Chapter 6 - The Muscular System

The Muscular System

Did you know that ? - more than 50% of body weight

is muscle !

- And muscle is made up of proteins and water

The Muscular System

• Muscles are responsible for all movement of the body

• There are three basic types of muscle– Skeletal– Cardiac– Smooth

Info About Muscles

• Only body tissue able to contract

• create movement by flexing and extending joints

• Body energy converters (many muscle cells contain many mitochondria)

3 Types of Muscles

Three types of muscle

Skeletal Cardiac Smooth

Classification of Muscle

Skeletal- found in limbs

Cardiac- found in heart

Smooth- Found in viscera

Striated, multi- nucleated

Striated, 1 nucleus

Not striated, 1 nucleus

voluntary involuntary involuntary

Characteristics of Muscle

• Skeletal and smooth muscle are elongated• Muscle cell = muscle fiber• Contraction of a muscle is due to movement

of microfilaments (protein fibers)• All muscles share some terminology

– Prefixes myo and mys refer to muscle– Prefix sarco refers to flesh

Shapes of Muscles

• Triangular- shoulder, neck• Spindle- arms, legs• Flat- diaphragm, forehead• Circular- mouth, anus

Shapes of Muscles

Skeletal Muscle

• Most are attached by tendons to bones• Cells have more than one nucleus

(multinucleated)• Striated- have stripes, banding• Voluntary- subject to conscious control• Tendons are mostly made of collagen fibers• Found in the limbs• Produce movement, maintain posture,

generate heat, stabilize joints

Structure of skeletal muscle

• Each cell (fibre) is long and cylindrical• Muscle fibres are multi-nucleated• Typically 50-60mm in diameter, and up

to 10cm long• The contractile elements of

skeletal muscle cells aremyofibrils

Skeletal muscle - Summary

• Voluntary movement of skeletal parts

• Spans joints and attached to skeleton

• Multi-nucleated, striated, cylindrical fibres

Smooth Muscle

• No striations• Spindle shaped• Single nucleus• Involuntary- no conscious control• Found mainly in the walls of hollow organs

Smooth muscle• Lines walls of viscera

• Found in longitudinal or circular arrangement

• Alternate contraction of circular & longitudinal muscle in the intestine leads to peristalsis

Smooth Muscle

Structure of smooth muscle

• Spindle shaped uni-nucleated cells• Striations not observed • Actin and myosin filaments are present(

protein fibers)

Smooth muscle - Summary

• Found in walls of hollow internal organs

• Involuntary movement of internal organs

• Elongated, spindle shaped fibre with single nucleus

Cardiac Muscle

• Striations• Branching cells• Involuntary• Found only in the heart• Usually has a single nucleus, but can have

more than one

Cardiac muscle

• Main muscle of heart• Pumping mass of heart• Critical in humans• Heart muscle cells

behave as one unit• Heart always contracts

to it’s full extent

Structure of cardiac muscle• Cardiac muscle cells (fibres) are

short, branched and interconnected• Cells are striated & usually have 1

nucleus• Adjacent cardiac cells are joined via

electrical synapses (gap junctions)• These gap junctions appear as dark

lines and are called intercalated discs

Cardiac muscle - Summary

• Found in the heart• Involuntary rhythmic

contraction• Branched, striated

fibre with single nucleus and intercalated discs

Muscle Control

Type of muscle

Nervouscontrol

Type of control

Example

SkeletalSkeletal Controlled by CNS

Voluntary Lifting a glass

Cardiac Regulated by ANS

Involuntary Heart beating

Smooth Controlled by ANS

Involuntary Peristalsis

Types of Responses• Twitch-

– A single brief contraction– Not a normal muscle function

• Tetanus– One contraction immediately followed by

another– Muscle never completely returns to a relaxed

state– Effects are compounded

Where Does the Energy Come From?

• Energy is stored in the muscles in the form of ATP

• ATP comes from the breakdown of glucose during Cellular Respiration

• This all happens in the Mitochondria of the cell

• When a muscle is fatigued (tired) it is unable to contract because of lack of Oxygen

Fast Twitch and Slow Twitch Fibers

Fast Twitch vs Slow Twitch

Exercise and Muscles

• Isotonic- muscles shorten and movement occurs ( most normal exercise)

• Isometric- tension in muscles increases, no movement occurs (pushing one hand against the other)

How are Muscles Attached to Bone?

• Origin- attachment to immovable bone• Insertion- attachment to a movable bone• Muscles are always attached to at least 2

points• Movement is attained due to a muscle

moving an attached bone

Muscle Attachments

Origin

Insertion

Muscle Attachments

• The origin is on the clavicle and sternum. • The insertion is on the skull. • When the muscle contracts it will shorten

the distance between the origin and insertion.

• The head will move when this muscle contracts.

FlexionTypes of Musculo-Skeletal Movement

Extension

Hyperextension

Abduction, Adduction & Circumduction

Rotation

More Types of Movement……

• Inversion- turn sole of foot medially• Eversion- turn sole of foot laterally• Pronation- palm facing down• Supination- palm facing up• Opposition- thumb touches tips of fingers

on the same hand

The Skeletal Muscles

There are about 650 muscles in the human body. They enable us to move, maintain posture and generate heat. In this section we will only study a sample of the major muscles.

SternocleidomastoideusFlexes and Rotates Head

Sternocleidomastoideus

• Sometimes called the sternocleitomastoid.• It is the same neck muscle shown on the previous slide. • This muscle has two origins.

– The first origin is on the sternum manubrium. – The second origin is on the clavicle.

• The insertion is on the mastoid process of the skull. • Contraction of both sternocleidomastoideus muscles

will flex the head. If just one of the muscles contracts, the head will rotate.

MasseterElevate Mandible

Masseter

• The masseter is one of major chewing muscles.

• The origin of the masseter is on the zygomatic arch.

• The insertion is on the mandible. • Contraction of the masseter will elevate the

jaw.

TemporalisElevate & Retract Mandible

Temporalis

• The temporalis is another chewing muscle.– Note how it attaches on the side of skull.

• It also elevates the mandible. • You do not need to know the insertions and

origins for this muscle

TrapeziusExtend Head, Adduct, Elevate or

Depress Scapula

Trapezius• The trapezius is a large muscle in the upper back. • It attaches to the skull, shoulder and vertebrae of

the back. • When this muscle contracts it will cause the head

to extend. • It will also move the scapula. • The direction the scapula moves depends on which

part of the trapezius contracts. • The trapezius may elevate or depress the scapula.

Latissimus DorsiExtend, Adduct & Rotate Arm Medially

Latissimus Dorsi• The latissimus dorsi is a large muscle in the back.

– It is often referred to as a lat. • It has origins on the vertebrae, ilium ribs and

scapula. • The insertion is on the humerus.

– When it contracts it moves the humerus. • It can extend, adduct and rotate the arm medially. • This is the main muscle used in movement such as

pounding a nail with a hammer.

DeltoidAbduct, Flex & Extend Arm

Deltoid• The deltoid covers the shoulder and has the shape of a

delta. • It has origins on the scapula and clavicle.

– The deltoid inserts on the deltoid tuberosity of the humerus.

• Contraction of the deltoid will adduct the arm. • If only the anterior fibers of the muscle contract it will

flex the arm. • Contraction of the posterior fibers will extend the

arm.

Pectoralis MajorFlexes, adducts & rotates arm medially

Pectoralis Major• The pectoralis major is a large muscle in the pectoral

region of the body. • It has origins on the clavicle and sternum.

– The insertion is on the greater tubercle of the humerus.

• Contraction of the pectoralis major will flex the arm.

• It will also adduct and rotate the arm medially. • The pectoralis major is used in movements such a

climbing, throwing and doing pushups.

Biceps BrachiiFlexes Elbow Joint

Biceps Brachii• The biceps brachii is located on the anterior side of the

upper arm. • It is often just called the biceps.

– There is a biceps femoris in the leg we will study shortly.

• The biceps has two origins. One origin is on the corocoid process and the other on the Glenoid cavity of the scapula.

• The “bi” in biceps refers to the two origins. – It inserts on the radial tuberosity.

• Contraction of the biceps will cause flexing at the elbow joint.

Triceps BrachiiExtend Elbow Joint

Triceps Brachii• The triceps is on the back of the upper arm. • It has three origins. • Two origins are on the back of the humerus

and one on the scapula. • The triceps inserts on the olecranon. • Movement of the triceps will extend the

elbow joint.

Rectus AbdominusFlexes Abdomen

Rectus Abdominus

• Rectus abdominus is a long muscle in the abdomen.

• The muscle originates on the pubis. • It inserts on the xiphoid process of the

sternum and also on cartilage of the ribs. • When rectus abdominus contracts it will

flex the abdomen.

External ObliqueCompress Abdomen

External Oblique

• Another muscle in the abdomen is the external oblique.

• It has muscle fibers that run in an oblique direction across the abdomen.

• Contraction of the external oblique will compress the abdomen.

External IntercostalsElevate ribs

External Intercostals

• There are two groups of muscles that run between the ribs.

• The first are the external intercostals. • They will elevate the ribs.

Internal IntercostalsDepress ribs

Internal Intercostals

• The internal intercostals are also located between the ribs.

• They will depress the ribs.

DiaphragmInspiration

Diaphragm

• This is an inferior view of the diaphragm. • This muscle separates the abdominal cavity

from the thoracic cavity. • When it contracts it will cause inspiration.

Forearm Muscles

Forearm Muscles• Flexor carpi—Flexes wrist• Extensor carpi—Extends wrist• Flexor digitorum—Flexes fingers• Extensor digitorum—Extends fingers• Pronator—Pronates • Supinator—Supinates

Gluteus MaximusExtends & Rotates

Thigh Laterally

Gluteus Maximus• The large muscle on the posterior side of the

body at the top of each leg is the gluteus maximus.

• The gluteus maximus originates on the ilium, sacrum and coccyx.

• It inserts on the gluteal tuberosity of the femur. • This muscle will extend and rotate the thigh

laterally.

Rectus Femoris

Flexes Thigh, Extends Lower Leg

Rectus Femoris

• Rectus femoris is located on the anterior side of the thigh.

• It originates on the ilium. • The insertion is on the patella and the tibial

tuberosity. • When rectus femoris contracts it will flex

the thigh and extend the lower leg.

GracilisAdducts and Flexes Thigh

Gracilis

• The gracilis is on the medial side of the thigh.

• It adducts and flexes the thigh.

SartoriusFlexes Thigh, & Rotates Thigh

Laterally

Sartorius• Sartorius is a long, strap like muscle. • It originates on the anterior superior iliac spine

of the ilium. • The insertion is on the medial side of the tibia. • Contraction of the sartorius flexes the thigh

and rotates the thigh laterally. • This is the muscle used when crossing the legs

to sit on the floor.

Biceps Femoris

Extends Thigh & Flexes Lower Leg

Biceps Femoris

• Biceps femoris is one of the hamstring muscles.

• The origin is on the ischial tuberosity.• Biceps femoris inserts on the tibia and

fibula. • This muscle extends the thigh and flexes the

lower leg.

GastrocnemiusPlantar Flexes Foot & Flex Lower Leg

Gastrocnemius

• Gastrocnemius is commonly called the calf muscle.

• It originates on the distal end of the femur. • The insertion is on the calcaneus bone of

the foot. • It will cause plantar flexion of the foot and

also flex the lower leg.

Tibialis AnteriorDorsiflexes and Inverts Foot

Tibialis Anterior

• Tibialis anterior is located on the anterior side of the tibia.

• It will dorsiflex and invert the foot.