Arm Muscles
The human arm is located between the shoulder joint and the elbow joint. The arm in the human body and the hands are responsible for performing very important functions in the human body. The parts of the human arm are made up of bones and muscles. The bones of the arm body are made up of the radius, ulna and humerus. The humerus is the longest bone of the arm. It is attached to the elbow from its lower end and to the pectoral girdle on its upper end. It forms a ball and socket joint with the pectoral girdle.
The Muscles of the Arm are:
Biceps brachii
Brachialis
Coracobrachialis
Triceps brachii
We will learn more about the arm structure, parts of the arm and arm muscles.
Arm Muscle Anatomy
The parts of the arm muscle are made up of four muscles. They are Biceps brachii, Brachialis, Coracobrachialis, Triceps brachii.
Biceps Brachii
It is a two-headed muscle. The major mass of this muscle is present anterior to the humerus. No attachments of this muscle to the bones are present. It helps in flexing the arm at the elbow and the shoulder. The long head of this muscle originates from the supraglenoid tubercle of the scapula and the short head originated from the coracoid process of the scapula. Both heads are then inserted into the radial tuberosity through the bicipital aponeurosis.
Coracobrachialis
It originated from the coracoid process of the scapula. Axilla is the place from where this muscle passes. It then gets attached to the medial side of the humeral shaft. It provides flexion to the arm at the shoulder and also in weal adduction.
Brachialis
This muscle is present in the deep of the biceps brachii. It is found more distally than the other muscles of the arm. This muscle originates from the medial and lateral surfaces of the humeral shaft. They are then inserted into the humeral tuberosity. Their function is to provide flexion at the elbow.
Triceps Brachii
The long head of these muscles is attached to the infraglenoid tubercle and the lateral head is attached to the humerus. Their function is to provide an extension of the arm towards the elbow.
Parts of the Arm
The arm muscles of humans are a part of the appendicular skeleton. It is a part of the human skeleton system. This system is made from external and internal structures that can be living or dead in nature. They are hardened structures that help in forming the support system to the body. They also serve the purpose of protection. 206 bones are present in an adult skeleton. Axial and appendicular skeleton are the subparts in which the skeletal system is divided. The long bones in the human body that make up the arms and legs are made up of an appendicular skeleton. The appendicular skeleton has 126 bones.
Human Arm Anatomy
In our body, we have two pairs of limbs. They are known as the forelimbs and the hindlimbs. The forelimbs and hindlimbs have 30 bones each. Humans have a pair of forelimbs. 30 bones are present in each of the forelimbs. These bones then help in forming the different parts of the arm. The different parts of arms are known as the upper arm, lower arm, forearm and hand. The humerus is the single long bone in the human body that is present in the upper arm. Radius and the ulna are also long bones. These bones are present in the lower arm. The radius and ulna run parallel to each other or they cross each other. The ulna is longer than the radius. The human hand is made up of 27 bones. Out of these 27 bones, 8 bones are present in the wrist region and 5 bones are present in the palm region. These 8 bones are known as carpal bones and the 5 bones are known as metacarpals. In the fingers, there are fourteen bones present. These all fourteen bones together are known as phalanges.
The 8 Bones of the Carpal are:
Trapezium
Trapezoid
Scaphoid
Lunate
Hamate
Capitate
Pisiform
Triquetrum
[Image will be Uploaded Soon]
Muscles and Their Types
Skeletal Muscle: They are also known as voluntary muscles or striated muscles. They are attached to the skeleton component of the body. They are involved in locomotory actions and are also responsible for body posture. Alternate dark and white bands are visible on them when they are viewed under a microscope, therefore, named striated muscles. They are voluntary muscles thus they are in control of the animals. Example: Muscles of hindlimbs and forelimbs.
Smooth Muscle: They are also known as unstriped muscles. Cells in these muscles are elongated and spindle in shape. They don't possess alternate dark and light bands. They give a smooth appearance when they are seen under a microscope. These muscles line the hollow organs and are involuntary in nature thus not in control of animals. Example: Posterior regions of oesophagus and stomach.
Cardiac Muscles: As it is there in their name, these muscles line the heart walls. Alternate light and dark bands appear in these muscles. They are responsible for increasing and decreasing muscular activity.
Movement of the External and Internal Body Parts
These all the bones of the hindlimb, forelimb and girdles help in the process of movement and locomotion. The movement is done by both the internal body parts and the external body parts.
Movements of External Body Parts Help in:
It helps to maintain the equilibrium of the body. It is done by limbs, heads and trunks.
The organisms are able to catch food by the movement of limbs, appendages, jaws and tentacles.
Ingestion, defence and locomotion are also done by external body parts.
Movement of Internal Body Parts:
These internal body parts help in the proper functioning of various cells, tissues and organs of the body. This in turn helps the organism to carry out other vital functions of the body.
The heart pumps blood to all the parts of the body.
The peristaltic movement of the food pipe helps in the process of digestion.
FAQs on Arm
1. What are the three main sections and bones of the human arm?
The human arm is anatomically divided into three sections: the upper arm, the forearm, and the hand. Each section contains specific bones:
- Upper Arm: This section contains a single long bone called the humerus, which runs from the shoulder to the elbow.
- Forearm: This section consists of two bones, the radius and the ulna, which are parallel to each other. The radius is on the thumb side, and the ulna is on the pinky finger side.
- Hand: The hand has a complex structure comprising 27 bones: the carpals (8 wrist bones), metacarpals (5 palm bones), and phalanges (14 finger bones).
2. What are the primary muscles in the upper arm and their main functions?
The primary muscles in the upper arm are the biceps brachii and the triceps brachii. They are responsible for moving the forearm at the elbow joint.
- Biceps Brachii: Located on the front of the upper arm, its main function is flexion of the forearm, which means it bends the elbow.
- Triceps Brachii: Located on the back of the upper arm, its main function is extension of the forearm, which means it straightens the elbow.
3. What is the difference between a tendon and a ligament in the arm?
While both are types of connective tissue, tendons and ligaments have different functions. A tendon connects muscle to bone. For example, the biceps tendon attaches the biceps muscle to the radius bone in the forearm, allowing the muscle to pull on the bone and cause movement. A ligament connects bone to bone, providing stability to joints. For instance, collateral ligaments in the elbow connect the humerus to the radius and ulna, preventing the joint from moving sideways.
4. How do the biceps and triceps muscles work as an antagonistic pair to move the forearm?
The biceps and triceps function as an antagonistic pair, meaning they work in opposition to create controlled movement. To bend the elbow (flexion), the biceps muscle contracts (acting as the agonist) while the triceps muscle relaxes (acting as the antagonist). Conversely, to straighten the elbow (extension), the triceps muscle contracts and the biceps muscle relaxes. This coordinated action allows for smooth and precise movements of the forearm.
5. What major types of synovial joints are found in the arm, enabling its wide range of motion?
The arm's remarkable mobility is due to several types of synovial joints:
- Ball-and-Socket Joint: The shoulder joint, connecting the humerus to the shoulder blade, allows for the widest range of motion, including rotation, flexion, and extension.
- Hinge Joint: The elbow joint, connecting the humerus to the ulna, primarily allows for movement in one plane, like a door hinge—bending (flexion) and straightening (extension).
- Pivot Joint: Located near the elbow, this joint between the radius and ulna allows the forearm to rotate, turning the palm up or down (supination and pronation).
6. Why is the shoulder joint more prone to dislocation compared to the elbow joint?
The shoulder's high mobility comes at the cost of stability. The ball-and-socket joint of the shoulder features a large, rounded head of the humerus fitting into a very shallow socket (the glenoid fossa). This shallow structure allows for a vast range of movement but makes it inherently less stable. In contrast, the hinge joint of the elbow is much more stable because the bones (humerus, ulna, and radius) interlock in a deeper, more constrained way, restricting movement to primarily one plane and making dislocation less common.
7. How does the intricate structure of the wrist and hand bones contribute to fine motor skills?
The hand's dexterity is a direct result of its complex bone structure. The wrist contains eight small carpal bones arranged in two rows, which form gliding joints that allow for subtle, combined movements. These connect to the five metacarpals of the palm and the fourteen phalanges of the fingers. This large number of small bones and associated joints provides the flexibility and range of motion necessary for precise, fine motor skills like writing, buttoning a shirt, or playing a musical instrument, which would be impossible with fewer, larger bones.
