Question

neural pathways case study packet
case 1: the broken reflex
marcus was riding his bike when he hit a pothole and flew over the handlebars. he landed hard on his lower back. since the accident, he no longer reacts when doctors tap below his knee with a reflex hammer, though he can still feel touch and pressure in his leg.
questions:

• 1. what type of response is being tested with the reflex hammer?
• 2. which neurons are likely still functioning? which might be damaged?
• 3. explain how this injury may have disrupted marcuss neural pathway.
• 4. is this a somatic or automatic response? why?

Explanation:

Question 2

To determine functioning/damaged neurons:

• Sensory neurons: Marcus feels touch/pressure, so sensory (transmit sensory info) work.
• Interneurons (in spinal cord): Sensory info reaches the brain (he feels touch), so interneurons relaying to brain are functional.
• Motor neurons: No reflex (muscle response), so motor neurons (transmit from spinal cord to muscle) are likely damaged.

Reflex pathway: Sensory → Interneuron (spinal) → Motor → Muscle.
Injury (lower back) likely damaged motor neurons or their pathway. Sensory/interneurons work (he feels touch), but motor neurons can’t send signals to leg muscles, so reflex (knee-jerk) is lost.

• Somatic response: Controlled by somatic nervous system, voluntary/involuntary (reflexes) involving skeletal muscles.
• The knee-jerk reflex uses skeletal muscle (quadriceps) and is a somatic reflex (part of somatic nervous system, which controls skeletal muscles). Automatic (reflex) but somatic, not autonomic (which controls smooth/cardiac muscles, glands).

Answer:

Likely still functioning: Sensory neurons (transmit touch/pressure) and interneurons (relay to brain).
Might be damaged: Motor neurons (fail to trigger muscle response for reflex).

Question 3