The Musculoskeletal System

Chapter 47

2

Types of Skeletal Systems

Changes in movement occur because muscles pull against a support structure, called the skeletal system

-Zoologists recognize three types:

-Hydrostatic skeletons

-Exoskeletons

-Endoskeletons

3

Chitinous outer covering

Exoskeleton

Sagittal section

Vertebral column

Pelvis

FemurTibiaFibula

UlnaRadius

Humerus

Skull

Scapula

Ribs

Exoskeleton

Endoskeleton

a.

b.

axial skeletonappendicularskeleton

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Changes in

movement

occur because

muscles pull

against a skeletal

system...

3 types

Hydrostatic skeletons

Found primarily in soft-bodied invertebrates

4

Hydrostatic Skeletons

Chaetae get lifted in regions of circular muscle contraction.

During longitudinal muscles contraction, chaetae

anchor into the ground

5

Hydrostatic SkeletonsLocomotion in aquatic

invertebrates occurs by

fluid ejections or jetting

-Jellyfish produce regular

pulsations in bell

-Squeezing some of water

contained beneath it

-Squids fill mantle cavity

with sea water

-Muscular contractions

expel water forcefully through

the siphon, and the animal

shoots backward

6

-Unlike chitin, bone and cartilage are living tissues...they change and remodel in response to injury or physical stress

-Echinoderms have calcite skeletons, that have calcium carbonate

-Bone, on the other hand, has calcium phosphate. Vertebrate endoskeletons have bone and/or cartilage

Endoskeletons

Endoskeletons vs. Exoskeletons

7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Undifferentiated Mesenchymal Cells

ChondroblastFibroblast Osteoblasts

ChondrocyteCollagen(fibrous tissue)

Osteocyte

Osteoclast

Secrete Alkaline phosphatasecauses Calcium Phosphate to formHydroxyapatiteIn the EXTRACELLULARMATRIX

Cells in Bone Tissue

Make cartilage = Chondroitin and collagen

8

Endoskeleton Bone

Bone is unique to vertebrates

Bones can be classified by the two fundamental modes of development-Intramembranous development (simple)

-E.g.: External bones of skull-Endochondral development (complex)

-E.g.: Bones that are deep in the body

9

Intramembranous Bone DevelopmentOsteoblasts from dermis in skin initiate bone development (onto collagen fiber scaffold).

Some cells become trapped in the bone matrix that they have produced... ...change into osteocytes, which reside in

tight spaces called lacunae The cells communicate through

little canals termed canaliculi.

Osteoclasts break down the bone matrix.

10

*First there is cartilage in the general shape of the bone

*A fibrous sheath with osteoblasts surrounds cartilage

*Osteoblasts use cartilage to make Calcium Phosphate (Extracellular Matrix)

*Blood vessels from fibrous sheath (now periosteum) go deeper into the original cartilage

*Osteoblasts and Osteoclasts follow blood supply to further change cartilage into bone tissue

Endochondrial Bone Development

11

Endochondral Development

Superficial cartilage that remains after the development of epiphyses serves as a pad between bone surfaces

Osteoclasts create medullary cavity

Growth plates made of cartilage grow towards distal ends until approaching bone coming from the shaft changes it all to bone

12

Vascular Bone StructureMost mammals retain internal blood vessels and are called vascular bones

These typically have osteocytes and are also called cellular Bones & have a Haversian system

Not seen fish and birds

13

Bone StructureBased on density and structure, bone falls into three categories

-Compact bone = Outer dense layer-Medullary bone = Lines the internal cavity...contains bone

marrow in some species (site of red blood cell production)

-Spongy bone = Honeycomb structure forms the epiphyses inside a thick shell of compact bone

14

Joints are the locations where one bone meets another

3 general kinds

15

Skeletal Muscle Structure

Each skeletal musclecontains numerous muscle fibers (CELLS)

Each muscle fiber encloses a bundle of structures called myofibrils

Each myofibril in turn is composed of thick and thin myofilaments

Bone periosteum& skeletal Muscle Are united by a tendon

16

Thick filament is composed of myosin protein, two polypeptide chains w/ aglobular head wrapped around each other

Thin filament Is two chains of actin protein,twisted together in a helix

17

Sarcomere

H band

A band I band

a.

b.

Z line

Thin filaments (actin) Thick filament (myosin)Cross-bridges

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Why do Myofibrils contract and shorten???Because thick and thin filaments slide over each other

Sarcomere = distance between 2 Zlines...Smallest subunit of muscle contraction

18

Cross-bridge

cycle

19

Relaxed Versus Contracted Muscle

Troponin + Tropomyosin = NO Muscle ContractionBecause Tropomyosin binds to Actin

Ca2+ + Troponin + Tropomyosin = Muscle Contraction Because Ca2+ + Troponin displace Tropomyosin...Actin-myosin cross-bridges form

20

Myofibril

Na+

SarcolemmaNeuromuscularjunction

Motor neuron Nerveimpulse

Neurotransmitter

Sarcoplasmicreticulum

Transversetubule(T tubule)

Release of Ca2+Ca2+

Muscle depolarization

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Skeletal Muscle Contractionacetylcholine

-The membrane becomes depolarized-Depolarization is conducted down the transverse tubules (T tubules)

21

A motor unit consists of a motor neuron and all of the muscle fibers it innervates

Recruitment is the cumulative increase in motor unit number and size leading to a stronger contraction

22

Types of Muscle Fibers

A muscle stimulated with a single electric shock quickly contracts and relaxes in a response called a twitch

Summation is a cumulative response when a second twitch “piggy-backs” on the first

Tetanus occurs when there is no relaxation between twitches-A sustained contraction is produced

23

Am

plit

ud

e o

f M

us

cle

Co

ntr

acti

on

s

Completetetanus

Twitches

Incompletetetanus

Time

Summation

Stimuli' ' ' ' ' '

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

24

Types of Muscle FibersSkeletal muscle fibers can be divided based

on their contraction speed

-Slow-twitch, or Type I, fibers-Rich in capillaries, mitochondria and myoglobin pigment (red fibers)-Sustain action for long periods of time

-Fast-twitch, or Type II, fibers-Poor in capillaries, mitochondria and myoglobin (white fibers)-Adapted for rapid power generation

25

Co

ntr

act

ion

Str

eng

th

Time (msec)

eye muscle (lateral rectus)

calf muscle (gastrocnemius)

deep muscle of leg (soleus)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Types of Muscle Fibers

Skeletal muscles have different proportions of fast-twitch and slow-twitch fibers

26

Types of Muscle Fibers

Skeletal muscles at rest get energy from aerobic respiration of fatty acids

During muscle use, energy comes from glycogen and glucose

Muscle fatigue is related with the production of lactic acid via anaerobic fermentation during glycolysis!!!