Download muscle structure - Evans Laboratory: Environmental Physiology

ANIMAL
PHYSIOLOGY
BIOL 3151:
Principles of Animal
Physiology
Dr. Tyler Evans
Email: tyler.evans@csueastbay.edu
Phone: 510-885-3475
Office Hours: M,W 10:30-12:00 or appointment
Website: http://evanslabcsueb.weebly.com/
PROBLEM SET #1
IN-CLASS ASSIGNMENT
WED OCT 16
• will test on Lectures 1-9
• will be in similar format to the midterm exam you will
take on Fri Oct 18th
• can use notes, textbook and discuss answers with
classmates
• bring notes from all lectures
• have the entire class to complete the assignment
LAST LECTURE
CELLULAR MOVEMENT AND MUSCLES
MICROTUBULES
• cells use this microtubule network to control the movement of vesicles and other
cargo to different parts of the cell
• e.g. color change in camouflaged animals
• Xenopus frog
darkens its skin by
transporting
pigment granules
from the
MICROTUBULE
ORGANIZING
CENTER to the
periphery of the
skin along
microtubules
Textbook Fig 5.3 pg 200
LAST LECTURE
CELLULAR MOVEMENT AND MUSCLES
MICROTUBULES
• squid chromatophores use the same mechanism
• use the polarity (charge difference) between the each end of the microtubule to
determine in which direction the pigment granules move (i.e. toward or away
from skin)
LAST LECTURE
CELLULAR MOVEMENT AND MUSCLES
TRANSPORT USING MICROTUBULES
• motor proteins recognize this polarity and each motor protein moves in a
characteristic direction:
• KINESIN: moves along the microtubule in the POSITIVE direction
• DYNEIN: moves along the microtubule in the NEGATIVE direction
KINESIN
DYNEIN
LAST LECTURE
CELLULAR MOVEMENT AND MUSCLES
TRANSPORT USING MICROTUBULES
e.g. neurotransmitters transport down axons
• neurotransmitters are released at synapses to induce a response
• neurotransmitters are carried from the cell body (i.e. soma) down the axon on
microtubules
• kinesin can transport neurotransmitters to the end of the synapse (+ direction)
• dynein then carries the empty synaptic vesicle back to the soma (- direction)
textbook Fig 4.16 pg 162
textbook Fig 5.7 pg 204
LAST LECTURE
CELLULAR MOVEMENT AND MUSCLES
MICROFILAMENTS
• microfilaments are the other type of cytoskeletal element used in movement
• also involved in transport within cells, but in cell shape changes and moving from
place to place
• microfilament based movement uses ACTIN and the motor protein MYOSIN
• microfilaments are composed of long string of ACTIN
• microfilaments form in much the
same way microtubules: “+” and
“-” ends of actin assemble
• actin monomers are termed GACTIN
• “G” stands for globular
• referred to as F-ACTIN when in
polymers
• “F” stands for filamentous
LAST LECTURE
CELLULAR MOVEMENT AND MUSCLES
SLIDING FILAMENT MODEL
• the myosin molecule extends by straightening its NECK (i.e. arms extending)
• the myosin HEAD then forms a bond with the actin filament (i.e. hands grasping
onto the rope)
• this strong interaction between actin and myosin is called a CROSS BRIDGE
• myosin bends and pulls the actin filament towards its tail (i.e. pull up)
• this step is called the POWER STROKE
• HEAD then uncouples from actin and myosin returns to the resting unattached
position
Textbook
Fig 5.12
pg 209
Actual movement depends on
whether it is actin or myosin that
is free to move
• if rope attached, you will pull
yourself (myosin is mobile)
• If rope not attached, you will
pull the rope (actin is mobile)
TODAY’S LECTURE
MUSCLE STRUCTURE AND REGULATION OF CONTRACTION
• large forces generated during muscle contraction are the result of combining the
actions of many polymers of myosin
• polymers of myosin are
called THICK FILAMENTS
• thick filaments are
doubled headed,
meaning they have
clusters of the myosin
head at each end
• in muscle tissue, thick
filaments of myosin slide
along polymers of actin
called THIN FILAMENTS
textbook Fig 5.15 pg 212
MUSCLE STRUCTURE
• in vertebrate STRIATED MUSCLE, thick and thin filaments are
arranged in a characteristic pattern
• cardiac (heart) and skeletal muscles are examples of striated
muscle
STRIATED MUSCLE
textbook Fig 5.16 pg 213
MUSCLE STRUCTURE
• basic unit of striated muscle is called the SARCOMERE
• muscles are comprised of many sarcomeres arranged in a repeated
pattern, that gives striated muscle striped appearance
SARCOMERE
textbook Fig 5.17 pg 215
MUSCLE STRUCTURE
• areas occupied by thick filaments appear darker than those lacking thick
filaments
• area occupied by thick filaments called the A-BAND
• lighter regions are areas lacking thick filaments and are comprised of thin
filaments and other cytoskeletal proteins
• this region is referred to as the I-BAND
• middle region where forming gap between extending thin filaments forms the
M-LINE
myosin
• Z-DISKS are plates that hold actin think filaments in place
actin
M-line
Z-disk
MUSCLE STRUCTURE
• basic unit of striated muscle is called the SARCOMERE
• sacromere is formed by a thick filament surrounded by an array of six
thin filaments
• at each end of the sacromere is a
protein plate called the Z-DISK
• thin filaments extend out from the
Z-disk
• the double headed thick filaments
are arranged between the two Zdisks
• thick filaments span two sets of
thin filaments, so that one end of
the thick filament can associate
with one set of thin filaments and
the other end with another set of
thin filaments
textbook Fig 5.18 pg 215
MUSCLE STRUCTURE
textbook Fig 5.17 pg 215
MUSCLE STRUCTURE
CHANGES IN ACTIN AND MYOSIN DURING MUSCLE CONTRACTION
• many myosin molecules extend their necks and attach to actin to form a CROSS
BRIDGE
• hydrolysis of ATP provides energy for POWER STROKE that pulls thin filaments,
which are attached to Z-disk, toward the M-line
• as a result, the sarcomere shortens or the muscle contract
MUSCLE STRUCTURE & CONTRACTION FORCE
CHANGES IN ACTIN AND MYOSIN DURING MUSCLE CONTRACTION
• the arrangement of the sarcomere determines contraction force
• if the sarcomere is too short, thin filaments will collide and there will be little
space for the muscle to contract
• the force generated will decrease
Normal Sarcomere
Too Short Sarcomere
textbook Fig 5.17 pg 215
MUSCLE STRUCTURE & CONTRACTION FORCE
CHANGES IN ACTIN AND MYOSIN DURING MUSCLE CONTRACTION
• if sarcomere is too long, some myosin heads will not overlap with thin filaments
and be unable to form cross-bridges
• fewer cross-bridges means less force generated during contraction
Normal Sarcomere
Too Long Sarcomere
textbook Fig 5.17 pg 215
MUSCLE STRUCTURE
• the arrangement of the sarcomere effects contraction force
textbook Fig 5.19 pg 216
MUSCLE CELL STRUCTURE
• muscle cells incorporate hundreds of thousands of repeating sarcomeres
• a single continuous stretch of interconnected sarcomeres is called a MYOFIBRIL
• MUSCLE CELLS are made of groups of myofibrils encased in a plasma
membrane called a SARCOLEMMA
REGULATION OF MUSCLE CONTRACTION
• first steps toward muscle contraction occur when action potentials from the
brain travel down motor neuron to the neuromuscular junction
• this triggers release of neurotransmitter ACETYLCHOLINE, which binds to a
receptor on the sarcolemma (muscle cell membrane)
• this binding induces an action potential to spread throughout the muscle cell
textbook Fig 4.16 pg 162
textbook Fig 5.7 pg 204
REGULATION OF MUSCLE CONTRACTION
• action potential generated when ACETYLCHOLINE binds to receptors spreads
across the SARCOLEMMA (muscle cell membrane)
• the sarcolemma has a unique feature important for contraction
• it is covered with pores called T-TUBULES that provide a pathway for action
potentials to spread across the muscle cell
• as the action potential spread across the muscle cell, it causes large amounts of
calcium (Ca+2) to be released from storage units called the SARCOPLASMIC
RETICULUM (in blue below)
REGULATION OF MUSCLE CONTRACTION
• the released Ca+2 is then used to regulate actin-myosin binding
• the Ca+2 signal is transmitted to actin and myosin by two proteins that associate
with the actin thin filaments: TROPONIN and TROPOMYOSIN
• when intracellular Ca+2 is low
the complex of troponin and
tropomyosin block myosin
binding sites on the thin
filament
textbook Fig 5.21 pg 220
• increases in intracellular Ca+2
causes complex of troponin
and tropomyosin to roll out of
the way and allow myosin to
bind to actin filament
REGULATION OF MUSCLE CONTRACTION
• TROPONIN is composed of three subunits (i.e. smaller proteins that group
together to form one large protein)
• TnC- is a Ca+2 sensor and can bind Ca+2 with high affinity
• TnI- blocks the myosin binding site
• TnT- binds tropomyosin and keeps complex associated with actin
C = calcium
I = inhibitory
T = tropomyosin
textbook Fig 5.21 pg 220
REGULATION OF MUSCLE CONTRACTION
• in a typical muscle cell, intracellular Ca+2 is very low and binding site on TnC are
empty.
• empty TnC interacts with TnI to block myosin from binding to actin
• when muscle is activated, intracellular Ca+2 spikes (100-fold) and binds to TnC
• binding of Ca+2 to TnC induces a change in conformation in TnI that exposes the
myosin binding site on actin
• because TnT is bound to tropomyosin the complex exposes the myosin
binding site by sliding down tropomyosin
INACTIVE
Myosin
head
ACTIVE
Troponin complex
(TnC, TnI, TnT)
tropomyosin
= exposed
myosin
binding site
actin
textbook Fig 5.22 pg 220
REGULATION OF MUSCLE CONTRACTION
SLIDING FILAMENT MODEL
• the myosin molecule extends by straightening its NECK (i.e. arms extending)
• the myosin HEAD then forms a bond with the actin filament (i.e. hands grasping
onto the rope)
• this strong interaction between actin and myosin is called a CROSS BRIDGE
• myosin bends and pulls the actin filament towards its tail (i.e. pull up)
• this step is called the POWER STROKE
• HEAD then uncouples from actin and myosin returns to the resting unattached
position
Textbook
Fig 5.12
pg 209
Actual movement depends on
whether it is actin or myosin that
is free to move
• if rope attached, you will pull
yourself (myosin is mobile)
• If rope not attached, you will
pull the rope (actin is mobile)
REGULATION OF MUSCLE CONTRACTION
• actin-myosin activity stops when action potentials from brain stop and
intracellular Ca+2 falls back to resting levels
• causes Ca+2 binding sites on TnC to be vacant again
• myosin binding sites in actin are once again blocked by TnI
Ca+2 and myosin binding
textbook Fig 5.22 pg 220
REGULATION OF MUSCLE CONTRACTION
• this relaxation phase is dependent on ACETYLCHOLINESTERASE, that breaks the
down acetylcholine to acetic acid and choline
• this stops action potential from triggering the release of Ca+2 from sarcoplasmic
reticulum
LECTURE SUMMARY
• large forces generated during muscle contraction are the result of combining
the actions of many polymers of myosin (THICK FILAMENTS) and actin (THIN
FILAMENTS)
• basic unit of striated muscle is called the SARCOMERE, which is highly patterned
and gives this type of muscle its striped appearance (know the structure)
• binding of acetylcholine to its receptor causes action potential to spread across
muscle cell membrane called the SARCOLEMMA
• aided by pores called T-TUBULES
• striated muscle contracts when action potential causes calcium (Ca+2) levels
increase within the myofibril
• the Ca+2 signal is transmitted to the contractile apparatus by two proteins
associated with thin filaments: TROPONIN and TROPOMYOSIN
• this relaxation phase is dependent on ACETYLCHOLINESTERASE that stops
action potential from triggering the release of Ca+2 from sarcoplasmic reticulum
NEXT LECTURE
MUSCLE DIVESITY IN VERTEBRATES AND
INVERTEBRATES
textbook Fig 5.34 pg 239