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132 Cards in this Set

  • Front
  • Back
What is adequate stimulus
adequate stimulus is the "best" stimulus for a given receptor
What is receptive field?
Presentation to the receptor's receptive field (the region of the receptor sheet that causes a change in the response of a receptor or neuron when stimulated) causes ion conductance changes that produces a generator potential
What is generator potential
generator potential is graded, local, and if sufficient to depolarize the neuron beyond threshold, causes action potentials to be generated.
Name the Coding mechanisms available for representing a stimulus in the nervous system
Modality (submodality; quality), Intensity, Location, and Timing (onset and offset).
All stimuli are "multi-dimensional" and have at least_____dimensions that the nervous system has to code in the action potentials of sensory neurons
____ of a stimulus: "What" the sensation is
Most often this information is carried in the nervous system by a code known as _____.
______ of a stimulus: "How much" sensation is present.
The code for stimulus intensity is known as the
"frequency code
This code includes the total number of_____ generated per unit time in affected sensory neurons as well as the total number of neurons activated.
action potentials
______ of a stimulus: "Where" the sensation originates.
concept of receptive field pertains to what coding mechanism
Precise location information is usually coded by the ___.
"population code".
____of a stimulus: "When" the stimulus starts and stops.
concept of adaptation pertains to what coding mechanism
Sensory receptors are classified as rapidly adapting or slowly adapting based upon their response to a _____.
sustained stimulus
"" coding accomplishes coding of stimulus onset, duration, and offset
Temporal pattern
Classification (traditional) by where they are:
Exteroceptive, proprioceptive, interoceptive
Classification by type of energy transduced
mechanoreceptors thermoreceptors
Submodality Subserved: Touch
Specialized Receptor :
Adequate Stimulus :
Specialized Receptor: Meissner?s Corpuscle (RA) Adequate Stimulus : Active skin displacement
Submodality Subserved:Pressure
Specialized Receptor :
Adequate Stimulus :
Specialized Receptor:Merkel Cells(SA)Ruffini Endings (SA)

Adequate Stimulus :Static skin displacement
Submodality Subserved:Vibration
Specialized Receptor :
Adequate Stimulus :
Specialized Receptor:Pacinian Corpuscles (RA)
Adequate Stimulus:Vibration (60-500 Hz)
Submodality Subserved:Flutter
Specialized Receptor :
Adequate Stimulus :
Specialized Receptor:Meissner?s Corpuscles (RA) Adequate Stimulus :Slow Vibration (5-40 Hz)
Submodality Subserved: Hair Movement
Specialized Receptor :
Adequate Stimulus :
Specialized Receptor:Hair Follicle Endings (RA) Adequate Stimulus :Hair deflection
Submodality Subserved: Position sense and kinesthesia
Specialized Receptor :
Adequate Stimulus :
Specialized Receptor:Joint, muscle, and skin receptors (RA and SA) Adequate Stimulus :Joint position and movement
Transducer mechanisms
Merkel cell
: stretch sensitive channels in the membrane of this specialized cell causes the release of a transmitter. This transmitter causes action potential generation in the first order sensory neuron.
Merkel cell
receptors (RA) signal dynamic (active or changing) stimulus properties; e.g. movement of the skin, velocity, acceleration.
Rapidly adapting
receptors (SA) signal static (steady state) properties; e.g. stimulus duration, intensity
Slowly adapting
: a recording from many neurons simultaneously. Differs from action potential in a single neuron. Instead of being all-or-none
Compound action potential
varies in amplitude and overall size depending upon the stimulus intensity.
compound action potential
Significance of multiple peaks in the waveform of a compound action potential - different peaks reflect of____ axons (conduction velocity);
peaks also have relationship to _______.
#Ia, Ib
Origin: Muscle spindle primary ending
Golgi tendon organ
Fiber Type:
# II
Touch, pressure, vibration, flutter, hair, proprioception
Muscle spindle secondary ending
Fiber Type: Ab
Origin:Fast pain, cold, some touch (non-discriminative)
Fiber Type: Ad
Origin: Slow pain, temperature, other receptors
Fiber Type:C
Two major systems are involved in detecting and processing somatosensory events
dorsal column system
anterolateral system
dorsal column system -- predominately concerned with discriminative aspects of ____ .
the ability to accurately detect the quality, intensity, location, and timing of somatic stimuli
anterolateral system
-- subserves pain and temperature and is believed to contribute less precise information about touch and pressure than the dorsal column system.
Segmental anatomy
: cross-sectional anatomy of the spinal cord
Longitudinal anatomy:
dermatomes and myotomes
dermatomes and myotomes
considered as spinal cord segments; each with input and output
ipsilateral projection via dorsal root to dorsal white matter without a synapse
Primary afferents (1st order neuron):
First synapse in dorsal column nuclei include.
(Nucleus Gracilis and n. Cuneatus)
First synapse in dorsal column nuclei what does it cause?
lateral inhibition and descending control of ascending information
Receptive field changes for 2nd order neurons
Lateral inhibition
Lateral inhibition is a mechanism that enhances contrast in the nervous system--helps distinguish ____stimuli, etc.
2 closely spaced
Efferent (descending) control of ______ information
Axons of 2nd order neurons form the ______.
medial lemniscus
2nd order neurons axons cross the midline of the nervous system as they project to the_____.
VPL nucleus of the thalamus contains the cell bodies of ____ neurons in this pathway
3rd order
The ______ is a major nucleus that processes virtually all ascending (sensory) information.
Axons of these neurons project to the somatosensory cortex
3rd order
SI =
(primary somatosensory cortex).
(secondary somatosensory cortex)
area coinsides with the postcentral gyrus (also known as Brodmann's areas 3a, 3b, 1 and 2.
information from the face and head is carried by a ___(the Trigeminal nerve) and projects to the thalamus (VPM) and cortex (SI and SII).
cranial nerve
Dorsal Column System Input via ________ nerve fibers
large myelinated
Representation of the body:
Spinal cord:
hand lateral, foot medial
Representation of the body: Dorsal column nuclei:
hand lateral, foot medial
Representation of the body: VPL of thalamus:
foot lateral, hand medial (face in VPM, medial to body representation)
Representation of the body:
Somatosensory cortex:
face lateral, foot medial
Most neurons have _________relatively contralateral receptive fields
small, localized,
Receptive fields on the distal portions of the limbs are _____ than on proximal body regions.
Most neurons are sensitive to ____ submodality of somatic sensation.
Somatotopic representation of the body and face
contralateral representation with disproportionately enlarged areas for the face, hand and foot
SI cortex: _____representations of the body
Multiple maps in different parts of SI: Areas 3a, 3b, 1 and 2. This indicates importance of
parallel processing
Somatosensory Cortex consist of:
SI cortex
Multiple maps
Columnar organization
SII cortex
Other areas may exist (SIII, SIV, etc
may be the functional unit of cortical organization.
___columns of cells have overlapping receptive fields and respond to the same submodality of stimulation
SII cortex: significance is ____.
Clinical Features of Lesions in the Dorsal Column System
lose precision in discriminative somesthesis. Extent of the deficit is usually proportional to the amount of tissue damage.
Clinical Features of Lesions in the Dorsal Column System
Increase in two-point threshold
Decrease in vibratory sensitivity.
Decrease in precision of position sense and kinesthesia
Increase in spontaneous pain (possibly due to interaction of this system with the anterolateral system
Concept of Pain
quantifiable sensory event,
2) An affective component, the reaction to pain; together these 2 components occur
the sensation of pain
Types of Pain
Superficial, Fast, Deep, Slow
pain - arising from skin and superficial tissues
Superficial (cutaneous)
pain: short latency, well localized, subsides quickly; has relatively minor affective component
Fast (pricking)
pain: longer latency, less well localized, longer duration with prolonged "after-discharge"; has strong affective component; difficult to endure.
Slow (burning)
- arising from deep tissues including visceral organs and muscles, fascia, joints and tendons.
Deep pain
- sensations of warm and cold; dual system. Better sensor of changing temperature than of static condition.
less "discriminative" than in the dorsal column system
Touch -
Submodalities of the anterolateral system
Pain, Temperature, Touch, Itch, Pressure
Submodality: Fast pain
Fiber Type:
Adequate Stimulus:
Fiber Type:Ad
Adequate Stimulus:Tissue damage
Submodality: Slow pain
Fiber Type:
Adequate Stimulus:
Fiber Type: C
Adequate Stimulus: Tissue damage
Submodality: Deep visceral pain
Fiber Type:
Adequate Stimulus:
Fiber Type: C
Adequate Stimulus: Distention
Submodality: Deep somatic pain
Fiber Type:
Adequate Stimulus:
Fiber Type:Ad ,C
Adequate Stimulus: Tissue damage
Submodality: Temperature
Fiber Type:
Adequate Stimulus:
Fiber Type:Ad , C
Adequate Stimulus:Skin temperature and temp. change
Submodality Touch
Fiber Type
Adequate Stimulus
Fiber Type Ad , C
Adequate Stimulus: Active skin displacement
Submodality Pressure
Fiber Type
Fiber Type Ad , C
Adequate Static skin displacement
Submodality Itch
Fiber Type
Fiber Type C
Adequate Light mechanical stimulation
Pain: nociceptors
Mechanical nociceptors -
Thermal nociceptors -
Polymodal nociceptors
Mechanical nociceptors -
high threshold mechanoreceptors
Thermal nociceptors -
temperatures greater than 45oC.
Polymodal nociceptors -
respond to mechanical, thermal, chemical energy; anything that causes tissue damage. Indicates that a common mechanism might exist, e.g. the release of a chemical from the damaged tissue that stimulates the receptors
Temperature: 2 types,
cold and warm.
Temperature Mechanism
Mechanism probably involves change in the rate of a chemical reaction in the receptor
Touch and pressure -
same as the other mechanoreceptors (dorsal column types).
Itch -
unknown mechanism
(1st order neurons): ipsilateral projection via the dorsal root to the spinal cord.
Primary afferents
First synapse in the ipsilateral spinal cord
1. Enters substantia gelatinosa
2. May ascend or descend 1 or 2 spinal segments before synapse
3. Synapse is in outer layers of the gray matter of the dorsal horn of the spinal cord.
cell body in dorsal horn.
Second order neuron
Axons cross the midline in the spinal cord to form __________.
contralateral anterolateral tract; often called the spinothalamic tract.
CNS targets are widespread, accounts for high arousal properties of
projects to VPL of thalamus and from there to SI and SII. Fast pain, mostly Ad input.
Spinothalamic portion:
projects to the reticular formation in the brainstem. The reticular formation has widespread connections to cortex and therefore has arousal properties; arousal is important for a pain pathway!
Spinoreticular portion:
projects mainly to a nucleus known as the periaqueductal gray matter. This nucleus has descending projections to the spinal cord that can reduce pain input from the nociceptors. It also releases endogenous opioid compounds (endorphins and enkephalin) that act as hormones to reduce pain perception.
Spinomesencephalic portion:
carries these submodalities from the face and head.
Cranial nerve input
Anterolateral System: Input via _____ myelinated and ______nerve fibers
Variable topographic representation of the body
Spinal cord:
VPL of thalamus:
Reticular formation and other targets in thalamus:
SI and SII
Pain and temperature have limited representation in the cortex; somatotopically organized within the sensory homunculus
SI and SII:
Foot lateral, hand medial (contralateral)
Spinal cord:
Foot lateral, hand medial; VPM of thalamus:
FaceVPL of thalamus:
Reticular formation and other targets in thalamus:
little or no somatotopic organization
Anterolateral System: Large, often ________fields for CNS neurons
bilateral receptive
Anterolateral System:
Older (more primitive) system than the Dorsal Column Pathway
Many neurons are sensitive to more than one submodality of input
Functional Properties of the Anterolateral System
Input via small myelinated and unmyelinated nerve fibers.

Variable topographic representation of the body.
Large, often bilateral receptive fields for CNS neurons
deep visceral pain often referred to superficial skin regions innervated by the same spinal cord segment; convergence may account for this phenomenon. Patterns of referred pain have obvious clinical diagnostic importance.
Referred pain:
Control of pain input to the CNS - 3 major sources:
Interaction with the Dorsal Column Pathway
Efferent (descending pathways)
Endogenous opiod compounds - Endorphins and Enkephalin
Interaction with the Dorsal Column Pathway:
Gate Control Theory
collaterals of first order fibers of the Dorsal column system can indirectly inhibit pain transmission at its first synapse
- nerve fibers from the cortex, reticular formation and other areas can modulate input of pain at all synaptic levels. (Efferent control operates in all sensory systems).
Efferent (descending pathways)
Endogenous opiod compounds - Endorphins and Enkephalin
Stimulation induced analgesia
Release of compounds with morphine-like action
Physiological significance of endorphins and enkephalins.
Stimulation induced analgesia
profound analgesia can result from electrical stimulation of some brain areas (areas produce endorphins and enkephalin) Substances are released as hormones into the blood--have widespread targets for blocking the reaction to pain; can also act directly as inhibitory neurotransmitters to block pain)
(act like morphine: this is the reason opiates have an effect--the brain has receptors sensitive to them
Release of compounds with morphine-like action
Physiological significance of endorphins and enkephalins.
(Important to sense trauma, not to be incapacitated by it, e.g., soldiers with wounds often not aware of injury until later, etc.)
Clinical features of lesions in the anterolateral system
A. Decrease in pain sensitivity (hypalgesia, analgesia)
B. Decrease in temperature sensitivity

C. Return of pain may occur after lesions of the system

D. Sensory dissociation with spinal cord hemisection (Brown-Sequard Syndrome)
This portion will present the structure and function of somatosensory receptors, with special emphasis on the low threshold mechanoreceptors of the skin.
Somatosensory receptors:
This spinal cord pathway is specialized for transmitting discriminative touch--sensations that are very precise in representing the intensity, location, submodality and timing of stimuli. We will study this pathway from skin receptors through processing in the cerebral cortex.
The Dorsal Column System:
This system is older phylogenetically, carries pain and temperature in addition to less precise touch and pressure sensations. We will again start at the periphery and carry the information transduced into the CNS and look at the processing of the information, especially pain.
The Anterolateral Pathway: