Sensation and sensory receptors Flashcards
How are sensory receptors specialized?
specialized to respond to stimuli.
- activation of a sensory receptor results in graded potentials that trigger nerve impulses along the afferent PNS fibers coursing to the CNS.
What are the 3 ways to classify sensory receptors?
(1) By the type of stimulus they detect
(2) By their body location
(3) By their structural complexity
What are mechanoreceptors?
respond to mechanical force such as touch, pressure (including blood pressure), vibration, stretch, and itch (causing the deformation of the membrane of the sensory ending)
How do thermoreceptors respond?
sensitive to temperature changes
How do photoreceptors respond?
respond to light (such as those of the retina of the eye)
How do chemoreceptors respond?
respond to chemicals in solution (molecules smelled or tasted, or changes in blood or interstitial fluid chemistry)
What are nociceptors?
sensitive to pain-causing stimuli (extreme heat, extreme cold, excessive pressure, and inflammatory chemicals are all interpreted as painful). These signals stimulate subtypes of thermoreceptors, mechanoreceptors, and chemoreceptors
What are exteroceptors?
- Respond to stimuli arising outside the body
- found near body surface
- Include skin and most receptors of the special senses (vision, hearing, equilibrium, smell, and taste)
- Sensitive to touch, pressure, pain, and temperature receptors
What is another name for interoceptors?
- Aso called visceroceptors
What are interoceptors?
- Respond to stimuli arising within the body
- Found in internal viscera and blood vessels
- Sensitive to chemical changes, tissue stretch, and temperature changes
- Sometimes their activity causes us to feel pain, discomfort, hunger, or thirst
What are proprioceptors?
- Found in: skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles
- Respond to degree of stretch of the organs they occupy
- Give information concerning movements and position of the body
- Constantly “advise” the brain of our body movements by monitoring how much the organs containing these receptors are stretched.
What are 2 types proprioceptors? How do they work?
- muscle spindle provides information about changes in muscle length
- The Golgi tendon organ is provides information about changes in muscle tension
What are some examples of complex receptors?
- Photoreceptors and retinal bipolar cell axons
- Hair cells and auditory axons nerve
- Taste cells and taste nerve axons
What are Tactile corpuscles or Meissner’s corpuscles
- Small receptors in which a few spiraling sensory terminals are surrounded by Schwann cells
and then by a thin egg-shaped connective tissue capsule - Mechanoreceptors; light pressure, vibration of low frequency, and are receptors for discriminative touch
What are Lamellar corpuscles or Pacinian corpuscles?
- Scattered deep in the dermis, and in subcutaneous tissue underlying the skin
- Mechanoreceptors; deep pressure and stretch, and vibration of high frequency
- largest corpuscular receptors
What are Bulbous corpuscles or Ruffini endings?
- Lie in the dermis, subcutaneous tissue, and joint capsules, contain a spray of receptor
endings enclosed by a flattened capsule - Mechanoreceptors; deep pressure and stretch
- role in other dense connective tissues where they respond to deep and continuous pressure
What are muscle spindles?
- fusiform (spindle-shaped) proprioceptors found throughout the perimysium that wraps individual fascicles of skeletal muscle.
- Muscle spindles detect muscle stretch and initiate a reflex that resists the stretch.
What are tendon organs?
- proprioceptors located in tendons, close to the junction between the skeletal muscle and the tendon
- When muscle contraction stretches the tendon fibers, the resulting compression of the nerve fibers activates the tendon organs. This initiates a reflex that causes the contracting muscle to relax.
What are joint kinesthetic receptors?
- proprioceptors that monitor stretch in the articular capsules that enclose synovial joints.
- Mechanoreceptors and nociceptors
What are sensory receptors?
Structures specialized to respond to stimuli
What happens when a sensory receptor is activated?
Activation of sensory receptors results in GP that trigger AP impulses along the nerve axon to the CNS
Where does sensation and perception occur?
cerebral cortex
For sensation to occur, a stimulus must excite a receptor and action potentials must reach the CNS. How does this happen?
- The stimulus energy must match the specificity of the receptor.
- The stimulus must be applied within a sensory receptor’s receptive field—the area the receptor monitors.
What is transduction?
When a stimulus energy is converted into the energy of a graded potential
What’s the difference between a generator potential and a receptor potential?
- Generated potential - When the receptor region is part of a sensory neuron since it generates actions potentials in a sensory neuron
- Receptor potent - When the receptor is a separate cell (as in most special senses)
Each axon (or nerve fiber) is surrounded by ?
endoneurium
What binds groups of axons into bundles called fascicles?
perineurium
Which tough fibrous sheath encloses all the fascicles to form the nerve?
Epineurium
What are the different nerve classifications?
- Mixed nerves contain both sensory and motor fibers and transmit impulses both to and from the central nervous system.
- Sensory (afferent) nerves carry impulses only toward the CNS.
- Motor (efferent) nerves carry impulses only away from the CNS.
What is the difference between ganglia and nuclei?
- Ganglia are collections of neuron cell bodies in the PNS,
- nuclei are collections of neuron cell bodies in the CNS
How are afferent and efferent ganglia different?
- Ganglia associated with afferent nerve fibers contain cell bodies of sensory neurons.
- Ganglia associated with efferent nerve fibers mostly contain cell bodies of autonomic motor neurons.
The distal axon tips of ganglia release chemicals that recruit____ that aid in tissue clearance
macrophages
Is damage to the axons of the brain or spinal cord reversible or irreversible?
irreversible
____ cells actively help peripheral axons regenerate
Schwann
_____ actively suppress CNS axon regeneration
oligodendrocytes
What are dermatomes?
- Dermatomes are areas of skin that send signals to the brain through the spinal nerves.
- The dermatome system covers the entire body from the hands and fingers to the feet and toes
The number of action potentials generated by a hypothetical, pressure-sensitive, sensory
afferent neuron is directly proportional to what?
stimulus intensity
What are phasic receptors?
- fast adapting receptors
- Receptors responding to pressure, touch, and smell adapt quickly.
- Examples are lamellar and tactile corpuscles.
What are tonic receptors?
- provide a sustained response with little or no adaptation.
- Receptors responding slowly include Merkel’s discs, Ruffini’s corpuscles, and interoceptors that respond to chemical levels in the blood
- Nociceptors and most proprioceptors (due to protective importance of their information)
What is sensory acuity?
refers to how accurately a stimulus can be located
What are the 3 main levels of neural integration in the somatosensory system?
- Receptor level= sensory receptors and first-order sensory neuron
- Circuit level= processing in ascending pathways
- Perception level= processing in cerebral cortex, interpretation of input into primary and association sensory cortex
What are first-order neurons?
- cell body resides in dorsal root or cranial ganglia, and conduct impulses from the skin to the spinal cord or brain stem.
- Central processes of first-order neurons branch diffusely when they enter the spinal cord. Some branches take part in local spinal cord reflexes.
What are second-order neurons?
soma reside in the dorsal horn of the spinal cord or medullary nuclei and axons cross the midline (decussate) to transmit impulses to the thalamus or cerebellum where they synapse.
What are third-order neurons
- located in the thalamus
- conduct impulses to the somatosensory cortex of the cerebrum. (There are no third-order neurons in the cerebellum.)
What are the pathways in which somatosensory information travels?
- Dorsal column–medial lemniscal
- spinothalamic pathway
- Spinocerebellar pathway
How does the Dorsal column–medial lemniscal function?
- Transmits impulses, via the thalamus to the sensory cortex for conscious interpretation.
- formed by the paired tracts of the dorsal white column of the spinal cord
- transmits touch and proprioception signals to the cerebral cortex.
How does the spinothalamic pathway function?
- Transmits impulses via the thalamus to the sensory cortex for conscious interpretation.
- pathways consist of the lateral and ventral (anterior) spinothalamic tracts. Their fibers cross over in the spinal cord.
- transmits impulses for pain and temperature (lat), but also for coarse touch and pressure (ant).
How does the spinocerebellar pathway function?
- terminates in the cerebellum,
- does not contribute to sensory perception,
- transmits proprioceptive information only to the cerebellum, and so is subconscious.
What is the name of the paired tracts of the dorsal white column of the spinal cord
- fasciculus cuneatus,
- fasciculus gracilis
- medial lemniscus.
Which pathway conveys information about muscles or tendon?
Ventral and dorsal spinocerebellar tracts
What is the difference between the sensory processing for touch and pain in the face?
- a touch component ends in the principle sensory nucleus of the trigeminal
- a pain component ends in the spinal nucleus of the trigeminal
The thalamus projects fibers to what?
- The somatosensory cortex
- Sensory association areas
Describe perceptual detection?
detecting that a stimulus has occurred.
- inputs from several receptors must be summed for perceptual detection to occur.
Describe magnitude estimation?
the ability to detect how intense the stimulus is.
*Perceived intensity increases as stimulus intensity increases because of frequency coding
Describe spatial discrimination?
allows us to identify the site or pattern of stimulation.
What are the different fibers for sharp pain and burning pain?
- Sharp pain is carried by the smallest of the myelinated sensory fibers, the A delta fibers,
- while burning pain is carried more slowly by small nonmyelinated C fibers.
What is nociception?
Nociception is the perception of stimuli (thermal, mechanical or anoxic) that have the potential to produce tissue damage.
What are some stimuli for visceral pain?
extreme stretching of tissue, ischemia (low blood flow), irritating chemicals, and muscle spasms.
