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2013-02-02 12:18:03
Anatomy Physiology

General Senses/Special Senses
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  1. Define:
    Sensation:the conscious or unconscious awareness of internal or external stimuli

    Perception:conscious awareness & interpretations of sensations

    Modality:attempts to explain how one sensation is different from another (pain, temp, touch
  2. Name and describe 4 components of Sensation
    1. Stimulation:stimulus that can initiate a nerve impulse

    2. Transduction: Detection of stimulus and conversion of stimulus into graded potentials (changes in resting membrand potential in a receptor cell)

    3. Conduction:transport of nerve impulse via neuronal pathway to the brain

    4. Integration: translation of nerve impulse into a sensation by a specific brain region
  3. What is a sensory receptor?
    • -specialized in dectecting stimulus
    • -can be simple (dendrite) or complex (dendrite w/connective or epithelial tissue)
    • -functions as tranducers (converts one form of energy into another like a light bulb)
  4. What is sensory transduction?
    converts energy of stimulus (receptor potential) into energy of nerve signal (action potential)
  5. What is receptor potential?
    • -local electrical change in receptor cell
    • -strong enough signal lead to firing of an action potential by sensory neuron
  6. Sensory Projection Pathway
    • 1st order neuron (afferent neuron)
    • -from body, enter dorsal horn of spinal cord via spinal nerves
    • -from head, enter pons and medulla via cranial nerve
    •   -touch, pressure and proprioception on large, fast, myelinated axons
    •   -heat and cold on small, unmyelinated, slow fibers

    • 2nd Order Neuron
    • -decussation to opposit side in spinal cord or medulla/pons
    • -end in thalamus, except fo proprioception (cerebellum)

    • 3rd order Nueron
    • -thalamus to primary sensory cortex of cerebrum
  7. Name the 3 different classification of receptors
    • 1. Simple vs. comlex
    • -can be simple (dendrite)
    • -free nerve endings:touch,pain, temperature
    • -Comples (dendrite w/ connective or epethelial tissue)
    •      -associated with special senses

    • 2. Location
    • -Exteroreceptors:located on or near the surface of the body ex touch & pain receptors
    • -Interoceptors:located in blood vessels and organs, provides info about internal environment (thermoreceptors & baroceptors)
    • -Proprioceptors:associated with muscles & tendons, joints, & inner ear. provide info about body position and tension in muscles an tendons

    • 3. By type of stimulus dectected
    • -Mechanoreceptors:pressure or stretching involved in touch, vibration, and balance
    • -Thermoreceptors: temperature changes
    • -Nociceptors: respond to noxious stimui that cause physical or chemical damage to tissues. Pain
    • -Photoreceptors-dectects light that hits retina
    • -Chemoreceptors-dectect chemicals (mouth=taste, nose=smell, body fluids=changes in pH and CO2 and O2
  8. Name the uncapsulated nerve endings
    • (Dendrites not wrapped in connective tissue)
    • 1. General sense receptors for pain and temperature
    • 2. Tactile Discs
    • -associated with cells at the base of epidermis
    • 3. Hair receptors
    • -monitor movement of hair

    (add picture here)
  9. Name the encapsulated Nerve endings
    • (dendrites wrapped by glial cells or connective tissue)
    • 1. Tactile (Messinner's) corpuscles-phasic
    • respond to light touch and texture
    • 2. Krause end bulb-phasic
    • tactile;in mucous membranes
    • 3. Ruffini corpuscles-tonic
    • heavy touch, pressure, joint movements and skin stretching
    • 4. Lamellated (Pacinian) corpuscles-phasic
    • deep pressure, stretch, tickle and vibration
  10. What is neural coding? Why is it necessary?
    It is the manner in which senory information is converted into a meaningful pattern.

    It is necesary because complex information is communicated about conditions in and around the body via action potential that are IDENTICAL for a given neuron.
  11. Neural Coding
    Each sensory nerve fiber traveling to the brain represents a line of communication that is labeled by the breain to represent a specific stimulus (a color of light, pitch of a sound etc)

    • -Labeled line code:brain knows what type of sensory info travels on each fiber (a map)
    • -Optic nerve will always carry signal from photoreceptors in the eye
  12. Coding for Stimulus Location
    • -Receptive fields form the basis for coding location of most stimuli
    • -Size and # of receptive fields, amount of overlap between receptive fields, and lateral inhibition determine acuity
    • -Acuity:precision with which a stimulus is perceived
  13. Two Point Discrimination
    • -Measurement of tactile acuity
    • -Threshold:minimum distance between 2 points for them to be percieved as seperate
    • -Only works when the two points are in the receptive fields of two different afferent neurons
  14. Duration of Stimulus
    • Duration-determined by manner in which nerve fibers change their firing frequency
    • -Tonic receptors: adapt slowly, generate impulses continually (proprioceptor) turns on and stays on
    • -Phasic receptor:burst of activity and quickly adapts (smell and hair receptors) on and off switch
    • -All receptors slowly but surely exhibit sensory adaptation over time
    • -Prolonged stimulus initiates a decrease in firing frequency and conscious sensation
  15. How is "intensity" encoded?
    • Neurons have different thresholds of excitation.
    • -Weak stimuli activate most sensitive neurons while stronger stimuli activate less sensitive neurons
    • -strong stimulus can recruit additional neurons
    • -Recruitment informs the brain about stimulus strength by frequency of action potentials and the # of receptors activated.
  16. Thermoreceptors
    • -Respond to the temperature of receptor ending and surrounding tissue
    • -do not respond to temperature of surroundings
    • -cold receptors:respond to temperatures between 35C-20C and temperatures greater than 45C (painfully hot stimuli)
    • -Warm receptors-respond to temperature between 30C-45C
    • -Thermoreceptors are free nerve endings which contain temperature sensitive ion channels
    •   -Transient receptor potential (TRP) channels
  17. Thermoreceptors Heat TRP channels
    • -TRP channels open or close in response to changes in temperature or to certain chemicals
    • -Can initiate signal transduction in reponse to temperature change or pain
    • -Heat activated TRP Channels:
    •  -TRPV1 & TRPV2-respond to temperatures greater than 42C
    •  -TRPV3 & TRPV4-respond to temperatures between 27 C-42 C and function as warm receptors
    • -TRPV3 also responds to camphor (induces a warming sensation
  18. Thermoreceptors Cold TRP channels
    • TRPM8: responds to temp less than 25 C and menthol and eucalyptus oil (cooling sensations)
    • TRPA1-responds temp less than 17 C and mustard oil, garlic, and cinnamon

    (Warm receptors and cold receptors respond raidly to temperature changes)
  19. Pain Nociceptors
    • Nociceptors-allow awareness of tissue injuries
    • -found in all tissues except brain

    Fast pain travels in myelinated fibers at 30 m/s (sharp, localized, stabbing pain perceived with injury)

    Slow pain travel unmyelinated fibers at 2 m/s (longer-lasting, dull, diffuse feeling)
  20. Pain
    • -Somatic painfrom skin, muscles, and joints
    • -Visceral pain from stretch, chemical irritants, or ischemia of viscera (poorly localized)
    • -Injured tissues release chemicals that stimulate pain fibers (bradykinin, histamine, prostaglandin)
  21. Projection Pathways for Pain
    Pain signals from the head travel to brainstem via cranial nerves V, VII, IX, and X.

    • From the neck down pain travels via the:
    • -spinothalamic tract *must know*
    • -spinoreticular tract
    • -gracile fasciculus

    Spinothalamic tract is the major pain pathway: carries most of the somatic pain signals to the cortex where we become aware of pain

    Spinoreticular tract:carries pain signals to reticular formation of brain stem and the hypothalamus and limbic system, triggers visceral, emotional, and behavioral reactions (nausea, fear, reflex responses)
  22. Referred Pain
    • Misinterpreted Pain
    • -1st order afferent neurons for visceral pain and cutaneous pain converge on same 2nd order neuron in spinal cord
    • -heart pain felt in shoulder or arm because both send pain input to spinal cord segments T1-T5
  23. CNS Modulation of Pain
    Analgesia-pain relief w/out loss of consciousness. Aspirin and ibuprofen prevent stimulation of nociceptors by blocking prostaglandin production

    • Morphine and Endogenous opioids block perception of pain in the brain
    • -enkaphalins
    • -endorphins
    • -dynorphins
    • -produced by CNS and other organs under stress or excercise
    • -act as neuromodulators block transmission of pain
    • -produce feelings of pleausure and euphoria
  24. Spinal Gating
    • Stops pain signals at dorsal horn
    • -Descending nerve fibers from brain stem travel down reticulospinal tract to dorsal horn in spinal cord
    •   -secrete serotonin onto inhibitory interneurons
    •   -interneurons secrete enkephalins blocking pain transmission by inhibiting 2nd order neurons
    • -pain signals never ascend

    Dorsal horn fibers inhibitied by input from mechanoreceptors (rubbing a sore arm reduces pain)
  25. Anesthesia
    • -General anesthesia:removes all sensation including pain
    • -Spinal Anesthesia: injection of drug into sub arachnoid space, blocking pain and sensation below point of injection
    • -Local Anesthesia-block nerve conduction (novacaine)
  26. Proproprioceptors
    • -Associated with skeletal muscles, tendons, joints, and inner ear
    • -Nerve impulses involved in muscle tone, movement of body parts, body position
    • -Muscle spindle-specialized muscle fivers
    • -Golgi tendon Organs-found associated with collagen fibers of a tendon
  27. The Muscle spindle
    • Sense organ (proprioceptor) that monitor length of muscle and how fast muscles change in length
    • Composed of intrafusal muscle fibers, afferent fibers and gamma motorneurons
  28. Golgi Tendon Reflex
    Proprioceptors in a tendon near its junction with a muscle --1mm long, encapsulated nerve bundle

    Excessive tension on tendon inhibits motor neuron (muscle contraction decreased)

    Also functions when muscle contracts unevenly
  29. Chemical Sense-Taste
    Gustation-sensation of taste, results from action of chemicals on taste buds

    • Lingual papillae
    • -Filiform (no taste buds) important for texture
    • -Foliate (no taste buds)
    • -Fungiform (at tips and sides of tongue)
    • -Vallate (Circumvallate) at rear of tongue, contains 1/2 of taste buds
  30. Taste bud Structure
    • Taste calls
    • -apical microvilli serve as recptor surface
    • -synapse with sensory nerve fibers at their base

    • Supporting Cells
    • Basal Cells
  31. Physiology of Taste
    Molecules must dissolve in saliva

    • 5 primary sensations-throughout tongue
    • 1. Sweet-concentrated on tip
    • 2. Salty-lateral margins
    • 3. Sour-lateral margins
    • 4. bitter-posterior
    • 5. Umami- tase of amino acids (MSG0

    Influenced by food texture, aroma, temperature, and appearance

    Mouthfeel-dectected by lingual nerve in papillae

    Hot pepper stimulates free nerve endings (pain)
  32. Mechanisms of Action (physiology of taste)
    • activate 2nd messenger systems
    • -sugars, alkaloids, and glutamates bind to receptors depolarize cells directly
    • -sodium and acids penetrate cells
  33. Projection Pahtways for Taste
    • Innervation of taste buds
    • -facial nerve (VII): anterior 2/3's of tongue
    • -glossopharyngeal nerve (IX)-posterior 1/3
    • -Vagus nerve (X)-palate, pharynx, epiglottis

    • To Medulla
    • To hypothalamus and amygdala
    • -activate autonomic reflexes ie salivation, gagging, and vomiting
    • To thalamus, then postcentral gyrus of cerefrum
    • -conscious sense of taste
  34. Chemical Sense-Smell
    • Olfactory Mucosa
    • -contains receptor cells for olfaction
    • -highly sensitive up to 10,000 odors
    • -on 5cm2 of superior concha and nasal septum
  35. Olfactory Epithelial Cells
    • Olfactory Cells
    • -Olfactory hairs neurons with 20 cilia
    • -bind odor molecules in thin layer of mucus
    • -axons pass through crbriform plate
    • -survive 60 days

    • Supporting Cells
    • Basal cells
    • -Divide
  36. Physiology of Smell
    • Molecules bind to receptor on olfactory hair
    • -hydophilic-diffuse through mucus
    • -hydrophobic- transport by odorant-binding protein

    • Activate G protein and cAMP System
    • Opens ion channels for Na or Ca (creates receptor potential
    • Action potential travels to brain
    • Receptors adapt quickly due to synaptic inhibition in olfactory bulbs
  37. Olfactory Pathway
    • Olfactory cells synapse in olfactory bulb
    • -on mitral and tufted cell dendrites
    • -in spherical clusters called glomeruli
    •   -each glomeruli dedicated to single odor
  38. Olfactory Pathway
    • Output from bulb forms olfactory tracts
    • -end in primary olfactory cortex and thalamus
    • -travel to insula and frontal cortex
    •   -identify odors
    •   -integrate taste and smell into flavor

    Travel to hypothalamus, amygdala, and hypocampus (memories, emotional, and visceral reactions)