1. Skeletal & Muscular Systems
Animal Locomotion
Skeletal & Muscular Systems

2. Learning Objectives (3/11/09)
Describe the types of skeletons that support and enable movement in animals, with examples.
Describe how muscles exert force against skeletal elements to maintain posture and produce movement.
Compare the structure and function of the three types of muscle tissue.
Differentiate between whole muscle contraction and contraction of a single muscle cell, including the sliding filament theory of muscle contraction.

3. Musculoskeletal Machines
The skeleton and muscles work together in lever systems
Muscles can only shorten by contraction, they cannot actively elongate.
An external force is needed to stretch a muscle back to its resting length.
Opposing muscle sets provide this external force.

4. Hydrostatic Skeletons
How do soft-bodied animals like worms and other forms that lack rigid skeletons operate opposing muscles?
p. 1046
Fluid held in internal compartments as a hydraulic fluid transfers force between opposing muscle sets.
As muscles contract, internal volume remains the same, so the opposing muscle set must stretch.
This stretch creates the potential to do work

5. Hydrostatic Skeleton
Sea anemones (Phylum ?) have cylindrical fluid-filled bodies that function as a hydrostatic skeleton.
They have both circular and longitudinal muscle that contract against the fluid in their gastrovascular cavity.

6. Nematode Worms
See p. 694
Roundworms have only longitudinal muscles, innervated by two nerve cords, and use a hydrostatic skeleton.
Their body can assume curved and S-shaped configurations to help them move through soil and other media.
Name the closed, water-filled body cavity that acts as the hydroskeleton.
nematode locomotion

7. Annelid Worms
Each segment in the worm body can act as an independent hydrostatic skeleton.
This permits much more complex changes in body shape.
The head is extended forward by contraction of circular muscles.
A wave of contraction of longitudinal muscles then anchors the segments near the head.
earthworm locomotion
See p. 724

8. Polychaete Worms
Contraction of longitudinal muscles on one side of a segment stretches the longitudinal muscles on the other side.
Parapodia act like paddles to push each segment toward the rear of the animal.
See p. 724
polychaete worm swimming

9. Exoskeletons
Exoskeletons are hardened outer surfaces to which internal muscles are attached.
Increased leg length allows greater speed and power in locomotion (simple lever systems).
Multiple, long legs create a potential problem of tripping over one’s legs.
Centipedes and crustaceans have staggered activity in their legs to prevent tripping.
More advanced forms (e.g. crustaceans and insects) fuse segments and reduce the number of legs.
p. 1046

10. Endoskeletons
Endoskeletons are internal, articulated systems of rigid supports consisting of bone and cartilage to which muscles are attached.
What are some of the advantages associated with endoskeletons, over exoskeletons?
How could you improve the efficiency of the lever system for arm flexion? 
p. 1046

11. Lever Systems
Muscles and bones work together around joints as systems of levers.
Lever systems of muscles and skeletons can be designed either for power or speed.
The ratio of load arm (resistance) to power arm (effort) determines the power.
A low load arm to power arm ratio provides high power but low speed
A high load arm to power arm ratio provides high speed but lower power.
Power L:P = 2
Speed L:P = 5

12. Internal organization of a muscle cell
What is stored within cisternae of muscle cells?
What is a myofibril?
p. 1072
Internal organization of a muscle cell
What is the functional unit of contraction in a muscle fiber? Circle and/or label one in this diagram.
Each t-tubule is an extension of the ________________.

13. Organization of Myofilaments in a Sarcomere
A sarcomere within a myofibril
p. 1070
myofibril
= actin
= myosin
Organization of Myofilaments in a Sarcomere

14. Events at the NMJ
p. 1072
Is the release of neurotransmitter active transport or passive transport?
Is the influx of Na+ ions by active transport or passive transport?
How does the influx of Na+ ions change the transmembrane electrochemical potential?

15. Are the calcium channels in cisternae voltage-gated or chemically-gated?
Besides Ca+2, what must also be present in order for myosin to bind to actin?

16. THANKS