General Sensory Mechanisms III Flashcards
What type of potential do receptors create?
A local, decremental potential that is essentially a local potential.
If the potential is strong enough (through summation), it may generate an action potential at the first node of Ranvier on the primary sensory neuron.
most pathways are made up of three neurons. What are these neurons?
Primary neurons
Secondry neurons
Tertiary neurons
Where do primary neurons originate from?
Peripheral receptors, such as Merkel’s receptors.
Where do primary neurons enter the spinal cord?
Via dorsal roots of the spinal (cranial) nerves.
They synapse in the spinal cord with secondary neurons.
Where do secondary neurons originate?
In the spinal cord gray matter.
They travel through the spinal cord in one of the myelinated columns.
Where do secondary neurons synapse?
The thalamus.
They synapse with tertiary neurons.
Where do tertiary neurons travel through?
The internal capsule.
It is a myelinated pathway between the thalamus and some of the basal nuclei.
Where do tertiary neurons synapse?
In the somatosensory cortex.
What is two-point discrimination touch?
It refers to the ability to distinguish two separate points as close as 2 millimeters apart.
Where does two-point discrimination touch travel?
In the dorsal column-medial lemniscal pathway.
What is the importance of lateral inhibition?
It blocks the lateral spread of excitatory signals, thereby increasing the degree of contrast in the cerebral cortex.
Where does lateral inhibition occur?
Dorsal column nuclei
Ventrobasal nuclei of thalamus
Somatosensory cortex
What is a pathway that carries two point discrimination touch?
Dorsal column-medial lemniscal pathway.
What is the pathway of the dorsal column-medial lemniscal pathway?
Peripheral receptors -> spinal nerve -> dorsal root of spinal nerve -> spinal cord
What are two regions that the dorsal column-medial lemniscal system travels through?
The thalamus to the somatosensory cortex. This is associated with secondary neurons.
The transmission of a pinpoint stimulus signal to the cerebral cortex requires synapses. Generally, the more synapses, the ___ the stimulus.
Stronger
Without lateral inhibition, how would a stimulus be felt?
It would be perceived only as one point instead of two.
Where do axons from the lower limbs travel?
In the medial portions of the dorsal columns.
Each of these areas of dorsal columns is called the fasciculus gracilis.
Where do axons from the upper limbs travel?
In the lateral portions of the two dorsal columns.
Each of these areas of the dorsal columns is called the fasciculus cuneatus.
Where do aons in the fasciculus gracilis synapse?
In the lower medulla in the nucleus gracilis.
Where do axons in the fasciculus cuneatus synapse?
In the lower medulla in the nucleus cuneatus.
What are the medial lemniscus?
Secondary neurons that travel through the brain stem as paired tracts.
Where do secondary neurons synapse?
In the basolateral nucleus of the thalamus with tertiary neurons.
Where do tertiary neurons travel through?
The internal capsule to the somatosensory cortex.
What neurons decussate?
Secondary neurons
What is fast pain generally elicited by?
Mechanical and thermal stimuli.
It is typically carried by Adelta pain fibers.
Where do fast pain fibers terminate?
In lamina I of the dorsal horns of the spinal cord.
What is slow pain?
Aching, slow burning, throbbing, nauseous and chronic.
It may be elicited by mechanical, thermal and chemical stimuli.
What type of fibers carry slow chronic pain?
Type C fibers.
They mostly terminate in layers II and III of the dorsal horns of the spinal cord.
Pain travels through what type of pathways?
Anterolateral pathways.
Where do primary pain fibers synapse?
In the dorsal horns of the spinal cord (layers 1, 2, or 3) with the secondary fibers.
The secondary fibers immediately decussate and make up the anterolatera pathways.
Fast pain fibers make up what type of tracts?
Neospinothalamic tracts.
They synapse and terminate the ventrobasal nuclei of the thalamus.
Where do tertiary fibers ascend to?
The somatosensory cortex.
What type of pain fibers make up the paleospinothalamic pathway?
Slow pain fibers.
Where do most of the paleospinothalamic secondary fibers terminate?
Throughout the brainstem, although some pass all the way to the thalamus.
What neurotransmitter is used by the A delta fibers of the fast-pain pathway?
Glutamate
What do type C fibers of the slow, chronic-pain path release?
Glutamate and substance P.
Glutamate acts instantaneously, but substance P is released more slowly.
What does Brown-Sequard syndome occur as a result of?
A hemisection of the spinal cord.
All motor functions are blocked on the side of the transection in all segments below the level of the transection.
You encounter a patient who has a transection of the right spinal cord. Sensation so f pain, heat and cold are lost on the left side of the body below the transection. They also have a loss of kinesthetic and position sensations, vibration sensation, and two point discrimination. What does the patient most likely have?
Brown-Sequard syndrome
In Brown Sequard Syndome, dorsal column sensation is lost on the ___ side of transcetion below the level of transection.
Same
Where do pain fibers synapse?
In the reticular formation.
Parts of it go to the thalamus.
What are the three major components of the analgesia system?
Periaqueductal gray and periventricular regions of the brainstem and third ventricle
Raphe magnus nucleus and reticular nuclei in medulla.
Pain inhibitory complex in dorsal horns of spinal cord.
What is the function of the analgesia system?
It is a pain control system
What is the function of an enkephalin neuron?
It suppresses pain by inhibiting synapses of primary and secondary neurons.
What are the three types of receptors that discriminate thermal gradations?
Cold
Warmth
Pain
What are warmth nerve endings mainly transmitted over?
C-tyep fibers.
What are cold and warmth receptors thought to be stimulated by?
Changes in their metabolic rates.
Thermal signals are transmitted in pathways parallel to those for pain signals.
What is referred pain?
Pain that occurs when visceral pain fibers are stimulated and stimulate some of the pain fibers that conduct pain signals from the skin.
What conditions result in severe pain?
Severe pain results when there is diffuse stimulation of pain nerve endings throughout the viscera.
Such diffuse pain can result from ischemia.
All visceral painf rom the thoracic and abdominal cavities is transmitted via what type of pain fibers?
Type C pain fibers.
What are headaches the 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
How are receptor potentials created?
By opening “modality” gated channls such as sodium channels that are opened in response to membrane deformation caused by the touch or pressure.
