Histo Lecture 14
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Histo Lecture 14
How do sensory receptors transmit information?
In a series of action potentials
What is the Labeled Line Principle?
Each type of sensation is projected to specific areas of the CNS
The frequency of AP is dependent upon what?
Intensity of the stimulus
Define somatosensory receptors
Specialized endings of primary afferent neurons
What can somatosensory receptors be found?
skin, viscera, muscles, joints, connective tissue
Name some somatic sensations
touch, pressure, vibration, body position, tickle, temperature, and pain (and itch)
Recetors transform mechanical, chemical, and/or thermal energy into what?
electrical energy (action potential)
Name the 5 classifications of receptors
What are the two discriminatios of touch?
Quality of touch (soft or coarse)
Area being touched (2pt discrimination)
What is Receptor Adaptation?
Diminishing rate of discharge of a somatosensory neuron occurs with continued stimulation of constant intensity (adaptation)
What is the purpose of adaptation?
Allows the nervous system to focus on new or altered stimuli without the "distraction" of the constant stimulus
What are rapidly adapting receptors called?
What are slowly adapting receptors called?
Describe Meissner's Corpuscle
Encapsulated, located in the ridges of superficial glaborous skin
Highly concentrated in the fingertips
: Light, touch, and discriminative touch
Describe Merkel's Disks
Un-encapsulated; Located in the superficial skin (hairy and glaborous)
Concentrated in the finger tips
Sensitive to discriminative touch
Describe Pacinian Corpuscles
: Dermis, subcutaneous fat, intramuscular connective tissue, and capsules of synovial joints
Detects pressure, vibration, and acceleration
Describe Ruffini's Endings
Encapsulated, flower-spray neural endings
Dermis, joints, glaborous, and hairy skin
Detects light touch
Describe the Hair Follicle
Nerve endings embedded in hair follicle, surrounding hair shaft
Deflection of hair deforms follicle, creating a stimulus for the receptor
Consist of rapidly and slowly adapting types
What are two types of Thermoreceptors?
Krause's bulb - for cold
Ruffini's ending - for warm
What are Nociceptors?
Stimulatd by mechanical, termal, or chemical stimuli
What are some chemical substances that stimulate nociceptors?
Bradykinin, serotonin, histamine, K+ and H+
Prostaglandins and substance P increase sensitivity to what?
Pain (sensitize free nerve endings)
What is hyperalgia?
Increased sensitivity to painful stimuli
What are Free Nerve Endings?
Mechanical, Chemical, and Thermal stimuli
Rate and extent of tissue damage is directly correlated with what?
Level of pain perceived
What are some causes of tissue damage?
Bacterial infection, tissue ischemia, tissue contusion
Describe fast pain
Elicited by mechanical and thermal stimuli
Transmitted on A-d (lower case greek delta) fibers
Sharp, easily localized pain
What is a receptor potential?
When a stimulus causes a change in the membrane electrical potential of a sensory receptor
What does a receptor potential cause?
A change in ion permeability of the receptor membrane and results in depolarization of receptor
A stronger stimulus results in what?
Increased action potential frequency
A receptor will continue to send action potentials as long as...
a stimulus is present (continued depolarization)
What is adaptation?
Diminishing rate of discharge of a somatosensory neuron that occurs with continued stimulation of constant intensity
What does adaptation allow?
Allows the nervous system to focus on new or altered stimuli without the distraction of the constant stimulus
What are some influenctial factors of adaptation rates?
Properties of excitability of the membrane of the sensory neuron
The non-neuronal accessory structure that surrounds the axon
What is referred pain?
Pain felt in part of the body that is remote from the tissue causing the pain
When does referred pain most frequently occur?
With injury to visceral organs (abdomen/thorax)
Where do visceral and skin pain fibers terminate? Why is this important?
Terminate at the same areas of spinal cord;
The CNS perceives the pain as coming from the skin rather than abdominal/thoracic organs
What is the modality and adaptation rate of Meissner's?
Discriminate touch, light touch, vibration
What is the modality and adaptation rate of Merkel's?
What is the modality and adaptation rate of Pacinian?
Pressure, vibration, acceleration
What is the modality and adaptation rate of Ruffini's?
Light touch, thermoreceptor
What is the modality and adaptation rate of hair end organs?
Rapid & slowly adapting
What is the modality and adaptation rate of free nerve endings?
Chemical, thermal, mechanical
Slow or no adapting