MUSCULAR SYSTEM
Muscle cells are specialized contractile cells , also called fibres.
There 3 types of muscle tissues are
1. Smooth muscle
2. Cardiac muscle
3. Skeletal muscle
SMOOTH MUSCLE :
1. Smooth muscle (involuntary or non-straited ) muscle is not under conscious control .
2. The cells are small , have one nucleus and are spindle shaped .
3. Smooth muscle forms sheets in the walls of hollow organs and tubular structures to regulate diameter and propel substances through tracts.
4. Some smooth muscle units have the ability to initiate their own contraction independently of nerve stimulation , cardiac muscle has this property too.
]me hormones and local metabolites may influence contraction. E.g Adrenaline (epinephrine ) from the adrenal medulla dilates the airways.
5. Smooth muscle do not exhibit cross-striations under microscope, being plan and smooth in form and their uniform appearance when viewed under a microscope has led to the term smooth muscle which is in contrast with striated appearance of skeletal and cardiac muscles.
6. They are supplied by autonomic nerves and
therefore, are not under voluntary control and respond slowly to stimuli.
therefore, are not under voluntary control and respond slowly to stimuli.
7. They provide motor power for regulating the internal environment related to digestion, circulation, secretion and excretion.
8. Smooth muscles are less dependent on nervous control, being capable of contracting automatically, spontaneously ,and often rhythmically and each muscle fiber is an elongated, spindle-shaped cell, with a single nucleus placed centrally; the myofibrils show longitudinal striations.
9. Muscles of the blood vessels, and the arrector pili or erector pili muscles of the skin are examples of smooth muscles.
CARDIAC MUSCLE :
1. This type of muscles are found in the heart.
2. It is intermediate in structure, being striated and at the same time involuntary.
3. It is meant for automatic and rhythmic –contractions and each muscle fiber.
4. These fibers have a single nucleus placed centrally which branches and anastomoses with the neighboring fibers at intercalated discs.
5. The cross- striations are less prominent than those in the skeletal muscle.
6. These muscles are found only in the heart and are responsible for pumping blood .
7. Cardiac muscle are also called as “involuntary muscles”.
8. Cardiac muscle is unique as it stimulates itself to contract by virtue of pacemaker which is also made of cardiac muscle tissue.
9. The cells of cardiac muscle tissue are striated –that is , they appear to have light and dark stripes when viewed under a light microscope, the arrangement of protein fibers inside of the cells causes these light and dark bands. Striations indicate that a muscle cell is very strong, unlike visceral muscles.
10. The cells of cardiac muscle are branched X or Y shaped cells tightly connected together by fingerlike projections from two neighboring cells (intercalated discs) that interlock and provide a strong bond between the cells.
11. The branched structure and intercalated discs allow the muscle cells to resist high blood pressures and strain continuous working. This features also help to spread electrochemical signals quickly from cell to cell so that the heart can beat as a unit.
SKELETAL MUSCLES:
1. Skeletal muscles are type of muscle which are most abundant and are found attached to skeleton. They are also called as Striped, striated, somatic or voluntary muscles.
2. They exhibit cross-striations under microscope, and are considered to be best differentiated form of muscle.
3. They are supplied by somatic (cerebrospinal) nerves and therefore are under voluntary control ,with certain exceptions.
4. They respond quickly to stimuli, being capable of rapid contractions, and help in adjusting the individual to external environment. They also get fatigued very easily.
5. Each muscle fiber of skeletal muscle is a multinucleated cylindrical cell, containing groups of myofibrils. Myofibrils are made up of myofilaments of three types (myosin, actin and tropomyosin). These are the actual contractile elements of the muscle.
6. Skeletal muscle are under highest nervous control of cerebral cortex.
7. Examples of these types of muscles are muscles of limbs and body wall, and bronchial muscles are examples of skeletal.
MUSCLES OF THE FACE
There are many muscles in changing facial expression and with movement of lower jaw during chewing and speaking. Some of the main muscles are present in pairs, one on each side.
1. OCCIPITOFRONTALIS (UNPAIRED)
This consists of a posterior muscle part over the occipital bone (occipitalis), an anterior part over the frontal bone (frontalis) and an extensive flat tendon or aponeurosis that stretches over the dome of the skull and joints the muscular parts .
it raises the eyebrows.
2. LEVATOR PALPEBRAE SUPERIORIS .
This muscle extends from the posterior part of the orbital cavity to the upper eyelid.
It raises the eyelid.
3. ORBICULARIS OCULI.
This flat muscle of the cheek draws the cheeks in towards the teeth in chewing and in forcible expulsion of air from the mouth (the trumpeter’s muscle).
4. ORBICULARIS ORIS (UNPAIRED)
This muscle surrounds the mouth and blends with the muscles of the cheeks. It closes the lips and , when strongly contracted, shapes the mouth for whistling.
5. MASSETER
This muscle is a broad muscle, extending from the zygomatic arch to the angle of the jaw.
In chewing it draws the mandible up to the maxilla, closing the jaw, and exerts considerable pressure on the food.
6. TEMPORALIS
This muscle covers the squamous part of the temporal bone.
It passes behind the zygomatic arch to be inserted into the coronoid process of the mandible.
It closes the mouth and assists with chewing.
7. PTERYGOID
This muscle extends from the sphenoid bone to the mandible.
It closes the mouth and pulls the lower jaw forward.
1. TRAPEZIUS .
This muscle covers the shoulder and the back of the neck. The upper attachment is to the occipital protuberance, the medial attachment is to the transverse processes of the cervical and thoracic vertebrae and the lateral attachment is to the clavicle and to the spinous and acromion processes of the scapula.
It pulls the head backwards, squares the shoulders and controls the movements of the scapula when the shoulder joint is in use.
2 TERES MAJOR .
This originates from the inferior angle of the scapula and is inserted into the humerus just below the shoulder joint.
It extends , adducts and medially rotates the arm.
1. PSOAS MUSCLE
This arises from the transverse processes and bodies of the lumbar vertebrae.
It passes across the flat part of the ilium and behind the inguinal ligament to be inserted into the femur.
Together with the iliacus it flexes the hip joint.
2. LATISSIMUS DORSI
This arises from the posterior part of the iliac crest and the spinous processes of the lumbar and lower thoracic vertebrae.
It passes upwards across the back then under the arm to be inserted into the bicipital groove of the humerus.
It adducts, medially rotates and extends the arm.
3. QUADRATUS LUMBORUM
This muscle originates from the iliac crest then it passé upwards, parallel and close to the vertebral column and it is inserted into the 12th rib .
Together the two muscles fix the lower rib during respiration and cause extension of the vertebral column (being backwards).
If one muscle contracts it causes lateral flexion of the lumbar region of the vertebral column.
4. SACROSPINALIS (ERECTOR SPINAE).
This is a group of muscles lying between the spinous and transverse processes of the vertebrae.
They originate from the sacrum and are finally inserted into the occipital bone.
Their contraction causes extension of the vertebral column.
Definition :
MUSCLES OF THE NECK
There are many muscles situated in the neck but only the two largest are considered.
1. STERNOCLEIDOMASTOID.
This muscle arises from the manubrium of the sternum and the clavicle and extends upwards to the mastoid process of the temporal bone.
It assists in turning the head from side to side.
When the muscle on one side contracts it draws the head towards the shoulder.
When both contract at the same time they flex the cervical vertebrae or draw the sternum and clavicles upwards when the head is maintained in a fixed position,e.g.in forced respiration.
2. TRAPEZIUS .
This muscle covers the shoulder and the back of the neck. The upper attachment is to the occipital protuberance, the medial attachment is to the transverse processes of the cervical and thoracic vertebrae and the lateral attachment is to the clavicle and to the spinous and acromion processes of the scapula.
It pulls the head backwards, squares the shoulders and controls the movements of the scapula when the shoulder joint is in use.
READ MORE - MUSCLES OF THE FACE
MUSCLES OF THE ABDOMINAL WALL
There are six pairs of muscles that form the abdominal wall. it from the surface inwards they are.
v Rectus abdominis
v External oblique
v Internal oblique
v Transversus abdominis
v Quadratus lumborum
v Psoas .
The anterior abdominal wall is divided longitudinally by a very strong midline tendinous cord, the linea alba (meaning ‘white cord’) which extends from the xiphoid process of the sternum to the symphysis pubis.
The structure of the abdominal wall on each side of the linea alba is identical.
RECTUS ABDOMINIS.
This is the most superficial muscle.
It is broad and flat ,originating from the transverse part of the pubic bone then passing upwards to be inserted into the lower ribs and the xiphoid process of the sternum.
Medially the two muscles are attached to the linea alba.
EXTERNAL OBLIQUE
This muscle extends from the lower ribs downwards and forwards to be inserted into the iliac crest and by an aponeurosis,to the linea alba .
Internal oblique
This muscle lies deep to the external oblique.
Its fibres arise from the iliac crest and by a broad band of fascia from the spinous processes of the lumbar vertebrae.
The fibres pass upwards towards the midline to be inserted into the lower ribs and by an aponeurosis , into the linea alba. The fibres are at right angles to those of the external oblique.
TRANSVERSE ABDOMINIS
This is the deepest muscle of the abdominal wall.
The fibres arise from the iliac crest and the lumbar vertebrae and pass across the abdominal wall to be inserted into the linea alba by an aponeurosis.
The fibres are at right angles to those of the rectus abdominis.
Functions
The main function of the four pairs of muscles is to form the strong muscular anterior wall of the abdominal cavity.
When the muscles contract together they:
Ø Compress the abdominal organs.
Ø Flex the vertebral column in the lumbar region.
Ø Contraction of the muscles on one side only bends the trunk towards that side. contraction of the oblique muscles on one side rotates the trunk.
INGUINAL CANAL
This canal is 2.5 to 4 cm long and passes obliquely through the abdominal wall.
It runs parallel to and immediately in front of the transversalis fascia and part of the inguinal ligament .
In the male it contains the spermatic cord and in the female, the round ligament.
It constitutes a weak point in the otherwise strong abdominal through which herniation may occur.
MUSCLES OF THE BACK
There are six pairs of large muscles in the back in addition to those that form the posterior abdominal wall.
The arrangement of these muscles is the same on each side of the vertebral column.
They are
1. Trapezius
2. Teres major
3. Psoas
4. Latissimus dorsi
5. Quadratus lumborum
6. Sacrospinalis.
MUSCLES OF THE BACK
There are six pairs of large muscles in the back in addition to those that form the posterior abdominal wall.
The arrangement of these muscles is the same on each side of the vertebral column.
They are
1. Trapezius
2. Teres major
3. Psoas
4. Latissimus dorsi
5. Quadratus lumborum
6. Sacrospinalis.
This muscle covers the shoulder and the back of the neck. The upper attachment is to the occipital protuberance, the medial attachment is to the transverse processes of the cervical and thoracic vertebrae and the lateral attachment is to the clavicle and to the spinous and acromion processes of the scapula.
It pulls the head backwards, squares the shoulders and controls the movements of the scapula when the shoulder joint is in use.
2 TERES MAJOR .
This originates from the inferior angle of the scapula and is inserted into the humerus just below the shoulder joint.
It extends , adducts and medially rotates the arm.
1. PSOAS MUSCLE
This arises from the transverse processes and bodies of the lumbar vertebrae.
It passes across the flat part of the ilium and behind the inguinal ligament to be inserted into the femur.
Together with the iliacus it flexes the hip joint.
2. LATISSIMUS DORSI
This arises from the posterior part of the iliac crest and the spinous processes of the lumbar and lower thoracic vertebrae.
It passes upwards across the back then under the arm to be inserted into the bicipital groove of the humerus.
It adducts, medially rotates and extends the arm.
3. QUADRATUS LUMBORUM
This muscle originates from the iliac crest then it passé upwards, parallel and close to the vertebral column and it is inserted into the 12th rib .
Together the two muscles fix the lower rib during respiration and cause extension of the vertebral column (being backwards).
If one muscle contracts it causes lateral flexion of the lumbar region of the vertebral column.
4. SACROSPINALIS (ERECTOR SPINAE).
This is a group of muscles lying between the spinous and transverse processes of the vertebrae.
They originate from the sacrum and are finally inserted into the occipital bone.
Their contraction causes extension of the vertebral column.
PELVIC FLOOR
Definition :
Pelvic floor is a muscular partition , which separates the pelvic cavity from the anatomical perineum
Muscle layers of the pelvic floor:
THE SUPERFICIAL LAYER:
This layer is composed of five muscles:
1. The external anal sphincter : it encircles the anus and is attached behind by the few fibres to the coccyx.
2. The transverse perineal muscles : it passes from the ischial tuberosity to the center of the perineum.
3. The bulbocavernosus muscles: it passes from the ischial tuberosity along the pubic arch to the corpora cavernosa.
4. The ischiocavernosus muscles: it passes from the ischial tuberosity along the pubic arch to the corpora cavernosa.
5. The membranous sphincter of the urethra: it is composed of muscle fibres passing above and below the urethra and attached to the pubic bones.
THE DEEP LAYERS:
This layer is composed of three pairs of muscles, which together are known as the levator ani muscles. They are called so because they lift or elevate the anus. Each levator ani muscle (left and right) consists of the following:
1. THE PUBOCOCCYGEUS MUSCLE: it passes from the pubis to the coccyx, with a few fibres crossing over in the perineal body to form its deepest.
2. THE ILIOCOCCYGEUS MUSCLE : it passes from the fascia covering the obturator internus muscle (white line of the pelvic fascia).
3. THE ISCHIOCOCCYGEUS MUSCLE: it passes from the ischial spine to the coccyx, in front of the sacrospinous ligament in between the muscle layers above and below, there are layers of pelvic fascia.
This is a loose areolar tissue that acts as a packing material in the spaces. The tissue that fills the triangular space between the bulbocavernsous, the ischiocavernsous and the transverse perineal muscles is known as the triangular ligament.
FUNCTIONS OF THE PELVIC FLOOR MUSCLES:
1. The pelvic floor supports the weight of the abdominal and pelvic organs.
2. Pelvic muscles are responsible are responsible for the voluntary control of micturition and defecation and play an important part in the sexual intercourse.
3. In childbirth it influences the passive movements of the fetus through the birth canal by facilitating the anterior internal rotation of the presenting part when it presses on the pelvic floor and relaxes to allow the exist of the fetus from the pelvis.
4. It helps to maintain the intra abdominal pressure by reflex responding to its changes.
5. Ischiococcygeus helps to stabilize the sacroiliac and sacrococcygeal joints.
6. It helps to steady the perineal body.
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