This document summarizes the functions of muscular tissue at the cellular level. It discusses the three main types of muscle tissue - skeletal, cardiac, and smooth muscle - and their distinct locations, functions, appearances, and methods of control. For each type of muscle tissue, it provides details on structure, contraction mechanisms, and proteins involved. It also examines the sliding filament model of muscle contraction and how calcium regulates the exposure of actin binding sites to trigger muscle shortening.

1. MO Figure
Muscle Function at
the Cellular Level
Michael Patrick O'Neill/Science Source.

2. Functions of Muscular Tissue
• Like nervous tissue, muscles are excitable
or "irritable”
they have the ability to respond to a stimulus
• Unlike nerves, however, muscles are also:
Contractible (they can shorten
in length)
Extensible (they can extend or
stretch)
Elastic (they can return to their
original shape)

3. Functions of Muscular Tissue
• Muscle makes up a large percentage of the
body’s weight
• Their main functions are to:
Create motion – muscles work with nerves,
bones, and joints to produce body movements
Stabilize body positions and maintain posture
Store substances within the body using
sphincters

4. Three Types of Muscular
Location Function Appearance Control
Skeletal
skeleton
movement,
heat, posture
striated, multi-nucleated
(eccentric),
fibers parallel
voluntary
Cardiac
heart
pump blood
continuously
striated, one central
nucleus
involuntary
Visceral
(smooth muscle)
G.I. tract,
uterus, eye,
blood vessels
Peristalsis,
blood pressure,
pupil size,
erects hairs
no striations, one
central nucleus
involuntary
Tissue

5. Three Types of Muscular Tissue
(a) Skeletal muscle
(b) Cardiac muscle (c) Visceral smooth muscle

6. Location Function Appearance Control
Skeletal
skeleton
movement,
heat, posture
striated, multi-nucleated
(eccentric),
fibers parallel
voluntary
Cardiac
heart
pump blood
continuously
striated, one central
nucleus
involuntary
Visceral
(smooth muscle)
G.I. tract,
uterus, eye,
blood vessels
Peristalsis,
blood pressure,
pupil size,
erects hairs
no striations, one
central nucleus
involuntary
Skeletal Muscle

7. Skeletal Muscle

8. Skeletal Muscle
Skeletal muscle fibers are very long “cells” - next to
neurons (which can be over a meter long),
perhaps the longest in the body
The Sartorious muscle contains
single fibers that are at least
30 cm long
A single skeletal muscle fiber

9. Motor neuron
Sarcolemma
Skeletal Muscle
The terminal processes of a motor
neuron in close proximity to the
sarcolemma of a skeletal muscle fiber

10. Skeletal muscle fibers
A muscle fiber consists of a single cell.
• The cell is long and multinucleated.
• The cytoplasm is called the sarcoplasm.
• Contains a specialized ER, called the
sarcoplasmic reticulum, that stores
calcium.
• Contains myofibrils made up of thick and
thin filaments.

11. The Skeletal Muscle Fiber
Increasing the level of magnification, the myofibrils are
seen to be composed
of filaments
Thick filaments
Thing filaments

12. The Skeletal Muscle Fiber
• The basic functional unit of skeletal muscle
fibers is the sarcomere: An arrangement of
thick and thin filaments sandwiched between
two Z discs
A scanning electron micrograph of a sarcomere

13. The Skeletal Muscle Fiber
• Muscle contraction occurs in the sarcomeres
The “Z line” is really a Z disc when considered in 3
dimensions. A sarcomere extends from Z disc to Z disc.

14. Muscle Proteins
• Myofibrils are built from three groups of
proteins
Contractile proteins generate force during
contraction
Regulatory proteins help switch the contraction
process on and off
Structural proteins keep the thick and thin
filaments in proper alignment and link the

15. Muscle Proteins
• The thin filaments are comprised mostly of
the structural protein actin, and the thick
filaments are comprised mostly of the
structural protein myosin

16. Muscle Proteins
• In the thin filaments actin proteins are strung
together like a bead of pearls
• In the thick filaments myosin proteins look
like golf clubs bound together

17. Muscle Proteins
In this first graphic, the myosin binding sites on the actin
proteins are readily visible.
The regulatory proteins troponin and tropomyosin have
been added to the bottom graphic: The myosin binding
sites have been
covered

18. Muscle Proteins
In this graphic the troponin-tropomyosin complex has
slid down into the “gutters” of the actin molecule
unblocking the myosin binding site
Myosin binding site exposed
The troponin-tropomyosin complex can slide back and
forth depending on the presence of Ca2+

19. Muscle Proteins
• Ca2+ binds to troponin which changes the shape of
the troponin-tropomyosin complex and uncovers
the myosin binding sites on actin

20. Muscle Proteins
• Besides contractile and regulatory proteins, muscle
contains about a dozen structural proteins which
contribute to the alignment, stability, elasticity, and
extensibility of myofibrils
• Titan is the third most plentiful protein in muscle,
after actin and myosin - it extends from the Z disc and
accounts for much of the elasticity of myofibrils
• Dystrophin is discussed later as it relates to the disease
of muscular dystrophy

21. The Sliding-Filament
Mechanism
• With exposure of the myosin binding sites on
actin (the thin filaments)—in the presence of
Ca2+ and ATP—the thick and thin filaments
“slide” on one another and the sarcomere is
shortened

22. The Sliding-Filament
Mechanism
• The “sliding” of actin on myosin (thick
filaments on thin filaments) can be broken

23. Figure 1
Sliding filament model
Thick (myosin) and thin (actin) filaments slide past one another
during muscle contraction. As a result, the sarcomere shortens.

24. Figure 2
Sarcomeres
C. F. Armstrong/Science Source.
Z-discs form dark lines in electron micrographs and give
skeletal muscle a striated appearance.

25. Figure 3

26. Figure 4
Muscle anatomy

27. Figure 4a

28. Figure 4b

29. Muscle energy storage
Glycogen
• Glucose polymer. Glucose is used in
cellular respiration to make ATP.
Creatine phosphate
• Transfers a phosphate to ADP to form
ATP.

30. Figure 5
Muscle innervation
Muscle fibers can be innervated by a single neuron, which
increases contraction strength at the expense of fine control, or by
multiple neurons, which allows finer control but with little strength.

31. Figure 5a

32. Figure 5b

33. Figure 6
Excitation-contraction coupling

34. Figure 7
Regulation of contraction
In resting muscle,
tropomyosin covers
myosin-binding sites
on actin. The
troponin complex
holds tropomyosin in
place. Ca2+ binding
to troponin causes
tropomyosin to shift,
which exposes the
myosin-binding sites.
Myosin binds actin,
and the muscle
contracts.

35. Figure 7a

36. Figure 7b

37. Figure 7c

38. MO Figure
Skeletal System
and Locomotion
Art Wolfe/Science Source

39. Skeletal systems
Endoskeleton: inside the animal
Exoskeleton: outside the animal
Hydrostatic skeleton: composed of
pressurized water in internal compartments.

40. Figure 1
Hydrostatic skeletons
© 2006 Nature Publishing Group Alvarado, A & Tsonis, P. Bridging the
regeneration gap: genetic insights from diverse animal models. Nature
Reviews Genetics 7, 873–884 (2006) doi:10.1038/nrg1923. Used with
permission.
This Hydra moves using a hydrostatic skeleton.

41. Figure 2
Peristaltic movement
Caused by
alternating
radial and
longitudinal
muscle
contractions
against a
fluid-filled
coelom.

42. Figure 2a

43. Figure 2b

44. Figure 3
Exoskeletons
© 2002 Nature Publishing Group GDC seeks members of new Appointing Body. British Dental Journal 193, 431–
433 (2002), doi:10.1038/sj.bdj.4801590. Used with permission.
Arthropod exoskeletons contain chitin.

45. Figure 4
The human skeleton

46. Figure 5
Antagonistic muscle pairs
Coordinated
movement
enables flexion
and extension
of a limb.

47. Figure 5a

48. Figure 5b

49. Figure 6
Balance and locomotion
During walking and
running, the feet are
used for balancing,
pushing off, and
maintaining momentum.

50. Figure 7
Terrestrial locomotion
Stephen Dalton/Science Source.
Energy stored in tendons enables this frog to jump.