PNS Flashcards
Mechanoreceptors
respond to touch, pressure, vibration, and stretch
Thermoreceptors
sensitive to changes in temperature
Photoreceptors
respond to light energy (example: retina)
Chemoreceptors
respond to chemicals (examples: smell, taste, changes in blood
chemistry)
Nociceptors
sensitive to pain-causing stimuli (examples: extreme heat or cold, excessive
pressure, inflammatory chemicals)
Exteroceptors
- Respond to stimuli arising outside body
- Receptors in skin for touch, pressure, pain, and temperature
Interoceptors (visceroceptors)
- Respond to stimuli arising in internal viscera and blood vessels
- Sensitive to chemical changes, tissue stretch, and temperature changes
- Sometimes cause discomfort but usually person is unaware of their workings
Proprioceptors
- Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue
coverings of bones and muscles - Inform brain of one’s movements
Receptors for the simple senses
- The special senses are Vision, hearing, equilibrium, smell, and taste
- All are housed in complex sense organs
Simple receptors for the general senses
- General senses include tactile sensations (touch, pressure, stretch, vibration),
temperature, pain, and muscle sense
-No “one-receptor-one-function” relationship but one type of receptor can respond to multiple stimuli
-These receptors are either Nonencapsulated (free) nerve endings or
Encapsulated nerve endings
Nonencapsulated (free) nerve endings (come back)
-abundant in epithelia and connective tissues.
* Most are nonmyelinated, small-diameter group C fibers; distal terminals have knoblike swellings
- Respond mostly to temperature, pain, or light touch
S e n s o r y P r o c e s s i n g
Survival depends upon:
* Sensation: the awareness of changes in the internal and external environment
* Perception: the conscious interpretation of those stimuli
Somatosensory system: part of sensory system serving body wall and limbs and Receives inputs from Exteroceptors, proprioceptors, and interoceptors - Input is then relayed toward head, but processed along the way
N e u r a l I n t e g r a t i o n in Somatosensory system
- Receptor level: sensory receptors
- Circuit level: processing in ascending pathways
- Perceptual level: processing in cortical sensory areas
Receptor Level Processing for Neural Integration
-Signal must be generated
-* For sensation to occur, the stimulus must excite a receptor, and the Action potential must reach CNS
-Transduction must occur where the Energy of stimulus is converted into graded potential called generator potential (encapsulated receptor) or receptor potential (special senses receptor) and reach threshold so that voltage-gated sodium channels on the axon are opened and nerve impulses are generated and propagated to the CNS.
-sensory receptors exhibit Adaptation which is the Change in sensitivity in presence of constant stimulus (For example, when you step into bright sunlight from a darkened room, your eyes are initially dazzled, but your photoreceptors rapidly adapt, allowing you to see both bright areas and dark areas in the scene)
-Phasic receptor = ast adapting, often giving bursts of impulses at the beginning and the end of the stimulus. Phasic receptors report changes in the internal or external environ- ment. Examples are lamellar and tactile corpuscles.
-Tonic receptors = provide a sustained response with little or no adaptation. Nociceptors and most proprioceptors are tonic receptors because of the protective importance of their
infonnation.
Circuit Level Processing for Neural Integration
- The axons of first-order sensory neurons, whose cell bodies are in the dorsal root or cranial ganglia, link the receptor and circuit levels of processing. -Central processes of first-order neu- rons branch diffusely when they enter the spinal cord and Some branches take part in local spinal cord reflexes
- Others synapse with second-order sensory neurons, which then synapse with the third-order sensory neurons that take the message to the cerebral cortex.
Perceptual Level Processing for Neural Integration
- Interpretation of sensory input depends on specific location of target neurons in sensory cortex
P a i n P e r c e p t i o n
- Warns of actual or impending tissue
damage so protective action can be taken
-Sharp pain is carried by the smallest of the myelinated sensory fibers, the A delta fibers, while burning pain is carried more slowly by small nonmyelinated C fibers.
-Both kinds of fibers release
neurotransmitters glutamate and
substance P - Some pain impulses are blocked by
inhibitory endogenous opioids (example:
endorphins - Pain tolerance
- Visceral and referred pain (results from noxious stimulation of receptors in the organs of the thorax and abdominal cavity - vague sensation of dull aching, gnawing, or burning - stimuli for visceral pain are extreme stretching of tissue, ischemia (low blood flow), irritat- ing chemicals, and muscle spasms - referred pain is when pain stimuli arising in one part of the body are perceived as coming from another part
P a i n P a t h o l o g i e s
- Long-lasting or intense pain, such as limb amputation, can lead to hyperalgesia (pain amplification), chronic pain, and phantom limb pain
–> NMDA receptors are activated by long-lasting or intense pain
–> Allow spinal cord to “learn” hyperalgesia
–> Early pain management critical to prevent
–> Phantom limb pain: pain felt in limb that has been amputated
–> Now use epidural anesthesia during surgery to reduce phantom pain
Classification of Nerves
- cranial or spinal depending on whether they arise from the brain or spinal cord.
-every nerve consists of parallel bundles of peripheral axons (some myelinated and some not) enclosed by successive wrappings of connective tissue
- Each axon is surrounded by endoneurium connective tissue that also encloses the fiber’s associated Schwann cells
