RESPIRATORY MOVEMENTS
Respiration occurs in two
phases namely inspiration and expiration. During inspiration, thoracic cage
enlarges and lungs expand so that air enters the lungs easily. During expiration,
the thoracic cage and lungs decrease in size and attain the preinspiratory
position so that air leaves the lungs easily. During normal quiet breathing,
inspiration is the active process and expiration is the passive
process.
MUSCLES OF
RESPIRATION
Respiratory muscles are of
two types:
1. Inspiratory muscles
2. Expiratory muscles.
However, respiratory
muscles are generally classified into two types:
1. Primary or major
respiratory muscles, which are responsible for change in size of thoracic cage
during normal quiet
breathing
2. Accessory respiratory
muscles that help primary respiratory muscles during forced respiration.
Inspiratory Muscles
Muscles involved in inspiratory
movements are known as inspiratory muscles.
Primary
inspiratory muscles
Primary inspiratory
muscles are the diaphragm, which is supplied by phrenic nerve (C3 to C5) and
external intercostal muscles, supplied by intercostal nerves (T1 to T11)
Accessory
inspiratory muscles
Sternocleidomastoid, scalene,
anterior serrati, elevators of scapulae and pectorals are the accessory
inspiratory muscles.
Expiratory Muscles
Primary
expiratory muscles
Primary expiratory muscles
are the internal intercostal muscles, which are innervated by intercostal
nerves.
Accessory
expiratory muscles
Accessory expiratory
muscles are the abdominal muscles.
MOVEMENTS OF THORACIC
CAGE
Inspiration causes enlargement
of thoracic cage. Thoracic cage enlarges because of increase in all
diameters, viz. anteroposterior, transverse and vertical diameters. Anteroposterior
and transverse diameters of thoracic cage are increased by the elevation of
ribs. Vertical diameter is increased by the descent of diaphragm. In general,
change in the size of thoracic cavity occurs because of the movements of four
units of structures:
1. Thoracic lid
2. Upper costal series
3. Lower costal series
4. Diaphragm.
Thoracic Lid
Thoracic lid is formed by manubrium
sterni and the first pair of ribs. It is also called thoracic
operculum.
Movement of thoracic lid
increases the anteroposterior diameter of thoracic cage. Due to the contraction
of scalene
muscles, the first ribs move upwards to a more horizontal position.
This increases the anteroposterior diameter
of upper thoracic cage.
Upper Costal Series
Upper costal series is
constituted by second to sixth pair of ribs. Movement of upper costal series
increases the anteroposterior and transverse
diameter of the thoracic cage.
Movement of upper costal
series is of two types:
i. Pump handle movement
ii. Bucket
handle movement Pump handle movement
Contraction of external
intercostal muscles causes elevation of these ribs and upward and forward
movement of sternum. This movement is called pump handle movement. It increases
anteroposterior diameter of the thoracic cage.
Bucket
handle movement
Simultaneously, the central
portions of these ribs (arches of ribs) move upwards and outwards to a more
horizontal position. This movement is called bucket handle movement and it
increases the transverse diameter of thoracic cage.
Lower Costal Series
Lower costal series includes
seventh to tenth pair of ribs. Movement of lower costal series increases the
transverse
diameter of thoracic cage by bucket handle movement.
Bucket
handle movement
Lower costal series of
ribs also show bucket handle movement by swinging outward and upward. This
movement increases the transverse
diameter of the thoracic cage.
Eleventh
and twelfth pairs of ribs are the floating ribs. These ribs are not involved
in changing the size of
thoracic cage.
Diaphragm
Movement of diaphragm increases
the vertical diameter of thoracic cage. Normally, before inspiration
the diaphragm is dome
shaped with convexity facing upwards. During inspiration, due to the
contraction,
muscle
fibers are shortened. But the central tendinous portion is drawn downwards so
the diaphragm is flattened. Flattening of diaphragm increases
the vertical diameter of the
thoracic cage
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