lecture 4,5 & 6 General Sensory Mechanisms Flashcards
what do type of endings do mechanoreceptors include
both free and encapsulated endings receiving tactile sensibilities
what are included in expanded tip endings of mechanoreceptors
merkel’s discs
what are included in encapsulated endings of mechanoreceptors
meissner’s corpuscles
kraus’ corpuscles
pacinian corpuscles
what is an example of a spray endings in mechanoreceptors
ruffini’s corpuscles
what are mechanoreceptors involved in
hearing: sound receptors of cochlea
equilibrium: vestibular receptors
arterial pressure: baroreceptors
define nocireceptors
free nerve endings responding to pain
define electromagnetic receptors
include rods and cones of the eye for vision
what do chemoreceptors sense
taste, smell, arterial oxygen, osmolarity, blood CO2, blood glucose, amino acids, and fatty acids
define differential sensitivity
each type of receptor is highly sensitive to one type of stimulus and is almost non responsive to other types
define modality
each of the principal types of sensation
define labeled line principle
specificity of nerve fibers for transmitting only one modality of sensation
what are the 4 mechanisms of stimulation for receptors
mechanical deformation,
application of a chemical,
temperature change,
electromagnetic radiation
what are characteristics of tonic receptors
slow adapting,
detect continuous stimulus strength,
transmit impulses as long as stimulus is present
what are types of tonic receptors
muscle spindles, golgi tendon organs, macula and vestibular receptors, baroreceptors, chemoreceptors
what are characteristics of phasic receptors
rapidly adapting,
do NOT transmit a continuous signal,
stimulated only when stimulus strength changes,
transmit information regarding rate of change
describe type A nerve fibers
large and medium sized myelinated fibers of spinal nerves
describe type C nerve fibers
small, unmyelinated fibers,
conduct signals at low velocity,
make up more than half of all sensory fibers in most peripheral nerves and all postganglionic autonomic fibers
what type of nerve fibers are in all postganglionic autonomic fibers
type C
describe group 1a nerve fibers
fibers from annulospiral endings of muscle spindles
describe group 1b nerve fibers
fibers from golgi tendon organs
describe group II nerve fibers
from cutaneous tactile receptors and flower-spray
describe group III nerve fibers
carry temperature, crude touch and pricking pain
describe group IV nerve fibers
carry pain, itch, temperature and crude touch
what group of nerve fibers is not Type A
group IV
define receptor field
in spatial summation, the entire cluster of nerve endings from one pain fiber covers this area of skin
define stimulatory field of neuronal pool
neuronal area within the pool stimulated by each incoming nerve fibers
where do the terminals of the stimulatory field of a neuronal pool lie
lie on the nearest neuron it its field
define discharge zone of neuronal pool
includes all the output fibers stimulated by the incoming fiber
describe diverging neuronal pathways
- may result in amplification of initial signal
* may allow transmission of original signal to separate areas
describe converging neuronal pathways
- multiple input fibers converge onto a single output neuron
* input fibers may be from a single source or from multiple separate sources
what are reverberatory circuits caused by
positive feedback within neuron circuit
define reverberatory circuits
also called oscillatory circuits: a circuit once stimulated that may discharge repetitively for a long time
define somatic senses
collect sensory info from all over the body
what are the types of somatic senses
mechanoreceptive, thermoreceptive, pain
define special senses
vision, hearing, smell, taste, and equilibrium
where do exteroreceptive sensations come from
from the surface of the body
what does proprioceptive sensations refer to
physical state of the body: position sensations, muscle and tendon sensations, pressure sensations, equilibrium
define deep sensations
deep pressure, pain and vibrations
define mechanoreceptive somatic senses
include both tactile and position senses that are stimulated by mechanical displacement of some tissue of the body
describe primary sensory neurons
from external receptors,
travel through dorsal roots of spinal cord,
synapse with secondary neurons
describe secondary neurons
make up tracts in spinal cord and brainstem,
usually terminate in thalamus,
synapse with tertiary neurons
describe tertiary neurons
from thalamus to primary sensory cortex,
travel through internal capsule
what ascending pathways are for conscious perception
spinothalamic and medial lemniscal
what ascending pathways are for unconscious perception
spinocerebellar,
spino-olivary,
spinotectal,
spinoreticular
what do lateral spinothalamic tracts carry
pain and temperature
where doe primary fibers of lateral spinothalamic tract ascend/descend
1-2 spinal cord segments before synapses with secondary fibers
where do the secondary axons of the lateral spinothalamic tract decussate
through anterior gray and white commissures
what do the secondary fiber collateral that project to reticular formation (lateral spinothalamic tract) stimulate
wakefulness and consciousness
what do tertiary fibers of the lateral spinothalamic tract form
part of internal capsule
what sensations does the anterior spinothalamic tract carry
light touch (crude touch), pressure, tickle, itch
where do the primary neurons of the anterior spinothalamic tract ascend
8-10 spinal cord segments before synapses with secondary neurons
where do tertiary fibers of the anterior spinothalamic tract ascend
through internal capsule to primary sensory cortex
what sensations does the medial lemniscus system carry
for 2 point sensation (fine touch), pressure and vibration
where do the primary fibers synapse with secondary neurons in the medial meniscus system
medulla
where do fibers of fasciculus gracilis synapse in
nucleus gracilis
what do the fibers of fasciculus gracilis synapse in nucleus gracilis convey (medial lemniscus system)
convey sensations from below mid thoracic level
what do the fibers of fasciculus cuneatus synapse in nucleus cuneatus convey
sensations from above mid thoracic level; also conveys proprioceptive sensations from arms to cerebellum
what is the primary somatosensory area made up of
Brodmann’s areas 1, 2, and 3
what is the somatosensory association area made up of
Brodmann’s areas 5 and 7
where does somatosensory area 2 receive signals from
brain stem, transmitted upward from both sides of the body, secondarily from somatosensory area 1, and other sensory areas of the body (including visual and auditory)
what do layers 1 and 2 of the somatosensory cortex do
receive input signals from lower brain centers
what do layers 2 and 3 of the somatosensory cortex do
send info through corpus callosum to opposite hemisphere
what do layers 5 and 6 of the somatosensory cortex do
large neurons in layer 5 project to distant areas (basal nuclei, brain stem, spinal cord) and axons from layer 6 project to thalamus
where do primary sensory neurons originate
from peripheral receptors
how do primary sensory neurons enter the spinal cord
via dorsal roots of spinal (cranial) nerves
where do primary sensory neurons synapse with secondary neurons
spinal cord
where do secondary sensory neurons synapse with tertiary sensory neurons
thalamus
why is lateral inhibition important for 2 point discrimination touch
important in blocking the lateral spread of excitatory signals, thereby increasing the degree of contrast in the cerebral cortex
where does lateral inhibition occur
(at each synaptic level): dorsal column nuclei, ventrobasal nuclei of thalamus, somatosensory cortex
where do axons from the lower limbs travel (for dorsal column-medial lemniscal pathway)
travel in the medial portions of the 2 dorsal columns in areas called fasciculus gracilis
where do the axons from the upper limbs travel (for dorsal column-medial lemniscal pathway)
in the lateral portions of the 2 dorsal columns (each of these areas is called fasciculus cuneatus)
where do the axons in the fasciculus gracilis synapse in the lower medulla?
nucleus gracilis
where do the axons in the fasciculus cuneatus synapse in the lower medulla?
nucleus cuneatus
what paired tracts do the secondary neurons travel through the brain stem as in the dorsal column-medial lemniscal pathway
medial lemniscus
what type of fibers typically carry fast pain
type A delta
where do pain fibers of fast pain typically terminate
lamina A (lamina marginalis) of the dorsal horns of the spinal cord
where do the pain fibers of slow pain typically terminate
layers 2 and 3 (substantial gelatinosa) of the dorsal horns of the spinal cord
what type of fibers is slow chronic pain typically carried on
C type fibers
what tract do the fast pain fibers make up
neospinaothalamic tracts
what tract do the slow pain fibers make up
paleospinothalamic
what neurotransmitter do fast pain fibers (type A-dalta) use
glutamate
what neurotransmitter do type C fibers use
glutamate and substance P
when does brown-sequard syndrome occur
when there is a hemisection of the spinal cord
what are the 3 components of the analgesia system
- periaquaductal gray and periventricular regions of the brainstem and 3rd ventricle
- raphe magnus nucleus and reticular nuclei in medulla
- pain inhibitory complex in dorsal horns of spinal cords
what are the 3 types of receptors that discriminate thermal gradation
cold, warmth, pain
describe warmth nerve endings
free nerve endings and mainly transmitted over C-type fibers
describe cold receptors
- 3-10 times as numerous as warm nerve receptors;
* small type A-delta myelinated endings
when does referred pain occur
when visceral pain fibers are stimulated and stimulate some of the pain fibers that conduct pain signals from the skin
how is all visceral pain from the thoracic and abdominal cavities tranmissted
via type C pain fibers
what are headaches the result of
pain referred to the surface of the head from deep head structures
