BIOS 252 Week 1 Case Study: Muscle
Student Name
Chamberlain University
BIOS-252: Anatomy & Physiology II with Lab
Prof. Name
Date
Muscles Severed During the Amputation Event
1. Name the muscles severed during the amputation event.
In the event of a forearm amputation, several muscles are commonly severed due to their anatomical location and functional role in hand and wrist movement. The following table outlines the key muscles affected:
| Muscle Name | Function |
|---|---|
| Flexor Carpi Ulnaris | Flexes and adducts the wrist |
| Extensor Carpi Ulnaris | Extends and adducts the wrist |
| Extensor Digiti Minimi | Extends the fifth digit (little finger) |
| Extensor Digitorum | Extends the medial four digits |
| Extensor Carpi Radialis Brevis | Extends and abducts the wrist |
| Extensor Pollicis Brevis | Extends the proximal phalanx of the thumb |
| Extensor Pollicis Longus | Extends the distal phalanx of the thumb |
| Extensor Indicis Proprius | Extends the index finger independently |
These muscles play critical roles in dexterity, grip strength, and coordinated finger movements. Their severance results in significant functional impairment of the hand and wrist.
Impact of Impaired Pronation
2. If the patient were no longer able to properly pronate his arm, which muscle do you think has been compromised?
The inability to pronate the forearm—rotating the palm downward—is typically due to damage or dysfunction in the pronator teres and pronator quadratus muscles. These two muscles are chiefly responsible for the pronation movement of the forearm.
- Pronator Teres originates from the medial epicondyle of the humerus and inserts into the lateral surface of the radius.
- Pronator Quadratus is located near the wrist and provides stability while assisting in pronation.
Injury to either or both of these muscles, or their innervating nerves (particularly the median nerve), can impair this movement.
Replantation Time Frame and Tissue Metabolism
3. Why does a severed limb have a smaller window of time for replantation compared to fingers? What does this imply about the metabolic demands of muscles, cartilage, and bone?
Severed limbs require more urgent replantation compared to fingers due to the greater metabolic demands and complex tissue composition in larger body parts. Limbs have a higher concentration of vascularized muscle tissue, which is highly sensitive to ischemia (oxygen deprivation). Without oxygen, muscle tissues can begin to undergo necrosis within 6 hours, whereas cartilage and bone are more resilient due to their lower metabolic rate.
BIOS 252 Week 1 Case Study: Muscle
This suggests the following relative metabolic demands:
| Tissue Type | Metabolic Demand | Reason |
|---|---|---|
| Muscle | High | Highly vascularized; oxygen-dependent; susceptible to ischemia |
| Cartilage | Low | Avascular; relies on diffusion; survives longer without oxygen |
| Bone | Moderate | Vascularized but more durable; less sensitive to ischemia |
The greater surface area, muscle mass, and complex vascular and neural networks in limbs increase the urgency for successful reattachment. In contrast, fingers contain fewer muscles and less vascular tissue, providing a slightly longer window for replantation.
Muscle Healing and Tissue Bridging
4. What tissue type can be found bridging the two halves of the once-severed muscle bellies? Why?
Following a muscle severance, connective tissue—particularly scar tissue and fibrous connective tissue—forms a bridge between the separated muscle bellies. While ligaments connect bones to other bones, the actual tissue that helps in muscle repair is fibrous scar tissue that fills in the gap created during trauma.
Muscle regeneration occurs through hypertrophy and, to a lesser extent, hyperplasia.
- Hypertrophy is the enlargement of muscle fibers due to an increase in the size of existing cells.
- Hyperplasia, although less common in humans, involves the generation of new muscle cells to increase tissue volume.
In healing, hypertrophy is more typical, with satellite cells (muscle stem cells) activating to repair or replace damaged fibers. However, the bridging tissue itself is often not functional muscle but a combination of collagen-based scar tissue and limited muscle regeneration, affecting long-term function unless surgical intervention (e.g., grafting) is performed.
References
Leversedge, F. J. (2018, April). Wrist Sprains. OrthoInfo. Retrieved from https://orthoinfo.aaos.org/en/diseases–conditions/wrist-sprains
BIOS 252 Week 1 Case Study: Muscle
Luna, D. (2021, March 22). Muscle Hypertrophy vs Hyperplasia: The Difference Explained. Inspire Us Foundation. Retrieved from https://www.inspireusafoundation.org/muscle-hypertrophy-vs-hyperplasia/