General Sensory Mechanisms II Flashcards
What are the three physiological types of somatic senses?
Mechanoreceptive
Thermoreceptive
Pain
What is exteroreceptive sensation?
Sensation that is from the surface of the body
What are proprioceptive sensations?
Sensations that refer to the physical state of the body. They include:
Position sensations
Muscle and tendon sensations
Pressure sensations
Equilibirum
What are deep sensations?
Sensation to deep pressure, pain and vibrations.
What are the three physiological types of somatic senses?
Mechanoreceptive
Thermoreceptive
Pain sense
What are visceral sensations?
Sensations of the body, specifically to sensations from internal organs.
What are the three differences among touch, pressure and vibration?
- Touch sensation generlly results from the stimulation of tactile receptors in the skin or tissues immediately beneath the skin.
- Pressure sensation generally results from the deformation of deeper tissues.
- Vibration sensation results from rapidly repetitive sensory signals, but some of the same types of receptors as those for touch and pressure are used.
What are the three neuron pathways?
Primary sensory neurons
Secondary neurons
Tertiary neurons
Where do primary sensory neurons arise from?
External receptors.
They travel through the dorsal roots of the spinal cord.
What do primary sensory neurons synapse with?
Secondary neurons
Where are seconday neurons comprised of?
Tracts in the spinal cord and brainstem.
Where do secondary neurons usually terminate?
In the thalamus.
What do secondary neurons synapse with?
Tertiary neurons.
What is the route of tertiary neurons?
From the thalamus to the primary sensory cortex.
What do tertiary neurons travel through in order to get from the thalamus to the primary sensory cortex?
The internal capsule
What are the two ascending pathways?
A pathway for conscious perception
A pathway for unconscious perception
What are the two pathways of conscious perception?
Spinothalamic system
Medial lemniscal system
What are the four pathways of unconscious perception?
Spinocerebellar
Spino-olivary
Spinotectal
Spinoreticular
What are the two tracts in the spinothalamic system?
Lateral spinothalamic tract
Anterior spinothalamic tract
What sensations are carried by the lateral spinothalamic tract?
Pain and temperature
Where does the lateral spinothalamic tract go before synapsing with secondary fibers?
It ascends or descends 1-2 spinal cord segments before synapsing with secondary fibers.
What does the term “decussate” mean?
To cross over
What kinds of axons make up the lateral spinothalamic tract traveling in the lateral column of the spinal cord?
Secondary aons
Before secondary axons make up the lateral spinothalamic tract traveling the lateral column of the spinal cord, what do they do?
They decussate through anterior gray and white commissures.
Secondary fibers are joined in the brainstem by fibers of what tract? What sensations are associated with this tract?
The trigeminothalamic tract.
Pain and temperature from the face and teeth are associated with this tract.
Where do secondary fiber collaterals of the lateral spinothalamic tract project to?
The reticular formation.
It stimulates wakefulness and consciousness.
Secondary fibers project to the trigeminothalamic tract and the reticular formation. Where is the third region that secondary fibers of the lateral spinothalamic tract project to?
The ventral posterolateral nucleus of the thalamus (VPL).
Secondary fibers also synapse with tertiary fibers in VPL.
Where do tertiary fibers (corticopetal fibers) synapse?
In the postcentral gyrus.
This includes somatic sensory areas 3, 1, 2.
Tertiary fibers from the lateral spinothalamic tract form what structure?
The internal capsule.
The internal capsule is a pathway for both corticopetal and corticofeudal fibers.
What sensations are associated with the anterior spinothalamic tract?
Light touch (crude touch), pressure, tickle, itch.
Where do secondary fibers of the anterior spinothalamic tract synapse?
With tertiary fibers in VPL nucleus of thalamus.
Before this, they decussate in anterior gray or white commissures.
Secondary fibers of the anterior spinothalamic tract synapse with tertiary fibers in VPL nucleus of the thalamus. Where do tertiary fibers ascend through?
They ascend through the internal cavpsule to primary sensory cortex.
What is another term for the medial lemniscus system?
The posterior column system.
What sensations are carried by the medial lemniscus system?
Fine touch, pressure and vibration
Where do primary fibers of the medial lemniscus system ascend and synapse?
Primary fibers ascend the entire length of the spinal cord and synapse with secondary neurons in the medulla:
Fasciculus gracilis
Fasciculus cuneatus
Where do fibers of the fasciculus gracilis synapse?
In the nucleus gracilis.
Fibers of the fasicuclus gracilis synapse in the nucleus gracilis. The nucleus gracilis conveys sensations from where?
From below the midthoracic level.
Where do fibers of the fasciculus cuneatus synapse?
In the nucleus cuneatus.
Fibers of the fasciculus cuneatus synapse in the nucleus cuneatus. What senses are conveyed by it?
Sensations from above the midthoracic level.
It also converys proprioceptive sensation from the arms to the cerebellum.
What do secondary fibers of the medial lemniscus system do before they ascend to synapse in the VPL of the thalamus?
They decussate.
After secondary fibers of the medial lemniscus system have decussated, where to they synapse?
In the VPL of the thalamus.
What is the route of tertiary fibers in the medial lemniscus system?
Tertiary fibers ascend through internal capsule to primary sensory cortex.
What are Brodmann’s areas?
About 50 distinct areas of the brain that are basted on histological structural differences.
It is used to refer to the many different functional areas of the human cortex.
What Brodmann’s areas make up the primary somatosensory area?
1, 2 and 3
What Brodmann’s areas make up the somatosensory association area?
5 and 7
Where is the somatosensory area located?
Between the primary motor cortex (near the central fissure) and somatosensory area II
What parts of the body is somatosensory area II responsible for?
Leg
Arm
Face
What parts of the body is somatosensory area I responsible for?
Thigh
Thorax
Neck
Shoulder
Head
Fingers
Tongue
Intra-abdominal
A widespread bilateral excision of the somatosensory area results in … ?
Loss of ability to localize the different sensations in the different parts of the body.
Los of ability to judge critical degrees of pressure against the body.
Loss of ability to judge weights of objects.
Loss of ability to judge shapes or forms
Loss of ability to judge texture of materials
Pain and temperature are present, but poorly localized.
Where does the somatosensory area II receive signals from?
Brain stem
Somatosensory area I
Visual and auditory areas of the body
True or false: projects for somatosensory area I are required for function of somatosensory area II
True
True or false: removal of somatosensory II has no apparent effect on the response of neurons in somatosensory area I
True
Layers I and II of the somatosensory cortex recepive input from where?
Lower brain centers.
What is the function of somatosensory cortex layers II and III?
They send information through the corpus callosum to the opposite hemisphere.
Where do neurons of layers V and VI project to?
Distant areas such as basal nuclei, brain stem and spinal cord.
Where do axons from layer VI project to?
The thalamus
What layer of the somatosensory cortex receives incoming sensory signals?
Layer IV
What is the difference between a somatic sense and special sense?
A somatic sense is a sense that is from the entire body. It includes mechanoreceptive, thermoreceptive, and pain senses.
Special senses are vision, hearing, smell, taste, equilibrium.
