Somatosensory System Flashcards
What side of the spinal cord are somatosensory neurons found?
The dorsal side
What side of the spinal cord are the motor neurons found?
The ventral side
What is meant by somatotropic maps?
The brain is organized in regions that correspond to different parts of the body. These regions are called somatotropic maps.
What two types of afferent fibers are part of the somatosensory system?
- The mechanosensory afferent (touch and pressure)
2. The Nocireceptive afferent (pain and temperature)
At what part of the brain will the mechanosensory fibers cross to the other side?
The Caudal Medulla
Where do the nociceptive fibers cross over?
They cross over immediately, in the spinal cord.
How does the mechanosensory fiber lead to an action potential?
The pressure on the skin leads to the phospholipid bilayer of the sensory neuron to go further apart. This drop in tension/pressure between the phospholipids leads to the opening of Na+ channels.
What is the difference between large and small receptive fields?
Large receptive fields have a low precision as stimulations in the field are hard to discriminate and they have a high sensitivity, as every stimulus will result in a response.
Name the types of mechanoreceptors.
- Meissner corpuscle (most abundant, but less sensitive than Merkel)
- Merkel cell (most precise, but less sensitive)
- Ruffini corpuscle (detects the direction of movement)
- Pacinian corpuscle (detects pressure)
What mechanosensors have a large receptive field?
Panacinian and Ruffini
What mechanosensors have a small receptive field?
Merkel and Meissner
What are the slow-adapting sensors and fast-adapting sensors good for?
The slow-adapting can keep feeling whether an object is touched and the rapidly adapting only feel change, but the stimulation quickly dies out.
Where are the receptors for proprioception found and how are they called?
They are found in the muscles.
- Muscle spindles (change in muscle length)
- Golgi Tendon (change in muscle tension)
Together they map the positioning of the limbs
What is a dermatome?
The innervated area of sensory axons of a single dorsal root ganglion.
what nerve mediates sensory input in the face?
Cranial nerve V (trigeminal nerve)
What happens if you lose a finger, for example?
The somatotropic map in the brain changes, so two areas that were unrelated start to represent the area that is missing. (phantom pain)
what nerves feel temperature and pain?
Free nerve endings
What receptors are found on the free nerve endings?
TRP channels that are adapted Ca2+ and Na+ transporters.
When do TRPs open?
They open in reaction to heat and chemical irritants (substances released by damaged tissues)
What is the effect of Capsaicin on the fibers?
Capsaicin affects C-fibers. they bind to the thermoreceptors and open their ion channels. This is perceived as heat by the body.
Why do people perceive acid reflux in the esophagus as the pain of the skin?
The sensory neurons responsible for the feeling of pain from the viscera project on the same neurons in the dorsal horn, making the brain process the information as skin pain.
What types of sensory fibers are there?
- AB - mechanoreceptor
- AD - Thermoreceptor and pain
- C-fiber - unmyelinated thin fibers, used for the longer perception of pain
How is the pain sensation being relieved?
Inhibitory neurotransmitters in the dorsal root ganglions are used to block certain pain signals.
What are the 5 important cell types in the retina? Briefly explain their function
- Photoreceptors (cones are rods) = detect light and create action potentials
- Horizontal cells = interconnect synapses between Bipolar and photoreceptor
- Bipolar cells = transports signals from cones and rods to ganglion cells
- Amacrine Cells = interconnect synapses between bipolar and ganglion
- Ganglion cells = they make up the optic nerve
What different kinds of colors do rods and cones see?
- Rods are sensitive to black and white light
2. Cones are sensitive to colored light
why are the photoreceptors located at the back of the retina, not the front?
Because light can cause a lot of damage. The cones and rods are tied to pigment epithelial cells that engulf and constantly repair the photoreceptors.
When are the Ca2+ and Na+ channels closed on the photoreceptors?
In presence of light. When light is absent, the ion gates are open and the membrane potential is close to 0.
Which molecule detects light?
Retinol - it changes configuration when photons are present. This, in turn, changes the GDP to GTP in the G-protein complex
What area of the retina is responsible for color vision?
The fovea - cones are extremely concentrated there
What is the optic disk?
The optic disk is a blind spot on the retina, where no cones or rods are present.
How do more rods projecting onto one bipolar cell lead to a higher sensitivity?
Because more rods are connected to one bipolar cell, a small signal coming from all the rods will sum up, leading to an action potential
How do cones project onto the bipolar cells?
one to one projection.
Briefly explain the ON and OFF centers in bipolar cells.
Cones release glutamate at the synaptic end in the absence of light (excited in dark). The glutamate then activates the OFF-center bipolar cell which then projects onto an OFF-ganglion. However, in the presence of light, the cones will inhibit the release of Glutamate. Less Glutamate will activate the ON-center bipolar cell, which will project onto an ON-ganglion.
Where are action potentials generated in the ear?
In the cochlea
what is the function of Organ of Corti?
The Organ of Corti is the place where hair cells are found, that can feel vibrations in the ear.
Where are high frequencies and low frequencies felt in the cochlea?
Low frequencies at the tip and high frequencies at the base.
How do the hair cells in the ear generate action potentials?
Just like mechanoreceptors, the hair cells in the ear can detect a change in pressure in the lipid bilayer. This in turn leads to the opening of the ion channels and thus depolarization.
What ion plays a role in the depolarization of the hair cells and why?
K+ , instead of Na+
The concentration of potassium drives the flow of potassium inward. The gradient of ions plays the greatest role in depolarization and the way they travel across the membrane
What is the pyriform cortex?
It is the olfactory cortex
What is different from the sense of smell, compared to other senses?
The sense of smell is the only one that does not use the Thalamus as a relay station. It directly projects on the Pyriform Cortex.
What parts of the Olfactory Receptor Neurons are picking up the molecules in the air?
The cilia of the neurons
Why do Olfactory Receptor Neurons regenerate?
They are located in the nose cavity and are thus susceptible to pathogens. The nose cavity has to be renewed from time to time to prevent permanent damage. Because of that, the neurons regenerate as well.
What type of receptor is used in the olfactory neurons?
A G-protein - activation by molecules lead to cleavage of the abc complex, which in turn activates different ion channels.
What are the factors that determine how we perceive a smell?
- The concentration of the odor molecule
2. The specificity of the olfactory neurons
Which receptors are important for detecting pheromones? (in rodents)
V1R and V2R
What cranial nerves are important for the relay of taste signals?
VII (7)
IX (9)
X (10)
How is salt and acid (sour) felt by the tongue?
Salt ha Na+ and acid has H+ which are both positive ions In high concentrations they can go across the membrane and depolarize the cell.
Na+ and H+ channels are always open.
How is Sweet, umami, and Bitter taste felt?
Those make use of G-proteins that activate the TRPM channel
