Sensory Physiology Flashcards
Afferent Pathways into
the CNS enters the spinal cord via
the
posterior/dorsal roots
Labeled Lines:
Receptors and neurons in the CNS are dedicated to carrying particular sensory information.
Greater than –% of all
sensory information is
discarded as irrelevant by the —
99
thalamus
Schematic of Sensory
Afferent) Pathways (5
• Receptor • First Order Neuron • Second Order Neuron • Third Order Neuron • Primary Somatosensory Cortex (Parietal Lobe)
input to the nervous system is provided by
sensory
receptors
Mechanoreceptors:
compression/stretch
Mechanoreceptors includes receptors in (5)
skin, muscle spindles, hearing, equilibrium, arterial pressure, etc.
Chemoreceptors:
ligands
Chemoreceptors includes receptors for (6)
taste, smell, arterial oxygen, osmolarity, blood gas, blood glucose, etc.
Thermoreceptors:
cold/warm
Nociceptors:
damage
Photoreceptors (electromagnetic receptors):
light
The particular form of energy to which a receptor is most sensitive is
called its
adequate stimulus
The particular form of energy to which a receptor is most sensitive is
called its adequate stimulus. Receptors do respond to forms of
energy, but the threshold for these nonspecific responses is much —
higher
Sensory Receptors are specific for a particular
energy type (or modality)
Activation of any sensory receptor changes — and produces what is called a
membrane potential (transduction) receptor potential (a graded potential).
Pacinian Corpuscle (mechanoreceptor) When the surrounding capsule is distressed, the central nerve fiber is in turn distorted, opening ion channels. The greater the depression, the
more ion channels will open, so a larger GP will be produced which leads to more APs.
Increases in stimulus strength will increase the — of
receptor potentials, but this is not a — relationship.
amplitude
direct (linear)
The intensity (or strength) of stimulus perception is determined by: (2)
- The frequency of action potentials (Temporal summation)
2. The total number of receptors activated (Spatial summation)
APs are All or None, so a stronger stimulus will NOT generate a
larger AP
A Stronger stimulus intensity produces a (3)
Larger Receptor (Graded) Potential, More Actions Potentials (Temporal Summation) and causes More neurotransmitter release into the synapse
Adaptation (2)
- Perceptual Threshold
- Adaptation can occur at the receptor or in the
neuron
If a stimulus of constant strength is
maintained on a sensory receptor, the
frequency of the action potentials in its
sensory nerve — over time
declines
In response to continual, high impulse sensory stimuli, the response of almost all receptors ---, but to varying degrees.
decreases
The longest measured time for
nearly complete adaptation of a
mechanoreceptor is
2 days – carotid
and aortic baroreceptors. This is
considered a tonic form of
adaptation.
Decrease in amplitude of receptor potential over time in
the presence of a constant stimulus (2)
– Corresponding decrease in frequency of APs
– Decreases perception of stimulus
Tonic Receptors help
differentiate stimulus
Intensity
Phasic Receptors
help differentiate
stimulus
Duration
Slowly Adapting/Tonic (4)
Golgi Tendon Organs,
Nociceptors,
Chemoreceptors,
Baroreceptors
Rapidly Adapting/Phasic (2)
Pacinian corpuscles,
Vestibular receptors in
the inner ear
Labeled Line Principle:
A precise modality
activates specific receptors and postsynaptic
cells. This information continues on a
predicted pathway such that particular kinds
of information are conveyed via specific
nerve fibers to specific regions of the CNS
that are programmed for perception of that
modality.
Homunculus correlates the
anatomical regions of the CNS
with where
interpretation and
awareness of sensations are
perceived
3 Neurons (3)
First-, Second- and
Third-Order
Receptive Field:
Region where a single fiber’s afferent receptors (primarily on dendrites) are located
There is often overlap between receptive
fields of adjacent neurons; overlap
improves
localization ability – two
point discrimination
Acuity is the
precision with
which a stimulus
is perceived
The process of — — enhances acuity.
lateral inhibition
Lateral Inhibition Improves —
Discrimination
Sensory stimulation of a single point on the skin can elicit excitation in one tract of post-synaptic cells while simultaneously
inhibiting lateral
neurons
Lateral inhibition occurs throughout the CNS and is advantageous since it diminishes
lateral spread of an excitatory signal and increases degree of contrasts in the sensory pattern perceived in the cortex
Lateral inhibition occurs at each synapse: (3)
(1) medulla,
(2) thalamus and
(3) cerebral cortex.
Nerve fibers that have
larger diameter axons
and/or that are myelinated
have a faster
conduction
velocities
Mechanoreceptors include (2)
TACTILE and POSITION
sensations that are stimulated by mechanical displacement of
some tissues in the body
tactile (3)
touch
pressure
vibration
Touch sensations from
stimulation of
tactile receptors
in the skin or tissues beneath
the skin.
Pressure sensations from
deformation of deeper tissues
Vibration sensations from
rapidly repetitive sensory signals
position (2)
static position
proprioception
Static position sense is
conscious perception of
orientation of different parts of
the body with respect to one
another
Rate of movement sense is also called (2)
kinesthesia or
dynamic proprioception
Examples of Mechanoreceptors: (6)
Free Nerve Endings, Pacinian Corpuscles, Meissner’s Corpuscles, Merkel’s Disks, Ruffini Endings, Hair End-Organs
Mechanoreceptors are sensitive to (3) so mechanical stimuli are
responsible for their activation.
pressure,
touch, and vibration
Free Nerve Endings
Detect:
Location:
Phasic/Tonic?
a. Detect touch & pressure (temp. & pain)
b. In skin, cornea, dental pulp, GI tract
c. Slow adaptation/ Tonic
Pacinian Corpuscles
Detect:
Location:
Phasic/Tonic?
a. Detect deep pressure, vibration
b. In subcutaneous tissue, viscera, joints
c. Rapid adaptation/Phasic
Higher frequency vibration (up to 700 cycles/sec) detected by --- --- while lower frequencies (below 200/sec) detected by --- --- as well.
Pacinian Corpuscles
Meissner’s Corpuscles
Vibration is only detected by —, so application of vibration (tuning fork) is a tool used to test integrity of the —
Dorsal Column Pathway
DCP
Meissner’s/Tactile Corpuscles (4)
Detect:
Location:
Phasic/Tonic?
a. Detect light touch, pressure, vibration
b. Localization
c. Found on glabrous skin
d. Rapid adaptation/Phasic
The density of Meissner’s corpuscles in skin can be determined by
two-point discrimination tests.
The number of tactile corpuscles in skin normally declines during adult life.
Merkel’s Disks
Detect:
Location:
Phasic/Tonic?
a. Localize continuous pressure and sensing an object’s texture
b. All skin
c. Slow adaptation/Tonic
Ruffini’s Endings
Detect:
Location:
Phasic/Tonic?
a. Sensitive to stretch or indentation; proprioception
b. Deep layers of skin, joints, surrounding tooth roots
c. Slow adaptation/Tonic
Periodontal mechanoreceptors in the
periodontal ligament are — -like
receptors.
Ruffini
Hair End-Organ (3)
a. Hair Movement
b. Base of hair follicle
c. Rapid Adaptation/Phasic
Dorsal Column–Medial Lemniscal Pathway
Mechanoreceptor Transmission (Touch, Pressure, Vibration)
The medial lemniscus is an ascending
bundle of heavily myelinated axons that
cross over in the –
medulla
Transmits signals to the brain at
velocities of
30-110 m/sec
The ascending sensory tract (first order) ascends the
spinal cord on the
same side as the
stimulus
The second order neuron crosses over in
the
medulla oblongata
Spinothalamic/Anterolateral Pathway (6)
Pain, Thermoreceptors, Crude
Tactile, Tickle, Itch and Sexual
Sensations
Transmits a broad spectrum of — modalities.
sensory
Sends signals to the brain at velocities
a few meters/section up to – m/sec.
Much less spatial organization than the
dorsal column pathway.
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The second order neuron crosses over in the --- --- and ascends in either the anterior or lateral spinothalamic tract on the --- side of the spinal cord from where the stimulus occurred.
spinal cord
opposite
With a UNILATERAL lesion of the spinal cord, one would expect to lose \_\_\_\_\_ lateral touch/pressure & \_\_\_\_\_ lateral pain/temperature sensations below the injury level
ipsilateral
contralateral
Amorphosynthesis
Damage to the somatosensory association
area on one side
Amorphosynthesis results in (2)
the inability to recognize complex objects and forms felt on the opposite side of the body.
Also loses sense of form of their own body on the opposite side; mainly oblivious to the opposite side of the body.
Proprioception:
Awareness of the body’s position in space
Proprioception: Receptor Types (4)
- Photoreceptors
- Touch & pressure receptors in skin, joints, ligaments (ex. periodontal ligament)
- Skeletal Muscle Receptors (unconscious proprioception)
- Vestibular Receptors
Skeletal Muscle Receptors (unconscious proprioception) (2)
a. Muscle Spindles
b. Golgi Tendon Organs
Extensive Innervation (2)
- Incredibly high sensitivity to stimuli
- Relatively large region of the cortex receives
information (Sensory Homunculus)
Cutaneous & Mucosal Receptors (3)
- Meissner, Merkel, Ruffini, and free nerve endings
a. No Pacinian Corpuscles - Also send proprioceptive information
- Mechanoreceptors can convey taste perception
Periodontal Mechanoreceptors (3)
- In the periodontal ligament
- Mostly complex Ruffini-like receptors; also free
nerve endings. Axons are large & myelinated. - Adaptation is both slow and fast
Location of receptors allow
them to respond to any
forces applied to the crown
of the teeth (when biting and
chewing)
Brisk tap on tooth — jaw
closing muscles
inhibits
ex. jaw opens to prevent damage
Weak tap on tooth — jaw
closing muscles
activates
ex. to hold onto food and adjust chewing force
