PP18
Muscle Anatomy
Chapter 2 pg 21-41
ANS 3043
University of Florida
Dr. Michael J. Fields
Muscle Function

Movement
– Locomotion, digestion, breathing, vision, circulation
– Due to unique ability of muscles to contract and shorten
– Conversion of chemical energy to mechanical energy
 20-25% efficient
 Remainder of energy lost as heat (i.e. shivering)
Direct Function : Voice Related Structures
 Indirect Function : Body Movements (road rage finger)

Muscle Function
Maintains body temperature in warm blooded
animals (cold climate causes energy use to keep
warm)
 Food source for other animals and humans (high
in protein, minerals and protein)

Types of Muscle

Based on microstructure and manner of
contraction
1. Smooth : blood vessels, GI tract, repro tissues
2. Cardiac : heart
3. Skeletal : striated
Cross
Section
Longitudinal Section
Note striations and nucleus
Anatomy of Skeletal Muscle

General
– Multinucleated with voluntary neural input
– Each cell has its own nerve, artery and vein
– Striated : consist of sliding filaments that contract and apply
force to muscle
– Large cells harnessed in a network of connective tissue
(Figure 2.22)
 Acts as a harness to transmit contractile force to bone or other
tissues
Anatomy of Skeletal Muscle

Macrostructure
– Epimysium : connective tissue that surrounds entire muscle
 Separates individual muscles into distinct units
 Avenue for blood vessels and nerves to enter muscle
– Perimysium
 Muscle bundles contain 20 to 40 muscle fibers
 Enmeshes and supports major blood vessels
 Intramuscular fat (marbling) deposited within perimysium (white
flecks of fat in membrane)
Anatomy of Skeletal Muscle
3. Endomysium : connective tissue that surounds
individual muscle fibers
–
–

Lies immediately adjacent to muscle cell membrane
Major connective tissue responsible for meat tenderness
(increases with age)
Microstructure : contains multiple fibrils
responsible for contraction
1. Muscle fibers or myofiber : structural unit of muscle
(Figure 2.23, 2.24)
Anatomy of Skeletal Muscle

Microstructure : contains multiple fibrils responsible for
contraction
1.Muscle fibers or myofiber : structural unit of muscle (Figure
2.23, 2.24)
– May extend total length of muscle but normally extends partial
length of muscle
– Growth in fiber length, increase in number of fiber and girth of
muscle
– Encased by sarcolemma (basement membrane)
Muscle bundle
Muscle
Muscle Bundle
Muscle Fiber/Myofiber
Myofibril
Z
Myosin
Z
Actin
Anatomy of Skeletal Muscle
2. Myofibrils (Fig 2.26 – 2.29)
–
–
–
–
Functional contractile unit of muscle composed of
microfilaments
Extends entire length of muscle cell
Bathed in cytoplasm, which is high in protein
Contains Sarcomeres : muscle unit
3. Sarcomeres
–
–
–
–
“z line” to “z line”
Repeating contractile unit of muscle that represents organization
of myofibrils
“Z lines :” outer demarcation of each sarcomere
Elongation of muscle occurs by addition of sarcomeres near bone
attachment
Anatomy of Skeletal Muscle
4. Myosin : Thick Filament (Figure 2.28)
–
–
–
–
–
Located in center of sarcomere and overlaps actin
Major component of muscle contraction and sarcomere
shortening
Heavy (contain head) and light chains held together by Cproteins
Bi-directional arrangement (head on both ends)
Head of heavy chain has ATPase activity : binds to actin and
serves to “rachet” or pull actin filaments together contracting
muscle
Anatomy of Skeletal Muscle
4. Myosin : Thick Filament (Figure 2.28)
–
–
Adjacent myosin molecules attached together at center
by m-protein (skelemin), which forms m-line
Isoforms of myosin, which are basis for different muscle
fiber types
Anatomy of Skeletal Muscle
5. Actin : Thin Filament (Figure 2.30)
–
Consists of subunit called globular (G) actin
–
–
–
400 G-actin molecules, which form double helical structure of the
filamentous (F) actin
Tropomyosin : occupies F-actin groove and is necessary for
development of cross bridges during muscle contraction and
serves as myosin binding site
Troponin T, I, C : Trimeric protein that binds to F-actin and
tropomyosin to regulate cross-bridge development during muscle
contraction
Surrounds muscle fiber/myofiber
Anatomy of Skeletal Muscle
6.
Intrasarcomeric Proteins
a. within myofibril to provide organization to sarcomere

Titin : maintains structure of the half sarcomere by being
associated with myosin
–

responsible for resting tension of muscle (spring-like)
Nebulin : associated with actin andmay serve as template
for building actin and maintaining F-actin
b. outside myofibril (Figure 2.33)

Desmin : protein responsible for tying myofibrils together
like a raft made of logs
Anatomy of Skeletal Muscle
7.
Costameres
–
–
–
Anchors myofibrils to sarcolemma
Transfers force generated from contracting
myofibrils to cell membrane
Consist of several aggregated proteins : filamin,
viniculin, talin
Muscle Fiber/Myofiber
Ultrastructure
Anatomy of Skeletal Muscle

Ultrastructure
1. Transverse tubules : continuous tubule system extending
from plasma membrane into interior of muscle fiber to
transmit action potential to initiate contraction of the fiber
2. Sarcoplasmic reticulum (SR) : system of tubules
surrounding myofibrils
–
–
Make up terminal cisternae and fenestrated collar
Serve as a storage unit during muscle relaxation
Anatomy of Skeletal Muscle
3. Combined, T-tubules and SR form the tubular
network that acts in the coupling of excitation,
contraction and relaxation of the muscle
–
–
Combined with voltage sensing receptors, allows for
calcium flow into cytoplasm
Calcium pumps : pump calcium back into SR where Ca
binds with a protein know as calsequestrin
Anatomy of Skeletal Muscle

Other important components
1. Nuclei
–
–
Muscle fibers are multinucleated
Elliptical and located on periphery beneath sarcolemma
2. Mitochondria (powerhouse of the cell)
–
–
–
–
–
Responsible for generating energy substrates for the cell
Contain enzymes associated with oxidative metabolism
If not enough oxygen muscle switches to anaerobic metabolism
and produces lactic acid
Clustered around periphery of cell
Generates ATP resulting in phosphorylating or tropomyosin and
troponin leading to contraction
Cardiac Muscle

Characteristics
– Mono and multinucleated with nucleus in center of
cell
– Striated but decreased and not as organized
compared to skeletal muscle
– Actin : Myosin filaments (2:1)
 Not cylindrical nor in discrete units like skeletal muscle
 Joined together and variable in number
Cardiac Muscle
Nuclei
Z line
Cardiac Muscle
Z line
Cardiac Muscle
– Contractions : involuntary neural input
 Intercalated discs – connections between cardiocytes
(muscle fibers)
 Run perpendicular to long axis of muscle
 Allows for electrical impulses to migrate through each cell
 Cardiac myofibrils attached directly to discs to allow heart
to act as a group
Smooth Muscle

Description
– Sheet-like muscle masses surrounding various organs

Functions and location in body
– Extreme elasticity and pliability but still allow for
contractions
 Uterus : very think in non-gravid uterus but thin during
pregnancy
– Allows for fluid movement through blood vessels and
intestinal tract
Smooth muscle
Smooth Muscle

Characteristics
– Mononucleated with centrally located cigar shaped nucleus
– Non-striated
 Myofilaments not aligned into myofibrils and repeating units like
skeletal muscle
 Actin : Myosin (15:1)
– Attached to cell membranes and strategically located throughout cell
– Contraction allows for the generation of force in several (unorganized)
directions
 Contracts by involuntary neural input and/or stimulation by
hormones/chemicals
– Slow prolonged contractions
Fibers scattered
throughout cell
Muscle- chemical composition
Nitrogenous
20.5%
Water 75% (65
– 80%)
Lipid 2.5%
(1.5 - 13.0%)
CHO 1.0%
Glycogen stored in muscle
Inorganic 1.0%