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Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion What do skeletons do? Support Protect Allow movement What are the 3 types of skeletons? Hydrostatic Fluid under pressure in a closed body compartment Muscles are used to change the shape of the compartment Cnidarians, flatworms, nematodes, annelids Exoskeleton Outside surface of the animal Chitin & other structural proteins Many molt Endoskeleton Support from within
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Figure 49.25 Peristaltic locomotion in an earthworm
(a) Body segments at the head and just in front of the rear are short and thick (longitudinal muscles contracted; circular muscles relaxed) and anchored to the ground by bristles. The other segments are thin and elongated (circular muscles contracted; longitudinal muscles relaxed.) (b) The head has moved forward because circular muscles in the head segments have contracted. Segments behind the head and at the rear are now thick and anchored, thus preventing the worm from slipping backward. (c) The head segments are thick again and anchored in their new positions. The rear segments have released their hold on the ground and have been pulled forward. Longitudinal muscle relaxed (extended) Circular muscle contracted relaxed Head Bristles
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Figure 49.26 Bones and joints of the human skeleton
1 Ball-and-socket joints, where the humerus contacts the shoulder girdle and where the femur contacts the pelvic girdle, enable us to rotate our arms and legs and move them in several planes. 2 Hinge joints, such as between the humerus and the head of the ulna, restrict movement to a single plane. 3 Pivot joints allow us to rotate our forearm at the elbow and to move our head from side to side. Key Axial skeleton Appendicular skeleton Skull Shoulder girdle Clavicle Scapula Sternum Rib Humerus Vertebra Radius Ulna Pelvic girdle Carpals Phalanges Metacarpals Femur Patella Tibia Fibula Tarsals Metatarsals 1 Examples of joints 2 3 Head of humerus
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Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion What do skeletons do? What are the 3 types of skeletons? What does a muscle cell look like?
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Figure 49.28 The structure of skeletal muscle
Bundle of muscle fibers Single muscle fiber (cell) Plasma membrane Myofibril Light band Dark band Z line Sarcomere TEM 0.5 m I band A band M line Thick filaments (myosin) Thin filaments (actin) H zone Nuclei Made of many fibers A single fiber is a muscle cell (multinucleated) Each muscle fiber has many myofibrils Myofibrils made of actin (thin) & myosin (thick) has head Sarcomere – functional unit of a muscle
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Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion What do skeletons do? What are the 3 types of skeletons? What does a muscle cell look like? How do myosin & actin cause muscle contraction?
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Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction
Thick filament Thin filaments Thin filament ATP Myosin head (low- energy configuration) Thick filament At rest: ATP bound to myosin head Head is cocked down & away from actin
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Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction
Thick filament Thin filaments Thin filament ATP ADP P i Myosin head (low- energy configuration) Thick filament Actin Cross-bridge binding site -Myosin head hydrolyzes ATP -Head cocked up & close to actin
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Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction
Thick filament Thin filaments Thin filament ATP ADP P i Cross-bridge Myosin head (low- energy configuration) Thick filament Actin Cross-bridge binding site Myosin head binds to actin forming a cross-bridge
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Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction
Thick filament Thin filaments Thin filament ATP ADP P i Cross-bridge Myosin head (low- energy configuration) + Thin filament moves toward center of sarcomere. Thick filament Actin Cross-bridge binding site The Sliding Filament Model -ADP & Pi release from myosin sliding actin across myosin. Binding of a NEW ATP breaks the cross-bridge How much ATP is directly used in a muscle contraction? NONE
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Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion What do skeletons do? What are the 3 types of skeletons? What does a muscle cell look like? How do myosin & actin cause muscle contraction? Why is Ca+2 important for a muscle contraction?
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(a) Myosin-binding sites blocked (b) Myosin-binding sites exposed
Figure 49.31 The role of regulatory proteins and calcium in muscle fiber contraction Actin Tropomyosin Ca2+-binding sites Troponin complex (a) Myosin-binding sites blocked Myosin- binding site Ca2+ (b) Myosin-binding sites exposed -Ca+2 binds to troponin complex causing tropomyosin to roll off of actin. -This exposes myosin-binding site on actin.
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Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion What do skeletons do? What are the 3 types of skeletons? What does a muscle cell look like? How do myosin & actin cause muscle contraction? Why is Ca+2 important for a muscle contraction? What is the signal that causes a muscle contraction?
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Figure 49.32 The roles of the sarcoplasmic reticulum and T tubules in muscle fiber contraction
Acetylcholine (Ach) depolarizes plasma membrane -Depolarization is carried deep into muscle by T tubules -Depolarization causes SR to release Ca+2 -Recall Ca+2 binds to troponin Motor neuron axon Mitochondrion Synaptic terminal T tubule Sarcoplasmic reticulum Myofibril Plasma membrane of muscle fiber Sarcomere Ca2+ released from sarcoplasmic reticulum
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Figure 49.33 Review of contraction in a skeletal muscle fiber
ACh Synaptic terminal of motor neuron Synaptic cleft T TUBULE PLASMA MEMBRANE SR ADP CYTOSOL Action potential is propa- gated along plasma membrane and down T tubules. Action potential triggers Ca2+ release from sarco- plasmic reticulum (SR). Acetylcholine (ACh) released by synaptic terminal diffuses across synaptic cleft and binds to receptor proteins on muscle fiber’s plasma membrane, triggering an action potential in muscle fiber. 1 2 3 Tropomyosin blockage of myosin- binding sites is restored; contraction ends, and muscle fiber relaxes. 7 Cytosolic Ca2+ is removed by active transport into SR after action potential ends. 6 Myosin cross-bridges alternately attach to actin and detach, pulling actin filaments toward center of sarcomere; ATP powers sliding of filaments. 5 Calcium ions bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin-binding sites exposed. 4 Ca2 P2
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Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion What do skeletons do? What are the 3 types of skeletons? What does a muscle cell look like? How do myosin & actin cause muscle contraction? Why is Ca+2 important for a muscle contraction? What is the signal that causes a muscle contraction? How are muscles contractions graded? By varying the number of muscle fibers that contract By varying the rate at which muscle fibers are stimulated
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Figure 49.34 Motor units in a vertebrate skeletal muscle
Spinal cord Nerve Motor neuron cell body Motor unit 1 Motor unit 2 Motor neuron axon Muscle Tendon Synaptic terminals Muscle fibers Recruitment – when more muscle fibers are activated to increase tension (force)
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Figure 49.35 Summation of twitches
Action potential Pair of action potentials Series of action potentials at high frequency Time Tension Single twitch Summation of two twitches Tetanus
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Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion What do skeletons do? What are the 3 types of skeletons? What does a muscle cell look like? How do myosin & actin cause muscle contraction? Why is Ca+2 important for a muscle contraction? What is the signal that causes a muscle contraction? How are muscles contractions graded? By varying the number of muscle fibers that contract By varying the rate at which muscle fibers are stimulated What are the different types of muscle fibers? Slow oxidative sustain long contractions core muscles – posture aerobic Fast oxidative brief, rapid, powerful contractions Fast glycolytic Primarily use glycolysis
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Table 49.1 Types of Skeletal Muscle Fibers
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