Download Chapter 2: Chemistry, Matter, and Life

Chapter 7:
The Muscular
System
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Taylor: Structure and Function of the Human Body
Types of Muscle
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Taylor: Structure and Function of the Human Body
The Muscular System
Skeletal Muscle Has Three Primary Functions:
• Skeletal movement
• Posture maintenance
• Heat generation
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Taylor: Structure and Function of the Human Body
The Muscular System
Muscle Structure
• Fascicles
– Bundles of muscle cells (fibers) that make up a whole
muscle
• Connective tissue
– Hold fascicles and whole muscle together
– Three layers
• Endomysium
• Perimysium
• Epimysium
• Tendons
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Taylor: Structure and Function of the Human Body
The Muscular System
Muscle Cells in Action
• Motor unit: A single neuron and all the muscle fibers it
stimulates
– Small motor units used for fine movements
– Large motor units used for broad movements
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Taylor: Structure and Function of the Human Body
The Muscular System
Muscle Cells in Action
• Neuromuscular junction (NMJ): The point at which a
nerve fiber contacts a muscle fiber
– A type of synapse
– NMJ anatomy
• Motor neuron
• Neurotransmitter (acetylcholine; ACh)
• Motor end plate (on muscle fiber)
 Contains acetylcholine receptors
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Taylor: Structure and Function of the Human Body
The Muscular System
Muscle Cells in Action
• NMJ allows motor neuron to stimulate muscle fiber to
become electrically excited (action potential)
• Action potential stimulates muscle contraction
• Events at the NMJ
– Ach is released from motor neuron into synaptic cleft
– Ach diffuses across synaptic cleft towards motor end
plate
– Ach binds to receptors on motor end plate and
stimulates action potential
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Taylor: Structure and Function of the Human Body
The Muscular System
Muscle Cells in Action
• The sarcomere is the functional unit of contraction in the
skeletal muscle fiber
• Sarcomere anatomy:
– Thick filaments (myosin)
– Thin filaments (actin)
– Regulatory proteins
• Troponin
• Tropomyosin
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Taylor: Structure and Function of the Human Body
The Muscular System
Muscle Cells in Action
•Sarcomeres contract via the sliding filament mechanism:
– Myosin heads bind to actin, forming cross-bridges
– Using stored energy, myosin heads pull actin
filaments together within the sarcomeres and the cell
shortens
– New ATP is used to detach myosin heads and move
them back into position for another “power stroke”
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
Figure 7-4 Sliding filament mechanism of skeletal muscle
contraction.
Sliding filament mechanism of skeletal muscle contraction.
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
The Muscular System
Muscle Cells in Action
• Calcium regulates sarcomeric contraction within the
muscle cell:
– Action potential from NMJ travels to sarcoplasmic
reticulum (SR)
– SR releases calcium into cytoplasm
– Calcium shifts troponin and tropomyosin off of thin
filament soit blocks the sites on actin filaments where
cross-bridges form
– Muscle relaxes when stimulation ends and calcium is
pumped back into SR
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
The Muscular System
Summary of Events in a Muscle Contraction
1. ACh is released from neuron ending into synaptic cleft
at NMJ
2. ACh binds to motor end plate and produces action
potential
3. Action potential travels to sarcoplasmic reticulum (SR)
4. SR releases calcium into cytoplasm
5. Calcium shifts troponin and tropomyosin so that
binding sites on actin are exposed
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Taylor: Structure and Function of the Human Body
The Muscular System
Summary of Events in a Muscle Contraction
(continued)
6.Myosin heads bind to actin, forming cross-bridges
7.Using stored energy, myosin heads pull actin filaments
together within sarcomeres and cell shortens
8.New ATP is used to detach myosin heads and move
them back to position for another “power stroke”
9.Muscle relaxes when stimulation ends and calcium is
pumped back into SR
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
The Muscular System
Energy Sources
• Muscle contraction requires ATP
• Skeletal muscle prefers to produces ATP via aerobic
metabolism, which requires
– Oxygen
– Glucose
• Storage compounds ensure an adequate supply of
oxygen and glucose for aerobic ATP metabolism
– Myoglobin
• Stores additional oxygen, located in muscle cells
– Glycogen
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Taylor: Structure and Function of the Human Body
The Muscular System
Energy Sources
• During strenuous activity, muscle cells use anaerobic
ATP metabolism which causes an oxygen debt and does
not require ATP
– Breakdown of creatine phosphate
– Anaerobic glycolysis
• Lactic acid accumulation and oxygen debt
• Excess postexercise oxygen consumption
– After strenuous exercise, person takes in extra
oxygen (via rapid breathing) to remove lactic acid
and replenish energy stores
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Taylor: Structure and Function of the Human Body
The Muscular System
Effects of Exercise
• Improved balance, joint flexibility
• Increased muscle size (hypertrophy)
• Improved muscle tissue
• Vasodilation
• Strengthened heart muscle
• Improved breathing and respiratory efficiency
• Weight control
• Stronger bones
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Taylor: Structure and Function of the Human Body
The Muscular System
Types of Muscle Contractions
• Partial (muscle tone or tonus)
– Partially contracted state that is normal
• Isotonic
– No change in tension
– Muscle length shortens
– Movement
• Isometric
– Great increase in tension
– Muscle length unchanged
– No movement
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Taylor: Structure and Function of the Human Body
The Mechanics of Muscle Movement
• Tendons attach muscles to bones.
– Origin: Attached to more fixed part of skeleton
– Insertion: Attached to more movable part of
skeleton
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Taylor: Structure and Function of the Human Body
Figure 7-6 Muscle attachments to bones.
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
The Mechanics of Muscle Movement
Muscles Work Together
• Many muscles function in pairs
– Prime movers
• Movement by a muscle
– Antagonists
• Produces opposite movment
– Synergists
• helpers
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Taylor: Structure and Function of the Human Body
The Mechanics of Muscle Movement
Levers and Body Mechanics
•Musculoskeletal system as a lever system
– Lever—bone
– Fulcrum—joint
– Force—applied by muscle
•Three classes of levers
– First class
– Second class
– Third class—most body systems
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
Skeletal Muscle Groups
Characteristics for Naming Muscles
Characteristic
Example
Location
Temporalis; near the skull’s temple
Size
Gluteus maximus; the largest
Shape
Serratus anterior; serrated edge
Direction
External oblique; runs obliquely
Number of heads
Biceps brachii; two heads
Action
Flexor digitorum; flexes toes
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
Skeletal Muscle Groups
Muscles of the Head and Neck
Name
Location
Function
Orbicularis oculi
Encircles eyelid
Closes eye
Levator palpebrae
superioris
Posterior orbit to
upper eyelid
Opens eye
Orbicularis oris
Encircles mouth
Closes lips*
Buccinator
Fleshy part of cheek
Flattens cheek; helps in
eating, whistling, and
blowing wind instruments
Temporalis
Above and near ear
Masseter
At angle of jaw
Sternocleidomastoid Along lateral neck,
to mastoid process
Closes jaw
Closes jaw-used for
chewing*
Flexes head; rotates
head toward opposite
side from muscle, moves
head*
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Taylor: Structure and Function of the Human Body
Figure 7-10 Muscles of the head and neck.
Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
Taylor: Structure and Function of the Human Body
Skeletal Muscle Groups
Muscles That Move the Shoulder and Arm
Name
Location
Function
Trapezius
Posterior neck and
upper back to clavicle
and scapula
Raises shoulder and pulls
it back; superior portion
extends and turns head
Latissimus dorsi
Middle and lower back,
to humerus
Extends and adducts arm
Pectoralis major
Superior, anterior chest, Flexes and adducts arm
to humerus
Serratus anterior Inferior to axilla on
lateral chest
Moves shoulder forward;
aids in raising arms,
punching, or reaching
forward
Deltoid
Abducts arm; flexes and
extends arm
Covers shoulder joint,
to lateral humerus
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Taylor: Structure and Function of the Human Body
Skeletal Muscle Groups
Muscles That Move the Forearm and Hand
Name
Location
Function
Biceps brachii
Anterior arm along
humerus, to radius
Flexes forearm;
supinates forearm and
hand
Brachialis
Deep to biceps brachii;
inserts at anterior elbow
joint
Forceful flexor of
forearm
Brachioradialis
Lateral forearm from
distal end of humerus
Flexes forearm
Triceps brachii
Posterior arm, to ulna
Extends forearm
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Taylor: Structure and Function of the Human Body
Skeletal Muscle Groups
Muscles That Move the Forearm and Hand
(continued)
Name
Location
Function
Flexor carpi
group
Anterior forearm, to hand Flexes hand
Extensor carpi
group
Posterior forearm, to
hand
Extends hand
Flexor digitorum
group
Anterior forearm to
fingers
Flexes fingers
Extensor
digitorum group
Posterior forearm to
fingers
Extends fingers
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Taylor: Structure and Function of the Human Body
Figure 711 Muscles
that move the
forearm
and hand.
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Taylor: Structure and Function of the Human Body
Skeletal Muscle Groups
Muscles of the Trunk
Name
Location
Function
Diaphragm
Dome-shaped
partition between
thoracic and
abdominal cavities
Dome descends to
enlarge thoracic cavity
from top to bottom
Intercostals
Between ribs
Elevate ribs and enlarge
thoracic cavity
Muscles of abdominal wall:
• External oblique
• Internal oblique
• Transversus abdominus
• Rectus abdominis
Anterolateral
abdominal wall
Compress abdominal
cavity and expel
substances from the
body; flex spinal column
Levator ani
Pelvic floor
Aids defecation
Erector spinae
Group of deep vertical
muscles between
sacrum and skull
Extends vertebral column
to produce erect posture
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Taylor: Structure and Function of the Human Body
Figure 7-12 Muscles of respiration.
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Taylor: Structure and Function of the Human Body
Figure 7-13 Muscles of
the abdominal wall.
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Taylor: Structure and Function of the Human Body
Skeletal Muscle Groups
Muscles That Move the Leg and Thigh
Name
Location
Function
Gluteus
maximus
Superficial buttock, to
femur
Extends thigh
Gluteus medius
Deep buttock, to femur
Abducts thigh
Iliopsoas
Crosses anterior hip
joint, to femur
Flexes thigh
Adductor group
Medial thigh, to femur
Adducts thigh
Sartorius
Crosses anterior thigh
from ilium to medial tibia
Flexes thigh and leg (to
sit cross-legged)
Gracilis
Pubic bone to medial
surface of tibia
Adducts thigh at hip;
flexes
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Taylor: Structure and Function of the Human Body
Skeletal Muscle Groups
Muscles That Move the Leg and Thigh (continued)
Name
Location
Function
Quadriceps femoris
• Rectus femoris
• Vastus medialis
• Vastus lateralis
• Vastus intermedius
Anterior thigh, to
tibia
Extends leg
Hamstring group
• Biceps femori
• Semimembranosus
• Semitendinosus
Posterior thigh;
ischium and femur
to tibia and fibula
Flexes leg at knee;
extends and rotates
thigh at hip
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Taylor: Structure and Function of the Human Body
Figure 7-15 Muscles of the thigh.
How many muscles make up the quadriceps femoris?
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Taylor: Structure and Function of the Human Body
Skeletal Muscle Groups
Muscles That Move the Foot
Name
Location
Function
Gastrocnemius
Posterior leg, to calcaneus,
inserting by the Achilles
tendon
Plantar flexes
foot
Soleus
Posterior leg deep to
gastrocnemius
Plantar flexes
foot
Tibialis anterior
Anterior and lateral leg, to
foot
Dorsiflexes and
inverts foot
Fibularis longus
Lateral leg, to foot
Everts foot
Flexor digitorum
group
Posterior leg and foot to
inferior surface of phalanges
Flexes toes
Extensor digitorum
group
Anterior surface of leg bones
to superior surface of
phalanges
Extends toes
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Taylor: Structure and Function of the Human Body
Figure 7-16 Muscles that move the foot.
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Taylor: Structure and Function of the Human Body
Effects of Aging on Muscles
• Beginning at about age 40
• Gradual loss of muscle cells
• Loss of power
• Tendency to flex hips and knees
• Decrease in height
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