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Transduction Stimulus is changed into electrical signal Different types of stimuli mechanical deformation chemical change in temperature Warmth, cold, nociceptors – PowerPoint PPT presentation

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Title: Transduction

  • Stimulus is changed into electrical signal
  • Different types of stimuli
  • mechanical deformation
  • chemical
  • change in temperature
  • Warmth, cold, nociceptors
  • electromagnetic
  • Rods and cones in the retina

Sensory systems
  • All sensory systems mediate 4 attributes of a
    stimulus no matter what type of sensation
  • modality
  • location
  • intensity
  • timing

Receptor Potential
  • Membrane potential of the receptor
  • A change in the receptor potential is associated
    with opening of ion (Na) channels
  • Above threshold as the receptor potential becomes
    less negative the frequency of AP into the CNS

Labeled Line Principle
  • Different modalities of sensation depend on the
    termination point in the CNS
  • type of sensation felt when a nerve fiber is
    stimulated (e.g. pain, touch, sight, sound) is
    determined by termination point in CNS
  • labeled line principle refers to the specificity
    of nerve fibers transmitting only one modality of

  • Slow-provide continuous information
    (tonic)-relatively non adapting-respond to
    sustained stimulus
  • joint capsul
  • muscle spindle
  • Merkels discs
  • punctate receptive fields
  • Ruffini end organs (corpusles)
  • activated by stretching the skin

  • Rapid (Fast) or phasic
  • react strongly when a change is taking place
  • respond to vibration
  • hair receptors 30-40 Hz
  • Pacinian corpuscles 250 Hz
  • Meissners corpuscles- 30-40 Hz
  • (Hz represents optimum stimulus rate)

  • Information transmitted to the brain from
    mechanoreceptors in fingers allows us to
  • feel the shape texture of objects
  • play musical instruments
  • type on computer keyboards
  • palpate and perform adjustments
  • perform a multitude of tasks using our hands
  • Tactile information is fragmented by receptors
    must be integrated by the brain

Tactile information
  • The ability to recognize objects placed in the
    hand on the basis of touch alone is one of the
    most important complex functions of the
    somatosensory system. (Gardner Kandel)
  • Tactile information obtained from palpation is
    crucial in the practice of chiropractic.

  • The ability to perceive form through touch
  • tests the ability of dorsal column-medial
    lemniscal system to transmit sensations from the
  • also tests ability of cognitive processes in the
    brain where integration occurs

Receptors in skin
  • Most objects that we handle are larger than the
    receptive field of any receptor in the hand
  • These objects stimulate a large population of
    sensory nerve fibers
  • each of which scans a small portion of the object
  • Deconstruction occurs at the periphery
  • By analyzing which fibers have been stimulated
    the brain reconstructs the pattern

  • No single sensory axon or class of sensory axons
    signals all relevant information
  • Spatial properties are processed by populations
    of receptors that form many parallel pathways
  • CNS constructs a coherent image of an object from
    fragmented information conveyed in multiple

  • Rapidly adapting cutaneous
  • Meissners corpuscles in glabrous (non hairy)
  • signals edges
  • Hair follicle receptors in hairy skin
  • Pacinian corpuscles in subcutaneous tissue
  • Slowly adapting cutaneous
  • Merkels discs have punctate receptive fields
  • senses curvature of an objects surface
  • Ruffini end organs activated by stretching the
  • even at some distance away from receptor

Somatic Sensory Cortex
  • Receives projections from the thalamus
  • Somatotopic organization (homoculus)
  • Each central neuron has a receptive field
  • size varies in different areas of skin
  • lateral inhibition can aid two point

Somatosensory Cortex
  • Two major pathways
  • Dorsal column-medial lemniscal system
  • Most aspects of touch, proprioception
  • Anterolateral system
  • Sensations of crude touch, nociception,
    temperature, tickle, itch and sexual sensations

(No Transcript)
Somatosensory Cortex (SSC)
  • Inputs to SSC are organized into columns by
  • cortical neurons defined by receptive field
  • some columns activated by rapidly adapting
    Messiners, others by slowly adapting Merkels,
    still others by Paccinian corp.
  • most nerve cells are responsive to only one
    modality e.g. superficial tactile, deep
    pressure, temperature, nociception

Somatosensory cortex
  • Brodman area 3, 1, 2 (dominate input)
  • 3a-from muscle stretch receptors (spindles)
  • 3b-from cutaneous receptors
  • 2-from deep pressure receptors
  • 1-rapidly adapting cutaneous receptors
  • These four areas are extensively interconnected
    (serial parallel processing)
  • Each of the 4 regions contains a complete map of
    the body surface

Somatosensory Cortex
  • Detailed features of a stimulus are communicated
    to the brain
  • in early stages of cortical processing the
    dynamic properties of central neurons and
    receptors are similar (eg rapidly adapting
    cutaneous receptors connected to rapidly adapting
    2nd and 3rd order neurons)
  • in the later stages of cortical processing the
    central nerve cells have complex feature
    detecting properties and integrate various
    sensory inputs

Somatosensory Cortex
  • 3 different types of neurons in BM area 1,2 have
    complex feature detection capabilities
  • Motion sensitive neurons
  • respond well to movement in all directions but
    not selectively to movement in any one direction
  • Direction-sensitive neurons
  • respond much better to movement in one direction
    than in another
  • Orientation-sensitive neurons
  • respond best to movement along a specific axis

Other Somatosensory Cortical Areas
  • Posterior parietal cortex (BM 5 7)
  • BM 5 integrates tactile information from
    mechanoreceptors in skin with proprioceptive
    inputs from underlying muscles joints
  • BM 7 receives visual, tactile, proprioceptive
  • intergrates stereognostic and visual information
  • Projects to motor areas of frontal lobe
  • sensory initiation guidance of movement

Secondary SSC (S-II)
  • Secondary somatic sensory cortex (S-II)
  • located in superior bank of the lateral fissure
  • projections from S-1 are required for function of
  • projects to the insular cortex, which innervates
    regions of temporal lobe believed to be important
    in tactile memory

Sensory innervation of Spinal joints
  • Tremendous amount of innervation with cervical
    joints the most heavily innervated
  • Four types of sensory receptors
  • Type I, II, III, IV

Type I mechanoreceptors
  • Outer layers of joint capsul
  • fire at a degree proportional to joint movement
    or traction
  • low threshold
  • dynamic-fire with movement
  • slow adapting
  • tonic effects on lower motor neuron pools

Type II Mechanoreceptors
  • Deeper layers of joint capsul
  • low threshold
  • rapidly adapting
  • completely inactive in imobilized joints
  • functions in joint movement monitering
  • phasic effects on lower motor neuron pools

Type III Mechanoreceptors
  • Recently found in spinal joints
  • very high threshold
  • slow adaptation
  • joint version of Golgi tendon organ

Type IV receptors
  • Nociceptors
  • very high threshold
  • completely inactive in physiologic normal joint
  • activation with joint narrowing, increased capsul
    pressure, chemical irratation

Pain Analgesia
  • Noxious Insults to Body stimulate Nociceptors
  • Nociceptors are activated by
  • Mechanical Stimuli
  • Thermal Stimuli
  • Chemical Stimuli

Sensations of Pain
  • Pricking
  • Burning
  • Aching
  • Stinging
  • Soreness

Pain vs. Nociception
  • Nociception-reception of signals in CNS evoked by
    stimulation of specialized sensory receptors
    (nociceptors) that provide information about
    tissue damage
  • Pain-perception of adversive or unpleasant
    sensation that originates from a specific region
    of the body

Perception of Pain
  • All perception involves an abstraction and
    elaboration of sensory inputs
  • highly subjective nature of pain is one the
    factors that makes it difficult to define and
    treat clinically

  • Conspicuous sensory experience that warns of
  • Chronic pain is a massive economic problem- in US
    more than 2 million people are incapacitated by
    pain at any give time
  • Drives most chiropractic practices

  • Least differentiated of all sensory receptors
  • Can be sensitized by tissue damage
  • hyperalgesia
  • repeated heating
  • axon reflex may cause spread of hyperalgesia in
  • sensitization of central nociceptor neurons as a
    result of sustained activation

Sensitization of Nociceptors
  • Potassium from damaged cells-activation
  • Serotonin from platelets- activation
  • Bradykinin from plasma kininogen-activate
  • Histamine from mast cells-activation
  • Prostaglandins leukotriens from arachidonic
    acid-damaged cells-sensitize
  • Substance P from the 1o afferent-sensitize

Nociceptive pathways
  • Fast
  • A delta fibers
  • glutamate
  • neospinothalamic
  • mechanical, thermal
  • good localization
  • sharp, pricking
  • terminate in VB complex of thalamus
  • Slow
  • C fibers
  • substance P
  • paleospinothalamic
  • polymodal/chemical
  • poor localization
  • dull, burning, aching
  • terminate RF
  • tectal area of mesen.
  • Periaqueductal gray

Nociceptive pathways
  • Spinothalamic-major
  • neo- fast (A delta)
  • paleo- slow (C fibers)
  • Spinoreticular
  • Spinomesencephalic
  • Spinocervical (mostly tactile)
  • Dorsal columns- (mostly tactile)

Cardinal signs of inflammation
  • Rubor-redness
  • Calor-heat
  • Tumor-swelling
  • Dolar-pain

Pain Control Mechanisms
  • Peripheral
  • Gating theory
  • involves inhibitory interneruon in cord impacting
    nocicep. projection neurons
  • inhibited by C fibers
  • stimulated by A alpha beta fibers
  • TENS
  • Central
  • Direct electrical to brain -gt analgesia
  • Nociceptive control pathways descend to cord
  • Endogenous opiods

Endogenous opioids
  • Periaquedutal gray
  • enkephalin projections to Raphe
  • Raphe N.
  • serotonin projections to the cord
  • Inhibitory interneurons in cord
  • release enkephalin which can cause presynatic
    inhibition of incoming C fibers and A delta fibers

Pain control
  • Endogenous opioid peptides and receptors are
    located at key points in the pain modulatory

Surgery to Alleviate Pain
  • Over the years surgical intervention to treat
    pain has been tried at every level of the nervous
    system from the primary afferent fiber to the
  • Procedures not very sucessful
  • Pain can return with new sensations often unlike
    anything the patients have felt before
  • spontaneous aching, shooting pain, numbness,
    cold, heaviness, burning, etc.

Surgery to alleviate pain (cont)
  • Central pain syndromes often cause more distress
    than the pain the operation was intended to
  • Many instances of chronic pain result from
    spontaneous lesions to central sites in
    nociceptive pathways
  • cases of intractable pain resulting from vascular
    damage to CNS (Dejerine Roussy)

  • Referred pain to surface of head
  • Intracranial origins
  • meningitis
  • inflammation of meninges
  • migraine
  • vasocontraction/vasodilatation
  • irritation of meninges
  • e.g. abuse of alcohol
  • constipation

Headache (cont.)
  • Extracranial origins
  • Muscle spasm
  • connective tissue bridges between muscle dura
    in upper cervical spine
  • Irritation of nasal passages and/or sinuses
  • eye disorders
  • cervical joint dysfunction
  • spill over of signals from cervical joints (C2)
    to nucleus of CN V
  • traction of dura
  • mandibular branch of CN V has a recurrent or
    meningeal branch which innervates part of dura

Relationship of Cervical Spine to HA
  • CN V sensory innervation of most of head face.
    (Three divisions).
  • CN V nucleus of termination extends all the way
    down to level of C2.
  • Some of cervical joint afferents synapse directly
    in CN V nuclei.
  • C2 afferents synapse both in dorsal horn (DRG)
    CN V nuclei.
  • Overlap between CN V C2 can cause headache
    associated w/ cervical dysfunction

Muscle Receptors
  • Muscle contain 2 types of sensory receptors
  • muscle spindles respond to stretch
  • located within belly of muscle in parallel with
    extrafusal fibers (spindles are intrafusal
  • innervated by 2 types of myelinated afferent
  • group Ia (large diameter)
  • group II (small diameter)
  • innervated by gamma motor neurons that regulate
    the sensitivity of the spindle
  • golgi tendon organs respond to tension
  • located at junction of muscle tendon
  • innervated by group Ib afferent fibers

Muscle Spindles
  • Nuclear chain
  • Nuclear bag
  • dynamic
  • static
  • A typical mammalian muscle spindle contains one
    of each type of bag fiber a variable number of
    chain fibers (? 5)

Muscle Spindles
  • sensory endings
  • primary-usually 1/spindle include all branches
    of Ia afferent axon
  • innervate all three types
  • much more sensitive to rate of change of length
    than secondary endings
  • secondary-usually 1/spindle from group II
  • innervate only on chain and static bag
  • information about static length of muscle

Golgi tendon organ (GTO)
  • Sensitive to changes in tension
  • each tendon organ is innervated by single group
    Ib axon that branches intertwines among braided
    collagen fascicles.
  • Stretching tendon organ straightens collagen
    bundles which compresses elongates nerve
    endings causing them to fire
  • firing rate very sensitive to changes in tension
  • greater response associated with contraction vs.
    stretch (collagen stiffer than muscle fiber)

CNS control of spindle sensitivity
  • Gamma motor innervation to the spindle causes
    contraction of the ends of the spindle
  • This allows the spindle to shorten function
    while the muscle is contracting
  • Spindle operate over wide range of muscle length
  • This is due to simultaneously activating both
    alpha gamma motor neurons during muscle
    contraction. (alpha-gamma coactivation)
  • In slow voluntary movements Ia afferents often
    increase rate of discharge as muscle is shortening

CNS control of spindle sensitivity
  • In movement the Ia afferents discharge rate is
    very sensitive to variartions in the rate of
    change of muscle length
  • This information can be used by the nervous
    system to compensate for irregularities in the
    trajectory of a movement to detect fatigue of
    local groups of muscle fibers

  • Spindles in conjunction with GTOs provide the
    CNS with continuous information about the
    mechanical state of a muscle
  • For virtually all higher order perceptual
    processes, the brain must correlate sensory input
    with motor output to accurately assess the bodies
    interaction with its environment
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