Muscular System

1
Muscular System
2
Key Concepts andVocabulary Words

• The muscular system produces movement and
  maintains posture.
• There are three kinds of muscles skeletal,
  cardiac, and smooth.
• Muscles are excitable, contractile, extensible,
  and elastic.
• Muscles are attached to bone by tendons and are
  arranged in opposing or antagonistic pairs.
• Sarcomeres are the contractile units of muscle.
• Muscle striations are caused by the arrangement
  of myofibrils within the muscle cell. Each
  myofibril contains groups of myofilaments
  composed of actin and myosin proteins.

3
Key Concepts andVocabulary Words

• A muscle contracts when myosin binds to actin
  causing the filaments to slide past one another.
• Contraction is powered by ATP and controlled by
  two regulatory proteins and calcium ions (sliding
  filament theory).
• Nerves stimulate muscle contraction at the
  neuromuscular junction.
• Acetylcholine, released from the motor neuron,
  causes a change in muscle cell permeability
  resulting in the release of calcium ions and
  contraction.
• A motor neuron and all the muscle cells it
  stimulates are called a motor unit.

4
Key Concepts andVocabulary Words

• A muscle twitch is the contraction caused by a
  stimulus to the muscle.
• The ATP required for muscle contraction comes
  from creatine phosphate, aerobic respiration, and
  lactic acid fermentation.
• Slow-twitch muscles, found in the abdomen and
  back, contract slowly, powerfully, and with
  endurance.
• Fast-twitch muscles, found in the arms and legs,
  contract rapidly and powerfully, but with less
  endurance.
• Aerobic exercise increases endurance while
  resistance exercise builds muscle mass.

5
Characteristics of muscle tissue

1. Excitability receive and respond to stimuli
2. Contractility shorten and thicken
3. Extensibility stretch and extend
4. Elasticity return to original shape after
   contraction or extension

6
Functions

1. Motion
2. Maintenance of posture
3. Heat production
4. Protection of internal organs

7
Origin of muscle tissue

• Forms from the mesoderm germ layer
• Triploblasts? simplest flatworms
• Segmentation ? annelids, arthropods, vertebrates

8
Types of muscle tissue

• Skeletal
• Attached to bones
• Striated and voluntary
• Cardiac
• Heart wall
• Striated and involuntary
• Smooth
• Walls of hollow internal structures
• Nonstriated and involuntary

• Striated
• Voluntary movements
• Longitudinal or circular in shape
• Smooth
• Involuntary movements

• Vertebrate muscles

• Invertebrate muscles

9
Muscle action

• Motion produced by action of muscles on bones ?
  levers
• Tendons ? attach muscles to bones (e.g. Achilles
  tendon)
• 1 fixed point of attachment (origin) and 1 moving
  point of attachment (insertion)
• Fascia ? sheets that cover muscles
• Muscles work in antagonistic or opposing pairs

10
Muscle movement

• Adduction
• Abduction
• Flexion
• Extension
• Rotation
• Sphincters
• Levators
• Depressors
• Supination
• Pronation

11
Human skeletal muscle groups
12
Anatomy of skeletal muscles
epimysium
perimysium
tendon
Muscle Fascicle
Surrounded by perimysium
endomysium
Skeletal muscle
Skeletal muscle fiber (cell)
Surrounded by epimysium
Surrounded by endomysium
13
Organization of skeletal muscles
14
Overview of the Sliding Filament Theory
The muscle fiber is stimulated.
Ca2 ions are released.
Thin filaments move to middle of sarcomere.
Muscle fiber contracts.
Muscle tension increases.
15
Muscle twitch

• Cycle of contraction and relaxation generated
  from one stimulus
• Force Summation
• Increasing and size of fibers contracting
• Increasing frequency at which action potentials
  are sent to muscle fibers
• Types of Twitches
• Slow Twitch
• More ATP from aerobic respiration
• Continuous extended contractions over time
• Fast Twitch
• Anaerobic metabolism (creatine phosphate and
  lactic acid fermentation)
• Short bursts of speed
• Fatigue quickly

16
Aerobic vs anaerobic exercise

• Aerobic exercise
• Moderate intensity
• Extended periods of time
• Anaerobic exercise
• High intensity
• Shorter periods of time

17
Cramps

• Painful sensations caused by contraction/
• overshortening of muscles
• Causes
• Hyperflexion
• Inadequate oxygenation
• Changes in temperature
• Dehydration
• Low amount of electrolytes in blood
• Treatment
• Correct breathing
• Increasing intake of water and electrolytes