VERTEBRATE
MUSCULAR SYSTEM
Mrs. Ofelia Solano Saludar
Department of Natural Sciences
University of St. La Salle
Bacolod City
HISTOLOGY: striated, cardiac, smooth
FUNCTION: contraction
 locomotion: result of muscle action
 posture determinant
 orientation of body in the environment
 heat production
 Myotomes of
epimere
 Lateral
mesoderm of
hypomere
1. Somatic:
body wall
muscles
2. Splanchnic:
smooth
muscle of
viscera
GROSS FEATURES OF SKELETAL MUSCLE
Origin & insertion; Tendon; Aponeurosis; Fascia, Action
Various wrappings of connective tissues
extend beyond the ends of the muscle fibers to
connect with the periosteum of the bone:
 Tendon - cordlike attachment consisting of
extensions of a muscle's tough connective
tissue sheath that anchor a muscle to its
origin & insertion
 Aponeurosis - thin flat sheet
o Fascia - thin flat sheets of connective
tissues that wrap and bind adjacent
muscle groups
o Raphe - junction of two muscles at a band
of connective tissue to form a line of
fusion, such as the linea alba
1. Agonistsprimary action
2. Antagonistic oppose or
resist the
action of
another
muscle
3. Synergistic work together
to produce a
common
effect
Names of skeletal muscles are
based on:
 action (e.g., levator
scapulae)
 direction of fibers
(e.g., oblique)
 location or position
(e.g., superficial)
 number of divisions
(e.g., triceps)
 shape (e.g., deltoid)
 origin and/or
insertion (e.g.,
iliocostalis)
 size (e.g., major)
… or some combination of these
STRIATED MUSCLE
 Skeletal, voluntary
muscles: axial, body
wall & tail,
hypobranchial &
tongue, extrinsic
eyeball, appendicular,
branchiomeric or
branchial muscles

Myofibrils are striated
cylinders within
syncytial myofibers
SOMATIC MUSCLES
VISCERAL MUSCLES
Histo
logy
Striated, skeletal, voluntary
Smooth, involuntary, includes
cardiac muscle
Seg
men
tation
Primitively segmented
(*partially unsegmented:
somitomeres)
Unsegmented
Origin
Myotomal/somitic
Lateral mesoderm
Loca
tion
Body wall & appendages
(*branchial region)
Splanchnopleure
Func
tion
Primarily for orientation in
external environment
Regulate internal environment
Inner
vation
Spinal nerves & cranial nerves
III, IV, VI & XII (except tongue)
Postganglionic fibers of ANS
TWITCH (RED)
Contraction
Fast to slow
contraction
TONIC (WHITE)
Slow contraction
Slow
Mammalian
postural muscles
Amphibian & reptilian
postural muscles
Fast
Most locomotor
muscles
Extraocular & ear
muscles of mammals
Single axon
All-or-none
Multiple axons
Variably fatigues
Can maintain tension
efficiently
Innervation
Action
potential
Onset of
fatigue
A temporal
summation with a
graded contraction
Muscles are mixtures of different fiber types; androgens &
continued use result in increase in size & strength of muscle
SLOW TWITCH
Type I of mammals
FAST OXIDATIVE
Type IIA of mammals
FAST GLYCOLYTIC
Type IIB of mammals
Fast
Posture or slow
repetitive movements
Powerful & fast
Fatigues slowly
Fatigues slowly
Fatigues quickly
Large # of
mitochondria
Large # of
mitochondria
Few mitochondria
High oxygen storage
proteins (myoglobin):
“red muscle”
ATP formed by
oxidative
phosphorylation
ATP formed by glycolysiswith possible oxygen
debt
“Dark meat” of fish &
fowl
Bird flight muscles
“White breast” of
domestic fowl
SMOOTH MUSCLE TISSUE


Fusiform, uninucleate cells with myofibrils but
without striations; occur in sheets
Two general types:
1. Unitary- has myogenic contraction to aid in
sustaining the rhythmic movement of the organ
2. Multiunit- has neurogenic contraction, which
requires action potentials sent by neurons
 Lateral plate
mesoderm in
origin
 Involuntaryinnervated by
ANS
 Muscles of tubes,
vessels, & hollow
organs; intrinsic
eyeball muscles;
erectors of
feathers & hair
 Regulates
internal body
temperature
CARDIAC
MUSCLE TISSUE

Heart muscle

Uninucleate,
striated cells
separated by
intercalated disks

Lateral plate
mesoderm in origin

Involuntary, self
depolarizes
(myogenic); ANS
nerves modify its
rhythmicity

Include the skeletal muscles of the trunk & tail

Are segmental because of their embryonic origin;
arise from segmental mesodermal somites

Metamerism is most evident in fishes and aquatic
amphibians where the axial muscles are used in
locomotion

Metamerism is obscured in tetrapods due to
presence of paired appendages responsible for
locomotion on land

Myotomes are separated by myosepta which serve
as muscle origins & insertions

Myoseptum becomes indistinct in amniotes

Myotomes become divided by the horizontal
skeletogenous septa into:
1. EPAXIALS- above the septum, dorsoflex spine
2. HYPAXIALS- below the septum, ventroflex spine
o
present in orbits
as extrinsic
eyeball muscles
o
extend forward
beneath the
pharynx as
hypobranchial
muscles &
muscles of the
tongue
Epaxial Muscles:
 Innervated by
dorsal rami of
spinal nerves
 Extend spine &
some lateral
bending
 Extrinsic eye
muscles
(innervated by
cranial nerves)
Hypaxial Muscles:

Innervated by ventral
rami of spinal nerves

Ventroflex and lateral
bending

Hypobranchial
muscles: hypaxial
muscles that
migrated forward &
come to lie on floor
of pharynx, pectoral
girdle to jaw;
function in
respiration &
feeding, e.g.
coracomandibularis
Epaxials are elongated bundles that extend through
many body segments located below the expanded
appendicular muscles; required to operate the limbs
lie along vertebral column
Urodeles & some lizards - epaxials (DORSALIS
TRUNCI) are still obviously metameric
Anterior lateral musculature of a urodele (Ambystoma or tiger salamander)



Beginning with fishes, epaxial bundles split into
longitudinal systems: long, short & segmented
Short & long bundles both arch & support the
vertebral column
Extend from base of the skull to tip of the tail
SHORT BUNDLES:
 Extend from the 1st vertebrae to the skull
(occipitals)
 Short segmental muscles (intervertebrals) include
several systems between various parts of the
vertebrae & ribs, with each member extending only
over one body segment
 Connect processes of adjacent vertebrae
 Tetrapod bundles perform same function as in
fishes (side-to-side movements of vertebral
column)
LONG BUNDLES:

Longissimus group- lies on transverse processes
of vertebrae; includes the longest epaxial bundles:
longissimus dorsi, longissimus cervicis,
longissimus capitis

Iliocostalis grouplateral to longissimus
& spinalis; arises on
ilium & inserts on
dorsal ends of ribs or
uncinate processes

Spinalis group- lies
close to neural arches;
connects spinous processes or transverse
processes with those several vertebrae anteriorly
Hypaxials:

Muscles of
lateral body
wall: oblique
(external &
internal),
transverse,
& rectus
muscles

Muscles that
form
longitudinal bands in roof of body cavity:
subvertebral muscles

Hypaxials of the abdomen have no myosepta &
form broad sheets of muscle
Early amphibians & reptiles: ribs developed in
myosepta along entire length of the trunk; Urodeles
still have myosepta the length of the trunk, but ribs
no longer form in all of them
oes, obliquus
externus
superficialis
oep, obliquus
externus
profundus
oi, obliquus
internus
ta,
transversus
abdominis
 Modern amniotes: myosepta & ribs are
restricted to the thorax, hence abdominal
muscles are not obviously segmented
 Hypaxials
are reduced
in volume
compared to
fishes;
support
contents
of
abdomen
& assist in
respiration
 Weakly developed
in most fishes but
stronger in
tetrapods
 Support ventral
body wall,
compresses
abdomen, assist
epaxials in bending vertebral column
 Consists of: rectus abdominis, cervicis, and
geniohyoid in front of hyoid apparatus
 Diaphragm – unique to mammals for
breathing
external & internal
intercostal
(respiration in
amniotes)
1. External intercostal
muscles
2. Internal intercostal
muscles
3. Ribs
4. Intercartilaginous
muscles
5. Sternum
6. Subcostal muscles
7. Vertebral column



Underneath &
against
transverse
processes of
vertebrae
Includes the
psoas & iliacus in
the lumbar region
& the longus colli
in the neck
Less developed in
the thorax; none
in the tail
EPAXIAL
HYPAXIAL
Intervertebrals: Intertransversarii,
Interspinalis, Interarcuales,
Interarticularis
Longissimus: L. capitis, L. cervicis,
L. dorsi, Extensor caudae
lateralis
Spinalis: S. dorsi, S. cervicis, S.
capitis, Transversospinalis
Iliocostales
Subvertebralis: Longus colli,
Quadratus lumborum, Psoas
minor
Oblique group (parietals): Internal
& External intercostals, Internal
& External oblique of abdomen,
Cremaster, Supracostals
(Scalenus, Serratus dorsalis,
Levatores costarum,
Transversus costarum)
Diaphragm
Transverse group (parietals):
Transversus costalis (subcostal),
Transversus abdominis
Rectus muscles: Rectus
abdominis, Pyramidialis
Muscles of the back:
Longissimus dorsi - extends vertebral
column
Iliocostalis - draws ribs together
Multifidus spinae - extends vertebral
column
Spinalis dorsi - extends vertebral
column
Abdominal muscles:
Rectus abdominis - compresses
abdomen
Internal oblique - compresses abdomen
External oblique - constricts abdomen
Internal oblique - constricts abdomen
Respiratory muscles:
Serratus - draw ribs cranially
Scalenus - flexes the neck
Diaphragm - separates the
thoracic/abdominal cavities,
functions in breathing
Intercostals - protract/retract ribs





Arise from preotic
somitomeres
6 voluntary
muscles
Obliques rotate eye
along its transverse
axis; rectus move
eyes up, down, left,
right; retractor in
some
Retractor bulbi
pulls the eyeball
further into the
orbit to allow for
coverage by the
nictitating
membrane (lacking
in humans)
Innervated by the
oculomotor nerve
 Develop from somitomeres & the myotomes
caudal to those that produce the ocular
muscles
 Closely associated with the visceral skeleton
so they are used in both breathing and feeding.
 Perform the function of operating the jaw,
opening and closing the spiracle
 Primitively had a levator & a constrictor muscle
series; in present vertebrates
coracobranchials, subarcuals and ventral
transversals are added
 May be subdivided based on what visceral arch
they are associated with

FISHES - operate the jaws: adductor mandibulae &
intermandibularis (mylohyoid in mammals)

TETRAPODS- muscles of 1st arch still operate
jaws; adductors of mandible: masseter &
temporalis, pterygoid, anterior belly of digastric,
tensor palati & tensor tympani of mammals

Constrictors: interhyoideus (posterior belly of
digastric) & constrictor colli of reptiles & birds
(platysma & facial muscles in mammals)
Levators become depressor mandibulae &
stapedius
In fishes, muscles become reduced because the
operculum plays important role in respiration






Levators: cucullaris of gill-bearing vertebrates
become the trapezius & sternocleidomastoid of
tetrapods
Constrictors have no representatives in tetrapods
In tetrapods, primary muscles include:
stylopharyngeus (Arch III) - used for swallowing
Remaining
arches give
rise to
intrinsic
muscles
of the
larynx or
‘voicebox’
 Hypobranchial- ventral muscles of the
head and trunk region that perform
functions associated with jaw and tongue
movement
 Extend forward from pectoral girdle &
insert on mandible, hyoid, & gill cartilages
 Strengthen floor of pharynx
 Assist branchiomeric muscles in elevating
floor of mouth, lowering jaw, & extending
gill pouches
Fishes- associated with feeding and breathing:
 Coracoarcuals - opens mouth
 Coracomandibular - opens mouth
 Coracohyoid - helps in feeding
 Coracobranchial - helps in swallowing
Tetrapods- associated with the hyoid apparatus &
tongue
 Tongue muscles: hyoglossus, styloglossus,
genioglossus (also speech & sound production)
 Geniohyoid: draws hyoid cranially
 Sternohyoid: draws hyoid posteriorly
 Sternothyroid: draws larynx caudally
Tongue of amniotes is a 'sac' anchored to hyoid skeleton & filled
with hypobranchial muscle
Hypobranchials ending in "hyoid" stabilize hyoid and
larynx; e.g. geniohyoid, sternohyoid, sternothyroid,
thyrohyoid

Those beginning or ending with "thyro" are attached to
the larynx; e.g. thyrohyoid

Those ending with “glossus” or start with “lingu” are
tongue muscles, e.g. lingualis, styloglossus
EYEBALL
Superior &
inferior
oblique
Medial &
lateral rectus
Superior &
inferior
rectus
HYPO
BRANCHIAL
(tongue)
Genioglossus
Hyoglossus
Styloglossus
Lingualis
BRANCHIOME
RIC (pharynx)
Mandibular
muscles
Hyoid muscles
Other branchial
muscles
 Muscles of girdles and appendages
 Move fins or limbs
 Innervated by ventral ramus of spinal nerves
 Two types based on origin:
o Extrinsic - originate on axial skeleton or
fascia or trunk & insert on girdles or
limbs
o Intrinsic - originate on girdle or proximal
skeletal elements of appendage & insert
on more distal elements
FISHES

Appendicular
muscles serve
mostly as stabilizers

Intrinsic muscles
are limited in
number and
undifferentiated

Originated as
extensions of
hypaxials of body
wall

Paired fins are
appendicular (from
myotome)
 Median dorsal
& ventral fins
are NOT
appendicular,
from myotome
of epaxials &
hypaxials
respectively
 Dorsal mass
on paired fins are extensors or abductors

Ventral mass on paired fins are flexors or
adductors
TETRAPODS

Appendicular
muscles are
much more
complicated than
in fish

Greater leverage
required for
locomotion on
land

Jointed
appendages (as
opposed to fins)
require complex
muscles

Form from blastemas
within the limb bud

Amphibians - much more
complex than in fish

Reptiles - more numerous
& diverse than in
amphibians; better
support of body &
increased mobility of
distal segments of the
limbs

Mammals - similar to
reptiles but more diverse
BIRDS
 Intrinsic
musculature is
reduced
 Pectoralis
(humerus
adductor), is the
largest flight
muscle that
lowers wing
 Supracoracoideus
elevates wing
 Dorsal group of the forelimbs (e.g., trapezius
and latissimus dorsi) arise on:
o fascia of trunk in lower tetrapods
o skull, vertebral column, & ribs to a point
well behind the scapula in higher
tetrapods & converge on the girdle & limb
 Ventral group (e.g., pectoralis) arises on
sternum & coracoid, & converge on limb
 RESULT = pectoral girdle & limb are joined to
trunk by extrinsic appendicular muscles
The 'muscular sling' of
tetrapods: Appendicular
muscles of the forelimbs
suspend the anterior body of
tetrapods from the shoulders:
axial muscles (rhomboideus
& serratus ventralis)
branchial muscles (trapezius)
forelimb musculature
(pectoralis)




The pelvic girdle requires no such muscular
anchoring because it is attached directly to the
vertebral column, resulting to relatively lesser
volume of extrinsic muscle in posterior limbs.
Referred to as 20 appendicular muscles because:
they arise from embryonic body wall & spread to
the girdles and limb buds
it was not their original function to operate
appendages
MAMMALS
EXTRINSIC: Forelimb only
REPTILES
Secondary appendicular:
Levator scapulae,
Rhomboideus, Serratus
ventralis
Primary appendicular:
Latissimus dorsi,
Pectorales
Secondary appendicular:
Levator scapulae,
Rhomboideus, Serratus
ventralis
Primary appendicular:
Latissimus dorsi,
Pectorales
GIRDLE (girdle to humerus,
proximally)
Deltoideus
Subscapularis
Teres minor
Supraspinatus
Infraspinatus
Coracobrachialis
Teres major
Deltoideus clavicularis
Dorsalis scapulae
Subcoracoscapularis
Scapulohumeralis anterior
Supracortacoideus
Coracobrachialis
Slip of Latissimus dorsi
UPPER ARM (girdle of humerus
to proximal end of radius or
ulna)
Triceps brachii
Biceps brachii
Brachialis
Epitrochleoanconeus
Anconeus
Triceps brachii
Biceps brachii
Brachialis
Epitrochleoanconeus
Anconeus
FOREARM (humerus &
proximal end of radius & ulna
to hand)
Extensors & flexors of carpus &
digits
Supinators & pronators of hand
Extensors & flexors of carpus &
digits
Supinators & pronators of hand
HAND
Extensors, flexors, abductors,
adductors of digits
Extensors, flexors, abductors,
adductors of digits
INTRINSIC:
Region of Body
Shark
Salamander
Mammal
Hypobranchial
(pharyngeal)
muscles
Coracoarcuales
Coracomandibularis
Coracohyoid
Tongue
Geniohyoid
Recus cervicis
Tongue
Geniohyoid
Sternohyoid, Sternothyroid
Pectoral
Appendages
Dorsal extensors
Latissimus dorsi
Latissimus dorsi,
cutaneous maximus
Deltoids, subscapularis,
teres major
Triceps, supinator (turn
hand up), extensors of
manus and digits
Pectoralis
Suprasinatus, infraspinatus
Biceps,pronator, flexors of
manus and digits
Shoulder muscles
Arm extensors
Ventral flexors
Branchial muscles
Pectoralis
Supracoracoid
Arm flexors
First Arch
Adductor mandibulae
Intermandibularis
Adductor mandibulae
Intermandibularis
Masseter, temporalis,
pterygoids
mylohyoid
Second Arch
Ventral constrictors
Levator
Subarcual rectus,
interhyoid, constrictor colli
platysma
Other arches
Trapezius (cucullaris)
Trapezius
Trapezius (and its smaller
units), sternomastoid,
cleidomastoid
 Move skin of amniotes
 Extrinsic, striated
muscle (e.g., platysma)
 Originate on the
skeleton & insert on
the underside of the
dermis
 Intrinsic integumentary muscles (arrector
pili muscles) lie entirely within the dermis;
found in birds & mammals; mostly smooth
muscles



Consist of electric discs
(up to 20,000) which are
modified muscle cell with
associated nerves &
mitochondria
Each disc (electroplax)
produces electric signals
that propagate through the
water.
Specialized skin receptors
can sense disturbances
which are sent up to
specialized regions of the
brain that compute a
"picture" of the fish's
environment.



Salt water eel
can emit up to
50V
Fresh water eel
can emit up to
500V
Functions:
communication,
orientation with
objects in
environment,
detection of
prey, offense &
defense,
locating prey
(electrolocation)