Download - Skeletal Muscle and the Molecular Basis of Contraction

Transcript
Page 1: Skeletal Muscle and the Molecular Basis of Contraction

Skeletal Muscle and the

Molecular Basis of Contraction

Lanny Shulman, O.D., Ph.D.

University of Houston College of

Optometry

Page 2: Skeletal Muscle and the Molecular Basis of Contraction

• Like neurons, all muscle cells can be excited chemically, electrically, and mechanically to produce an action potential.

• Contractile proteins: actin and myosin (also troponin and tropomyosin)

• Actin-binding protein myosin is a molecular motor that converts energy from ATP hydrolysis into movement

Page 3: Skeletal Muscle and the Molecular Basis of Contraction

• Three Types:

– Smooth

lacks cross striations

found in hollow viscera

functionally syncytial

– Cardiac

has cross striations

functionally syncytial

contracts rhythmically in the absence of

external innervation due to the presence of

pacemaker cells

– Skeletal

Page 4: Skeletal Muscle and the Molecular Basis of Contraction

Skeletal Muscle

• Movement of bones and joints

• Cross-striations

• Neural control

• Voluntary control

• Twitch responses

Page 5: Skeletal Muscle and the Molecular Basis of Contraction
Page 6: Skeletal Muscle and the Molecular Basis of Contraction
Page 7: Skeletal Muscle and the Molecular Basis of Contraction
Page 8: Skeletal Muscle and the Molecular Basis of Contraction
Page 9: Skeletal Muscle and the Molecular Basis of Contraction
Page 10: Skeletal Muscle and the Molecular Basis of Contraction
Page 11: Skeletal Muscle and the Molecular Basis of Contraction
Page 12: Skeletal Muscle and the Molecular Basis of Contraction
Page 13: Skeletal Muscle and the Molecular Basis of Contraction
Page 14: Skeletal Muscle and the Molecular Basis of Contraction
Page 15: Skeletal Muscle and the Molecular Basis of Contraction
Page 16: Skeletal Muscle and the Molecular Basis of Contraction
Page 17: Skeletal Muscle and the Molecular Basis of Contraction
Page 18: Skeletal Muscle and the Molecular Basis of Contraction
Page 19: Skeletal Muscle and the Molecular Basis of Contraction

Contractile Properties of Skeletal

Muscle

• Two mechanisms control the amount

of force generated by a muscle:

1. Recruitment of more motor units

2. Increase firing frequency

Page 20: Skeletal Muscle and the Molecular Basis of Contraction
Page 21: Skeletal Muscle and the Molecular Basis of Contraction
Page 22: Skeletal Muscle and the Molecular Basis of Contraction
Page 23: Skeletal Muscle and the Molecular Basis of Contraction

Fiber Types of Striated Muscle

(except ocular)

1. Slow (Red) fibers:

– Moderate power output

– Moderate ATP consumption

– Fatigue resistant

2. Fast (White) fibers:

– Maximum power output

– Maximum ATP consumption

– Fatigable

Page 24: Skeletal Muscle and the Molecular Basis of Contraction
Page 25: Skeletal Muscle and the Molecular Basis of Contraction

Extraocular Muscles Are Different From Other

Striated Muscles

1. Smaller diameter: 5-40mm

2. Smaller motor unit: 10 fibers / motor neuron

3. Higher discharge rates than spinal motor

neurons

4. Innervation pattern is different in oculomotor

muscles

5. Extraocular muscles have twitch and non-

twitch fibers

6. Fatigue resistance in extraocular muscles is

the highest of any skeletal muscle

7. Extraocular muscles differ in fiber type

Page 26: Skeletal Muscle and the Molecular Basis of Contraction

Actions of the Extraocular MusclesMuscle Innervation Primary Action Secondary Action

Medial Rectus

Oculomotor N

(inferior

branch)

Adduction

Inferior Rectus

Oculomotor N

(inferior

branch)

Depression Excyclotorsion

Inferior Oblique

Oculomotor N

(inferior

branch)

Excyclotorsion Elevation

Superior Rectus

Oculomotor N

(superior

branch)

Elevation Incyclotorsion

Lateral RectusAbducens N

(CNVI)Abduction

Superior ObliqueTrochlear N

(CNIV)Incyclotorsion Depression

Levator Palpebrae

SuperiorisOculomotor N

Elevation/retraction

of the upper eyelid

Page 27: Skeletal Muscle and the Molecular Basis of Contraction

Extraocular Muscles Mnemonic

• Extraocular muscles cranial nerve

innervation:

• LR6-SO4-R3

• Lateral Rectus is 6th CN

• Superior Oblique is 4th CN

• Rest are all 3rd CN

Page 28: Skeletal Muscle and the Molecular Basis of Contraction

Anatomy of the Extraocular

Muscles

Page 29: Skeletal Muscle and the Molecular Basis of Contraction

Anatomy of the Extraocular

Muscles

Page 30: Skeletal Muscle and the Molecular Basis of Contraction

Anatomy of the Extraocular

Muscles

Page 31: Skeletal Muscle and the Molecular Basis of Contraction

Extraocular Muscles Controlled

by CN III• Medial Rectus Muscle

• Superior Rectus Muscle

• Inferior Rectus Muscle

• Inferior Oblique Muscle

Page 32: Skeletal Muscle and the Molecular Basis of Contraction

Overview of the Oculomotor

Nerve

Page 33: Skeletal Muscle and the Molecular Basis of Contraction

CNIII coursing through the area

of the right cavernous sinus

Page 34: Skeletal Muscle and the Molecular Basis of Contraction

Oculomotor Nuclear Complex &

Innervation of EOMs

Page 35: Skeletal Muscle and the Molecular Basis of Contraction

Primary Actions of the Extraocular

Muscles Innervated by CNIII

Page 36: Skeletal Muscle and the Molecular Basis of Contraction

CN III Innervates the Levator

Palpebrae Superioris Muscle

Page 37: Skeletal Muscle and the Molecular Basis of Contraction

Parasympathetic Innervation of the Iris

Sphincter Muscle & Ciliary Muscle

Page 38: Skeletal Muscle and the Molecular Basis of Contraction

Parasympathetic Innervation of the Iris

Sphincter Muscle & Ciliary Muscle

Page 39: Skeletal Muscle and the Molecular Basis of Contraction

Direct and Consensual Light

Reflex

Page 40: Skeletal Muscle and the Molecular Basis of Contraction

Superior Oblique Muscle

Page 41: Skeletal Muscle and the Molecular Basis of Contraction

Trochlear Nerve (IV) Innervates the

Superior Oblique Muscle

Page 42: Skeletal Muscle and the Molecular Basis of Contraction

Trochlear Nerve (IV) Innervates the

Superior Oblique Muscle

Page 43: Skeletal Muscle and the Molecular Basis of Contraction

Actions of the Superior Oblique Muscle

https://www.youtube.com/watch?v=eqV_t1-kP5c

Page 44: Skeletal Muscle and the Molecular Basis of Contraction

Lateral Rectus Muscle

Page 45: Skeletal Muscle and the Molecular Basis of Contraction

CN VI-Abducens Nerve

Page 46: Skeletal Muscle and the Molecular Basis of Contraction

CN VI-Abducens Nerve

Page 47: Skeletal Muscle and the Molecular Basis of Contraction

CN VI Through the Cavernous Sinus

Page 48: Skeletal Muscle and the Molecular Basis of Contraction

CN VI-Final Innervation

Page 49: Skeletal Muscle and the Molecular Basis of Contraction

Lateral Rectus Palsy

Page 50: Skeletal Muscle and the Molecular Basis of Contraction

Actions of the Extraocular

Muscles• https://www.youtube.com/watch?v=vd7OOJ7c1q4

Page 51: Skeletal Muscle and the Molecular Basis of Contraction

Orbicularis Muscle

• Innervated by Facial Nerve (CN VII)

• Function: closes the eyelid, involuntary reflex

blinking, voluntary wink

• Antagonist: Levator Palpebrae Superioris

Page 52: Skeletal Muscle and the Molecular Basis of Contraction

Corneal Reflex

• Lightly touching the cornea with a tissue

induces a rapid blink reflex

• It is a reliable evaluation of afferent CN V

(V1) and efferent CN VII fibers

• Corneal reflex is used as part of some

neurological exams.

– Reflex may be slowed or absent in some

conditions such as coma, stroke or a lesion

involving the trigeminal or facial nerve

Page 53: Skeletal Muscle and the Molecular Basis of Contraction