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Questions and Answers

Which type of receptor is responsible for detecting high-frequency vibrations?

  • Lamellated (pacinian) corpuscles (correct)
  • Ruffini corpuscles
  • Muscle spindles
  • Corpuscles of touch
  • Which of these receptors are specifically responsible for detecting skin stretching and pressure?

  • Ruffini corpuscles (correct)
  • Corpuscles of touch
  • Muscle spindles
  • Lamellated (pacinian) corpuscles
  • Which type of receptor is most closely associated with the sensation of touch and low-frequency vibrations?

  • Tendon organs
  • Muscle spindles
  • Lamellated (pacinian) corpuscles
  • Corpuscles of touch (correct)
  • Which of these receptors exhibit a rapid adaptation rate?

    <p>Lamellated (pacinian) corpuscles (B)</p> Signup and view all the answers

    Which type of receptor is responsible for detecting muscle tension?

    <p>Tendon organs (A)</p> Signup and view all the answers

    Which type of receptor is responsible for detecting warmth or cold?

    <p>Warm and cold receptors (D)</p> Signup and view all the answers

    Which of these is NOT a type of tactile receptor?

    <p>Muscle spindles (D)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of Ruffini corpuscles?

    <p>They are most abundant in the fingertips. (C)</p> Signup and view all the answers

    Which of these is a type of proprioceptor?

    <p>Tendon organs (A)</p> Signup and view all the answers

    Which type of touch receptor is responsible for detecting pressure?

    <p>Ruffini corpuscles (A), Merkel discs (D)</p> Signup and view all the answers

    Which type of touch receptor is responsible for detecting lower-frequency vibrations?

    <p>Meissner corpuscles (A)</p> Signup and view all the answers

    What is the main function of Merkel cells?

    <p>They contribute to the sense of touch and pressure by interacting with Merkel discs. (D)</p> Signup and view all the answers

    Where are Pacinian corpuscles NOT found?

    <p>Brain (B)</p> Signup and view all the answers

    Which of the following is NOT a known trigger for itch?

    <p>Sunlight (C)</p> Signup and view all the answers

    Which of the following chemicals is known to stimulate itch?

    <p>Bradykinin (D)</p> Signup and view all the answers

    Which of these best describes the relationship between Meissner corpuscles and Pacinian corpuscles?

    <p>They are responsible for detecting different frequencies of vibration. (B)</p> Signup and view all the answers

    What type of sensory information does the anterolateral or spinothalamic pathway carry?

    <p>Pain and temperature (A)</p> Signup and view all the answers

    Where do first-order neurons of the spinothalamic pathway synapse with second-order neurons?

    <p>Posterior gray horn of the spinal cord (B)</p> Signup and view all the answers

    Which tract carries pain and temperature sensations in the spinothalamic pathway?

    <p>Lateral spinothalamic tract (A)</p> Signup and view all the answers

    Where do third-order neurons of the spinothalamic pathway project?

    <p>Cerebral cortex (D)</p> Signup and view all the answers

    What type of sensory information does the trigeminothalamic pathway carry?

    <p>Somatic sensations from the face (A)</p> Signup and view all the answers

    Where are the cell bodies of first-order neurons in the trigeminothalamic pathway located?

    <p>Trigeminal ganglia (C)</p> Signup and view all the answers

    Whichcranial nerve is involved in the trigeminothalamic pathway?

    <p>CN V (Trigeminal) (D)</p> Signup and view all the answers

    Where do some first-order neurons of the trigeminothalamic pathway synapse with second-order neurons?

    <p>Pons (C)</p> Signup and view all the answers

    How does proprioception differ from kinesthesia?

    <p>Proprioception involves knowing where the limbs are located in space, while kinesthesia involves sensory perception of body movements. (C)</p> Signup and view all the answers

    What is the main function of muscle spindles?

    <p>To monitor changes in muscle length. (A)</p> Signup and view all the answers

    Which of the following statements accurately describes proprioceptive adaptation?

    <p>Proprioceptors adapt slowly, gradually adjusting to maintain a sense of body position. (D)</p> Signup and view all the answers

    What is the role of proprioceptors in weight discrimination?

    <p>Proprioceptors assess the weight of an object and help determine the muscular effort required to lift it. (A)</p> Signup and view all the answers

    Which part of the brain processes proprioceptive information consciously?

    <p>Cerebral cortex (D)</p> Signup and view all the answers

    What kind of muscle fibers are found within muscle spindles?

    <p>Intrafusal muscle fibers (C)</p> Signup and view all the answers

    Where are tendon organs located?

    <p>Within tendons (D)</p> Signup and view all the answers

    Which of the following best describes the function of the spinocerebellar pathways?

    <p>Conveying proprioceptive impulses from the trunk and limbs to the ipsilateral cerebellum. (A)</p> Signup and view all the answers

    What is the primary role of the ventral posterior nucleus of the thalamus in the trigeminothalamic pathway?

    <p>Receiving sensory input from the face and transmitting it to the contralateral cerebral cortex. (B)</p> Signup and view all the answers

    Which of the following is NOT a sensory modality carried by the trigeminothalamic tract?

    <p>Proprioception (D)</p> Signup and view all the answers

    Which cranial nerve conveys impulses for most somatic sensations from the left side of the face into the pons?

    <p>Trigeminal nerve (CN V) (B)</p> Signup and view all the answers

    What is the main consequence of damage to the posterior column of the spinal cord?

    <p>Loss of conscious proprioception. (D)</p> Signup and view all the answers

    How does the homunculus illustrate the organization of the primary somatosensory area?

    <p>It shows that the brain devotes more space to areas of the body with a higher density of sensory receptors. (B)</p> Signup and view all the answers

    What is meant by the term ‘plasticity’ in the context of the primary somatosensory area?

    <p>The ability to learn and adapt to new experiences, resulting in changes in the cortical representation of sensory input. (D)</p> Signup and view all the answers

    Which of the following best describes the relationship between the trigeminothalamic tract and the spinocerebellar tracts?

    <p>They both carry sensory information from the periphery to the contralateral cerebral cortex. (B)</p> Signup and view all the answers

    Which of the following sensations are NOT carried by the posterior column-medial lemniscus pathway?

    <p>Pain (B), Temperature (C)</p> Signup and view all the answers

    Where do the axons of second-order neurons in the posterior column-medial lemniscus pathway cross to the opposite side of the brain?

    <p>Medulla (B)</p> Signup and view all the answers

    What is the name of the structure in the thalamus that receives input from the medial lemniscus?

    <p>Ventral posterior nucleus (A)</p> Signup and view all the answers

    Which of the following is NOT a component of the posterior column-medial lemniscus pathway?

    <p>Lateral spinothalamic tract (A)</p> Signup and view all the answers

    What is the function of the gracile fasciculus?

    <p>Carries sensory information from the lower limbs and the lower trunk (A)</p> Signup and view all the answers

    Flashcards

    Posterior Column

    A part of the spinal cord consisting of the gracile and cuneate fasciculi.

    Gracile Fasciculus

    Part of the posterior column carrying impulses from lower body regions.

    Cuneate Fasciculus

    Part of the posterior column transmitting impulses from upper body regions.

    Medial Lemniscus

    A tract where second-order neuron axons cross and ascend to the thalamus.

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    Thalamus Connection

    Where second-order neurons synapse with third-order neurons before reaching the cortex.

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    Meissner's Corpuscles

    Tactile receptors in dermal papillae for touch and low-frequency vibrations; rapid adaptation.

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    Hair Root Plexuses

    Free nerve endings around hair follicles that detect movements; rapid adaptation.

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    Type I Cutaneous Mechanoreceptors

    Tactile discs in epidermis for continuous touch and pressure; slow adaptation.

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    Type II Cutaneous Mechanoreceptors

    Ruffini corpuscles sensitive to skin stretching and pressure; slow adaptation.

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    Pacinian Corpuscles

    Lamellated receptors for high-frequency vibrations; rapid adaptation.

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    Nociceptors

    Free nerve endings for pain sensation; adapts slowly, located in all tissues except brain.

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    Muscle Spindles

    Proprioceptors that measure muscle length; adapts slowly.

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    Tendon Organs

    Proprioceptors that monitor muscle tension; adapts slowly, found at tendon junctions.

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    Trigeminothalamic pathway

    A neural pathway carrying sensory information from the face to the thalamus and cortex.

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    First order neurons

    Neurons that carry sensory impulses from receptors to the spinal cord or brainstem.

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    Second order neurons

    Neurons that receive input from first order neurons and cross to the opposite side before ascending.

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    Ventral posterior nucleus of the thalamus

    Thalamic nucleus where second order neurons synapse with third order neurons.

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    Primary somatosensory area

    Region in the parietal lobes responsible for processing sensory input from the body.

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    Homunculus

    A visual representation of how sensory receptors are distributed across the body.

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    Spinocerebellar pathways

    Neural tracts transmitting proprioceptive information from the body to the cerebellum.

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    Neurosyphilis

    Neurological condition resulting from late-stage syphilis affecting the spinal cord.

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    Proprioception

    The ability to sense the position and movement of one's body parts.

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    Kinesthesia

    The perception of body movements and the ability to sense muscle contractions.

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    Proprioceptors

    Sensory receptors that provide information about body position and movement.

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    Joint Kinesthetic Receptors

    Proprioceptors located in or around joint capsules, providing feedback on joint position.

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    Weight Discrimination

    The ability to assess the weight of an object and adjust muscular effort accordingly.

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    Cerebellum vs. Cerebral Cortex

    Cerebellum processes unconscious proprioceptive information; cerebral cortex processes conscious proprioceptive information.

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    Anterolateral Pathways

    A 3-neuron pathway that carries pain, temperature, tickle, and itch sensations.

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    Lateral Spinothalamic Tract

    Carries pain and temperature sensations to the brain.

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    Anterior Spinothalamic Tract

    Carries tickle, itch, crude touch, pressure, and vibrations.

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    Trigeminal Ganglia

    Contains cell bodies of first-order neurons from the face.

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    Second-order Neurons in Pons

    Some axon terminals of first-order neurons synapse with second-order neurons in the pons.

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    Pressure Sensation

    Sustained sensation detected over a large area, involving Type I and II mechanoreceptors.

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    Vibration Sensation

    Result from rapidly repetitive sensory signals, primarily from Meissner and Pacinian corpuscles.

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    Itch Mechanism

    A sensation triggered by stimuli such as chemicals and temperature, involving bradykinin and histamine.

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    Bradykinin and Histamine

    Chemicals that are known to stimulate itch sensations.

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    Study Notes

    Receptor Types and Structures

    • Tactile receptors (touch, pressure, vibration, itch, tickle): Meissner corpuscles (rapid adaptation), hair root plexuses (rapid adaptation), Type I cutaneous mechanoreceptors (tactile discs) (slow adaptation), Type II cutaneous mechanoreceptors (Ruffini corpuscles) (slow adaptation), Lamellated (Pacinian) corpuscles (rapid adaptation)
    • Thermoreceptors (warmth and cold): Free nerve endings (initial rapid, then slow adaptation)
    • Nociceptors (pain): Free nerve endings (slow adaptation)
    • Proprioceptors (muscle length and tension, joint position and movement): Muscle spindles (slow adaptation), tendon organs (slow adaptation), joint kinesthetic receptors (rapid adaptation)

    Tactile Sensations

    • Tactile sensations include touch, pressure, and vibration, plus itch and tickle.
    • Differences in these sensations arise from activation of multiple receptor types and multiple stimuli from different receptors.

    Touch

    • Crude touch—the ability to perceive something has touched the skin, without being able to determine specific location, shape, or texture.
    • Discriminative touch—provides specific information like exact location, shape, size, and texture of the stimulus, is carried along separate pathways.

    Touch (Rapidly Adapting Receptors)

    • Corpuscles of touch (Meissner’s corpuscles)—located in dermis of glabrous (hairless) skin. Abundant in fingertips, hands, eyelids, tongue tip, lips, nipples, soles, clitoris, and penis tip. Each corpuscle has egg-shaped collection of dendrites.
    • Hair root plexuses—located in hairy skin; consist of free nerve endings wrapped around hair follicles. Detect movement on skin surface that disturbs hairs (e.g., bug landing).

    Touch (Slowly Adapting Receptors)

    • Type I cutaneous mechanoreceptors (Merkel discs)—sausage-shaped flattened free nerve endings that make contact with Merkel cells in the stratum basale. Function in touch and pressure. Most abundant in fingertips, hands, lips, and external genitalia

    Touch (Type II Receptors)

    • Type II cutaneous mechanoreceptors (Ruffini corpuscles)—encapsulated receptors. Found deep in dermis and in ligaments and tendons. Abundant in hands, especially fingers and soles. Respond to stretching of skin, and also helps to detect pressure

    Pressure

    • Pressure is a sustained sensation over a large area.
    • Type I and Type II cutaneous mechanoreceptors contribute to pressure sensation.

    Vibration

    • Sensations of vibration result from repetitive stimulation of tactile receptors.
    • Meissner corpuscles detect lower frequency vibrations. Pacinian corpuscles detect higher frequency vibrations.
    • Lamellar corpuscles (Pacinian) are distributed throughout the body in dermis, and subcutaneous tissue, muscles, tendons, and around joints, mammary glands, external genitalia, pancreas and urinary bladder.

    Itch and Tickle

    • Itch is thought to involve mechanical, temperature, or chemical stimuli (e.g., bradykinin and histamine).
    • Itch is not fully understood.
    • Tickle is thought to involve free nerve endings, and is not fully understood.

    Phantom Limb Sensations

    • Patients with an amputated limb may experience sensations as if the limb were still present.
    • An older explanation suggests the cerebral cortex interprets as coming from the phantom limb.
    • Neurons in the brain that previously received signals re-organizes (plasticity), and now sensations elsewhere in the body create a phantom sensation from the former limb.

    Thermal Sensations

    • Cold receptors—located in stratum basale of epidermis; attached to medium-diameter myelinated A fibers, and few unmyelinated C fibers. Activated by temperatures between 10° and 35°C (50–95°F).
    • Warm receptors—located in dermis; attached to small-diameter, unmyelinated C fibers. Activated by temperatures between 30° and 45°C (86–113°F). Respond rapidly at first, but generate low-frequency impulses. Pain is produced below 10°C and above 45°C.

    Pain Sensations

    • Free nerve endings, activated by intense thermal, mechanical, or chemical stimuli, present in virtually all body tissues, except the brain.
    • Tissue irritation or injury releases chemicals (e.g., prostaglandins, substance P, kinins, potassium ions) that stimulate nociceptors.
    • Pain may persist even after the initial stimulus is removed, because pain-mediating chemicals linger.
    • Conditions such as excessive distention, prolonged contractions, muscle spasms, and ischemia can elicit pain.

    Pain Sensations (Fast Pain)

    • Occurs rapidly (0.1 second) after stimuli, felt as acute, sharp, or pricking pain
    • Felt in the skin, propagate along medium-diameter, myelinated A fibers.

    Pain Sensations (Slow Pain)

    • Begins more slowly and increases in intensity, felt as burning, aching, or throbbing pain,
    • Occurs in both the skin and internal organs. Propagates along small-diameter, unmyelinated C fibers.

    Pain Sensations (Visceral Pain)

    • Unlike somatic pain, usually felt in or just under the skin that overlies the stimulated organ.
    • Can be caused by localized damage (e.g., cutting intestines) or diffuse stimulation (e.g., distension of a bile duct from a gallstone, or distension of the ureter from a kidney stone)
    • Can be referred, meaning felt in a surface area far from the stimulated organ

    Pain Threshold vs. Pain Tolerance

    • Pain threshold—the minimum stimulus intensity required to elicit a pain response.
    • Pain tolerance—the maximum amount of pain an individual can endure. Vary widely between individuals and is not well-understood.

    Drugs for Pain

    • Analgesics block prostaglandin and thromboxane formation, which stimulate nociceptors.
    • Local anesthetics block voltage-gated sodium channels in the axons of first-order pain neurons.
    • Opiates alter pain perception in the brain, but pain may still be perceived differently.

    Proprioception

    • Proprioception is the awareness of the position, location, and movement of one's body parts, without having to look.
    • Kinesthesia is the perception of body movements

    Proprioceptors

    • Embedded in muscles, tendons, and joints, helping to understand the degree of muscle contraction, tension on tendons, and joint position.

    Muscle Spindle

    • Located in skeletal muscles, monitors changes in muscle length, participates in stretch reflex.
    • Consists of slowly adapting sensory nerve endings
    • Surrounded by extrafusal fibers, which are controlled by alpha motor neurons.

    Golgi Tendon Organ (GTO)

    • Located at the junction of tendons and muscles, detects changes in muscle tension or excessive tension
    • Generates nerve impulses that go to the CNS, providing information about muscle tension changes
    • Helps to inhibit muscle contraction, relieves excessive tension

    Joint Kinesthetic Receptors

    • Located within and around the articular capsules of synovial joints.

    Somatic Sensory Pathways

    • Relay information about somatic receptors to the primary somatosensory area in cerebral cortex and cerebellum.
    • Usually made up of first-order, second-order, and third-order neurons.

    Somatic Sensory Pathways (First-Order Neurons)

    • Conduct impulses from somatic receptors to the CNS (brainstem or spinal cord).

    Somatic Sensory Pathways (Second-Order Neurons)

    • Conduct impulses from CNS to thalamus—crosses over to the opposite side of the body in the brainstem or spinal cord before ascending to the thalamus—Sensory info from one side of body reaches the contralateral half of the thalamus

    Somatic Sensory Pathways (Third-Order Neurons)

    • Conduct impulses from the thalamus to the primary somatosensory area in the cortex, (post-central Gyrus in parietal lobe)

    Somatic Sensory Pathways (Posterior Column-Medial Lemniscus Pathway)

    • Conducts impulses for touch, pressure, vibration, and conscious proprioception from upper limbs, trunk, neck, and posterior head
    • Impulses travel up the spinal cord cuneate fasiculus to the cuneate nuclei
    • Impulses from lower limbs and trunk go up the gracile fasiculus to the gracile nuclei

    Somatic Sensory Pathways (Anterolateral Pathways)

    • Mainly carries pain, temperature, crude touch, tickle, and itch sensations.
    • Impulses poorly localised on these pathways.

    Somatic Sensory Pathways (Trigeminothalamic Pathways)

    • Pathway for most somatic sensation (tactile, thermal, pain, and proprioception) from the face, nasal cavity, oral cavity, and teeth that ascends to cerebral cortex
    • Consists of 3-neuron sets.

    Somatic Sensory Pathways (Spinocerebellar Pathways)

    • Major proprioceptive impulses from the trunk and limbs to the ipsilateral cerebellum
    • Critical for posture, balance, and smooth movement

    Primary Somatosensory Area

    • Located in the postcentral gyri of the parietal lobes.
    • Receives signals from the opposite side of the body.
    • The degree of sensitivity is proportional to the number of sensory receptors in a given area.

    Syphilis

    • Bacterial infection (Treponema pallidum)
    • Late stage neurosyphilis: progressive spinal cord degeneration.
    • Posterior column damage: loss of conscious proprioception, results in gait disturbances.

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    Description

    Test your knowledge on the various types of sensory receptors responsible for detecting touch, pressure, temperature, and vibrations. This quiz covers key concepts such as proprioceptors and the characteristics of different tactile receptors. Challenge yourself and enhance your understanding of sensory physiology!

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