Lecture 6 -- Sensory Systems Flashcards
(14 cards)
What is the concept of labeled lines?
The concept that each nerve input to the brain reports only a particular type of information.
- the brain recognizes stimuli as separate due to the action potentials being carried in dedicated nerves.
- It’s how we can distinguish different touch stimuli
What is a receptor potential?
A local change in the resting potential of a receptor cell in response to stimuli, which may initiate an action potential.
What are the roles of different skin receptors in touch perception?
Meissner’s corpuscles detect changes and localized movement.
Merkel’s discs respond to edges and points for shape/form detection.
Ruffini corpuscles detect skin stretch during motion.
Free nerve endings sense pain, itch, temperature.
These receptors are densest in sensitive areas like fingertips, lips, and tongue.
How does the Pacinian corpuscle transduce sensory stimuli into neural signals
When stimulated (under 200 Hz), it stretches the sensory nerve membrane, opening mechanically gated sodium channels (via Piezo proteins).
This generates a graded receptor potential, proportional to stimulus intensity. If the potential exceeds threshold, it triggers an action potential sent to the spinal cord.
how is a sensory event is encoded in action potentials in sensory fibers?
- Sensory events are encoded by the number, frequency, and pattern of action potentials in sensory neurons.
- Differences in stimulus intensity are represented by changes in the rate and timing of these spikes.
- Spatial location is conveyed through labeled lines
Why do some receptor cells respond only to strong stimuli?
- Some receptor cells have higher activation thresholds.
- This allows the sensory system to cover a wide range of intensities by recruiting different neurons as stimulus strength increases.
- Using multiple receptors with varying sensitivities ensures accurate encoding of both weak and strong stimuli
What are receptive fields and how scientists detect them?
A receptive field is the specific region of space where a stimulus will alter a sensory neuron’s firing rate.
Scientists detect receptive fields by recording a neuron’s response while applying stimuli to different areas.
Somatosensory receptive fields often have excitatory centers and inhibitory surrounds (or vice versa), helping the brain detect edges and fine spatial details.
What are a couple of processes that change a sensory neuron’s response to stimuli?
Adaptation
- A decrease in response to a sustained stimulus.
- Phasic receptors adapt quickly (e.g., ignoring clothing on skin)
- tonic receptors adapt slowly or not at all (e.g., pain sensors).
Filtering and selection:
- Sensory systems selectively emphasize important stimuli and suppress irrelevant ones before the signal reaches the brain, ensuring efficient and meaningful perception.
The main somatosensory pathway is the dorsal column system.
Somatosensory touch receptors send their axons from the skin to the dorsal part of the spinal cord.
Axons ascend as part of the spinal cord’s dorsal column system and synapse onto neurons in the brainstem, which then project contralaterally and go to the thalamus.
From the thalamus, the sensory information is directed to cortex.
Inputs are organized according to a somatosensory map of the body surface, divided into dermatomes, each innervated by a particular spinal dorsal root.
Where is the primary somatosensory cortex located? How is it organized?
In the postcentral gyrus, the long strip of tissue that lies posterior to the central sulcus, which separates the parietal lobe from the frontal lobe.
Cells in S1 are arranged as a map of the body, but it is a distorted map—the size of each region is proportional to the density of sensory receptors in that skin area (homunculus diagram)
- Different cortical regions may receive and process the same information, often in collaboration with the primary sensory cortex.
- Interactions between modalities can occur in the nonprimary sensory cortex, where different aspects of perceptual experience may be integrated.
- Polymodal neurons allow different systems to converge
- For example, humans detect a visual signal more accurately if it is accompanied by a sound from the same part of space
What is the primary somatosensory cortex?
(also called S1)
the initial destination of touch information in the cortex.
It lies in the postcentral gyrus and receives touch information from the opposite side of the body.
It is organized into a map of the body, where areas with more sensory receptors have larger representations.
What is the primary sensory cortex?
the initial destination of sensory inputs to the cortex.
Examples include the primary somatosensory cortex, primary auditory cortex, and so on. Each is dedicated to processing input from one specific sense.
What is the nonprimary sensory cortex?
other cortical regions that receive and process the same sensory information, often working in collaboration with the primary sensory cortex. These regions process different aspects of perceptual experience.
