The fibrous skeleton of the heart: 1. Lies between the atria and ventricles. 2. Is composed of dense connective tissue that forms fibrous rings around the four heart valves. 3. Acts as an electrical insulator to prevent direct spread of electrical impulses from the atria to the ventricles, ensuring impulses pass through the bundle of His for coordinated ventricular contraction.

1. FIBROUS SKELETON OF
THE HEART

2. FIBROUS SKELETON OF THE
HEARTA] composed of dense
connective tissue.
B] lies in the plane
between the atria
and the ventricles.
C] This plane
corresponds to
atrioventricular
groove/ orifices of
heart.
RV RVLV LV

3. D] is Present in the
form of circular
fibrous ring,,
interconnected by
intervening
fibrous tissue.
E] surrounds the
four valves

4. F] There are four such
rings-- ,, for four orifice
of heart
i & ii- - Atrioventricular
rings– for tricuspid
opening & for bicuspid
opening. It is 8-shaped
iii- aortic ring ---------- at
root of aorta
iv-pulmonary ring------ at
root of pulmonary trunk
superior view of AV-
plane
(Front)
posterior

5. G] Rings are
interconnected
1] AV-ring is connected to
AORTIC ring by a large
mass of fibrous tissue
called trigonum fibrosum
dextrum.
2] Mitral ring is connected
to aortic ring by small
mass of fibrous tissue
called trigonum fibrosum
sinistrum
3] Pulmonary ring & aortic
ring are connected by
tendon of infundibulum.
m
m

7. trigonum fibrosum
dextrum.
trigonum fibrosum
sinistrum
Aortic valves
pulmonary
valves

8. 1.It forms the central
support of the heart
2.Provides attachment to
i- bicuspid & tricuspid
valves directly
ii-cardiac muscle fibres
of atria & ventricles
iii- membranous part of
interventricular
septum
3. Keeps the cardiac
valves competent
4. Acts as an electrical
insulator
• It blocks the direct spread of
electrical impulses from the
atria to the ventricles.
Impulses go only through
bundle of His.
5.prevents overdilation of
the valve openings
H] FUNCTION OF FIBROUS SKELETON
Applied– weakening of it may lead
to cardiac valves incompetence---
means incomplete closure
leading to mitral regurgitation,
aortic regurgitation, tricuspid
regurgitation, ..

9. NOTE
• tricuspid valves & mitral valves are directly
attached to ring
• semilunar valves are directly attached to
wall of vessel ,, not to ring

10. Conductive system of the heart
• Conductive system of the heart is ----
--made up of specialised cardiac muscle fibres,,
-- responsible for initiation and conduction of
cardiac impulse/A.P ,, by its own.
---- these impulses cause cardiac muscle
contraction

11. Components of Conducting
Systemare:
1] Sinoatrial
node/SA node
2]Atrioventricular
node/AV node
3]Atrioventricular
bundle [bundle of
His]
4] Right and left
branches of AV
bundle (of His)
5] Purkinje fibers

12. SA node• Also k/a node of Keith &
Flack
• Situated in the wall of Rt.
Atrium ,in the upper part
of sulcus terminalis just
below the opening of SVC.
• It is called PACEMAKER
of the heart bcz it
generates impusle
&initiates the contraction
of cardiac muscle
producing heart beat.
• Impulse travels through
atrial wall to reach the AV
node
• impulse or heart beat or
heart rate=70-100
beat/min. [average
approx.70/min.]

13. Atrioventricular node/ AV node
• Also k/a node of
Tawara
• Smaller than SA node
• Located in the traingle
of Koch /or / in the
lower & dorsal part of
the atrial septum just
above the opening of
coronary sinus
• It generates impulse at
the rate of 40-60 beat
/min.

14. Atrioventricular bundle [bundle of
His]
• It begins from AV
node &crosses the AV
ring & travel along
the interventricular
septum.[membranous
part].
• Divides at the upper
part of muscular part
of IV-septum.
• Divides into two
branches– Rt. & Lt.
Bundle branch

15. Bundle branch
• Right branch of AV
bundle—
• Passes down on right
side of
interventricular
septum.
• Large part of it enters
the moderator band
to reach anterior wall
of Rt. Ventricle ,
• where it divides into
purkinje fibres.
• Likewise,,Left
branch of AV
bundle— goes on
left side in left
ventricle.

16. Purkinje fibres
• These are terminal
branches of Rt. &
Lt. Branches of
Bundle of His.
• Form sub-
endocardial plexus.
• They generates
impulse at the rate
of 20-35 beat /min.
applied--- arrhythmia– it is loss of
normal rhythm of contraction/ heart
beat.
-- due to damage of conductive
system.
blood supply –nearly whole
conductive system except left branch
AV bundle –is supplied by RCA.
Left br. Of AV bundle by LCA.

17. Heart is myogenic
1] Means A.P. is
generated by muscle
itself,, not by nerve.
2] Conductive system
of heart is made up
of cardiac muscles.
3] Nerves supplying
the heart, can only
influence / modify
the rate of impulse
production or A.P.
4] If all nerves are cut
even then heart will
continue to beat.[d/t
impulse from SA node]
5] Sympathetic nerve
stimulation increase
the rate of impulse
generation.
6] Para-Sympathetic
[vagus] nerve
stimulation decrease
the rate of impulse
generation.

19. • Conductive system of the heart is made up
of specialised cardiac muscle fibres,, which
is responsible for initiation and conduction
of cardiac impulse/A.P ,, by its own.
• [ process of impulse generation /A.P.
independent of nerve supply.]MEANS----
• if all nerve connections to the heart are cut ,
even then the heart continues to produce A.P.
& beat/CONTRACT rhythmically. Hence our
heart is myogenic.

20. • BUT sympathetic & parasympathetic nerves
can modify the heart rate & force of
contraction.
• Sympathetic stimulation increase heart rates &
force of contraction
• Para-Sympathetic stimulation decrease heart
rates & force of contraction
•

21. Innervation
• Although the heart’s
inherent rate of
contraction is set by the
SA node, this rate can be
altered by extrinsic
neural controls

22. Innervation
• The nerves to the heart
consist of visceral
sensory fibers
• Parasympathetic fibers
that slow heart rate
• Sympathetic fibers that
increase the rate and
force of heart
contractions

24. 19-24
Cardiac Conduction System
1
2
3
4
5

25. 1. Sinoatrial
(SA) node
Right
atrium
2. Internodal
pathway
5a. Right
branch
of bundle
of His
Right
ventricle
6. Purkinje
fibers
Left
ventricle
5b. Left branch
of bundle of His
4. Bundle of His or
AV bundle
3. Atrioventricular
(AV) node
Interatrial
pathway
19-25

26. Interatrial pathway
Right atrium Left atrium
SA node
Internodal
pathway
AV node
Purkinje
fibers
Right ventricle Left ventricle
Bundle
of His
1st
beat
2nd
beat
19-26

27. 19-27
Our focus

28. • The fibrous skeleton of the heart lies in the
plane between the atria and the ventricles
• Muscles of atria is not in continuity with
muscles of ventricle [d/t fibrous skeleton]
• This fibrous skeleton is bad conductor of
electrical impulse. So it prevents direct entry
of electrical impulse from atria to ventricle.
4. ACTS AS AN ELECTRICAL INSULATOR:

29. • Electrical impulse from atria to ventricle goes
through bundle of Hiss only.
• Although each cardiac muscle has capacity to
generate & conduct (carry) electrical impulse.
• Thus fibrous skeleton helps in coordinated
conduction of A.P. or electrical impulse to
ventricle.-------- coordinated ventricular
contraction.