Lecture on muscular system

Muscular system

1. 1
9. Muscular System:
Histology and Physiology
Prepared by: Mirza Anwar Baig
M.Pharm (Pharmacology)
Anjuman I Islam's Kalsekar Technical Campus,
School of Pharmacy.
New Panvel,Navi Mumbai
1

2. 2
Contents
:
1.
Cardiac muscles
2.
Smooth muscles
3.
Skeletal muscles
4.
Neuromuscular transmission and contraction
of skeletal muscle
5.Energy metabolism in the muscle
6.Types of muscle contractions
7.Muscle tone

3. 3
Functions of Muscular System
1.
Body movement (Locomotion)
2.
Maintenance of posture
3.
Respiration
Diaphragm and intercostal contractions
4.
Communication (Verbal and Facial)
5.
Constriction of organs and vessels
1.
Peristalsis of intestinal tract
2.
Vasoconstriction of b.v. and other structures (pupils)
6.
Heart beat
7.
Production of body heat (Thermogenesis)
3

4. 4
Properties of Muscle
1.
Excitability:
capacity of muscle to respond
to a stimulus
2.
Contractility:
ability of a muscle to shorten
and generate pulling force
3.
Extensibility:
muscle can be stretched back
to its original length
4.
Elasticity:
ability of muscle to recoil to
original resting length after stretched
4

5. 5
Types of Muscle
•
Skeletal
–
Attached to bones
–
Makes up 40% of body weight
–
Responsible for locomotion, facial expressions, posture,
respiratory movements, other types of body movement
–
Voluntary in action; controlled by somatic motor neurons
•
Smooth
–
In the walls of hollow organs, blood vessels, eye, glands,
uterus, skin
–
Some functions: propel urine, mix food in digestive tract,
dilating/constricting pupils, regulating blood flow,
–
Controlled involuntarily by endocrine and autonomic nervous
systems
•
Cardiac
–
Heart: major source of movement of blood
–
Autorhythmic
–
Controlled involuntarily by endocrine and autonomic nervous
systems
5

6. 6
Connective Tissue Sheaths
•
Connective Tissue of a Muscle
–
Epimysium
. Dense regular, surrounding entire muscle
•
Separates muscle from surrounding tissues and organs
•
Connected to the deep fascia
–
Perimysium
. Collagen and elastic fibers surrounding a
group of muscle fibers called a
fascicle
•
Contains b.v and nerves
–
Endomysium
. Loose connective tissue that surrounds
individual
muscle fibers
•
Also contains b.v., nerves, and satellite cells
(embryonic stem cells function in repair of muscle
tissue
•
Collagen fibers of all 3 layers come together at each end
of muscle to form a
tendon
or
aponeurosis.

6

7. 77

8. 8
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
8

9. 9
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 attach-
ment
9

10. 10
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 to 4 cm
in length
•
Develop from myoblasts;
numbers remain constant
•
Striated appearance
•
Nuclei are peripherally located
10

11. 11
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)
11

12. 12
Sarcoplasmic Reticulum (SR)
•
SR is fluid-filled system of membranous sacs
–
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
12

13. 13
Sarcoplasmic

Reticulum

(
SR
)
Figure 9.5
13

14. 14
Parts of a Muscle
14

15. 15
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
µ
m

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
15

16. 16
Structure of Actin and Myosin
16

17. 17
Myosin (Thick) Myofilament
•
Many elongated myosin molecules
shaped like golf
clubs
.
•
Single
filament contains roughly
300 myosin
molecules
•
Molecule consists of two heavy myosin molecules
wound together to form a rod portion lying parallel to
the myosin myofilament and two heads that extend
laterally.
Myosin heads:
•
Can bind to active sites on the actin molecules to form
cross-bridges. (
Actin binding site
)
•
Attached to the rod portion by a hinge region that can
bend and straighten during contraction.
•
Have ATPase activity:
activity that breaks down
adenosine triphosphate (ATP), releasing energy.
•
Part of the
energy is used to bend the hinge region
of
the myosin molecule during contraction.

18. 18
Structure

and

Arrangement

of

Myosin

Molecules

Within

Thick

Filament
18

19. 19
Actin (Thin)
Myofilaments
•
Thin

Filament
:
composed

of
3
major

proteins
1.
F
(
fibrous
)
actin
2.
Tropomyosin
3.
Troponin
•
Two

strands

of

fibrous
(
F
)
actin

form

a

double

helix

extending

the

length

of

the

myofilament
;
attached

at

either

end

at

sarcomere
.
–
Composed

of

G

actin

monomers

each

of

which

has

a

myosin
-
binding

site

(
see

yellow

dot
)
–
Actin

site

can

bind

myosin

during

muscle

contraction
.
•
Tropomyosin
:
an

elongated

protein

winds

along

the

groove

of

the

F

actin

double

helix
.
•
Troponin

is

composed

of

three

subunits
:
–
Tn
/
A
:
binds

to

actin
–
Tn
/
T
:
binds

to

tropomyosin
,
–
Tn
/
C
:
binds

to

calcium

ions
.

19

20. 20
Role

of

Calcium

in

Cross
-
Bridge

Formation
•
During

relaxed

state

20

21. 21
Role

of

Calcium

in

Cross
-
Bridge

Formation
•
Excited

21

22. 2222

23. 2323

24. 24CROSS-BRIDGE CYCLE
24

25. 25
Changes in Banding Pattern During Shortening
25

26. 26
Sliding Filament Mechanism
Cross

bridge

interaction

between

actin

and

myosin

brings

about

muscle

contraction

by

means

of

the

sliding

filament

mechanism
.
26

27. 27
Sliding Filament Mechanism
•
Increase

in

Ca
2+

starts

filament

sliding
•
Decrease

in

Ca
2+

turns

off

sliding

process
•
Thin

filaments

on

each

side

of

sarcomere

slide

inward

over

stationary

thick

filaments

toward

center

of

A

band

during

contraction
•
As

thin

filaments

slide

inward
,
they

pull

Z

lines

closer

together
•
Sarcomere

shortens
27

28. 28
Sliding Filament Mechanism
•
All

sarcomeres

throughout

muscle

fiber
’
s

length

shorten

simultaneously
•
Contraction

is

accomplished

by

thin

filaments

from

opposite

sides

of

each

sarcomere

sliding

closer

together

between

thick

filaments
.
28

29. 29
Power

Stroke
•
Activated

cross

bridge

bends

toward

center

of

thick

filament
,
“
rowing
”

in

thin

filament

to

which

it

is

attached
–
Sarcoplasmic

reticulum

releases

Ca
2+

–
Myosin

heads

bind

to

actin
–
Hydrolysis

of

ATP

transfers

energy

to

myosin

head

and

reorients

it
–
Myosin

heads

swivel

toward

center

of

sarcomere
(
power

stroke
)
–
ATP

binds

to

myosin

head

and

detaches

it

from

actin
29

30. 30
Contraction
-
Relaxation

Steps

Requiring

ATP
•
Splitting

of

ATP

by

myosin

ATPase

provides

energy

for

power

stroke

of

cross

bridge
•
Binding

of

fresh

molecule

of

ATP

to

myosin

lets

bridge

detach

from

actin

filament

at

end

of

power

stroke

so

cycle

can

be

repeated
•
Active

transport

of

Ca
2+

back

into

sarcoplasmic

reticulum

during

relaxation

depends

on

energy

derived

from

breakdown

of

ATP
30

31. 31
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
31

32. 32
Motor

Unit
:
The

Nerve
/
Muscle

Functional

Unit
Figure 9.12
(a)
32

33. 33
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
33

34. 34
Motor Unit: The Nerve-Muscle
Functional Unit contd...
•
Muscle

fibers

from

a

motor

unit

are

spread

throughout

the

muscle
–
Not

confined

to

one

fascicle
•
T
herefore
,
contraction

of

a

single

motor

unit

causes

weak

contraction

of

the

entire

muscle
•
Stronger

and

stronger

contractions

of

a

muscle

require

more

and

more

motor

units

being

stimulated
(
recruited
)
34

35. 35
Neuromuscular

Junction
Figure 9.7 (a-
c)
35

36. 3636

37. 37
Generation of action potential
37

38. 38
Muscle

contraction
38

39. 3939

40. 40
Major

Events

in

Neuromuscular

Transmission
•
Motor

neuron

depolarization

causes

action

potential

to

travel

down

the

nerve

fiber

to

the

neuromuscular

junction
(1).
•
Depolarization

of

the

axon

terminal

causes

an

influx

of

Ca
2+
(2)
which

triggers

fusion

of

the

synaptic

vesicles
(3)
and

release

of

neurotransmitter
(
Acetylcholine
;
ACh
) (4).
•
ACh

diffuses

across

the

synaptic

cleft

and

binds

to

post
/
synaptic

ACh

receptor
(
AChR
)
located

on

the

muscle

fiber

at

the

motor

end
/
plate
(5).
•
Binding

of

ACh

to

AChRs

opens

the

channels

causing

an

influx

of

Na
(5),
depolarization

of

the

sarcolemma

that

travels

down

the

t
/
tubules
(6)
and

ultimately

causes

the

release

of

Ca
2+

from

the

sarcoplasmic

reticulum

/

CONTRACTION
.
•

Unbound

ACh

in

synaptic

cleft

defuses

away

or

is

hydrolyzed
(
inactivated
)
by

acetylcholinesterase
(
AChE
)
(7).
40

41. 41
Muscle Response to Strong Stimuli
•
Muscle force depends
upon the
number
of
fibers stimulated
–
More fibers contracting
results in greater muscle
tension
•
Muscles can continue to
contract unless they run
out of energy
41

42. 42
How Do Muscles Get Energy?
•
Initially
,
muscles

use

stored

ATP

for

energy
–
ATP

bonds

are

broken

to

release

energy
–
Only

4
–
6
seconds

worth

of

ATP

is

stored

by

muscles
•
After

this

initial

time
,
other

pathways

must

be

utilized

to

produce

ATP
42

43. 43
Skeletal

muscle

energy

metabolism
43

44. 44
1. Creatine Phosphate (high-energy molecule)
•
Muscle cells store CP
•
CP transfers energy to ADP, to
regenerate ATP by direct
phosphorylation of ADP
•
Creatine synthesize in
liver,pancrease,kidneys
•
The
enzyme creatine kinase

forms CP from creatine and
ADP
44

45. 45
2.Anaerobic Respiration
•
Anaerobic glycolysis and
lactic acid formation
–
Reaction that breaks
down glucose without
oxygen
–
Glucose is broken down
to pyruvic acid to
produce some ATP
–
Pyruvic acid is converted
to lactic acid
•
This reaction is not as
efficient, but is fast
–
Huge amounts of glucose
are needed
–
Lactic acid produces
muscle fatigue
45

46. 46
3.Aerobic Respiration
•
Glucose is broken
down to carbon
dioxide and water,
releasing energy (ATP)
•
This is a
slower

reaction that requires
continuous oxygen
•
A series of metabolic
pathways occur in the
mitochondria
46

47. 47
Muscle Fatigue & Oxygen Debt
•
When a muscle is fatigued, it is
unable to contract even with a
stimulus
•
Common cause for muscle
fatigue is
oxygen debt
–
Oxygen must be
“
repaid
”
to
tissue to remove oxygen
deficit
–
Oxygen is required to get rid
of accumulated lactic acid
•
Increasing acidity (from lactic
acid) and lack of ATP causes
the muscle to contract less
47

48. 48
48

Smooth

Muscle
•
Located in
the blood vessels, the
respiratory tract, the iris of the eye,
the gastro-intestinal tract
•
The contractions are slow and
uniform
•
Functions
to alter the activity
of
various body parts to meet the needs
of the body at that time
•
Is fatigue resistant
•
Activation is
involuntary

49. 49
Smooth

Muscle
•
Cells are not striated
•
Fibers smaller than those
in skeletal muscle
•
Spindle-shaped; single,
central nucleus
•
More actin than myosin
•
No sarcomeres
–
Not arranged as
symmetrically as in
skeletal muscle, thus NO
striations.
•
Dense bodies instead of Z
disks

–
Have
noncontractile
intermediate filaments
49

50. 50
Smooth

Muscle
Figure 9.24
•
Grouped into sheets in walls of hollow organs
•

Longitudinal layer

–
muscle fibers run parallel to
organ
’
s long axis
•

Circular layer

–
muscle fibers run around
circumference of the organ
•
Both layers participate in peristalsis
50

51. 51
51
Cardiac

Muscle
•
Has characteristics of both skeletal
and smooth muscle
•
Functions to provide the contractile
activity of the heart
•
Contractile activity can be gradated
(like skeletal muscle)
•
Is
very fatigue resistant
•
Activation of cardiac muscle is
involuntary
(like smooth muscle)

52. 52
Cardiac Muscle
•
Found only in heart where it forms a thick layer
called the
myocardium
•
Striated fibers that branch
•
Each cell usually has
one centrally-located nucleus
•
Fibers joined by intercalated disks
–
IDs are composites of
desmosomes
and
gap
junctions
–
Allow excitation in one fiber to spread quickly to
adjoining fibers
•
Under control of the ANS (involuntary) and endocrine
system (hormones)
•
Some cells are
autorhythmic
–
Fibers
spontaneously
contract ( Pacemaker cells)
52

53. 53
Cardiac

Muscle

Tissue
Figure 10.10a
53

54. 54
Cardiac

Muscle

and

Heart

Function
•
Cardiac

muscle

fibers

are

striated

–

sarcomere

is

the

functional

unit
•
Fibers

are

branched
;
connect

to

one

another

at

intercalated

discs
.

The

discs

contain

several

gap

junctions
•
Nuclei

are

centrally

located
•
Abundant

mitochondria
•
SR

is

less

abundant

than

in

skeletal

muscle
,
but

greater

in

density

than

smooth

muscle
•
Sarcolemma

has

specialized

ion

channels

that

skeletal

muscle

does

not

–

voltage
/
gated

Ca
2+
channels
•
Fibers

are

not

anchored

at

ends
;
allows

for

greater

sarcomere

shortening

and

lengthening
54

55. 5555

56. 56
How

are

cardiac

contractions

started
?
Cardiac

conduction

system
•
Specialized

muscle

cells

“
pace
”

the

rest

of

the

heart
;
cells

contain

less

actin

and

myosin
,
are

thin

and

pale

microscopically
•
Sinoatrial
(
SA
)
node
;
pace

of

about
65
bpm
•
Internodal

pathways

connect

SA

node

to

atrioventricular
(
AV
)
node
•
AV

node

could

act

as

a

secondary

pacemaker
;
autorhythmic

at

about
55
bpm
•
Bundle

of

His
•
Left

and

right

bundle

branches
•
Purkinje

fibers
;
also

autorhythmic

at

about
45
bpm
ALL

CONDUCTION

FIBERS

CONNECTED

TO

MUSCLE

FIBERS

THROUGH

GAP

JUNCTIONS

IN

THE

INTERCALATED

DISCS
56

57. 57
Muscle tone:
•
Muscle tone (tonos=tension), a small amount of tautness
or tension in the muscle due to weak, involuntary
contractions of its motor units.
•
Muscle tone keeps skeletal muscles firm, but it does not
result in a force strong enough to produce movement.
For example,

1.
Upright position of head
:
when the muscles in the back of
the neck are in normal tonic contraction, they keep the head
upright and prevent it from slumping forward on the chest.
2.
Gastrointestinal tract:
where the walls of the digestive organs
maintain a steady pressure on their contents.
3.
Walls of blood vessels:

plays a crucial role in maintaining
blood pressure.

58. 58
Disorders of Muscle tone:
•
Hypotonia
refers to decreased or lost muscle tone.
•
Such muscles are said to be
flaccid
.
•
Flaccid muscles are loose and appear flattened rather
than rounded.
•
Certain disorders of the nervous system and disruptions
in the balance of electrolytes (especially sodium,
calcium, and, to a lesser extent, magnesium) may result
in
flaccid paralysis
, which is characterized by loss of
muscle tone, loss or reduction of tendon reflexes, and
atrophy (wasting away) and degeneration of muscles.

59. 59
Hypertonia
refers to increased muscle tone and is
expressed in two ways:
spasticity or rigidity.

1.Spasticity
is characterized by increased muscle tone
(stiffness)

•
Certain disorders of the nervous system and
electrolyte disturbances such as those previously
noted may result in
spastic paralysis, partial
paralysis
in which the muscles exhibit spasticity.

2.
Rigidity
refers to increased muscle tone in which
reflexes are not affected.

60. 60
Types of Muscle Contractions
•
Isometric

contractions
–
Tension

in

the

muscles

increases
–
The

muscle

is

unable

to

shorten

or

produce

movement
•
Isotonic

contractions
–
Myofilaments

are

able

to

slide

on

each

other

during

contractions
–
The

muscle

shortens

and

movement

occurs
60

61. 61
THANK

YOU