Lecture 2: Somatosensory system Flashcards
N.C
In what kind of stimuli is the somatosensory system involved?
Tactile, pain, temperature and proprioception stimuli
What is proprioception?
Sense of self-movement and posture of body parts
What are tactile stimuli?
Physical sensations experienced through the sense of touch (Pressure, vibration, texture, etc. detected by mechanoreceptors receptors in the skin)
For the sensory function ‘touch’ we have mechanoreceptors.
What are mechanoreceptors and which do we have?
Mechanoreceptors are sensory receptor cells in the skin.
We have:
(Bare nerve endings), Meissner’s corpuscle, Merkel disk receptor, Ruffini endings and Pacinian corpuscle
Why do we need 4 different receptor types?
Because each receptor type is sensitive to a certain type of information.
One of the characteristics of a stimulus that should be encoded is time. One specific part that should be encoded is the adaptation. What kind of receptors are slowly adapting and which rapidly adapting. Name the receptors that belong to the right category.
Slowly adapting:
- Tonic receptors: they respond for the duration of a stimulus
- Merkel & Ruffini
Rapidly adapting:
- Phasic receptors: they respond rapidly to a constant stimulus and turn off immidiatly. + they fire once more when the sitmulus turns off
- Meissner & Pacinian
What happens when pressure is applied to the mechanoreceptors?
The membrane of the cell will stretch, which causes ion channels to open. Na+ will enter the cell which can create an AP. This depends on the intensity of the stimuli.
(With a weak or moderate stimulus, there usually is a receptor potential = NOT AP)
Which mechanoreceptors are responsible for detecting low frequency and high-frequency vibrations, and what types of objectes do they help perceive?
Low-frequency: Detected by Meissner’s corpuscles, which helps perceive textured objects.
High-frequency: Detected by Pacinian corpuscles, which helps perceive fine surface objects.
How does transmission from the PNS to the CNS work: What is the pathway and what are the relay stations?
Tranmission goes via the Dorsal-colum-medial-lemiscus pathway.
- Stimuli will go via the dorsal root of the spinal nerve to the midline of the spinal cord.
- Then it will cross the midline of the medulla (relay station 1)
- Next it will cross the ventral posteriolateral nucleus of the thalamus (relay station 2)
- Eventually sensations are perceived in the primary somatic sensory cortex.
What is a receptive field
The part of the skin that is innervated by one mechanoreceptor
Which of the slowly and rapidly adapting mechanoreceptors have a small/large receptive field?
Slowly adapting:
- Merkel disk cells have a small receptive field
- Ruffini endings have a large receptive field
Rapidly adapting:
- Meissner corpuscles have a small receptive field
- Pacinian corpuscles have a large receptive field
NOTE: receptors with a large field are located in deep layers in the skin
In which case is the perception capacity of the somatosensory system to precisely locate stimuli on the skin the highest?
With small, closely spaced receptive fields
Receptive field relay station:
Each neuron in the relay nucleus receives input from multiple receptors and therefore have a larger receptive field than the receptors.
What is the difference in fire pattern between receptors and that of relay neurons?
Relay neurons have a more spatial distribution of excitation in comparison to receptors.
In relay neurons you have a spontaneous firing rate
What is lateral inhibition, and how do inhibitory neurons contribute to it?
Lateral inhibition is a process where excited sensory neurons reduce the activity of neighboring neurons through inhibitory interneurons, enhancing contrast and sharpening perception. It helps the brain detect edges, fine details, and differences in sensory input by suppressing weaker or adjecent signals.
What is somatotopy?
Regions on the cerebral cortex that correspond to certain area of the body
