7.1 Peripheral nervous system Flashcards
explain division of the PNS -> what are the two main divisions?
- two main divsions= sensory (afferent) and motor (efferent)
describe sensory recpetors
- 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
how are sensory receptors classified?
- Functionally by type of stimulus detected
- Location of stimulus
- Structural complexity
what are the subcategories of the functionality by type of stimulus detected
-
Nociceptors: pain receptos
- myelinated type A fibers: carry sensations of fast pain
- unmyelinated type C fibers: carry sensations of slow pain
- Thermoreceptors: temerapture receptors
- Chemoreceptors: respond to water soluble and lipid soluble substances dissolved in body fluids
-
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
what are the subcategories under location of stimulus
- Exteroceptors
- Interoceptors (visceroceptors)
- proprioceptors
describe exteroceptors
* receptor classification describe by location of stimulus
- Respond to stimuli arising outside body
- Receptors in skin (touch, pressure, pain, & temperature) & most special sense organs
describe interoceptors
*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
descirbe proprioceptors
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
what are the subcategories under the calssification by strutural complexity
- classified as unencapsulated nerve endings vs encapsulated nerve endings
Describe unencapsulated nerve endings
- 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
describe encapsulated enrve fibers
- subcategory within the receptor classification by structural complexity
- all are mechanoreceptors
- enclosed by connective tissue capsule
describe hair follice receptors
*uncapsulated dendritic endings (classified by structural complexity)
Mechanoreceptors wrapped around hair; activated by deflection of hair
-Rapidly adapting
describe free nerve endings
*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)
describe merkel discs
*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
can are the types of encapsulated dendritic endings?
-
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
what encapsulated dendritic endsings are fast adapting vs slow adapting?
which are superfiical vs deep?
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
muscle spindles, (golgi)tendon organs and joint kinestheric recptoers have ____ dendritic endings
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
sensation vs preception
sensation: awareness of changes in internal & external environment
Perception: conscious interpretation of stimule (how we choose to respond)
what are the 3 basal levels of neural integration in sensory systems
- receptor level: sensory reception and transmission to CNS
- Circuit level: processing in ascening pathways
- 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
Describe the criteria required for generation of a signal for processing at the receptor level
- 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
describe adaptation for processing at receptor level
- 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
Describe processing at Cirucit level
- pathway of 3 neurons conduct sensory impulses received from receptors upward t appropriate cortical regiosn
what is processing at the perceptual level
interpretation of sensory input depends on specific location of target neurons in sensory cortex
what is perceptual detection
* aspects of sensory perception
ability to detect stimulus (pick up that a change occured)
what is magnitude estimation
aspects of sensory perception
- intensity coded in frequency of impulses
What is spatial discrimination
aspects of sensory perception
- indentifying site or pattern of stimulus
what is feature abstraction
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)
what is quality discrimination
aspects of sensory perception
*higher order processing
- ability to identify submodalities of a sensation (ex sweet vs sour taste)
what is pattern recognitiion
aspects of sensory perception
*higher order processing
- recognition of familiar or significant patterns in stimuli
describe perception of pain
- 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)
describe the gate control theory of pain modulation
- 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
Describe descending pain conrol in pain modulation
- 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
Describe homeostatic imbalance
- 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
What is Phantom limb pain
- felt in limb no longer present
- now use epidural anesthesia to reduce
anesthetic at spinal chrod, prevents pain transmittion during amputation
describe visceral pain
- visceral pain results from stimulation of visceral organ receptors
- felt as vauge aching, snawing, curning (not precise, poorly localized, v general)
describe referred pain
- pain from one body region perceived as coming from a different region
(bdoy misinterprets the source)
describe the regeneration of nerve fibers
- 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
why cant nerve fibers in the CNS be regenerated?
CNS oligodendrocytes bear growth-inhibiting proteins & astrocytes form scar tissue that prevent CNS fiber regeneration
describe the process of axon regeneration to damaged nerve cell
* only in PNS
1. axon becomes fragmented at injury site
- Macrophages clean out dead axon distal to injury
- axon sprouts (of filaments) grow through regeneration tube formed by Schwann cells
- Axon regenerats & a new myelin sheath forms
how are peripheral nerves classifed
cranial (comes off brain) or spinal (off spine)
*msot nerves are mis of afferent and efferent somatic and autonomic visceral fibers
