Neuro 400FT Chapter 16 Quiz 2 PDF

RECEPTOR TYPE RECEPTOR STRUCTURE AND LOCATION SENSATIONS ADAPTATION RATE TACTILE RECEPTORS Corpuscles of touch (Meissner Capsule surrounds mass of dendrites in dermal papillae of hairless...

RECEPTOR TYPE RECEPTOR STRUCTURE AND LOCATION SENSATIONS ADAPTATION RATE TACTILE RECEPTORS Corpuscles of touch (Meissner Capsule surrounds mass of dendrites in dermal papillae of hairless Onset of touch and low-frequency vibrations. Rapid. corpuscles) skin. Hair root plexuses Free nerve endings wrapped around hair follicles in skin. Movements on skin surface that disturb hairs. Rapid. Type I cutaneous mechanoreceptors Saucer-shaped free nerve endings make contact with tactile epithelial Continuous touch and pressure. Slow. (tactile discs) cells in epidermis. Type II cutaneous mechanoreceptors Elongated capsule surrounds dendrites deep in dermis and in Skin stretching and pressure. Slow. (Ruffini corpuscles) ligaments and tendons. Oval, layered capsule surrounds dendrites; present in dermis and Lamellated (pacinian) corpuscles subcutaneous layer, submucosal tissues, joints, periosteum, and some High-frequency vibrations. Rapid. viscera. Itch and tickle receptors Free nerve endings in skin and mucous membranes. Itching and tickling. Both slow and rapid. THERMORECEPTORS Free nerve endings in skin and mucous membranes of mouth, Warm receptors and cold receptors Warmth or cold. Initially rapid, then slow. vagina, and anus. PAIN RECEPTORS Nociceptors Free nerve endings in every body tissue except brain. Pain. Slow. PROPRIOCEPTORS Sensory nerve endings wrap around central area of encapsulated Muscle spindles Muscle length. Slow. intrafusal muscle fibers within most skeletal muscles. Capsule encloses collagen fibers and sensory nerve endings at Tendon organs Muscle tension. Slow. junction of tendon and muscle. Lamellated corpuscles, type II cutaneous mechanoreceptors, tendon Joint kinesthetic receptors Joint position and movement. Rapid. organs, and free nerve endings.  Tactile Sensations  Tactile sensations are touch, pressure, and vibration plus itch and tickle.  Perceive differences among these sensations, but arise by activation of some of the same types of receptors.  Also, some receptors sense multiple stimuli 2  Tactile Sensations  Touch  crude touch is ability to perceive something has touched the skin, even though its exact location, shape, size or texture cannot be determined  discriminative touch provides specific information about a touch sensation, such as exactly what point on the body is touched plus the shape, size and texture of the source of stimulation The two are carried on separate spinal pathways discussed next class 3  Touch  Two types of rapidly adapting touch receptors  Corpuscles of touch aka Meissner corpuscles Receptors for touch located in the dermal papillae of glabrous skin Abundant in the fingertips, hands, eyelids, tip of the tongue, lips, nipples, soles, clitoris, and tip of the penis. ✯Each corpuscle is an egg-shaped mass of dendrites enclosed by a capsule of connective tissue. 4  Touch  Hair root plexuses ✯Found in hairy skin ✯Consist of free nerve endings wrapped around hair follicles. ✯Detect movements on the skin surface that disturb hairs. ✯E.g., an insect landing on a hair causes movement of the hair shaft that stimulates the free nerve endings.  Touch  Two types of slowly adapting touch receptors  Type I Cutaneous mechanoreceptors aka Merkel discs ✯Saucer-shaped, flattened free nerve endings that make contact with Merkel cells of the stratum basale ✯Function in touch and pressure ✯Most abundant in fingertips, hands, lips and external genitalia 6  Touch  Type II cutaneous mechanoreceptors aka Ruffini corpuscles ✯Elongated, encapsulated receptors located deep in the dermis, and in ligaments and tendons. ✯Abundant in hands (especially fingers) and the soles, but found all over the body ✯Sensitive to stretching of skin that occurs as digits or limbs are moved. Also helps detect pressure  Pressure  Pressure is sustained sensation over a large area  Receptors that contribute to sensations of pressure include Type I and Type II cutaneous mechanoreceptors 8  Vibration  Sensations of vibration result from rapidly repetitive sensory signals from tactile receptors.  Receptors for vibration sensations are Meissner corpuscles and pacinian corpuscles.  Meissner corpuscles can detect lower-frequency vibrations, and pacinian corpuscles detect higher-frequency vibrations. 9  Vibration Lamellar corpuscles adapt rapidly – distributed throughout the body (in dermis, and SubQ; submucosal tissues that underlie mucous and serous membranes; around joints, tendons and muscles; in periosteum; in mammary glands, external genitalia; certain viscera such as pancreas and urinary bladder.  Itch Itch is a bit of a mystery ❖ Triggers include mechanical stimulus, electricity, temperature and certain chemicals ❖ Bradykinin and histamine are well known itch stimulators. When do we see these? ❖ There is no agreed upon theory as to what the functionality of itch is in humans 12  Tickle Tickle is also a bit of a mystery ❖ Tickle is stimulation of free nerve endings only by someone else We aren’t sure why we can’t tickle ourselves, but many ideas have been presented ❖ Tickle can be divided into 2 categories ❖ one of these evokes laughter and the other is considered annoying ❖ Like itch, we aren’t certain why the sensation of tickle exists ❖ Pacinian corpuscles also thought to mediate tickle response  Phantom Limb Sensation Patients with a limb amputated may still experience sensations such as itching, pressure, tingling, or pain as if the limb were still there.  75% of amputees experience this, the majority of these experience painful sensations  One older explanation: cerebral cortex interprets impulses arising from the distal portions of damaged sensory neurons that previously carried impulses from the limb as coming from the nonexistent (phantom) limb.  Phantom Limb Sensation  Another newer explanation : the brain contains networks of neurons that generate sensations of body awareness.  neurons in the brain that previously received sensory impulses from the missing limb are reorganized (plasticity), and now sensations from other areas of the body create a phantom sensation from the former limb  Very distressing to an amputee – most report that the pain is severe, and that it often does not respond to traditional pain medication therapy.  alternative treatments may include electrical nerve stimulation, acupuncture, and biofeedback, mirror therapy.  Thermal Sensations  Free nerve endings with 1mm diameter receptive fields on the skin surface  Cold receptors  Located in the stratum basale of the epidermis  Attached to medium-diameter, myelinated A fibers (few connect to small-diameter, unmyelinated C fibers)  Temperatures between 10° and 35°C (50–95°F) activate cold receptors. 16  Thermal Sensations  Warm receptors  Not as abundant as cold receptors  Located in the dermis  Attached to small-diameter, unmyelinated C fibers  Activated by temperatures between 30° and 45°C (86– 113°F).  Both adapt rapidly at first, but continue to generate impulses at a low frequency  Pain is produced below 10 deg C and over 45 deg C.  Pain Sensations  Free nerve endings found in almost every tissue of the body (not found in the brain)  Activated by intense thermal, mechanical, or chemical stimuli  Tissue irritation or injury releases chemicals such as prostaglandins, substance p, kinins, and potassium ions (K+) that stimulate nociceptors. 18  Pain Sensations  May persist even after a pain-producing stimulus is removed because pain-mediating chemicals linger  Exhibit very little (if any) adaptation (tonic)  Conditions that can elicit pain include (massage related)  excessive distention (stretching) of a structure  prolonged muscular contractions  muscle spasms  ischemia  Pain Sensations  Fast pain (acute)  occurs rapidly after stimuli (0.1 second)  pain is often felt as acute, sharp, or pricking pain pain felt from a needle puncture or knife cut to the skin  not felt in deeper tissues  nerve impulses propagate along medium- diameter, myelinated A fibers. 20  Pain Sensations  Slow pain (chronic)  begins more slowly & increases in intensity  may be excruciating – felt as chronic, burning, aching, or throbbing pain  pain associated with a toothache  can occur both in the skin and in deeper tissues or internal organs  pain conducted along small-diameter, unmyelinated C fibers 21  Pain Sensations  You can perceive the difference in onset of these two types of pain best when you injure a body part that is far from the brain because the conduction distance is long.  When you stub your toe, you feel the sharp sensation of fast pain and then feel the slower, aching sensation of slow pain.  Somatic pain that arises from the stimulation of receptors in the skin is superficial somatic pain,  Somatic pain that arises from skeletal muscle, joints, and tendons is deep somatic pain. 22  Pain Sensations  Visceral pain, unlike somatic pain, is usually felt in or just under the skin that overlies the stimulated organ  localized damage (cutting) intestines may cause no pain, but diffuse visceral stimulation can be severe ✯distension of a bile duct from a gallstone ✯distension of the ureter from a kidney stone  pain may also be felt in a surface area far from the stimulated organ in a phenomenon known as referred pain (Figure 16.3). 23  Referred Pain  Visceral pain that is felt just deep to the skin overlying the stimulated organ or in a surface area far from the organ.  Skin area & organ are served by the same segment of the spinal cord.  Heart attack is felt in skin along left arm since both are supplied by spinal cord segment T1-T5 24 Pain Threshold vs Tolerance  Pain threshold: How strong does the stimulation have to be before it elicits a pain response? Ie. Before the stimulus reaches receptor threshold Involves only the PNS Constant among population  Pain tolerance: How much pain an individual can take?  Involves the CNS  varies widely among population Not well understood 25  Drugs for Pain  Analgesic drugs such as aspirin, ibuprofen and naproxen block formation of prostaglandin and thromboxane, which stimulate nociceptors.  Inhibit the cyclooxygenase enzyme  Local anesthetics, such as Novocaine® or Lidocaine, are sodium channel blockers. They provide short-term pain relief by inhibiting the response of voltage-gated sodium channels along the axons of first-order pain neurons. 26  Drugs for Pain  Morphine and other opiates alter the quality of pain perception in the brain; pain is still sensed in the PNS, but the signal is affected in the CNS to either be blocked or perceived differently.  Causes euphoria  Many pain clinics use anticonvulsant and antidepressant medications to treat those suffering from chronic pain.  Ie. Gabapentin 27  Proprioception  Proprioceptive sensations allow us to know where our head and limbs are located and how they are moving even if we are not looking at them, so that we can walk, type, or dress without using our eyes.  Kinesthesia is the perception of body movements. 28  Proprioception  Proprioceptors  embedded in muscles (especially postural muscles) tendons and joints, inform us of the degree to which muscles are contracted, the amount of tension on tendons, and the positions of joints.  This awareness of the activities of muscles, tendons, and joints and of balance or equilibrium is known as the proprioceptive or kinesthetic sense. 29  Proprioception  Proprioceptors adapt slowly and only slightly (tonic)  brain continually receives nerve impulses related to the position of different body parts and makes adjustments to ensure coordination.  Proprioceptors allow weight discrimination, the ability to assess the weight of an object.  helps to determine the muscular effort necessary to perform a task.  E.g., as you pick up an object you quickly realize how heavy it is, and you then exert the correct amount of effort needed to lift it. 30  Proprioception  Proprioceptive information is sent to both the cerebellum & cerebral cortex  Cortical information is conscious  Cerebellar information is unconscious  3 types of proprioceptors:  muscle spindles within skeletal muscles  tendon organs within tendons  joint kinesthetic receptors in or around joint capsules. 31  Muscle Spindle  Proprioceptors in skeletal muscles that monitor changes in the length of skeletal muscles and participate in the stretch reflex  Each muscle spindle consists of several slowly adapting sensory nerve endings that wrap around 3 to 10 specialized muscle fibers, called intrafusal muscle fibers. 32  Muscle Spindle  Main function of muscle spindles is to measure muscle length—how much a muscle is being stretched.  Either sudden or prolonged stretching of the central areas of the intrafusal muscle fibers stimulates the sensory nerve endings.  The resulting nerve impulses propagate into the CNS – to the somatic sensory areas of the cerebral cortex, which allows conscious perception of limb positions and movements.  Impulses from muscle spindles also pass to the cerebellum, where the input is used to coordinate muscle contractions. 33  Muscle Spindle  In addition to their sensory nerve endings near the middle of intrafusal fibers, muscle spindles contain motor neurons called gamma motor neurons.  These terminate near both ends of the intrafusal fibers and adjust the tension in a muscle spindle to variations in the length of the whole muscle. 34  Muscle Spindle  E.g., when a muscle shortens, gamma motor neurons stimulate the ends of the intrafusal fibers to contract slightly.  Keeps the intrafusal fibers taut and maintains the sensitivity of the muscle spindle to stretching of the muscle.  As the frequency of impulses in its gamma motor neuron increases, a muscle spindle becomes more sensitive to stretching of its mid-region. 35  Muscle Spindle  Surrounding the muscle spindles are muscles fibers called extrafusal muscle fibers  supplied by large-diameter A fibers called alpha motor neurons.  cell bodies of both γ and α motor neurons are located in the anterior gray horn of the spinal cord (or in the brain stem for muscles in the head). 36  Muscle Spindle  During the stretch reflex, impulses in muscle spindle sensory axons propagate into the spinal cord and brain stem and activate alpha motor neurons that connect to extrafusal muscle fibers in the same muscle.  Activation of its muscle spindles causes contraction of a skeletal muscle, which relieves the stretching. 37  Muscle Spindle  Specialized intrafusal muscle fibers enclosed in a CT capsule and innervated by gamma motor neurons  Stretching of the muscle stretches the muscle spindles sending sensory information back to the CNS  Spindle sensory fiber monitor changes in muscle length  Brain regulates muscle tone by controlling alpha motor neuronss 38  Golgi Tendon Organ  Protect tendons and their associated muscles from damage due to excessive tension.  Penetrating the capsule s one sensory nerve ending that entwines among and around the collagen fibers of the tendon.  When tension is applied to a muscle, the GTO generate nerve impulses that propagate into the CNS, providing information about changes in muscle tension.  Tendon reflexes decrease muscle tension by causing inhibition of a muscle 39  Golgi Tendon Organ  Found at junction of tendon & muscle  Consists of an encapsulated bundle of collagen fibers laced with sensory fibers  When the tendon is overly stretched, sensory signals propagate toward the CNS & result in muscle relaxation 40 Joint Kinesthetic Receptors  Present within and around the articular capsules of synovial joints.  Free nerve endings and Ruffini corpuscles in the capsules of joints respond to pressure.  Small pacinian corpuscles in the connective tissue outside articular capsules respond to changes of speed of joints during movement. 41 RECEPTOR TYPE RECEPTOR STRUCTURE AND LOCATION SENSATIONS ADAPTATION RATE TACTILE RECEPTORS Corpuscles of touch (Meissner Capsule surrounds mass of dendrites in dermal papillae of hairless Onset of touch and low-frequency vibrations. Rapid. corpuscles) skin. Hair root plexuses Free nerve endings wrapped around hair follicles in skin. Movements on skin surface that disturb hairs. Rapid. Type I cutaneous mechanoreceptors Saucer-shaped free nerve endings make contact with tactile epithelial Continuous touch and pressure. Slow. (tactile discs) cells in epidermis. Type II cutaneous mechanoreceptors Elongated capsule surrounds dendrites deep in dermis and in Skin stretching and pressure. Slow. (Ruffini corpuscles) ligaments and tendons. Oval, layered capsule surrounds dendrites; present in dermis and Lamellated (pacinian) corpuscles subcutaneous layer, submucosal tissues, joints, periosteum, and some High-frequency vibrations. Rapid. viscera. Itch and tickle receptors Free nerve endings in skin and mucous membranes. Itching and tickling. Both slow and rapid. THERMORECEPTORS Free nerve endings in skin and mucous membranes of mouth, Warm receptors and cold receptors Warmth or cold. Initially rapid, then slow. vagina, and anus. PAIN RECEPTORS Nociceptors Free nerve endings in every body tissue except brain. Pain. Slow. PROPRIOCEPTORS Sensory nerve endings wrap around central area of encapsulated Muscle spindles Muscle length. Slow. intrafusal muscle fibers within most skeletal muscles. Capsule encloses collagen fibers and sensory nerve endings at Tendon organs Muscle tension. Slow. junction of tendon and muscle. Lamellated corpuscles, type II cutaneous mechanoreceptors, tendon Joint kinesthetic receptors Joint position and movement. Rapid. organs, and free nerve endings. Somatic Sensory Pathways  Somatic sensory pathways relay information from somatic receptors to the primary somatosensory area in the cerebral cortex and to the cerebellum.  The pathways consist (usually) of three neurons  first-order  second-order  third-order  Axon collaterals of somatic sensory neurons simultaneously carry signals into the cerebellum and the reticular formation of the brain stem. 43 Somatic Sensory Pathways  First-order neurons conduct impulses from the somatic receptors into the CNS (brainstem or spinal cord)  From the face, mouth, teeth and eyes, somatic sensory impulses propagate along cranial nerves to the brain stem  From the body, neck and posterior head, somatic sensory impulses propagate along spinal nerves into the spinal cord. 44 Somatic Sensory Pathways  Second-order neurons conducts impulses from CNS to the thalamus  cross over to opposite side of body in the brainstem or spinal cord before ascending to the thalamus  Sensory information from one side of the body reaches the contralateral half of the thalamus  Third-order neurons conduct impulses from the thalamus to the primary somatosensory area (postcentral gyrus of the parietal lobe) 45 Somatic Sensory Pathways  Somatic sensory impulses entering the spinal cord ascend to the cerebral cortex via two general pathways  The posterior column pathway  The anterolateral pathways aka spinothalamic pathways  Also have the pathways to reach the cerebellum via the spinocerebellar tracts 46 Posterior Column – Medial Lemniscus Pathway  Nerve impulses for touch, pressure, vibration, and conscious proprioception from the limbs, trunk, neck, and posterior head ascend to the cerebral cortex via the PCML  Name of the pathway comes from the names of two white-matter tracts that convey the impulses: the posterior column of the spinal cord and the medial lemniscus of the brain stem. 47 Posterior Column – Medial Lemniscus Pathway  Impulses conducted along this pathway  Discriminative touch – ability to recognize specific information about a touch sensation, such as point of touch, shape, size and texture of source aka Stereognosis (the ability to perceive the form of an object by using sense).  Proprioception – awareness of the precise position of body parts  Kinesthesia – awareness of directions of movement  Weight discrimination – ability to assess weight of an object  Vibration and pressure 48  Posterior Column – Medial Lemniscus Pathway  First-order neurons extend from sensory receptors in the limbs, trunk, neck, and posterior head into the spinal cord and ascend to the ipsilateral medulla oblongata  The cell bodies of these first- order neurons are in the posterior (dorsal) root ganglia of spinal nerves. 49 Posterior Column – Medial Lemniscus Pathway  In the spinal cord, their axons form the posterior (dorsal) columns, which consist of two parts: the gracile fasciculus and the cuneate fasciculus.  First-order neurons synapse with second-order neurons whose cell bodies are located in the gracile nucleus or cuneate nucleus of the medulla. 50 Posterior Column – Medial Lemniscus Pathway  Nerve impulses for touch, pressure, vibration and conscious proprioception from the upper limbs, upper trunk, neck, and posterior head propagate along axons in the cuneate fasciculus and arrive at the cuneate nucleus.  Nerve impulses for touch, pressure, vibration and conscious proprioception from the lower limbs and lower trunk propagate along axons in the gracile fasciculus and arrive at the gracile nucleus. 51 Posterior Column – Medial Lemniscus Pathway  The axons of the second-order neurons cross to the opposite side of the medulla and enter the medial lemniscus  Thin ribbon-like tract that extends from the medulla to the ventral posterior nucleus (VPN) of the thalamus  In the thalamus the axon terminals of second-order neurons synapse with third-order neurons, which project their axons to the primary somatosensory area of the cerebral cortex. 52 53  Anterolateral or Spinothalamic Pathways  3-neuron pathway  The anterolateral or spinothalamic pathways carry mainly pain and temperature impulses, but also tickle and itch sensations, crude poorly localized touch, pressure and vibration Touch, pressure and vibration are all poorly localized on these tracts 54  Spinothalamic Pathways  First-order neurons travel through the posterior (dorsal) roots of spinal nerves to connect to second order nerves at the level of the spine in which they entered  Synapse with second-order neurons in the posterior gray horn of the spinal cord 55  Spinothalamic Pathways  Second-order neurons cross to the opposite side of SC – continue upward via either the lateral spinothalamic tract or the anterior spinothalamic tract  Lateral spinothalamic tract carries pain & temperature  Anterior tract carries tickle, itch, crude touch, pressure and vibrations  Axons of second order neurons synapse with third-order neurons in the thalamus (VPN) –  Third-order neurons project into the primary somatosensory area of cerebral cortex 56 57 Trigeminothalamic Pathway  Nerve impulses for most somatic sensations (tactile, thermal, pain, proprioception) from the face, nasal cavity, oral cavity ascend to the cerebral cortex along the trigeminothalamic pathways  Consists of a 3-neuron set  First order neurons extend from somatic sensory receptors in the face, nasal cavity, oral cavity and teeth into the brain stem through the trigeminal (CN?) nerve 58 Trigeminothalamic Pathway  The cell bodies of these first order neurons are in the trigeminal ganglia  Axon terminals of some 1st order neurons synapse with second order neurons in the pons.  Axons of other 1st order neurons descend into the medulla to synapse with second order neurons  Axons of second order neurons cross to the opposite side of the pons and medulla (some do not) and then ascend as the trigeminothalamic tract 59  Trigeminothalamic  Pathway Go to the ventral posterior nucleus of the thalamus and synapse with third order neurons  Third order neurons project axons to the primary somatosensory area on the same side of the cerebral cortex as the thalamus 60 61 Which cranial nerve conveys impulses for most somatic sensations from the left side of the face into the pons? 62 Spinocerebellar Pathways  Two tracts in spinal cord - posterior spinocerebellar tract and anterior spinocerebellar tract – major proprioceptive impulses from trunk and limbs of one side of the body to the ipsilateral cerebellum  These pathways are critical for maintenance of posture and balance and to coordinate, smooth and refine skilled movements. 63 Spinocerebellar Pathways 64 Primary Somatosensory Area  Occupies the postcentral gyri of the parietal lobes  Somatic sensory signals from the left side of the body to the right cerebral hemisphere and vice versa  The lips, face, tongue and thumb provide input to large regions in the somatosensory area  Relative sizes of cortical areas are presented as the homunculus  proportional to number of sensory receptors  proportional to the sensitivity of each part of the body 65 Primary Somatosensory Area  Can be modified with learning (plasticity)  learn to read Braille & will have larger area representing fingertips 66  Syphilis Bacterial infection caused by treponema pallidum Late stage syphilis can show neurological signs and symptoms at which point it is known as neurosyphilis One such sign is progressive degeneration of the posterior portion of the spinal cord As the posterior column takes up most of the posterior spinal cord, symptoms will mainly include a loss of the sensory information carried on this tract The most noticeable of these symptoms is the loss of conscious proprioception Sufferers walk with noticeable gait impairment 67