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Major Joints of the Human Body

Major Joints of the Human Body

Major joints of the human body will be discuses in this article and I will describe the bones and muscles involved in each joint.  The major joints are the: knee joint, ankle joint and foot joint, spine joints, shoulder joint, elbow joint, and forearm joint.  As an athlete or someone involved in physical fitness, it is important that you have an understanding of the biomechanical and kinesiological actions of the key muscles involved along with how the joint works in a strength exercises.  It is also important that you are able to determine which joint actions and muscles play a role in an exercise and if that exercise is effective and safe.  Hence, an understanding of the musculoskeletal system in regards to joint action, joint makeup, muscle involvement, and the associated relationships between various muscle groups in the body.

Joints of the Human Body

The Knee Joint

Knee Joint

The knee joint is made up of the ends of the femur and tibia bones.  The stability of the knee joint is very week and the stability this joint is improved upon by the many ligaments that surround the knee joint.  These ligament include the posterior cruciate ligament, anterior cruciate ligament, popliteal ligament, and the patella ligament.

The knee joint is must be able to withstand the forces created by the body and the forces generated with participating in various activities.  Because of this it is important that ligaments and muscles surrounding the knee joint are healthy and strong.  The muscles and ligaments around the knee joint play a critical role together.  When the knee joint is flexed the ligament actually loosen which allows for greater movement.  When this happens, the muscles must be capable of taking over the role of stabilizing the knee joint.

The knee joint is stabilized on the anterior side (the front) by the quadriceps, on the medial side (inside of your thigh) by the sartorius and gracilis, on the lateral side (your outside) by the tensor fascia latae, and on the posterior side (the back) by the hamstring muscles from above, and the gastrocnemius from below.

Major Movements of the Knee Joint

The major movements of the knee joint are flexion and extension.  Medial and lateral rotation of the knee joint takes place only when the knee is flexed.  This allows the foot to turn when it is free to, and your trunk to move when your feet and fixed to the ground.

The Muscles of the Knee Joint

Muscles of the Knee Joint

Most of the muscles of the knee joint are two-joint muscles.  A two joint muscle is a muscle that, from origin to insertion, crosses two joints, and thus can produce an action at both joints. These muscles are the hamstrings, rectus femoris of the quadriceps group, gracilis, sartorius, gastrocnemius, and the tensor fascia latae muscles. These two joint muscles provide efficiency of movement in walking and running, but they cannot stretch enough to allow for full range of motion in both joints at the same time.

Posterior

The muscles that form the hamstring group are the biceps femoris (attached on the lateral side) and the semimembranosus and semitendinosus (attached on the medial side of the knee).  The hamstring muscles work to flex the knee joint.  Whereas the muscles of the quadriceps group work to extend the knee joint.

Relationships Between the Muscles of the Knee Joint

The Gastrocnemius and the Hamstrings

The gastrocnemius is the major muscle of the posterior shin (your calves) and its function is to extend the foot (plantar flexion, or toes down). It ties in at the hamstrings at the knee joint where there function together is knee flexion.  The insertion gastrocnemius is on the femur which helps provide stability.  [The "insertion" end refers to the end which is attached to a moveable bone which this muscle will move when it is contracted. The "origin" end is usually the most distal (farthest) attachment and is the bone that the muscle attaches to and it does not move].

The Quadriceps and the Hamstrings

The hamstring muscles (anterior) should always be stronger than the quadriceps (posterior) is almost all instances.  The quadriceps group is made up of three very large muscles and one smaller muscle.  The muscle mass of the quadriceps is much larger than that of the hamstrings because its workload is much greater.  The quadriceps are the muscles the keep you erect and move you in actions such as walking and running.

Read more about the ACL Ligament of the knee and about an ACL Rehab program.

Joints of the Human Body

The Ankle Joint

Bones, ligaments and tendons of the Ankle Joint

The bones of the ankle are the tibia and the talus bones.  The bony stability of the ankle joint is rather strong.  There are very strong ligaments surrounding the ankle joint to help withstand the stresses put on the ankle and to provide greater stability.

The foot also has another joint at the ankle called the subtalar joint.  This joint is located between the talus and the calcaneus.  Typically, this is the joint that is injured in ankle sprains.  While the ankle joint has only two bony parts the subtalar joint is an intertarsal joint that is comprised of several bones of the foot.  The subtalar joint provides for different positions of the foot and leg in response to weight bearing activities.  It is also the main connection between foot mobility and stability of the ankle and leg.

Major Movements of the Ankle Joint

The movements that are possible at the ankle joint are flexion (dorsiflexion or toes up) and extension (plantar extension or toes down).

The Muscles of the Ankle Joint

Muscles of the Ankle Joint

Posterior

On the posterior side, the gastrocnemius is the major ankle extensor muscle of the shin.  At its upper end its two tendons attaches to the femur, while at its lower end its two tendons attach at the Achilles tendon.  Directly beneath the gastrocnemius is the soleus and has a similar function as the gastrocnemius. It upper attachment is on the tibia and fibula while its lower attachment blends into the Achilles tendon on the calcaneus.  The muscle group of the gastrocnemius and the soleus are called the triceps surae, and together they are very strong.

Anterior

On the anterior side the tibialis anterior is the main muscle of the shin.  Its tendons at the lower end crosses over the ankle and inserts on the inner and under surface of the foot arch.  The tibialis anterior is responsible for dorsiflexion and turning the sole of the foot inward (supination).

Joints of the Human Body

The Spine

The Spinal Column

The spine is a very important functional unit of the human body.  It protects the spinal cord and provides the main structural support for most movements of the body.  The spinal column is broken down into five different sections.  Starting from the head and working down to the tail bone the sections are the cervical, thoracic, lumbar, sacrum, and coccyx.

Major Movements of the Spine

The movements of the spinal column include movements of one vertebra on another separated by intervertebral disks.  The joint movement between any two adjacent disks small, however; multiple joints working together create a great range of motion.  The major movements of the spinal column are flexion, extension, hyperextension, lateral flexion, and rotation.  Movement in the thoracic area is limited because of the attachment of the ribs.  In and of itself, the vertebral column lacks great bony stability and relies on the ligaments and muscles for support.

The Muscles of the Spine

Anterior

On the anterior midsection the major muscles of the spine are the rectus abdominis, internal oblique, external oblique, and transverse abdominis (collectively called the abdominal musculature).  The rectus abdominis acts to pull the anterior pelvis toward the sternum which results in spinal flexion.  The internal oblique and external oblique play a roll in the rotation if the spinal column.  The muscles of the anterior midsection provide safety and strength to the core area of the body.

There is a lot of interaction of the muscles of the anterior midsection with the muscles of the back and even some interaction with other anterior muscles.  This can be seen with the interaction between the pectoralis major and the external oblique muscle.

Posterior

On the posterior side there are many deep muscular pairs that span over one or more vertebrae.  All of these muscles are situated to act to stabilize the spinal column.  Of these muscles the large ones are collectively known as the erector spinae and they run from the sacrum to the head.  The erector spinae muscles are the biggest and the strongest muscles in the lumbar area.  There man function is to hold the truck erect with secondary functions in spinal flexion and rotation to the rear.

The extensor muscles of the back are responsible for posture.  The extensor muscles are attached to the posterior (back) of the spine and enable standing and lifting objects. These muscles include the large paired muscles in the lower back (erector spinae), which help hold up the spine, and gluteal muscles

Relationships Between the Muscles of the Spine

The Abdominal Muscles and the Hip Flexors

Overdeveloped and tight hip flexors can contribute to lower back pain by causing the pelvis to tilt forward. To counteract this, you must stretch the hip flexors and strengthen the Abdominal muscles. This will reduce pelvic tilt and decrease lower back pain. Strengthening the lower back can also help improve the balance between the muscles of the hip region.

Joints of the Human Body

The Shoulder Joint and Shoulder Girdle

Bones of the Shoulder Joint

The shoulder joint consists of a shallow socket called the glenoid fossa, into which the round head of the humerus fits.  Less than half of the humerus is actually in the socket and therefore the shoulder joint is weak.

Major Movements of the Shoulder Joint

The shoulder joint is a ball and socket type joint and allows for the following movements: flexion, extension, hyperextension, abduction, adduction, medial rotation, lateral rotation, and circumduction.  Because the shoulder joint is designed for mobility it lacks bony and ligamentous stability.

The Muscles of the Shoulder Joint

Stabilizer Muscles

The muscles of the shoulder joint are arranged to provide stability.  The four rotator cuff muscles (supraspinatus, teres minor, infraspinatus, and subscapularis) are part of the large stabilizing muscles of the shoulder.  The deltoids also play a large stabilizing role in the shoulder.  These muscles include the anterior deltoid, posterior deltoid, and the middle deltoids  Additional stability is provided by  the long heads of the bicep brachii on the anterior shoulder and the triceps on the posterior side.

Primary Mover Muscles

Muscles of the Shoulder Joint

The muscles that act as the primary movers of the shoulder joint are the deltoid, coracobrachialis, pectoral major, latissimus dorsi, teres major, the long and short heads of the biceps, and the long heads of the triceps.

The latissimus dorsi and the teres major muscles rotate the arm medially at the shoulder joint.  The infraspinatus, terse minor, and the subscapularis act in a wheel and axle like mechanism to laterally rotate the arm.  Arm abduction is a very complex movements and consists of the supraspinatus and the deltoids muscles.

The Shoulder Girdle

The bones of the shoulder girdle are the clavicle and the scapula. The movements of the shoulder girdle are elevation, depression, upward rotation, downward rotation, abduction (protraction) and adduction (retraction).  Like the shoulder joint the shoulder girdle is designed for mobility and is lacking in a strong bony and ligament configuration.  The muscles of the shoulder must be strong to provide the shoulder girdle the stability it needs..

The Relationship between the Shoulder Joint and Shoulder Girdle

The shoulder joint muscles are responsible for moving the arm while the shoulder girdle muscles are responsible for moving the scapula and clavicle.  This is important because full range of motion is only accomplished by these two groups of muscles working in unison together.  Another muscle group that aids in the coordinated movements of the shoulder joint and the shoulder girdle is the trapezius muscles. The trapezius muscles are divided into four sections.  The upper section is involved in scapula elevation. Below this section some of the muscle fibers aid in elevation of the scapula while the others aid in upward rotation of the scapula.  The very bottom section of the trapezius the muscles fibers pull down on the inner border of the scapula to rotate the scapula upwards.  And the middle section of the trapezius is involved in adduction of the scapula in which the scapula moves inward toward the spine.

Joints of the Human Body

The Elbow Joint

Bones of the Elbow Joint

The bones of the elbow joint are the humerus, ulna, and the radius.  The stability of the elbow joint is very strong because of the bony configuration and because of all the muscles that act to stabilize it on the anterior side. The only movements at the elbow joint are flexion and extension.

The Muscles of the Elbow Joint

Anterior

The major anterior muscles of the elbow joint are the main joint flexors.  They include the biceps, brachialis, brachioradialis, and pronator teres.  Secondary muscles such as the wrist flexors and wrist extenders pass over the elbow to insert onto the humerus.

Muscles of the Elbow Joint

Posterior

The main extensor muscle of the elbow joint on the posterior side is the triceps.  The triceps is attached to the olecranon process of the ulna and it covers the length of the humerus.

The Relation between the Shoulder Joint and the Elbow Joint

The actions of the triceps and biceps at the shoulder joint are secondary to those at the elbow joint.  The muscles of the shoulder must contact to hold the shoulder and arm in place.  The two heads of the biceps cross the shoulder joint to attach to the scapula but their action at the shoulder joint is very weak.

The Radioulnar Joint of the Forearm

The radioulnar joint is a combination of three joints located at the wrist, elbow and in between the ulna and the radius bones.  These joints are not stable and need the support of the surrounding ligaments.  The movements of the radioulnar joint are pronation and supination.  The muscles of the radioulnar joint act as stabilizers and include the biceps, supinator, pronator teres, and pronator quadratus.

Joints of the Human Body

The Wrist Joint

Bones of the Wrist Joint

The bones of the wrist joint consist of the ends of the radius and ulna, and the carpal bones of the hand.  The movements of the wrist include flexion, extension, hyperextension, radial flexion, ulna flexion (abduction and adduction).  The bony stability of the wrist joint is weak, but it has strong ligaments to help with stability.

The Muscles of the Wrist Joint

The major flexor muscles of the wrist are the flexor carpi radialis, flexor carpi ulnaris, and the palmaris longus. The major extensor muscles of the wrist are the exterior carpi radialis longus, exterior carpi radialis brevis, and extensor carpi ulnaris.

Muscles of the Wrist Joint

The Relationship between the Elbow and the Wrist Muscles

The elbow and wrist are tied in via the wrist flexor and extensor muscles.  These muscles cross over the wrist and elbow joints.

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