Chapter 49: Sensory & Motor MechanismsOur focus: Movement & Locomotion1. What do skeletons do?

- Support - Protect- Allow movement

2. 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

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.

Longitudinalmuscle relaxed(extended)

Circularmusclecontracted

Circularmusclerelaxed

Longitudinalmusclecontracted

HeadBristles

1 Ball-and-socket joints, where the humerus contactsthe shoulder girdle and where the femur contacts thepelvic girdle, enable us to rotate our arms andlegs and move them in several planes.

2 Hinge joints, such as between the humerus andthe head of the ulna, restrict movement to a singleplane.

3 Pivot joints allow us to rotate our forearm at theelbow and to move our head from side to side.

KeyAxial skeleton

Appendicularskeleton

Skull

Shouldergirdle

Clavicle

Scapula

Sternum

Rib

Humerus

Vertebra

RadiusUlnaPelvicgirdle

Carpals

Phalanges

Metacarpals

Femur

Patella

Tibia

Fibula

TarsalsMetatarsalsPhalanges

1

Examplesof joints

2

3

Head ofhumerus

Scapula

Humerus

Ulna

UlnaRadius

Figure 49.26 Bones and joints of the human skeleton

Chapter 49: Sensory & Motor MechanismsOur focus: Movement & Locomotion1. What do skeletons do?2. What are the 3 types of skeletons?3. What does a muscle cell look like?

Figure 49.28 The structure of skeletal muscleMuscle

Bundle ofmuscle fibers

Single muscle fiber(cell)

Plasma membrane

Myofibril

Lightband Dark band

Z line

Sarcomere

TEM 0.5 m

I band A band I band

M line

Thickfilaments(myosin)

Thinfilaments(actin)

H zoneSarcomere

Z lineZ line

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

Students-Get test folders from center table-Remaining essays-Review session – Monday 7AM-AP exam $$ - March 9

Chapter 49: Sensory & Motor MechanismsOur focus: Movement & Locomotion1. What do skeletons do?2. What are the 3 types of skeletons?3. What does a muscle cell look like?4. How do myosin & actin cause muscle contraction?

Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction

Thick filament

Thin filaments

Thin filament

ATPMyosin head (low-energy configuration)

Thick filament

At rest:-ATP bound to myosin head-Head is cocked down &

away from actin

Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction 

Thick filament

Thin filaments

Thin filament

ATP

ADPP i

Myosin head (low-energy configuration)

Myosin head (low-energy configuration)

Thick filament

Actin

Cross-bridge binding site

-Myosin head hydrolyzes ATP-Head cocked up & close

to actin

Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction 

Thick filament

Thin filaments

Thin filament

ATP

ADP

ADP

P i

P i

Cross-bridge

Myosin head (low-energy configuration)

Myosin head (low-energy configuration)

Thick filament

Actin

Cross-bridge binding site

Myosin head binds to actinforming a cross-bridge

Fig. 49.30 Myosin-actin interactions underlying muscle fiber contractionThick filament

Thin filaments

Thin filament

ATP

ATP

ADPADP

ADP

P i P i

P i

Cross-bridge

Myosin head (low-energy configuration)

Myosin head (low-energy configuration)

+

Thin filament moves toward center of sarcomere.

Thick filament

Actin

Cross-bridge binding site

Myosin head (low-energy configuration)

-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?

The Sliding Filament Model

NONE

Chapter 49: Sensory & Motor MechanismsOur focus: Movement & Locomotion1. What do skeletons do?2. What are the 3 types of skeletons?3. What does a muscle cell look like?4. How do myosin & actin cause muscle contraction?5. Why is Ca+2 important for a muscle contraction?

Figure 49.31 The role of regulatory proteins and calcium in muscle fiber contraction

ActinTropomyosin 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.

Chapter 49: Sensory & Motor MechanismsOur focus: Movement & Locomotion1. What do skeletons do?2. What are the 3 types of skeletons?3. What does a muscle cell look like?4. How do myosin & actin cause muscle contraction?5. Why is Ca+2 important for a muscle contraction?6. What is the signal that causes a muscle contraction?

Figure 49.32 The roles of the sarcoplasmic reticulum and T tubules in muscle fiber contraction

Motorneuron axon

Mitochondrion

Synapticterminal

T tubule

Sarcoplasmicreticulum

Myofibril

Plasma membraneof muscle fiber

Sarcomere

Ca2+ releasedfrom sarcoplasmicreticulum

-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

Figure 49.33 Review of contraction in a skeletal muscle fiber

ACh

Synapticterminalof motorneuron

Synaptic cleft T TUBULEPLASMA MEMBRANE

SR

ADP

CYTOSOL

Action potential is propa-gated along plasmamembrane and downT tubules.

Action potentialtriggers Ca2+

release from sarco-plasmic reticulum(SR).

Acetylcholine (ACh) released by synaptic terminal diffuses across synapticcleft 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; contractionends, and muscle fiber relaxes.

7

Cytosolic Ca2+ is removed by active transport into SR after action potential ends.

6

Myosin cross-bridges alternately attachto actin and detach, pulling actinfilaments toward center of sarcomere;ATP powers sliding of filaments.

5

Calcium ions bind to troponin;troponin changes shape,removing blocking actionof tropomyosin; myosin-bindingsites exposed.

4

Ca2

Ca2

P2

Chapter 49: Sensory & Motor MechanismsOur focus: Movement & Locomotion1. What do skeletons do?2. What are the 3 types of skeletons?3. What does a muscle cell look like?4. How do myosin & actin cause muscle contraction?5. Why is Ca+2 important for a muscle contraction?6. What is the signal that causes a muscle contraction?7. How are muscles contractions graded?

- By varying the number of muscle fibers that contract- By varying the rate at which muscle fibers are stimulated

Figure 49.34 Motor units in a vertebrate skeletal muscle

Spinal cord

Nerve

Motor neuroncell body

Motorunit 1

Motorunit 2

Motor neuronaxon

Muscle

Tendon

Synaptic terminals

Muscle fibers

Recruitment – when more muscle fibers are activated to increase tension (force)

Figure 49.35 Summation of twitches

Actionpotential Pair of

actionpotentials

Series of action potentials at

high frequency

Time

Ten

sion

Singletwitch

Summation of two twitches

Tetanus

Chapter 49: Sensory & Motor MechanismsOur focus: Movement & Locomotion1. What do skeletons do?2. What are the 3 types of skeletons?3. What does a muscle cell look like?4. How do myosin & actin cause muscle contraction?5. Why is Ca+2 important for a muscle contraction?6. What is the signal that causes a muscle contraction?7. How are muscles contractions graded?

- By varying the number of muscle fibers that contract- By varying the rate at which muscle fibers are stimulated

8. What are the different types of muscle fibers?- Slow oxidative

- sustain long contractions - core muscles – posture - aerobic

- Fast oxidative - brief, rapid, powerful contractions - aerobic

- Fast glycolytic- Primarily use glycolysis

Table 49.1 Types of Skeletal Muscle Fibers