Skeletal MuscleSkeletal Muscle

Skeletal Muscle AnatomySkeletal Muscle Anatomy

Figure 12-3a-2: ANATOMY SUMMARY: Skeletal Muscle

Figure 12-4: T-tubules and the sarcoplasmic reticulum

Myofibrils: Site of Myofibrils: Site of ContractionContraction

Figure 12-3c-f: ANATOMY SUMMARY: Skeletal Muscle

Smooth muscle fasciclesSmooth muscle fascicles!!

Smooth MuscleSmooth Muscle

• The smooth The smooth muscle looks muscle looks smooth and works smooth and works automatically.  It automatically.  It can be found in can be found in the intestines, the intestines, lungs, and lungs, and bladder.bladder.

Cardiac MuscleCardiac Muscle

Cardiac muscle is located only in the heart.  It Cardiac muscle is located only in the heart.  It has a striated appearance and is involuntarily has a striated appearance and is involuntarily controlled.  Cardiac muscle also has a feature controlled.  Cardiac muscle also has a feature that is foreign to the other muscle types: that is foreign to the other muscle types: intercalated discs.  intercalated discs.  

• This muscle is This muscle is striped and striped and branched (like a branched (like a tree!)  It keeps tree!)  It keeps your heart beating your heart beating automatically.  automatically.  Where is it found? Where is it found? 

Intercalated Disc

Skeletal Muscles:Skeletal Muscles:Muscular MachinesMuscular Machines

VII. Interactions of Skeletal VII. Interactions of Skeletal Muscles in the BodyMuscles in the Body

A. A. Attachment Points (could be one or Attachment Points (could be one or multiple):multiple):

1. 1. OriginOrigin- point of attachment on bone; - point of attachment on bone; does not move during contractiondoes not move during contraction

2. 2. InsertionInsertion- point of attachment; does - point of attachment; does move during contractionmove during contraction

Muscles work in groups- some Muscles work in groups- some contract and some relax and contract and some relax and

some assist.some assist.• Four functional classificationsFour functional classifications– Prime MoversPrime Movers– AntagonistAntagonist– SynergistSynergist– FixatorsFixators

Prime MoverPrime Mover

• AgonistAgonist• Provides the major force for Provides the major force for

producing a specific producing a specific movementmovement

• For elbow flexion: biceps For elbow flexion: biceps brachiibrachii

AntagonistsAntagonists

• Muscles that oppose, or reverse, a particular Muscles that oppose, or reverse, a particular movementmovement

• When the prime mover is active, the antagonist When the prime mover is active, the antagonist muscles are often stretched and may be relaxedmuscles are often stretched and may be relaxed– Ex. Triceps brachii- rest during flexEx. Triceps brachii- rest during flex

• Prime movers and its antagonist are located on Prime movers and its antagonist are located on opposite sides of the jointsopposite sides of the joints

• Flexion of the arm by the biceps brachii muscle Flexion of the arm by the biceps brachii muscle of the arm is antagonized by the triceps brachii, of the arm is antagonized by the triceps brachii, the prime mover for extending the forearmthe prime mover for extending the forearm

SynergistsSynergists• Help the prime movers byHelp the prime movers by

– Adding a little extra forceAdding a little extra force– Reducing undesirable or unnecessary Reducing undesirable or unnecessary

movements that might occurmovements that might occur– Ex. Brachioradialis- assists in flexEx. Brachioradialis- assists in flex

They act as stabilizers: They act as stabilizers: When muscles cross two or more joints it’s When muscles cross two or more joints it’s

contraction causes movement of all the spanned contraction causes movement of all the spanned joints so these muscles act to stabilize the jointsjoints so these muscles act to stabilize the joints

FixatorsFixators

• Synergist that immobilize a boneSynergist that immobilize a bone– FixatorFixator- joint stabilizers; maintain - joint stabilizers; maintain

posture/balanceposture/balance– Ex. Deltoid- maintains shoulder joint stabilityEx. Deltoid- maintains shoulder joint stability

– Scapula is held to the axial skeleton only Scapula is held to the axial skeleton only by muscles and the scapula is freely by muscles and the scapula is freely moveable. The fixator muscles can moveable. The fixator muscles can immobilize immobilize the scapula so only desired the scapula so only desired movements occur at the shoulder jointmovements occur at the shoulder joint

Most skeletal muscles have names that describe some feature of the muscle. Often several criteria are combined into one name.

Associating the muscle's characteristics with its name will help you learn and remember them. The following are some terms relating to muscle features that are used in naming muscles.

1. Location:“brachii” means arm

Ex. Brachialis in upper arm

1. Location: 1. Location: – pectoralis (chest)pectoralis (chest)– gluteus (buttock or rump)gluteus (buttock or rump)– brachii (arm)brachii (arm)– supra- (above)supra- (above)– infra- (below)infra- (below)– sub- (under or beneath)sub- (under or beneath)– lateralislateralis (lateral).(lateral).

2. Function2. Function- direction of - direction of movementmovement

Ex. Ex. AdAdductor longus in thigh moves ductor longus in thigh moves leg towards median leg towards median

3. 3. Shape-Shape- “delta” means triangle “delta” means triangleEx. Deltoid on shoulder is Ex. Deltoid on shoulder is

triangular.triangular.• deltoid (triangular)deltoid (triangular)• rhomboid (like a rhombus with equal and rhomboid (like a rhombus with equal and

parallel sides)parallel sides)• latissimus (wide)latissimus (wide)• teres (round)teres (round)• trapezius (like a trapezoid, a four-sided trapezius (like a trapezoid, a four-sided

figure with two sides parallel).figure with two sides parallel).

4. Direction of fibers4. Direction of fibers-- “rectus” means “rectus” means straightstraight

Ex. Ex. RectusRectus abdominis muscle runs abdominis muscle runs straight up and down on abdomenstraight up and down on abdomen

• rectus (straight)rectus (straight)• transverse (across)transverse (across)• oblique (diagonally)oblique (diagonally)• orbicularis (circular)orbicularis (circular)

5. Number of origins5. Number of origins-- “cep” means “cep” means headhead

Ex. BiEx. Bicepceps brachii has two heads or s brachii has two heads or attachments to the shoulderattachments to the shoulder

• biceps (two heads)biceps (two heads)• triceps (three heads)triceps (three heads)• quadriceps (four heads) quadriceps (four heads)

6. Size: 6. Size: • vastus (huge)vastus (huge)• maximus (large)maximus (large)• longus (long)longus (long)• minimus (small)minimus (small)• brevis (short)brevis (short)

Muscle MechanicsMuscle Mechanics

For anatomical purposes muscles are classified by their structure rather than their composition.

Muscle types can be grouped into one of four classes based on the orientation of the fasciculi:

CircularConvergentParallelPennate

Arrangement of Fascicles-determine range of Arrangement of Fascicles-determine range of motion & powermotion & power

1. Circular- concentric rings 1. Circular- concentric rings

Ex. Orbicularis orisEx. Orbicularis oris

2. Convergent- broad origin 2. Convergent- broad origin single insertion single insertion

Ex. Pectoralis MajorEx. Pectoralis Major

3. Parallel- strap-like 3. Parallel- strap-like

Ex. SartoriusEx. Sartorius

4. Unipennate- insert into 1 side of tendon 4. Unipennate- insert into 1 side of tendon

Ex. Extensor digitorum longusEx. Extensor digitorum longus

5. Bipennate- insert into tendon from 2 sides 5. Bipennate- insert into tendon from 2 sides

Ex. Rectus femorisEx. Rectus femoris

6. Fusiform- spindle-shaped Ex. Biceps brachii6. Fusiform- spindle-shaped Ex. Biceps brachii

7. Multipennate- many feathers situated side by side 7. Multipennate- many feathers situated side by side

Ex. DeltoidEx. Deltoid

Circular Muscles

• In a In a circular musclecircular muscle, or , or sphinctersphincter, the fibers are , the fibers are concentrically arranged around concentrically arranged around an opening or a recess. When an opening or a recess. When the muscle contracts, the the muscle contracts, the diameter of the opening diameter of the opening decreases. Circular muscles decreases. Circular muscles guard entrances and exits of guard entrances and exits of internal passageways such as internal passageways such as the digestive and urinary the digestive and urinary tracts. An example is the tracts. An example is the orbicularis oris muscle orbicularis oris muscle of the of the mouthmouth

Convergent MuscleConvergent Muscle

• In a In a convergent muscleconvergent muscle, the , the muscle fibers are spread over a muscle fibers are spread over a broad area, but all the fibers broad area, but all the fibers converge at one common converge at one common attachment site. They may pull on a attachment site. They may pull on a tendon, an aponeurosis (tendinous tendon, an aponeurosis (tendinous sheet), or a slender band of collagen sheet), or a slender band of collagen fibers known as a fibers known as a rapheraphe. .

Parallel MusclesParallel Muscles

• In a In a parallel muscleparallel muscle, the fascicles are parallel to the , the fascicles are parallel to the long axis of the muscle. Most of the skeletal muscles in long axis of the muscle. Most of the skeletal muscles in the body are parallel muscles. Some are flat bands the body are parallel muscles. Some are flat bands with broad attachments with broad attachments (aponeuroses)(aponeuroses) at each end; at each end; others are plump and cylindrical with tendons at one others are plump and cylindrical with tendons at one or both ends. In the latter case, the muscle is spindle-or both ends. In the latter case, the muscle is spindle-shaped , with a central shaped , with a central bodybody, also known as the , also known as the belly,belly, or or gastergaster. The . The biceps brachii muscle biceps brachii muscle of the arm is a of the arm is a parallel muscle with a central body. When a parallel parallel muscle with a central body. When a parallel muscle contracts, it gets shorter and larger in muscle contracts, it gets shorter and larger in diameter. You can see the bulge of the contracting diameter. You can see the bulge of the contracting biceps brachii on the anterior surface of your arm biceps brachii on the anterior surface of your arm when you flex your elbow.when you flex your elbow.

PennatePennate

• In a In a pennate musclepennate muscle, the fascicles form a common , the fascicles form a common angle with the tendon. They are short and attach angle with the tendon. They are short and attach obliquely. Because the muscle cells pull at an obliquely. Because the muscle cells pull at an angle, contracting pennate muscles do not move angle, contracting pennate muscles do not move their tendons as far as parallel muscles do. But a their tendons as far as parallel muscles do. But a pennate muscle contains more muscle fibers--and, pennate muscle contains more muscle fibers--and, as a result, produces more tension--than does a as a result, produces more tension--than does a parallel muscle of the same size. parallel muscle of the same size.

• If all the muscle fibers are on the same side of the If all the muscle fibers are on the same side of the tendon, the pennate muscle is tendon, the pennate muscle is unipennate.unipennate. The The extensor digitorum muscle, extensor digitorum muscle, a forearm muscle that a forearm muscle that extends the finger joints, is unipennateextends the finger joints, is unipennate

Bipennate MuscleBipennate Muscle

• More commonly, a More commonly, a pennate muscle has pennate muscle has fibers on both sides fibers on both sides of the tendon. Such a of the tendon. Such a muscle is called muscle is called bipennate.bipennate. The The rectus rectus femoris femoris muscle, muscle, a prominent a prominent muscle that extendsmuscle that extends the knee, is the knee, is bipennatebipennate

MultipennateMultipennate

• If the tendon If the tendon branches within a branches within a pennate muscle, pennate muscle, the muscle is said the muscle is said to be to be multipennate. multipennate. The The triangular triangular deltoid deltoid muscle muscle of the of the shoulder is shoulder is multipennatemultipennate

Range of Power and Range of Power and MotionMotion

• A skeletal muscle cell can contract until it has A skeletal muscle cell can contract until it has shortened by roughly 30 percent. shortened by roughly 30 percent.

• Because the fibers in a parallel muscle are Because the fibers in a parallel muscle are parallel to the long axis of the muscle, when parallel to the long axis of the muscle, when the fibers contract together, the entire muscle the fibers contract together, the entire muscle shortens by the same amount. shortens by the same amount.

• If the muscle is 10 cm long, the end of the If the muscle is 10 cm long, the end of the tendon will move 3 cm when the muscle tendon will move 3 cm when the muscle contracts. contracts.

• The tension developed during this contraction The tension developed during this contraction depends on the total number of myofibrils the depends on the total number of myofibrils the muscle contains.muscle contains.