Download Hydrostatic Skeletons

Animal Skeletons
The Musculo-Skeletal System
Functions:
•Support
•Protection
•Movement
all movement results from:
muscle working against a skeleton
3 Types of skeletons
•hydrostatic
•exoskeleton
•endoskeleton
Hydrostatic Skeletons
• A hydrostatic skeleton
• fluid held under pressure in a closed body
compartment
typical
of
•
• cnidarians
• flatworms
• nematodes
• annelids
Earthworm peristaltic movement
Exoskeleton
Hard encasement
deposited on
outside of animal
Typical of
mollusca
arthropoda
Thigh bone connected to the...
• The mammalian skeleton is built from more than 200 bones
• Some fused together and others connected at joints by ligaments that allow
freedom of movement
• are bones alive?
• osteoblasts, osteocytes
Endoskeleton
Hard supporting elements deposited on inside of
animal
Typical of
sponges
echinoderms
chordates
Do you know your bones?
Types of joints in the appendicular skeleton
Muscles move the skeleton
• What is always the action of muscle cells?
Vertebrate Skeletal
Muscle
• Skeletal muscles are attached to the skeleton in antagonistic
pairs
Contraction
Vertebrate Skeletal
Muscle
Vertebrate Skeletal
Muscle
Vertebrate Skeletal
Muscle
Sliding filament theory
• Mechanism of contraction?
• thick and thin filaments...
• slide past one another.
• Mechanism of sliding filaments?
• Interaction between...
• actin and myosin:
• The “head” of a myosin molecule binds to an actin
filament
• Forming a cross-bridge and pulling the thin filament
toward the center of the sarcomere
Sliding filament theory
Sliding filament theory
•ATP binds to myosin head
•Head releases from actin site
•Energized by phosphoryllation of ATP,
•Myosin head now able to bind to actin site
Sliding filament theory
Sliding filament theory
•Binding to actin site releases ADP + Phosphate
•Myosin head bends into low E config
Sliding filament theory
The Role of Calcium and
Regulatory Proteins
• If ATP available, why doesn’t muscle just keep contracting?
• Regulation
• Contraction stimulated by:
• a motor neuron
• At rest, myosin-binding sites blocked by:
• tropomyosin (regulatory protein)
Tropomyosin
Ca2+-binding sites
Actin
(a) Myosin-binding sites blocked
Troponin complex
The Role of Calcium and
Regulatory Proteins
• What do calcium ions (Ca2+) do?
• Bind to the troponin complex,
• which uncovers myosin-binding sites
Ca2+
Myosin-
binding site
The Role of Calcium and
Regulatory Proteins
• Where does Ca2+ come from? How do Ca2+ ions get released?
• Action potential (AP) in a motor neuron that synapses w/
the muscle fiber…
• releases acetylcholine (n.t.)…
• depolarizes the muscle and causing it to produce an AP
• causes the sarcoplasmic reticulum (SR) to release Ca2+
• “SR?”
• = modified ER
(b) Myosin-binding sites exposed
Neural Control of Muscle Tension
• Contraction of a whole muscle is graded
– Which means that we can voluntarily alter the
extent and strength of its contraction
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• There are two basic mechanisms by which the
nervous system produces graded contractions
of whole muscles
– the number of fibers that contract
– the rate at which muscle fibers are stimulated
• In a vertebrate skeletal muscle
– Each branched muscle fiber is innervated by
only one motor neuron
• Each motor neuron
– May synapse with multiple muscle fibers
Motor
unit 1
Spinal cord
Motor
unit 2
Synaptic terminals
Nerve
Motor neuron
cell body
Motor neuron
axon
Muscle
Muscle fibers
Figure 49.34
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A motor unit
– Consists of a single motor neuron and all the
muscle fibers it controls
• Recruitment of multiple motor neurons
– Results in stronger contractions
Tendon
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A twitch
– Results from a single action potential in a
motor neuron
• More rapidly delivered action potentials
– Produce a graded contraction by summation
Tension
Tetanus
Summation of two twitches
Single
twitch
Action
potential
Time
Pair of
action
potentials
Figure 49.35
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Series of action potentials at high frequency
• Tetanus is a state of smooth and sustained
contraction
– Produced when motor neurons deliver a volley
of action potentials
Types of Muscle Fibers
“Slow-twitch” vs “Fast twitch?”
white meat vs dark meat
muscle that needs energy for prolonged contraction/
exercise needs more Oxygen
= more myglobin, more pigment, darker
Skeletal muscle fibers are classified as slow oxidative,
fast oxidative, and fast glycolytic
Based on their contraction speed and major
pathway for producing ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Other Types of Muscle
• Types of skeletal muscles
• Cardiac muscle, found only in the heart
– Consists of striated cells that are electrically
connected by intercalated discs
– Can generate action potentials without neural
input
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In smooth muscle, found mainly in the walls of
hollow organs
– The contractions are relatively slow and may
be initiated by the muscles themselves
• In addition, contractions may be caused by
– Stimulation from neurons in the autonomic
nervous system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings