lab midterm #4 Flashcards
(7 cards)
- What must happen for your participant to feel two distinct points of contact?
Activation of Separate Receptive Fields
* The two points must stimulate different receptive fields in the skin, meaning that two separate groups of sensory neurons must be activated.
2. Sufficient Distance Between Stimuli
* The two stimuli must be far enough apart to avoid spatial summation, where the signals blend into one.
* The required distance varies based on body region due to differences in receptor density (e.g., fingertips have smaller receptive fields and better discrimination than the back or thigh).
3. Separate Processing in the Somatosensory Cortex
* The sensory neurons must send distinct signals to the brain’s somatosensory cortex in the parietal lobe.
4. Minimal Lateral Inhibition
* The nervous system uses lateral inhibition to sharpen sensory perception by suppressing signals from surrounding neurons.
* If lateral inhibition blurs the distinction between the two points, they may be perceived as a single stimulus.
- What are the physiological properties of the receptive fields in the area with the highest two-point threshold (smallest distance) vs. the lowest two-point threshold (largest distance)?
Areas with the Lowest Two-Point Threshold (Highest Sensitivity, e.g., Fingertips, Lips)
* Small Receptive Fields → Each sensory neuron covers a small area of skin, leading to high spatial resolution.
* High Receptor Density → Many mechanoreceptors (e.g., Merkel discs, Meissner’s corpuscles) are packed closely together.
* Strong Lateral Inhibition → Nearby neurons inhibit each other’s signals to enhance contrast and improve discrimination.
2. Areas with the Highest Two-Point Threshold (Lowest Sensitivity, e.g., Back, Thigh)
* Large Receptive Fields → Each sensory neuron covers a larger area, making it harder to distinguish between two stimuli.
* Low Receptor Density → Fewer mechanoreceptors per unit area, leading to poorer spatial resolution.
* Weaker Lateral Inhibition → Less refinement in signal contrast, making it more likely that two points will be perceived as one.
- You tap on the subject’s patella ligament with a tendon tap hammer. List the physiological responses that occur to elicit a slight extension of the leg (make sure to name specific structures).
- Mechanical Stimulus Detected (Receptor Activation)
* The tendon tap stretches the quadriceps muscle slightly, pulling on its muscle spindles (sensory receptors within the muscle).
* Muscle spindles (specifically the Ia afferent fibers in the spindle) detect this sudden stretch. - Sensory Signal Sent to Spinal Cord
* The Ia afferent neurons send an action potential through the femoral nerve to the spinal cord (L2-L4 region of the lumbar spinal cord).
* This signal enters the dorsal horn of the spinal cord. - Direct Synapse with Motor Neuron (Monosynaptic Pathway)
* The Ia afferent neuron directly synapses with an alpha motor neuron in the ventral horn of the spinal cord.
* Since it is a monosynaptic reflex, there is only one synapse, leading to a very fast response. - Motor Signal Sent to Quadriceps Muscle
* The alpha motor neuron sends an action potential back through the femoral nerve to the quadriceps muscle.
* The quadriceps muscle contracts, causing knee extension. - Reciprocal Inhibition of Antagonistic Muscles
* The Ia afferent neuron also synapses with an inhibitory interneuron in the spinal cord.
* This interneuron inhibits the alpha motor neurons of the hamstring muscles (antagonists of the quadriceps), preventing them from contracting.
* This process, called reciprocal inhibition, ensures smooth knee extension.
- During the Knee-jerk reflex exercise, what does latency period indicate about what is happening in the body?
The latency period during the jendrassik manoeuvre typically does not change, but the magnitude of the response increases… why?
- Same reflec pathway and conduction speed
- No additional synapses or delays
- During the knee-jerk reflex exercise, what does the response amplitude indicate about what is happening in the body?
A strong response amplitude suggests that the monosynaptic reflex arc (sensory neuron → spinal cord → motor neuron) is functioning well.
the motor neurons (specifically the alpha motor neurons) are effectively stimulating the quadriceps to contract strongly.
- While performing the Jendrassik maneuver does the participant’s response amplitude change? Why did or why didn’t it change?
While the latency period remains the same, the amplitude of the response increases because:
1. Reduced Inhibitory Input from the Brain
o activates descending motor pathways that inhibit spinal cord inhibitory interneurons.
o This reduces inhibition of the alpha motor neurons, allowing for greater quadriceps contraction.
2. Increased Corticospinal Excitability
o Engaging upper-body muscles through the maneuver may increase overall spinal cord excitability, amplifying the reflex.
3. Distraction Effect
The maneuver distracts the participant, preventing conscious suppression of the reflex, leading to a more pronounced knee-jerk response
- During the Knee-jerk reflex exercise, what does latency period indicate about what is happening in the body?
The latency period in the knee-jerk reflex refers to the short delay between the tendon tap and the leg extension response. This period reflects the time required for neural transmission and processing in the reflex pathway.
