Lecture Outline: Muscles

I. Neural-Muscular System

A. Brain
B. Three kinds of muscle

1. Skeletal Muscle
2. Cardiac (Heart) Muscle
3. Smooth Muscle

II. Muscle is Contractile - Stimulation >> Shortens

A. Skeleton - 3 kinds - essential for muscle action
B. Muscle attaches to skeleton across a joint, causing joint to bend
C. Muscle Groups work in opposition to effect movement

III. Muscle Anatomy

A. Muscle - Comprised of many cells called Fibers
B. Fibers are comprised of many Myofibrils -- contractile proteins

IV. Contractile Mechanism: interaction between thin and thick filaments

A. Actin - thin filaments
B. Myosin - thick filament

V. Control

1. Neural - neuro-muscular synapse
2. Myosin - Actin Interaction
3. Ca⁺⁺ regulation

VI. Behavior

Lecture Notes: Muscle

I. Neural-Muscular System

A. Brain

1. Environmental Sensory Input
2. Output >> Muscle
3. Sensory Feedback from body (muscle, etc.)

B. Three kinds of muscle - Central Property >>> Contractile

1. Skeletal Muscle

a. Striated
b. Stimulated by Somatic Nervous System

2. Cardiac (Heart) Muscle

a. Striated
b. spontaneous - autonomous (self stimulating): pace maker cells
c. modulated by autonomous nervous system (Vegus Nerve)
d. modulated by hormones

3. Smooth Muscle

a. not visibly striated
b. intestine, blood vessels
c. no pace maker but cells are electrically coupled
d. neurally stimulated but self conducting
c. modulated by hormones

II. Muscle is Contractile - Stimulation >> Shortens

A. Skeleton - essential for muscle action

1. Internal Skeleton (like ours)
2. External Skeleton (like a crab or insect)
3. Hydrostatic Skeleton (like a worm, our heart, our intestine)

B. Muscle attaches to skeleton across a joint, causing joint to bend
C. Muscle Groups work in opposition to effect movement

III. Muscle Anatomy

A. Muscle - Comprised of many cells called Fibers

1. "Fibers" are multinucleate; cells fuse during development

B. Fibers are comprised of many Myofibrils

1. Myofibrils are contractile bundles
2. Myofibrils consist of several proteins, including actin and myosin

IV. Contractile Elements: interaction between thin and thick filaments

A. Actin - thin filaments

1. comprised of protein dimers linked in "chains"
2. each actin monomer has a myosin binding site
3. thin filaments are anchored at one end to "Z-line" proteins
4. thin filaments are free at other end
5. "sarcomere" is the name for unit between "Z-lines"

B. Myosin - thick filament

1. Twisted Dimer: 2 heads, one (twisted) tail
2. Myosin dimers polymerize together forming thick filament
3. Heads form "fingers";

- each filament end has region of fingers in oriented in opposite directions

4. during activation, myosin heads interact with actin filament

a. interaction is ATP dependent - each interaction consumes one ATP
b. interaction is cyclic
c. myosin walks along actin filaments, drawing Z-lines together

V. Control

1. Neural - neuro-muscular synapse

a. Motor Neuron innervates Muscle cells - synapse
b. Action Potential >> NT release >> Receptor activation >> Muscle Excitation
c. In Vertebrate Skeletal Muscle:

- NT is Acetylcholine, Receptor is ligand gated ion channel
- NT is degraded after release by enzyme acetylcholine esterase (AChE)

-- NT degradation important to remove NT quickly after nerve stimulation -- AChE is Nerve Gas Target

2. Myosin - Actin Interaction

a. Requires ATP - Movement (walking) of myosin heads requires ATP
b. Requires Ca⁺⁺

- each actin monomer has a myosin binding site
- at rest, these binding sites are covered by a protein called tropomyosin
- tropomyosin is attached to actin by protein called troponin
- Ca⁺⁺ binds to troponin, troponin moves and pulls tropomyosin away

-- myosin binding sites are uncovered on actin
-- with ATP, myosin starts walking along actin
-- Z-line proteins are pulled together, fiber shortens, muscle contracts

3. Ca⁺⁺ regulation

a. Ca⁺⁺ is sequestered (pumped and stored) in Sarcoplasmic Reticulum (SR)

- SR is the endoplasmic reticulum of muscle cells
- SR is intracellular Ca⁺⁺ store

b. Ca⁺⁺ is actively pumped into SR from muscle cytoplasm
c. neural activation >> muscle is electrically excited >> AP

AP ionic currents reach SR, open voltage sensitive Ca⁺⁺ channels
Ca⁺⁺ rushes out of SR, binds to tropomyosin,
actin-myosin permitted to interact >> contraction

d. AP stops, voltage sensitive Ca⁺⁺ channels close,

Ca⁺⁺ rapidly pumped into SR, tropomyosin returns,
actin-myosin interactions blocked >> relaxation

4. ATP dependence - high O2 demand - many mitochondria

VI. Behavior

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