Somatic Sensations Flashcards
an elon gated encapsulated nerve ending of a large (type A β) myelinated sensory nerve iber.
present in the nonhairy parts of the skin
sensitive to movement of objects over the surface of the skin, as well as to lowfrequency vibration.
Meissner’s corpuscle
touch receptor with great sensitivity
six entirely diferent types of tactile receptors
free nerve endings,
Meissner’s corpuscle
expanded tip tactile receptors, one type of which is Merkel’s discs,
hair end-organ
Ruffini’s endings,
Pacinian corpuscles
they transmit an initially strong but partially adapting signal and then a continuing weaker signal that adapts only slowly
responsible for giving steadystate signals that allow one to determine continuous touch of objects against the skin.
Merkel’s discs,
play extremely important roles in localizing touch sensations to speciic surface areas of the body and in determining the texture of what is felt.
Merkel’s discs
Meissner’s corpuscles
found in joint capsules and help to signal the degree of joint rotation
multibranched, encapsulated endings
important for signaling continuous states of deformation of the tissues, such as heavy prolonged touch and pressure signals.
Ruffini’s endings
stimulated only by rapid local compression of the tissues because they adapt in a few hundredths of a second.
important for detecting E
tissue vibration or other rapid changes
Pacinian corpuscles
Merkel discs are often grouped together in a receptor organ called the
Iggo dome receptor,
Not all tactile receptors are in volved in detection of vibration, diferent recep tors detect diferent frequencies of vibration.
False. All tactile receptors are in volved in detection of vibration, although diferent recep tors detect diferent frequencies of vibration.
Pacinian corpuscles can detect signal vibrations from
30 to 800 cycles/sec because they respond extremely rapidly to minute and rapid deformations of the tissues.
transmission velocities ranging from 30 to 70 m/sec
Almost all specialized sensory receptors transmit their signals in type Aβ nerve ibers
com
posed of large, myelinated nerve ibers that transmit signals to the brain at velocities of 30 to 110 m/sec,
high degree of spatial orientation of the nerve ibers with respect to their origin
dorsal column–medial lemniscal system
composed of smaller myelinated ibers that transmit signals at velocities ranging from a few meters per second up to 40 m/sec.
anterolateral system
he anterolateral system has a special capability that the dorsal system does not have
ability to transmit a broad spectrum of sensory modalities, such as pain, warmth, cold, and crude tactile sensation
local neurons in the intermediate and anterior portions of the cord gray matter serve three functions:
give of ibers that enter the
dorsal columns of the cord and then travel upward to the brain
terminate
locally in the spinal cord gray matter to elicit local spinal cord relexes,
give rise to the spinocerebellar tracts
thalamic sensory relay area
ventrobasal complex
From the ventrobasal complex, third-order nerve fibers project mainly to the post- central gyrus of the cerebral cortex, which is called
somatic sensory area I
Spatial Orientation of the Nerve
Fibers in the Dorsal Column–Medial
Lemniscal System
Fibers from the lower parts of the body lie toward the center of the cord, whereas those that enter the cord at progressively higher segmen
tal levels form successive layers laterally.
True or False
True
Spatial Orientation of the Nerve
Fibers in the Dorsal Column–Medial
Lemniscal System
tail end of the body represented by the most medial portions of the ventrobasal complex and the head and face represented by the lateral areas of the complex
True or False
False
tail end of the body represented by the most lateral portions of the ventrobasal complex and the head and face represented by the medial areas of the complex
the portion of the cerebral cortex anterior to the central issure and constituting the posterior half of the frontal lobe is called
motor cortex
lies immediately behind the central issure, located in the postcentral gyrus of the human cerebral cortex
Somatosensory Area I
Those in layer
VI are generally larger and project to more distant
areas, such as to the basal ganglia, brain stem, and
spinal cord, where they control signal transmission.
True or False
False. Layer v
signals from these sensory columns then spread anteriorly, directly to the motor cortex located immediately forward of the central issure.
Brodmann’s area 3A
The Sensory Cortex Is Organized
in horizontal Columns of Neurons;
True or False
False. Vertical
Functions of Somatosensory Area I
localize discretely the dif ferent sensations in the diferent parts of the body. Judge critical degrees of pressure weights of objects. shapes or forms of objects. (astereognosis) And texture of materials
he capability of the sensorium to distinguish this presence of two points of stimulation is strongly inluenced by
lateral inhibi-
tion,
It is likely that these are the receptors most responsible for detecting rate of movement.
Pacinian corpuscles and muscle spindles
cross immediately in the anterior commissure of the cord to the opposite anterior and lateral white columns, where they turn upward toward the brain by way of the anterior spi-
nothalamic and lateral spinothalamic tracts.
anterolateral ibers
transmitted in the backward direction from the cerebral cortex to the lower sensory relay stations of the thalamus, medulla, and spinal cord; they control the intensity of sensitivity of the sensory input.
corticofugal signals
when sensory input intensity becomes too great, the corti cofugal signals automatically decrease transmission in the relay nuclei
True or False
True
Three Types of Stimuli Excite Pain Receptors
Mechanical, Thermal, and Chemical
enhance the sensitivity of pain endings but do not directly excite them.
prostaglandins and substance P
especially important in stimulating the slow, sufering type of pain that occurs after tissue injury.
chemi-
cal substance
increase in sen-
sitivity of the pain receptors
hyperalgesia
pain resulting from heat is closely correlated with the rate at which damage to the tissues is occurring and not with the total damage that has already occurred.
True or False
True
neurotransmitter substance secreted in the spinal cord at the type Aδ pain nerve iber endings.
Glutamate
the Probable Slow-Chronic Neurotrans- mitter of Type C Nerve Endings
Substance P
natural opiate of the brain.
All are breakdown products of three large protein molecules:
pro-opiomelanocortin, proenkephalin, and prodynorphin.
Only one tenth to one fourth of the ibers pass all the way to the thalamus. Instead, most terminate in one of three areas:
1) the reticular nuclei of the medulla, pons, and mesencephalon; (2) the tectal area of the mesencephalon deep to the superior and inferior colliculi; or (3) the periaqueductal gray region surrounding the aqueduct of Sylvius.
he analgesia system consists of three major components:
periaqueductal gray and periventricular areas
raphe magnus nucleus and nucleus reticularis paragiganto-
cellularis
a pain inhib-
itory complex located in the dorsal horns of the spinal cord.
a thin midline nucleus located in the lower pons and upper medulla,
raphe magnus nucleus
Among the more important of these opiate-like sub-
stances are
β-endorphin, met-enkephalin, leu-enkephalin, and dynorphin.
True or False
inactivation of pain pathways by morphine-like drugs, can almost totally suppress many pain signals entering thru the peripheral nerves
True
the basis of pain relief by acupuncture.
simultaneous psychogenic excitation of the central analgesia system
stimulation of large-type Aβ sensory ibers from peripheral tactile receptors can depress transmission of pain signals
Causes of True Visceral Pain
ischemia of visceral tissue,
chemical damage to the surfaces of the viscera,
spasm of the smooth muscle of a hollow viscus,
excess distention of a hollow viscus, and
stretching of the connective tissue surrounding or within
theory that explains migraine headache must also
explain the prodromal symptoms.
prolonged
emotion or tension causes relex vasospasm of some of the arteries of the head
spreading cortical
depression,
psychological abnormalities,
and vasospasm
caused by excess local potassium in the cerebral extracel-
lular luid.
genetic predisposition
Most areas of the body have 3 to 10 times as many cold spots as warmth spots,
True or False
True
thermal detection probably results from direct phy- sical efects of heat or cold on the nerve endings
True or False
False. thermal detection probably results not from direct phy- sical efects of heat or cold on the nerve endings but from chemical stimulation of the endings as modiied by temperature.
