Chapter 29 The Skeletal and Muscular
Systems
Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Artificial limb: ©Jeff J Mitchell/Getty Images
Muscles Interact with the Skeleton
Section 29.1
Most animal movements require interaction between the muscular and skeletal systems.
Section 29.1
The muscular system provides motion. Muscle cells contract when stimulated by the nervous system.
Muscle
Muscles Interact with the Skeleton
Section 29.1
The skeleton adds a firm supporting structure that muscles pull against.
Muscle
Muscle attachment to bone
Skeleton
Muscles Interact with the Skeleton
Section 29.1
Scientists classify skeletons into three categories:• Hydrostatic skeleton• Exoskeleton• Endoskeleton
Skeletons Take Many Forms
Figure 29.1Jellyfish: © Gabriel Bouys/AFP/Getty Images; crab: © Photodisc/Getty Images RF; fish X-ray: © Jim Wehtje/Getty Images RF
Hydrostatic skeleton
Exoskeleton
Endoskeleton
Section 29.1
A hydrostatic skeleton is fluid constrained within a layer of flexible tissue. Many invertebrates have hydrostatic skeletons.
Figure 29.1
Skeletons Take Many Forms
Jellyfish: © Gabriel Bouys/AFP/Getty Images
Section 29.1
An exoskeletonprotects an animal from the outside. Animals with exoskeletons must periodically molt.
Figure 29.2
Skeletons Take Many Forms
Crab: © Photodisc/Getty Images RF
Section 29.1
An endoskeleton is an internal support structure. An endoskeleton grows with the animal and weighs less than an exoskeleton, but external soft tissues are not protected.
Figure 29.3
Skeletons Take Many Forms
Clicker Question #1
The graph below depicts the growth of an animal over time. What sort of skeleton does the animal probably have?
A. endoskeletonB. exoskeletonC. hydrostatic skeleton
Flower: © Doug Sherman/Geofile/RF
Time
Bo
dy
size
(m
m)
Clicker Question #1
The graph below depicts the growth of an animal over time. What sort of skeleton does the animal probably have?
A. endoskeletonB. exoskeletonC. hydrostatic skeleton
Flower: © Doug Sherman/Geofile/RF
Time
Bo
dy
size
(m
m)
29.1 Mastering Concepts
Describe similarities and differences among the three main types of skeletons.
Artificial limb: ©Jeff J Mitchell/Getty Images
Section 29.2
Bones are the organs of the vertebrate skeleton. They are grouped into two categories: •Axial skeleton (tan)•Appendicular skeleton (blue)
The Vertebrate Skeleton: An Overview
Figure 29.4
Section 29.2
The axial skeleton is located along the central axis of the body. It consists of:
• Bones in the head• Bones of the rib cage• The vertebral column
The Vertebrate Skeleton: An Overview
Figure 29.4
Section 29.2
The axial skeleton shields soft body parts. • The skull protects the brain
and the sense organs.• The ribs protect the heart and
lungs. • The vertebral column protects
the spinal cord.
The Vertebrate Skeleton: An Overview
Figure 29.4
Section 29.2
The appendicular skeleton consists of the appendages and the bones that support them.• The pectoral girdle connects
the forelimbs to the axial skeleton.
• The pelvic girdle attaches the hind limbs to the axial skeleton.
The Vertebrate Skeleton: An Overview
Figure 29.4
Section 29.2
The vertebrate skeleton consists of many bones.
The Vertebrate Skeleton: An Overview
Figure 29.4
29.2 Mastering Concepts
Describe the two subdivisions of the human skeleton.
Artificial limb: ©Jeff J Mitchell/Getty Images
The Skull and Associated Bones
Sutures
• Sutures – Immovable joints that join skull bones together
• Form boundaries between skull bones
• Four sutures:
– Coronal – between parietal and frontal
– Sagittal– between parietal bones
– Lambdoid – between the parietal and occipital
– Squamous – between the parietal and temporal
Fontanels – usually ossify by 2 years of age
Frontal
(Coronal)
Sagittal
Squamous
Lambdoid
Sutures
•skull = 22 bones
•cranium = 8 bones: frontal, occipital, 2 temporals, 2 parietals, sphenoid and
ethmoid
•facial bones = 14 bones: nasals, maxillae, zygomatics, mandible, lacrimals,
palatines, inferior nasal conchae, vomer.
•skull forms a larger cranial cavity
-also forms the nasal cavity, the orbits, paranasal sinuses
mandible and auditory ossicles are the only movable skull bones
•cranial bones also: attach to membranes called meninges
-stabilize positions of the brain, blood vessels
-outer surface provides large areas for muscle attachment that
move the head or provide facial expressions
The Adult Skull
Bones of the Cranium
Frontal View
Frontal
Frontal View
Parietal
Frontal View
Temporal
Frontal View
Nasal
Frontal View
Vomer
Frontal View
Zygoma
Frontal View
Maxilla
Frontal View
Mandible
Frontal View
FrontalParietal
Temporal
Zygoma
Nasal
Vomer
Maxilla
Mandible
Frontal View
Lateral View
Frontal
Lateral View
Parietal
Lateral View
Temporal
Lateral View
Nasal
Lateral View
Zygoma
Lateral View
Maxilla
Lateral View
Mandible
Lateral View
Occipital
Lateral View
Mastoid Process
Lateral View
External Auditory Meatus
Lateral View
Frontal
Nasal
ZygomaMaxilla
Mandible
Parietal
Sphenoid
Temporal
Occipital
External Auditory Meatus
Mastoid Process
Lateral View
Figure 6.4 Sectional Anatomy of the Skull, Part I
14 Facial Bones
Nasal (2) Maxillae (2) Zygomatic (2)
Mandible (1) Lacrimal (2) Palatine (2)
Inferior nasal conchae (2) Vomer (1)
Section 29.3
Bones consist mostly of specialized cells suspended in a hard extracellular matrix.
Bone Structure and Function
Section 29.3
Bones are lightweight and strong because they are porous, not solid.
Bone Structure and Function
Section 29.3
Bone Structure and Function
Figure 29.6
The shaft of a long bone contains a marrow cavity, which houses red or yellow bone marrow.
Cartilage: © Chuck Brown/Science Source; bone:© Ed Reschke
Section 29.3
Bone Structure and Function
Figure 29.6
Red bone marrowis a nursery for blood cells and platelets.
Cartilage: © Chuck Brown/Science Source; bone:© Ed Reschke
Section 29.3
Bone Structure and Function
Figure 29.6
Yellow bone marrow replaces red marrow in adult limb bones. It does not produce blood, but can revert to red marrow if necessary.
Cartilage: © Chuck Brown/Science Source; bone:© Ed Reschke
Section 29.3
Bone Structure and Function
Figure 29.6
Bones also contain nerves and blood vessels.
Cartilage: © Chuck Brown/Science Source; bone:© Ed Reschke
Section 29.3
Bone Structure and Function
Figure 29.6
Bone cells are called osteocytes.They secrete a hard extracellular matrix that consists of collagen and minerals.
Cartilage: © Chuck Brown/Science Source; bone:© Ed Reschke
Section 29.3
Bone Structure and Function
Figure 29.6
Collagen adds flexibility, and the minerals add hardness and rigidity.
Cartilage: © Chuck Brown/Science Source; bone:© Ed Reschke
Section 29.3
Bone Structure and Function
Figure 29.6
Compact bone is hard and dense. Spongy bone is light and porous.
Cartilage: © Chuck Brown/Science Source; bone:© Ed Reschke
Section 29.3
Bone Structure and Function
Figure 29.6
The vertebrate skeleton also has cartilage, which serves as a shock absorber.
Cartilage: © Chuck Brown/Science Source; bone:© Ed Reschke
Section 29.3
Bone Structure and Function
Figure 29.7
Bone tissue replaces cartilage as an individual develops. In children, bone growth occurs at growth plates made of cartilage.
Section 29.3
Bone Structure and Function
Table 29.1
The vertebrate skeleton has several important functions.
Section 29.3
Bone Structure and Function
Table 29.1
Especially notable is the skeleton’s role in calcium homeostasis.
Section 29.3
Bone Structure and Function
Figure 29.9
Bones are a reservoir for calcium, which has many essential functions in the body. Thyroid and parathyroid hormones regulate calcium homeostasis.
If bones consistently lose more calcium than they add, then osteoporosisdevelops, in which bones become less dense.
Section 29.3
Bone Structure and Function
Figure 29.10Healthy bone: © Prof. P.M. Motta/Science Source; osteoporosis:© Dee Breger/Science Source
Section 29.3
Bone Structure and Function
Figure 29.10
Sometimes, disuse causes bones to become less dense.
Healthy bone: © Prof. P.M. Motta/Science Source; osteoporosis:© Dee Breger/Science Source
Section 29.3
Bone Meets Bone at a Joint
Figure 29.11
A joint is an area where two bones meet.
Section 29.3
Bone Meets Bone at a Joint
Movable joints have fluid-filled capsules of connective tissue, allowing bones to move against each other with little friction.
Figure 29.11
Section 29.3
Bone Meets Bone at a Joint
Bands of connective tissue help stabilize movable joints. Ligaments connect bone to bone. Tendons connect bone to muscle.
Figure 29.11
Clicker Question #2
A painful condition called “tennis elbow” is caused by inflammation of the tissue that connects a muscle to an arm bone. Tennis elbow therefore reflects a problem with a
A. joint.B. ligament.C. tendon.D. muscle fiber.E. bone.
Flower: © Doug Sherman/Geofile/RF
Clicker Question #2
A painful condition called “tennis elbow” is caused by inflammation of the tissue that connects a muscle to an arm bone. Tennis elbow therefore reflects a problem with a
A. joint.B. ligament.C. tendon.D. muscle fiber.E. bone.
Flower: © Doug Sherman/Geofile/RF
29.3 Mastering Concepts
What are the main parts of a long bone?
Artificial limb: ©Jeff J Mitchell/Getty Images
Section 29.4
Muscle Contraction Requires ATP
As we’ve seen, movement relies on interaction between bones and muscles.
Section 29.4
Muscle Contraction Requires ATP
Muscles have many other functions too.
Table 29.2
Section 29.4
Muscle Contraction Requires ATP
The human body has more than 600 skeletal muscles, which generate voluntary movements.
Figure 29.12
Section 29.4
Muscle Contraction Requires ATP
Pairs of muscles work together to generate body movements.
Figure 29.12
Section 29.4
Muscle Contraction Requires ATP
Muscles have a hierarchical organization.
Figure 29.14
Section 29.4
Muscle Contraction Requires ATP
Muscles consist mainly of bundles of muscle fibers.
Figure 29.10
Section 29.4
Muscle Contraction Requires ATP
Each muscle fiber is a single cell.
Figure 29.10
Section 29.4
Muscle Contraction Requires ATP
Each muscle cell is packed with myofibrils.
Figure 29.10
Section 29.4
Muscle Contraction Requires ATP
Figure 29.10
Myofibrils are divided into functional units called sarcomeres.
Section 29.4
Muscle Contraction Requires ATP
Figure 29.10
Each sarcomere contains thick and thin protein filaments.
Clicker Question #3
If you arrange the following items in order from largest to smallest, which item is THIRD on the list?
myofibril, muscle fiber, sarcomere, muscle, actin subunit
A. muscle fiberB. sarcomereC. muscleD. actin subunitE. myofibril
Flower: © Doug Sherman/Geofile/RF
Clicker Question #3
If you arrange the following items in order from largest to smallest, which item is THIRD on the list?
myofibril, muscle fiber, sarcomere, muscle, actin subunit
A. muscle fiberB. sarcomereC. muscleD. actin subunitE. myofibril
Flower: © Doug Sherman/Geofile/RF
Section 29.4
Muscle Contraction Requires ATP
When a muscle cell contracts, its sarcomeres become shorter.
Figure 29.15
Section 29.4
Muscle Contraction Requires ATP
According to the sliding filament model, sarcomeres contract because the thin actin filaments slide between the thick myosin filaments.
Figure 29.15
Section 29.4
Muscle Contraction Requires ATP
How does this sliding action occur?
Figure 29.15
Section 29.4
Muscle Contraction Requires ATP
Before the thick and thin filaments of a sarcomere can slide passed one another, the muscle cell must be stimulated.
Figure 29.16
Section 29.4
Muscle Contraction Requires ATP
An action potential travels along a motor neuron. When it reaches the axon terminal, the cell releases neurotransmitters.
Figure 29.16
Section 29.4
Muscle Contraction Requires ATP
Neurotransmitters bind to the muscle cell, starting an electrical wave that propagates along the muscle cell membrane.
Figure 29.16
Section 29.4
Muscle Contraction Requires ATP
As the electrical wave spreads down T tubules, it causes the nearby sarcoplasmic reticulum to release calcium into the sarcomere.
Figure 29.16
Section 29.4
Muscle Contraction Requires ATP
The presence of calcium allows filaments to slide. Let’s look more closely at a sarcomere.
Figure 29.16
Section 29.4
Muscle Contraction Requires ATP
Figure 29.17
Muscle contraction at a molecular scale:
Section 29.4
Muscle Contraction Requires ATP
In step 1, actin and myosin filaments are near each other but not touching. The muscle has received a signal from the nervous system.
Figure 29.17
Section 29.4
Muscle Contraction Requires ATP
Calcium binds to a thin-filament protein called troponin, causing it to change shape and pull on another protein called tropomyosin.
Figure 29.17
Section 29.4
Muscle Contraction Requires ATP
With tropomyosin pulled aside, binding sites on actin are exposed.
Figure 29.17
Section 29.4
Muscle Contraction Requires ATP
In step 2, myosin binds to exposed binding sites on actin, forming cross bridges.
Figure 29.17
Section 29.4
Muscle Contraction Requires ATP
In step 3, the cross bridge changes shape from straight to bent. This “power stroke” pulls on the actin filament.
Figure 29.17
Section 29.4
Muscle Contraction Requires ATP
A new ATP molecule comes in at step 4. It binds to the cross bridges, which causes them to separate from the actin binding sites.
Figure 29.17
Section 29.4
Muscle Contraction Requires ATP
In step 5, hydrolysis of ATP provides the energy to return myosin to its straight conformation.
Figure 29.17
Section 29.4
Muscle Contraction Requires ATP
Myosin is now ready to bind to actin again.
Figure 29.17
Section 29.4
Muscle Contraction Requires ATP
Once the electrical stimulation from the nervous system subsides, calcium will release from troponin, and myosin can no longer bind to actin.
Figure 29.17
Clicker Question #4
Amyotrophic lateral sclerosis (ALS), also called Lou Gehrig's disease, is a disorder in which motor neurons are destroyed. How would this disorder affect muscle function?
A. Muscles fail to contract because ATP is not available.B. Muscles fail to contract because they do not receive a signal to do so.C. Muscles are continually contracted because ATP is not available.D. Muscles are continually contracted because they do not receive a signal to relax.
Flower: © Doug Sherman/Geofile/RF
Clicker Question #4
Amyotrophic lateral sclerosis (ALS), also called Lou Gehrig's disease, is a disorder in which motor neurons are destroyed. How would this disorder affect muscle function?
A. Muscles fail to contract because ATP is not available.B. Muscles fail to contract because they do not receive a signal to do so.C. Muscles are continually contracted because ATP is not available.D. Muscles are continually contracted because they do not receive a signal to relax.
Flower: © Doug Sherman/Geofile/RF
29.4 Mastering Concepts
Describe how sliding filaments shorten a sarcomere.
Artificial limb: ©Jeff J Mitchell/Getty Images
Section 29.5
Muscle Fibers Generate ATP in Multiple Ways
As we’ve seen, ATP is important for muscle contraction.
Figure 29.17
Section 29.5
Muscle Fibers Generate ATP in Multiple Ways
A resting muscle cell generates ATP in aerobic respiration.
Figure 29.18
Section 29.5
Muscle Fibers Generate ATP in Multiple Ways
During activity, muscle cells replenish ATP with creatine phosphate, a molecule that donates a phosphate to ADP.
Creatine: © Alan Mather/Alamy; runners: © Photodisc Inc./ Getty Images RF
Section 29.5
Muscle Fibers Generate ATP in Multiple Ways
But creatine phosphate supply is depleted in less than a minute of continuous exercise.
Creatine: © Alan Mather/Alamy; runners: © Photodisc Inc./ Getty Images RF
Section 29.5
Muscle Fibers Generate ATP in Multiple Ways
After creatine phosphate is gone, aerobic respiration continues to produce ATP if muscles are receiving enough oxygen.
Creatine: © Alan Mather/Alamy; runners: © Photodisc Inc./ Getty Images RF
Section 29.5
Muscle Fibers Generate ATP in Multiple Ways
Otherwise, the cells switch to fermentation, an anaerobic pathway of ATP production that generates lactic acid as a byproduct.
Creatine: © Alan Mather/Alamy; runners: © Photodisc Inc./ Getty Images RF
Section 29.5
Muscle Fibers Generate ATP in Multiple Ways
Muscle cell metabolism also explains why a dead body “goes stiff.” After death, cells no longer produce ATP. Actin cannot separate from myosin, resulting in rigor mortis.
Photo: © Brand X Pictures/Punchstock/RF
29.5 Mastering Concepts
Describe the role of creatine phosphate in muscle metabolism.
Artificial limb: ©Jeff J Mitchell/Getty Images
Section 29.4
Muscles Are Organized into Motor Units
Motor neurons send impulses from the central nervous system to muscle cells, causing them to contract.
Figure 29.19
Section 29.4
One motor neuron typically synapses with several muscle cells, forming a motor unit that contracts together.
Figure 29.19
Muscles Are Organized into Motor Units
Section 29.4
Motor units may be small (consisting of few muscle cells) or large. Smaller motor units produce fine, precise movements.
Figure 29.19
Muscles Are Organized into Motor Units
Section 29.4
The nervous system stimulates of many motor units in concert to produce smooth, coordinated movements.
Figure 29.19
Muscles Are Organized into Motor Units
Section 29.6
Muscle Fiber Types Influence Athletic Performance
Figure 29.20
Skeletal muscles contain two types of cells, distinguished by how quickly they contract and tire.
Woman runner: © RubberBall/Getty Images RF; muscle fiber: © G.W. Willis/Visuals Unlimited;
weight lifter: © Jack Mann/Photodisc/Getty Images RF
Section 29.6
Muscle Fiber Types Influence Athletic Performance
Figure 29.20
Slow-twitch fibers are small, use energy slowly, and have high endurance.
Woman runner: © RubberBall/Getty Images RF; muscle fiber: © G.W. Willis/Visuals Unlimited;
weight lifter: © Jack Mann/Photodisc/Getty Images RF
Section 29.6
Muscle Fiber Types Influence Athletic Performance
Figure 29.20
Fast-twitch fibers are large, use bursts of energy, and tire quickly.
Woman runner: © RubberBall/Getty Images RF; muscle fiber: © G.W. Willis/Visuals Unlimited;
weight lifter: © Jack Mann/Photodisc/Getty Images RF
Section 29.6
Muscle Fiber Types Influence Athletic Performance
Figure 29.20
The proportion of slow- and fast-twitch fibers in an individual’s muscles is mostly genetically determined. However, it is possible to alter the ratio through exercise.
Woman runner: © RubberBall/Getty Images RF; muscle fiber: © G.W. Willis/Visuals Unlimited;
weight lifter: © Jack Mann/Photodisc/Getty Images RF
Section 29.6
Muscle Fiber Types Influence Athletic Performance
Figure 29.20
Exercise also increases
• the size of muscle cells• the efficiency of muscle cell
metabolism • blood flow to muscles• bone strength
Woman runner: © RubberBall/Getty Images RF; muscle fiber: © G.W. Willis/Visuals Unlimited;
weight lifter: © Jack Mann/Photodisc/Getty Images RF
Clicker Question #5
An athlete supplements her diet with creatine phosphate. How might her athletic performance improve?
A) She might be more competitive in long triathlons. B) She might be able to run a marathon much more quickly.C) She might be able to sprint for slightly longer.D) More than one of these choices is correct.
Flower: © Doug Sherman/Geofile/RF
Clicker Question #5
An athlete supplements her diet with creatine phosphate. How might her athletic performance improve?
A) She might be more competitive in long triathlons. B) She might be able to run a marathon much more quickly.C) She might be able to sprint for slightly longer.D) More than one of these choices is correct.
Flower: © Doug Sherman/Geofile/RF
29.6 Mastering Concepts
Why do endurance sports require a high proportion of slow-twitch muscle fibers, whereas power sports require more fast-twitch muscle fibers?
Artificial limb: ©Jeff J Mitchell/Getty Images
Section 29.7
Investigating Life: Did a Myosin Gene Mutation Make Humans Brainier?
Myosin genes encode proteins abundant in muscle cells. A myosin gene expressed in jaw muscles is mutated in human DNA but active in related primates.
Figure 29.22
The myosin mutation explains why humans have small and weak jaw muscles compared to our relatives, but how does it relate to our intellectual abilities?
Figure 29.22Section 29.7
Investigating Life: Did a Myosin Gene Mutation Make Humans Brainier?
Large jaw muscles have larger attachment areas on the skull than small jaw muscles, which might put a constraint on brain size.
Figure 29.22Section 29.7
Investigating Life: Did a Myosin Gene Mutation Make Humans Brainier?
Weak jaw muscles might have lifted this constraint on brain size, changing the course of human evolution.
Figure 29.22Section 29.7
Investigating Life: Did a Myosin Gene Mutation Make Humans Brainier?
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