Muscular SystemMuscular System

Josefino R. CastilloJosefino R. CastilloUniversity of Santo Tomas

Skeletal muscle, striated, voluntary; multinucleated, linear, unbranched

The muscle tissuesThe muscle tissues

Smooth muscle, spindle-shaped, involuntary; found in digestive tract

Cardiac muscle, striated, involuntary; found in the heart; presence of intercalated disk (see arrow)

TerminologyTerminology

Origin – the fixed part of a muscle; usually proximal in position Insertion – the movable part of a muscle; usually distal in position Belly – the part of the muscle with the widest diameter Action – the contraction or relaxation of the muscle resulting in any

of the following: Flexor – reduces a joint angle Extensor – increases a joint angle Adductor – draws a limb toward the central body mass Abductor – draws a limb away from the central body Levator – raises a part Depressor – lowers a part Constrictor – reduces an opening Dilator – increases an opening

TerminologyTerminology

DevelopmentDevelopment

mesoderm

epimere

mesomere – (reproductive system)

dermatome (dermis of the skin)sclerotome (skeletal system)myotome (voluntary muscles)

hypomere – (branchial/branchiomeric muscles)

• The mesoderm divides into three: the dorsal epimere, the lateral mesomere, and the ventral hypomere.

• Soon, each region differentiates into different organs

• The epimere divides into three: the dermatome that gives rise to the dermis of the skin; the sclerotome, that gives rise to the entire skeletal system; and the myotomes for the voluntary muscles.

• The entire reproductive system is derived from the mesomere

• The branchial/branchiomeric (involuntary) muscles of gills/ gill arches in fishes are derived from the hypomere

Groups of Somatic MusclesGroups of Somatic MusclesMuscle Groups Innervation (based on shark)Axial muscles  Extrinsic ocular muscles Oculomotor (III), trochlear (IV), and

abducens (VI) nerves  Branchiomeric muscles    Mandibular muscles Trigeminal (V) nerve    Hyoid muscles Facial (VII) nerve    Branchial muscles Glossopharyngeal (IX) and vagus (X) nerves  Epibranchial muscles Dorsal rami of occipital and anterior

spinal nerves  Hypobranchial muscles Ventral rami of spino-occipital nerves,

form hypobranchial nerve   Trunk and tail muscles    Epaxial muscles Dorsal rami of spinal nerves    Hypaxial muscles Ventral rami of spinal nervesAppendicular muscles  Dorsal group Ventral rami of spinal nerves  Ventral group Ventral rami of spinal nerves

Embryonic DevelopmentEmbryonic Development

Embryonic DevelopmentEmbryonic Development

Embryonic DevelopmentEmbryonic Development

Parietal musculatureParietal musculature

• The muscle is divided into epaxial muscles (lying above the lateral line (horizontal skeletogenous septum) and hypaxial (lying below the line)

• Muscles are separated by connective tissue partitions (myosepta)

Epaxial vs. Hypaxial muscles

• In fishes, the epaxial and hypaxial muscles are made up of longitudinal bundles which are modified for lateral movement

• In amphibians, the muscles are specialized for dorsoventral movement

NOTE: Be familiar with the names of the muscles in the diagram

Epaxial vs. Hypaxial muscles

• In reptiles, the dorsalis trunci is split into longissimus dorsi and iliocostalis while the interspinalis is now called the transverso-spinalis

• The obliques are now more developed

• The rectus abdominis lies over part of the internal oblique and transversus abdominis

Branchial/branchiomeric musclesBranchial/branchiomeric muscles

The branchial and/or branchiomeric muscles are found in the gill region of fishes and in the head and neck of tetrapods

In the shark, (see diagram in previous slide) this consists of the superficial constrictor above the gill slits, the ventral hyoid constrictor, intermandibularis, adductor mandibulae, preorbitalis, and other muscles shown in brown

These muscles are used in opening the mouth or moving water into and out of the gill chamber, i.e. respiration and feeding

Branchial/branchiomeric musclesBranchial/branchiomeric muscles

Branchiomeric and shoulder musclesBranchiomeric and shoulder muscles

Branchiomeric and shoulder musclesBranchiomeric and shoulder muscles

In the salamander, the same muscles (also shown in brown) are attached to the mouth

This includes adductor mandibulae, depressor mandibulae, levatores arcuum, sphinctor colli and the muscles attached to the mandible

Note the presence of the cucullaris which is also found in sharks

The shift in habitat from aquatic to terrestrial resulted in a change in musculature that should provide dorsoventral movement of the head which has to be raised from the ground

Muscles of the head in manMuscles of the head in man

In man, the head is not as muscular as it is in lower craniates

Some superficial muscles are found in front while the back (dorsal) is merely covered by skin

Hypobranchial musculature

Hypobranchial musculature

The hypobranchial muscles are found below the mandible of fishes and in the neck of tetrapods

In the shark, (see diagram in previous slide) this consists of (from the ventral side) coracomandibularis, intermandibularis, coracohyoideus and interhyoideus

In mammals (cat), this includes the derivatives of the rectus cervicis namely: the geniohyoid, omohyoid, sternothyroid, thyrohyoid, and sternohyoid

Other muscles of the neck include the sternomastoid that forms a V-shaped structure at the base of the neck, the mylohyoid that runs across the floor of the mouth, the digastric, and the stylohyoid

Dorsal trunk muscles

• The epaxial muscle in amphibians are almost undifferentiated, collectively called dorsalis trunci

• In mammals (rabbit), the epaxial muscle is divided into an iliocostalis adjacent to the horizontal skeletogenous septum; the longissimus dorsi at the lumbar region, that extends to the head as the longissimus capitis; and a multifidus spinae in the lumbar region, extending anteriorly as the spinalis dorsi in the chest region, and as semispinalis capitis et cervicis into the head and neck

Trunk muscles

Pls refer to the table towards the end of this presentation for a comparison of trunk muscles

Limb muscles

Limb muscles Note: compare the

muscles shaded green

These muscles are generally used for walking instead of swimming, hence a change from dorsal or ventral fin constrictors or levators to complex flexors and extensors is in order

Limb muscles

Special Sense Organs

Electric organs which are modified from muscles can generate electricity in these fishes

Comparative Anatomy of the Vertebrate Comparative Anatomy of the Vertebrate Muscular SystemMuscular SystemChordate Epaxial muscles Hypaxial muscles

Amphioxus -undifferentiated; myotomes found as V-shaped myotomes separated by connective tissue partitions, the myosepta

Fishes - dorsal longitudinal muscle bundles; with similar partitions as the amphioxus

-lateral and ventral longitudinal muscle bundles; no rectus abdominis

Amphibians -modified into dorsalis trunci; longissimus dorsi found at the back; iliolumbaris, and coccygeoiliacus, coccygeosacralis found posteriorly; separated from hypaxial muscles by horizontal skeletogenous septum

-modified into external oblique, and transversus abdominis; rectus abdominis found on either side of the linea alba, divided into segments by inscriptiones tendinae (tendinous inscriptions)

Reptiles -presence of a transverse spinalis system; longissimus divided into longissimus capitis going to the head, and a longissimus dorsi proper in the lumbar region

-modified into external oblique, and an internal oblique; rectus abdominis also present as in amphibians

Birds -modified for flight, highly reduced as a result of merging of muscles

-well-developed chest muscles adapted for flight

Mammals -multifidus spinae on either side of the middorsal line of the lumbar region homologous to transverse spinalis system of reptiles; presence of two bundles of longissimus dorsi proper and a lateral iliocostalis adjacent to the horizontal (or lateral) skeletogenous septum; anteriorly, the multifidus spinae is found as the semispinalis dorsi

-presence of an outer external oblique that runs posteroventrally, an internal oblique running anteroventrally, and a transversus abdominis that runs across the abdomen; the rectus abdominis continues into the neck as the rectus cervicis and differentiates into five muscles: the sternohyoid, sternothyroid, thyrohyoid, geniohyoid and omohyoid

Questions: How are epaxial muscles separated from the hypaxial muscle in tetrapods?

How do you know if the abdominal muscle is external, internal or transversus?

Dermal musclesDermal muscles

Chordate Dermal muscles Location/function

Fishes none none

Amphibians cutaneous pectoris on top of chest muscles; more prominent in toads than in frogs

Reptiles costocutaneous parietal muscles

in snakes (i.e. python), for progressive locomotion

Birds none none

Mammals mimetic muscles muscles of facial expression; more commonly found in monkeys

panniculus carnosus stretching the entire back portion of many mammals, i.e. carabaos; used for moving the back without moving any other part of the body, to drive away birds and insects from the animal's back