chapter 45 Flashcards
Overview of Sensory Receptors
Sensory receptors provide information from our internal and external environments that is crucial for survival and success
Exteroceptors sense external stimuli
Detect light, sound waves
Interoceptors sense internal stimuli
Detect muscle tension, pain, limb position, blood chemistry, blood volume, pH, temp., touch
Receptors can be grouped into three classes
1.Mechanoreceptors are stimulated by mechanical forces such as pressure—displacement of tissue; receptors for touch, hearing and balance (hair cells)
2. Chemoreceptors detect chemicals or chemical changes—receptors for taste, smell
3. Electromagnetic receptors react to heat and light energy—receptors for light (photoreceptors, thermoreceptors
–Receptors can be free nerve endings on the
dendrites of sensory neurons
or
Specialized epithelial cells in association with
a sensory neuron
Sensory information is conveyed to the CNS and perceived in a four-step process: Stimulation Transduction Transmission Interpretation
Sensory cells respond to stimuli via stimulus-gated ion channels in their membranes
Open or close depending on the sensory system involved
In most cases, a depolarization of the receptor cell occurs
Analogous to the excitatory postsynaptic potential (EPSP)
Referred to as receptor potential
Receptor potential like a graded potential
The larger the sensory stimulus, the greater the degree of depolarization
The greater the sensory stimulus, the greater the depolarization of the receptor potential and the higher the frequency of action potentials
Mechanoreceptors
Cutaneous receptors
Receptors in the skin
Classified as interoreceptors
Respond to stimuli at the border between internal and external environments
Receptors for pain, heat, cold, touch, and pressure
Nociceptors
Transmit impulses perceived as pain
Sensitive to noxious substances and tissue damage
Most consist of free nerve endings located throughout the body, especially near surfaces
Thermoreceptors
Naked dendritic endings of sensory neurons that are sensitive to changes in temperature
Stimulated by a rise or fall in temperature.
Cold receptors are located higher in the skin
Cold receptors are more numerous than warm receptors
Also found in hypothalamus—monitor temp. of blood
Stimulate responses to increase or decrease core temp
Several types of mechanoreceptors in the skin detect the sense of touch
Contain sensory cells with ion channels that open in response to membrane distortions
2 types
Phasic – intermittently activated
Hair follicle receptors, Meissner corpuscles, Pacinian corpuscles
Tonic – continuously activated
Ruffini corpuscles, Merkel’s disks
Proprioceptors
Monitor muscle length and tension
Provide information about the relative position or movement of animal’s body parts
Examples
Muscle spindles – monitor stretch on muscle – receptors that lie in parallel with muscle fibers – knee jerk reflex
Golgi tendon organs – monitor tension on tendons – reflex inhibits motor neurons – prevents damage to tendons
Baroreceptors
Monitor blood pressure
Located at carotid sinus and aortic arch
Detect tension or stretch in the walls of these blood vessels
When blood pressure decreases, the frequency of impulses produced by baroreceptors decreases
Results in increased heart rate and vasoconstriction
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Hearing Structure in Fish
Hearing structures in fish
Called otoliths
Composed of calcium carbonate crystals
Contained in the otolith organs of the membranous labyrinth
Otoliths vibrate against stereocilia projecting from hair cells
Produces action potentials
Ear Structure of Land Vertebrates
Air vibrations are channeled through the ear canal of the outer ear
Vibrations reach the tympanic membrane causing movement of three small bones (ossicles) in the middle ear
Malleus (hammer), incus (anvil), and stapes (stirrup)
The stapes vibrates against the oval window, which leads into the inner ear
The inner ear consists of the cochlea
Bony structure containing part of the cochlear duct
The vestibular canal lies above this duct, while the tympanic canal lies below it
All three chambers are filled with fluid
Pressure waves travel down the tympanic canal to the round window, which is another flexible membrane
Transmits pressure back to middle ear
As pressure waves are transmitted through the cochlea to the round window, they cause the cochlear duct to vibrate
Organ of Corti
Basilar membrane contains sensory hair cells
Stereocilia from hair cells project into tectorial membrane
Bending of stereocilia depolarizes hair cells
Hair cells send action potentials to the brain
Basilar membrane of the cochlea consists of elastic fibers that respond to different frequencies, or pitch, of sound
Hair cell depolarization is greatest in region that responds to a particular frequency
Afferent axons from that region stimulated more
Brain interprets that as representing sound of a particular frequency or pitch
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Detection of Body Position
Most invertebrates can orient themselves with respect to gravity using a statocyst
Consists of ciliated hair cells embedded in a membrane with calcium carbonate stones (statoliths)
In vertebrates, the gravity receptors consist of two chambers in the membranous labyrinth
Utricle and saccule
Within the utricle and saccule are hair cells with stereocilia and a kinocilium
Processes embedded in the calcium carbonate-rich otolith membrane
Utricle more sensitive to horizontal acceleration
Saccule more sensitive to vertical acceleration
Both types of accelerations cause cilia to bend, thus producing an action potential in an associated sensory neuron
The utricle and saccule are continuous with three semicircular canals that detect angular acceleration in any direction
At the ends of the canals are swollen chambers called ampullae
Groups of cilia protrude into them
Tips of cilia are embedded within a gelatinous cupula that protrudes into the endolymph fluid of each canal
When the head rotates, the semicircular canal fluid pushes against the cupula, causing the cilia to bend
Bending in the direction of the kinocilium causes a receptor potential
Stimulates an action potential in the associated sensory neuron
Saccule, utricle, and semicircular canals are collectively called the vestibular apparatus
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Chemoreceptors
Bind to particular chemicals in the extracellular fluid
Membrane of sensory neuron becomes depolarized and produces action potentials
Chemoreceptors are used in the senses of taste and smell
Also important in monitoring the chemical composition of blood
