The biomechanics of the lower jaw is considered from the point of view of the functional purpose of the dental system (speech, chewing, swallowing). Movements of the lower jaw are realized as a result of the interaction of the temporomandibular joint (TMJ), teeth and masticatory muscles.
This interaction is coordinated and controlled by the central nervous system. Voluntary and reflex movements are regulated by the neuromuscular system; they are carried out sequentially.
For example, the initial movements—biting food and placing it in the oral cavity—are voluntary. Chewing and swallowing are then carried out unconsciously.
Everything is not as simple as it seems
Shoulder joint
Shoulder joint, articulatio humeri,
connects the humerus, and through it the entire free upper limb, with the girdle of the upper limb, in particular with the scapula. The head of the humerus, which participates in the formation of the joint, has the shape of a ball. The articular cavity of the scapula that articulates with it is a flat fossa.
Along the circumference of the cavity there is a cartilaginous articular lip, labrum glenoidale
, which increases the volume of the cavity without reducing mobility, and also softens shocks and shocks when the head moves. The articular capsule of the shoulder joint is attached on the scapula to the bony edge of the glenoid cavity and, covering the humeral head, ends at the anatomical neck.
As an auxiliary ligament of the shoulder joint, there is a slightly denser bundle of fibers coming from the base of the coracoid process and woven into the joint capsule, lig. coracohumerale
. In general, the shoulder joint does not have real ligaments and is strengthened by the muscles of the upper limb girdle.
This circumstance, on the one hand, is positive, since it contributes to extensive movements of the shoulder joint, necessary for the function of the hand as an organ of labor. On the other hand, weak fixation in the shoulder joint is a negative point, causing frequent dislocations.
The synovial membrane lining the inside of the joint capsule gives rise to two extra-articular protrusions. The first of them, vagina synovialis intertubercularis
, surrounds the tendon of the long head of the biceps muscle, lying in
the sulcus intertubercularis
; another protrusion, bursa m. subscapuldris subtendinea, located under the upper section of m. subscapularis.
Representing a typical multi-axial ball and socket joint, the shoulder joint is characterized by great mobility. Movements occur around three main axes: frontal, sagittal and vertical. There are also circular movements (circumduction). When moving around the frontal axis, the arm produces flexion and extension. Abduction and adduction occur around the sagittal axis.
The limb rotates outward (supination) and inward (pronation) around the vertical axis. Flexion of the arm and abduction are possible, as stated above, only to the level of the shoulders, since further movement is inhibited by the tension of the articular capsule and the support of the upper end of the humerus into the arch formed by the acromion of the scapula and lig. coracoacromiale
.
If the movement of the arm continues above the horizontal, then this movement is no longer performed in the shoulder joint, but the entire limb moves together with the belt of the upper limb, and the scapula rotates with a shift of the lower angle anteriorly and to the lateral side.
The human hand has the greatest freedom of movement. Freeing the hand was a decisive step in the process of human evolution. Therefore, the shoulder joint has become the loosest joint in the human body. As a result, we can reach any point of our body with our hands and manipulate our hands in all directions, which is important during labor processes.
On the posterior radiograph of the shoulder joint, the cavitas glenoidalis is visible, having the shape of a biconvex lens with two contours: medial, corresponding to the anterior semicircle of the cavitas glenoidalis, and lateral, corresponding to its posterior semicircle. Due to the characteristics of the x-ray picture, the medial contour turns out to be thicker and sharper, as a result of which the impression of a half-ring is created, which is a sign of normality (“clear half-ring symptom”).
In old age and with certain diseases, the lateral contour also becomes emphasized, and then the normal “semi-ring symptom” of cavitas glenoidalis
is replaced by a pathological “ring symptom”.
The head of the humerus on the posterior radiograph in its inferomedial part is superimposed on the cavitas glenoidalis. Its contour is normally smooth, clear, but thin. Between the cavitas glenoidalis scapulae and the caput humeri, the x-ray gap of the shoulder joint is visible. The “X-ray joint space” of the shoulder joint looks like a curved clearing located between the clear contours of the medial (anterior) edge of the cavitas glenoidalis and caput humeri
.
To determine the dislocation or subluxation of the shoulder joint, it is very important to know the normal relationships between the articular surfaces of the articulatio humeri
.
On a radiograph taken in the correct posterior projection with the limb extended along the body, these relationships are characterized by the fact that the inferomedial part of the head is layered on the cavitas glenoidalis
and is always projected above its lower border.
The shoulder joint receives nutrition from the rete articulare, formed by the branches of a. circumflexa humeri anterior, a. circumflexa humeri posterior, a. thoracoacromialis (from a. axillaris
).
Venous outflow occurs in the veins of the same name, flowing into v. axillaris
.
The outflow of lymph is through the deep lymphatic vessels - into the nodi lymphatici axillares
.
The joint capsule is innervated from n.
axillaris .
Source
Functional significance of the tubercles
The buccal cusps of the upper and lower molars, as well as the lingual cusp of the lower molar, perform a protective function. The palatal cusp of the upper molar is the supporting one.
In the process of closing the teeth in the central position, contact occurs between the palatal tubercles of the upper teeth and the central fossae or marginal projections of the molars and premolars of the lower jaw. There is also contact between the buccal tubercles of the lower teeth and the central fossae and marginal projections of the molars and premolars located above.
Note! The buccal tubercles of the teeth of the lower jaw and the palatine tubercles of the upper are supporting and holding ones. The lingual cusps of the lower teeth and the buccal cusps of the upper teeth are guides and protective (prevent biting the cheek and tongue).
When performing chewing movements, the lower jaw should slide over the surface of the upper jaw teeth without obstacles. The tubercles slide smoothly along the antagonist slopes without disrupting occlusal relationships.
At the same time, they must maintain tight contact. Sagittal and lateral movements are reflected on the surface of the first molars of the mandible by the arrangement of transverse and longitudinal fissures, this is called the “occlusal compass”.
Important! This landmark is necessary in the process of modeling the occlusal surface of the teeth.
During the movement of the lower jaw forward, the guide tubercles of the chewing teeth of the upper localization slide along the central fissure of the teeth located below. During lateral movements, gliding occurs along the fissure that separates the median buccal and posterobuccal cusps of the lower molar.
In the process of combined movement, gliding occurs along the diagonal fissure that divides the median buccal tubercle. The “occlusal compass” is characteristic of all teeth of the lateral group.
“Occlusal compass” - A and C - sagittal movements, B and E - transversal, D - combined.
Another important factor in the biomechanics of the lower jaw is the height of the cusps of the chewing teeth. This parameter determines the amount of initial joint displacement.
This is due to the fact that during the lateral movements of the lower jaw, the head on the working side moves outward before the rotational movements begin, while the head on the balancing side moves inward. This type of movement occurs within 0-2 mm.
The greater the flatness of the slopes of the tubercles, the greater will be the magnitude of the initial articular shift. This is how the free mobility of the dentition relative to each other within the boundaries of central occlusion is determined.
Note! In the process of modeling artificial teeth, it is very important to take into account the characteristics of the tubercles, as well as the inclinations of the slopes of the chewing teeth. Otherwise, disturbances in the interaction of the elements of the TMJ are possible, that is, the progression of joint dysfunction.
Movements in the joints using the example of the ankle and foot
Greetings, dear colleagues!
In one of the previous articles, we examined axes and planes.
And in this article we’ll talk about the movements that joints make along axes in the planes of the human body.
This knowledge will help you better understand the material that is given in various fitness trainings.
To avoid confusion (the names of the axes and planes are the same), I recommend re-reading the article on anatomical terms.
So, movements around all three axes are possible in the joints:
Based on the “standard” anatomical position, i.e. palms are directed forward, pronation will be turning the palm back, i.e. movement of the hand around a vertical axis, in which the thumb and index finger move forward in a circle towards the body (into a handshake position).
Supination , respectively, is the opposite, turning the palm forward.
Medical students use the mnemonic: I pour SOUP, SPILL SOUP.
Indeed, supination is a “scooping” movement of a spoon from a plate, and pronation is a “plunging” movement of a spoon into a plate.
The greatest difficulties in designating movements arise in the joints of the legs.
Movements at the ankle joint
The ankle joint is capable of flexion and extension.
Moreover, flexion is considered to be lowering the sole, which is performed by the triceps surae and not only. Therefore, in functional anatomy this movement is called plantar flexion (planta).
Abduction and adduction of the ankle are possible with full plantar flexion.
Foot movements
In the foot as a whole, movements around all axes are possible, and on their basis, combined three-plane movements arise. Due to the disagreements mentioned above, there is no single classification, and both options will be given below.
Option 1 (see table).
In my opinion, it is more logical from the point of view of “standard” anatomy, and it is precisely this that can be heard from the lips of Dmitry Gorkovsky in the “Body Architecture” course (or in the Prehab )
In the block on working with the foot, Dmitry explains why adduction is never combined with pronation, and abduction is never combined with supination.
- triceps surae muscle - m. triceps surae :
— anterior and posterior tibial muscles – mm. tibiales anterior et posterior ;
- long flexor and extensor fingers - mm. flexor et extensor digitorum longi ;
- long flexor and extensor of the big toe (hallux) - mm. flexor et extensor hallucis longi ;
- long, short, third peroneal muscles - mm. peronei longus, brevis, tertius .
Option 2. Among the famous instructors-methodologists, it is taught by Kirill Shlykov (“School of Podiatry”) and it is spoken by Georgy Temichev in the “
Prehab ”
. If we use this terminology: adduction is never combined with eversion, and abduction is never combined with inversion.
Colleagues refer to different authors, different sources, and there is no right/wrong here.
However, after reading this note, I think the meaning of the terms has become clearer to you:
Professional terminology will allow you to communicate with colleagues in a language that everyone understands, without having to explain every time what you meant.
A competent trainer or doctor will always understand what you are talking about when you use the term eversion or inversion.
Just as you will understand the doctor’s recommendations or the story of a fellow trainer using professional terminology.
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