Block I presentacion Nivia 2 Flashcards
What are receptors?
cells that detect changes
Mention the types of sensations
Superficial
Deep
Visceral
special sense
In what is the sensory system based?
Perception, Conduction and Integration of sensory inputs 9external and internal environment)
What are exteroreceptors and what do they sense?
located in the skin, detect stimuli outside the body such as: pain, temperature, touch and pressure
What are propioreceptors and what do they sense?
Located in the muscles, tendons and joints have signal awareness of body position and movements by muscles or joint position.
What are enteroreceptors and what do they sense?
LOcated on the viscera and monitor events within (inside) the body
Classification of sensory receptors
Somatic, visual, auditory, vestibular (balance), taste (tongue) and olfactory system
Chemoreceptors, photoreceptors, mechanoreceptors, thermoreceptors, nociceptors:
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
1st classification of Sensory Receptors
Modality - type of stimulus:
▫Chemicals (chemoreceptors)
▫ Light (photoreceptors)
▫ Pressure (mechanoreceptors)
▫ Temperature (thermoreceptors)
▫ Pain (nociceptors)
What are the modalities of somatic sensations?
-Discriminative Touch
-Crude (nondiscriminative) touch
-Pain = Nociceptive (fast, low)
-propioception
-thermal (hot,cold)
2nd classification of sensory receptors?
Intensity: The lowest level of strength a stimulus must reach to produce a Sensory threshold [from unipolar neuron to somatosensorial cortex]
3rd classification of sensory receptors?
Duration:
Time the sensory stimulation
continues
▫ Adaptation - less sensitive to the
stimulus
Explain slowly adapting (tonic) adaptation
Fire continuously throughout the
stimulus (duration and intensity of
stimulus). Fast at first but then continuous.
Explain rapid adapting (phasic) adaptation
Signal the onset and cessation of the stimuli
(activity reflects the rate of application of the
stimulus)
It adapts rapidly y deja de disipar potenciales de accion
4th classification of sensory receptors?
Location
▫ Site and ability to distinguish between stimuli
▫ Cutaneous (skin)
▫ Muscle spindles contain mechanoreceptors that detect stretch in muscles
5th classification of sensory receptors?
Morphology
▫ Free nerve endings
▫ Nociceptors
▫ Thermoreceptors
▫ Encapsulated receptors
describe light touch
Two-point discrimination
1. Stereognosis
-ability to recognize objects by touch alone
2. Graphesthesia
-ability to recognize numbers or letters drawn
on the skin, it requires memory
describe pressure
Referred to deep touch
Describe vibration sense
-Requires intact pathway from deep structures
-Low frequency 128 vibrations/second are
associated with the light touch pathways
What is two point discrimination?
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
Describe receptive field (rf)
The space or region over which a stimulus alters neuronal activity
What is stimulus transduction?
Sensory receptors convert a stimulus into a neural activity (opening of ion channels in mechanoreceptors)
types of sensory receptors?
simple
complex neural
special senses receptors
What do primary afferent fibers consist of?
- Peripheral process
- Pesudounipolar cell body
- Central process
What are primary sensory neurons?
First order neurons; unipolar; Dorsal root (spinal) ganglia and the homologous ganglia of the Trigeminal (CN V), Facial (CN VII), Glossopharyngeal (CN IX)
and Vagus (CN X) nerve
Second order neurons?
Seen in the neuraxis of spinal cord or brainstem; decussate in the thalamus
Where are exteroreceptors located?
in skin; stimulating by changes in external modalities: tactile, pressure, pain, temperature
Where are propioceptors located?
in muscles, fascia, ligaments, articulations; stimulated by body changes; proprioception
Where are enteroceptors located?
in viscera (GVA);
how can receptors be classified?
1 cutaneous fibers:
- presence or absence of myelin
-conduction velocity (I, II, III, IV)
-axon diameter
- Contribution to a compound action potential
-(A, B and C waves)
Mention myelinated fibers of Ia/Ib?
Aa, 17um, 80-120m/sec; Fibers from annulospiral endings of the muscle spindle
Limb position & motion; Ib: 16um and Fibers from Golgi tendon organs
Mention myelinated fibers of II?
AB; 8um; 35-75m/sec; Fibers from the flower-spray endings of muscle spindles; cutaneous tactile receptors Tactile, pressure, vibration
Mention myelinated fibers of III?
Agamma; 1-5um; 5-30m/sec; Fibers conducting crude touch, temperature and pain sensations
Fast pain, Temp (cool)
Mention unmyelinated fibers of IV?
C; 0.2-0.5um; 0.5-2m/sec; Fibers carrying pain and temperature sensations Slow pain, Temp (warm), itch
What does the dermis respond to?
Pressure, stretching and vibration
By what do mechanoreceptors differ?
- Morphology (structure and location)
- Physiologically (size and receptive fields)
- Functional information that they encode
Which tactile receptors are encapsulated?
- Meissner’s corpuscle
- Pacinian’s corpuscle
- Ruffini’s ending
Which tactile receptors are unencapsulated?
- Merkel’s disks/cells
- Hair follicle receptors
iDENTOFY STRUCTURES
Where can we find Meissner’s corpuscles? describe them
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)
Where can we find Pacinian corpuscles? describe them
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).
Where can we find Ruffini’s corpuscles? describe them
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
Where can we find merkel’s receptor (discs)? describe them
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 lowfrequency
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
Where can we find hair follicle receptor? describe them
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
Which receptor types are small explain?
Meissner’s corpuscle (RA)
-Tap.flutter 5-40 Hz
->100 in fingertop; 40 in palm
-(54.9 +-8.6)
Merkel’s disk/cell (SA)
-Touch-pressure
(44.7)
70 in fingertip; 10 palm
Which receptor types are large explain?
pacinian
-vibration 60-300Hz
-20 fingertips; 10 palm
Ruffinis
-skin stretch
-50 fingertips; 15 palm
Tactile sensations by adapting rate (rapid)
meissner (small)
pacicnian (large)
Important for sensing movement of an object across the skin
Tactile sensations by adapting rate (slow)
Merkel (small)
Ruffini (large)
Provides input related to displacement and velocity of the stimulus
Signaling the pressure and shape of the object
through the skin
What are the types of propioception?
Consciously
Uncosnciously
What are the modalities of propioception?
Limb position sense
Kinesthesia
-joint position
-direction
-velocity of joint movements
What detects muscle length and muscle strength?
muscle spindes and golgi tendon organs
By what is muscle pain detected?
free nerve endings
WHat are the rapid adapting joint receptors?
Golgi-mazzoni corpuscule
Paciniform corpuscule
Provide information regarding
the dynamic aspect of
kinesthesia
Movement, direction and
velocity of its movement
WHat are the slow adapting joint receptors?
Golgi organ
Ruffini ending
Provide information about static
aspect of kinesthesia
Position judgment
What does the muscle spindle do?
Detect changes in muscle length
* Present in skeletal muscles
▫ Extrafusal fibers
Innervated by alpha motor
neurons
How many intrafusal fibers does the spindles have?
connective tissue capsule containing 8 to 10 intrafusal fibers, which are parallel to extrafusal fibers.
▫ Innervated by spinal gamma motor neurons
What are the types of intrafusal fibers?
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
§ Largest intrafusal fiber
What are the primary afferents of intrafusal?
Annulospiral endings (type Ia)
-Innervate the middle portion of both nuclear chain and bag fibers
What are the secondary afferents of intrafusal?
Flower-spray endings
§ Located at the end of the nuclear bag fiber
What inervates the polar end?
Efferent axons of gamma motor neurons (ventral horn of spinal cord) causing intrafusal fibers to contracts and remain responsive
explaein myotatic reflex
teh intrafusal fiebrs sense a stimulus that through a-motorneuron contrcats extrafusal fibers; efferent fibers trasnport to the instrafusal fibers through Ia; they travel through sensory fibers located on the dorsal root ganglion. Enter through the dorsal horn, innervate gamma fibers, go out through ventral horn an innervate intrafusal fibers and the extrafusal causing increase in muscular tension this resulting in myotatic reflex
Learn
What are golgi tendon organs and where are they located
Slowly adapting mechanoreceptor that
are stimulated by tension in thew tendon
- High-threshold
tendon-muscle junction
By what are glgi tendon organs innervated?
type Ib afferent fibers
How are golgi tendon organs arranged?
Arranged in series with the extrafusal
fibers, consisting of a mesh-like weave of
collagenous bundles within a thin
capsule
Where are ruffini endings and pacician located and function?
Connective tissue external to
the capsule:
Respond to start and stop of movement
Position of the joint
Where are nerve endings located and fucntion?
Within and around capsule joints
Pain info
Learn
Describe mechanical pain receptor
Aδ afferents (thinly myelinated)
Sharp, pricking
Fast and acute pain sensations
(noiceptive)
Describe thermal and mechano-thermal pain receptor
Aδ afferents (thinly myelinated)
Slow burning, cold sharp, pricking
Fast and acute pain sensations
(noiceptive)
Describe polymodal pain receptor
Unmyelinated (C)
Hot, burning sensation, cold, mechanical stimuli
Tissue damage, slow, chronic pain sensation
WHat are the pathways?
Posterior Column-Medial Lemniscal
Principal Trigeminal Sensory Nucleus
Spinocerebellar
Anterolateral System
