Download Skeletal Muscle Tissue

Muscular System
Poudre High School
Human Anatomy/Physiology
Mr. Bradley
1
The Muscular System
 Muscles are responsible for all types of
body movement
 Three basic muscle types are found in
the body
 Skeletal muscle
 Cardiac muscle
 Smooth muscle
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Characteristics of Muscles
 Muscle cells are elongated
(muscle cell = muscle fiber)
 Contraction of muscles is due to the
movement of microfilaments
 All muscles share some terminology
 Prefix myo refers to muscle
 Prefix mys refers to muscle
 Prefix sarco refers to flesh
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3
Skeletal Muscle
striated, voluntary
 Multi-nucleated – fibers in bundles
 1-40 mm long, 10-100 microns thick
 42% of male body weight, 36% in females


General
sarcoplasm – cytoplasm of muscle fibers
 2. sarcolemma – plasma membrane covering the
muscle fibers
 3. location – any muscle attached to bones as
well as in the tongue, the pharynx, and certain
muscles of the eye
 4. functions – locomotion, posture, transport of
blood and lymph, and heat production (85% of
the body’s heat)
 1.
4
Cardiac Muscle


heart muscle, involuntary
branched fibers & striated
Similar to skeletal muscles
 Involuntary control


purkinje fiber (conduction myofiber)



Stimulate actual contraction of the ventricles
innervation – autonomic nervous system
Functions

Move blood through the heart and through the
vessels
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Smooth Muscle







Involuntary – maintenance of the body’s internal
environment
Nonstriated
Spindle shaped
15-500 microns long
contractions are slow
Location – in the walls of internal organs such as
digestive organs, trachea, gall bladder, blood
vessels, urinary and genital ducts, and the iris of the
eye
Functions – propulsion,expulsion, regulation of
openings, and regulation the diameter of tubes /
blood vessels
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Characteristics of Muscle Tissue

Excitability – ability to receive and respond to
stimuli

Contractility – ability to shorten and thicken

Extensibility – ability to stretch

Elasticity – ability to return to the original
shape
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Skeletal Muscle Tissue

Connective tissue components

Fascia – sheet or broad band of fibrous
connective tissue
superficial – under the skin
 deep – holds the muscles together thus
forming functional groups

Epimysium – fibrous connective tissue
surrounding an entire muscle
 Perimysium – covers a bundle of fibers called
fascicles
 Endomysium – surrounds each muscle fiber
 Aponeurosis –
the tendon that extends as a broad, flat layer
around the skull or as a part of the abs – figure
7-14

8
Connective Tissue Wrappings of
Skeletal Muscle
 Endomysium –
around single
muscle fiber
 Perimysium –
around a
fascicle
(bundle) of
fibers
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Figure 6.1
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Connective Tissue Wrappings of
Skeletal Muscle
 Epimysium –
covers the
entire skeletal
muscle
 Fascia – on the
outside of the
epimysium
Figure 6.1
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10
Nerve and Blood supply

MUST HAVE:

Action Potential – the electric current stimulation
necessary for contraction

Nerve impulse – causes the stimulation

Muscle action potential – the result

Blood to bring nutrients and oxygen, as well as to
carry wastes
 Generally
there is one artery along with 1 or 2
veins to accompany each nerve
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Structure – Skeletal Muscle Fibers





Sarcolemma – coverings
Sarcoplasm – “stuff” inside – many nucleii, and
mitochondria
Sarcoplasmic reticullum – network of tubules
similar to E.R.
Transverse tubules – Perpendicular to the S.R. –
open to exterior of the muscle fiber
Myoglobin – reddish pigment similar to
hemoglobin that carries 02
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Fibers - continued

Myofibrils – Cylindrical structures that run
longitudinally through the fibers and contain:
thin myofilaments – Made mostly of actin
(protein) and small amounts of tropomyosin and
troponin
 thick myofilaments – made mostly of myosin
(protein)

 Shaped
like a golf club
 Heads are called cross-bridges
13
Microscopic Anatomy of Skeletal
Muscle
 Organization of the sarcomere
 Thick filaments = myosin filaments
 Composed of the protein myosin
 Has ATPase enzymes
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Microscopic Anatomy of Skeletal
Muscle
 Organization of the sarcomere
 Thin filaments = actin filaments
 Composed of the protein actin
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More - fibers
Sarcomeres – Basic compartments of
myofilaments – functional unit

“A” bands – dark area composed of overlapping
actin and myosin

“H” bands (zone) – narrow area in the center of
the A band that contains only myosin

“I” bands – contains only actin

“Z” bands – (discs) – dense material between
sarcomeres where the myofilaments attach
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Microscopic Anatomy of Skeletal
Muscle
 Myofibril
 Bundles of myofilaments
 Myofibrils are aligned to give distrinct bands
 I band =
light band
 A band =
dark band
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17
Microscopic Anatomy of Skeletal
Muscle
 Sarcomere
 Contractile unit of a muscle fiber
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18
Microscopic Anatomy of Skeletal
Muscle
 Myosin filaments have heads
(extensions, or cross bridges)
 Myosin and
actin overlap
somewhat
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19
Microscopic Anatomy of Skeletal
Muscle
 At rest, there is a bare zone that lacks
actin filaments
 Sarcoplasmic
reticulum
(SR) – for
storage of
calcium
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20
Muscle Contraction

Sliding filament mechanism –
 The
myofilaments slide inward towards the
center of the sarcomere so the sarcomere
shortens but the myofilaments DO NOT!
Ca2+ and adequate energy are
required (ATP)
 Sufficient
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The Sliding Filament Theory of Muscle
Contraction
 Activation by nerve
causes myosin
heads
(crossbridges) to
attach to binding
sites on the thin
filament
 Myosin heads then
bind to the next site
of the thin filament
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22
The Sliding Filament Theory of Muscle
Contraction
 This continued
action causes a
sliding of the myosin
along the actin
 The result is that the
muscle is shortened
(contracted)
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23
Neuromuscular Junction
(Motor-end plate)

Consists of a motor neuron and the muscle fibers
it stimulates






Precise movements require 10:1 or less fiber to MEP ratio
Gross movements may have as many as 2000:1 ratio
Synaptic vesicles – Sacs at the end of the axon of a
neuron
Synaptic cleft – The space between the axon and the
sarcolemma of the the muscle fiber
Acetylcholine(ACh) – A neurotransmitter that is released as
a result of Ca2+ from the interstitial fluid
+
 Changes the permeability (especially to Na )
 Carries the impulse to receptors on sarcolemma
Cholinesterase(AChE) – found in the synaptic cleft
 Deactivates ACh within 1/500 of a second by breaking it
into acetate and choline thus preventing continuous
stimulation
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Neuromuscular Junction – cont.
25
Physiology of contraction
1. The relaxed muscle is low in Ca2+ because the S.R. has
calcium active pumps to remove it from the sarcoplasm.
2. When the action potential travels along the sarcolemma
Ca2+ channels open in the S.R. and a flood of Ca2+ move
into the sarcoplasm around the thick and thin myofiliments
3. Ca2+ combine with troponin changing it’s shape thus the
troponin –tropomyosin complex move away from the
bonding sites on actin (exposed)
4. ATP attaches to the myosin crossbridges
5. A portion of each myosin head acts as ATPase (enzyme)
which splits ATP into ADP+P
6. The myosin head becomes energized
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Physiology of contraction – cont.
7. This causes the myosin heads to bind to the binding sites on
the the troponin- tropomyosin complex
8. Now the heads pivot causing the “power stroke” of muscle
contraction.
9. As the thin filaments draw past the thick filaments they
release ADP
10. ATP reforms and returns to the myosin crossbridges and the
myosin detaches from the actin . ( about ½ of the crossbrides
are bound and ½ are preparing to bind at any one time)
* * As long as ATP is available and the Ca2+ is high the
contraction will repeat.
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Relaxation

2 changes permit the muscle to relax

ACh is broken by AChE which prevents the action
potential by stopping Ca2+ release

Calcium active transport pumps remove the Ca2+
from the sarcoplasm rapidly
death Ca2+ leaks and causes rigor mortis – no ATP
to release the actin from the myosin
 At
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Energy for muscle contraction

ATP is the immediate energy source but the muscle only
contains enough for 5-6 seconds of sustained activity.

Creatine Phosphate – high energy molecule found in
muscles that can break down into creatine, phosphate, and
energy to form enough ATP to last for 15 more seconds.

Now we must access glucose for energy - respiration
 Glucose is stored as glycogen in the muscle
 Glycogen
is broken into 2 pyruvic acids(glycolysis)
anaerobically (no O2 needed) – this requires 2 ATP but it
produces 4 ATP – 30-40 seconds of energy 29
Energy for muscle contraction
 Pyruvic
acid enters the
mitochondria to be catabolized
into C02 and water – Aerobic (02
required)
 This
is called the Krebs cycle or
the citric acid cycle
 This
will occur 100,000
times/second as long as there is
pyruvic acid and O2 available
 Each
ATP
cycle will produce 36 – 38
30