Sensory Receptors 1-2 Flashcards
Describe the structure of cutaneous receptors.
A cutaneous receptor is the type of sensory receptor found in the skin (the dermis or epidermis).
- Merkel Discs: Discriminative touch (fine touch, texture).
- Meissner’s Corpuscles: Light touch, vibration.
- Pacinian Corpuscles: Deep pressure, high-frequency vibration.
- Ruffini Endings: Skin stretch, proprioception.
- Cold Receptors: Cold temperature detection.
- Warm Receptors: Warm temperature detection.
- Nociceptors: Pain detection.
- Hair Follicle Receptors: Hair movement detection.
Explain the mechanisms of sensory transduction in the skin.
Stimulus (touch, pressure, temperature, pain) activates a specific cutaneous receptor.
The receptor undergoes mechanotransduction (for mechanoreceptors) or thermotransduction (for thermoreceptors), or nociception (for pain receptors), which causes ion channels to open.
The opening of ion channels leads to the depolarization of the nerve ending, generating a receptor potential.
If the receptor potential reaches the threshold, an action potential is generated and transmitted along sensory afferent fibers to the spinal cord and then to the brain.
The brain processes and interprets the signal to produce a sensory perception.
Explain the concept of frequency coding.
Frequency coding is a concept used in neuroscience and signal processing to describe how information is encoded in the frequency or rate of repetitive signals, such as neuronal firing. Instead of using a fixed pattern of signals to convey information, frequency coding relies on the rate or frequency at which an event (like a neuron firing) occurs.
Here’s how it works:
Basic Principle: In many sensory systems, such as hearing or touch, the frequency of a signal (like the number of spikes or pulses over time) can represent the intensity or strength of a stimulus. For example, if a sensory receptor receives a strong stimulus, it might fire at a higher frequency (more spikes per unit of time), while a weaker stimulus results in a lower firing frequency.
Neuronal Firing: In the brain, neurons communicate via electrical signals, often called action potentials or “spikes.” Instead of encoding information through the precise timing of each individual spike, neurons may encode information by how quickly they fire. A higher firing rate can indicate a stronger or more intense stimulus, whereas a lower rate can signify a weaker one.
Encoding Stimulus Properties: Frequency coding is often used to encode properties like the intensity of a stimulus, not the specific timing of individual spikes. For instance, a loud sound may result in a higher rate of neuron firing than a soft sound. This allows the brain to interpret the strength or magnitude of external stimuli based on how frequently neurons are activated.
~ In summary, frequency coding is a mechanism where the rate at which neurons fire conveys information about the intensity or magnitude of stimuli, helping the brain interpret different sensory inputs efficiently.
Describe the structure and function of the muscle spindle.
They monitor muscle length and rate of change of muscle length - they control reflexes and voluntary movements.
Structure of the Muscle Spindle:
Capsule:
- The muscle spindle is enclosed in a connective tissue capsule, which helps protect and contain the sensory components.
- Intrafusal Muscle Fibers: Inside the capsule, there are specialized muscle fibers called intrafusal fibers. These fibers are different from the regular muscle fibers (called extrafusal fibers) that make up the bulk of the muscle. Intrafusal fibers are smaller and do not generate significant force during muscle contraction. There are two main types of intrafusal fibers:
- Nuclear bag fibers: These have a central region with a cluster of nuclei and are sensitive to changes in muscle length (static sensitivity) and the speed of those changes (dynamic sensitivity).
- Nuclear chain fibers: These fibers have a more uniform distribution of nuclei along their length and primarily respond to changes in muscle length.
- Sensory Endings:
- Primary (annulospiral) endings: These are wrapped around the central region of the nuclear bag and nuclear chain fibers. They are sensitive to both the length of the muscle and the rate of change in length (dynamic response). These endings are involved in detecting rapid changes in muscle stretch.
- Secondary (flower-spray) endings: These are located primarily on the ends of the nuclear chain fibers. They are mainly sensitive to muscle length and provide information about the static position of the muscle, meaning how much the muscle is stretched but not necessarily how quickly it’s changing.
- Gamma Motor Neurons: The intrafusal fibers are innervated by gamma motor neurons, which adjust the sensitivity of the spindle by causing the intrafusal fibers to contract slightly. This keeps the spindle responsive to changes in muscle length, even when the muscle is actively contracted.
Explain the mechanisms of efferent control of spindle function.
- Gamma motor neurons (dynamic and static) control the tension of the intrafusal fibers within the muscle spindle.
- This control ensures that the spindle remains sensitive to muscle length changes, even when the muscle is contracting or in use.
- The interaction between alpha motor neurons (which control the extrafusal fibers) and gamma motor neurons (which control the intrafusal fibers) through alpha-gamma coactivation is crucial for maintaining accurate proprioceptive feedback and effective muscle reflexes.
Describe the role and mechanism of action of the Golgi tendon organ.
- The Golgi tendon organ is a sensory receptor located in the tendon that monitors the tension exerted by muscle contraction.
- It sends signals to the CNS when excessive force or tension is detected.
- Through a disynaptic reflex arc and autogenic inhibition, the GTO helps to prevent muscle injury by inhibiting excessive muscle contraction.
- This feedback mechanism contributes to muscle safety, postural control, and fine motor coordination, ensuring that muscles do not produce forces that could damage the muscle-tendon unit.
