2. Objectives
By the end of the lecture, learners
should be able to;
Define muscle tissue
Describe the characteristics of muscle
tissues
Discuss the types of muscle tissues
3. Introduction
Muscle tissue is the fourth basic
tissue type
Have a contractility property
All muscle cells are of mesodermal
origin
differentiate by a gradual process of cell
lengthening with abundant synthesis of
the myofibrillar proteins actin and
myosin.
4. Cont...
Some cells function as single
cell contractile units, e.g.
◦myoepithelial cells (in glands),
◦pericytes (surround blood
vessels)
◦myofibroblasts (scar formation)
5. Introduction cont..
Muscle cells function as
multicellular contractile units
actin microfilaments and associated
proteins generate the forces necessary for
the muscle contraction, which drives
movement
contraction is caused by the sliding
interaction of thick myosin filaments along
thin actin filaments in all muscles.
6. Types of muscles
3 types
distinguished based on
morphological and functional
characteristics
◦ skeletal
◦ cardiac
◦ smooth
each structural type is adapted to its
physiological role
7.
8. Characteristics of each muscle
Skeletal Cardiac Smooth
-bundles very long,
-multinucleated cells
-nucleus peripherally
located
-cross-striations
-has cross-striations
-elongated, branched cells
-intercalated discs
- nucleus centrally located
-fusiform cells
-lack striations
- nucleus centrally
located
-contraction is quick,
forceful,
-under voluntary control
-Contraction is involuntary,
-vigorous, and
-rhythmic.
-resistant to fatigue
-abundant mitochondria
-have slow,
involuntary
contractions
12. Skeletal (striated) Muscle
Associated with the skeleton
moves the skeleton and organs i.e.
eye and tongue.
Voluntary muscle
Arrangement of contractile proteins
form cross striations - striated
muscle
Contractions are fast and forceful
13. Skeletal Muscle cont..
Consists of muscle fibres
Long cylindrical multinucleated cells
◦ diameter; 10 to 100 µm, length up-to 35cm
Multinucleation results from fusion of
embryonic mononucleated myoblasts
(muscle cell precursors)
Progenitor cells called muscle satellite cells
remain adjacent to most fibres
Nuclei are found at the periphery of the cell
under the sarcolemma
14. Muscle development
During embryonic muscle development,
mesenchymal myoblasts fuse, forming
myotubes with many nuclei.
Myotubes then further differentiate to form
striated muscle fibers.
Myotubes synthesize the proteins to
make up myofilaments
Elongated nuclei are found peripherally
just under the sarcolemma,
16. Cont…
a characteristic nuclear location unique
to skeletal muscle fibers/ cells.
A small population of reserve progenitor
cells called muscle satellite cells
remains adjacent to most fibers of
differentiated skeletal muscle.
Satellite cells proliferate and produce
new muscle fibers following muscle
injury.
17. Cont…
variation in diameter of muscle fibers
depends on factors such as the;
◦ specific muscle
◦ age, gender
◦ nutritional status, and
◦ physical training of the individual
18. Organisation of a skeletal muscle
Epimysium; external sheath of thick
dense CT surround entire muscle
continuous with fascia and the tendon
binding muscle to bone
◦ the septa extends inwards carrying along
blood vessels, lymphatics and nerves
20. Cont…
Perimysium: thin dense CT surround
each bundle of muscle fibres called the
fascicle
Each fascicle form a functional unit
Nerves, blood vessels, and lymphatics
penetrate the perimysium to supply each
fascicle
Endomysium; delicate layer of reticular
fibres and scattered fibroblasts surround
external lamina of individual muscle fibre
21.
22. Cont…
CT present helps to transmit
mechanical forces generated by
contracting muscle cells
individual muscle cells do not extend
from one end of a muscle to the other
Some skeletal muscles taper at their
ends,
where the epimysium is continuous
with the dense regular connective
tissue of a tendon at myotendinous
junctions
25. Organisation within muscle
fibers
Longitudinally sectioned ms fibre
shows cross-striation of
alternating light and dark
bands
Dark bands- A bands
(anisotropic)
Light bands- I band (isotropic do
not alter polarised light)
26. Organisation cont..
I band is bisected by a dark transverse line
Z disc (Z-Z disc sarcomere)
Sarcoplasm contains long cylindrical
filaments called myofibrils
Myofibrils consists of an end to end
repetitive arrangement of sarcomere
Sarcomere is the functional subunit of the
contractile apparatus
Sarcomere extend from Z disc to Z disc
Thick and thin myofilaments composed of
myosin and F actin
27.
28. Innervation
Skeletal muscles – motor nerves
Innervation of single muscle fibres by single motor
neurons provides precise control of muscle activity
Each axonal branch forms a dilated termination
situated within a trough on the muscle cell surface.
This synaptic structure is called the motor end
plate (MEP), or Neuromuscular Junction (NMJ)
Axon + muscle fibers= Motor Unit
neurotransmitter is acetylcholine.
31. Myasthenia
gravis is an autoimmune disease
characterised by progressive muscular
weakness caused by reduction in the
number of functionally active
acetylcholine receptors at the
neuromuscular junction.
This reduction is caused by binding of
the circulating antibodies to the
acetylcholine receptors, thereby
preventing the effective nerve muscle
communication.
32. Duchenne muscular dystrophy
(DMD)
is a hereditary disease of skeletal
muscle, which usually affects males.
This disease is due to mutation of a
gene responsible for formation of
protein dystrophin on the inner surface
of sarcolemma.
The skeletal muscle becomes
progressively weak from early
childhood and by adolescence the
person becomes immobile.
34. Cardiac muscle
the mesoderm cells of the primitive heart
tube align into chainlike arrays
cells form complex junctions between
interdigitating processes
Cells within a fiber often branch and bind
to cells in adjacent fibers
Exhibit a cross-striated banding pattern.
possesses only one (or two) centrally
located nucleus
35.
36. Characteristics
A unique and distinguishing
characteristic is the presence of dark-
staining transverse lines (intercalated
discs) that cross the chains of cardiac
cells at irregular intervals
intercalated discs represent the
interface between adjacent muscle
cells and contain many junctional
complexes
Strong continuous contraction
39. Junctional complexes
Transverse regions of these step-like discs
have many;
◦ desmosomes and
◦ fascia adherentes
together these serve to bind cardiac muscle
cells firmly together to prevent their pulling
apart under constant contractile activity
Longitudinal oriented portions of each disc
have many;
◦ gap junctions
providing ionic continuity between cells serve
as “electrical synapses”
40.
41. Organisation of cardiac ms
Structure and function of the contractile
proteins in cardiac cells are essentially the
same as in skeletal muscle
T-tubules are more numerous and larger
Sarcoplasmic reticulum is less abundant
Cardiac muscle cells contain numerous
mitochondria
42. Cont..
Contractions are intrinsic and
spontaneous.
Impulses for the rhythmic contraction are
initiated, regulated and coordinated by
nodes.
rate of contraction is modified by
autonomic innervation of the nodes of
conducting cells
sympathetic nerve supply accelerate
parasympathetic supply decrease the
44. Smooth muscle
Also called visceral muscle.
Specialised for slow, steady contraction.
Cells are relatively small with a single elongated
nucleus, centrally located.
Elongated, spindle shaped (Fusiform) cells with
tapered ends
May be bifurcated occasionally.
Fibers are bound together in irregular branching
fasciculi
Non striated
Basal lamina
45. Cont…
All cell are linked by gap junctions
short membrane invaginations, called
caveolae, are often frequent at the
smooth muscle cell surface.
Caveolae contain several pumps and
ion channels
serve to organize proteins signaling
calcium release at myofibrils
lack T tubules
46.
47. Organisation
The characteristic contractile activity of
smooth muscle is generated by myofibrillar
arrays of actin and myosin
organized differently from those of striated
muscles.
bundles of thin and thick myofilament criss
cross obliquely through the cell.
Myosin filaments have a less regular
arrangement among the thin filaments and
fewer cross bridges
actin filaments lack troponin,
instead use calmodulin and Calcium in the
contraction mechanism.
48. Innervation
smooth muscle contraction is most often
spontaneously
its nerve supply serves primarily to modify
activity rather than to initiate it
Contraction control involve;
◦ autonomic nerves,
◦ a variety of hormones and similar substances,
◦ local physiologic conditions such as the degree of
stretch
receives both adrenergic and cholinergic nerve
endings that
act antagonistically, stimulating or depressing its
49. Regeneration of Muscle Tissue
three types of adult muscle have different
potentials for regeneration after injury
In skeletal ms source of regenerating cells is
the mesenchymal satellite cells that
lies within the external lamina of each mature
muscle fiber
After injury the quiescent satellite cells
become activated, proliferate and fuse to
form new skeletal muscle fibers
regenerative capacity is limited
occurring less well after major muscle
trauma.
50. Cont..
Cardiac muscle lacks satellite cells
shows very little regenerative
capacity beyond early childhood.
Defects or damage (eg, infarcts) to
heart muscle are generally replaced
by;
◦ proliferating fibroblasts and growth of
connective tissue, forming myocardial
scars.
51. Cont..
Smooth muscle, composed of simpler,
smaller, mononucleated cells,
is capable of a more active regenerative
response.
After injury, viable smooth muscle cells
undergo mitosis and replace the
damaged tissue
Contractile pericytes from the walls of
small blood vessels participate in the
repair of vascular smooth muscle
52. Clinical anatomy
Hypertrophy is the process,
characterized by increased cell volume
Hyperplasia is the tissue growth by an
increase in the number of cells
Ischemia or tissue damage due to lack
of oxygen when coronary arteries are
occluded by heart disease
Benign tumors called leiomyomas
commonly develop from smooth muscle
fibers but are seldom problematic
53. Activity
1. State the types of muscle tissue
2. Describe the characteristics of each
type of muscle
3. Discuss the junctional complexes
found in cardiac muscle
4. Compare and contrast the
regenerative capacities of each type
of muscle tissue
5. Outline the nervous innervation of
each muscle tissue
