Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

45. Nervous System

Central and Peripheral Nervous System

General Biology

45. Nervous System

Central and Peripheral Nervous System

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2:28 minutes

Problem 5

Textbook Question

Joe accidentally touched a hot pan. His arm jerked back, and an instant later, he felt a burning pain. How would you explain the fact that his arm moved before he felt the pain?
a. His limbic system blocked the pain momentarily, but the important pain signals eventually got through.
b. His response was a spinal cord reflex that occurred before the pain signals reached the brain.
c. Motor neurons are myelinated; sensory neurons are not. The signals traveled faster to his muscles.
d. This scenario is not actually possible. The brain must register pain before a person can react.

Verified step by step guidance

Step 1: Begin by understanding the concept of reflex actions. Reflexes are automatic, involuntary responses to stimuli that occur without conscious thought. They are designed to protect the body from harm and are mediated by the spinal cord rather than the brain.

Step 2: Recognize the role of the spinal cord in reflex actions. When Joe touched the hot pan, sensory neurons in his skin detected the heat and sent signals to the spinal cord. The spinal cord then immediately activated motor neurons to move his arm away from the pan, bypassing the brain for faster response.

Step 3: Consider the delay in pain perception. Pain signals are transmitted by sensory neurons to the brain, where they are processed and interpreted. This process takes slightly longer than the reflex action because it involves higher-level processing in the brain.

Step 4: Evaluate the options provided in the question. Option b correctly describes the mechanism: Joe's response was a spinal cord reflex that occurred before the pain signals reached the brain. The other options either misrepresent the physiological process or are incorrect.

Step 5: Conclude that reflex actions are a critical survival mechanism, allowing the body to respond quickly to harmful stimuli before the brain has fully processed the sensation of pain.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reflex Arc

A reflex arc is a neural pathway that controls a reflex action. It typically involves sensory neurons that detect a stimulus, interneurons in the spinal cord, and motor neurons that trigger a response. This process allows for rapid reactions to stimuli, such as pulling away from a hot surface, without the delay of processing the information in the brain.

Pain Perception

Pain perception is the process by which the brain interprets signals from sensory neurons that indicate damage or potential harm. While pain signals travel to the brain, reflex actions can occur simultaneously through the spinal cord, allowing for immediate responses to harmful stimuli before the sensation of pain is consciously felt.

Myelination and Signal Transmission

Myelination refers to the presence of a fatty sheath around certain neurons, which increases the speed of electrical signal transmission. Motor neurons are often myelinated, allowing them to transmit signals quickly to muscles, while sensory neurons may not be as heavily myelinated, resulting in slower signal transmission to the brain. This difference can influence the timing of reflex actions versus pain perception.

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The reflex that pulls your hand away when you prick your finger on a sharp object relies on a neuronal circuit with two synapses in the spinal cord. Using a circle to represent a cross-section of the spinal cord, draw the circuit. Label the types of neurons, the direction of information flow in each, and the locations of synapses.

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