1. MUSCULAR SYSTEM

2. INTRODUCTION

What are the three muscle
types?
• Skeletal Muscle
• Smooth Muscle
• Cardiac Muscle
Skeletal muscle is an organ of the muscular system and consist
of skeletal muscle tissue, nervous tissue, blood, and connective
tissue.

3. Structure of a Skeletal Muscle





Fascia - a connective tissue that separates adjacent
muscles and attaches the muscle to the bone.
Epimysium – a layer of connective tissue that closely
surrounds a skeletal muscle.
Perimysium – separates muscle cells into fascicles.
Fascicles – bundles of skeletal muscle fibers.
Endomysium – separates each individual muscle
fiber.
What do all of these have in common?

4. Skeletal Muscle Fibers

A skeletal muscle fiber is a
single cell that contracts
and relaxes
What causes the cell to
contract and relax?


Nerve stimulation
Sarcolemma- muscle cell
membrane.
 Sarcoplasm- cell’s
cytoplasm

5. Skeletal Muscle Fibers

Myofibrols
– Play a fundamental roll in
muscle contraction.
– They contain two kinds of
proteins filaments
MYOSIN & ACTIN

Myofibril
Myosin & Actin are
responsible for the light
and dark STRIATIONS
or bands of skeletal
muscle.
Filaments
Muscle fiber

6. Skeletal Muscle Fibers
The Striation part of skeletal pattern consist of two main parts
1. I Bands ( light
bands ) are
composed of thin
ACTIN filaments
attached to Z lines.
2. A Bands ( dark
bands ) are
composed of
overlapping thick
& thin bands.

7. Skeletal Muscle Fibers
 Sarcomere – the
segment of a myofibril
that extends from one
“z” line to another.
sarcomere
Z Lines

8. Skeletal Muscle Fibers
 Sarcoplasmic
reticulum– network of
membranous channels… similar to
endoplasmic reticulum of other cells.
• Responsible for releasing calcium ions.
 Transverse
tubules ( T-tubules ) – extent
inward and contain extracellular fluid.

9. Skeletal Muscle Fibers

10. Skeletal Muscle Fibers




Describe how connective tissue is part of a
skeletal muscle.
Describe the general structure of a skeletal
muscle fiber.
Explain why skeletal muscle fibers appear
striated.
Explain the relationship between the
sarcoplasmic reticulum and the transverse
tubules.

11. Neuromuscular Junction

What is the stimulant that moves
a muscle?


Nerve impulse
Motor neuron – A nerve fiber that
extends outward from the brain or
spinal cord and connected to a skeletal
muscle fiber.


The connection between the two is called a
neuromuscular junction and motor end
plate.
Neurotransmitters – chemicals that
are stored in tiny vesicles (synaptic
vesicles) that stimulates muscle fiber
to contract.

12. Neuromuscular Junction
A neuromuscular junction showing motor end plate.
A motor unit. A muscle fiber
usually has a single motor end
plate. However a motor neuron
may connect to several muscle
fibers.

13. Skeletal Muscle Contraction
The role of myosin and actin


Myosin – contain protein
strands that look like
“Golf Clubs” called Cross
Bridges.
Actin molecule contains
protein binding sites.
Tropomyosin
Actin
Thick
Filament
Myosin Crossbridge

14. Skeletal Muscle Contraction

Sliding Filament Theory

The head of the myosin crossbridge attaches to the actin
binding site & pulls the actin
filament along.

ATP is used to set the crossbridge.
relaxed

Myosin
Z line
As the cross-bridges pull, the
actin filament moves toward
the center of the sarcomere and
they shorten.
contracted
Actin

15. Skeletal Muscle Contraction

16. Skeletal Muscle Contraction




Describe a neuromuscular junction.
Define motor unit.
Explain how the filaments of a myofibril
interact during muscle contraction.
Explain how a motor nerve impulse can
trigger a muscle contraction.

17. Support & Movement

Oxygen Dept


When muscles are used during exercise
oxygen is used up quickly. The body reverts
to anaerobic respiration to produce oxygen,
with the help of pyruvic acid. In low oxygen
levels pyruvic acid reacts to produce lactic
acid which accumulate in the muscles.
As lactic acid accumulate a person develops
Oxygen Dept.

18. Support & Movement
 Muscle Fatigue
 Muscles lose the ability to contract.
– Lactic acid
– Lack of acetylcholine
– Interruption of blood supply
 Cramps
 A sustained involuntary contraction
 Rigor Mortis, myosin and actin filaments
remained linked until muscles begin to
decompose. ( 72 hrs )

19. Muscle Responses

Threshold Stimulus


The minimal strength required to cause a
contraction.
All-or-None Response
– A muscle fiber when excited does not contract
partially, if it contracts at all, it contracts
completely

Twitch

A single contration that lasts only a fraction of a
second

20. Muscle Responses

Latent Period


The time the stimulus is applied and the contraction
occurs (0.01s)
Muscle Tone



Even when a muscle appears to be at rest, a certain
amount of sustained contraction occurs in its fibers.
Muscle tone is a response to nerve impulses that
originate repeatedly.
Is particularly important in maintaining posture.

21. Support and Movement
Questions (p189)

Define threshold stimulus.

What is a none-or-all response?

Distinguish between a twitch and a
sustained contraction.

How is muscle tone maintained?