The Skeletal and Muscular Systems
LECTURE NOTES
Axial skeleton
skull (cranium and facial bones)
hyoid bone (anchors tongue and muscles
associated with swallowing)
vertebral column (vertebrae and disks)
thoracic cage (ribs and sternum)
Appendicular skeleton
pectoral girdle (clavicles and scapulae)
upper limbs (arms)
pelvic girdle (coxal bones, sacrum, coccyx)
lower limbs (legs)
The Human Skeleton
1. Carpals
2. Cranium
1. Clavicle
3. Femur
2. Fibula
4. Innominate
3. Humerus
5. Mandible
4. Patella
6. Metacarpals
5. Radius
7. Metatarsals
6. Sternum
8. Phalanges
7. Tarsals
9. Rib
8. Tibia
10. Scapula
9. Ulna
11. Sacrum
12. Vertebra
What are the Five main functions of the human
skeleton
1. Protect the vital organs we talked about last week
2. Give us shape
3. Allow us to move because our muscles
are attached to our bones
4. Storage of nutrients such as calcium and silicon
5. Formation of blood cells
Classification of Bones on the
Basis of Shape
Types of Bone Cells
 Osteocytes Mature bone
Osteoblasts(remove calcium from blood and build
new matrix. They become trapped
osteoclasts)
Bone-forming cells
•Osteoclasts remove damaged cells and release
calcium into blood (Bone-destroying cells)
 Break down bone matrix for remodeling and release of
calcium
 Bone remodeling is a process by both osteoblasts and
osteoclasts
Interesting Facts about the Skeletal System
• Do we have more bones when we are a baby or when we are all grown up?
Baby has 305 bones and an adult has 206 bones. This is because as we grown some of our
bones join together to form one bone.
• The longest bone in our bodies is the femur (thigh bone).
• The smallest bone is the stirrup bone inside the ear.
• Each hand has 26 bones in it.
• our nose and ears are not made of bone; they are made of cartilage, a flexible substance that
is not as hard as bone.
Compact bone
osteocytes within lacunae
arranged in concentric circles called lamellae
This surround a central canal; complex is called
Haversian system
Canaliculi connect osteocytes to central canal and
to each other
Structures Associated with the
Synovial Joint
 Bursae – flattened fibrous sacs
 Lined with synovial membranes
 Filled with synovial fluid
 Not actually part of the joint
 Tendon sheath
 Elongated bursa that wraps around a tendon
Types of Joints
Hinge- A hinge joint allows extension and
retraction of an appendage. (Elbow, Knee)
Types of Synovial Joints Based on
Shape
Types of Synovial Joints Based on
Shape
Types of freely movable joints
Saddle: carpal and metacarpal bones of thumb
Ball and socket: shoulder and hip joints
Pivot- rotation only: proximal end of radius and ulna
Hinge- up and own movement in one plane:
knee and elbow
Gliding- sliding and twisting: wrist and ankle
Condyloid- movement in different planes but not
rotations: btw metacarpals and phalanges
Ball and Socket- A ball and socket joint
allows for radial movement in almost
any direction. They are found in the hips
and shoulders. (Hip, Shoulder)
Gliding- In a gliding or plane joint bones
slide past each other. Mid-carpal and midtarsal joints are gliding joints. (Hands,
Feet)
Saddle- This type of joint occurs when the
touching surfaces of two bones have both
concave and convex regions with the
shapes of the two bones complementing
one other and allowing a wide range of
movement. (Thumb)
Types of movement and examples (with muscles)
flexion- move lower leg toward upper
extension- straightening the leg
abduction- moving leg away from body
adduction- movong leg toward the body
rotation- around its axis
supination- rotation of arm to palm-up position
pronation- palm down
circumduction- swinging arms in circles
inversion- turning foot so sole is inward
eversion- sole is out
Elevation and depression- raising body part up
or down
Aging and bones
both bone and cartilage tend to deteriorate
cartilage: chondrocytes die, cartilage
becomes calcified
osteoporosis
bone is broken down faster
than it can be built
bones get weak and brittle; tend to fracture
easily
Risk factors for osteoporosis
Inadequate calcium
Little weight-bearing exercise
Drinking alcohol, smoking
Being female: decreased estrogen secretion
after menopause
Types of bone breaks
Simple- skin is not pierced
Compound- skin is pierced
Complete- bone is broken in half
Partial- broken lengthwise but not into two
parts
Greenstick- incomplete break on outer arc
Comminuted- broken into several pieces
Spiral- twisted
Arthritis
Osteoporosis
• Osteoporosis is a term that means
"porous bones.”.
• Osteoporosis is a condition in which
bones have lost minerals especially
calcium, making them weaker, more
brittle, and susceptible to fractures
(broken bones).,
• the most common places where fractures
occur are the back (spine), hips, and
wrists.
Scurvy
• We depends on exogenous dietary sources
to meet vitamin C needs.
• Consumption of fruits and vegetables or
diets fortified with vitamin C are essential to
avoid ascorbic acid deficiency.
• Even though scurvy is uncommon, it still
occurs and can affect adults and children
who have chronic dietary vitamin C
deficiency.
Bursitis
• Inflammation of the Bursa (fluid
filled sac surrounding the joint).
• A bursa can become inflamed from
injury, infection (rare in the
shoulder), or due to an underlying
rheumatic condition.
• Bursitis is typically identified by
localized pain or swelling,
tenderness, and pain with motion of
the tissues in the affected area.
Skeleton and other systems
Skin makes vitamin D which enhances calcium
absorption
Skeleton stores calcium for muscle contraction,
nervous stimulation, blood clot formation
Red marrow- site of blood cell formation
Calcium levels regulated by
parathyroid hormone and calcitonin
kidneys (can help provide vitamin D)
digestive system (can release calcium
into blood
Muscular System Functions
• Body movement (Locomotion)
• Maintenance of posture
• Respiration
– Diaphragm and intercostal contractions
• Communication (Verbal and Facial)
• Constriction of organs and vessels
– Peristalsis of intestinal tract
– Vasoconstriction of b.v. and other structures (pupils)
• Heart beat
• Production of body heat (Thermogenesis)
Properties of Muscle
• Excitability: capacity of muscle to respond
to a stimulus
• Contractility: ability of a muscle to shorten
and generate pulling force
• Extensibility: muscle can be stretched back
to its original length
• Elasticity: ability of muscle to recoil to
original resting length after stretched
Interesting facts about the Muscular System
• Muscle: A tissue composed of fibers capable of
contracting to effect bodily movement
• There are about 650 muscles in the human
body.
Some Muscles
1. Gastrocnemius
2. Sartorius
3. Deltoid
4. Sternocleidomastoid
5. Tibialis
6. Hamstring group
7. Rectus Abdominus
8. Triceps
9. Biceps
10. Extensor Group
Types of muscles
Skeletal muscles:
Attached to bones. (what happens
when you extend your arm?)
Tendons
Muscle
Smooth muscle:
Surround organs, tubes, eg. stomach,
urinary bladder, blood vessels. Contract
propels content through organs (eg.
expel urine).
Cardiac muscles:
Heart muscle makes your heart pump
blood.
Muscle
fibre
Blood vessel
Connective
tissue
Muscle Classification
Functionally
1. Voluntarily
2. Involuntarily
Structurally
1. Striated
2. Smooth
Combined
1. Visceral
2. Cardiac
3. Skeletal
Nerve and Blood Vessel Supply
• Motor neurons
– stimulate muscle fibers to contract
– Neuron axons branch so that each muscle fiber (muscle cell) is
innervated
– Form a neuromuscular junction (= myoneural junction)
• Capillary beds surround muscle fibers
– Muscles require large amts of energy
– Extensive vascular network delivers necessary oxygen and
nutrients and carries away metabolic waste produced by
muscle fibers
Basic Features of a Skeletal Muscle
• Muscle attachments
– Most skeletal muscles
run from one bone to
another
– One bone will move –
other bone remains fixed
• Origin – less movable
attach- ment
• Insertion – more
movable attachment
Basic Features of a Skeletal Muscle
• Muscle attachments (continued)
– Muscles attach to origins and insertions by
connective tissue
• Fleshy attachments – connective tissue fibers are short
• Indirect attachments – connective tissue forms a
tendon or aponeurosis
– Bone markings present where tendons meet
bones
• Tubercles, trochanters, and crests
Skeletal Muscle Structure
• Composed of muscle cells (fibers),
connective tissue, blood vessels, nerves
• Fibers are long, cylindrical, and
multinucleated
• Tend to be smaller diameter in small
muscles and larger in large muscles. 1
mm- 4 cm in length
• Develop from myoblasts; numbers
remain constant
• Striated appearance
• Nuclei are peripherally located
Muscle Fiber Anatomy
•
•
Sarcolemma - cell membrane
– Surrounds the sarcoplasm (cytoplasm of fiber)
• Contains many of the same organelles seen in other cells
• An abundance of the oxygen-binding protein myoglobin
– Punctuated by openings called the transverse tubules (T-tubules)
• Narrow tubes that extend into the sarcoplasm at right angles to the
surface
• Filled with extracellular fluid
Myofibrils -cylindrical structures within muscle fiber
– Are bundles of protein filaments (=myofilaments)
• Two types of myofilaments
1. Actin filaments (thin filaments)
2. Myosin filaments (thick filaments)
– At each end of the fiber, myofibrils are anchored to the inner surface of
the sarcolemma
– When myofibril shortens, muscle shortens (contracts)
Sarcoplasmic Reticulum (SR)
• SR is an elaborate, smooth endoplasmic reticulum
– runs longitudinally and surrounds each myofibril
– Form chambers called terminal cisternae on either side
of the T-tubules
• A single T-tubule and the 2 terminal cisternae form
a triad
• SR stores Ca++ when muscle not contracting
– When stimulated, calcium released into sarcoplasm
– SR membrane has Ca++ pumps that function to pump
Ca++ out of the sarcoplasm back into the SR after
contraction
Sarcoplasmic Reticulum (SR)
Parts of a Muscle
•
Sarcomeres: Z
Disk to Z Disk
Sarcomere - repeating functional units of a
myofibril
– About 10,000 sarcomeres per myofibril, end
to end
– Each is about 2 µm long
•
Differences in size, density, and distribution
of thick and thin filaments gives the muscle
fiber a banded or striated appearance.
– A bands: a dark band; full length of thick
(myosin) filament
– M line - protein to which myosins attach
– H zone - thick but NO thin filaments
– I bands: a light band; from Z disks to ends of
thick filaments
• Thin but NO thick filaments
• Extends from A band of one sarcomere to A
band of the next sarcomere
– Z disk: filamentous network of protein. Serves
as attachment for actin myofilaments
– Titin filaments: elastic chains of amino acids;
keep thick and thin filaments in proper
alignment
Structure of Actin and Myosin
Sarcomere
Z
A
Z
A
Z
A (I)
I
Z
Z
Z
Myofilaments
1. Myosin: 110Å thick; confined to the
A-band. (Mole. wt. 500,000 deltons; 200
molecules/myofilament)
A. Tail- 800Å long, composed of a double helix
B. Head (cross bridges)-600Å terminating in a
globular double structure. Contains binding sites
for actin & ATP
Myofilaments
2. Actin: 60A thick; runs from Z-line (disc) to just
inside A-band. Mole wt. 60,000 deltons.
G-actin (globular units): contracted form
F-actin (fibrous polymers): relaxed form
Actin associated proteins
A. Tropomyosin
B. Troponin
Neuromuscular Junction
• Region where the motor neuron stimulates the muscle
fiber
• The neuromuscular junction is formed by :
1. End of motor neuron axon (axon terminal)
• Terminals have small membranous sacs (synaptic vesicles)
that contain the neurotransmitter acetylcholine (ACh)
2. The motor end plate of a muscle
• A specific part of the sarcolemma that contains ACh receptors
• Though exceedingly close, axonal ends and muscle fibers
are always separated by a space called the synaptic cleft
Neuromuscular Junction
Motor Unit: The Nerve-Muscle
Functional Unit
• A motor unit is a motor neuron and all the
muscle fibers it supplies
• The number of muscle fibers per motor unit can
vary from a few (4-6) to hundreds (1200-1500)
• Muscles that control fine movements (fingers,
eyes) have small motor units
• Large weight-bearing muscles (thighs, hips) have
large motor units
Motor Unit: The Nerve-Muscle Functional Unit
Mechanics of Muscle Contraction
1. An action potential is generated by a motor
nerve.
2. This causes the release of acetylcholine from
the axon terminals at the neuromuscular
junctions.
3. This Ach causes an increase in membrane
permeability at the motor-end plate, causing
the production of an end-plate potential
(EPP).
Mechanics of Muscle Contraction
4. The EPP depolarizes the fiber membrane
(sarcolemma) causing a muscle action
potential which spreads over the entire
surface of the fiber membrane.
5. This depolarizes the T-tubules, causing ionic
conduction through their extracellular fluid,
and the release of inositol triphosphate as a
second messenger.
Mechanics of Muscle Contraction
6. Ca++ is then released from the endoplasmic
reticular fluid of the cisterns (lateral sacs) into the
surrounding myofibril.
7. Ca++ binds to the actin associated protein
troponin, allowing the attachment of actin to the
myosin-ATP complex to form a strong ATPase.
8. The ATPase splits ATP, releasing the energy
needed for the movement of the myosin cross
bridges.
Mechanics of Muscle Contraction
9. Energy from creatine phosphate replaces ADP
on the myosin cross bridges, thereby breaking
the A-M bond and allowing the cross bridges
to relax.
10. The Ca++ are forced back into the walls of
the longitudinal tubules by active transport.
11. This restores the inhibitory action of the
troponin-tropomyosin complex.
A
I
H
Z
Muscle Energy
• Hold two books above your head for as
long as you can…..
• How is the muscle able to do this?
Where does it get its energy from?
• When your exercising how does this
process change?
•Muscle needs energy to move just as we do.
•Its energy can run out and needs to be replenished
•Muscle gets its energy from the oxygen we breathe and
the food we eat.
•Muscle stores its food in the muscle fibres themselves.
This food is called glycogen and is a type of sugar.
•When we exercise, these stores are used to make
energy and can run out.
•We need to replenish our muscle food stores by eating
carbohydrates
Selective Terms
1. Motor Unit: consists of all the muscle fibers innervated by
terminals from a single axon.
(Range from 23 - 2,000 fibers)
2. All or None Law: at or above threshold levels; the degree of
contractile response of a single muscle fiber (or motor unit) is
independent of stimulus strength
3. Tension: force exerted by a contracting muscle
4. Load: force exerted on a muscle by the weight of an object
5. Isotonic contraction (same tension): the tension developed by
the contracting is greater than the load. Therefore, the muscle
shortens.
Selective Terms
6. Isometric contraction (same length): the strength of the
load is greater than the tension of the muscle. Therefore,
the muscle remains at the same length.
7. Muscle spindle apparatus: a series of small spindle
shaped fibers within the muscle for detecting changes in
the length (stretch) of the muscle.
8. Golgi tendon organ: tension receptors located in tendons,
and activated by the pull of a contracting muscle