Lec 2: Receptors and Afferent Pathways of Somatosensation and Proprioceptio

Question 1

Purpose of somatosensation and proprioception

Answer 1

Explore, Identify, Increase feedback, Prevent Injury

Question 2

Sensory Information Promotes

Answer 2

-adaptations in posture and movement (planned and reactive)
-sent from peripheral receptors

Question 3

Perception Definition

Answer 3

-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)

Question 4

Cutaneous Sensory Receptors and Specialized Sensory Receptors

Answer 4

1. Mechanoreceptors (pressure, touch -discriminative vs crude-, vibration, proprioception)
2. Thermoreceptors (hot vs cold)
3. Nociceptors (pain)

Specialized receptors in vessels, CT (pain), ligaments, tendons, viscera

Question 5

Meissner Corpuscle

Answer 5

-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

Question 6

Pacinian Corpuscles

Answer 6

-Subcutaneous
-Higher density in finger tips
-Large receptive fields (>4mm)
-Responds to: High frequency vibrations (100-300 Hz: tickle), Pressure (deep) over large space

Question 7

Merkel’s Discs

Answer 7

-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

Question 8

Ruffini’s Corpuscles

Answer 8

-Subcutaneous Skin
-Large receptive fields (>4mm)
-Detects skin stretch: direction and force

Question 9

Free Nerve Endings

Answer 9

-throughout skin and visceral
-found in epidermis
-temperature, pain, tickle & itch

Question 10

Pain Stimulus can be …. and translate ….

Answer 10

1. mechanical, thermal, or chemical
2. translate potentially damaging stimuli into electrochemical signals

Question 11

Types of Pain

Answer 11

1. Nociceptive- results from activation of pain receptors in body due to tissue injury/inflammation (NORMAL RESPONSE)
2. Neuropathic- direct injury to neural tissue, typically results in a burning sensation, radiating, following peripheral nerve

Question 12

Pain receptors in skin vs organs

Answer 12

1. Pain receptors in skin are plentiful and capable of transmitting precise information (where injury is and characterize if injury is sharp/dull)
2. Pain receptors in organ are not as precise (often refers pain to other locations)

Question 13

Nociceptor Types (free nerve endings)

Answer 13

1. Myelinated (delta) afferent fibers
   -carry sharp, stabbing, pricking pain, or cold (<5 degrees Celsius)
   -high threshold pain receptors
   -immediate pain
2. Unmyelinated (C) afferent fibers
   -carry dull and achey pain
   -activation threshold is higher
   -polymodal pain receptors (chemical, heat ->45 degrees Celsius-, mechanical, & hypoxic)

Question 14

Receptive Fields in finger tips vs forearms

Answer 14

Fingertips: many sensory neurons, small receptive field (3mm)
Forearm: fewer sensory neurons, larger receptive field (40mm)

Question 15

Different Sizes of Axons (motor and sensory) from Large —> Small

Answer 15

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

Question 16

Muscle Spindle transmits…. sends…

Answer 16

-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)
-

Question 17

Muscle spindle is …

Answer 17

-an encapsulated intrafusal receptor parallel with extrafusal muscle fibers
-contractile at polar ends

Question 18

Muscle spindle components … and … info about … and …

Answer 18

-receives (gamma efferent) and sends (1a neurons) information about velocity and length of stretch

Question 19

What is Golgi Tendon Organs (GTO) structures?

Answer 19

-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

Question 20

What is the function of the GTO?

Answer 20

-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

Question 21

What type of receptor is within the GTO?

Answer 21

-mechanoreceptors
-monitor and regulate tension of muscle force
-prevent muscle damage

Question 22

What does the GTO do?

Answer 22

-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

Question 23

GTO is also known as…

Answer 23

1. autogenic inhibition
2. inverse stretch reflex (inhibitory interneuron inhibits excessive muscle contraction)

Question 24

Muscle spindle: Axon? Function? Activation?

Answer 24

1. Ia (sensory)
2. Monitors length and velocity of muscle
3. Tendon reflex

Question 25

Gamma motor neurons: Axon? Function? Activation?

Answer 25

1. II (motor)
2. Resets muscle spindle after activation
3. Brain modulated muscle spindle to stretch

Question 26

GTO: Axon? Function? Activation?

Answer 26

1. Ib (sensory)
2. Monitors and regulates tension of muscle force. Also distributes workload (makes sure all MU working efficiently)
3. Inverse Stretch Reflex

Question 27

AMN: Axon? Function? Activation?

Answer 27

1. Alpha (motor)
2. Activates muscle
3. Force production