Download Chapter 7 The Muscular System

Chapter 7 The Muscular
System
Specialized tissue that enable the
body and its parts to move.
Alireza Ashraf, M.D.
Professor of Physical Medicine & Rehabilitation
Shiraz Medical school
Summary
Functions of skeletal muscle
 Structure of skeletal muscle
 Contraction
 Muscles

– Head and neck
– Upper extremity
– Trunk
– Lower extremities

Types of movements
Functions of Skeletal Muscle

Movement – muscle move bones by
pulling not pushing.
– Synergists – any movement is generally
accomplished by more than one muscle. All
of the muscles responsible for a particular
movement are synergists. The one that is
most responsible for the movement is the
Prime Mover.
– Antagonists - muscles and muscle groups
usually work in pairs – example the biceps
flex your arm and its partner, the triceps,
extend your arm. The two muscles are
Functions of Skeletal Muscle

Maintenance of posture or muscle tone
– We are able to maintain our body position because of tonic
contractions in our skeletal muscles. These contractions
don’t produce movement yet hold our muscles in position.

Heat production – contraction of muscles
produces most of the heat required to
maintain body temperature.
Structure of Skeletal Muscle

Composed of striated muscle cells
(=muscle fibers) and connective tissue.
– Tendons anchor muscle firmly to bones.
– Most muscles attach to 2 bones that have a moveable joint
between them.
Structure of Skeletal Muscle

Bursae – small fluid
filled sacs that lie
between some
tendons and the
bones beneath them.
They are made of
connective tissue and
are lined with synovial
membrane that
secretes synovial
fluid.
Figure
Structure of Skeletal Muscle

Contribution of the nervous system
– Electrochemical impulses travel from the
frontal lobes of the cerebrum via motor
nerves to the muscle fibers and cause them to
contract.
– Sensation is a function of the brain – impulses
are integrated in the parietal lobes of the
cerebrum (conscious muscle sense) and in the
cerebellum (unconscious). These activities
promote coordination.
Structure of Skeletal Muscle

Microscopic anatomy
– Muscle cells (fibers) are grouped in a highly organized way
in the muscle. The membrane that surrounds each muscle
cell is called the sarcolemma.
– Muscle cells are filled with 2 types of fine threadlike
proteins called myofilaments:
– The myofilaments are arranged in the cells in small units
called sarcomeres.
Structure of Skeletal Muscle

Neuromuscular junction
– Spot where the axon of a motor nerve nears
the muscle fiber.
– The axon terminal does not touch the muscle
but comes close. The space between the
axon and the muscle cell is called the
synapse.
– Within the terminal end of the axon are small
sacs filled with a neurotransmitter called
acetylcholine.
Muscle Contraction

Sequence
– Electrical impulse travels down a motor neuron. When it
reaches the end, acetylcholine (chemical) is released into
the synapse.
– Acetylcholine binds to special receptors on the muscle cell
and causes an electrical impulse to spread over the cell.
– The sarcomeres shorten and the muscle cell contracts.
– Excess acetylcholine is destroyed by acetylcholinesterase.
*Myesthenia gravis
Muscle Contraction
Muscles contract only when the stimulus
from the motor neuron is strong enough =
Threshold stimulus is the minimum level
of stimulation necessary to cause a
contraction.
 Additional stimuli arriving rapidly cause an
increase in the force of the muscle
contraction.
 Botox

Types of Skeletal Muscle Contraction
Twitch –
 Tetanic –

*Tetanus
 Isotonic contraction –
 Isometric contraction –

Energy for Contraction
Muscles require energy in the form of ATP
to contract. ATP is produced by aerobic
respiration.
 Secondary sources

– Creatine phosphate stored in the muscle is
broken down to produce more ATP.
– Glycogen stored in the muscle and liver is
broken down into glucose which is broken
down to produce ATP. This process requires
O2.
Energy for Contraction
O2 is transported to the muscle by the
circulatory system (hemoglobin in RBCs).
Some O2 is stored in the muscle by
myoglobin.
 Strenuous exercise can cause the muscles
to “run out” of O2 resulting in oxygen
debt. Glucose is only partially broken
down to lactic acid which causes muscle
fatigue.

Movements Produced by Muscle Contractions
Flexion – movement reduces the angle
between two bones at their joint.
 Extension – opposite of flexion – increases
the angle at a joint.
 Abduction – moving a body part away
from the midline of the body.
 Adduction – moving a body part toward
the midline of the body.
 Rotation – movement of a body part
around an axis.

Movements Produced by Muscle Contractions
Supination – refers to hand position –
movement turns palm up to the anterior
position (anatomical position).
 Pronation – palm of hand turned
posteriorly.
 Dorsiflexion – top of foot is elevated with
toes pointing upward.
 Plantar flexion – foot directed downward
(standing on your toes).

Muscles

Head and Neck
– Frontal (frontalis) – over the frontal skull bone
raise your eyebrows.
– Orbicularis oculi – closes the eye.
– Orbicularis oris – around the mouth; kissing
muscle.
– Masseter – elevates mandible allowing use to
close our mouth and chew food.
– Temporal (temporalis) – assists the masseter
in closing the jaw.
Muscles

Head and neck
– Sternocleidomastoid – flexes the head toward
the chest.
– Trapezius – helps elevate, lower, and adducts
the shoulders (scapula) and extend the head
backwards.
Muscles

Upper extremities
– Pectoralis major – upper anterior chest; flexor of the upper
arm
– Latissimus dorsi – extensor of the upper arm.
– Deltoid – powerful abductor of the upper arm.
– Biceps Brachii – 2-headed muscle that serves as the
primary flexor of the forearm.
– Triceps brachii – 3 headed muscle on the posterior surface
of the upper arm; extensor of the elbow/forearm.
Muscles

Trunk
– Anterior abdomen – 3 layers of muscles whose fibers run
in different directions – girdle effect.
 External oblique – outermost layer
 Internal oblique – middle layer
 Transversus abdominis – innermost layer
– Rectus abdominus runs down the midline of the abdomen
from the thorax to the pubis. (6-pack)
– Respiratory muscles
 Intercostal muscles – between the ribs
 Diaphragm – separates the thoracic and abdominal
cavities.
Muscles

Lower Extremities
– Gluteus maximus – forms the buttock;
extensor of the thigh, supports the torso.
– Gluteus medius – abducts the femur; injection
site.
– Hamstring muscles – flexors of the lower leg
 Semimembranosus
 Semitendinosus
 Biceps femoris
Muscles

Lower extremities
– Quadriceps femoris – covers the upper thigh,
extends the leg.
 Rectus femoris
 Vastus lateralis – injection site
 Vastus medialis
 (Vastus intermedius)
– Tibialis anterior – dorsiflexes the foot
– Gastocnemius – primary calf muscle, plantar
flexion of the foot.
Intramusclular Injection Sites
Deltoid
 Gluteus medius
 Vastus lateralis
