Spinal Reflex Arc Diagram

Let's go through each question in the worksheet and solve them step by step, with explanations.

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Question 1: Which structure is the red arrow pointing to in the image?

Image Description:
The diagram shows a spinal reflex arc, including:
- A receptor (at the top left)
- A sensory neuron (carrying signal from receptor to spinal cord)
- An interneuron in the spinal cord
- A motor neuron carrying signal to the effector (muscle)
- The effector (muscle at the bottom)

The red arrow points to the nerve fiber extending from the receptor into the spinal cord.

#### Analysis:
- The receptor detects the stimulus.
- The sensory neuron transmits the signal from the receptor to the spinal cord.
- The red arrow is showing the pathway of the sensory neuron from the receptor toward the spinal cord.

So, the red arrow is pointing to the sensory neuron.

> ✔ Correct answer: a. Sensory neuron

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Question 2: In the knee jerk reflex, tapping the tendon is the:

Understanding the Knee Jerk Reflex:
- This is a simple reflex arc involving the quadriceps muscle.
- When you tap the patellar tendon (just below the kneecap), it stretches the muscle.
- This stretch activates muscle spindles (receptors), which send signals via sensory neurons to the spinal cord.
- The spinal cord sends a signal back via motor neurons to contract the quadriceps, causing the leg to kick.

#### What is "tapping the tendon"?
- It is the initial event that triggers the reflex.
- It is the stimulus that causes the reflex response.

> ✔ Correct answer: a. Stimulus

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Question 3: When you shine a light into the right eye, which of the following should occur?

This tests your knowledge of the pupillary light reflex.

#### Key Facts:
- The pupillary light reflex is a consensual reflex.
- When light hits one eye, both pupils constrict.
- This happens because:
- Light is detected by the retina in the right eye.
- Signals travel to the pretectal nucleus in the midbrain.
- Then, the Edinger-Westphal nucleus sends parasympathetic signals to both eyes via the oculomotor nerve (CN III).
- This causes both pupils to constrict — even the non-stimulated eye.

So, shining light into the right eye causes:
- Right pupil constricts (direct response)
- Left pupil constricts (consensual response)

> ✔ Correct answer: b. The right pupil should constrict; the left pupil should also constrict.

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✔ Final Answers:

1. a. Sensory neuron
2. a. Stimulus
3. b. The right pupil should constrict; the left pupil should also constrict.

Let me know if you'd like a visual explanation or summary!