General Sensory Mechanisms II (Lec 4) Flashcards
What does widespread bilateral excision of somatasensory area I cause?
loss of ability to localize discretely the different sensations in the different parts of the body, loss of ability to sense pressure and weight, loss of ability to judge weight, shape, and texture of objects
Where does the somatosensory area II receive signals from?
brain stem, secondarily from somatosensory area II, visual/auditory areas
True or False?
projections from somatosensory area I are not required for function of somatosensory area II
false, they are required
What do layers I and II of the somatosensory cortex receive input signals from?
lower brain centers
What do layers II and III of the somatosensory cortex send information through?
corpus callosum to opposite hemisphere
What are found in layers V and VI and where do they project to?
large neurons in layer V project to distant areas such as basal nuclei, brain stem, and spinal cord
axons from layer VI project to thalamus
How is receptor potential created?
by opening “modality” gated channels such as sodium channels that are opened in response to membrane deformation caused by the touch or pressure
Most sensory pathways are made up of how many neurons?
three
Where do primary sensory neurons originate from and where do they go?
originate from peripheral receptors such as Merkel’s receptors; enter spinal cord or brain via dorsal roots of cranial nerves and synapse with secondary neurons
note: primary neuron cell bodies are located in the dorsal root ganglia
Where do secondary sensory neurons originate from and where do they go?
originate in spinal cord gray matter; travel through spinal cord and synapse in thalamus with tertiary neurons
Where do tertiary sensory neurons travel through?
internal capsule: myelinated pathway between thalamus and basal nuclei and synapse in somatosensory cortex
What is two-point discrimination touch and where does it travel?
the ability to distinguish two separate points as close as 2 mm apart; travels in the dorsal column-medial lemniscal pathway
In the dorsal column-medial lemniscal pathway, where do axons from the lower limbs travel?
in the medial portions of the two dorsal columns
In the dorsal column-medial lemniscal pathway, where do axons from the upper limbs travel?
in the lateral portions of the two dorsal columns
What are the two subdivisions of the dorsal column that make up the two tracts in the medial lemniscus?
fasciculus gracilis; fasciculus cuneatus
What are pain receptors (nociceptors)?
free nerve endings
What are some of the characteristics of fast pain?
felt within 0.1 seconds after stimulus is applied; not felt in deep tissue; generally elicited by mechanical and thermal stimuli; is typically carried by pain fibers
Where do fast pain fibers terminate?
in lamina I of the dorsal horns of the spinal cord
What are some of the characteristics of slow pain?
felt about 1 second after stimulus is applied and increases over several seconds; aching/slow burning/throbbing/nauseous/chronic; elicited by mechanical, thermal, and chemical stimuli; carried by C type fibers
Where C type fibers in slow pain terminate?
layers II and III of the dorsal horns of the spinal cord
Pain travels through ____ pathways
anterolateral
Secondary fibers in pain pathways immediately decussate and make up what pathways?
the anterolateral pathways
Fast pain fibers make up what tract? Where do they terminate?
make up neospinothalamic tract; terminate in ventrobasal nuclei of thalamus
Slow pain fibers make up what pathway? Where do they terminate?
make up paleospinothalamic pathway; terminate throughout the brainstem
What do the fibers of the fast pain path use as their NT?
glutamate
What do Type C fibers of the slow path release as NTs?
glutmate instantaneously; substance P which is released more slowly
What is Brown-Sequard syndrome?
occurs when there is a hemisection of the spinal cord - all motor functions are blocked, sensations of pain are lost, and two-point discrimination type sensations are lost
What does the analgesia system consist of?
periaquaductal gray and periventricular regions of brainstem and third ventricle, raphe magnus nucleus and reticular nuclei in medulla, an drain inhibitory complex in dorsal horns of spinal cord
What are the three types of receptors that discriminate thermal gradations?
cold; warmth; pain
Warmth is transmitted over what type of fibers?
C-type
Cold is transmitted over what type of fibers?
Small type fast (Abomb symbol) myenlinated endings
Which receptor is more numerous, cold or warmth?
cold; 3-10 times as numerous
What stimulates cold and warmth receptors?
changes in metabolic rates
What is referred pain?
occurs when visceral pain fibers are stimulated and stimulate some of the pain fibers that conduct pain signals from the skin
Severe referred pain can result from what?
ischemia
What causes headaches?
result of pain referred to the surface of the head from deep head structures
True or False?
The brain itself is almost completely insensitive to pain
true
What is the primary somatosensory area made up of?
Brodman’s areas 1, 2, 3
Brodman’s areas 5 & 7 make up what?
The somatosensory association area
All visceral referred pain from the thoracic and abdominal cavities is transmitted via what type of fiber?
Type c pain fibers
