Human Functional Anatomy 213
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Human Functional Anatomy 213
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SKELETAL MUSCLE
HUMAN FUNCTIONAL ANATOMY 213
Uniarticular muscles and muscle action
Objectives
Muscle fascicles
The grain you can
see in meat
Surrounded by
perimysium
1. To understand the muscles mechanism contraction
2. To relate that to the function and structure of muscles
3. To understand types of muscle contraction
4. Nerve supply of muscles
Muscle fibres
Are the multinucleated cells of
muscle
Surrounded by
endomysium
In this lecture:
Muscle
Length – tension relationship
Architecture
Nerve supply of muscles
Uniarticular muscles
Types of muscle action
Soleus muscle structure and function
Muscle fibres are
composed of
myfibrils
Readings
1. Introductory section on muscle in any anatomy text
2. Sensory receptors in the neurology section of Gray’s
anatomy.
3. Carpenter’s “Human Neuroanatomy. Receptors and
effectors.
4. Grants method of anatomy – section on the shoulder and
arm.
Human Functional Anatomy 213
Whole muscles
Include connective tissue elements such as tendons
Surrounded by epimysium = deep fascia
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Myofibrils are
composed of
myofilaments
The myofilaments
of muscle are the actin and myosine molecules which together make the
functional unit of muscle => THE SARCOMERE
Human Functional Anatomy 213
THE SARCOMERE
MUSCLE ARCHITECTURE
Length – Tension relationship
Length – Tension relationship
Z disc
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H zone
Actin (thin filaments)
Myosin (thick filaments)
Crossbridges on thin filaments
Bond with thick filaments
Generate force which shortens sarcomere (muscle)
Muscles are composed of sarcomeres, so the same properties apply:
A muscle fibre, or fascicle can shorten by about 40%
Whole muscles’ properties depend on the arrangement of muscle fibres
EXAMPLES USING 10 SARCOMERES
1. The strap muscle – many sarcomeres in series (end-to-end)
Can shorten a lot, but is not very strong
As the sarcomere changes length the number of effective crossbridges
changes = LENGTH v TENSION relationship
2. A short, broad muscle has many sarcomeres in
parallel (side-by-side)
It can only shorten a little, but is much
stronger
(It is also very bulky and needs large
attachments)
Tension
(force)
1.0 1.5 2.0 2.5 3.0 3.5 4.0
Length (microns)
The sarcomere has an effective contraction of about 40% of its resting
length
3. A bipennate muscle has fibres arranged around a tendon
It can still only shorten a little but is strong, and compact
Most
attach near joints and so do not need to shorten much
But they do need to be strong.
muscles
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DELTOID MUSCLE
1. CONCENTRIC
The muscle develops sufficient tension to overcome the resistance and
shorten, thus moving a part of the body.
1. The middle part of deltoid is the
only muscle that can abduct the arm
at the glenohumeral joint. The
produce 90o abduction, the deltoid
need only shorten by about 1cm.
Therefore each muscle fibre needs to
be about 2.5cms long.
Eg. The action of brachialis when bringing a glass up towards the
mouth.
In this situation the muscle is the prime mover or agonist
2. ISOMETRIC
The muscle develops tension equal to the opposing force. It does not
change in length and the body part does not move.
However because it is the only muscle that
abducts the arm, middle deltoid needs to
be quite strong, so there are a large
number of muscle fibres arranged around
intermuscular tendons – ie
MULTIPENNATE .
Eg. The action of brachialis holding the glass between drinks.
In this situation the muscle is acting as a stabiliser
3. ECCENTRIC
The muscle develops tension less than the opposing force. The
opposing force overcomes the muscle force and the muscle lengthens.
The part of the body moves against the muscle.
Eg. The action of brachialis when lowering the glass
In this situation the muscle is acting as an antagonist
2. The anterior and posterior parts
The anterior and posterior parts assist in adduction, flexion and
extension of the shoulder. They need to shorten a greater distance, so
the muscle fibres need to be quite long – these parts are STRAP
MUSCLES – they shorten quite a lot but they are not very strong. They
don’t need to be very strong because there are other muscles to assist in
those movements.
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NERVE SUPPLY OF MUSCLES
Muscles have both motor and sensory nerve endings.
The main motor endings are large myelinated nerves that connect to
the muscle fibres at motor end plates (MEP). – Every muscle fibre has
an MEP
Motor units – the nerve fibres that supply the muscle branch and
supply more than one muscle fibre.
Some muscles have small motor units, where each nerve supplies only
a few muscle fibres – these muscles are very precise (eg extra-ocular
muscles).
Other muscles have large motor units where each nerve fibre supplies
many muscle fibres – these muscles have gross actions (eg. Gluteus
maximus).
Sensory nerves of muscles
End in receptors within the muscle or its tendon and provide feedback
about muscle tension and joint position (proprioception). Some
participate in reflexes.
Neuromuscular spindles are
specialised muscles fibres that have
sensory endings that are sensitive to the
length of the muscle. When the muscle
is stretched they send messages back the
spinal cord that trigger a reflex
contraction of the whole muscle. Eg.
Knee-jerk reflex.
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3 TYPES OF MUSCLE ACTION
The Deltoid muscle has three parts.
Each has a different action.
Human Functional Anatomy 213
Human Functional Anatomy 213
SYNERGIST
A muscle acts as a synergist when it prevents the unwanted action of
another muscle. Also called stabilising or neutralising
Eg. When the middle part of deltoid contracts there is a tendency for the
humerus to be pulled up and bump into the underside of the acromion.
The rotator cuff muscles hold the humeral head in place.
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SENSORY NERVES OF MUSCLES
Neuromuscular spindles also have a motor supply that causes little
muscles inside the spindle to contract – thus stretching the sensory
endings. This also causes something like the knee-jerk reflex to
increase stimulation to the whole muscle – MUSCLE TONE. This
prepares the muscle
for action like when
you are in the starting
blocks for a race.
They also increase
muscle tone (tension)
when you are thinking
about the exams!
Golgi tendon organs
These are found in the tendons and are also sensitive to stretching of the
tendon. They work in a protective reflex that switches the muscle off if
the tendon is stretching dangerously.
Pacinian and Ruffini endings are sensitive to pressure and tension.
They are found in the capsules of joints, and provide information about
joint position.
All these sensory nerves (neuromuscular spindles, golgi tendon organs,
Pacinian and Ruffini corpuscles) provide sensory information that does
not reach your consciousness but give feedback to spinal and cerebellar
reflexes.
Free nerve endings
These endings are sensitive to pain and this does reach your
consciousness.
Human Functional Anatomy 213
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Human Functional Anatomy 213
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The SOLEUS MUSCLE
UNIARTICULAR MUSCLES
Uniarticular muscles cross only one joint (eg deltoid)
With Deltoid we found that the muscle fibres
were the right length to move the joint through
the full range of motion of the joint.
SHOULDER
Deltoid
Rotator cuff group
Teres major
Coracobrachialis
We assumed that the same would be the case
for the other uniarticular muscles – like soleus
CALF MUSCLES:
Gastrocnemius crosses the knee and ankle.
Soleus crosses only the ankle.
ELBOW
Triceps (medial and lateral heads)
Brachialis
1. We assumed that it would move the ankle
joint through its full range of motion.
2. The heel (Achilles tendon) moves about
50mm between flexion and extension.
3. So we expected the muscles fibres in
soleus to be about 125mm long
4. But all the muscle fibres in the
soleus muscle are about 30mm
long
5. Therefore they can shorten by
about 12mm
6. So the soleus muscle can only
move the ankle through 24% of its
range
FOREARM
Supinator
Pronator quadratus
HIP
Gluteals
6 lateral rotators
Pectineus
Adductor group
KNEE
Vastus group
Popliteus
ANKLE
Soleus
All other muscles cross more than one joint – they are Biarticular
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SOLEAL ACTION RATIO
Is the percentage of ankle flexion that the soleus can perform by active
contraction.
In humans it is 24% and this
suggests that the soleus is
important for fine tuning
ankle posture. Required for
maintaining balance
The Soleal Action Ratio in
other primates…
Different primates
with different
locomotor styles
Soleal Action Ratio
70
Leapers
60
50
40
30
Quadrupeds
Biped
20
10
0
Homo
Different leverages at
the foot (ie longer
heels for power:
shorter heels for
speed)
Macaca
Lemur
Siamang Gibbon
Langur
Soleal Action Ratio
70
60
50
40
30
20
10
0
0.15
Leapers
Speed
Quadrupeds
Biped
0.2
0.25
0.3
0.35
Heel / Foot ratio
0.4
Power
0.45