Muscle And Movement

The masseter muscle is located below the zygomatic bone and its main action is to elevate the mandible. This muscle is responsible for closing the jaw and is one of the main muscles involved in chewing. It is a powerful muscle that helps in the grinding and crushing of food.

The rectus abdominis is a paired muscle that runs vertically along the front of the abdomen. Its main function is to compress the abdomen and flex the trunk. This means that when the rectus abdominis contracts, it helps to bring the ribcage closer to the pelvis, resulting in flexion of the trunk. Additionally, it assists in compressing the abdominal contents, providing support and stability to the core. The other options listed, such as extending the head, flexing the leg at the knee, and flexing the wrist, are not actions associated with the rectus abdominis.

The action of the sternocleidomastoid muscle is to rotate and flex the head. This muscle is located in the neck and connects the sternum and clavicle to the mastoid process of the skull. When both sides of the muscle contract together, they flex the head forward. When only one side contracts, it rotates the head to the opposite side. The sternocleidomastoid plays an important role in various movements of the head and neck, such as turning the head to look over the shoulder or tilting the head to the side.

The correct answer is compress abdomen. The transversus abdominis, external oblique, and internal oblique are all muscles involved in the action of compressing the abdomen. This action involves contracting these muscles to decrease the volume of the abdominal cavity, which can help with core stability and support. Flexing the leg and extending the forearm are unrelated actions and not performed by these muscles.

The internal intercostal muscles are responsible for depressing the ribs during expiration. When we breathe out, these muscles contract and pull the ribs downward, reducing the volume of the thoracic cavity and forcing air out of the lungs. This action helps in the process of expiration or exhaling.

The muscle that flexes the wrist is the flexor carpi radialis. This muscle is located in the forearm and is responsible for flexing and abducting the hand at the wrist joint. It plays a role in movements such as wrist flexion and radial deviation. The brachioradialis muscle is also located in the forearm but is not involved in wrist flexion. The diaphragm is a muscle located in the thoracic cavity and is responsible for breathing. Therefore, the correct answer is flexor carpi radialis.

The term "primmover" refers to the muscle that is actively performing the action. In other words, it is the muscle that is responsible for initiating and carrying out the movement. This term is commonly used in anatomy and physiology to distinguish the muscle that is actively contracting and causing the movement from other muscles that may be assisting or supporting the action.

The diaphragm is a muscle located in the thorax and is responsible for breathing. It is the primary muscle involved in the process of respiration. As the diaphragm contracts and relaxes, it creates changes in the volume of the thoracic cavity, allowing for the inhalation and exhalation of air. The diaphragm is grouped with the breathing muscles because it plays a vital role in the process of breathing.

The term "synergist" refers to muscles that assist the prime mover muscle in performing a specific action. These muscles work together with the prime mover to enhance its effectiveness and provide additional support. Therefore, the correct answer "helper muscles" accurately describes the role of synergist muscles in assisting the main muscle in carrying out a particular movement or action.

The correct answer is flexes and adducts upper arm. The pectoralis major is a large muscle located in the chest. It is responsible for flexing the upper arm at the shoulder joint, bringing it closer to the body, and adducting the upper arm, moving it towards the midline of the body. This muscle is involved in movements such as hugging, throwing, and pushing.

The biceps brachii and triceps brachii muscles are located in the upper arm. The biceps brachii is located on the front of the upper arm, while the triceps brachii is located on the back of the upper arm. These muscles work together to cause different actions in the forearm. The biceps brachii flexes the forearm, allowing it to bend towards the body, while the triceps brachii extends the forearm, allowing it to straighten away from the body. Therefore, the correct answer is "all of the above" as both muscles are located in the upper arm and cause the mentioned actions.

The orbicularis oris is the muscle that closes the mouth and protrudes the lips. This muscle is responsible for various movements of the lips, such as puckering, kissing, and whistling. It forms a circular shape around the mouth and helps in controlling the opening and closing of the lips, allowing us to speak, eat, and perform various facial expressions. The other options listed are muscles that are not directly involved in the closing and protruding of the lips.

The deltoid is a muscle located in the upper arm. It is responsible for multiple actions, including abduction (moving the arm away from the body), flexion (bending the arm), and extension (straightening the arm). Therefore, the correct answer is "all of the above" as the deltoid performs all of these actions.

The trapezius muscle is responsible for elevating the shoulders or extending the head. It is a large, triangular muscle that extends from the base of the skull to the middle of the back and attaches to the shoulder blade and collarbone. When the trapezius contracts, it pulls the shoulders upward, allowing for shoulder elevation. Additionally, it can also extend the head by pulling it backward. Therefore, the correct answer is that the trapezius muscle elevates the shoulders or extends the head.

The gluteus maximus is a muscle that is responsible for extending the thigh. It is the largest muscle in the buttocks and plays a crucial role in movements such as walking, running, and climbing stairs. When the gluteus maximus contracts, it pulls the thigh backwards, allowing for the extension of the leg at the hip joint. This action is particularly important in activities that require powerful movements of the lower body, such as jumping or sprinting.

The rectus femoris is a muscle located in the front of the thigh. It is responsible for extending the leg at the knee joint, which means straightening the leg. Additionally, it also flexes the thigh at the hip joint, which means bringing the thigh towards the abdomen. Therefore, the correct answer is "extends leg at knee and flexes thigh."

The vastus lateralis, medialis, and intermedius muscles all work together to extend the leg at the knee joint. When these muscles contract, they cause the leg to straighten and extend at the knee. This action is important for movements such as kicking, jumping, and standing up from a seated position.

The rectus abdominis is the abdominal muscle that has more than one action. It is responsible for flexing the trunk, as well as assisting in forced expiration and increasing intra-abdominal pressure. The other three muscles mentioned in the question, the external oblique, internal oblique, and transversus abdominis, each have their own specific actions but do not have multiple actions like the rectus abdominis.

The correct answer is "both a and b". The gastrocnemius muscle is located in the calf and is responsible for flexing the leg at the knee joint, which is known as knee flexion. Additionally, the gastrocnemius muscle is also involved in plantar flexion, which is the movement that points the foot downward. Therefore, both options a (flexes leg at knee) and b (plantar flexion) are correct explanations for the function of the gastrocnemius muscle.

The biceps femoris, semitendinosus, and semimembranosus muscles are all part of the hamstring group. They flex the leg at the knee and extend the thigh. Their origin is at the ischium. Therefore, all of the statements mentioned above are correct.

The external intercostals are the muscles responsible for elevating the ribs during inspiration. When we breathe in, these muscles contract, causing the ribs to move upwards and outwards, expanding the chest cavity and allowing air to enter the lungs. Therefore, the correct answer is external intercostals.

The gluteus medius and minimus muscles are responsible for extending and abducting the thigh. These muscles work together to move the thigh away from the midline of the body and to extend it backward. They do not have any role in extending or flexing the leg at the knee joint. Therefore, the correct answer is that they extend the thigh and abduct the thigh.