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Muscle shapes and fiber alignment

This figure shows the human body with the major muscle groups labeled.
The skeletal muscles of the body typically come in seven different general shapes.

Biceps brachii muscle contraction

This photo shows a person flexing her biceps.
The large mass at the center of a muscle is called the belly. Tendons emerge from both ends of the belly and connect the muscle to the bones, allowing the skeleton to move. The tendons of the bicep connect to the upper arm and the forearm. (credit: Victoria Garcia)

Circular muscles are also called sphincters (see [link] ). When they relax, the sphincters’ concentrically arranged bundles of muscle fibers increase the size of the opening, and when they contract, the size of the opening shrinks to the point of closure. The orbicularis oris muscle is a circular muscle that goes around the mouth. When it contracts, the oral opening becomes smaller, as when puckering the lips for whistling. Another example is the orbicularis oculi, one of which surrounds each eye. Consider, for example, the names of the two orbicularis muscles (orbicularis oris and oribicularis oculi), where part of the first name of both muscles is the same. The first part of orbicularis, orb (orb = “circular”), is a reference to a round or circular structure; it may also make one think of orbit, such as the moon’s path around the earth. The word oris (oris = “oral”) refers to the oral cavity, or the mouth. The word oculi (ocular = “eye”) refers to the eye.

There are other muscles throughout the body named by their shape or location. The deltoid is a large, triangular-shaped muscle that covers the shoulder. It is so-named because the Greek letter delta looks like a triangle. The rectus abdomis (rector = “straight”) is the straight muscle in the anterior wall of the abdomen, while the rectus femoris is the straight muscle in the anterior compartment of the thigh.

When a muscle has a widespread expansion over a sizable area, but then the fascicles come to a single, common attachment point, the muscle is called convergent    . The attachment point for a convergent muscle could be a tendon, an aponeurosis (a flat, broad tendon), or a raphe (a very slender tendon). The large muscle on the chest, the pectoralis major, is an example of a convergent muscle because it converges on the greater tubercle of the humerus via a tendon. The temporalis muscle of the cranium is another.

Pennate muscles (penna = “feathers”) blend into a tendon that runs through the central region of the muscle for its whole length, somewhat like the quill of a feather with the muscle arranged similar to the feathers. Due to this design, the muscle fibers in a pennate muscle can only pull at an angle, and as a result, contracting pennate muscles do not move their tendons very far. However, because a pennate muscle generally can hold more muscle fibers within it, it can produce relatively more tension for its size. There are three subtypes of pennate muscles.

In a unipennate    muscle, the fascicles are located on one side of the tendon. The extensor digitorum of the forearm is an example of a unipennate muscle. A bipennate    muscle has fascicles on both sides of the tendon. In some pennate muscles, the muscle fibers wrap around the tendon, sometimes forming individual fascicles in the process. This arrangement is referred to as multipennate    . A common example is the deltoid muscle of the shoulder, which covers the shoulder but has a single tendon that inserts on the deltoid tuberosity of the humerus.

Because of fascicles, a portion of a multipennate muscle like the deltoid can be stimulated by the nervous system to change the direction of the pull. For example, when the deltoid muscle contracts, the arm abducts (moves away from midline in the sagittal plane), but when only the anterior fascicle is stimulated, the arm will abduct    and flex (move anteriorly at the shoulder joint).

The lever system of muscle and bone interactions

Skeletal muscles do not work by themselves. Muscles are arranged in pairs based on their functions. For muscles attached to the bones of the skeleton, the connection determines the force, speed, and range of movement. These characteristics depend on each other and can explain the general organization of the muscular and skeletal systems.

The skeleton and muscles act together to move the body. Have you ever used the back of a hammer to remove a nail from wood? The handle acts as a lever and the head of the hammer acts as a fulcrum, the fixed point that the force is applied to when you pull back or push down on the handle. The effort applied to this system is the pulling or pushing on the handle to remove the nail, which is the load, or “resistance” to the movement of the handle in the system. Our musculoskeletal system works in a similar manner, with bones being stiff levers and the articular endings of the bones—encased in synovial joints—acting as fulcrums. The load would be an object being lifted or any resistance to a movement (your head is a load when you are lifting it), and the effort, or applied force, comes from contracting skeletal muscle.

Chapter review

Skeletal muscles each have an origin and an insertion. The end of the muscle that attaches to the bone being pulled is called the muscle’s insertion and the end of the muscle attached to a fixed, or stabilized, bone is called the origin. The muscle primarily responsible for a movement is called the prime mover, and muscles that assist in this action are called synergists. A synergist that makes the insertion site more stable is called a fixator. Meanwhile, a muscle with the opposite action of the prime mover is called an antagonist. Several factors contribute to the force generated by a skeletal muscle. One is the arrangement of the fascicles in the skeletal muscle. Fascicles can be parallel, circular, convergent, pennate, fusiform, or triangular. Each arrangement has its own range of motion and ability to do work.

Questions & Answers

how is blood pressure measured
Ryan Reply
blood pressure
a sphygmomanometer is tied in the upper left arm and air is pumped in. The sthesthoscope is placed just below the sphygmomanometer (on brachial artery, above the antecubital fossa). The beginning and ending of pulse is noted which acts as systolic and diastolic pressure.
any other method?
what is protoncogen
how to mesured hear rate&pluse
cancer stimulating factors
structure of the cell
what do u want to know about the structure of the cell?
Process of bone healing
Thelma Reply
The fractured bones are brought closer (reduction of fracture). the fibroblast cells at broken ends divide rapidly and secrete collagen that forms collar of callus. The callus holds the bones together which slowly clacifies (remodelling) and later replaced by bone tissue.
what is the name of the two subunits of L chain of a antibody structure
Arshi Reply
The pituitary gland lies in the
Aamir Reply
bony cavity,sella tursica
how does endochrondral ossification start in short bones?
Steven Reply
the chondroblast cells forms a cartilaginous bone model which becomes calcified in mid region and is innervated by perosteal capillaries. These capillaris replaces cartilages with bone tissue.
define negative feedback
mechanism that cause supression of another process. eg. the secretion of one hormone can supress the other hormone secretion.
simply a self regulating mechanism which retun a deviated parameter to normal condition
secretion of hormones get supressed by other hormone secretion
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what is RH blood group
kuukyile Reply
It is a type of system for classifying blood groups according to the presence or absence of the Rh antigen.
What is the most important organ in the human body?
Gbemi Reply
the heart
or brain
the brain specifically is referred to as the control centre ..all nerve impulses are send to the brain which stimulates other specific parts of the body
please if l am Blood group B+ can l marry a lady with O- blood group?
structure of a serous membrane
Ziyanda Reply
are you asking?
In anatomy, serous membrane (or serosa) is a smooth tissue membrane consisting of two layers of mesothelium, which secrete serous fluid. The inner layer that covers organs (viscera) in body cavities is called the visceral membrane. A second layer of epithelial cells of the serous membrane, called th
The two layers of serous membranes are named parietal and visceral. Between the two layers is a thin fluid filled space.[2] The fluid is produced by the serous membranes and stays between the two layers to reduce friction between the walls of the cavities and the internal organs when they move with
a continuation from the 1st one:: A second layer of epithelial cells of the serous membrane, called the parietal layer, lines the body wall. Between the two layers is a potential space, mostly empty except for a few milliliters of lubricating serous fluid that is secreted by the two serous membranes
Lubricated secretion of skin is called sebum
what is the greater tronchanter?
the greater trochanter is  femur is a large, irregular, quadrilateral eminence and a is a part of the system of the skeleton
Thanks Jessie...
what is the easiest way to learn labels of Anatomical structures?
what's the anatomical plan of the horse lung
Name the two phases of metabolism
Grace Reply
reproduction and growth
how about anabolism and catabolism?
In Simply Anabolism means formation... Catabolism means breakdown
two phases of reproductio?
Anabolism indicates potential & catabolism potential converts to kinetic
Name the most important life process in the human body in terms of anatomy and physiology
Nervous system
Every system is important for body functions
what is the difference between the functions of the adhesion belt and the desmosomes?
Mason Reply
what are the derivatives of the germ layer?
Miriam Reply
Pls explain the atlas of the cervical vertebral column
Ifunanya Reply
why does the material not allow in mri
Simran Reply
what do you mean 'mri'
short for magnetic resonance imaging. "the researchers used MRI to record the brain activity" a medical examination performed using magnetic resonance imaging. "he's having an MRI to determine the extent of the injury" an image obtained by magnetic resonance imaging. "after looking at the MRI, the d
what is the meaning of sutures
Ibrahim Reply
i do not know
immovable joints btn two bones.eg the skull bones
Really,it's true
Sutures are immovable junction between two bones e.g those of the skull

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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