chapter 6 the skeleto-muscular system copyright © 2013 by john wiley & sons, inc. all rights...

Chapter 6

The Skeleto-Muscular System

Copyright © 2013 by John Wiley & Sons, Inc. All rights reserved.

Movement is a Defining Characteristic of Animal Life

• Humans move by applying tension to the bones and joints of the skeletal system– Tension is applied by the muscular

system

• The skeletal and muscular systems work as a cooperative unit– Skeletal muscles connect to bones– As the muscle contracts, it pulls on the

bone, causing the bone to move

© 2013 by John Wiley & Sons, Inc. All rights reserved.

The Skeleto-Muscular System Performs Several Key Functions

• Provides movement and locomotion• Protects organs in the thoracic and abdominopelvic cavities• Helps maintain homeostasis by generating internal heat• Maintains upright posture and bipedalism• Manipulates the environment• In addition, the skeleton

– Produces blood cells (hematopoiesis)– Stores and releases minerals such as calcium and phosphorus

• Calcium is required for skeletal muscle contraction – thus a vast calcium store is readily available for skeletal muscles to tap into as they lie next to bones


Movement

• The skeleton holds the body together while muscles enable movement• Movement is possible because of the unique arrangement of muscle and

bone • All human skeletal muscles have a similar function and structure– They contract, or get shorter, to produce movement– Muscles can relax to their original (resting) length – Or even elongate beyond that point


Bone and Skeletal Muscle

• Both bone and muscle are living tissue– Separately neither is able to produce movement

• Skeletal muscular tissue contracts (gets shorter)– When the skeletal muscle shortens, it pulls on the bone

• Bones are held together by joints, most of which permit movement between the bones– Pulling on one bone causes movement at the accompanying joint


Bone Tissue Comes in Two Forms

• Compact (dense) bone usually occurs at the outer edges of the bone and is composed of many individual osteons– Osteons are concentric rings of bone matrix laid by osteocytes– The bone matrix consists of minerals (calcium and phosphate)– The bone matrix also contains collagen fibers

• These collagen become mineralized – turning solid and firm• This is in contrast to collagen fibers found in other connective tissues,

which remain flexible

• Spongy bone usually forms within the deeper portions of the bone, providing inner support– Spongy bone is porous, less organized than compact bone, and lacks osteons– Spongy bone has trabeculae, or struts, that form in response to stress


Structure of Bone


Osteon Structure

• Concentric rings of bone matrix • The center of each osteon contains a

central canal (Haversian canal)– The central canal of each osteon houses

the blood and nerve supply for the bone

• Bone matrix is formed and maintained by osteocytes

– Osteocytes live in lacunae (small lakes), which are small holes in bone matrix

– Canuliculi (tiny canals) extend between each lacuna, containing nutrient fluids• Material passes to (and between)

osteocytes in lacuna as it flows through the canuliculi


Long Bones

• The ends of mature long bones, or epiphyses, include the epiphyseal plate– An area of cartilage where long bones

continue to grow during childhood and adolescence

– When bones stop growing, this cartilage is replaced by bone, leaving the epiphyseal line

• A layer of hyaline cartilage is present in the area where two bones meet– This articulating cartilage prevents bone

from grinding against bone at a joint


Bone Marrow

• In mature long bones– Epiphyses is made of spongy bone– Contains red marrow, where blood cells

form– The diaphysis forms the middle portion

of the bone and is made of compact bone• The hollow interior is called the

medullary cavity– Contains yellow marrow

• The fat in yellow marrow functions as stored energy


Bone Formation

• Bones are a form of connective tissue produced by immature bone cells called osteoblasts

• Ossification (bone formation) occurs in two ways– Endochondral ossification

(formed within cartilage) is the way most bones form

– Intramembranous ossification forms the flat bones of the skull, clavicle, and mandible


Bones Grow Longer and Thicker

• Growth occurs at the outer surface of the bone • Cells within the periosteum (the membrane that covers the bone)

differentiate into osteoblasts – The osteoblasts add matrix to the exterior of the bone

• The accumulating matrix entraps the osteoblasts– The trapped osteoblasts mature into osteocytes– The osteocytes maintain the structure of the bone


Bones are Dynamic Structures

• Bones stop growing in length at maturity, but continue to change shape throughout life as they are remodeled to suit the needs of the body

• Bone remodeling of existent bone is different from original bone formation (ossification)– Bones are a storehouse for calcium needed in physiological processes such as

nerve impulse transmission and muscle contraction – Calcium within each bone is constantly being removed and new calcium is

added in response to blood calcium levels and the amount of stress placed on the bones• When blood calcium levels drop, osteoclasts release calcium from the

bone matrix, adding it to the blood• When blood calcium levels rise, osteoblasts create new matrix and add

calcium to it, thus removing excess calcium from the blood


Osteoclasts and Osteoblasts

• The interplay between osteoclasts and osteoblasts remodels bones• Osteoclasts adhere to the surface of bones

– Release acids and enzymes used to breakdown bony matrix– Add calcium and other minerals to the bloodstream

• Osteoblasts build the mineral structure of bone back up, pulling calcium and minerals from the bloodstream– First secrete an organic matrix called osteoid – Then increase the local calcium concentration around the osteoid, converting

the osteoid to bone– Whole process takes upwards of three months to complete


Bone Repair is a Drastic Version of Remodeling

• For bone to heal, the ends of the fracture must be aligned and immobilized– Closed reduction – when alignment is possible without disturbing the skin– Open reduction – when the skin must be cut, and often metal screws, plates,

or pins are used to fix the bones in place – as with compound fractures

• Complete immobilization may not be ideal for healing bone– Limited movement, stress, or partial weight-bearing activities can actually help

the bones grow– Stresses on bone matrix stimulates bone formation (bone deposition)


The Human Skeleton is Composed of 206 Bones

• The skeleton is divided into two parts

• Axial skeleton– The central axis of the body

• Appendicular skeleton– The appendages

• Arms• Legs• Hands• Feet

– The girdles • Attach the appendages

to the axial skeleton


The Axial and Appendicular Skeletons

• The axial skeleton is comprised of– Cranial bones, facial bones – Hyoid bone – Ribs, vertebrae

• Ribs and vertebrae give us our upright posture and protect the organs in our thoracic cavity

• The appendicular skeleton includes all the bones that are attached, or appended, to the axial skeleton– The pectoral girdle (shoulder bones)– The upper appendages (arms and hands)– The pelvic girdle– The lower appendages (legs and feet)


The Axial Skeleton - Cranial Bones

• The cranial bones surround and protect the brain– The parietal bones and temporal bones are paired

• Parietal bones protect the upper sides of the head• Temporal bones protect the middle sides of the head and support the ears

– The frontal bone, occipital bone, ethmoid, and sphenoid are single bones• The frontal bone at the forehead protects the frontal lobe of the brain• The entire back of the skull is a single bone (occipital bone)• Two cranial bones comprise the floor of the cranial cavity• The ethmoid forms the floor of the front portion of the cranial cavity• The sphenoid provides the base for the cranium, supporting the brain

• All 8 cranial bones are held together by fixed joints called sutures


The Cranial Bones


The Axial Skeleton - Facial Bones

• There are 15 facial bones– Fourteen facial bones protect the entrances to the respiratory and digestive

systems, and the sensory organs– The 15th facial bone - hyoid bone - lies below the tongue

• Some may not include the hyoid bone as a facial bone– Three facial bones are single, and 12 occur in pairs

• Three single facial bones– The single hyoid bone, which lies below the tongue, is the only bone of the

skeleton that is not directly attached to any other bony structure• It is instead suspended by the throat muscles

– The single vomer bone is the bony separation between nasal passages – The single mandible bone is the only bone of the skull attached by a movable

joint• It articulates with the mandibular fossae of the temporal bone at the

temporomandibular joint (TMJ)


The Axial Skeleton - Facial Bones

• Twelve paired facial bones– The paired maxillae and paired palatine bones make up the front (maxillae)

and roof of the mouth (the palatine bones) – The small, thin, paired nasal bones form the bridge of the nose– The small paired lacrimal bones are located on either side of the nose

• A small passage in these bones allows tears to collect and pass through the skull into the nasal cavity

– The paired zygomatic bones (cheek bones) bulge outward and help protect the eyes

– The paired inferior nasal conchae bones form the swirling surface of the nasal cavity, helping to warm and moisten the air we inhale


The Facial Bones


The Axial Skeleton – Vertebral Column

• The vertebrae bones form the vertebral column– 24 vertebrae in the adult vertebral column– One sacrum

• Consisting of five fused vertebrate that form a sturdy base for the pelvic girdle

– Three to five coccyx bones (tailbone)

• The vertebral column allows upright posture and protects the spinal cord – Together with the ribs, a cage is formed

which protects the organs within the thoracic cavity• Heart, lungs, etc…


The Vertebral Column is Divided into Three Regions

• The cervical region (vertebrae C1–C7)• The thoracic region (T1–T12)• The lumbar region (L1–L5)• Moving down the column

– The bodies of the vertebrae grow larger– Larger bones can support more weight

• Between each vertebra is a pad of fibrocartilage, the intervertebral disc – Serves as a shock absorber– Prevents vertebrae from rubbing against

one another and crushing under body's weight

– Allows limited motion between vertebrae


The Axial Skeleton – The Vertebrae

• A typical vertebra is composed of three parts– The vertebral body– The vertebral arch– The vertebral articular

processes

• The vertebral articular processes– Serve as attachment

points between adjacent vertebra

– Also sites for muscle attachment


The Axial Skeleton – The Ribs and Sternum

• We have seven pairs of true ribs and five pairs of false ribs – True ribs

• Ribs 1 to 7 attach directly to the sternum and the costal (rib) cartilage, which in turn is directly attached to the sternum

– False ribs• Ribs 8, 9, 10 attach to the costal cartilage, which connects to the costal

cartilage of rib 7, which is connected to the sternum• Ribs 11 and 12 are not attached to costal cartilage (floating ribs)

• The sternum, or breastbone, protects the anterior of the chest • The sternum has three parts

– The manubrium - articulates with the appendicular skeleton– The body– The xiphoid process - a small tab of cartilage at the end of the body


The Axial Skeleton - The Thoracic Cage


The Appendicular Skeleton

• The appendicular skeleton includes all the bones that are attached, or appended, to the axial skeleton– The pectoral girdle

(shoulder bones)– The upper appendages

(arms and hands)– The pelvic girdle– The lower appendages

(legs and feet)


The Appendicular Skeleton - The Pectoral Girdle• The pectoral girdle

– Two pectoral girdles, each consisting of a clavicle and scapula– The scapulae connect to the strong back muscles and articulate only with the

clavicles• Gives each shoulder joint greater range of motion

• The upper appendages– The humerus is the longest and strongest bone in the upper appendicular

skeleton– The ulna is on the medial side of the forearm– The radius is on the thumb side of the forearm– The elbow is the joint formed by the distal end of the humerus and the proximal

ends of the radius and ulna• The olecranon forms the point of the elbow

– The wrist bones (carpals) are in two rows of four short bones– The metacarpals make up the structure of the hand– The phalanges (finger bones) are considered long bones

• Each finger has three bones: the proximal, middle, and distal phalanx • The thumb (pollex) has only two phalanges


The Pectoral Girdle and Upper Appendages


The Appendicular Skeleton - The Pelvic Girdle

• The pelvic girdle– Composed of the hip bones and lower vertebrae– Denser, stronger, and less flexible than the appendicular girdle – The pelvis girdle is made of two large coxal bones (hip bones), the sacrum, and

the coccyx• The lower appendages

– The hip bone emerges from three bones that fuse in early puberty • The ilium, ischium, pubic bone• The femur articulates at the junction of these three bones• The acetabulum is the curved recess that serves as a socket for the head

of the femur • The patella (kneecap)

• Male and female hip bones are visibly different– The modification of the female hip bones enlarge part of the birth canal in the

pelvis to ease in childbirth


The Pelvic Girdle and Right Lower Limb


Joints Link the Skeletal System Together

• Joints exist wherever two bones meet– Classified by function or structure

• Functionally, joints are– Immovable or synarthrotic– Slightly movable or amphiarthrotic– Freely movable or diarthrotic (synovial)

• Structurally, joints are classified into four types– Bony fusion– Fibrous– Cartilaginous– Synovial


Joints


Muscular Tissue is Contractile Tissue

• There are three types of muscular tissue– Skeletal muscle, cardiac muscle, smooth muscle

• Skeletal muscle is part of the skeleto-muscular system– Functions to move bones– In general, each skeletal muscle has a

• Belly – the middle portion of the muscle• Origin - an end that remains stationary when the organ shortens• Insertion - an end that moves during contraction• Knowing the origin and insertion of any skeletal muscle offers clues about

its function– Skeletal muscle is composed of numerous elongated muscle cells

• Spanning from origin to insertion, one nested inside another• Muscle cells also are called muscle fibers• Muscle cells must shorten, creating tension

– Connective tissue structurally supports skeletal muscle


Skeletal Muscular Tissue

• Most skeletal muscles work in pairs

• Synergistic pairs – Work together to cause

movement in the same direction

– i.e., muscles of the quadriceps or muscles of the hamstrings

• Antagonistic pairs – Cause movement in

opposite directions, opposite to one another

– i.e., biceps and triceps


The Skeleto-Muscular System


Structure of Skeletal Muscle


Skeletal Muscle Contracts as Thick and Thin Filaments Slide Past One Another

• The sliding filament model explains our best understanding of how muscle cells shorten– In this process, calcium initiates contraction, and proteins slide past one

another – With millions of sarcomeres lined up in each muscle cell, these tiny chemical

reactions shorten the entire muscle– Thick and thin filaments do not change length during contraction/relaxation

• Contraction occurs as…– Thin filaments slide over the thick filament, sarcomeres shorten

• Relaxation occurs as…– Thin filaments slide back to their original positions, sarcomeres elongate as

they return to their pre-contraction length


The Muscle Contraction Cycle


Contraction Begins at the Neuromuscular Junction

• A nerve cell ends very close to a group of muscle cells– The nerve and muscle cells are separated by a small fluid-filled space– This is the neuromuscular junction

• The nerve cell sends a contraction impulse across the neuromuscular junction via chemical messengers, called neurotransmitters– The neurotransmitter at the neuromuscular junction is acetylcholine (ACh)

• A contraction in the muscle cell is initiated when the ACh reaches and interacts with the muscle cell’s plasma membrane (the sarcolemma)


The Initiation of a Contraction at the Neuromuscular Junction


Muscle Contraction


There are Three Types of Muscle Cells

• Fast Twitch (or fast glycolytic)– Anaerobic, fatigue quickly– Provide a short burst of extreme energy and contraction power – Thicker, contain fewer mitochondria, usually contain larger glycogen – Responsible for hypertrophy

• Because short bursts of power come from these fibers, exercises that continuously require bursts of power will enlarge them

• Weight training puts demands on fast twitch fibers, resulting in the hypertrophy (muscle enlargement) we associate with body-building


• Intermediate (or fast oxidative-glycolytic)

• Slow Twitch (or slow oxidative)– Appear red, have a large blood supply, have many mitochondria within their

sarcolemma, and store an oxygen-carrying protein called myoglobin – Are sometimes called nonfatiguing or aerobic cells

• Distance running and other aerobic sports stimulate these cells • Efficiency and strength come not from increasing mass but from using

oxygen more efficiently– Although training can alter the functioning of both red (slow twitch) and white

(fast twitch) fibers, it does not change their proportions • The percentage of fast and slow twitch fibers is genetically determined

There are Three Types of Muscle Cells


chapter 6 the skeleto-muscular system copyright © 2013 by john wiley & sons, inc. all rights...

Documents

john wiley sons

bone tissue

structure of bone

osteonsspongy bone

compact bone

flexiblespongy bone

skeletal muscleboth

phosphatethe bone matrix