ME03 - Somatosensory Systems Flashcards
Two types of General Sense and examples
Somatic (Cutaneous) senses
- Touch, pressure, vibration, warmth, cold, pain, tickle, itch and proprioception
Visceral senses
- Stretch, pain, chemo-, osmotic-, baro-
What are Special Senses
Olfaction, vision, taste, hearing and equilibrium
Transmits information to the CNS about the state of the body and its contact with the environment
SOMATOSENSORY SYSTEM
Pathway of Somatosensory System
Sensory receptor cells»_space; Neural Pathways»_space; Brain Cortex
Specialized epithelial cells that receive stimuli from the external or internal environment
Sensory receptor cells
Neurons that transduce environmental signals (light, temperature) into neural signals
Sensory receptor cells
Conduct information from the receptors to the brain or spinal cord
Neural pathways
Deal primarily with processing the information
Brain cortex
Information processed by a sensory system may or may not lead to conscious awareness of the stimulus
Sensory information
State of (conscious or unconscious) awareness of external and internal conditions in the body
Sensation
Conscious recognition of sensation
Damaged neural networks may give faulty perceptions
Phantom limb: sensation of a limb that has been amputated
PERCEPTION
Receptors are particularly distinct to a specific type of environmental change and less sensitive to other forms of stimuli
Selective Response of Sensory Receptors
Example of Selective Response of Sensory Receptors
Vision receptors contain pigment molecules that respond to light
What are the different mechanoreceptors and their location and functions
PACINIAN CORPUSCLE - Deep skin layer; Vibration (tapping)
MEISSNER’S CORPUSCLE - Superficial skin layer; Superficial touch (flutter and stroking movements)
RUFFINI’S CORPUSCLE - Deep skin layer; Skin stretch
MERKEL’S DISK - Superficial skin later; Steady pressure and texture
PROPRIOCEPTORS - Muscle, joints, tendons; Position
What are the different SOMATOSENSORY Receptors, Location and functions
WARM RECEPTORS Skin; Warm Temperature (30-45C)
COLD RECEPTORS Skin; Cold Temperature (20-35C)
NOCICEPTORS Skin, Muscle, Viscera; Noxious stimuli, extreme of temperature
Identify different types of SOMATIC SENSATION
Tactile sensations
- Touch, pressure, vibration, tickle, itch
Themoreceptive sensation
- Heat and cold
-
Pain
Proprioception
- Receptors from this sensations comes from the skin, muscles, bones, tendons, and joints
Mechanoreceptors with nerve endings linked to net-works of collagen fibers within a capsule
Touch-Pressure Receptors
What are Rapid adapting receptors
Touch, movement, and vibration sensations
What are Slow adapting receptors
Pressure
Muscle-spindle stretch receptors in skeletal muscles, mechanoreceptors in the joints, tendon organs (Gol-gi), ligaments, and skin
Also supported by vision and the vestibular organs
Posture & Movement
Types of Stretch Receptors
Muscle spindle
- Activity depends on muscle length
- Annulospiral, flower-spray endings
Golgi tendon
- Passive stretch and active contraction increases the tension of the tendon that activate the tendon organ receptor
What activates with stimuli outside the absolute temperature?
Nocireceptors, because of high probability of tissue damage
Range of temperature the body can only adapt
20 and 40 C
Skin thermoreceptors play a role in temperature regulation, which is controlled by
Centers in Hypothalamus
Gradiations of temperature
Blue to Red
(freezing cold > cold > cool > indifferent > warm > hot
> burning hot)
Cold spots>warm spots: located beneath the skin at discrete spots. Which spots are cold and warm receptors located
Warm receptors- free nerve endings, transmitted thru type c fibers
Cold receptors- type A delta nerve fibers, some type c
Different types of Headache:
Tension
Sinus
Cluster
Migraine
Different types of Headache:
Tension - Pain experienced as a squeezing band around the head
Sinus - Pain behind browbone and/or cheekbones
Cluster - Pain localized in one eye
Migraine - Typical signs are pain, nausea and altered vision.
Free nerve endings that are stimulated when there is tissue damage
Pain: Nociceptors
Different qualities of pain
Cutaneous pricking pain: well localized and easily tolerated
Burning pain: poorly localized and poorly tolerated
Deep pain: arising from the viscera, musculature and joints, poorly localized, can be chronic and often as-sociated with referred pain
Sensitive to a stimuli causing tissue injury
Nociceptors
Chemical mediators of Nociceptors include:
Histamine, bradykinin & prostaglandins from site of injury
ATP & 5-HT (serotonin) from platelets activated by injury
Substance P from the primary sensory neurons
Effect of mechanoreceptive pain receptors, ischemia
Muscle spasm
Pain from deep structures of the head referred to the surface
Headache
Areas that are pain sensitive
Venous sinuses
Tentorium
Dura at the brain base
Meningeal blood vessels
Middle meningeal artery
Types of Headache
Headache of meningitis
Low CSF pressure headache
Migraine headache
Alcoholic headache
Headache cause by constipation
Severe headache from the inflammation of meninges
Headache of meningitis
Headache of Unknown mechanism
Starts with a prodrome lasting minutes to an hour
Migraine headache
Best time to intervene in a migraine headache
Prodrome
Different theories of migraine headache
Vasospasm of the arteries producing ischemia
Spreading cortical depression
Psychological abnormalities
Vasospasm by excess potassium in the ECF
Headache Alcohol- toxic to tissues
Alcoholic-headache
Headache From absorbed toxic products or fluid loss in the gut
Headache caused by constipation
Types of Extracranial headache
Headache from muscle spasm
Headache from irritation of nasal and accessory nasal structures
Headache caused by eye disorders
Muscle contraction
Excessive irradiation
Pain of visceral origin is referred to sites on the skin and follows the dermatome rule
Sites are innervated by nerves that arise from the same segment of the spinal cord
Referred Pain
Example of Referred Pain
Ischemic heart pain is referred to the chest and shoulder
Type of Referred Pain that is localized in the dermatomal segments from which the organs originated in the embryo
Referred Visceral Pain | e.g. Heart pain fibers enter C3 and T5
Referred pain occurs because both visceral and so-matic afferents often converge on the same neurons in the spinal cord. True or False
TRUE
What are the causes of true visceral pain?
Ischemia of visceral tissue
Chemical damage to the visceral surface
Spasm of hollow viscus smooth muscle
Overdistention of hollow viscus
Stretching of tissues surrounding or within the viscera
Visceral disease spreads to parietal peritoneum, pleura or pericardium. True or False
True.
What causes “sharp pain” | Ex. Appendicitis
Parietal surface supplied with pain innervation
Follow pain pathway on referred pain to the umbilicus (APPENDICITIS)
Inflamed appendix pass pain impulses into the spinal cord levels T10 or T11 referred pain to the umbilicus
Impulses from the parietal peritoneum where the inflamed appendix directly touches causes sharp RLQ pain
Follow the pathway for SENSORY TRANSDUCTION
Transformation of stimulus energy»_space; Receptor potentials»_space; Action potentials in nerve fibers
Mechanisms of Receptor Potentials By mechanical deformation
Stretches the receptor membrane
Opens ion channels
Mechanisms of Receptor Potentials By application of a chemical
Opens ion channels
Mechanisms of Receptor Potentials By change of the temperature of the membrane
Alters the permeability of the membrane
Basic cause of the change in membrane potential is a change in membrane permeability of the receptor. True or False
TRUE
Function of a Pacinian corpuscle
Eliciting an Action Potential
Components of a Pacinian corpuscle
Central nerve fiber extending through its core.
Surrounding multiple concentric capsule layers
Central fiber of the pacinian corpuscle
- The tip of the central fiber - unmyelinated
What happens if there is Compression anywhere on the outside of the corpuscle
Compression anywhere on the outside of the corpus-cle will
- Elongate
- Indent or
- Deform the central fiber
Follow the pathway for Stimulus arrivin at a sensory receptor
Stimulus arrives at sensory receptor»_space; Opening of ion channels»_space; Receptor Potential»_space; (Depolarization; Hyperpolarization)»_space; Threshold reached»_space; Action Potential
A single afferent neuron with all its receptor endings
Sensory unit
Area of the body when stimulated, changes the firing
Receptive field
Example of a Receptive field
Ice cube on the skin give rise to sensations of touch and temperature simultaneously
Receptive fields overlap so that when 1 point is stimulated it activates several sensory units. True or False
TRUE
Differentiate Large & Small Receptive Field
Large receptive field: less precise perception
Small receptive field: more precise perception
Conversion of receptor potentials into action poten-tials that conveys sensory information to the CNS
Sensory Coding
Nature of a sensation and the type of reaction gener-ated vary according to the destination of sensory im-pulses in the CNS. True or False
True.
Different Characteristics of the stimuli
Type (Modality)
Intensity
Location
Duration
Property by which one sensation is distinguished from another
Modality of sensation
Different types of Modalities and Submodalities
Modalities: Touch-Pressure, Posture-movement, Temperature, Pain
- Submodalities: Warmth, cold (Temperature)
The type of sensory receptor activated by a stimulus plays the primary role in coding the stimulus modality. True or False?
TRUE
Calling in or activation of receptors on addition-al afferent neurons
Recruitment
Relationship between Intensity of stimulation and Frequency
Increased stimuli, increased action potential
Relation Between Receptor Potential and the Action Potential Frequency:
The more the receptor potential rises above the threshold level, the greater action potential frequency.
Relation Between Stimulus Intensity and the
Receptor Potential
Stevens Power Law | Weber-Fechner Law
- Very intense stimulation causes progressively less and less additional increase in amplitude of receptor potentials
- Allows the receptors to have an extreme range of response
- From very weak to very intense
The magnitude of a subjective sensation increases proportional to a POWER of the stimulus intensity
Steven’s Power Law
The magnitude of a subjective sensation increases proportional to the LOGARITHM of the stimulus intensity
Weber-Fechner Law
[Localization of Stimuli] where the stimulus is being applied
Location
[Localization of Stimuli] Precision in locating the stimulus
Acuity
In Acuity, small receptive field size, more precise localization. True or False
True.; Example: Two point discrimination
Receptors are at the edge of a stimulus is strongly inhibited compared to information from the stimuluss center
Lateral inhibition
Receptors adapt either partially or completely to any constant stimulus after a period of time. True or False
TRUE
Explain Adaptation of Receptors.
When a continuous sensory stimulus is applied,
- The receptor responds at a high impulse rate at first
- Then progressively slower rate until
- Finally the rate of action potentials decreases to very few to none at all
Two types of Adaptation Receptors?
Tonic Receptors; Phasic Receptors
Differentiate Tonic & Phasic Receptors
Adaptation: Tonic receptors
Muscle spindle; pressure; slow pain
Slowly adapting
Respond repetitively to a prolonged stimulus
Detect a steady stimulus
Adaptation: Phasic Receptors
Pacinian corpuscle; light touch
Rapidly adapting
Action potential frequency declines with time in re-sponse to a constant stimulus | Detect onset and Offset of a stimulus
What are the Different Fiber Types
> > Fastest Conduction Velocity
A-alpha (Large a-motorneurons) IA Muscle spindle afferents IB Golgi Tendon Organ»_space; Largest Diameter
> > Medium Diameter & Conduction Velocity
A-beta (Touch, Pressure) II Secondary afferents of muscle spindles; Fine touch and pressure
A-gamma (y-motorneurons to muscle spindles/intrafusal)
> > Small Diameter & Medium Conduction Velocity
A-delta (Touch, Pressure, Temperature and Pain) III Crude touch, pressure, sharp and fast pain and temperature
B preganglionic autonomic fibers
> > Smallest Diameter & Slowest Conduction Velocity
C-slow pain, postganglionic fibers IV-Slow and Dull Pain and Temperature (unmyelinated)
Transmit signals in varying frequencies
Diameter is proportional to conduction velocity
Sensory nerve fibers
Nerve fibers are specific in transmitting only one modality of sensation
Labeled line principle
Signals are subject to modification at the various synapses along the sensory pathways before they reach higher levels of the CNS. What principle is applied?
Control of Incoming Sensory Signals
Information is reduced or even abolished by inhibition from collaterals from other ascending neurons (e.g., lateral inhibition) or by pathways descending from higher brain centers. True or False
True.
What are the different Somatosensory Pathways?
Ascending pathway (Sensory) | Nonspecific ascending pathway |
Ascending pathway (Sensory)
Consists of a bundle of 3-afferent sensory neuron chains that run parallel to each other in the CNS and carry information to the cerebral cortex*
Differentiate Specific & Nonspecific Ascending Pathway
Specific ascending carry a single type of stimulus
Nonspecific ascending different stimuli
Specific ascending Pathway
Transmit information from somatic receptors pass the brainstem and thalamus into the Somatosensory cortex
Processing of afferent information does not end in the primary cortical receiving areas but continues to association areas of the cerebral cortex
Nonspecific ascending Pathway
Polymodal neurons different stimuli
Convey information from more than one type of sen-sory unit to the brainstem reticular formation and re-gions of the thalamus that are not part of the specific ascending pathways
Specific regions of the Primary Somatosensory area (postcentral gyrus, posterior to the central sulcus) receive somatic sensory input from different parts of the body
Somatosensory Cortex
What are the major somatosensory areas of the cerebral cor-tex
SI and SII
Follow the Sensory pathway: Receptors to the Cortex
First-order neurons - Cell bodies are in the dorsal root or spinal cord ganglia
Second-order neurons - Located in the spinal cord or brain stem
Third-order neurons - located in the relay nuclei of the thalamus
Fourth-order neurons - located in the appropriate sensory area of the cerebral cortex
Primary afferent neurons that receive the transduced signal and send the information to the CNS
First-order neurons (DRG/ Spinal cord ganglia)
Receive information from primary afferent neu-rons in relay nuclei and transmit it to the thala-mus
Axons may cross the midline in a relay nucleus in the spinal cord before they ascend to the thala-mus - sensory information originating on one side of the body ascends to the contralateral thala-mus.
Second-order neurons (located in the spinal cord/brainstem)
Responsible for the information that ascends to the cerebral cortex
Third-order neurons (relay nuclei of the thalamus)
Information received by this neuron results in a conscious per-ception of the stimulus
Fourth-order neuron (sensory area of the cerebral cortex)
What are the Neural pathways of the Somatosensory system
Ascending Anterolateral pathway/ Spinothalamic pathway
Dorsal column pathway
Pathways cross from the side where the afferent neu-rons enter the central nervous system to the opposite side either in the spinal cord (Anterolateral system) or in the brainstem (Dorsal column system)
Neural pathways
Pathway responsible for the Fine touch, pressure, two-point discrimination, vibra-tion, and proprioception
Consists primarily of group II fibers
Dorsal column system
Explain the course of Dorsal column system
Primary afferent neurons: cell bodies in the dorsal root, axons ascend ipsilaterally to the nucleus gracilis and nucleus cuneatus of the medulla
Second-order neurons cross the midline and ascend to the contralateral thalamus
Third-order neurons ascend to the somatosensory cortex, where they synapse on fourth-order neu-rons+A110
Pathway responsible for the Temperature, pain, and light touch
Group III and IV fibers enter the spinal cord and terminate in the dorsal horn
Anterolateral pathway
Explain the course of Anterolateral Pathway
Primary afferent neurons: cell bodies in the dorsal root, axons ascend ipsilaterally to the nucleus gracilis and nucleus cuneatus of the medulla Second-order neurons cross the midline to the anterolateral quadrant of the spinal cord and ascend to the contralateral thalamus
Third-order neurons ascend to the somatosen-sory cortex, where they synapse on fourth-order neurons
Destruction of the thalamic nuclei results in _____________?
Loss of sensation on the contralateral side of the body
Little man
SI has a somatotopic representation similar to that in the thalamus
Sensory homunculus
- The largest areas represent the face, hands, and fingers, where precise localization is most im-portant.
What are the Sensory Pathways for Pain
Paleospinothalamic tract
Neospinothalamic tract
Processes pain and temperature information
Spinothalamic pathway
Fast pain
- Mechanical (intense pressure), thermal pain stim-uli ( >45 or
Neospinothalamic tract
Pathway for Spinothalamic
Nociceptors _ spinal cord (layer I) _ crossed_LST_ VPL and VPI of the thalamus _SC I - Long fibers that cross immediately to the opposite side of the cord through the anterior commissure and then turn upward, passing to the brain in the anterolateral columns
Slow pain
- Polymodal nociceptors (high-intensity persisting mechanical, thermal or chemical stimuli)
- C fiber (group IV)
Paleospinothalamic tract
Pathway for Paleospinothalamic
Peripheral fibers terminate in the spinal cord al-most entirely in laminae II and III of the dorsal horns, which together are called the substantia gelatinosa
- Enters mainly lamina V, also in the dorsal horn
- Join the fibers from the fast pain pathway, pass-ing first through the anterior commissure to the opposite side of the cord, then upward to the brain in the anterolateral pathwbay
Clinical Abnormalities of the Sensory Pathway
Brown Sequard syndrome
Syringomyelia
Tabes dorsalis
Loss of sensation and motor function paralysis and ataxia caused by the lateral hemisection (cutting) of the spinal cord
Brown Sequard syndrome
Pain, temperature sensations lost on the opposite side of the body(Spinothalamic pathway)
Kinesthetic, position, vibration, discrete localization and two-point discrimination lost on the side of the transection (Dorsal column)
Crude touch retained
Chronic disease of the spinal cord characterized by the presence of fluid-filled cavities and leading to spasticity and sensory disturbances
Syringomyelia
Syringomyelia is usually seen in what part of the body
Generally in the cervical region, with resulting neuro-logic defects; thoracic scoliosis is often present
Parenchymatous neurosyphilis marked by degenera-tion of the posterior columns and posterior roots and ganglion of the spinal cord
Tabes dorsalis
Manifestationsof Tabes dorsalis
muscular incoordination
- paroxysms of intense pain
- visceral crises
- disturbances of sensation
- Trophic disturbances, especially of bones and joints(tabes-wasting)
Selective suppression of pain without effects on con-sciousness or other sensations
Analgesia
System of Analgesia (process of analgesia)
Descending pathways selectively inhibit the transmis-sion of information originating in nociceptors -> re-lease certain endogenous opioids -> inhibit the prop-agation of input through the higher levels of the pain system e.g. morphine
Gating Theory of Pain modulation
Transmission turns on gate for pain
Inhibitory cells shut the gate
Perception of pain is subject to modulation
Analgesia system: Pain suppression in the brain and spinal cord
Periaqueductal gray and periventricular area of mes-encephalon and upper pons Raphe magnus nuclei, nucleus reticullaris pargigan-tocellular
Pain inhibitory complex
Dorsal horn of Spinal Cord
Stimulation of higher brain centers that suppress per-iaqueductal gray area can also suppress pain:
Periventricular nuclei in the hypothalamus
Medial forebrain bundle
Transmitters involved in the Analgesia system:
Enkephalin presynaptic and postsynaptic inhibi-tion of type Adelta and C fibers
Serotonin
Painful site itself or the nerves leading from it are stimulated by electrodes placed on the of the skin
Transcutaneous Electric Nerve Stimulation (TENS)
Stimulation of non-pain, low threshold afferent fibers (touch receptor fibers) leads to the inhibition of neu-rons in the pain pathways. True or False
True.
Needles are introduced into specific parts of the body to stimulate afferent fibers, and this causes analgesia
Acupuncture
Endogenous opioid neurotransmitters are involved in acupuncture analgesia. True or False
TRUE
What are the Most important Opiate-like substances
Met and leu-enkephalin
_-endorphin
Dynorphin
Inhibits the synthesis of prostaglandins and slows the transmission of pain signals from the site of injury
Aspirin
Act directly on opioid receptors in the brain, which activate descending pathways that inhibit incoming pain signals
Opiates (endogenous opioids: endorphins & enkepha-lins)
