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Neuro Block 1 > Somatosensory receptors > Flashcards

Somatosensory receptors Flashcards

1
Q

How we feel? - Sensation

A

Superficial- Touch, Pain, Temperature Two-point discrimination

Deep- Muscle & joint position sense Vibration

Visceral- Hunger, nausea & visceral pain

Special sense- Smell, vision, hearing, taste, equilibrium

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2
Q

Sensory system

A

Perception, Conduction and Integration of sensory inputs

  • external
    -internal enviroment
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3
Q

Peripheral receptors

A

Exteroceptors (skin)
-Stimuli outside the body
Pain, temperature, touch, pressure

Proprioceptors (muscles, tendons,joints)
-Signal awareness of body position and movements
Movement, Joint position

Enteroceptors (viscera)
Monitor events within the body

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4
Q

Sensory receptors can be classified by stimulus

A

Somatic, visual, auditory, vestibular, taste and olfactory system

Chemoreceptors – detect chemicals

Photoreceptors – a specialized neuron able to detect and react to light during vision

Mechanoreceptors – detect mechanical forces
(movement, tension and pressure)

Thermoreceptors – detect changes in temperature

Nociceptors – detect pain

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5
Q

Receptors are widely distributed throughout the body

A

Classification of Sensory Receptors
▫ Modality: Type of Stimulus
▫ Chemicals (chemoreceptors)
▫ Light (photoreceptors)
▫ Pressure (mechanoreceptors)
▫ Temperature (thermoreceptors)
▫ Pain (nociceptors)

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6
Q

Somatic sensations: Modalities

A

Descriminative touch
Crude (nondiscriminative touch)
Pain = nociceptive ( fast / low)
Flutter- vibration
Proprioception
Thermal (hot / cold)

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7
Q

Receptors are widely distributed throughout the body

A

Classification of Sensory Receptors

▫ Intensity
– The lowest level of strength a stimulus must reach to produce a Sensory threshold

▫ Duration
▫ Time the sensory stimulation
continues
▫ Adaptation - less sensitive to the stimulus

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8
Q

Adaptation (Tonic/Phasic)

A

-Slowly adapting (Tonic) = Fire continuously throughout the stimulus (duration and intensity of stimulus

-Rapidly adapting (Phasic) = Signal the onset and cessation of the stimuli (activity reflects the rate of application of the stimulus)

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9
Q

Sensory Receptors: continuation

A

▫ Location
▫ Site and ability to distinguish
between stimuli
▫ Cutaneous (skin)
▫ Muscle spindles contain mechanoreceptors that detect stretch in muscles

Morphology
▫ Free nerve endings
▫ Nociceptors
▫ Thermoreceptors
▫ Encapsulated receptors

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10
Q

General Senses

A

Light Touch
▫ Two-point discrimination
▫ Stereognosis
– ability to recognize objects by touch alone
▫ Graphesthesia
– ability to recognize numbers or letters drawn
on the skin, it requires memory

  • Pressure
    ▫ Referred to deep touch
  • Vibration Sense
    ▫ Requires intact pathway from deep structures
    ▫ Low frequency 128 vibrations/second are associated with the light touch pathways
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11
Q

Two Point Discrimination

A

The minimum distance needed between two stimuli to perceive them as two units.

Tactile acuity threshold are determined by Merkel’s receptors which are densely packed in the fingerprints.

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12
Q

Receptive Field (rf)

A

The space or region over which a stimulus alters neuronal activity

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13
Q

Stimulus Transduction

A

Sensory receptors convert a stimulus into a neural activity

Stimulus –>Mechanoreceptors (Stimulated by mechanical opening of ion channels) –> Receptor potential (Tonic/Phasic)—> stimulus transduction

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14
Q

Sensory receptor types

A

Simple receptors - are neurons w. free nerve endings

Complex neural receptors - have nerve ending enclosed in connective tissue capsules

Special sense receptors- are cells that release neurotransmitter onto sensory neurons, initiating an action potential (ej. hair cell)

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15
Q

Neuron types

A

Bipolar
Pseudo-unipolar***
Multipolar

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16
Q

Peripheral components

A

Primary Afferent fibers consists of:

  1. Peripheral process –
    extending from posterior root ganglion that contact a mechanoreceptor or end as free nerve endings (Unmyelinated fibers)
  2. Pseudounipolar cell body – in the dorsal root ganglion (Unmyelinated fibers)
  3. Central process – to CNS (Myelinated)
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17
Q

Primary Sensory Neuron
First order neurons

A

Dorsal root (spinal) ganglia and the homologous ganglia of the:

Trigeminal (CN V)
Facial (CN VII)
Glossopharyngeal (CN IX)
Vagus (CN X) nerve

18
Q

RECEPTORS CLASSIFICATION

A
  • In base of localization:

▫ exteroceptors: in skin; stimulating by changes in external modalities: tactile, pressure, pain, temperature

▫ proprioceptors: in muscles, fascia, ligaments, articulations; stimulated by body changes; proprioception

▫ enteroceptors: in viscera (GVA); we will NOT discuss this topic

19
Q

Receptors can be classified based on

A

cutaneous fibers or contribution to a compound action potential

  1. Cutaneous fibers:
    * Presence or absence of myelin
    * Conduction velocity (I, II, III, IV) * Axon diamete
  2. Contribution to a compound action potential (A, B and C waves).

***estudiar tabla Slide 21

20
Q

Skin

A

larger organ in the body

Epidermis
▫ Outer layer composed of
dead skin cells

  • Dermis
    ▫ Below the epidermis
    ▫ Composed of mechanoreceptors that respond to pressure, stretching and vibration
21
Q

Tactile Receptors

A

Mechanoreceptors differ by:

  1. Morphology (structure and location)
  2. Physiologically (size and receptive fields)
  3. Functional information that they encode

Epidermis - touch / pressure / vibration
Dermis - sensitive

Each mechanoreceptors has different receptive field and respond different to tactile sensation

Encapsulated
* Meissner’s corpuscle
* Pacinian’s corpuscle
* Ruffini’s ending

Unencapsulated
* Merkel’s disks/cells
* Hair follicle receptors

22
Q

Tactile Receptors: Meissner’s Corpuscles

A

Found in glabrous skin
* Fingers, hand (palm), foot (plantar), toes
* Stacks of horizontal flattened epithelial cells (encapsulated)
* Low-threshold
* Rapidly adapting (RA) – fire at onset and offset of stimulation
* Sensitive to light touch
* Response for abrupt changes in the shape and edges of objects
* Vibration below 100 Hz
* Small receptive field

Fine touch perception, which is essential for tactile discrimination, and reading Braille.

23
Q

Pacinian Corpuscles

A

Encapsulated mechanoreceptors, located deeper in the skin
▫ Found in Hairy & Glabrous skin
▫ Skin of hands, feet, nipples, mammary glands, walls of mesentery, periosteum, joint capsules
* Concentric lamellae of flattened cells that are supported by collagenous tissue
* Low threshold
* Rapidly adapting (RA)
* Large receptive fields
* Sensitive to rapid indentation of skin, vibration and pressure.
* Sensation caused by a high frequency vibration (100-400 Hz).

e.g. rough versus smooth surface texture

24
Q

Ruffini’s Corpuscles (Endings)

A

Located in the deep layer of the skin (dermis)
▫ Found in Hairy & Glabrous skin
▫ Skin of hands, feet, nipples,
mammary glands
* Widely distributed
* Low threshold
* Slowly adapting (SA)
* Detect skin stretching and pressure (magnitude & direction; mechanical information within joints)
* Also acts as thermoreceptors
- In a case of a deep burn to the body, there will be no pain as these receptors will be burned off

25
Q

Merkel’s Receptors (Discs)

A

Nonencapsulated
* Located in the basal cell layer of the epidermis, below glabrous skin of:
▫ Lips
▫ Extremities (distal part)
▫ Genitalia (external)
* Low threshold
* Slow adapting (SA)
* Sensitive to pressure and low- frequency vibration
▫ Signal discrete indentation
* Each ending consists of a Merkel cell in close apposition with an enlarged nerve terminal, up to 90, sometimes called as a Merkel cell-neurite complex.
* Small receptive fields

26
Q

Hair Follicle Receptors

A

A mesh-like arrangement of axons around a hair follicle

  • Provide information to the brain about discrete tactile stimulation
  • Rapid and Slow adapting
  • Sensitive to touch
27
Q

Cutaneous Mechanoreceptors and Their Associated Fiber Types and Sensations

A

Accuracy of stimulus depends on:
1. Density of receptors
2. Size of receptive fields

SLIDE 30 ver tabla***

28
Q

TACTILE SENSATION

A

Meissner (Adaptive rate: rapid / receptive fiel: small)
Pacinian (Adaptive rate: rapid / receptive fiel: large)

important for sensing movement of an object across the skin

Merkel (Adaptive rate: slow / receptive fiel: small)
Ruffini (Adaptive rate: slow / receptive fiel: large

Provides input related to displacement and velocity of the stimulus
–Signaling the pressure and shape of the object through the skin

29
Q

PROPRIOCEPTION

A

Distributed throughout the musculoskeletal system

  • Respond to mechanical forces (position and movement of extremities),
    within the body itself.
  • Play an important role in posture and movement
  • The body’s ability to transmit position sense (from proprioceptors), interpret the information received and respond
  • Afferent nerves that receive and send information from skin, tendons, joints and muscles to the CNS
30
Q

PROPRIOCEPTION

A

Types of Proprioception:
▫ Consciously
▫ Unconsciously

Modalities:
▫ Limb position sense ▫ Kinesthesia
– joint position
– direction
– velocity of joint movements

Proprioceptors provide sensory information to the cerebral cortex:

Muscles and tendons have receptors that detect:
Muscle length = muscle spindles
Muscle strength = Golgi tendon organs

Muscle pain is detected by free nerve endings

Proprioceptors in the joints detect information regarding its position

31
Q

Conscious Awareness: Receptors

A

Joint Receptors & Ligaments
* Free nerve endings
* Encapsulated receptors
▫ Low-threshold mechanoreceptors
▫ Rapid adapting
– Provide information regarding the dynamic aspect of kinesthesia
– Movement, direction and velocity of its movement
▫ Slowly adapting
– Provide information about static aspect of kinesthesia – Position judgment

32
Q

NonConscious Awareness: Receptors

A

Muscle spindle
Detect changes in muscle length
* Present in skeletal muscles
▫ Extrafusal fibers

– Innervated by alpha motor
neurons

Each spindle consist of a connective tissue capsule containing 8 to 10 intrafusal fibers, which are parallel to extrafusal fibers.

▫ Innervated by spinal gamma motor neurons

33
Q

Types of Intrafusal fibers

A

Nuclear chain fiber
§ Single row of central nuclei
§ Smaller and shorter than the nuclear bag fiber

Nuclear bag fiber
§ Cluster of nuclei located in a bag-like dilation at the center of the fiber
§ Larges intrafusal fiber

34
Q

Afferents from intrafusal fibers

A
  1. Annulospiral endings (primary afferents; type Ia sensory endings)
    § Innervate the middle portion of both nuclear chain and bag fibers
  2. Flower-spray endings (secondary afferents)
    § Located at the end of the nuclear bag fiber

Muscles spindles detect changes in muscle length.

Efferent axons of gamma motor neurons (ventral horn of spinal cord) innervate the polar end.

35
Q

Motor innervation to intrafusal fibers

A

Efferent axons of gamma (ɣ) motor neurons (ventral horn of spinal cord) innervate the polar end, causing intrafusal fibers to contract and remain responsive.

36
Q

Muscle spindle density

A

Varies among different muscles.

Those muscles that requires precise movements, such as the extraocular muscles, have higher density of muscle spindles than muscles responsible for gross movements.

37
Q

Stretch reflex (myotonic reflex)

A

intrafusal fiber –> (a-Alpha) motor neuron –> reflex-induced contraction of extrafusal fiber

38
Q

Golgi Tendon Organs

A

Located at the tendon-muscle junction

  • Slowly adapting mechanoreceptor that
    are stimulated by tension in thew tendon
  • High-threshold
  • Arranged in series with the extrafusal fibers, consisting of a mesh-like weave of collagenous bundles within a thin capsule
  • Sensory neuron conduct impulses to spinal cord
  • Innervated by type Ib afferent fibers
  • Senses changes in tendon tension/force
39
Q

Joint Receptors

A

Within and around capsule joints–>Nerve endings–>Pain information

Connective tissue external to the capsule–>Ruffini endings Pacinian—>Respond to start and stop of movement & Position of the joint

40
Q

Pain Receptors

A

Found in cutaneous as well as in deep structures

Mechanical–>Aδ afferents (thinly myelinated)–>Sharp, pricking–>fast and acute pain sensations

Thermal and Mechano-thermal–>Aδ afferents (thinly myelinated)–>Slow burning, cold sharp, pricking–>Fast and acute pain sensations

Polymodal–>Unmyelinated (C)–>Hot, burning sensation, cold, mechanical stimuli–>Tissue damage Slow, chronic pain sensation

ptt foto

Neuro Block 1 (6 decks)

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