46 Skeletal Muscular System



46 Skeletal Muscular System

1. List and describe the four types of tissues that make up the human body.

A. Body Tissues

1. A tissue is a collection of cells that are similar in structure and that work together to perform a particular function

2. The human body has four main types of tissues: muscle, nervous, epithelial, and connective

a. Muscle Tissue

1) Muscle tissue is composed of cells that can contract

2) The human body has three types of muscle tissue: skeletal, smooth, and cardiac

a) Skeletal muscle moves the bones in your trunk, limbs, and face

b) Smooth muscle handles body functions that you cannot control consciously, such as the movement of food through your digestive system

c) Cardiac muscle, found in your heart, pumps blood through your body

b. Nervous Tissue

1) Nervous tissue contains cells that receive and transmit messages in the form of electrical impulses

2) These cells, called neurons, are specialized to send and receive messages from muscles, glands, and other neurons throughout the body

3) Nervous tissue makes up your brain, spinal cord, and nerves

4) Nervous tissue provides sensation of the internal and external environment, and it integrates sensory information

5) Coordination of voluntary and involuntary activities and regulation of some body processes are also accomplished by nervous tissue

c. Epithelial Tissue

1) Epithelial tissue consists of layers of cells that line or cover all internal and external body surfaces

2) Each epithelial layer is formed from cells that are tightly bound together, providing a protective barrier for these surfaces

3) Epithelial tissue is found in various thicknesses and arrangements, depending on where it is located

a) The most easily observed epithelial tissue, the body’s outer layer of skin, consists of sheets of dead, flattened cells that cover and protect the underlying living layer of skin

d. Connective Tissue

1) Connective tissue binds, supports, and protects structures in the body

2) Connective tissues are the most abundant and diverse of the four types of tissue, and include bone, cartilage, tendons, fat, blood, and lymph

3) Characterized by cells that are immersed in matrix

2. Explain how tissues, organs, and organ systems are organized.

A. Tissues, Organs and Organ Systems

1. A tissue is a collection of cells that are similar in structure and that work together to perform a particular function

a. Examples: Muscles, nervous, epithelial, and connective

2. An organ consists of various tissues that work together to carry out a specific function

a. A single organ, such as the stomach, usually does not function in isolation

b. Examples: The stomach, heart, lungs, brain

3. Each organ system has organs associated with it according to the organ’s primary function, although the boundaries are not always well defined

a. For example, in the digestive system, the mouth, esophagus, stomach, small intestine, large intestine, liver, and pancreas all work together to break down food into molecules the body can use for energy

b. Each organ system carries out its own specific function, but for the organism to survive, the organ systems must work together

c. Organs and organ systems are housed in the body’s various body cavities.

1) Cranial

2) Spinal

3) Thoracic

4) Abdominal

3. Explain the function and structure of bones.

A. The adult human body consists of approximately 206 bones, which are organized into an internal framework called the skeleton. Because the human skeleton is an internal structure, biologists refer to it as an endoskeleton.

The Skeleton

1. The human skeleton is composed of two parts—the axial skeleton and the appendicular skeleton

a. The bones of the skull, ribs, spine, and sternum form the axial skeleton

b. The bones of the arms and legs, along with the scapula, clavicle, and pelvis, make up the appendicular skeleton

2. The bones that make up the skeleton function in a variety of ways

a. Bones provide a rigid framework against which muscles can pull, give shape and structure to the body, and support and protect delicate internal organs

b. Bones also store minerals, such as calcium and phosphorus, which play vital roles in important metabolic processes

c. In addition, the internal portion of many bones produces red blood cells and certain types of white blood cells

B. Bone Structure

1. Despite their number and size, bones make up less than 20 percent of the body’s mass

a. Bones are not dry, rigid structures, as they may appear in a museum exhibit

1) They are moist, living tissues

2) A long bone consists of a porous central canal surrounded by a ring of dense material

b. The bone’s surface is covered by a tough membrane called the periosteum

1) This membrane contains a network of blood vessels, which supply nutrients, and nerves, which signal pain

c. Under the periosteum is a hard material called compact bone

1) A thick layer of compact bone enables the shaft of the long bone to endure the large amount of stress it receives upon impact with a solid object

2) Compact bone is composed of cylinders of mineral crystals and protein fibers called lamellae

a) In the center of each cylinder is a narrow channel called a Haversian canal

b) Blood vessels run through interconnected Haversian canals, creating a network that carries nourishment to the living bone tissue

c) Several layers of protein fibers wrap around each Haversian canal

d) Embedded within the gaps between the protein layers are living bone cells called osteocytes

d. Inside the compact bone is a network of connective tissue called spongy bone

1) Although its name suggests that it is soft, this tissue is hard and strong

2) Spongy bone has a latticework structure that consists of bony spikes

3) It is arranged along points of pressure or stress, making bones both light and strong

e. Many bones also contain a soft tissue called bone marrow, which can be either red or yellow

1) Red bone marrow—found in spongy bone, the ends of long bones, ribs, vertebrae, the sternum, and the pelvis—produces red blood cells and certain types of white blood cells

2) Yellow bone marrow fills the shafts of long bones

a) It consists mostly of fat cells and serves as an energy reserve

b) It can also be converted to red bone marrow and produce blood cells when severe blood loss occurs

D. Bone Development

a. Most bone forms from cartilage. During fetal development,

osteocytes begin to develop and deposit minerals in the cartilage

1) The process of turning cartilage into bone is called

ossification

b. Growth in the bones takes place at the epiphyseal plate

2) Growth continues until all of the cartilage in the epiphyseal

plate is replaced by minerals

4. List three types of joints, and give an example of each.

Joints

1. The place where two bones meet is known as a joint

2. Tough tissue called ligament hold joints in place

3. Joints that are subject to a great deal of pressure are surrounded by synovial fluid

a. Painful or swollen joints are said to be arthritic

1) Rheumatoid arthritis – the immune system attacks the joints

2) Osteoarthritis – a degenerative disease in which the cartilage that surrounds the joints start to become thinner and rougher

4. Three kinds of joints are found in the human body—fixed, semimovable, and movable

5. Joint Function

a. Fixed joints prevent movement

1) They are found in the skull, where they securely connect the bony plates and permit no movement of those bones

2) A small amount of connective tissue in a fixed joint helps absorb impact to prevent the bones from breaking

b. Semimovable joints permit limited movement

1) For example, semimovable joints hold the bones of the vertebral column in place and allow the body to bend and twist

2) The vertebrae of the spine are separated by disks of cartilaginous tissue

3) These tough, springy disks compress and absorb shocks that could damage the fragile spinal cord

4) Semimovable joints are also found in the rib cage, where long strands of cartilage connect the upper seven pairs of ribs to the sternum, allowing the chest to expand during breathing

c. Most of the joints in the body are movable joints

1) These joints enable the body to perform a wide range of movements and activities

2) Movable joints include hinge, ball-and-socket, pivot, saddle, and gliding joints

a) An example of a hinge joint is found in the elbow, which allows you to move your forearm forward and backward, like a hinged door

b) An example of a ball-and-socket joint is the shoulder joint, which enables you to move your arm up, down, forward, and backward, as well as to rotate it in a complete circle

c) The joint formed by the top two vertebrae of your spine is an example of a pivot joint; it allows you to turn your head from side to side, as when shaking your head “no”

d) The saddle joint, found at the base of each thumb, allows you to rotate your thumbs and helps you grasp objects with your hand

e) Finally, gliding joints allow bones to slide over one another

1) Examples are the joints between the small bones of your foot, which allow your foot to flex when you walk

5. Distinguish between the three types of muscle tissues.

A. Muscle Types

1. A muscle is tissue that can contract in a coordinated fashion and includes muscle tissue, blood vessels, nerves, and connective tissue

2. Recall that the human body has three types of muscle tissues: skeletal, smooth, and cardiac

a. Skeletal muscle is responsible for moving parts of the body, such as the limbs, trunk, and face

1) Skeletal muscle tissue is made up of elongated cells called muscle fibers

2) Each muscle fiber contains many nuclei and is crossed by light and dark stripes, called striations

3) Skeletal muscle fibers are grouped into dense bundles called fascicles

4) A group of fascicles are bound together by connective tissue to form a muscle

5) Because their contractions can usually be consciously controlled, skeletal muscles are described as voluntary muscles

b. Smooth muscle forms the muscle layers found in the walls of the stomach, intestines, blood vessels, and other internal organs

1) Individual smooth muscle cells are spindle-shaped, have a single nucleus, and interlace to form sheets of smooth muscle tissue

2) Notice that smooth muscle lacks the striations found in skeletal muscle tissue

3) Smooth muscle fibers are surrounded by connective tissue, but the connective tissue does not unite to form tendons as it does in skeletal muscles

4) Because most of its movements cannot be consciously controlled, smooth muscle is referred to as involuntary muscle

c. Cardiac muscle makes up the walls of the heart

1) Cardiac muscle shares some characteristics with both skeletal muscle and smooth muscle

2) As with skeletal muscle, cardiac muscle tissue is striated; as with smooth muscle, it is involuntary and each cell has one nucleus

3) A bundle of specialized muscle cells in the upper part of the heart sends electrical signals through cardiac muscle tissue, causing the heart to rhythmically contract and pump blood throughout the body

6. Describe the structure of skeletal muscle fibers.

Muscle Structure

1. A muscle fiber is a single, multinucleated muscle cell

2. A muscle may be made up of hundreds or even thousands of muscle fibers, depending on the muscle’s size

3. Connective tissue covers and supports each muscle fiber and reinforces the muscle as a whole

4. A muscle fiber consists of bundles of threadlike structures called myofibrils

a. Each myofibril is made up of two types of protein filaments—thick ones and thin ones

1) Thick filaments are made of the protein myosin, and thin filaments are made of the protein actin

2) Myosin and actin filaments are arranged to form an overlapping pattern, which gives muscle tissue its striated appearance

3) Thin actin filaments are anchored at their endpoints to a structure called the Z line

4) The region from one Z line to the next is called a sarcomere

7. Explain how skeletal muscles contract.

Muscular Contraction

1. The sarcomere is the functional unit of muscle contraction

a. When a muscle contracts, myosin filaments and actin filaments interact to shorten the length of a sarcomere

1) Myosin filaments have extensions shaped like oval “heads”

2) Actin filaments look like a twisted strand of beads

b. When a nerve impulse stimulates a muscle fiber to contract, the heads at the end of the myosin filaments attach to points between the beads of the actin filaments

c. The myosin heads then bend inward, pulling the actin filaments with them

d. The myosin heads then let go, bend back into their original position, attach to a new point on the actin filament, and pull again

e. This action shortens the length of the sarcomere

f. The synchronized shortening of sarcomeres along the full length of a muscle fiber causes the whole fiber, and hence the muscle, to contract

2. Like all cellular activities, muscle contraction requires energy, which is supplied by ATP

a. This energy is used to detach the myosin heads from the actin filaments

b. Without ATP, the myosin heads would remain attached to the actin filaments, keeping a muscle permanently contracted

1) Rigor mortis occurs during death because there is not ATP to

allow the detachment to happen

3. Muscle contraction is an all-or-none response—either the fibers contract or they remain relaxed

8. Explain how muscles move bones.

A. Muscular Movement of Bones

1. Generally, skeletal muscles are attached to one end of a bone, stretch across a joint, and are fastened to the end of another bone

2. Muscles are attached to the outer membrane of bone, either directly or by a tough fibrous cord of connective tissue called a tendon

a. For example one end of the large biceps muscle in the arm is connected by tendons to the radius and ulna in the forearm, while the other end of the muscle is connected to the scapula in the shoulder

b. When the biceps muscle contracts, the forearm flexes upward while the scapula remains stationary

1) The point where the muscle attaches to the stationary bone—in this case, the scapula—is called the origin

2) The point where the muscle attaches to the moving bone—in this case the bones in the forearm—is called the insertion

3. Most skeletal muscles are arranged in opposing pairs

a. One muscle in a pair moves a limb in one direction; the other muscle moves it in the opposite direction

b. Muscles move bones by pulling them, not by pushing them

1) For example, when the biceps muscle contracts, the elbow bends

a) The biceps muscle is known as a flexor, a muscle that bends a joint

2) Contraction of the triceps muscle in the upper arm straightens the limb

a) The triceps muscle is an example of an extensor, a muscle that straightens a joint

3) To bring about a smooth movement, one muscle in a pair must relax while the opposing muscle contracts

9. Describe the integumentary system

A. Skin is the body’s largest organ

B. It consists of 2 layers, the dermis and the epidermis

1. Dermis – the inner layer, which is composed of living cells, and specialized structures such as sensory neurons, blood vessels, hair follicles, and glands

2. Epidermis – the outer layer which is composed of dead cells

3. They are filled with keratin, which gives skin its waterproof ability. It also contains melanin, which is a pigment that absorbs harmful UV radiation

4. The skin also contains glands. The main types are the exocrine glands such as the sweat glands and oil glands

a. Sweat glands regulate temperature

b. Oil glands secrete sebum, which prevents excess water loss and lubricates and softens the skin and hair

1) If oil glands become clogged, acne often occurs

C. Hair and nails are also part of the integumentary system

Chapter 46 Skeletal, Muscular, and Integumentary Systems

□ A tissue is a collection of cells that work together to perform a particular function.

□ The human body has four main types of tissue: muscle, nervous, epithelial, and connective.

□ An organ consists of various tissues that work together to carry out a specific function.

□ An organ system is a group of organs interacting to perform a life process.

□ Many organs and organ systems in the human body are housed in body cavities.

□ The human skeleton is composed of the axial skeleton (skull, ribs, spine, and sternum) and the appendicular skeleton (arms and legs, scapula, clavicle, and pelvis).

□ Bones support muscles and organs, give structure to the body, protect internal organs, store minerals, and manufacture blood cells.

□ Bones are made up of minerals, protein fibers, and cells called osteocytes. Most consist of compact and spongy bone and may contain bone marrow.

□ Most bones develop from cartilage through a process called ossification.

□ Bone elongation occurs near the ends of long bones, at the epiphyseal plate.

□ The human body has three types of joints—fixed, semimovable, and movable.

□ The human body has three types of muscle tissues—skeletal muscle, smooth muscle, and cardiac muscle.

□ Skeletal muscles consist of groups of muscle fibers that contain threadlike myofibrils. Each myofibril is made up of two types of protein filaments, thin actin filaments and thick myosin filaments.

□ A sarcomere is the fundamental unit of a muscle contraction. During a muscle contraction, myosin and actin filaments interact to shorten the length of a sarcomere.

□ Most skeletal muscles are arranged in opposing pairs.

□ Skin, hair, and nails act as barriers that protect the body from the environment.

□ Skin is composed of two layers: the epidermis (composed of dead, keratin-filled cells) and the dermis (composed of living cells and a variety of structures).

□ Hair and nails are composed of the protein keratin; they grow from a bed of rapidly dividing cells.

□ Sweat glands produce sweat, which evaporates and helps cool the body. Oil glands secrete sebum, which helps soften the skin and prevents hair from drying out.

Vocabulary List

Abdominal cavity

Actin

Appendicular skeleton

Axial skeleton

Ball-and-socket joint

Bone marrow

Cardiac muscle

Compact bone

Connective tissue

Cranial cavity

Dermis

Diaphragm

Epidermis

Epiphyseal plate

Epithelial tissue

Exocrine gland

Extensor

Fascicles

Fixed joint

Flexor

Gliding joint

Haversian canal

Hinge joint

Insertion

Involuntary muscle

Joint

Keratin

Ligament

Matrix

Movable joint

Muscle fiber

Muscle tissue

Myofibril

Myosin

Nervous tissue

Neuron

Origin

Ossification

Osteocyte

Periosteum

Pivot joint

Saddle joint

Sarcomere

Semimovable joint

Skeletal muscle

Skeleton

Smooth muscle

Spinal cavity

Spongy bone

Striation

Sweat gland

Tendon

Thoracic cavity

Voluntary muscle

Z line

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