Somatosensory System Flashcards
Somatosensory system includes… sensation
- Proprioceptive
● Positional
● Vibratory
● Fine touch (epicritic) (leer braille)
● Spatial discrimination (saber si nos están tocando)
● Crude touch (protopathic) (algo que me aplasta el brazo)
● Temperature (hot and cold)
● Pain
Receptors in somatosensory system
Propioceptors and mechanoreceptors
Anterolateral system detects…
- Temperature: cold and heat (termorreceptores)
- Pain: Fast (Aδ) Slow (C)
- Crude touch (protopathic)
Clasification of sensory fibers based on their diameter and conduction velocity
Fibras finas
Fibras de tipo C
Fibras gruesas y rápidas (mielinizadas)
I y II
Lloyd no hizo clasificación de fibras…
Sensitivas
Slow
Fast
Fatigue-resistant and Non fatigue-resistant fibers
Extrafusal muscle fibers: conventional muscle fibers, the ones that make the force
(Nuclear chain, Nuclear bag fibers) They are in charge of proprioception in muscles and they house the neuromuscular spindles (composed of a muscle fiber and a sensory fiber surrounding it).
Intrafusal muscle fibers
…. neurons allow the perception of muscle stretch during muscle contraction, adjusting the spindles
Gamma motor: neurona que contrae fibras instrafusales.
(Pero solo se activan con orden voluntaria, en caso de ser un reflejo tan solo se activan las alfa)
SKIN RECEPTORS (SOMATOSENSORY SYSTEM)
The receptor is the ….of the dendrite of dorsal root ganglion neurons
Terminal process
Los mecanoreceptores más abundantes en las manos son…
Los correspondientes a la presión principalmente: MEISSNER
Cuanto más profundo el receptor…
Más amplio el campo, menos receptores hay (como en el caso de los Ruffini=estiramiento, o Pacini=vibracion )
SENSORY FIBERS CLASSIFICATION (GASSER AND LLOYD)
Which type of fibers are in charge of proprioception?
Aalpha/I
SENSORY FIBERS CLASSIFICATION (GASSER AND LLOYD)
Which type of fibers have the highest myelinization and are the fastest ones?
Aalpha/I
SENSORY FIBERS CLASSIFICATION (GASSER AND LLOYD)
Which type of fibers are in charge of touch, pressure and vibration?
Abeta/II
SENSORY FIBERS CLASSIFICATION (GASSER AND LLOYD)
Which kind of fibers are in charge of touch, heat and cold?
Adelta/ III
SENSORY FIBERS CLASSIFICATION (GASSER AND LLOYD)
Which kind of fibers are in charge of heat and pain?
C and IV
SENSORY FIBERS CLASSIFICATION (GASSER AND LLOYD)
Which kind of fibers are unmyelinated and are the slowest ones?
C / IV
CLASSIFICATION OF MOTOR FIBERS
Fastest somatic afferents
Aalpha
CLASSIFICATION OF MOTOR FIBERS
Slowest somatic efferents
Agamma
CLASSIFICATION OF MOTOR FIBERS
Preganglionic, little myelin and fastest in ANS
B fibers
CLASSIFICATION OF MOTOR FIBERS
Postganglionic, no myelin, slower in ANS
C fibers
SENSORY FIBERS (GASSER AND LLOYD) and MOTOR FIBERS CLASSIFICATION (SCHEME)
PROPRIOCEPTION: Neuromuscular spindles
Neuromuscular spindles are composed of…
A muscle fiber and a sensory fiber surrounding it
PROPRIOCEPTION: Neuromuscular spindles
Nuclear bag intrafusal fibers are usually surrounded by…
ANNULOSPIRAL ENDINGS, which travel with type Ia fibers
PROPRIOCEPTION: Neuromuscular spindles
Nuclear chain intrafusal fibers are usually surrounded by…
Flower spray endings, which travel with type II fibers
How do neuromuscular spindles work?
The muscle feels stretch, it becomes thinner, nerve endings surrounding them get stretched, mechanoreceptors are activated and a motor fiber is activated to generate a reflex + other fibers go to cortex to make it conscious.
Why are nerve terminals surrounding muscle fibers in the neuromuscular spindles?
They let us know when the muscle is being contracted INVOLUNTARILY (from its resting position). It detects stretching.
As when we contract the muscle voluntarily, the fibers do not become thinner: contraction is detected, but it does not involve stretching.
ANNULOSPIRAL terminale and type Ia fibers detect…
Speed of stretch
Flower spray terminals and type II fibers detect…
Degree of stretch
Extrafusal muscle fibers are innervated by..
A-alpha fibers
Intrafusal muscle fibers are innervated by…
A-gamma fibers
NEUROMUSCULAR SPINDLES
NEUROMUSCULAR SPINDLES
Difference between stretch and tension
Tension does not involve a change in length, stretch does.
With Golgi tendon we cannot detect …, it detects …
stretch, degree of tension
Fibers in Golgi-tendon organs
Type I-beta fibers in tendons
Functions of Golgi tendon organs
- PROPRIOCEPTIVE: knowing the egress of tension
- PROTECTIVE: an inhibitory reflex (which causes the muscles to relax) is generated when too much tension is detected. En example would be when pushing against the wall.
Skin receptors in somatosensory system
Mechanoreceptors, thermal receptors, nociceptors.
Receptive fields overlap and act as a safety mechanism. Why is this?
Because if we lose one neuron, we will not lose sensation in so much territory of the skin, thanks to this overlap.
SKIN RECEPTORS
What type of resolution do we find in fingertips?
Higher resolution=more neurons with smaller receptive fields (this is why blind people can read braille)
SKIN RECEPTORS
What type of resolution do we find in the back?
Less resolution=lower number of neurons that cover big receptive fields.
Exclusive receptors in glabrous skin (no hair)
MEISSNER corpuscles
Exclusive receptors in hairy skin
Hair follicle receptors
Complete the scheme
A mosquito moving in an arm will be detected by … (skin receptor)
Hair follicles and MEISSNER skin receptors
The shape of an object we are holding would be detected by … (skin receptors)
Tactile discs and Merkel’s
Ruffini and Pacinian corpuscles have … receptive fields
A large: they do not require a precise discrimination.
In Meisner / hair-follicle receptors and Merkel’s / Tactile receptors we find a … receptive field
Small: we need precision
Meissner (fast pressure) and Pacinian corpuscles (vibration) are … receptors
Phasic
Merkel’s / tactile discs (sustained pressure) and Ruffini’s corpuscles (stretch) are .. receptors
Tonic
TYPES OF MECHANORECEPTORS
Small receptive field, fast adaptating: RA I
MEISSNER/ hair-follicle receptors (when we have an ant on our arm)
TYPES OF MECHANORECEPTORS
Small receptive field, slow adaptation: SA I
Merkel’s / Tactile discs (when we determine the shape of an object for example)
TYPES OF MECHANORECEPTORS
Large receptive field, fast adaptating: RA II
Pacinian corpuscles (for vibration)
TYPES OF MECHANORECEPTORS
Large receptive field, slow adaptating: SA II
Ruffini’s corpuscles: for stretch info
Cold receptors work from … degrees to … degrees
5-30/34
Heat receptors work from … degrees to … degrees
32, 45
Above … degrees, stimuli on the skin will be detected as pain.
45
Thermoreceptors are both … This is the reason why in the shower, under hot water, at first it may feel very hot but after a while it feels fine.
Tonic and phasic
In relation to thermoreceptors, there are specific fibers for heat and cold (T/F)
True
Types of nociceptors
Family of receptors for temperature and pain
Transient receptor potential family: present in Aδ and C fibers
Types of thermoreceptors in Transient Receptor Potential Family
Some of the TRP family can be activated by substances (T/F)
True
