B3.3  Muscle and Motility

Theme:  Form and Function

Anatomical forms create the mechanical basis for generating, controlling, and optimizing movement in different environments.

• ​Sliding filament mechanism works through the specific arrangement of actin and myosin filaments in sarcomeres, where molecular structure directly determines contractile function.
  
• Titin protein structure provides elastic recoil and prevents overstretching, showing how molecular form creates functional properties.
• Motor unit organization connects motor neurons to muscle fibers through neuromuscular junctions, creating the structural basis for controlled movement.
• Skeletons serve as anchorage points and levers. Exoskeletons in arthropods provide external support while endoskeletons in vertebrates enable internal leverage systems.
• Synovial joint structure enables movement through coordinated components: bones provide rigid levers, cartilage reduces friction, synovial fluid lubricates, ligaments provide stability, and tendons connect muscles to bones.
• Antagonistic muscle arrangement is necessary because muscles can only contract, requiring opposing pairs for controlled movement. 
• Joint range of motion reflects structural constraints on movement possibilities.
• ​Movement serves survival functions (foraging, escape, mating, and migration) that depend on structural adaptations in all organisms, whether motile species with specialized locomotory structures or sessile species with internal movement systems.

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How do muscles contract and cause movement?
• What are the benefits to animals of having muscle tissue?

​​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What are the advantages and disadvantages of dispersal of offspring from their parents?
• In what ways does locomotion contribute to evolution within living organisms? 

Key Terms to Know: all are higher level only

Actin
Antagonistic Muscles
Arthropod
Bone
Cartilage
Contraction
Endoskeleton
Exoskeleton
External Intercostals
Femur
Filament
Flipper
Fluke
Foraging

Goniometer
Hip
Internal Intercostals
Joint Angle
Lever
Ligament
Locomotion
Marine Mammal
Migration
Motile
Motor Neuron
Motor Unit
Muscle
Muscle Fibre

Myosin
Neuromuscular Junction
Pelvis
Potential Energy
Sarcomere
Sessile
Skeleton
Sliding-Filament Theory
Streamlining
Synovial Fluid
​Synovial Joint
Tendon
Titin
Vertebrate

AHL ​​B3.3.1-- Adaptations for movement as a universal feature of living organisms.

• State that movement can occur within a body or as locomotion from one place to another.
• Compare movement in motile and sessile species.
• List an example of a motile and a sessile species.​

AHL ​​B3.3.2— Sliding filament model of muscle contraction.

• Outline the relationship between muscle fibers, myofibrils and sarcomeres.
• Annotate a diagram of the sarcomere, including the role of the Z-line, titin, thin actin filaments, thick myosin filaments, light band and dark band.
• Explain the sliding-filament mechanism of muscle contraction, including the role of actin, myosin heads, cross bridges, ATP, and the power stroke.​

AHL ​​B3.3.3— Role of the protein titin and antagonistic muscles in muscle relaxation.

• State that a muscle can only exert force when it contracts. 
• State that lengthening of a muscle happens when it relaxes. 
• Define antagonistic pairs in relation to muscle movement.
• State an example of an antagonistic pair of muscles.
• Outline the role of the titin protein in muscle stretching.  
• Outline the mechanism by which the protein titin stores potential energy.​

AHL ​​B3.3.4— Structure and function of motor units in skeletal muscle.

• Outline the structure and function of a motor unit. 
  
• Annotate a diagram of a neuromuscular junction, including the function of the motor neuron, acetylcholine, and muscle fibre. ​​

AHL ​​B3.3.5— Roles of skeletons as anchorage for muscles and as levers.

• Compare and contrast the structure and function of endoskeletons with exoskeletons.
• Compare the function of muscles, joints and bones to that of a lever.​

AHL ​​B3.3.6- Movement at a synovial joint.

• Define synovial joint.
• State the function of structures found in a synovial joint, including the bones, cartilage, synovial fluid, ligaments, muscles and tendons. 
• Label a diagram of the human hip joint inclusive of:  femur, pelvis, joint capsule, synovial fluid, muscles, ligament and cartilage.

AHL ​​B3.3.7— Range of motion of a joint.

• Compare the articulation of hinge joints with that of a ball and socket joint.
• Measure the range of motion of the human hip in terms of flexion, extension, rotation, abduction and adduction.

AHL ​​B3.3.8- Internal and external intercostal muscles as an example of antagonistic muscle action to facilitate internal body movements.

• State the location of the internal and external intercostal muscles. 
• Describe the state of contraction of the internal and external intercostal muscles during inspiration and expiration.
• Outline the mechanism by  potential energy is stored during contraction of antagonistic muscles. 

AHL ​​B3.3.9- Reasons for locomotion.

• List reasons animal locomotion, with one example of each.

AHL ​​B3.3.10- Adaptations for swimming in marine mammals.

• Outline the adaptations for streamlining, locomotion and ventilation of lungs in marine mammals.