Transcript BIO 2310 - MSU Denver

Muscular System

Function
– Locomotion
– Posture
– Protection
– Heat production
Muscle Classification

Skeletal Muscle
– Attached to skeleton
– Striated
– Muscle fiber = Muscle cell
 Multinucleate
 Myofibrils are striated cylinders within myofiber
Skeletal Muscle

Myofilaments are proteins within the
myofibrils that result in contraction
– Actin – thin & has a receptor site for myosin
– Myosin – thick & has a receptor site for actin
and ATP
– Contraction – Myosin heads attach to actin and
with ATP perform a Power Stroke
Skeletal Muscle

Sarcomere
 The distance from Z line to Z line
 The basic unit of contraction
 Sarcomere gets smaller as Power Stroke
occurs
Key Points

Why is the sarcomere the functional unit of
contraction?
 Why does the power stroke result in
contraction?
 What would happen to contraction if you
ran out of ATP?
Motor Neurons

Skeletal muscle cannot contract without
stimulation from a motor neuron
 Motor Unit = The motor neuron plus the
myofiber(s) it innervates
Key Points

Why would a spinal cord injury result in
paralysis?
Somatic Muscles
All of the body’s skeletal muscles except
the branchiomeric muscles
 Voluntary
 Body wall & Appendage muscles

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–
–
–
Trunk and Tail
Hypobranchial
Tongue
Extrinsic Eyeball
Somatic Muscles

Myotome derivatives primarily
 Some from hypomere
Key Points

What is a myotome?
Somatic Muscles

Orient the body in the environment
Somatic Muscles

Red Fibers
– More blood supply for aerobic metabolism
– Myoglobin for oxygen storage
– Fatigue resistant
– Fish for cruising long distances, tetrapods for
posture
Somatic Muscles

White fibers
– Less blood supply; geared for anaerobic
metabolism
– Fatiguable
– Fish for spurts of swimming
– Tetrapods for sprints
Key Points

Why is the breast meat of the goose dark,
but the breast meat of the chicken is white?
Cardiac Muscle

Striated with intercalated disks
 Involuntary
 Lateral plate mesoderm (hypomere) in
origin
Smooth Muscle
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Involuntary
Lateral plate mesoderm in origin
Regulates internal environment
Innervated by Autonomic Nervous System
Found in the wall of tubes and hollow organs
Intrinsic Eye muscles
Erectors of feathers and hairs
Key Points

Besides those mentioned, give a specific
example of where might you find smooth
muscle?
Gross features of skeletal muscle

Origin, insertion
 Tendon
 Aponeurosis
 Fascia
Muscle shapes
Skeletal Muscle Actions

Flex/Extend
 Adduct/Abduct
 Levator/Depressor
 Protract/Retract
 Constrictor/Dilator
 Rotator
Skeletal Muscle Actions

Supinator/Pronator
 Tensor (taut)
Skeletal Muscle Actions
Agonist – primary mover
 Antagonist – opposes primary mover
 Synergist – helps primary mover

Development & Phylogeny

Position
 Embryology
 Nerve supply
Development

Dorsal Mesoderm – Epimere – Somite
– Myotome
– Sclerotome & Dermatome

Lateral plate Mesoderm – Hypomere
– Somatic – body wall muscles
– Splanchnic – smooth muscle of viscera
AXIAL MUSCLES

Trunk
 Tail
 Hypobranchial
 Tongue
 Extrinsic Eye
Axial Muscles

Metamerism as in myomeres
Axial Muscles

Agnathans
 Simple
 Segments (myomeres)
 Myotome derivatives
Axial Muscles – Jawed Fish

Horizontal or Lateral Septum
 Epaxial Muscles
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–
–
–
From myotomes in embryology
Innervated from dorsal rami of spinal nerves
Extend spine & some lateral bending
Extrinsic eye muscles (innervated by cranial
nerves)
– Epibranchial muscles
Axial Muscles – Jawed Fish
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Hypaxial Muscles
 From Myotomes
– Innervated by ventral rami of spinal nerves
– Ventroflex and lateral bending
Hypaxial Muscles – Jawed fish

Hypobranchial muscles
 Located on floor of pharynx, pectoral girdle
to jaw
 Are hypaxial muscles that migrated forward
 Function in respiration & feeding
 E.g. Coracomandibularis, Coracohyoid
Axial Muscles - Tetrapods

Epaxial trunk muscles
 Dorsal muscles from skull to tail
 Dorsalis trunci in amphibians
 Longissimus – long dominant spine
extensor in amniotes
 Iliocostalis – most lateral epaxial spine
muscle important in reptiles
Epaxial Muscles

See Vertebrate Muscles page
Epaxial Muscles in Tetrapods

Trends
 Decreased except in neck
 Fewer myosepta
Axial Muscles - Tetrapods

Hypaxial Muscles
 Tend to form sling-like sheets
 Lateral muscles support & compress body
wall
 Obliques
 Transversus
 Intercostals in amniotes only
Hypaxial Muscles - Tetrapods
Rectus abdominis – ventroflexes and
compresses abdomen
 Diaphragm – unique to mammals for
breathing

Hypaxial Muscles in tetrapods

See Vertebrate Muscles page
Hypobranchial and Tongue
Muscles - tetrapods
Function – stabilizes hyoid and larynx
 E.g. geniohyoid, sternohyoid, sternothyroid,
thyrohyoid

Hypobranchial & Tongue
muscles in tetrapods

Tongue muscles
 Lingu-; Gloss Anchors to hyoid
 E.g. lingualis, styloglossus
Hypobranchial & Tongue
muscles in Tetrapods

See Vertebrate Muscles page
Extrinsic Eye muscles in
tetrapods

Voluntary
 Obliques – rotates eye along its transverse
axis
 Rectus – up, down, left, right
 Retractor in some
Extrinsic Eye muscles

See Vertebrate Muscles Page