Chapter 13 Part 1) PNS

Question 1

Structres In the PNS

Answer 1

• All nerual Structures outside brain and Spinal Chord
  
  • Sensory Receptors
  • Afferent and Efferent Nerves and their Ganflia
  • Motor Endings

Question 2

Sensory Receptors

Answer 2

• Specialized to respond to changes in the environment (stimuli)
  
  • Triggers nerve impule with a graded potential
• Awarness of Stimulus (sensation) and interpretation of meaning of stimlus (perception) occur in brain
• Three ways to classify receptors
  
  • Type of Stimulus
  • Body location
  • Structural Complexity

Question 3

Sensory Receptors by Stimilus type

Answer 3

• Mechanoreceptors
  
  • respond to touch, pressure, vibration, and stratch
• Thermoreceptors
  
  • sensitive to changes in temperature
• Photoreceptors
  
  • respond to light energy (example: retina)
• Chemoreceptors
  
  • Respond to chemicals (smell, taste, changes in internal chemistry)
• Nociceptors
  
  • Senestive to Pain Causing Stimuli

Question 4

Sensory Recepetors by Locaction

Answer 4

• Exteroceptors
  
  • Stimilus outside body
  • Receptors in skin for touch, pressure, pain and temprature
  • Most receptors of our special senses (vision, tate, hearing, smell, equilibrium)
• Interoceptors (Visceroreceptors)
  
  • Respond to stililus from organs and blood vescels
  • Senative to chemical change, tissue stretch, and tempratue change
  • Sometimes cause doscomfort because person is unaware of workings around them,
• Proprioceptors
  
  • Inform brain of ones own movment (proprioception)
  • Respond to muscles, tendons and joints

Question 5

Sensory Recepors by Stucture

Answer 5

• Simple Receptors = General Senses
  
  • Modified dendritic endings of sensory nuerons
  • Found throuought the body and moniter most general sensory info
• Modified Receptors = Special Senses
  
  • Vison, hearing, equalibrium, smell, and taste
  • All found in complex sense organs

Question 6

Noncapsualated Nerve (free) endings

Answer 6

• Abundent in Epithelia Tissue and CT
• Most are nonmyelinated, small diameter fibers
• Respond mostly to changes in Temprature and pain.
  
  • some respond to pressure
• Temprature
  
  • Respond to cold temp (10-40 degrees C) superficial dermis
  • Respond to heat (32 to 48 degrees C) deeper dermis

Question 7

Ensapsulated Nerve Endings

Answer 7

• Almost all are Mechanoreceptors with a termial encased in connective tissue
• Diffrent Types
  
  • Tactile (Meissner’s) corpusles) small receptors involved in discriminative touch
    
    • Found in sensative epodermos areas
  • Lamellar (Pacinian) Corpsules) Resond to deep pressure and vibration when applied
    
    • turn off after a while
  • Bulbous Corpuscles (Ruffini Endings) Respond to deep and continous pressure. Found in dermis and hypodermis
  • Muscle Spindles) Proprioceptors that resond to muscle stretch in skeletal muscle
  • Tendon Organ) Proprioceptors in Tendon that detect streatch
  • Joint kinesthetic receptors) Proprioceptors that moniter joint position and motion

Question 8

Sensory Processing

Answer 8

• Our Survival depends on
  
  • Sensation) awarness of change in internal and external environment
  • Perception) Interpretation of Sensation

Question 9

Somatosensory system

Answer 9

• The part of sensory system serving the body wall and limbs
• Recives input from
  
  • Ecteroceptors
  • Interoceptors
  • Proprioceptors
• Input is relayed toward head but processed along the way
• Three levels of processing
  
  • Receptor level) at receprto
  • Circut Level) in ascending pathways
  • Perceptual Level) in cortical sensory areas.

Question 10

Processing at the Receptor Level

Answer 10

• First a Stimilus must exite a receptor and the AP must reach CNS
• For this to happen

1. Stimulus energy must match receptor
   
   • Touch receptors will not respond to light
2. Stililus must be applied withinn a sensors receptive feild
   
   • Smaller the feild= better ability to localize site
3. Tranduction must occur
   
   • Energy of stimilus is converted into graded potetial
   • Generator potential) general receptors
   • Receptor potential) special sense receptor
4. Graded Potenial must cross threshold to generate AP

Question 11

Adaptation of Sensory Receptors

Answer 11

• Change in sensitivity in the presance of a constant stimulus
  
  • Eyes ajusting to outside light is example
• Receptor Membranes become less responsive and potentials decline in frequency or stop.
• Two Types
  
  • Phasic Receptors (fast-adapting)
  • Tonic Receptors) Adapt slowly or not at all
    
    • Nociceptor and most propioceptors

Question 12

Processing at the Circut Level

Answer 12

• Pathways of Three Nuerons conduct sensory impuleses received from receptors upward to appropriate cortucal regions
  
  • First Order Sensory Nuerons) Conduct impulses from receptor to spinal level or second order nueron in CNS
  • Second Order Sensory Nuerons) Transmit impules to Third Order Nuerons (Internuerons)
  • Third Order Sensory Nuerons) Conduct Impulses from Thalamus to Stomosensory cortex (perception)

Question 13

Processing at the Perceptual Level

Answer 13

• Interpretaion of Sensory Stimilus depends on the location of the nuerons in the Sensory Cortex (brain)
• Aspects of Sensory Perception
  
  • Perceptual Detection) ability to detect a stimlus (summation)
  • Magnitude Estimation) Ability to detect how intense a stimilus is
  • Spatial Discrimination) Ability to determine the site or pattern of stimilus
  • Feature Abstraction) Indentifcation of several stimulus properites (ex: texture of velvet is diffrent than texture of linnen)
  • Quality Discrimination) able to identify submodalitys of a sensation (ex; Sweet vs sour, loud vs quiet)
  • Pattern Recoginition) Recognition of familiar or signifigant patterns

Question 14

Perception of Pain

Answer 14

• Warning of Impending or Current Tissue damage
  
  • occurs so preventative actions can be taken
• Pain Receptors are activated by
  
  • Extreme Pressure and Temprature changes
  • Chemicals released frominjured tissue
• Nuerotransmiters that iniate pain resposne
  
  • Glutamate and Substance P
• Pain Suppresion
  
  • The brain can supress pain with opoids such as endorphins and enkephalins
  • Descending fibers release enkephalins; an inhibitory nuerotranmitter
• Pain Tolerance
  
  • We all percive pain at the same intensity, but our tolerance to pain differs from person to person

Question 15

Phantom Limb Pain

Answer 15

• Long Lasting or Intense pain can lead to hyperglasia (pain amplification)
  
  • Spinal chord will “learn” hyperaglesia and will send pain signals even if not there
  • This is why early pain managment is critical
• Phantom Limb Pain
  
  • Pain felt in limb that has been amputated due to hyperalgesia
  • Due to spinal chord still reveiving pain signals during amputation
  • Epidural Anesthetics are now used to block nuerotranmison in the spinal chord which reduces the likliness of phantom limb pain.

Question 16

Visceral and Referred Pain

Answer 16

• Visceral Pain) results from stimulation of visceral organ receptors
  
  • Felt as aching, gnawing, bruning
  • Activated when tissues streath, chemicals release, and muscle spasms.
• Referred Pain) Pain from one body region perceived as coming from a diffrent region
  
  • Visceral and Somatic fibers travel on same nerve so the brain can confuse visceral pain as coming from a common somatic area
  • EX) heart attack pain felt in left arm

Question 17

Structure of a Nerve

Answer 17

• Nerve) Cordlike organ found in PNS
  
  • Bunde of myelinated and unmylinated axons enclosed in CT
• Classified as either Spinal or Cranial depending on origin
• Connective Tissuse Coverings
  
  • Endonuerium) Loose CT that enclosed axons and myelin sheaths
  • Perineurium) Coarse CT that bundles fibers into Fasicles
  • Epineurium) Tough Fibrous Sheath around all fassicles which forms a nerve

Question 18

Structure and Classification of Nerves

Answer 18

• Most Nerves are mixtures of Afferent and Efferet fibers and Somatic and Autonomic (visceral) fibers.
• Classified accoring to direction impules move
• Types of Nerves
  
  • Mixed Nerves) Both Sensory and Motor Fiber. Send impules to and from CNS
  • Sensory (affrent) Nerves) sends impules only to CNS
  • Motor (efferent) Nerves) receives impules from CNS
    
    • Pure Sensory or Motor are rare, Most are mixed
• Types of Fibers in Mixed Nerves
  
  • Somatic Afferent (Muscle Sensory receptors to CNS)
  • Somatic Efferent (Motor cortex in CNS to muscle)
  • Visceral Afferent (Visceral sensory receptors to CNS)
  • Visceral Efferent (Motor area in CNS to organs)

Question 19

Ganglia

Answer 19

• Ganglia contain Nueron Cell Bodies associated with nerves in PNS
• Afferent Nerve Fibers
  
  • Dorsal root ganglia (Sensory)
  • contain sensory nuerons
• Efferent Nerve Fibers
  
  • Ventral root ganglia
  • Cotain Motor nuerons

Question 20

Regeneration of Nerve Fibers

Answer 20

• Nuerons are amitotic but if soma (cell body) is intace reganeration may occur
• CNS Axons) Will not regenerate. This is why spinal chord injuries are devestating and paralysis occurs
  
  • Oligodendrocytes contain growth-inhibiting protiens
• PNS axons) Will regenrate if damage is not severe
  
  1. Axon Fragmans and Mylin Sheaths distal to injury degenerate
     
     • Spreads down axon
  2. Macrophages clean up dead axon debris; Schwann cells begin to divide
  3. Axon Filaments grow through regenreation tube
  4. Axon regeneartes and new myelin sheath forms
• The greater the distance between severed ends the worse the chance of regenration is

Question 21

Cranial Nerves

Answer 21

• Twelve nerves associated with the brian (I to X11)
  
  • most are mixed, two are sensory
• On occasion, our trusty truck acts funny—very good
  vehicle anyhow. (Memonic)

Question 22

Olfactory Nerve (I)

Answer 22

• Sensory) Nerves of sense of smell
• Location
  
  • Run from nasal mucosa to olfactory bulbs
  • Pass through cribriform plate of ethmoid bone
  • Fibers synapse in olfactory bulbs
  • Pathway terminates in primary olfactory cortex
• Purley Sensory (Olfaction)
  
  • carry afferent impules for smell.

Question 23

Optic Nerves (II)

Answer 23

• Purley Sensory (Visual)
• Origin) Retinas
• Pass through opic canals and cross over at optic chaisma
• Synapse in thalamus, then fibers run to Visual Cortex

Question 24

The Oculomotor Nerves (III)

Answer 24

• Purly Motor
  
  • raises eyelids, directing eyeball
  • Constricts iris and controls lense shape (parasympathetic)
• Fibers extend from ventral midbrain through superior orbital fissures to eye muscles

Question 25

Trochlar Nerve (IV)

Answer 25

• Purly motor
  
  • Primary motor nerve that directs eyeball
  • Innervates one of the superior oblique muslces
• Fibers orginate in Dorsal midbrain and enters orbit via superior orbital fissue

Question 26

Trigeminal Nerves (V)

Answer 26

• Mixed Nerve. Three divisons
  
  • Opthalimic (V1) Sensory impules from areas of the face
    
    • Passes through superior orbital fissures
  • Maxillary (V2) Sensory impules from area of face
    
    • Passes through framen rotundum
  • Mandibular (V3) Mastication
    
    • Passes through froamen ovale.
• Largest cranial Nerve. Orginates at Pons

Question 27

Abducens Nerves

Answer 27

• Primarily Motor) moves eye muscle
  
  • Innervates the Lateral Rectus Muscle in eye

Question 28

Facial Nerves (VII)

Answer 28

• Mixed Motor Nerve
  
  • Motor) Facial expression, i
    
    • Impluses to tear and salivary glands (parasumpathetic)
  • Sensory) Taste, convays sensory impules from anterior two-thirds of tounge.
• Mixed nerve with five pathways
  
  • Temporal, Zygomatic, Buccal, Mandibular, and Cervical

Question 29

The Vestibulocochlear Nerves (VIII)

Answer 29

• Mixed Nerve
  
  • MOSTLY SENSORY) hearing receptors and equilibrium receptors
  • small motor componant for adjsutment of sensors
• Fibers orginate from receptors and pass through innear ear at acusitic meatisus and insert on brain stem at pons/medulla border
• Formally the auditory nerve

Question 30

The Glossopharyngeal Nerves (IX)

Answer 30

• Mixed Nerve
  
  • Motor function) innervate part of tounge and pharynx for swallowing
    
    • Provide parasympathetic fibers to activate salivary glands
  • Sensory Funtion) Taste and general impules from pharune and posterior tounge
    
    • Impules from chemoreceptors and baroreceptors
• Fibers Run from Medulla through the jugular froamen and run to the throat.

Question 31

Vagus Nerves (X)

Answer 31

• Only Nerve that Leaves head
• Fibers run from medulla and exit via jugular froamen to heart, lungs, and abdominal viscera
• Mixed Nerve
  
  • Motor Functions) Parasympathetic activities of heart, lungs, and abdominal organs
  • Sensory Funtion) Impules from thoracic and abdominl organs
    
    • Baroreceptors, chemoreceptors, and tastebuds of posterior tounge and pharynx (same as IX)

Question 32

Accessory Nerves

Answer 32

• Mostly Motor Function
  
  • Innerviates Trapezius and Sternocleoidmastoic muscles
• Orginated from ventral rootlets of C1-C5 region of spinal chord. Rootlets go up each froamen magnum and exit via the jugular froman and insert on the mucles mentioned.

Question 33

Hypoglossal Nerve (XII)

Answer 33

• Motor Function
  
  • Innerviate mucles of tounge that contribute to speach and swallowing
• Fibers exit medulla via hypoglossal canal.

Question 34

Composition Of Cranial Nerves

Answer 34

• Special Sensory
  
  • Olfactory and Optic Nerves
• Sensory Nuerons
  
  • V,VII, IX, X
• To remember primary functions as motor, sensory or both
  
  • “Some say marry money, but my brother believes (it’s) bad business (to) marry money.”