Lec 2: Receptors and Afferent Pathways of Somatosensation and Proprioceptio Flashcards
Purpose of somatosensation and proprioception
Explore, Identify, Increase feedback, Prevent Injury
Sensory Information Promotes
-adaptations in posture and movement (planned and reactive)
-sent from peripheral receptors
Perception Definition
-awareness of stimuli
-interprets sensory information into meaningful forms
e.g. reaching for keys, stepping on tack, trying to open locked door
-active and ongoing process (acting within the environment)
e.g. feedback about ankle position (proprioception)
e.g. light changes while driving and pedestrians (visual)
e.g. tripping and falling—> UE protective response (vestibular)
Cutaneous Sensory Receptors and Specialized Sensory Receptors
- Mechanoreceptors (pressure, touch -discriminative vs crude-, vibration, proprioception)
- Thermoreceptors (hot vs cold)
- Nociceptors (pain)
Specialized receptors in vessels, CT (pain), ligaments, tendons, viscera
Meissner Corpuscle
-Cutaneous receptor
-Found in superficial skin, greater density at finger tips
-Small receptive fields (2-4mm)
-Responds to: Discriminative touch (2 point), Low frequency vibrations (30-50 Hz: flutter), & is Velocity sensitive
Pacinian Corpuscles
-Subcutaneous
-Higher density in finger tips
-Large receptive fields (>4mm)
-Responds to: High frequency vibrations (100-300 Hz: tickle), Pressure (deep) over large space
Merkel’s Discs
-Found in superficial skin
-Greater density at finger tips
-Dermis and hair follicles
-Small receptive fields (2-4mm)
-Responds to: Pressure (discriminate shapes/edges), Touch & Form
Ruffini’s Corpuscles
-Subcutaneous Skin
-Large receptive fields (>4mm)
-Detects skin stretch: direction and force
Free Nerve Endings
-throughout skin and visceral
-found in epidermis
-temperature, pain, tickle & itch
Pain Stimulus can be …. and translate ….
- mechanical, thermal, or chemical
- translate potentially damaging stimuli into electrochemical signals
Types of Pain
- Nociceptive- results from activation of pain receptors in body due to tissue injury/inflammation (NORMAL RESPONSE)
- Neuropathic- direct injury to neural tissue, typically results in a burning sensation, radiating, following peripheral nerve
Pain receptors in skin vs organs
- Pain receptors in skin are plentiful and capable of transmitting precise information (where injury is and characterize if injury is sharp/dull)
- Pain receptors in organ are not as precise (often refers pain to other locations)
Nociceptor Types (free nerve endings)
- Myelinated (delta) afferent fibers
-carry sharp, stabbing, pricking pain, or cold (<5 degrees Celsius)
-high threshold pain receptors
-immediate pain - Unmyelinated (C) afferent fibers
-carry dull and achey pain
-activation threshold is higher
-polymodal pain receptors (chemical, heat ->45 degrees Celsius-, mechanical, & hypoxic)
Receptive Fields in finger tips vs forearms
Fingertips: many sensory neurons, small receptive field (3mm)
Forearm: fewer sensory neurons, larger receptive field (40mm)
Different Sizes of Axons (motor and sensory) from Large —> Small
Larger size of myelinated axon = Greater speed of transmission
1. LARGEST. A (alpha)= alpha motor neuron
2. A (beta)= Meissner, Merkel, Pacinian, Ruffini
3. A (delta)= free nerve ending (pain and temp)
4. SMALLEST. C (unmyelinated)= pain
Muscle Spindle transmits…. sends…
-transmits information on Length of muscles and Speed of muscles
-sends information to cerebellum to calculate joint position and other variables necessary to make appropriate movement (cerebellum houses motor memory)
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Muscle spindle is …
-an encapsulated intrafusal receptor parallel with extrafusal muscle fibers
-contractile at polar ends
Muscle spindle components … and … info about … and …
-receives (gamma efferent) and sends (1a neurons) information about velocity and length of stretch
What is Golgi Tendon Organs (GTO) structures?
-encapsulated receptor/sensory organ located @ musculotendinous junction
-in series with extrafusal fibers
-3-50/muscle
-distal and proximal parts of tendon-spindle innervated by afferent (Ib) fibers
What is the function of the GTO?
-detects small change in muscle contraction (<1g force)
-reflex regulation of alpha motor neuron activity
-sensitive to twitch contractions (active)
-compensates for fatigue in motor units
-facilitates or inhibits muscle contractions
-context/task dependent
What type of receptor is within the GTO?
-mechanoreceptors
-monitor and regulate tension of muscle force
-prevent muscle damage
What does the GTO do?
-maintains muscle tension within optimal range
-prevents excessive force from being generated (preventing damage)
-senses excessive muscle tension –> causes inhibition of Alpha MN –> reduces rate of contraction
GTO is also known as…
- autogenic inhibition
- inverse stretch reflex (inhibitory interneuron inhibits excessive muscle contraction)
Muscle spindle: Axon? Function? Activation?
- Ia (sensory)
- Monitors length and velocity of muscle
- Tendon reflex
Gamma motor neurons: Axon? Function? Activation?
- II (motor)
- Resets muscle spindle after activation
- Brain modulated muscle spindle to stretch
GTO: Axon? Function? Activation?
- Ib (sensory)
- Monitors and regulates tension of muscle force. Also distributes workload (makes sure all MU working efficiently)
- Inverse Stretch Reflex
AMN: Axon? Function? Activation?
- Alpha (motor)
- Activates muscle
- Force production
