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Questions and Answers
Which type of channel is opened by extreme temperatures and capsaicin in the pain transduction process?
What role do chemical mediators play in pain sensation?
What initiates the opening of specific transduction channels in pain sensation?
What neurotransmitter is released by Aδ fibers during pain transmission?
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Which type of pain receptor is stimulated by extreme temperatures?
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Which type of sensation is NOT classified as somatic sensation?
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Which of the following sensations is classified as interoceptive?
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The sense of two-point discrimination is primarily associated with which type of sensation?
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The pathway for crude touch sensation primarily involves which type of afferent nerve fibers?
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Which type of mechanoreceptive sensation involves the recognition of familiar objects by touch?
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Which of the following terms refers to sensations received from internal organs?
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Which type of sensation is characterized by poor localization and is tested by stroking the skin lightly?
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Which receptors are primarily involved in fine touch sensation?
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What mechanism primarily allows for temperature sensation?
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Which of the following is a characteristic of deep sensations classified as proprioceptive?
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Which type of receptors is primarily responsible for proprioceptive sensations in the body?
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What type of sensations arise from the stimulation of free nerve endings in the skin?
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Which receptors are most sensitive to high-frequency vibrations?
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What distinguishes cold receptors from warm receptors in terms of their numerical presence?
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Which central pathway is primarily involved in transmitting proprioceptive sensations?
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What type of nerve fibers are mainly associated with the afferent nerves for tickling and itching sensations?
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What temperature range stimulates cold pain receptors?
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Which type of receptor responds to low-frequency vibrations, around 80Hz?
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Which statement about warm receptors is correct regarding their activation?
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What characteristic of thermoreceptors allows them to adapt to temperature changes?
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Which type of pain is defined as being well localized and primarily caused by mechanical and thermal stimuli?
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What type of nerve fibers are primarily responsible for fast pain sensation?
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Which of the following is a characteristic of slow pain compared to fast pain?
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In which central pathway is fast pain transmitted?
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What is the primary stimulus type for slow pain sensation?
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Which locations in the body predominantly lack pain receptors?
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What is the accurate description of the pain threshold?
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Which reflexes are generally associated with slow pain?
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What is primary hyperalgesia?
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Which type of pain is characterized as dull and diffuse, often associated with bradycardia?
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What type of reflex is involved in the immobilization response to pain?
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Which of the following causes visceral pain?
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How does ischemic pain generally manifest?
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What are the primary mechanisms that lead to ischemic pain?
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Which of the following is an example of deep pain?
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What reaction is commonly associated with moderate pain from the autonomic reflexes?
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Study Notes
Sensation
- Sensation is the understanding of a stimulus.
- Sensations can be classified into somatic, visceral, special, and organic sensations.
Somatic Sensations
- Somatic sensations are from the skin and deep structures like muscles, bones, joints, and ligaments.
- Somatic sensations are classified by:
By Site
- Exteroceptive sensations (superficial sensations): Pain, touch, and temperature from the skin. - Interoceptive sensations (deep sensations): Sensations from deep structures such as muscle tension sense, muscle sense (pressure pain), and proprioceptive sensations (kinesthetic sensation). - Combined sensations: Vibration sense.By Modality
- Mechanoreceptive sensations: Tactile sensations (touch, pressure, vibration, tickle) and Position and movement sensations (proprioceptive sensations). - Thermoreceptive sensations: Heat and cold sensations - Pain sensation: Cutaneous, deep, visceral, or neuropathic pain sensation.
Mechanoreceptive Sensations
- Include touch, pressure, vibration, tickle, and proprioception.
Touch Sensation
- Crude Touch: A poorly localized touch, like the feeling of clothes.
- Receptors: Free nerve endings & hair end organs.
- Afferent nerves: Aδ fibers.
- Central pathway: Ventral spinothalamic tract.
- Test: Lightly stroking the skin with cotton.
- Fine Touch: Includes tactile localization, tactile discrimination, stereognosis, and texture of material.
- Receptors: Meissner’s corpuscles and Merkel’s disks.
- Afferent nerves: Aᵦ fibers.
- Central Pathway: Gracile and cuneate tract (dorsal column).
- Tactile Localization: Identifying the point of touch with eyes closed.
- Tactile Discrimination: Feeling two points touched simultaneously as two separate points with eyes closed.
- The distance between the two points must be above the threshold distance (narrowest at fingertips and lips, widest on the back).
- This depends on the number of receptors in the area, their receptive field, convergence in the pathway, and area of cortical representation.
- Stereognosis: Recognizing familiar objects (key or coin) in the hand with eyes closed.
- Depends on cutaneous and deep sensations, and prior knowledge about the object.
- Texture of Material: Identifying the texture of materials (silk, wool, cotton) by touching with eyes closed.
Pressure Sense
- The ability to discriminate between different weights by pressure on the hands.
- Receptors: Mainly Pacinian corpuscles.
- Afferent nerves: Aᵦ fibers.
- Central pathway: Gracile and cuneate tract (dorsal column).
Vibration Sense
- Feeling the rhythmic repetitive pressure of a tuning fork on bony prominences (bone is insensitive to vibration but magnifies the wave).
- Ranges from 30-800Hz.
- Receptors: Meissner’s corpusles (low frequency vibration & Pacinian corpuscles (high frequency vibration).
- Afferent nerves: Aᵦ fibers.
- Central pathway: Gracile and cuneate tract (dorsal column).
Tickle and Itch
- Tickle: Pleasurable sensation (often causing laughter) from mild tactile stimulation of the skin.
- Itch: An annoying sensation from skin irritation by a moving tactile stimulus (e.g., crawling flea) or chemical substances released in the skin (e.g., histamine in allergic conditions).
- Receptors: Free nerve endings.
- Afferent nerves: Unmyelinated C fibers.
- Central pathway: Ventral spinothalamic tract.
Proprioception
- Sensations from muscles and joints.
- Receptors: Present in joint capsule, ligaments, tendons, and tissue around joints.
- Slowly adapting Ruffini’s end organs for sense of position (static proprioception).
- Rapidly adapting Pacinian corpuscles for sense of movement (dynamic proprioception).
- Afferents: Aα and Aᵦ fibers.
- Central pathway: Gracile and cuneate tract (dorsal column).
Thermoreception
- The perception of cold and heat.
- Receptors:
- Warm receptors: Free nerve endings attached to C fibers.
- Cold receptors: Free nerve endings attached to C and Aδ fibers.
- Two subtypes of pain receptors:
- Cold pain receptors: Produce a freezing sensation.
- Heat pain receptors: Produce a burning sensation.
- Mechanism of Stimulation: Changes in metabolite concentration within the receptors.
- Increased temp.: Increase in receptor metabolic rate.
- Decreased temp.: Decrease in receptor metabolic rate.
- Characters of Thermal Receptors:
- Located immediately under the skin.
- Small receptive field, widely separated.
- Cold receptors more numerous than warm receptors.
- Moderate adaptation but cold receptors adapt more slowly than warm receptors.
- Distribution: More in lips>fingers>trunk.
- Receptors:
Pain Sensation
- An unpleasant sensation despite its protective role.
- Mechanism: Damaged tissues and surrounding blood vessels release chemical mediators of pain (pain producing substances/ pain sensitizers) such as histamine, serotonin, prostaglandins, bradykinins, K+ ions, and proteolytic enzymes. These substances increase the sensitivity of pain receptors and decrease their pain threshold.
Transduction of Pain Signals
- Nociceptors are stimulated by specific stimuli, opening specific transduction channels:
- Degenerin channels: Opened by injurious mechanical stimuli.
- Vanilloid channels: Opened by extreme temperature (hot or cold) and capsaicin.
- Acid sensing channels: Opened by chemical stimuli .
- Opening of these channels leads to Na+ and Ca2+ inflow and depolarization.
- Activation of pain afferent neurons releases neurotransmitters to the spinal cord (Aδ fibers release glutamate, C fibers release substance P).
Pain Receptors
- Free nerve endings are slowly adapting and there are four types:
- Mechanical pain receptors: Stimulated by mechanical injurious stimuli.
- Thermal pain receptors: Stimulated by extremes of temperature (cold pain and heat pain receptors).
- Chemical pain receptors: Stimulated by chemical injurious stimuli (e.g., pain of gastric ulcer from excess HCl).
- Polymodal pain receptors: Respond to all types of stimuli.
- Present more in skin, periosteum, arterial wall, joint surfaces, falx cerebri and tentorium cerebelli and absent in liver parenchyma, lung alveoli, brain tissue, and bones.
- Afferent fibers: Aδ & C fibers.
- Central pathway: Lateral spinothalamic tract.
Types of Pain Sensation
- Classified by site and quality.
Pain by Site
- Cutaneous pain: Pain produced by stimulation of pain receptors in the skin. Accurately localized because of a large number of pain receptors in the skin, fast pain reaching the sensory cortex, and contributions from touch and vision. Consists of two phases: Fast pricking pain followed by slow burning pain.
- Deep pain: Pain from muscles, joints, ligaments, and periosteum of bones. Slow pain conducted by C fibers that is diffuse, dull aching, and associated with depressor effects.
- Causes: inflammation, ischemia, muscle spasm, bone fractures.
- Visceral pain: Pain from internal viscera of the thorax, abdomen, and pelvis. Few visceral pain receptors, requiring diffuse stimulation.
- Afferents: From viscera along C fibers, from peritoneum, pleura, or pericardium along Aδ fibers.
- Causes: Ischemia (accumulation of metabolites), Inflammation (peritoneal covering), Irritation by chemical agents (e.g., HCl in peptic ulcer), Compression or infiltration by tumor, Overdistention of viscus (e.g., distended bladder).
- Neuropathic pain: A complex painful sensation caused by damage to the nervous system.
- It is often described as burning, tingling, or shooting pain and can be chronic in nature.
Pain by Quality
- Fast Pain (Acute Sharp Pricking pain)
- Site: Skin, mainly. May occur in the pleura, pericardium, and peritoneum.
- Stimulus: Mainly mechanical and thermal noxious stimuli.
- Quality: Pricking (sharp-acute) well localized.
- Perception: 0.1 seconds after stimulation.
- Duration: Short duration.
- Afferent nerve: Aδ fibers, release glutamate.
- Tract: Neospinothalamic tract.
- Center: Mainly cerebral cortex.
- Blocked by: Pressure and hypoxia.
- Reaction to pain: Somatic protective reflexes (e.g., withdrawal reflex).
- Slow Pain (Chronic Burning Dull Aching Pain)
- Site: Skin, deep tissues, and viscera.
- Stimulus: All noxious stimuli, especially chemical ones.
- Quality: Burning (aching-chronic) poorly localized.
- Perception: 1 second or more after stimulation.
- Duration: Long duration.
- Afferent nerve: C fibers, release substance P.
- Tract: Paleospinothalamic tract.
- Center: Mainly the thalamus.
- Blocked by: Local anesthetics.
- Reaction to pain: Autonomic and somatic reflex responses.
Pain Threshold
- The same for all individuals (skin temperature reaches 45oC or more).
- Individuals differ in their reactions to pain.
Reactions to Pain
- Somatic reflexes: Protective reflexes that originate in the spinal cord.
- Withdrawal reflex (e.g., flexion withdrawal reflex).
- Immobilisation reflex (e.g., rigidity of overlying muscles - guarding).
- Autonomic reflexes:
- Moderate pain: Sympathetic effects (tachycardia, hypertension).
- Severe pain: Parasympathetic effects (bradycardia, hypotension).
- Emotional reactions: Crying, anxiety, depression.
Cutaneous Hyperalgesia (Tenderness)
- Pathological hypersensitivity to pain.
- Commonly accompanies skin injuries, inflammation, and burns.
- Non-noxious stimuli (that are normally not painful) elicit pain sensation (e.g., touch elicited pain).
- Types:
- Primary hyperalgesia: At the site of injury.
- Secondary hyperalgesia: Healthy area around the injury.
Ischemic Pain
- Type of deep pain in muscles when blood supply is decreased.
- Causes: Intravascular thrombosis (clot formation), Narrowing of blood vessel lumen due to inflammation or compression.
- Mechanism: Accumulation of lactic acid, release of proteolytic enzymes from ischemic tissue.
- Examples: Cardiac muscle ischemia (angina pectoris), Skeletal muscle ischemia (intermittent claudications).
- Aggravated by exercise, relieved or decreased by rest.
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Description
Test your knowledge on sensation and its classifications, particularly focusing on somatic sensations. This quiz covers exteroceptive, interoceptive, and combined sensations, as well as modalities like mechanoreceptive and thermoreceptive sensations. Challenge yourself and deepen your understanding of how we perceive stimuli.
