that has already been applied, but over time sensitivity decreases. (e.g. tactile receptors of the skin that sense the increased pressure if we are pinched)
Adaptation
Phasic receptors can undergo adaptation. Change in which a reduction in sensitivity to a continually applied stimulus
General senses
Temp., pain, touch, stretch, & pressure. Receptors are distributed throughout the skin and organs
Special senses
Gustation, olfaction, vision, equilibrium, & hearing. Receptors housed w/in complex organs in the head
3 criteria used to describe receptors
Receptor distribution, stimulus origin, and modality of stimulus
Receptors are subdivided into two categories
Somatic receptors, visceral receptors
Somatic receptors
Housed w/in the body wall; include receptors for external stimuli, including chemicals, temp. pain, touch, proprioception & pressure
Visceral receptors
located in walls of the viscera; respond to chemicals, temp. and pressure & sometimes called interoceptors or visceroceptors
Receptors for special senses
Located w/in some sense organs & housed only in the head
What are the 5 special senses
1) Gustation (taste)
2) Olfaction (smell)
3) Vision
4) Equilibrium
5) Hearing (audition)
Exteroceptors
Detect stimuli from the external environment. Receptors in skin are exteroceptors because external simuli typically cause sensations to the skin. Receptors for special senses are considered exteroceptors
Phantom pain
Sensation associated w/ a body part that has been removed. The stimulation of a sensory neuron pathway from the removed limb on the remaining intact portion of the pathway propagates nerve impulses & conducts them to the CNS, where they are interpreted as originating in the amputated limb.
How can people still feel sensations after a limb has been removed?
Because the cell bodies of the sensory neurons that provided sensation to the limb remain alive because they were not part of that limb
Referred pain
Occurs when impulses from certain viscera are perceived as originating not from the organ, but in dermatomes of the skin. Numerous cutaneous & visceral neurons conduct nerve impulses through the same ascending tracts w/in the spinal cord. As a result impulses conducted along ascending pathways may be localized incorrectly. The sensory cortex in the brain is unable to differentiate between the actual & false sources of the stimulus
Interceptors
Also called visceroceptors. Detect stimuli in internal organs (viscera). Primarily stretch receptors in the smooth muscle of these organs. Report on pressure, chemical changes in the visceral tissue, & temp.
Are we aware of interceptors?
Most of the time we are unaware, but when the smooth muscle stretches to a certain point (when eating a large meal) we may become aware of these sensations
Proprioceptors
Located in muscles, tendons, and joints. Detect body and limb movements, skeletal muscle contraction and stretch, & changes in joint capsule structure
What do proprioceptors play in our awareness of our body joints?
Even if your not looking at your body joints, you are aware of their positioning & the state of contraction of your skeletal muscles, because proprioceptors send this info to the cns
Chemoreceptors
Detect chemicals such as specific molecules dissolved in fluid in our external & internal environments, including ingested food & drink, body fluids, & inhaled air
Give an example of chemoreceptors
The receptors in taste buds on our tongue because they respond to the specific molecules in injested food. Also chemoreceptors in some of our blood vessels monitor the concentration of O2 & carbon dioxide molecules in our blood
Thermoreceptors
Respond to changes in temp.
Photoreceptors
Located in the eye, detect changes in light intensity, color, & movement
Mechanoreceptors
Respond to touch, pressure, vibration, & stretch. Most of the cutaneous receptors are mechanoreceptors, because they respond to pressure & touch on the skin. Also located in the ear for equilibrium & hearing
Baroreceptors
Detect changes in pressure w/in body structures. These sensory receptors branch repeatedly w/in the connective tissues in vessel or organ walls, especially the elastic layer
Any pressure stimulus that causes wall deformation results in a?
change in the nerve impulse rates from the receptors & a pressure sensation
Nociceptors
Respond to pain caused by either external or internal stimuli
Somatic nociceptors detect?
Chemical, heat, or mechanical damage to the body surface or skeletal muscles
Exposed to acid, touching a hot pan, or sprained ankle stimulate what?
Somatic nociceptors
Visceral nociceptors detect?
Internal body damage w/in the viscera due to excessive stretching of smooth muscle, O2 deprivation of the tissue, or chemicals released from damaged tissue
Cutaneous receptors
Receptors in your skin
Free nerve endings
Terminal branches of dendrites. Least complex of tactile receptors & reside closest to the surface of the skin, usually in the papillary layer of the dermis. Primarily detect pain and temp. stimuli but some also detect light touch & pressure
Root hair plexuses
Specialized free nerve endings that form a weblike sheath around hair follicles in the reticular layer of the dermis. Any movement or displacement of the hair changes the arrangement of these branching dendrites, initiating a nerve impulse. They quickly adapt & our conscious awareness subsides until restimulated
Tactile corpuscles
Previously called Meissner corpuscles, they are physically different from the unencapsulated tactile discs. large encapsulated oval receptors, formed from highly intertwined dendrites enclosed by modified neurolemmocytes, which are then covered w/ dense irregular connective tissue. Phasic receptors for light touch, shapes, & texture. Housed w/in the dermal papillae of the skin, especially in the lips, palms, eyelids, nipples, & genitals
Lamellated corpuscles
Previously called Pacinian corpuscles. Large receptors that detect deep pressure & high frequency vibration. Center of the receptor houses several dendrite endings of sensory neurons wrapped w/in numerous concentric layers of flat, fibroblast like cells. This structure ensures that only deep pressure stimuli will activate the receptor. Found deep w/in the reticular layer of the dermis; in the subcutaneous layer of the palms of the hands, soles of the feet, breasts and external genitalia; int he synovial membranes of joints, & in the walls of some organs
Krause bulbs
Located near the border of stratified squamous epithelium in the mucous membranes of the oral cavity, nasal cavity, vagina, & anal canal. Detect light pressure stimuli & low frequency vibration
Ruffini corpscles
Detect both continuous deep pressure & distortion in the skin. Tonic receptors that do not exhibit adaptation; housed w/in the dermis & subcutaneous layer