SDL: Sensory receptors Flashcards
the three groups of sensory receptors
- exteroreceptors a. telereceptors b. contact receptors
- interoceptors
- proprioceptors
what do exteroceptors (teleceptors and contact receptors) sense?
signals that come from outside of the body (contact receptors: heat, cold, touch, pressure; teleceptors: sound to the ears, light to the eyes, chemicals to the nose)
what do interoceptors sense?
blood vessel and viscera signals
what do proprioceptors sense?
signals from somatic structures that contribute to sense of orientation and movement of the body in space
these three sensory receptors detect tactile stimuli
meissner’s corpuscle, hair follicle receptor, Merkel disc receptors
what do free nerve endings function as?
thermoreceptors, some also function as nociceptors that detect noxious stimuli
what two receptors detect displacement of the skin?
pacinian corpuscle (deep touch), Ruffini ending (stretching of the skin)
what happens when the pacinian corpuscle is stimulated?
an ion channel will open that leads to formation of a “generator potential” with graded and non-propagating potentials
describe the generator potential
the potential generated depends on the intensity of the stimulus; the info does not propagate along the sensory neuron buried inside
how is a stimulus to the pacinian corpuscle transmitted along the neuron?
when its strong enough, the AP is generated and propagated along the sensory neuron. during this, a mechanical signal is converted into an electric signal and transmitted
how does an AP tell the brain what is actually happening on the skin?
neuronal coding created by a series of APs that encode intensity, velocity, and duration of the stimuli
describe pattern theory of sensation
pattern created by series of APs by a single group of sensory fibers to tell the brain the nature of the stimulus
describe the specific nerve energies theory of sensation
each receptor is sensitive to a particular stimulus (adequate stimuli OR specific energy)
what is sensory adaptation?
sensory receptor decreases its firing frequency after being exposed to the stimulus constantly for a while
receptors that completely adapt to the stimulus, i.e. stop firing after some time
phasic receptor
receptors that continue to fire as long as the stimulus is present
tonic receptor
when the brain pays less attention to a constant stimulus, regardless of the fact that the receptor is firing
habituation
the area of the body from which a stimulation influences the discharge rate of that neuron
receptor field (small on finger tips, large on back of the torso)
the ability to tell whether the skin is stimulated by one or two points
two-point discrimination (easy on finger tip, poor on the back)
why should we care about two-point discrimination?
if there is a lesion somewhere in the sensory receptor to brain pathway, it will cause poor two-point discrimination
neural syphilis can destroy..
the dorsal column of the spinal cord, thus making the patient show a very poor two-point discrimination
relative size of nerve fiber types from greatest to least
A>B>C
which nerve fiber type has the slowest speed?
dorsal root: pain, reflex responses
pain is transmitted by which two fiber types?
dorsal root (C), A-delta (pain, temp, touch)
somatosensory receptors send the info through..
A-beta, A-delta, and C
relative conduction velocity of nerve fiber types from greatest to least
A>B>C
what activates the nociceptors (free nerve endings)?
noxious mechanical, thermal, or chemical stimuli will activate the nociceptor and cause pain
describe pricking pain: also called? fiber type? easy to localize?
fast pain, first pain; A-delta; yes
describe burning pain: also called? fiber type? easy to localize?
slow pain, second pain; C; no.
what does lidocaine block? what type of pain does it block?
Na+ channels on C (pain) fibers; burning, slow, second pain.
subtances released during tissue damage
bradykinin, serotonin, histamine, K+, acids, ACh, proteolytic enzymes, prostaglandins, substance P
what leads to hyperalgesia after tissue damage?
prostaglandin and substance P release, which increase the sensitivity of nerve endings that causes a sensitive or painful area during the healing process
the characteristics of the triple vascular response
redness (local vasodilation), flare (vasodilation), weal (edema)
two muscle receptors and their locations
- Golgi tendon organ (in the tendon of a muscle) 2. muscle spindle (in the belly of skeletal muscle mass)
how is the Golgi tendon organ arranged? what does it detect? what nerve fiber does it use to send info?
series with the muscle mass; detects tension; sends info by the I-b nerve fiber (type of A-alpha)
regular muscle fibers that can contract and generate force
extrafusal muscle fibers
what type of fibers does the muscle spindle consist of?
intrafusal fibers, which can be nuclear chain fibers or nuclear bag fibers
what neurons are intrafusal fibers activated by? what neurons are extrafusal fibers activated by?
efferent gamma-motor neuron; alpha-motor neuron
when the muscle spindle is activated, it sends info to the spinal cord via
Group Ia (A-alpha) and Group II (A-beta) fibers
how is muscle spindle arranged? what type of stimuli does it detect?
parallel with extrafusal fibers; detects stretch- reports change of muscle length and rate of change of muscle length
if muscle spindle detects stretch, what happens when the muscle contracts?
the alpha-motor neuron causes muscle contraction, muscle spindle becomes floppy and does not detect anything
when the muscle is stretched, the muscle spindle is activated as well as the
Golgi tendon organ
when the intrafusal muscle fibers become floppy, it can’t send its signal out; if muscle spindle becomes inactive each time a muscle contracts, how does the nervous system solve this problem?
alpha-gamma linkage or co-activation
describe alpha-gamma linkage
the alpha-motor neuron causes muscle contraction, also gamma-motor neurons activate the intrafusal muscle fibers and cause it to contract, so muscle spindle does not become floppy and will remain sensitive to the length of the muscle mass
T/F: a nuclear bag fiber is a type of extrafusal muscle fiber
false, its an intrafusal muscle fiber
what is the role of an alpha-motor neuron?
activate extrafusal fibers, leads to muscle contraction
does alpha-motor neuron cause contraction of intrafusal muscle fibers?
yes
what is the idea behind alpha-gamma linkage?
using alpha and gamma-motor neurons to activate the intrafusal fibers and cause contraction of muscle, so that the muscle spindle doesn’t become floppy, and will remain sensitive to the length of the muscle mass
knowing the location of an extremity without looking at it is called
joint position sense
what are the determinants for having good joint position sense?
sensory receptors in the joints, skin, and the muscle
the basis of knee jerk reflex and other stretch reflexes is activation of..
muscle spindle
