Chapter 47 - Guyton Flashcards
mechanoreceptive somatic senses
both tactile and position sensations that are stimulated by mechanical displacement of some tissue of the body
thermoreceptive senses
detect heat and cold
three physiologic types of somatic senses
mechanoreceptive, thermoreceptive, pain
Exteroreceptive sensations
surface of the body
Proprioceptive sensations
physical state of the body, including position sensations, tendon and muscle sensations, pressure sensations from the bottom of the feet, and sensation of equilibrium
Visceral sensations
from the viscera of the body; refers specifically to sensations from the internal organs
Deep sensations
from deep tissues, such as from fascia,
muscles, and bone; include mainly “deep” pressure, pain, and vibration
Principle differences among tactile sensations.
1) touch sensation from
stimulation of tactile receptors in skin or just below; 2) pressure sensation from deformation of deeper tissues; 3) vibration sensation results from rapidly repetitive sensory signals, but some of the same types of receptors as those for touch and pressure are used
These tactile receptors are found everywhere in the skin and in many other tissues.
free nerve endings
These tactile receptors present in the nonhairy parts of the skin and are particularly abundant in the fingertips, lips, and other areas of the skin where one’s ability to discern spatial locations of touch sensations is highly developed.
Meissner’s corpuscle (great sensitivity)
These tactile receptors are responsible for giving
steady-state signals that allow one to determine continuous touch of objects against the skin.
Merkel’s discs (hairy and non-hairy skin)
These tactile receptors play extremely important roles in localizing touch sensations to specific surface areas of the body and in determining the texture of what is felt.
Meissner’s corpuscle and Merkel’s discs
An entire group of Merkel’s discs would be innervated by which type of fiber?
a single large, myelinated nerve fiber (type A beta)
Merkel’s discs are often grouped together in a
receptor organ called:
Iggo dome receptor
These endings adapt very slowly and, therefore, are important for signaling continuous states of deformation of the tissues, such as heavy prolonged touch and pressure signals (also in joint capsules and sense degree of joint rotation).
Ruffini’s end-organs
They are particularly important for detecting tissue vibration or other rapid changes in the mechanical state of the tissues.
Pacinian corpuscles
Free nerve ending tactile receptors transmit signals mainly by way of which type of fiber?
type A delta, 5-30 m/sec
Almost all specialized sensory receptors, such as
Meissner’s corpuscles, Iggo dome receptors, hair receptors, pacinian corpuscles, and Ruffini’s endings transmit their signals in which type of fiber?
type A beta nerve fibers that have
transmission velocities ranging from 30-70 m/sec
Some tactile free nerve endings transmit by way of
type C unmyelinated fibers at velocities from a fraction of a meter up to 2 m/sec; these send signals into the spinal cord and lower brain stem, probably subserving mainly the sensation of:
tickle
Which tactile receptors can detect vibration?
all but mainly pacinian and meissner’s
From the entry point into the cord and then to the brain, the sensory signals are carried through one of two alternative sensory pathways:
1) the dorsal column–medial
lemniscal system or 2) the anterolateral system (come back together at the thalamus)
Sensory information that must be transmitted rapidly and with temporal and spatial fidelity is transmitted mainly in the:
dorsal column-medial leminiscal system (large, myelinated fibers)
Sensory information which does not
need to be transmitted rapidly or with great spatial
fidelity is transmitted mainly in the:
anterolateral system (small, myelinated fibers)
The ability to transmit a broad spectrum of sensory modalities—pain, warmth, cold, and crude tactile sensations is transmitted by:
anterolateral system
Dorsal Column-Medial Leminiscal System
- Touch sensations requiring a high degree of
localization of the stimulus - Touch sensations requiring transmission of fine
gradations of intensity - Phasic sensations, such as vibratory sensations
- Sensations that signal movement against the skin
- Position sensations from the joints
- Pressure sensations having to do with fine degrees of judgment of pressure intensity
Anterolateral System
- Pain
- Thermal sensations, including both warmth and
cold sensations - Crude touch and pressure sensations capable only of crude localizing ability on the surface of the
body - Tickle and itch sensations
- Sexual sensations
In the dorsal columns of the spinal cord, the fibers from the lower parts of the body lie toward the ______ of the cord, whereas those that enter the cord at progressively higher segmental levels form successive layers ______.
center, laterally
Contains large, myelinated fibers for fast transmission (30-110 m/sec).
dorsal column system
Contains smaller myelinated and unmyelinated fibers for slow transmission (0.5-40 m/sec).
anterolateral system
Where does the crossing of fibers occur in the Dorsal Column-Medial Lemniscal System.
medulla
Somatic Sensory Cortex
located in the post-central gyrus, highly organized distinct spatial orientation, each side receives info from opposite side of body
In the somatic sensory cortex, which areas have the greatest representation.
lips, face, thumb
In what layer do incoming signals enter the cerebral cortex?
layer IV and spread up and down (layers I and II receive diffuse input from lower brain centers)
Which layers send axons to closely related portion of the cortex for communicating?
layers II and III
Layer V sends axons to:
brain stem and spinal cord
Layer VI sends axons to:
thalamus
Damage to Somatic Area I could result in?
loss of discrete localization ability, inability to judge degree of pressure, inability to determine weight of an object, inability to determine shape or form of object (astereognosis), inability to judge texture
Somatic Association Areas
located behind the somatic sensory cortex in the parietal area of the cortex; receives input from somatic sensory cortex, ventrobasal nuclei of thalamus, visual and auditory cortex; functions to decipher sensory meaning
Special Aspects of Thalamus Function
some ability to discriminate tactile sensation, important role in perception of pain and temperature
Damage to what area might result in a person being unable to sense the form of one side of the body (amorphosynthesis).
Somatic Association Area
What occurs during two-point discrimination in the nervous system to help distinguish the point of touch?
lateral inhibition
It is likely that these are the receptors most responsible for detecting rate of movement.
pacinian corpuscles and muscle spindles
These fibers are inhibitory and can suppress the sensory input. They function to decrease the spread of signal, sharpen the degree of contrast, and adjust the sensitivity of the system.
corticofugal fibers (run backwards from cortex to thalamus, medulla, and spinal cord)
