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Sensory Receptors

What is a free nerve ending? Bare dendrites
What fibers have free nerve endings? Pain, temperature, tickle, itch, and light touch
What are encapsulated nerve endings? Dendrites enclosed in CT capsule
What fibers have encapsulated nerve endings? Pressure, vibration, and deep touch
What are separate sensory cells? Specialized cells that respond to stimuli - vision, taste, hearing, balance
What is the function of encapsulation? Enhance sensitivity or specificity of receptor
Where are proprioceptors located? Muscle, tendon, joint, and internal ear
What do proprioceptors detect? Senses body position and movement by detecting muscle length and tension
What is the destination for impulses from proprioceptors? Cerebellum and primary somatosensory area
When would we want adapting receptors? When there isn't a change to stimuli that's not painful - like putting clothes on
When would we want non-adapting receptors? Pain, body position
Mechanoreceptors detect deformation (pressure or touch), what are the 4 main ones? Merkel's disks, Meissner's corpuscles, Ruffini endings, and Pacinian corpuscle
Where are the mechanoreceptors located, relative to each other? Merkel's disks and Meissner's corpuscle are smaller and located towards surface. Ruffini endings and Pacinian corpuscle are larger and located deeper.
Where are free nerve endings located? Epidermis interspersed among keratinocytes, papillary layer of dermis, many other tissues
Because Merkel's disks and Meissner's corpuscles are located towards the surface, what is a common stimuli? Touch
Because Meissner's corpuscle is stimulated by fine touch and low frequency vibration, what can we infer about its location? In areas with maximum sensitivity - dermal papillae of thick skin (digits, palmar surface of hands/feet), eyelids, external genitalia, nipples, lips
Where are Merkel endings? Stratum basale with extension of pseudopodia into keratinocyte layer - most numerous in thick skin
Where are pacinian corpuscle located? Dermis and subcutaneous tissue - also in mesenteries, bladder wall, joint capsules, external genitalia
How does the adaptation of pacinian corpuscle's differ from the rest of the mechanoreceptors? Responds to ion channels in nerve membranes which open in response to compression
What are Krause end bulbs? Somatic receptor that responds to pressure and coldness
Where are Krause end bulbs located? Papillary dermis of the conjunctivea, CT of mouth, tongue, pharynx, and external genitalia
What are Ruffini corpuscle? Somato receptor that responds to tension generated in surrounding collagen fibers of CT and heat
What is the implication of the stimuli of Ruffini corpuscle? Because they detect tension, it contributes to proprioception and kinesthesia
Where are Ruffini corpuscle located? Deep in dermis, numerous on plantar surface of feet
How do Ruffini corpuscle contribute to proprioception and kinesthesia? Provides feedback for grabbing objects, controlling finger position, and movement
What somatic receptors are rapidly adapting? Meissner's corpuscle and hair root plexus
What are slow adapting somatoreceptors? Merkel and Ruffini
What receptors detect touch? Meissner's, hair root plexus, Merkel, and Ruffini
What receptors detect pressure? Pacinian, Ruffini, Krause
What receptors detect vibration? Meissner (low), Pacinian (high)
What receptors detect itch/tickle? Free nerve endings
What receptors detect temperature? Cold: free nerve endings in stratum basale, Krause. Warm: free nerve endings in dermis, Ruggini
What cold temperatures are detected? 10-40 celsius
What warm temperatures are detectedd=? 32-48 celsius
What temperature produces pain? Below 10 and over 48 celsius
Describe the adaptation for thermal sensation Rapidly at first but continue to generate impulses at low frequency
Where are pain receptors located? Nearly every tissue except brain
What stimulates pain receptors? Excessive distension, muscle spasm, inadequate blood flow
What do tissues release to stimulate nociceptors? K, kinins, or prostaglandins
What is fast pain? Acute - sharp pain like needle puncture or cut - not felt in deeper tissues
What fibers detect fast pain? Larger A nerve fibers
What is slow pain? Chronic - begins more slowly and increases in intensity - aching, throbbing - in both superficial and deeper tissues
What fibers detect slow pain? Smaller C nerve fibers
What is referred pain? Visceral pain that is felt in surface area far from stimulated organ
Visceral sensory nerves travel with what type of fibers? Sympathetic nerve fibers T1-L2
What is the innervation of the foregut? Greater splanchnic nerve from sympathetic (T5-T9), vagus from parasympathetic
Where would referred pain for the foregut be felt? Epigastric region
What comprises the foregut? Stomach, spleen, liver, pancreas, kidneys, small intestine
What is the innervation of the midgut? Lesser splanchnic nerve from sympathetic (T10-T12), vagus from parasympathetic
Where would referred pain for the midgut be felt? Umbilical region
What comprises the midgut? Small intestine, proximal colon
What is the innervation of the hindgut? Lumbar (least) splanchnic nerve from sympathetic (Y12-L1), S2/3/4 from parasympathetic
Where would referred pain of the hindgut be felt? Hypogastric region
What organs comprises the hindgut Distal colon, rectum, anal canal
What nerve keeps diaphragm alive? Phrenic nerve - C3/4/5
What does the sensory phrenic nerve supply? Peritoneum that covers the diaphragm from below
How does referred pain travel? Somatic to somatic, not visceral to somatic
How can referred pain be felt through the phrenic nerve Supplied to peritoneum to dermatome of phrenic nerve
Which dorsal branch doesn't have sensory? C1
Where would liver and gallbladder be felt? Right shoulder, right lower back, right area underneath scapula
Where would gallbladder be felt? Umbilical and right lumbar
Where would stomach be felt? Epigastric
Where would kidneys be felt? Entire lower abdomen - hypogastric, right/left iliac
Where would heart be felt? Left chest, traveling down ulnar side of left arm
What is proprioceptive or kinesthetic sense? Awareness of body position and movement
Where are golgi tendon organs found? Junction of tendon and muscle
What makes up a golgi tendon organ? Encapsulated bundle of collagen fibers laced with sensory fibers
What do golgi tendon organs detect? When tendon is overly stretched → will send signals to CNS → results in muscle relaxation. Detects force of muscle contraction.
Where are joint kinesthetics receptors found? Around articular capsules of synovial joints
What do joint kinesthetic receptors detect? Detect pressure from free nerve endings and Ruffini corpuscle, acceleration and deceleration of joints during movement from small pacinian corpuscles
What do muscle spindles detect? Amount of stretch or lengthening of muscle
What are muscle spindles? Specialized intrafusal muscle fibers enclosed in a connective tissue capsule, innervated by gamma motor neurons
How does the brain regulate muscle tone? Controlling gamma fibers
What two fibers make up a skeletal muscle? Intrafusal muscle fibers and extrafusal muscle fibers
What do extrafusal muscle fibers do? Job of the muscle - contracting and producing movement
What is the relationship between the amount of muscle spindles in a muscle and movement? More spindles means more awareness of muscle which is needed for fine movements - more would be in hands
What muscle does not have muscle spindles? Middle ear muscles because not in charge of tension control
What layer of the grey matter is in charge of conveying pain and temperature? Laminae 2 - substantia gelatinosa
How can pain be modulated by free nerve endings are non-adapting? Gate pain theory - signals must be allowed through a gate before they can actually make it to the brain
What NT carries pain info? Substance P
How can the gate be closed? Degrade NT, suppressing synapse - rubbing it away or willing it away
What does it mean to will it away? CNS can send inhibitory signals (enkephalins, endorphins) to gate which block action of substance P
What are ways to "will it away" for pain modulation? Meditation, hypnosis, distraction, placebos
What does it mean to "rubbing it away"? Touch fibers enter spinal cord also have collateral synapses with gate - NT being serotonin
What class of fibers are temperature carried in? III and IV
What class of fibers are pain carried in? Sharp - III, Aching - IV
What class of fibers are proprioceptive carried in? I and II
What class of fibers are tactile carried in? II
What class of fibers are golgi tendon organs carried in? I
What class of fibers are joint kinesthetic carried in? II
How do we generally sense things? Receptor is disturbed → membrane permeability changes → generator potential →strong enough generator potential → create an AP in appropriate sensory nerve → AP is propagated and carries info to spinal cord and brain
What is a graded response? Greater stimulus, greater the generator potential, and the higher frequency of the AP
How is a generator potential different from the action potential Amplitude: GP - depends on strength, AP - all or none. Origin: GP - arises in dendrites and cell body, AP - trigger zones and propagate along axon
What does not having refractory period mean? Allows for summation of stimuli - repeated stimuli can create a larger generator and more frequent AP than a single
How does signal intensity affect nerve impulses? Characteristic of each nerve pulse. Different sensory signal intensity can be transmitted either by using increased number of fibers or by sending more AP along a single nerve fiber
What is spatial summation Summation of effects of NTs released from several neurons onto one neuron
What is temporal summation? Summation of effects of NT released from 2 or more firing of the SAME neuron in rapid succession onto a second neuron
What is the perception of intensity for temporal summation? Stronger stimulus translate into more frequent APs
What is the perception of intensity for spatial summation? Stronger stimulus hits more receptors and therefore sends APs along more nerve fibers
How do we differentiate a light tough from a firmer tough, in regards to frequency of impulses? Firm pressure generates impulses at a higher frequency (temporal summation)
How do we differentiate a light tough from a firmer tough, in regards to number of sensory neurons activated? Firm pressure stimulates more neurons than a light tough - spatial summation
What summation does firm vs light tough have? Both summations at the same time
What is lateral inhibition? Capacity of an excited neuron to reduce activity of its neighbors
What is the mechanism behind lateral inhibition? After being touched, sensory neurons in the skin next to another are stimulated. Fired neurons suppress the stimulation of neighboring neurons - most stimulated neuron and least inhibited will fire so firing pattern tends to concentrate at stimulus peaks
What is the receptor field? Region of space in which the presence of a stimulus will alter the firing of that neuron
Where are receptor fields located in the somatosensory system? Skin of internal organs
What do large receptor fields allow? Allows detection of change over a wider area but lead to less precise perception
What do smaller receptor fields allow Detect fine detail - more precise
What pathway does lateral inhibition use? Posterior column of spinal cord
What is two point discrimination? Ability to discern that two nearby objects touching skin are truly two distinct points, not one
How does the receptor area relate to two-point discrimination? Smallest, most dense receptor area have greater cortical representation - able to recognize two separate points at a much smaller distance (more precision) than large receptor areas which has less precision
What would happen if there is something wrong with the posterior spinal cord? Will not have two-point discrimination
Created by: nnguyen44
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