Overview of Muscle Tissue &
How it Contracts
Anatomy & Physiology
Muscle Tissue: Comparisons
• Skeletal
▫ attached to bones or skin
▫ cells singular, very long, cylindrical,
multinucleated
▫ voluntary
▫ striated
▫ contractions slow to fast
Skeletal Muscle Fibers
Muscle Tissue:Comparisons
• Cardiac:
▫ walls of the heart
▫ branching chains of cells connected by
intercalated discs,
▫ uninucleated & striated
▫ involuntary: pacemaker & nervous system control
▫ slow contraction, rhythmic
Cardiac Muscle
Muscle Tissue: Comparisons
• Smooth:
▫
▫
▫
▫
walls of hollow viscera (except heart)
cells singular, fusiform
uninucleated, no striations
involuntary, controlled by nervous system,
hormones, some chemicals, & stretch
▫ contractions slow
Smooth Muscle Fibers
Muscle Fibers
• all skeletal muscle cells referred to as
fibers
• all 3 muscle tissue type contract because
of same 2 microfilaments: actin & myosin
• all have subunits with prefixes: myo- or
sarco-
Connective Tissue Wrappings of
Skeletal Muscle
Smooth Muscle Layers in GI
Tract: Circular Inner/
Longitudinal Outer
Muscle Functions
1.
2.
3.
4.
Movement
Posture /Balance
Stabilizing Joints
Generating Heat
Skeletal Muscle Microanatomy
•
•
•
•
•
•
•
Sarcolemma: plasma membrane
Sarcoplasma: cytoplasm
Myofilaments: actin or myosin
Myosin: 1 of 2 principle contractile proteins
Actin: 2nd principle contractile protein
Sarcoplasmic Reticulum: SER
T-Tubules: ordered invaginations of
sacroplasmic reticulum into sarcoplasma
Skeletal Muscle Properties
1. Irritability
▫
ability to receive & respond to stimuli
2. Contractility
▫
ability to forcibly shorten when adequate
stimulus received
Nerve Stimulus
• 1 motor neuron (nerve cell that innervates a
muscle fiber) may stimulate a few fibers or
hundreds of them
• motor unit: 1 motor neuron & all the muscle
fibers it stimulates
Nerve Stimulus
• axon: extension from cell body that carries the
nerve impulse (action potential) to wherever
neuron needs to send it
• axon terminal: end of axon
Neuromuscular Junction
• junction between axon terminals surface
of muscle fiber
• Synapse: (synaptic cleft) gap filled with
interstitial fluid
NMJ
• neurotransmitter : chemical (messenger
molecule) released from axon terminal
• synaptic vesicles: vesicles that store
neurotransmitter molecules in axon bulb
until action potential hits which causes
vesicle  exocytose
• acetylcholine: neurotransmitter in all
motor neurons
• motor end plate: portion of sarcolemma
that has receptor proteins for
acetylcholine
Neuromuscular Junction
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/cha
pter10/animation__function_of_the_neuromus
cular_junction__quiz_3_.html
• http://www.wisconline.com/objects/ViewObject.aspx?ID=AP28
04
• http://faculty.massasoit.mass.edu/whanna/201
/201_content/topicdir/muscle/muscle_media/
muscle_VD/page142/page142.html
Mechanisms of Muscle
Contraction
Sliding Filaments Animation
• http://www.sci.sdsu.edu/movies/actin_myosin
_gif.html
• http://www.3dotstudio.com/zz.html
• http://www.blackwellpublishing.com/matthews
/myosin.html
Muscle Movements
• Origin: muscle attachment to the
immovable or less movable bone
• Insertion: muscle attachment to the
movable bone
Flexion
• generally in sagittal plane
• decreases the angle of the joint & brings 2
bones closer together
• Hinge Joints
• Ball-and-Socket Joints
Extension
• movement that increases the distance
between 2 bones or parts of the body
• If > 180◦ it is hyperextension
Rotation
• movement of a bone around its
longitudinal axis
• Ball-and-Socket Joints
• Atlas/Dens (shaking head “no”)
Abduction
• moving a limb away fro the midline, or
median plane
• includes fanning fingers or toes
Adduction
• movement of a limb toward midline
Circumduction
• proximal end stationary
• distal end moves in a circle
• limb as a whole outlines a cone
Dorsiflexion
• lifting foot so the dorsum of the foot (top
of foot) approaches the shin
• corresponds to extension of the hand
Plantar Flexion
• depressing the foot ( pointing the toes)
• corresponds to flexion of the hand
Inversion of the Foot
• turn sole medially
Eversion of the Foot
• turn sole laterally
Supination
• “turning backward”
• forearm rotates laterally so palm faces
anteriorly
• radius &ulna are parallel
Pronation
• “turning forward”
• forearm rotates medially so palm faces
posteriorly
• radius crosses ulna
Opposition
• thumb touches tips of other fingers on
same hand