Key Parts of the Human Hand and Their Roles
The human hand generally has five digits - one thumb and four fingers in one hand, but the thumb is also included as fingers. Hands have hard tissues which give shape and stability. The hand is the grasping organ, forelimb of certain vertebrates that exhibits great flexibility in the digits and in the human body.
Hands are made up of the phalanges, the carpal bones, the metacarpal bones and the wrist joint. The function of the hand is locomotion; a manipulative function. In the tip of fingers, the upper part is covered with fingernails, to improve that manipulation, whereas palms and undersides of the finger are marked by creases and ridges known as palm prints and fingerprints. The function of the palm is to improve the grip and sensitivity of the body.
Bones of the Hand
In the human hand, bones are divided into three distinct groups:
Carpals
Metacarpals
Phalanges
Carpals
The carpal bones have eight smalls that make the wrist of the human body, which connects the hand to the forearm. The word “carpel” is derived from “carpus”. The set of small irregular shaped bones, a total of eight are located in the wrist area.
These bones are organised into two distinct rows proximal and distal.
Proximal Row (Lateral to Medial)
Scaphoid
Lunate
Triquetrum
Pisiform (a sesamoid bone, formed within the tendon of the flexor)
Distal Row (Lateral to Medial)
Trapezium
Trapezoid
Capitate
Hamate (projection on its palmar surface, called the hook of hamate)
Basically, the carpal bones form an arch in the coronal plane. The flexor, retinaculum, a membranous band, spans between the medial and lateral edges of the arch, forming the carpal tunnel. Whereas the scaphoid and lunate articulate with the radius to form the wrist joint (also known as the radio carpel), distal rows have both the articulate with the metacarpals.
Metacarpals
These bones articulate with carpals, and distally with the proximal phalanges.
They are in roman number and each associated with the counting.
Metacarpal IN - Thumb
Metacarpal II - index finger
Metacarpal III - middle finger
Metacarpal IV - ring finger
Metacarpal V - little finger
Metacarpals consist of a shaft, a head and a base. The medial and lateral surfaces of the metacarpals are allowing attachment of the interossei muscles.
Phalanges
These are the bones of the fingers. The thumb has proximal and distal phalanx, while the rest of the digits have a middle, proximal and distal phalanges.
Muscles of the Hand
Muscles play a very important role in our body which can be divided into two groups
Extrinsic muscles
Intrinsic muscles
Extrinsic Muscles
The extrinsic muscles are located in the posterior and anterior compartments of the forearm. They control harsh movements and a powerful grip.
Intrinsic Muscles
These muscles of the hands are located within the hand itself. They are responsible for the fine motor function of the human hand.
The muscles consist of five parts:
Thenar muscles
Hypothenar muscles
Lumbricals
Palmar interossei
Dorsal interossei
Thenar Muscles
There are four total thenar muscles in the human hand, they are easy and evident on the whiter side of the palmar surface of the hands, at the base of the thumb. These muscles form the ball and fleshy part of the thumb called the thenar eminence,
These are named as follows
Adductor pollicis, abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.
These muscles are responsible for various thumb movements, abduction, adduction, flexion, and opposition.
Hypothenar Muscles
The hypothenar muscles are the four small muscles of the medial compartment of the hand. The hypothenar muscles are palmaris, brevis, abductor digiti minimi, minimi muscles, opponens digiti.
These muscles are intrinsic muscles of the hand located within the medial side of the palm. They span between the medial aspect of the carpal and metacarpal bones of the finger. These muscles form a fleshy prominence on the medial side of the palm the hypothenar eminence.
The hypothenar muscles have great functions like little finger lateral rotation, abduction, flexion and opposition.
Lumbrical Muscles
The lumbrical muscles, the word lumbrical comes from the Latin word ‘lumbricidae’, which means earthworm. There are four small intrinsic muscles of the hand located between the metacarpal bones, and the deep to the palmar fascia.
The first lumbrical forms from the palmar surface and radial side of the tendon of the index finger.
The second lumbrical forms from the radial side and palmar surface of the tendon of the middle finger.
The third lumbrical forms from the radial side of the ring and the ulnar side of the middle finger tendon.
The fourth lumbrical forms from the radial side of the little finger tendon and the ulnar side of the ring finger tendon.
Palmar Interossei Muscles
These muscles are small unipennate intrinsic muscles of the hand. These muscles lie on The palmar surface of the hand and along with the dorsal interossei muscles complete the space between metacarpal bones.
Palmar interossei contain four muscles connected to the 1st, 2nd, 3rd, 4th, and 5th fingers.
Sometimes, the 1st finger is rudimentary, the 3rd finger does not have palmar interosseous muscles. These muscles are strong adductors of the fingers, but also greatly contribute to flexion and the extension of the 2nd, 4th, and 5th finger.
Dorsal Interossei Muscles
In the hand anatomy, these are four muscles in the back of the hand that act to abduct ring fingers, index assists in the flexion.
FAQs on Hand Anatomy: Bones, Muscles, and Functions
1. What are the three main groups of bones that make up the human hand?
The human hand consists of 27 bones, which are organised into three distinct groups to allow for a wide range of motion:
- Carpals (Wrist Bones): A set of eight small, irregularly shaped bones arranged in two rows that form the flexible wrist joint.
- Metacarpals (Palm Bones): Five long bones that connect the carpals to the phalanges, forming the supportive framework of the palm.
- Phalanges (Finger Bones): A total of fourteen bones that constitute the fingers and thumb. Each finger has three phalanges (proximal, middle, and distal), whereas the thumb has only two (proximal and distal).
2. What are the primary functions of the muscles in the hand?
The muscles of the hand are responsible for its incredible dexterity and strength. Their primary functions include enabling a wide variety of grips, from powerful grasps to the precision grip needed for writing. They control the flexion, extension, abduction, and adduction of the fingers and thumb, allowing us to perform complex tasks with high accuracy.
3. What is the difference between the intrinsic and extrinsic muscles of the hand?
The key difference between intrinsic and extrinsic hand muscles is their location of origin:
- Intrinsic muscles are located entirely within the hand itself. They are responsible for fine, intricate motor movements, such as adjusting finger positions for writing or buttoning a shirt.
- Extrinsic muscles originate in the forearm and connect to the hand bones via long tendons. These larger muscles are responsible for generating powerful movements like bending the wrist and making a strong fist.
4. What important roles do the bones of the hand play?
The bones of the hand serve two main purposes. First, they provide structural support, creating a rigid framework that gives the hand its shape and protects the delicate nerves and blood vessels within. Second, they act as a system of levers for the muscles, forming numerous joints that allow for the complex and precise movements essential for our daily activities.
5. Why is the opposable thumb a critical feature of human hand anatomy?
The opposable thumb is a critical anatomical feature because it can be moved across the palm to touch the tips of the other fingers. This unique movement, primarily controlled by the thenar muscles, allows for a 'precision grip'. This grip is fundamental to human dexterity, enabling us to manipulate tools, write, and perform countless other complex tasks that distinguish human capabilities.
6. How do ligaments and tendons differ in their function within the hand?
While both are vital connective tissues, ligaments and tendons have distinct functions. Ligaments are strong, fibrous bands that connect bone to bone, providing stability to the many joints in the wrist and hand. In contrast, tendons are tough, flexible cords that connect muscle to bone. They work by transmitting the force generated by muscle contractions to the skeleton, thereby causing movement.
7. What are the thenar and hypothenar eminences found in the palm?
The thenar and hypothenar eminences are the two fleshy, muscular mounds visible on the palm of the hand.
- The thenar eminence is the larger muscular bulge located at the base of the thumb. It houses the muscles that control the thumb's fine movements, including opposition.
- The hypothenar eminence is the smaller muscular pad on the opposite side, at the base of the little finger. It contains the muscles responsible for moving the little finger.
