Flashcards in Chapter 47 Deck (44):
What signals the "touch" sensation?
results from stimulation of tactile receptors in the skin or in tissues immediately beneath the skin
What are free nerve endings responsible for?
touch and pressure (also tickle and itch); found all over the skin (ex: cornea)
What are Meissner's corpuscles responsible for?
Touch (great sensitivity); encapsulated nerve ending of a large myelinated sensory nerve fiber
What are Merkel's discs responsible for?
Extremely sensitive protruding/dome shaped receptor and aid in localizing touch sensations to specific surface areas and texture
What are Hair end organs responsible for?
detects mainly movement of objects on the surface of the body or initial contact with the body (touch receptors); found at the base of the hair (basal nerve fiber)
What are Ruffini endings responsible for?
multibranched encapsulated endings that adapt slowly, detect continuous states of deformation of the tissues (ex: heavy prolonged touch and pressure signals)
Found in joint capsules (signal the degree of joint rotation)
What are Pacinian corpuscles responsible for?
stimulated only by rapid local compression of the tissues (adapt very very quickly) and vibrations; found just beneath the skin and deep in the fascial tissues.
Meissner’s corpuscles, Iggo dome, hair, pacinian corpuscles, and Ruffini’s endings utilize what types of neurons?
Type Aβ nerve fibers
Tactile free nerve endings utilize what types of neruons?
What is the nerve topography in the Dorsal Column-Medial Lemniscal System?
Carries signals upward to the medulla of the brain mainly in the dorsal columns of the cord
Signals synapse and cross to the opposite side in the medulla
Cont. upward through the brain stem to the thalamus by way of the medial lemniscus
What types of sensations are felt in the dorsal columns?
Touch sensations requiring 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 related to fine degrees of judgment of pressure intensity
Where are the 1st, 2nd, and 3rd-order synapses for the dorsal column neurons?
First-order: dorsal column nuclei (cuneate and gracile nuclei)
Second-order: Ventrobasal complex (in the thalamus; where the medial lemniscus fibers end)
Third-order: Somatic Sensory Area I of the Postcentral gyrus in the Cerebral Cortex
What types of fibers are in the dorsal column, with respect to size and myelination and CV?
Composed of large myelinated nerve fibers that transmit signals to the brain at velocities of 30 to 110 m/sec
What is the nerve topography in the ALS?
Dorsal nerve roots spinal cord synapse in dorsal horns cross to the opposite side of the cord and ascend via the anterior and lateral white columns of the cord terminate at all levels of the lower brainstem and thalamus
What types of fibers are in the ALS with respect to size and myelination and CV?
Smaller myelinated fibers that transmit signals @ velocities ranging from a few meters-40m/sec
What types of sensations are felt in the ALS?
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
Where are the 1st, 2nd, and 3rd-order synapses for the ALS?
First-Order: dorsal horn in Lamina I, V (Aδ fibers) and Lamina II (C fibers)
Second-Order: Ventero-Posterior Lateral nucleus of the thalamus
Third-Order: Somatic Sensory Area I of the Postcentral gyrus in the Cerebral Cortex
Where is the somatosensory cortex (area I)?
Somatosensory area I lies right behind the central fissure and is located in the postcentral gyrus; it displays high degree of localization of different parts of the body
Size of the different parts of the bodoy on the homunculus is directly proportional to what?
The # of sensory fibers in each area.
If there is a lesion in the somatosensory area I, what will be the response to different sensations?
Person is unable to localize discretely the different sensations in the different parts of the body
However they can localize these sensations crudely, such as to a particular hand, to a major level of the body trunk, or to one of the legs
If there is a lesion in the somatosensory area I, what will be the response to sensing pressure?
Person is unable to judge critical degrees of pressure against the body
If there is a lesion in the somatosensory area I, what will be the response to weight of objects?
Person is unable to judge the weights of objects
What is the function of the somatosensory association area?
Aids in deciphering deeper meanings of the sensory information in the somatosensory areas
Where does the somatosensory association areas get info from?
Receives info from: somatosensory area I, ventrobasal nuclei of thalamus, other areas of thalamus, visual cortex, and auditory cortex
What are the Sx of lesions to the somatosensory area I?
The sensory modalities are still preserved both in quality and intensity however the sensations are poorly localized
What are the Sx of lesions to the somatosensory association area?
The person loses the ability to recognize complex objects and complex forms felt on the opposite side of the body.
Loses most of the sense of form of his or her own body or body parts on the opposite side; forgets its even there (amorphosynthesis)
Which area of the somatic sensory Cx is excited first?
What do layers I and II receive? Their Fxn?
Layers I and II receive diffuse, nonspecific input signals from brain centers that facilitate specific regions of the cortex; controlling overall excitability of the respective regions stimulated
Where do layers II and III send axons?
Neurons in layers II and III send axons to related portions of the cerebral cortex on the opposite side of the brain through the corpus callosum
Where does layer V send axons?
Axons in layer V project to more distant areas (basal ganglia, brain stem, and spinal cord) where they control signal transmission
What is the fxn of layer VI?
Layer VI (axons extend to thalamus) provides signals from the cerebral cortex that interact w/ and help to control the excitatory levels of incoming sensory signals entering the thalamus
What is 2-point discrimination?
Tests tactile discrimination by using two needles pressed lightly against the skin at the same time, and the person determines whether two points of stimulus are felt or one point; different parts of body display different distances of the needles due to the different concentrations of tactile receptors present in the tissue
Ex: Finger tip: 1-2 mm Back: 30-70mm
What is the role of surround inhibition in enhancinh sensory contrast?
When a sensory pathway is excited it gives rise simultaneously to lateral inhibitory signals; these spread to the sides of the excitatory signal and inhibit adjacent neurons via inhibitory transmitters.
This blocks the lateral spread of the excitatory signals and therefore increases the degree of contrast in the sensory pattern perceived in the cerebral cortex
What is the Weber-Fechner Principle?
Interpreted Signal Strength= Log (stimulus) + Constant
Greater the background sensory intensity = Greater the additional change must be for the mind to detect the change
What is the power law?
Interpreted Signal Strength= K x (Stimulus-k)y
K,k, and y are different for each type of sensation
This equation shows a linear relation can be attained btwn interpreted stimulus strength and actual stimulus strength over a large range for almost any type of sensory perception
What is proprioception?
unconscious perception of movement and spatial orientation arising from stimuli within the body itself
What is Static Position Sense?
conscious perception of the orientation of the different parts of the body with respect to one another
Knowledge of position, both static and dynamic, depends on knowing what 2 factors?
degrees of angulation of all joints in all planes and their rates of change
What types of information does the ALS pathway signal?
Pain, heat, cold, crude, tactile, tickle, itch, and sexual sensations
Where is the first-order synapse for the ALS pathway?
dorsal root sensory nerve fibers synapse in the Dorsal horn laminae I, IV, V, and VI
Where is the ALS decussation?
ALS fibers cross in the anterior commissure of the cord to the opposite anterior and lateral white columns (anterior and lateral spinothalamic tracts)
Where is the 2nd-order synapse for the ALS pathway?
upper terminus of the 2 spinothalamic tracts is mainly twofold
Reticular nuclei of the brain stem (pain signals)
Two different nuclear complexes of the thalamus: ventrobasal complex (tactile signals) and intralaminar nuclei (pain signals)
Where is the 3rd-order synapse for the ALS pathway?
Somatic Sensory Area I of the Postcentral gyrus in the Cerebral Cortex