PNS

Question 1

What are PNS receptors?

Answer 1

Peripheral Nervous System: Somatosensory System

• Types of Receptors and Sensory Information Processed
  
  • Tactile Senses: Crude Touch (feel something but can’t discriminate it), Fine Discriminative Touch or Localization, Light and Deep Touch, Pressure, and Vibration
  • Temperature Senses: Hot to Cold
  • Pain Senses: Sharp, Dull, Burning, Prickling
  • Proprioceptive Senses: Position in Space, Static and Kinesthesia (Moving Sense)

Question 2

What are 4 specific sensory receptors and their detection?

Answer 2

Sensory Receptors

• Types
  
  • Mechanoreceptors detect physical stimuli (i.e., touch, pressure, stretch of muscle, vibration, and proprioception)
  • Chemoreceptors detect chemical released (Co2 levels) or from food or odors
  • Thermoreceptors detect changes in temperature
  • Nociceptors detect damaged tissue or noxious stimuli; Associated with thermal, chemical, mechanoreceptors, joint and visceral receptors

Question 3

Name 3 superficial cutaneous mechanoreceptors.

Answer 3

Peripheral Nervous System: Sensory Receptors

Superficial Cutaneous Mechanoreceptors

• Meissner’s Corpuscles
  
  • Light touch discriminative sense
  • Vibration sense
• Merkel’s Disks
  
  • Pressure discriminative sense
• Hair Root Plexus (follicle nerve ending)
  
  • Light touch discriminative sense

Question 4

What are 2 subucutaneous mechanoreceptors?

Answer 4

Subcutaneous Mechanoreceptors

• Ruffini’s Endings
  
  • Continuous heavy touch (stretch of skin) and deep touch
• Pacinian Corpuscles
  
  • Deep touch and vibration

Question 5

What is a receptor field?

Answer 5

Receptor Fields and Receptor Adaptation

Receptor Fields

• Definition: A Sensory Representation of the Receptor Field in the Cerebral Cortex (Homunculus)
• Small Receptor Field for Fine Discriminative Senses has a Large Cortical Representation or Distribution (i.e., hand/fingers, feet, mouth/tongue)
• Large Receptor Field for Gross Discriminative Senses has a Small Cortical Representation or Distribution (i.e, lower and upper limbs, abdomen, and back)

Question 6

What is propriocetion?

Answer 6

• Definition: A feedforward and feedback loop among (three types) Muscle Spindles, Golgi Tendon Organs (GTOs), and Joint Receptors resulting in information about one’s position in space

Question 7

What is a muscle spindle?

Answer 7

Muscle Spindle (AKA Stretch Receptor)

• Definition: A proprioceptor located within skeletal muscle that provides constant feedback about changes in muscle length, muscle tension and muscle tone
• Comprised of:
  
  • Small Receptor Organ containing small muscle fibers AKA Intrafusal Muscle Fibers in a cigar shaped capsule or spindle
  • Note: Rest of skeletal muscle surrounding capsule AKA Extrafusal Muscle Fibers
  • As Extrafusal Muscle Fibers or skeletal muscle stretches, Intrafusal Muscle Fibers of Muscle Spindle stretches

Question 8

What is the intrafusal muscle fiber made of?

What does is control?

Answer 8

Muscle Spindle

Intrafusal Muscle Fibers

• Comprised of:
  
  • Nuclear Chain Fibers: Nuclei are lined up in a single file and respond to a new muscle length
  • Nuclear Bag Fibers: Nuclei are arranged more broadly and respond to changes in muscle length and velocity/rate of stretch

Question 9

What are the 2 mm spindle sensory endings?

Answer 9

Two Types of Muscle Spindle Sensory Endings

• Ia Primary Endings (On Bag and Chain Fibers) AKA Annulospiral Endings
• II Secondary Endings (On Chain Fibers) AKA Flower-Spray Endings

Question 10

What is the Sequence of Muscle Spindle Activity?

Answer 10

Sequence of Muscle Spindle Activity:

• Stretch occurs in Skeletal Muscle or Extrafusal Muscle Fibers
• Causes stretch of Intrafusal Muscle Fibers
• Note: Middle of the muscle spindle does not contract due to sensory region with Ia Primary and II Secondary Endings
• Results in firing of Ia Primary and II Secondary Endings
• Proprioceptive Sensory Information proceeds into Dorsal Horn of the Spinal Cord
• Ia and II fibers synapse with Alpha Motor Neuron (AMN) (AKA Lower Motor Neuron or Anterior Horn Cell) in Ventral Horn

Question 11

What are the 4 possible scenarios for the muscle spindle activity?

Answer 11

Then to one of 4 locations for: 4 scenarios

• Autogenic Excitation: AMN of same muscle AKA Agonist Muscle to facilitate muscle contraction
• Reciprocal Inhibition: AMN of opposing muscle AKA Antagonist Muscle to inhibit muscle contraction
• Renshaw Cells (Interneurons in Spinal Gray Matter) to inhibit synergistic movement and allow isolated muscle control (OOP- out of pattern or isolated mm movements) (pt who can’t isolate movements; messed up synergy motions)
• To Cerebellum (via Spinocerebellar and Cuneocerebellar Tracts) to relay information about muscle length and position to regulate movement

Question 12

Whats is a GTO? What is it’s sequence of activity?

Answer 12

Golgi Tendon Organ (GTO)

• Definition: A proprioceptor located at the junction of the muscle and tendon that provides information about and detection of muscle tension or force in the tendon of a contracting muscle
• GTO Sensory Endings
  
  • Ib Afferent Endings
• Prevents muscle from too forceful of a contraction
• Sequence of GTO Activity:
  
  • GTO detects muscle tension from contracting Agonist Muscle
  • Information sent along Ib Afferents into Dorsal Horn of Spinal Cord where Ib Afferents synapse with Interneuron
  • Interneuron synapses with Alpha Motor Neuron (AMN) in Ventral Horn of Spinal Cord

Question 13

What are the 3 possible scenarios for GTOs?

Answer 13

• Then to one of 3 locations for:
  
  • Autogenic Inhibition: Inhibit contraction of same muscle AKA Agonist Muscle
  • Facilitate contraction of opposing muscle AKA Antagonist Muscle
  • To Cerebellum (via Spinocerebellar and Cuneocerebellar Tracts) to provide proprioceptive information about posture

Question 14

What is a joint receptor and what are the 3 joint receptor endings?

Answer 14

Joint Receptors

• Definition: A specialized mechanoreceptor located in the joint capsule that provides information about one’s position in space
• Three types of Joint Receptor Endings
  
  • Ruffini Endings
    
    • Stretch of joint capsule
  • Pacinian Corpuscle
    
    • Movement of joint capsule
  • Ligament Receptor
    
    • Tension of joint capsule

Question 15

What is a gamma motor neuron? What is it’s sequence?

Answer 15

Relationship of Proprioception (Sensory System) to the Motor System

Introduction to Gamma Motor Neuron (GMN)

• Efferents and part of the Motor System
• Definition: Neurons that regulate muscle length and muscle tone
• GMN found in the Ventral Horn of Spinal Cord (with AMN/LMN) and innervates the Muscle Spindle

Sequence of GMN Activity:

• GMN stimulated in Ventral Horn
• Causes contraction of Bag and Chain Fibers of Muscle Spindle
• Ia Afferents fire causing AMN of Skeletal Muscle to fire
• Results in Contraction of Skeletal Muscle