Question

1. practice: tissues in the human body self assessment 13. practice: tissues in the human body respond to the following based on your reading. question 1 explain the differences between osteoblasts, osteoclasts, and osteocytes. how do these cells work together to remodel bone? what happens if the activities of osteoblasts and osteoclasts are imbalanced? check my answer question 2 explain what happens at a microscopic level inside a muscle fiber during contraction, beginning with the nerve impulse.

Explanation:

Osteoblasts build bone, osteoclasts break it down, and osteocytes are mature bone - cells. They work together in bone remodeling. An imbalance can lead to bone diseases like osteoporosis (more breakdown) or osteopetrosis (more building). For muscle fiber contraction, a nerve impulse triggers calcium release, which allows myosin and actin filaments to slide, causing contraction.

Answer:

Question 1: Osteoblasts are bone - forming cells, secreting the bone matrix. Osteoclasts are bone - resorbing cells, breaking down bone tissue. Osteocytes are mature bone cells embedded in the bone matrix. In bone remodeling, osteoclasts first break down old or damaged bone, then osteoblasts deposit new bone matrix. If osteoblast and osteoclast activities are imbalanced, excessive osteoclast activity can lead to bone loss (e.g., osteoporosis), while excessive osteoblast activity can cause abnormal bone thickening (e.g., osteopetrosis).
Question 2: A nerve impulse arrives at the neuromuscular junction, causing the release of acetylcholine. This triggers an electrical signal (action potential) in the muscle fiber. The action potential travels down the T - tubules, causing the sarcoplasmic reticulum to release calcium ions. Calcium binds to troponin, which causes a conformational change that exposes binding sites on actin. Myosin heads then bind to actin and undergo a power stroke, pulling the actin filaments towards the center of the sarcomere, resulting in muscle fiber contraction.