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Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion
1. 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.)
Longitudinal
muscle relaxed
(extended)
Bristles
(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.
Circular
muscle
contracted
Circular
muscle
relaxed
Longitudinal
muscle
contracted
Head
Figure 49.26 Bones and joints of the human skeleton
Key
Axial skeleton
Appendicular
skeleton
Skull
Examples
of joints
Head of
humerus
Scapula
1
Shoulder
girdle
Clavicle
Scapula
Sternum
Rib
Humerus
2
Vertebra
3
Radius
Ulna
Pelvic
girdle
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.
Humerus
Carpals
Phalanges
Ulna
Metacarpals
Femur
Patella
2 Hinge joints, such as between the humerus and
the head of the ulna, restrict movement to a single
plane.
Tibia
Fibula
Ulna
Tarsals
Metatarsals
Phalanges
Radius
3 Pivot joints allow us to rotate our forearm at the
elbow and to move our head from side to side.
Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion
1. 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 muscle
Muscle
-Made of many fibers
Bundle of
muscle fibers
Nuclei
Single muscle fiber
(cell)
-A single fiber is a muscle cell (multinucleated)
Plasma membrane
Myofibril
Z line
Light
band
-Each muscle fiber has many myofibrils
Dark band
Sarcomere
0.5 m
TEM
I band
A band
I band
M line
-Myofibrils made of actin (thin) & myosin (thick)
has head
Thick
filaments
(myosin)
Thin
filaments
(actin)
Z line
H zone
Sarcomere
Z line
-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 Mechanisms
Our focus: Movement & Locomotion
1.
2.
3.
4.
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?
Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction
Thick filament
Thin filaments
At rest:
-ATP bound to myosin head
-Head is cocked down &
away from actin
Thin filament
ATP
Myosin head (lowenergy configuration)
Thick
filament
Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction
Thick filament
Thin filaments
Thin filament
ATP
Myosin head (lowenergy configuration)
Thick
filament
-Myosin head hydrolyzes ATP
-Head cocked up & close
to actin
Cross-bridge
binding site
Actin
ADP
Pi
Myosin head (lowenergy configuration)
Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction
Thick filament
Thin filaments
Thin filament
Myosin head (lowenergy configuration)
ATP
Thick
filament
Cross-bridge
binding site
Actin
ADP
Pi
Myosin head binds to actin
forming a cross-bridge
ADP
Pi
Cross-bridge
Myosin head (lowenergy configuration)
Fig. 49.30 Myosin-actin interactions underlying muscle fiber contraction
Thick filament
The Sliding Filament Model
Thin filaments
Thin filament
Myosin head (lowenergy configuration)
ATP
ATP
Thick
filament
Thin filament moves
toward center of sarcomere.
+
Pi
ADP
Pi
Actin
ADP
Myosin head (lowenergy configuration)
ADP
Cross-bridge
binding site
Pi
Myosin head (lowenergy configuration)
Cross-bridge
-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
Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion
1.
2.
3.
4.
5.
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?
Figure 49.31 The role of regulatory proteins and calcium in muscle
fiber contraction ActinTropomyosin Ca -binding sites
2+
Troponin complex
(a) Myosin-binding sites blocked
Ca2+
Myosinbinding site
(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 Mechanisms
Our focus: Movement & Locomotion
1.
2.
3.
4.
5.
6.
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?
Figure 49.32 The roles of the sarcoplasmic reticulum and T
tubules in muscle fiber contraction
Motor
neuron axon
Mitochondrion
Synaptic
terminal
-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
T tubule
Sarcoplasmic
reticulum
Ca2+ released
from sarcoplasmic
reticulum
Myofibril
Plasma membrane
of muscle fiber
Sarcomere
Figure 49.33 Review of contraction in a skeletal muscle fiber
Synaptic
terminal
of motor
neuron
1 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.
Synaptic cleft
2
ACh
PLASMA MEMBRANE
T TUBULE
Action potential is propagated along plasma
membrane and down
T tubules.
SR
3 Action potential
triggers Ca2+
release from sarcoplasmic reticulum
(SR).
Ca2
7 Tropomyosin blockage of myosinbinding sites is restored; contraction
ends, and muscle fiber relaxes.
Ca2
4 Calcium ions bind to troponin;
troponin changes shape,
removing blocking action
of tropomyosin; myosin-binding
sites exposed.
CYTOSOL
ADP
P2
6 Cytosolic Ca2+ is
removed by active
transport into
SR after action
potential ends.
5 Myosin cross-bridges alternately attach
to actin and detach, pulling actin
filaments toward center of sarcomere;
ATP powers sliding of filaments.
Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion
1.
2.
3.
4.
5.
6.
7.
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
Figure 49.34 Motor units in a vertebrate skeletal muscle
Motor
unit 1
Spinal cord
Motor
unit 2
Synaptic terminals
Nerve
Motor neuron
cell body
Motor neuron
axon
Muscle
Muscle fibers
Tendon
Recruitment – when more muscle fibers are activated to increase tension (force)
Figure 49.35 Summation of twitches
Tension
Tetanus
Summation of
two twitches
Single
twitch
Action
potential
Time
Pair of
action
potentials
Series of action
potentials at
high frequency
Chapter 49: Sensory & Motor Mechanisms
Our focus: Movement & Locomotion
1.
2.
3.
4.
5.
6.
7.
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
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