7.1 Peripheral nervous system

Question 1

explain division of the PNS -> what are the two main divisions?

Answer 1

• two main divsions= sensory (afferent) and motor (efferent)

Question 2

describe sensory recpetors

Answer 2

• specialized to respond to changes in their environment
• Receptors have specificity for stimulus energy (ex retina can only pick up light, cant feel light)
• stimulus must be appleid in a recpetive field
• transduction occurs:
• > stimulus energy is converted into a graded potential
• > must reach threshold for nerve impulse

Question 3

how are sensory receptors classified?

Answer 3

1. Functionally by type of stimulus detected
2. Location of stimulus
3. Structural complexity

Question 4

what are the subcategories of the functionality by type of stimulus detected

Answer 4

1. Nociceptors: pain receptos
   
   • myelinated type A fibers: carry sensations of fast pain
   • unmyelinated type C fibers: carry sensations of slow pain
2. Thermoreceptors: temerapture receptors
3. Chemoreceptors: respond to water soluble and lipid soluble substances dissolved in body fluids
4. Mechanoreceptors: sensitive to stimuli that distory plasma membranes (mechanicaly gated ion channels)
   
   • proprioceptors: monitor position of joint and muscles
   • Baroreceptors: detect pressue changes
   • Tactile receptors: provide sensations of touch, pressure and vibration

Question 5

what are the subcategories under location of stimulus

Answer 5

1. Exteroceptors
2. Interoceptors (visceroceptors)
3. proprioceptors

Question 6

describe exteroceptors

Answer 6

* receptor classification describe by location of stimulus

• Respond to stimuli arising outside body
• Receptors in skin (touch, pressure, pain, & temperature) & most special sense organs

Question 7

describe interoceptors

Answer 7

*receptor type describred by location of stimulus

aka viscerocepors

*stim inside the body

• Respond to stimuli arising in internal viscera & blood vessels
• Sensitive to chemical changes, tissue stretch, & temperature changes

Question 8

descirbe proprioceptors

Answer 8

receptor type describred by location of stimulus

• Respond to stretch in skeletal muscles, tendons, joints, ligaments, & connective tissue coverings of bones & muscles
• Inform brain of one’s movements

Question 9

what are the subcategories under the calssification by strutural complexity

Answer 9

• classified as unencapsulated nerve endings vs encapsulated nerve endings

Question 10

Describe unencapsulated nerve endings

Answer 10

• subcategory within the receptor classification by structural complexity
• Not protected by accessory structures

Present throughout body (abundant in epithelial & connective tissue)

• Mainly group C-fibers (slow)
  include: hair follice receptors, free nerve endsings and merkel discs

Question 11

describe encapsulated enrve fibers

Answer 11

• subcategory within the receptor classification by structural complexity
• all are mechanoreceptors
• enclosed by connective tissue capsule

Question 12

describe hair follice receptors

Answer 12

*uncapsulated dendritic endings (classified by structural complexity)

Mechanoreceptors wrapped around hair; activated by deflection of hair

-Rapidly adapting

Question 13

describe free nerve endings

Answer 13

*uncapsulated dendritic endings (classified by structural complexity)

• thermoreceptors: Cold receptors (10-40 Csuperficial; Heat receptors (32-48 C) deeper
• mechanoreceptors: pressure
  chemoreceptors: itch (histamine), pH
• Nociceptors: pinching, chemicals frmo damages tissue, extreme temps, capsaicin (spicy)

Question 14

describe merkel discs

Answer 14

*uncapsulated dendritic endings (classified by structural complexity)

* in deepest skin epithelial layer

• Mechanoreceptor for light steady pressure
• Tactile cell in basal layer of epidermis
• Slowly adapting

*can also esist as capsulated

Question 15

can are the types of encapsulated dendritic endings?

Answer 15

• Meissners corpuscles:
  
  • ​light pressure, discriminative touch, low freq vibrations
  • dermal papillae of hairless skin
• Pacinian corpsulces
  
  • deep pressure, stretch, high freq vibration
  • dermis and hypodermis
  • big onions
• Ruffini endings:
  
  • deep continuous pressure and stretch
  • dermis, hypodermis, joint capsule
• Markel discs
  
  • mechanoreceptor for light steady pressue
  • basal layer of dermid

Question 16

what encapsulated dendritic endsings are fast adapting vs slow adapting?

which are superfiical vs deep?

Answer 16

Meissner corpuscles: superfiical and fast adapting

Merkel cells: superficial and slow adapting

Pacinian corpuscles: Deep and fast adapting

Ruffini endings: deep and slow adapting

*fast adapting gives tingling and vibratory sensations

*slow adapting gives snesations of steady pressure

Question 17

muscle spindles, (golgi)tendon organs and joint kinestheric recptoers have ____ dendritic endings

Answer 17

ecapsulated dendritic endings

muscle spindles: do muscle stretch and skeletal uscle perimysium

Golgi tendon organs: strench in tnedond

Joint kinestheic receptors: stretch in articular capsules

Question 18

sensation vs preception

Answer 18

sensation: awareness of changes in internal & external environment

Perception: conscious interpretation of stimule (how we choose to respond)

Question 19

what are the 3 basal levels of neural integration in sensory systems

Answer 19

1. receptor level: sensory reception and transmission to CNS
2. Circuit level: processing in ascening pathways
3. Perceptual level; processing in cortical sensory centers

*input comes in from receptors and is processed (moves thru NS) as it is relayed towards the brain

Question 20

Describe the criteria required for generation of a signal for processing at the receptor level

Answer 20

• for sensation to occur, stimulus must excit receptor, and AP must reach CNS
• stimulus energy must beapplied within receptive field
• transduction must occur: energy of stimulus is converted into graded potential
• > generator potential in general receptors
• > receptor potential in psecial sense receptors
• graded potentials must reach threshold -> AP

Question 21

describe adaptation for processing at receptor level

Answer 21

• Adaptation: Change in sensitivity in presence of constant stimulus
• > receptor memrbanes become less responsive
• recpeotr potential decline in freq or stop
• phasic receptors (fast adapting) send signals at beginning or end fo stimulus
  ex: receptors for pressure, touch, and smell (quickly get used to smell)
• tonic receptors: adapt slowly or not at all (dont want fast adaption to pain)
  ex: nociceptors and most proprioceptors

Question 22

Describe processing at Cirucit level

Answer 22

• pathway of 3 neurons conduct sensory impulses received from receptors upward t appropriate cortical regiosn

Question 23

what is processing at the perceptual level

Answer 23

interpretation of sensory input depends on specific location of target neurons in sensory cortex

Question 24

what is perceptual detection

Answer 24

* aspects of sensory perception

ability to detect stimulus (pick up that a change occured)

Question 25

what is magnitude estimation

Answer 25

aspects of sensory perception - intensity coded in frequency of impulses

Question 26

What is spatial discrimination

Answer 26

aspects of sensory perception - indentifying site or pattern of stimulus

Question 27

what is feature abstraction

Answer 27

aspects of sensory perception \*higher order processing - indentification of more complex aspects and several stimulus porperties (ex: velvet is warm, compressible and smooth but not completely continuous)

Question 28

what is quality discrimination

Answer 28

aspects of sensory perception \*higher order processing - ability to identify submodalities of a sensation (ex sweet vs sour taste)

Question 29

what is pattern recognitiion

Answer 29

aspects of sensory perception \*higher order processing - recognition of familiar or significant patterns in stimuli

Question 30

describe perception of pain

Answer 30

- warns of actual or impending damage - stimuli include: extreme pressure and temp, chemicals released by tissues (histamine, K+, ATP, acids, bradykinin) - impulses travel onL thinly myelinated Aδ fibers -\> release glutamate (fast pain) - unmyelinated C fibers release glutamate + substance P (pain substance, these are slow apin)

Question 32

describe the gate control theory of pain modulation

Answer 32

- non painful inputs (Aβ) inhibit pain transmission (C fibers) \*if hammer hits hand, you rub/touch it - \> slow pain comes in and synpases on ascending neurons get a strong painful stimulus to brain - \> have a tonically active inhibitory interneuron -\> if touch/non painful stim you increase firing of the Aβ fiber and get inhibiton of the pain transmission form C fiber - \> get less pain sensation to the brain

Question 33

Describe descending pain conrol in pain modulation

Answer 33

- some pain impulses are blocked by inhibitory endogenous opioids (endorphins and enkephalins) - **descening fibers** from cortex and hypothalamus release inhibitory neurotransmitters that suppress pain signals \*if a lot of activation in hypothalamus in stressful situation you dont realize you are in pain bc signals are repressed \* pain suppression occurs ar **periaquductal gray**

Question 34

Describe homeostatic imbalance

Answer 34

- long lasting/intense pain -\> hyperalgesia (pain amplification), chronic pain and phantom limb pain \*pathways used again and again, circuit becomes stronger and more efficiency in pian transmission -\> learn pain, can lead to chornic pain - modulated by NMDA receptors - allow spinal chord to "learn" hyperalgesia \*early pain management is critical

Question 35

What is Phantom limb pain

Answer 35

- felt in limb no longer present - now use epidural anesthesia to reduce **anesthetic at spinal chrod, prevents pain transmittion during amputation**

Question 36

describe visceral pain

Answer 36

- visceral pain results from stimulation of visceral organ receptors - felt as vauge aching, snawing, curning (not precise, poorly localized, v general)

Question 37

describe referred pain

Answer 37

- pain from one body region perceived as coming from a different region (bdoy misinterprets the source)

Question 38

describe the regeneration of nerve fibers

Answer 38

- mature neurons are amitotic - if soma of damaged nerve is intact, axon can regenerate \*if damage body of nerve it cant regenerate - involves coordinated activity between: macrophages, schwann cells and axons

Question 39

why cant nerve fibers in the CNS be regenerated?

Answer 39

CNS oligodendrocytes bear growth-inhibiting proteins & astrocytes form scar tissue that prevent CNS fiber regeneration

Question 40

describe the process of axon regeneration to damaged nerve cell

Answer 40

\* only in PNS 1. axon becomes fragmented at injury site 2. Macrophages clean out dead axon distal to injury 3. axon sprouts (of filaments) grow through regeneration tube formed by Schwann cells 4. Axon regenerats & a new myelin sheath forms

Question 41

how are peripheral nerves classifed

Answer 41

cranial (comes off brain) or spinal (off spine) \*msot nerves are mis of afferent and efferent somatic and autonomic visceral fibers