Transcript Chapter 49: Sensory and Motor Mechanisms

Skeletal Muscular Systems
Campbell, 5th ed, Chapter 49
Nancy G. Morris
Volunteer State Community College
Intro to Sensory Reception
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Action potentials that reach the brain via
sensory neurons are called sensations.
Interpretation of the sensation by the brain
is perception.
Perceptions (colors, smells, sounds, tastes)
are constructed in the brain & do not exist
outside it.
An age old question…
If a tree
falls in the
forest and
no one is
there to
hear it, is
there a
sound?
The fall produces
pressure waves in the air,
but if we define sound
as perception, then
there can be no sound
unless sensory receptors
detect the waves & an
animal’s brain perceives
them.
Sensory reception
Sensations, & their perceptions in the brain,
begin with sensory reception, the detection
of the stimulus by sensory cells.
 Sensory receptors: specialized neurons or
epithelial cells existing singly or in groups
 Exteroreceptors – detect stimuli from
outside the body (heat, light, pressure, etc.)
 Interoreceptors – detect stimuli within the
body (blood pressure , body position)
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Skin
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Receptors that detect the
sense of touch are called
mechanoreceptors.
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It also contains:
thermoreceptors,
pain receptors,
chemoreceptors
(gustatory, olfactory)
Figure 49.1
Sensory
receptors in
human skin
Functions of the Integument
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1)
2)
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4)
5)
6)
Largest organ of the body
Protection
Waterproofing layer
Temperature regulation
Sensory response to stimuli
Source of vitamin D (ultraviolet
cholesterol)
rays convert
Horny layer – dead, filled with keratin, constantly sloughed off
Continuous division at the basement membrane
Hearing & equilibrium
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The mammalian hearing organ is within
the inner ear
The inner ear also contains organs of
equilibrium
A lateral line system & inner ear detect
pressure waves in most fishes & aquatic
amphibians
Many invertebrates have gravity
sensors & are sound-sensitive
Ear and hearing …
Movement & locomotion
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Movement is the hallmark of
animals
Locomotion is active
movement from one place to
another
Locomotion
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Animals may swim, crawl, walk, run, hop,
or fly
In all forms, locomotion requires that an
animal expend energy to overcome two
forces that tend to keep it stationary:
friction and gravity.
Skeletons
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1) Protection (skull, ribs cage, etc.)
2) Support
3) Movement (lever systems)
In vertebrates:
4) Responsible for blood cell production
5) Store minerals
Three main types of skeletons:
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Hydrostatic skeletons
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Exoskeletons
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earthworms
arthropods
Endoskeletons
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vertebrates
Endoskeletons:
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Consist of hard supporting
elements, such as bones, buried
within the soft tissues of the
animal
Sponges – spicules
Echinoderms – hard dermal plates
beneath the skin and ossicles
Figure 49.23
Peristaltic
locomotion in
the earthworm
Figure 49.25
Exoskeleton
of an
arthropod
Endoskeletons:
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Found only in Chordates
Composed of cartilage, bone,
or combination
Mammalian skeleton has
approximately 200 major
bones
Major Divisions of Human Skeleton
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Axial Skeleton
• Cranium, hyoid, vertebral column, sternum and ribs
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Appendicular Skeleton
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Pectoral girdle & bones of upper appendages
• Clavicle, scapula, humerus, ulna, radius, phalanges,
metacarpals, carpals
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Pelvic girdle & bones of lower appendages
• Pubis, ilium, ischium, femur, patella, tibia, fibula,
tarsals, metatarsals, phalanges
Figure 49.24
The human
skeleton
A cast of your skull, sir, until the original is available, would
"
be an ornament to any anthropological museum. It is not my
intention to be fulsome, but I confess that I covet your skull.
"
The Hound of the Baskervilles, Chapter 1, Sir Arthur Conan Doyle
Major Joints of Human Skeleton
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Ball-and–socket joint
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Rotation
• Shoulder & hip joints
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Hinge joint
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Restrict movement to a single plane
• Knee & elbow
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Pivot joint
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Rotation
• Ulna, radius & tibia, fibula
Muscles
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Move skeletal parts by contracting
Action of the muscle is always to
contract. (Muscles only pull -NEVER push.)
Arranged in antagonistic pairs
with each muscle working against the
other
Figure 49.25
Cooperation
of muscles
& skeletons
in movement
Structure
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&
Function
of
Vertebrate Skeletal Muscle
skeletal muscle characterized by smaller and
smaller parallel units
bundles of long fibers running the length of
the muscle
each fiber is a multinucleated single cell
each fiber is a bundle of smaller myofibrils
each myofibril is composed of two
myofilaments: Actin (thin) & Myosin (thick)
Figure 49.26
The
structure
of skeletal
muscle
Skeletal muscle
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striated (repetition of light & dark bands)
each repeating unit is a sarcomere, the functional
unit of muscle contraction
borders of sarcomeres, Z lines, are lined up in
adjacent myofibrils
thin actin filaments attach to the Z lines & project
toward the center
thick myosin filaments are centered in the
sarcomere and “stitched together” at the M line
Actin & Myosin filaments
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ACTIN
Thin filaments
Composed of many globular
actin molecules (beads)
assembled in a long chain
(necklace)
Two protein chains are wound
around one another to produce
a single actin filament
Contain troponin & tropomyosin
proteins which in the presence
of Ca2+ “uncover” binding sites
on actin
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MYOSIN
Thick filaments
Longest known protein chain:
1,800 amino acids
200 or more parallel protein
molecules with free globular
“heads”
Myosin heads:
1) binding sites for
contraction and
2) contain enzymes that
split ATP to power the
contraction
Ultra Structure
of the
Sarcomere
M line – connection between
the thick myosin filaments
H zone – (from Latin ‘hell’ meaning bright or clear) the central
zone in the relaxed sarcomere containing only myosin filaments
I band – zone around the Z line that contains only actin
filaments
A band – marks the extent of the myosin filaments in the
sarcomere
Z line – the dark stripe in the center of the I band (bulkhead)
Skeletal Muscle
Sliding Filament Theory 1
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Contraction involves the sliding of thin actin filaments
between thick myosin filaments.
Innervation by the motor neuron stimulates the muscle
fiber. The neurotransmitter, acetylcholine, acts as the
chemical mediator diffusing across the membrane.
Acetylcholine generates electrical depolarization (by
pumping Ca2+ out) in the sarcoplasmic reticulum of the
entire muscle. Ca2+ binds to troponin of the thin actin
filaments causing tropomyosin to “uncover” the binding
sites.
Figure 49.30
Roles of
sarcoplasmic
reticulum & T
tubules in
contraction
Figure 49.29
The control
of muscle
contraction
Role of calcium in contraction
Sliding Filament Theory 2
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Myosin’s globular heads, acting like hooks, attach to
the uncovered binding sites on actin. The result is a
temporary cross-bridge. These cross-bridges form,
break, & reform rapidly as one filament slides (or is
pulled) past another.
Myosin heads contain enzymes that release the energy
in ATP (ADP + Pi ) to power contraction. It is the
chemical combination with the next ATP that releases
the myosin head from the actin binding site breaking
the temporary cross-bridge.
Rigor mortis results when the cross-bridges are
“locked” in place because no more ATP is available to
release myosin from its binding site.
Sliding Filament Theory 3
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Because the cross-bridges are forming,
breaking, & reforming, the actin filaments
are pulled toward the center of the H zone
causing contraction of the sarcomere.
The filaments themselves do not change
length. In response to the stimulus to
contract, the filaments slide past one
another and increase the amount by which
they overlap, thereby shortening
(contracting) the sarcomere.
Figure 49.28
Interaction of
actin & myosin in
muscle contraction
Figure 49.27
The slidingfilament model
of muscle
contraction
What zones & bands are
missing in the contracted
sarcomere?
Skeletal Muscle
Motor Units in Vertebrates
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Each muscle fiber (cell) has a single
neuromuscular junction, or synaptic
connection, with the motor neuron that
controls it.
Each motor neuron branches & controls
several muscle fibers.
A motor neuron & all the fibers it controls
constitute a motor unit.
Figure 48.32
Motor units in
vertebrate muscle
A motor unit …
Figure 49.31
Temporal
summation
of muscle
cell
contractions
A muscle twitch results from a single stimulus. More rapidly
delivered signals produce a graded contraction obtained by
summation. Tetanus is a state of smooth & sustained contraction
obtained when motor neurons deliver a volley of action potentials
Smooth Muscle Tissue Review
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Found throughout the body
particularly lining vessels & hollow
organs; responsible for peristalsis
Single nucleated cell with tapered
ends
Non-striated because actin &
myosin filaments are not regularly
arranged
Contracts slowly, but greater range
than striated
Cardiac Muscle Tissue Review
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Found only in the heart
Multinucleated
Striated, branching cells electrically
connected by intercalated discs
(specialized gap junctions that couple cells
electrically). An actin potential
generated in one part of the heart will
spread to all the cardiac muscle cells, &
the whole heart will contract.
Generates action potentials without neural
input
Plasma membrane has pacemaker
properties