2. TOPICS TO BE COVERED
BONES
JOINTS
MUSCLES
PARTS OF RESPIRATORY SYSTEMS
TYPES OF RESPIRTAION
MECHANISM OF BREATHING
REGULATION OF RESPIRATION
3. BONES
TYPES OF BONES & FUNCTION
PHYSIOLOGY OF BONE
FORMATION
DIVISION OF SKELETON
4. The word skeleton comes from the Greek word meaning “dried-up body,” our
internal framework is beautifully formed and proportioned
The bones of the skeleton are part of the skeletal system, which also includes
joints, cartilages, and ligaments
270 to 206
The skeleton is divided into two parts:
axial skeleton
appendicular skeleton
6. FUNCTIONS OF BONES:
Support:
Form the internal framework that supports the body and cradles its soft organs.
The bones of the legs act as pillars to support the body trunk when we stand, and the
rib cage supports the thoracic wall
Protection:
Bones protect soft body organs. For example, the fused bones of the skull provide a
snug enclosure for the brain.
Allow movement:
Skeletal muscles, attached to bones by tendons, use the bones as levers to move the
body and its parts.
7. Storage:
Fat is stored in the internal (marrow) cavities of bones. Bone itself serves as a
storehouse for minerals, the most important of which are calcium and phosphorus
Blood cell formation:
Blood cell formation, or hematopoiesis occurs within the marrow cavities of certain
bones
8. TYPES OF BONES:
There are two basic types of osseous, or bone, tissue:
Compact bone dense and looks smooth and homogeneous
Spongy bone spiky, open appearance like a sponge
9. Bones are classified according to shape into four groups:
long
short
flat
irregular
10. LONG BONE:
Long bones are typically longer than they are wide.
As a rule, they have a shaft with enlarged ends.
Long bones are mostly compact bone but also contain spongy
bone at the ends.
All the bones of the limbs, except the patella (kneecap) and the
wrist and ankle bones, are long bones.
11. SHORT BONE:
Short bones are generally cube-shaped and contain mostly
spongy bone with an outer layer of compact bone.
The bones of the wrist and ankle are short bones.
Sesamoid bones, which form within tendons, are a special type
of short bone.
The best-known example is the patella
12.
13. FLAT BONE:
Flat bones are thin, flattened, and usually curved.
They have two thin layers of compact bone
sandwiching a layer of spongy bone between them
Most bones of the skull, the ribs, and the sternum are
flat bones.
14. IRREGULAR BONE:
Bones that do not fit one of the preceding categories
are called irregular bones.
The vertebrae, which make up the spinal column, fall
into this group.
Like short bones, they are mainly spongy bone with an
outer layer of compact bone.
15. STRUCTURES OF LONG BONE:
The epiphyses are the ends of long bones consists of a thin layer of
compact bone enclosing an area filled with spongy bone
The diaphysis or shaft, makes up most of the bone’s length and is
composed of compact bone
The diaphysis is covered and protected by a fibrous connective tissue
membrane, the periosteum
In adult bones, there is a thin line of bony tissue spanning the
epiphysis is the epiphyseal line
The epiphyseal plate (a flat plate of hyaline cartilage) seen in a
young, growing bone cause the lengthwise growth of a long bone
16. The inner bony surface of the shaft is covered by a delicate connective tissue
called endosteum.
In infants, the cavity of the shaft, called the medullary cavity, is a storage area for
red marrow, which produces blood cells.
Children’s bones contain red marrow until the age of 6 or 7, when it is gradually
replaced by yellow marrow, which stores adipose (fat) tissue.
In adult bones, red marrow is confined to cavities in the spongy bone of the axial
skeleton, the hip bones, and the epiphyses of long bones such as the humerus and
femur
17. BONE FORMATION:
The skeleton is formed from two of the strongest and most supportive tissues in
the body
Cartilage
Bone
In embryos, the skeleton is primarily made of hyaline cartilage, but in young
children, most of the cartilage has been replaced by bone.
Cartilage remains only in isolated areas such as the bridge of the nose, parts of
the ribs, and the joints.
18. The process of bone formation, or ossification involves two major phases
The hyaline cartilage model is completely covered with bone matrix by bone-building cells called osteoblasts
In the fetus, the enclosed hyaline cartilage model is replaced by bone, and the center is digested away, opening up a
medullary cavity within the newly formed bone
19. By birth or shortly after, most hyaline cartilage models have been converted to
bone except for two regions—the articular cartilages (that cover the bone ends)
and the epiphyseal plates.
In order for bones to increase in length as the infant grows into a child, new
cartilage is formed continuously on the external face (joint side) of the articular
cartilage and on the epiphyseal plate surface that faces the bone end
At the same time, the old cartilage abutting the internal face of the articular
cartilage and the medullary cavity is broken down and replaced by bony matrix
20. Growing bones also widen as they lengthen to maintain proper proportion
Osteoblasts in the periosteum add bone matrix to the outside of the diaphysis as
cells called osteoclasts in the endosteum remove bone from the inner face of the
diaphysis wall, enlarging the medullary cavity.
Because these two processes occur at about the same rate, the circumference of
the long bone expands, and the bone widens and the process by which bones
increase in diameter is called appositional growth
The growth in length, is controlled by hormones and most important hormones
are growth hormone and, during puberty, the sex hormones.
It ends during adolescence, when the epiphyseal plates are completely converted
to bone.
21. BONE REMODELLING:
Bones are remodeled continually in response to changes in two factors:
(1) The calcium ion level in the blood
(2) The pull of gravity and muscles on the skeleton
22. When the blood calcium ion level drops below
its homeostatic level
The parathyroid glands are stimulated
Releases parathyroid hormone (PTH) into the
blood.
PTH activates osteoclasts, giant bone-
destroying cells in bones, to break down bone
matrix
Release calcium ions into the blood
When the blood calcium ion level is
too high (hypercalcemia)
Osteoblastic activity
Calcium is deposited in bone matrix
as hard calcium
23. Bone remodeling is essential if bones are to retain normal proportions and
strength during long-bone growth as the body increases in size and weight.
It also accounts for the fact that bones become thicker and form large projections
to increase their strength in areas where bulky muscles are attached.
At such sites, osteoblasts lay the down new matrix and become trapped within it.
Once they are trapped, they become osteocytes, or mature bone cells.
In contrast, the bones of bedridden or physically inactive people tend to lose mass
and to atrophy because they are no longer subjected to stress.
24.
25. These two controlling mechanisms—calcium uptake and release as well as bone
remodeling work together.
PTH determines when bone is to be broken down or formed in response to the
need for more or fewer calcium ions in the blood.
The stresses of muscle pull and gravity acting on the skeleton determine where
bone matrix is to be broken down or formed so that the skeleton can remain as
strong and vital as possible.
26. PATHOANATOMY OF BONES:
RICKETS:
Rickets is a disease of children in which the bones fail to calcify.
As a result, the bones soften, and the weight-bearing bones of the legs become bowed.
Rickets is usually due to a lack of calcium in the diet or lack of vitamin D, which is
needed to absorb calcium into the bloodstream
27. FRACTURES:
Despite their remarkable strength, bones are susceptible to fractures, or breaks
A fracture in which the bone breaks cleanly but does not penetrate the skin is a
closed (or simple) fracture.
When the broken bone ends penetrate through the skin, the fracture is open (or
compound).
A fracture is treated by reduction, which is the realignment of the broken bone
ends, followed by immobilization
28. The repair of bone fractures involves four major events :
Hematoma forms
Fibrocartilage callus forms
Bony callus forms
Bone remodeling occur
29. DIVISION OF SKELETON SYSTEM:
The skeleton is divided into two parts:
axial skeleton
appendicular skeleton
30. AXIAL SKELETON:
The axial skeleton forms the longitudinal axis of the
body
It can be divided into three parts:
the skull
the vertebral column
the thoracic cage
31. SKULL:
The skull is formed by two sets of bones.
Cranium
Facial bones
The cranium encloses and protects the fragile brain tissue.
The facial bones form a cradle for the eyes that is open to the anterior and allow the facial muscles to show
our feelings through smiles or frowns.
All but one of the bones of the skull are joined together by sutures, which are interlocking, immovable joints.
Only the mandible (jawbone) is attached to the rest of the skull by a freely movable joint.
32. CRANIUM:
The boxlike cranium is composed of eight large flat bones
Frontal Bone The frontal bone forms the forehead, the
bony projections under the eyebrows, and the superior part
of each eye’s orbit.
33. Parietal Bones The paired parietal bones form most
of the superior and lateral walls of the cranium. The
sagittal suture is formed at the midline where the two
parietal bones meet and the coronal suture is formed
where the paired parietal bones meet the frontal
bone.
34. Temporal Bones The temporal bones lie inferior
to the parietal bones and join them at the squamous
the squamous sutures.
Several important bone markings:
external acoustic meatus
styloid process
zygomatic process
mastoid process
jugular foramen
35. Occipital Bone The occipital bone is the most posterior bone of the cranium.
It forms the base and back wall of the skull.
The occipital bone joins the parietal bones anteriorly at the lambdoid suture.
In the base of the occipital bone is a large opening, the foramen magnum
(literally, “large hole”).
The foramen magnum surrounds the lower part of the brain and allows the spinal
cord to connect with the brain. Lateral to the foramen magnum on each side are
the rockerlike occipital condyles, which rest on the first vertebra of the spinal
column
36.
37. Sphenoid Bone The butterfly-shaped sphenoid bone
spans the width of the skull and forms part of the floor of
the cranial cavity
Ethmoid Bone The ethmoid bone is very irregularly
shaped and lies anterior to the sphenoid. It forms the roof
of the nasal cavity and part of the medial walls of the
orbits.
38. FACIAL BONES:
Fourteen bones make up the face. Twelve are paired; only the mandible and vomer are single
Maxillae The two maxillae or maxillary bones, fuse to form the upper jaw. All facial bones except the mandible
join the maxillae
Palatine Bones The paired palatine bones lie posterior to the palatine processes of the maxillae. They form
the posterior part of the hard palate
Zygomatic Bones The zygomatic bones are commonly referred to as the cheekbones. They also form a good-
sized portion of the lateral walls of the orbits.
Lacrimal Bones The lacrimal bones are fingernail-sized bones forming part of the medial wall of each orbit.
Each lacrimal bone has a groove that serves as a passageway for tears
39.
40. Nasal Bones The small rectangular bones forming the bridge of the nose are the nasal bones
Vomer Bone The single bone in the median line of the nasal cavity is the vomer. The vomer forms the inferior
part of the bony nasal septum, which separates the two nostrils
Inferior Nasal Conchae The inferior nasal conchae are thin, curved bones projecting medially from the lateral
walls of the nasal cavity
Mandible The mandible, or lower jaw, is the largest and strongest bone of the face. It joins the temporal bones
on each side of the face, forming the only freely movable joints in the skull
41. HYOID BONE:
Though not really part of the skull, the hyoid bone is closely related to the mandible and temporal
bones.
The hyoid bone is unique in that it is the only bone of the body that does not articulate (form a
joint) with any other bone.
Instead, it is suspended in the midneck region about 2 cm (1 inch) above the larynx (voicebox),
where it is anchored by ligaments to the styloid processes of the temporal bones.
Horseshoe-shaped, with a body and two pairs of horns, the hyoid bone serves as a movable base
for the tongue and as an attachment point for neck muscles that raise and lower the larynx when
we swallow and speak
42.
43. VERTEBRAL COLUMN:
The vertebral column, or spine, extends from the skull, which it supports, to the
pelvis, where it transmits the weight of the body to the lower limbs
The spine is formed from 26 irregular bones connected and reinforced by
ligaments
Before birth, the spine consists of 33 separate bones called vertebrae, but 9 of
these eventually fuse to form the two composite bones, the sacrum and the
coccyx
Of the 24 single bones, the 7 vertebrae of the neck are cervical vertebrae, the next
12 are the thoracic vertebrae, and the remaining 5 supporting the lower back are
lumbar vertebrae.
44.
45. INTERVERTEBRAL DISCS:
The individual vertebrae are separated by pads of flexible fibrocartilage—
intervertebral discs— that cushion the vertebrae and absorb shock while allowing
the spine flexibility.
In a young person, the discs have a high water content (about 90 percent) and are
spongy and compressible.
But as a person ages, the water content of the discs decreases (as it does in other
tissues throughout the body), and the discs become harder and less compressible
46. CURVATURES:
The spinal curvatures in the thoracic and sacral regions are referred to as primary
curvatures because they are present when we are born.
Together the two primary curvatures produce the C-shaped spine of the newborn
baby.
The curvatures in the cervical and lumbar regions are referred to as secondary
curvatures because they develop some time after birth.
In adults, the secondary curvatures allow us to center our body weight on our
lower limbs
47. All vertebrae have a similar structural pattern. The common features of vertebrae include the
following:
Body, or centrum: disc like, weight-bearing part of the vertebra facing anteriorly in the vertebral column.
Vertebral arch: arch formed from the joining of all posterior extensions, the laminae and pedicles, from the
vertebral body.
Vertebral foramen: canal through which the spinal cord passes.
Transverse processes: two lateral projections from the vertebral arch.
Spinous process: single projection arising from the posterior aspect of the vertebral arch (actually the fused
laminae).
Superior articular process and inferior articular process: paired projections lateral to the vertebral foramen,
allowing a vertebra to form joints with adjacent vertebrae.
48.
49. THORACIC CAGE:
The sternum, ribs, and thoracic vertebrae make up the
bony thorax which is routinely called the thoracic cage.
STERNUM:
The sternum (breastbone) is a typical flat bone and the
result of the fusion of three bones—the manubrium,
body, and xiphoid process. It is attached directly to the
first seven pairs of ribs via costal cartilages.
The sternum has three important bony landmarks—
the jugular notch
the sternal angle
the xiphisternal joint
50. RIBS:
Twelve pairs of ribs form the walls of the bony thorax.
All the ribs articulate with the vertebral column posteriorly and then curve downward and
toward the anterior body surface.
True ribs the first seven pairs, attach directly to the sternum by costal cartilages.
False ribs the next five pairs, either attach indirectly to the sternum or are not attached to the
sternum at all.
Floating ribs The last two pairs of false ribs lack the sternal attachments, so they are also
called floating ribs.
The intercostal spaces spaces between the ribs, filled with the intercostal muscles, which aid
in breathing.
51.
52. APPENDICULAR SKELETON:
The appendicular skeleton is composed of 126 bones of the limbs (appendages)
The pectoral and pelvic girdles, which attach the limbs to the axial skeleton.
58. Joints, also called articulations, are the sites where two or more bones meet.
They have two functions: They hold the bones together securely but also give the
rigid skeleton mobility
Stability
Mobility
Joints are classified in two ways
functionally
structurally
61. STRUCTURALLY:
These classifications are based on whether fibrous tissue, cartilage, or a joint cavity
separates the bony regions at the joint.
As a general rule, fibrous joints are immovable, and synovial joints are freely
movable and cartilaginous joints have both immovable and slightly movable
62. FIBROUS JOINT:
In fibrous joints, the bones are united by fibrous tissue.
Three types:
Sutures eg. the sutures of the skull
Gomphoses eg. “peg-in-socket” fibrous joints that are found where the teeth
Syndesmoses eg. the distal ends of the tibia and fibula is a syndesmosis
63. CARTILAGINOUS JOINT:
Cartilaginous joints come in two varieties, which differ in the type of cartilage
involved.
Synchondroses are immoveable joints linked by hyaline cartilage. Examples include the
epiphyseal plates of growing long bones and the joints between ribs 1–7 and the
sternum
Symphyses are slightly moveable joints linked by discs of fibrocartilage. Examples
include the intervertebral discs of the spinal column and the pubic symphysis of the
pelvis
64. SYNOVIAL JOINT:
Synovial joints are joints in which the articulating bone ends are separated by a
joint cavity containing synovial fluid
All joints of the limbs are synovial joints.
65. Features of synovial joint:
Articular cartilage: Articular (hyaline) cartilage covers the ends of the bones
forming the joint.
Articular capsule: The joint surfaces are enclosed by a sleeve, or layer, of fibrous
connective tissue, which is lined with a smooth synovial membrane (the reason
these joints are called synovial joints).
Joint cavity: The articular capsule encloses a cavity, called the joint cavity, which
contains lubricating synovial fluid secreted by the synovial membrane
Reinforcing ligaments: The fibrous layer of the capsule is usually reinforced with
ligaments.
66. Types of synovial joint:
The shapes of the articulating bone surfaces determine what movements are allowed at a
joint.
Based on such shapes, our synovial joints can be classified as :
plane
Hinge
pivot
condylar
saddle
ball-and-socket joints.
67.
68. PLANE
In a plane joint, the articular surfaces are essentially flat, and only short slipping or
gliding movements are allowed.
The movements of plane joints are nonaxial; that is, gliding back and forth does
not involve rotation around any axis.
Example: The intercarpal joints of the wrist
69. HINGE
In a hinge joint, the cylindrical end of one bone fits into a trough-shaped surface
on another bone.
Angular movement is allowed in just one plane, like a door hinge.
Hinge joints are classified as uniaxial they allow movement around one axis
only
Examples: elbow joint, ankle joint, and the joints between the phalanges of the
fingers.
70. PIVOT
In a pivot joint, the rounded end of one bone fits into a sleeve or ring of bone
(and possibly ligaments).
Because the rotating bone can turn only around its long axis, pivot joints are also
uniaxial joints.
Example: The proximal radioulnar joint and the joint between the atlas and the
dens of the axis
71. CODYLOID
In a condylar joint, the eggshaped articular surface of one bone fits into an oval
cavity into another.
Both of these articular surfaces are oval.
Condylar joints allow the moving bone to travel from side to side and back and
forth, but the bone cannot rotate around its long axis.
Movement occurs around two axes; hence, these joints are biaxial (bi = two),
Example: knuckle (metacarpophalangeal) joints.
72. SADDLE
In saddle joints, each articular surface has both convex and concave areas, like a
saddle for a horse.
These biaxial joints allow essentially the same movements as condylar joints.
Example: the carpometacarpal joints in the thumb, which are responsible for our
opposable thumbs.
73. BALL AND SOCKET
In a ball-and-socket joint, the spherical head of one bone fits into the round
socket in another.
These multiaxial joints allow movement in all axes, including rotation, and are the
most freely moving synovial joints.
Examples: The shoulder and hip joints
75. The essential function of muscle is to contract, or shorten a unique
characteristic that sets it apart from other body tissues.
As a result of this ability, muscles are responsible for all body movements and can
be viewed as the “machines” of the body
76. There are three types of
muscle tissue:
skeletal
smooth
cardiac
78. The organs of the respiratory system include the nose, pharynx, larynx, trachea, bronchi
and their smaller branches, and the lungs, which contain the alveoli, or terminal air sacs
Because gas exchange with the blood happens only in the alveoli, the other respiratory
system structures are really just conducting passageways that carry air through the
lungs.
Upper respiratory tract The passageways from the nose to the larynx
Lower respiratory tract those from the trachea to the alveoli.
These conducting passageways also purify, humidify, and warm incoming air. Thus, the
air finally reaching the lungs has fewer irritants (such as dust or bacteria) than the air
outside, and it is warm and damp
79. NOSE:
The nose, whether “button” or “hooked” in shape, is the only externally visible part
of the respiratory system.
During breathing, air enters the nose by passing through the nostrils, or nares.
The interior of the nose consists of the nasal cavity, divided by a midline nasal
septum.
The olfactory receptors for the sense of smell are located in the mucosa in the
slitlike superior part of the nasal cavity, just beneath the ethmoid bone.
The lateral walls of the nasal cavity are uneven, owing to three mucosa-covered
projections, or lobes, called conchae (kong′ke). The conchae greatly increase the
surface area of the mucosa exposed to the air
80. the sticky mucus produced by this mucosa’s glands moistens the air and traps incoming
bacteria and other foreign debris, and lysozyme enzymes in the mucus destroy bacteria
chemically.
The ciliated cells of the nasal mucosa create a gentle current that moves the sheet of
contaminated mucus posteriorly toward the throat (pharynx), where it is swallowed and
digested by stomach juices
The nasal cavity is separated from the oral cavity below by a partition, the palate.
Anteriorly, where the palate is supported by bone, is the hard palate; the unsupported
posterior part is the soft palate
81. PHARYNX:
The pharynx is a muscular passageway about 13 cm (5 inches) long that vaguely
resembles a short length of red garden hose.
Commonly called the throat
The pharynx serves as a common passageway for food and air
It is continuous with the nasal cavity anteriorly via the posterior nasal aperture.
The pharynx has three regions.
Nasopharynx
Oropharynx
Laryngopharynx
82. Clusters of lymphatic tissue called tonsils are also found in the pharynx.
The single pharyngeal tonsil, often called the adenoid, is located high in the
nasopharynx.
The two palatine tonsils are in the oropharynx at the end of the soft palate, as are
the two lingual tonsils, which lie at the base of the tongue.
The tonsils also play a role in protecting the body from infection
83. LARYNX:
The larynx or voice box, routes air and food into the proper channels and plays a
role in speech.
Located inferior to the pharynx, it is formed by eight rigid hyaline cartilages and a
spoon-shaped flap of elastic cartilage, the epiglottis.
The largest of the hyaline cartilages is the shield-shaped thyroid cartilage, which
protrudes anteriorly and is commonly called the Adam’s apple.
The epiglottis protects the superior opening of the larynx
84. During regular breathing, the epiglottis allows the passage of air into the lower
respiratory passages.
When we swallow food or fluids, the situation changes dramatically
The larynx is pulled upward, and the epiglottis tips, forming a lid over the larynx’s
opening.
This routes food into the esophagus, which leads to the stomach, posteriorly.
If anything other than air enters the larynx, a cough reflex is triggered to prevent
the substance from continuing into the lungs
85. Part of the mucous membrane of the larynx forms a pair of folds, called the vocal
folds, or true vocal cords, which vibrate with expelled air.
This ability of the vocal folds to vibrate allows us to speak.
The vocal folds and the slit like passageway between them are called the glottis
91. Breathing, or pulmonary ventilation, is a mechanical process that depends on
volume changes occurring in the thoracic cavity.
The mechanics of breathing: Volume changes lead to pressure changes, which
lead to the flow of gases to equalize the pressure.
Two phases of breathing:
Inspiration when air is flowing into the lungs
Expiration when air is leaving the lungs.
92. INSPIRATION:
Inspiratory muscles: diaphragm and external intercostals
When these muscles contract, the size of the thoracic cavity increases
As the dome-shaped diaphragm contracts inferiorly, the superior- inferior
dimension (height) of the thoracic cavity increases
Pump handle movement: Contraction of the external intercostals lifts the rib
cage and thrusts the sternum forward, which increases the anteroposterior and
lateral dimensions of the thorax
93. Because of the surface tension of the fluid between the pleural membranes the lungs adhere tightly to
the thorax walls and they are stretched to the new, larger size of the thorax.
As intrapulmonary volume (the volume within the lungs) increases, the gases within the lungs spread
out to fill the larger space.
The resulting decrease in gas pressure in the lungs produces a partial vacuum (pressure less than
atmospheric pressure outside the body), which causes air to flow into the lungs.
Air continues to move into the lungs until the intrapulmonary pressure equals atmospheric pressure.
This series of events is called inspiration (inhalation).
94. Contraction of diaphragm and
external intercostal muscles
Decreased intrapleural pressure
Expansion of thoracic cage
Negative pressure in alveoli
Air flows into the lungs
95. EXPIRATION:
Expiration (exhalation) in healthy people is largely a passive process
As the inspiratory muscles relax and resume their initial resting length, the rib
cage descends, the diaphragm relaxes superiorly, and the lungs recoil
Thus, both the thoracic and intrapulmonary volumes decrease.
As the intrapulmonary volume decreases, the gases inside the lungs are forced
more closely together, and the intrapulmonary pressure rises to a point higher
than atmospheric pressure
This causes the gases to passively flow out to equalize the pressure with the
outside.
98. NEURAL REGULATION:
The activity of the respiratory muscles, the diaphragm and external intercostals, is
regulated by nerve impulses transmitted from the brain by the phrenic nerves and
intercostal nerves
Neural centers that control respiratory rhythm and depth are located mainly in the
medulla and pons
99. The medulla contains two respiratory centers:
ventral respiratory group (VRG)
dorsal respiratory group (DRG)
VRG:
contains both inspiratory and expiratory neurons that alternately send impulses to control the rhythm of
breathing.
The inspiratory neurons stimulate the diaphragm and external intercostal muscles via the phrenic and
intercostal nerves, respectively, during quiet breathing.
Impulses from the expiratory neurons stop the stimulation of the diaphragm and external intercostal
muscles, allowing passive exhalation to occur.
Impulses from the VRG maintain a normal quiet breathing rate of 12 to 15 respirations/minute,
100. DRG:
Integrates sensory information from chemoreceptors and peripheral stretch receptors.
The DRG communicates this information to the VRG to help modify breathing rhythms.
PONS RESPIRATORY CENTRES:
Also communicate with the VRG, help to smooth the transitions (modify timing) between inhalation and
exhalation during activities such as singing, sleeping or exercising.
101. The bronchioles and alveoli have stretch receptors that respond to extreme over
inflation (which might damage the lungs) by initiating protective reflexes.
In the case of over inflation, the vagus nerves send impulses from the stretch
receptors to the medulla and soon thereafter, inspiration ends and expiration
occurs. This is one example of DRG integration during respiratory control.
102. NON NEURAL FACTORS:
Physical Factors:
Although the medulla’s respiratory centers set the basic rhythm of breathing, physical
factors such as talking, coughing, and exercising can modify both the rate and depth of
breathing.
Increased body temperature also causes an increase in the rate of breathing.
Volition (Conscious Control) :
voluntary control of breathing is limited, and the respiratory centers will simply ignore
messages from the cortex (our wishes) when the oxygen supply in the blood is getting
low or blood pH is falling. The involuntary controls take over and normal respiration
begins again.
103. Emotional Factors:
Emotional factors also modify the rate and depth of breathing
Reflexes initiated by emotional stimuli acting through centers in the hypothalamus.
Chemical Factors:
The most important factors are chemical—the levels of carbon dioxide and oxygen in the
blood
An increased level of carbon dioxide and a decreased blood pH are the most important
stimuli leading to an increase in the rate and depth of breathing
Changes in the carbon dioxide concentration or H+ ion concentration (which affects pH) in
brain tissue seem to act directly on the medulla centers by influencing the pH of local tissues
in the brain stem
104. Conversely, changes in oxygen concentration in the blood are detected by
peripheral chemoreceptor regions in the aortic arc and the carotid body
Send impulses to the medulla when the blood oxygen level is dropping.
When oxygen levels are low, these same chemoreceptors are also able to detect
high carbon dioxide levels. Although every cell in the body must have oxygen to
live, it is the body’s need to rid itself of carbon dioxide that is the most important
stimulus for breathing.
A decrease in the oxygen level becomes an important stimulus only when the level
is dangerously low.
