sensory information - gets to central nervous system through 4 steps
- 4-step process
- stimulation - activates sensory neuron
- transduction - stimulus transformed into graded potentials
- transmission - action potential lead to central nervous system
- interpretation - brain analyzes/perceives senses from electrochemical messages
- 3 types of stimuli
- mechanical forces - stimulate mechanoreceptors
- chemicals - stimulate chemoreceptors
- electromagnetic/thermal energy - stimulate photoreceptors
- free nerve endings - simplest sensory receptors, respond to mov’t of sensory neuron membrane, temperature change, chemicals in extracellular fluid
- exteroceptors - receptors receiving info from external environment
- most developed in water for vertebrates
- interoceptors - receptors receiving info from within body
- usually more simple than exteroceptors
- stimuli >> stimulus-gated ion channels open >> depolarization (receptor potential) >> info sent to brain
cutaneous receptors - skin receptors, respond to stimuli at border between external/internal
- thermocreceptors - sensitive to changes in temperature
- cold receptors - found right below epidermis
- warm receptors - found deeper in dermis
- nociceptors - sensitive to pain
- pain = stimulus causing damage to tissue
- overstimulated sensory receptors can also produce pain
- mechanoreceptors - sensitive to forces applied to membrane
- phasic receptors - intermittently activated, hair follicle receptors, Meissner’s corpuscles
- tonic receptors - always activated, Ruffini corpuscles, touch dome endings (Merkel cells)
- Pacinian corpuscles - monitor onset/removal of pressure
proprioceptors - muscle spindles giving info about position/mov’t of body parts
- activated when muscle is stretched
- not found in bony fishes
- inhibits somatic motor neurons when muscle contracts too strongly
baroreceptors - monitor tension/stretch in blood vessel walls
- measures blood pressure at carotid sinus (supplies blood to brain) and aortic arch (part of aorta very close to heart)
- low blood pressure >> less impulses from baroreceptors >> central nervous system stimulates sympathetic division to increase heart rate
chemoreceptors - chemicals/ligands lead to depolarization
- used in smell/taste
- taste buds - collections of epithelial cells connected to neurons
- most sensitive chemoreceptors in vertebrates
- insects taste w/ their feet
- papillae - raised areas in tongue/oral cavity where taste buds are found
- sour/salty tastes act w/ ion channels
- sweet/bitter tastes act w/ G proteins
- smell - receptors found in upper part of nasal passages
- air particles must become extracellular fluid before activating the neurons
- humans can tell apart many times more smells than tastes
- peripheral/central chemoreceptors - detect pH changes in blood and cerebrospinal fluid
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