Sensory System Flashcards
What are the typical large and medium sized, myelinated fibers of spinal nerves?
Type A: alpha beta gamma delta
What are the small, unmyelinated fibers that conduct impulses at low velocities?
Type C
Which fibers constitute more than half of the sensory fibers in most peripheral nerves as well as postganglionic autonomic fibers?
Type C
Pain is felt through which fibers?
Type A and C
Sensory functions of Type C fibers
Crude touch/pressure
Tickle
Aching pain
Cold/warmth
Sensory functions of type A alpha fibers
Muscle spindle Muscle tendon Hair receptors Vibration (pancinian) High discrimination touch (meissner's)
Sensory functions of type A gamma fibers
Muscle spindle Hair receptors High discriminatory touch Prickling pain Deep pressure and touch Cold
Sensory functions of type A delta fibers
Deep pressure and touch
Prickling pain
Cold/warmth
Motor functions of type A alpha fibers
Skeletal muscle
Motor functions of type A gamma fibers
Muscle spindle
Motor functions of type C fibers
Sympathetic
Labeled Line principle
Nerve fibers are specific for transmitting only one modality of sensation. ie: pain receptors will only sense pain.
Types of sensory receptors based on function (5)
Mechanoreceptors Thermoreceptors Nociceptors Photoreceptors Chemoreceptors
5 types of mechanoreceptors
Skin tactile - dermis and eipdermis, free nerve ending (Merkel’s discs, Ruffini’s endings, Meissner’s and Krause’s corpuscles)
Deep tissue - Muscle spindles, golgi tendon receptors (Ruffini’s endings, Pancinian corpuscles)
Hearing - sound receptors of cochlea
Equilibrium/balance - Vestibular receptors
Arterial - baroreceptors of carotid sinuses and aorta
Function of thermoreceptors
Feeling temperature (warm and cold) Free nerve endings
Function of nociceptors
Pain receptors
Free nerve endings
Function of photoreceptors
Vision
Rods and cones
6 types of chemoreceptors
Taste - taste buds
Smell - olfactory epithelium receptors
Arterial O2 - aortic and carotid sinus
Osmolality - neurons in/near supraortic nuclei
Blood CO2 - in/on surface of medulla and in aortic and carotid bodies
Blood Glu, AA, FA - in hypothalamus
Muscle spindle and golgi tendon are what kind of receptors?
mechanoreceptors
What kind of receptor consists of an encapsulated, intrafusal group of 3-12 small skeletal muscle fibers buried among extrafusal fibers, that detects muscle length/stretch?
Muscle spindle
What are the functions of the ends and middle of the muscle spindle?
Ends: contractile elements innervated by Type A gamma fibers
Middle: innervated by sensory neurons, send info about muscle stretch to CNS
What is the purpose of muscle spindles?
Correct for changes in muscle length
What kind of mechanoreceptor is an encapsulated sensory receptor that 10-15 muscle fibers pass through, and detects muscle tension?
Golgi tendon
How does the Golgi tendon receptor prevent excess muscle tension?
Provides insight to NS on degree of tension, then prevents excess tension via inhibitory interneurons in the spinal cord
4 ways to stimulate a receptor potential
- Mechanical deformation
- Application of a chemical to a membrane
- Changing the temperature of the membrane
- Effects of electromagnetic radiation (light on a retinal visual receptor)
What is acuity?
The precision of a stimulus location. Smaller locations have greater acuity (lip vs back with 2 pressure points)
What is receptor amplification?
Up regulation. Intensity of stimulus is increased by the frequency of action potentials or number of receptors activated. The more the receptor potential rises above the threshold, the greater the action potential frequency.
What is receptor adaptation?
Down regulation of a sensory receptor to a constant stimulus (resting hand on a table). If there is no change in pressure, the receptor won’t send signals.
Do pain receptors adapt?
No (usually)
Tonic receptors
Slow adapting, continue to transmit impulses for minutes or hours (baro and chemoreceptors)
Phasic receptors
Fast adapting, stimulated only when stimulus strength changes (pancinian)
Somatic sensations
touch
pain
temperature
body position
Visceral sensations
stretch
distention
spasm
inflammation and ischemia
Definition of pain
perception of a noxious stimulus
What is a nociceptor?
Pain receptor
Free nerve ending
Where are nociceptors found?
Superficial layers of skin Periosteum Arterial walls Joint surfaces Areas of the skull
What types of nerve fibers sense pain?
Type A delta - fast pain
Type C - slow pain
What kind of nerve fiber senses fast pain like a needle stick that could cause tissue damage, and responds quickly?
Type A delta
What kind of nerve fiber senses slow pain, relating to tissue destruction and suffering, and responds slowly?
Type C
Since there are multiple, bilateral paths for conveying noxious stimuli to the brain, what does a loss of nociception mean for the patient?
Extensive destruction of spinal cord, very poor prognosis
What are the 3 stimuli that excite pain receptors?
Mechanical (fast/slow)
Thermal (fast/slow)
Chemical (slow only)
How can pain be modulated by encephalin and endorphins?
By binding to opiate receptors, they can terminate the signal by inhibiting the release of neurotransmitters from the presynaptic terminal.
*morphine also works in this way
How can inhibitory interneurons help modulate pain?
Pinprick axons work with inhibitory interneurons to stop the pain signal quickly
What is proprioception?
Knowledge of one’s position
What kind of receptors are used for proprioception?
Skin tactile
Deep receptors near joints
Hair cells
Cranial nerves V and VIII
Skin tactile and deep receptors (4)
Muscle spindles
Golgi tendon
Pacinian corpuscles (deep pressure)
Ruffini’s endings (continuous pressure)
What do the hair cells in the vestibular apparatus of the inner ear do?
Supply information about head position and movement
Proprioception of the head, its muscles, and joints uses mainly what cranial nerves?
V - trigeminal
VIII - vestibulochochlear
Conscious proproception
conscious awareness of body position and movement of body parts
What type of proprioception is based around stretch and tension of muscles, tendons, and ligaments while at rest and during movement, and spatial orientation of the body?
Subconscious proprioception
What enables the cerebral cortex to plan and refine voluntary and learned movement
conscious proprioception
How does the cerebellum get info it needs to coordinate posture and locomotion?
subconscious proprioception
Role of vestibular system in proprioception
Provides info about head position and movement to set balance and posture
“Knuckling” indicates a problem with…
conscious proprioceptive pathway
If a patient is not able to keep its limbs under its center of gravity, this indicates a dysfunction with the…
subconscious proprioceptive pathway
Visceral receptors detect…
change in visceral structures due to abnormal physical and pathological conditions
Limitations of visceral receptors
Not sensitive to cold/heat/cutting
Few general afferent fibers - pain is poorly localized
Types of physiological receptors in the viscera
Mechanoreceptors
Chemoreceptors
What mechano/chemoreceptors in the viscera respond to?
Change in BP
Change in pO2/pCO2
Coughing reflex
Sense of fullness (stomach or bladder stretch)
Physiologic receptors send info through viscerosensory fibers of…
Parasympathetic nerves
Nociceptors send info through viscerosensory fibers of…
Sympathetic nerves
