Muscular System

- The skeleton and muscles function together as the

musculoskeletal system.

- This system plays an important homeostatic role:

allowing the individual to move to more favorable

external conditions.

Muscular System

The muscular system is the biological system of

humans that allows to move.

Muscle (from Latin musculus “little mouse”).

• More than 50% of body weight is muscle!!!

• Muscles convert chemical energy into mechanical

energy.

• Muscles NEVER push, they ONLY pull.

Muscular System

DeltoidPectoralis major

Biceps brachi

Gluteus maximus

Rectus femoris

Gastrocnemius

Muscular System

Classification of muscles:

I- Voluntary muscles

II- Involuntary muscles

Muscular System

Classification of muscles:

I- Voluntary muscles

- Voluntary muscles are controlled by thinking

about what you want them to do.

- People can run and talk because of voluntary

muscles.

- e.g., skeletal muscles

Muscular System

Classification of muscles:

II- Involuntary muscles

- Involuntary muscles are controlled by the brain

without thinking about them.

- e.g., Heart and blood vessels.

• Some muscles are both voluntary and involuntary, the

muscles that control breathing are an example.

Muscular System

Functions of the muscles

1. Movement

2. Warmth

3. Posture

Muscular System

Functions of the muscles

1. Movement: almost all movements by the

human body result from muscle

contraction.

Muscular System

Functions of the muscles

2. Warmth: any activity by muscles

generates heat as a byproduct, which is

vital in maintaining normal body

temperature

Muscular System

Functions of the muscles

3. Posture: muscle lend support to the

body and help it maintain posture against

the force of gravity.

Muscular System

Muscle Properties

1. Ability to contract

2. Ability to be stretched

3. Ability to respond to a stimulus

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• Muscle is attached to the bone by tendons

(tough connective tissue) and other tissues.

• Tendons attach muscle to bone; the origin is the

more stationary bone, the insertion is the more

movable bone.

Muscular System

Muscular System

Functional Organization of Skeletal Muscle

1)Single Muscle Fibers

i. A muscle fiber is a single, multinucleated

muscle cell.

ii. A muscle is made up of hundreds or even

thousands of muscle fibers, depending on

the muscle size.

Muscular System

1)Single Muscle Fibers, cont’d

iii. The health of muscle depends on a sufficient

nerve and blood supply, each skeletal

muscle has a nerve ending that controls its

activity (innervation), and an individual

system to supply and drain blood

(vascularization).

Muscular System

Functional Organization of Skeletal Muscle

2) Bundles of Muscles

i. Muscle fibers consist of bundles of

threadlike structures called myofibrils.

ii. Each myofibrils is made up of two types of

protein filaments, (Thick called myosin, Thin

called actin).

Muscular System

2) Bundles of Muscles, cont’d

iii. Thin actin filaments are anchored at their

midpoints to a structure called the z-line.

iv. The region from one z-line to the next is

called a sarcomere, which is the functional

unit of muscle contractions.

Muscular System

• All muscle cells produce

adenosine triphosphate

(ATP) molecules which are

used to power the

movement of the myosin.

Myosin

Actin

Sarcomere

Muscular System

- whereas most cells have a

single nucleus, muscle fibers

have as many as 100 or more

nuclei (multinucleated)

- The other difference is that they

can extend the entire length of a

muscle.

Muscular System

- Each of more than 650 muscles is served

by nerves which link the muscle to the brain

and spinal cord (Neuromuscular system).

Muscular System

- When they receive a signal from the brain,

muscle fibers can contract.

- The strength of a muscle contraction depends

on how many fibers contract at the same time.

Muscular System

Muscular System

- In order for a muscle to contract or shorten,

muscle fibers must be stimulated by nerve

impulses sent through motor neurons or nerves

(Neuromuscular junctions).

- These impulses originate in the brain, then

rundown the spine, then they branch out to all

parts of the body.

Muscular System

• In order to create movement, muscles must act

in pairs.

• Muscles are arranged on the skeleton on such

a way that the flexing or contracting of one

muscle is usually balanced by the lengthening

or relaxation of another muscle or group of

muscles. In other words, when one muscle or

set of muscle contracts, the other relaxes.

Muscular System

Muscular System

- When a nerve impulse reaches the end of the

motor neuron at the neuromuscular junction,

acetylcholine (a chemical neurotransmitter) is

released, then it travels across a small gap

between the motor neuron and the muscle fiber

and attaches to receptors on the membrane of

muscle fiber.

Muscular System

Muscular System

Muscle Types

1. Skeletal

2. Smooth

3. Cardiac

Muscular System

Muscular System

1.Skeletal muscles or Striated muscles

• The tissue is made of long fibers, with multiple nuclei.

• They are attached to bones by tendons.

• Many of these are voluntary, but some are involuntary.

• The most abundant tissue in the human body.

Muscular System

1.Skeletal muscles: cont’d

• They are controlled by the somatic nervous system.

• An average adult male is made up of 40-50% of skeletal muscle

• an average adult female is made up of 30-40%.

Muscular System

2. Smooth muscles or Visceral muscles

• Are involuntary muscles, and found within the walls of organs and structure such as esophagus, stomach, intestines etc…

• Smooth muscle is NOT under conscious control.

• They are also found in blood vessels.

Muscular System

2. Smooth muscles: cont’d

• Smooth muscle occurs at various scales in almost every organ.

• In the skin (in which it controls erection of body hair) to the blood vessels and digestive tract (in which it controls the caliber of the lumen).

• Smooth muscle cells are elongated, have only one nucleus.

Muscular System

3. Cardiac muscles

• These muscles are attached to other muscles instead of bones and tendons.

• These muscles are involuntary.

• They are striated with multiple nuclei.

• Is a specialized kind of muscle found only within the HEART.

Muscular System

3. Cardiac muscles: cont’d

• Cardiac muscle are typically branched like a tree branch and connect to other cardiac muscle fiber through intercalated discs.

• Although that they are considered involuntary muscles, they do respond to psychological states such as stress and excitement.

Muscular System

• All three muscles use the movement of actin

against myosin to create contraction.

• In skeletal muscle, contraction is stimulated by

electrical impulses transmitted by the nerves.

Muscular System

• Cardiac and smooth muscle contractions are

stimulated by internal pacemakers cells who

regularly contract, and propagate contractions

to other muscle cells they are in contact with.

• All skeletal muscle and many smooth muscle

contractions are facilitated by the

neurotransmitter acetycholine.

Muscular System

• Cardiac and skeletal muscles are “striated”

and they contain sarcomeres and are packed

into highly-regular arrangements of bundles;

smooth muscle has neither.

Cardiac Smooth Skeletal

Muscular System

• While skeletal muscles are arranged in

regular, parallel bundles, cardiac muscle

connects at branching, irregular angels.

Cardiac Smooth Skeletal

Muscular System

• Striated muscles contracts and relaxes in

short, intense bursts, whereas smooth muscle

sustains longer or even near-permanent

contractions.

Cardiac Smooth Skeletal

Muscular System

Muscle tone

• Even when the body is at rest, certain muscle

fibers in all muscles are contracting. This

activity is directed by the brain and cannot be

controlled consciously.

• This state of continuous partial muscle

contraction is known as muscle tone.

Muscular System

Muscle tone

• These contractions are not enough to produce

movement, but do tense and firm the muscles.

In doing so, they keep the muscles firm,

healthy and ready for action.

• Muscle tone is important because it helps

individuals maintain an upright posture.

Muscular System

Muscle facts:

- Smallest muscle in the body: (Stapedius) the muscle that activates the stirrup, the small bone that sends vibrations from the eardrum to the inner ear.

- Largest muscle in the body: (Latissimus dorsi) the large, flat muscle that covers the middle and lower back.

Muscular System

Muscle facts:

- Longest muscle in the body: (Sartorius) the

straplike muscle that runs diagonally from the

waist down across the front of the thigh to the

knee.

- Strongest muscle in the body: (Glutus

maximus) the muscle pair of the hip that form

most of the flesh of the buttocks.

Muscular System

Muscle facts:

- Fastest-reacting muscle in the body: (Orbicularis oculi) the muscle that encircles the eye and closes the eyelid. It contracts in less than 0.01 second.

- Contrary to popular belief, the number of muscle fibers cannot be increased through exercise; instead, the muscle cells simply get bigger (hypertrophy) or split (hyperplasia).