Chapter 12 Flashcards
The human body has three types of muscle tissue:
skeletal
muscle, cardiac muscle, and smooth muscle
skeletal
Most skeletal
muscles are attached to the bones of the skeleton, enabling
these muscles to control body movement
cardiac
Cardiac muscle
{kardia, heart} is found only in the heart and moves blood
through the circulatory system
which muscles are classified as striated and why
Skeletal and cardiac muscles
are classified as striated muscles {stria, groove} because of their alternating light and dark bands seen under the light
microscope
soothie muscle
Smooth muscle is the primary muscle of internal organs
and tubes, such as the stomach, urinary bladder, and blood vessels. Its primary function is to influence the movement of material into, out of, and within the body
skeletal muscle fibers
s are large,
multinucleate cells that appear
striped or striated under the
microscope.
cardiac muscle fibers
are also striated but they are smaller, branched, and uninucleate. Cells are joined in series by junctions called intercalated disks.
smooth muscle fibers
are small
and lack striations
why isnt smooth muscle striated
Its lack of banding results from
the less organized arrangement of contractile fibers within the
muscle cell
Skeletal muscles are unique in that they contract only in
response to a
a signal from a somatic motor neuron. They cannot
initiate their own contraction, and their contraction is not influenced directly by hormones.
In contrast, cardiac and smooth muscle have multiple levels
of control. T- explain
Their primary extrinsic control arises through autonomic innervation, but some types of smooth and cardiac muscle
can contract spontaneously, without signals from the central nervous system. In addition, the activity of cardiac and some smooth
muscle is subject to modulation by the endocrine system. Despite
these differences, smooth and cardiac muscle share many properties with skeletal muscle
how are skeletal muscles usually attached to bones, what is an origin and an insertion of a muscle
Skeletal muscles are usually
attached to bones by tendons made of collagen [p. 80]. The
origin of a muscle is the end of the muscle that is attached closest to the trunk or to the more stationary bone. The insertion
of the muscle is the more distal {distantia, distant} or more mobile
attachment
flexor
The
muscle is called a flexor if the centers of the connected bones
are brought closer together when the muscle contracts, and the
movement is called flexion
extensor
The muscle is called an extensor if
the bones move away from each other when the muscle contracts,
and the movement is called extension
A skeletal muscle is a collection of muscle cells, or
muscle fibers, just as a nerve is a
collection of neurons
what does a skeletal muscle fiber look like
Each skeletal muscle fiber is a long, cylindrical cell with up to several hundred nuclei near the surface of the fiber. they are the largest cells in the body, created by the fusion of many individual embryonic muscle cells
myofibril
The main
intracellular structures in striated muscles are myofibrils {myo-,
muscle}, highly organized bundles of contractile and elastic proteins that carry out the work of contraction
what is the Sr wrapped around
each myofibril
terminal cisternae
The sarcoplasmic reticulum consists of longitudinal tubules with
enlarged end regions called the terminal cisternae
t-tubules
The terminal cisternae are adjacent to and closely associated
with a branching network of transverse tubules, also known as
t-tubules (FIG. 12.4). One t-tubule and its two flanking terminal
cisternae are called a triad. The membranes of t-tubules are a continuation of the muscle fiber membrane, which makes the lumen
of t-tubules continuous with the extracellular fluid
go over graph on pg 415
ok lol
crossbridge
Most of the time, the parallel thick and thin filaments of
the myofibril are connected by myosin crossbridges that
span the space between the filaments. Each G-actin molecule
has a single myosin-binding site, and each myosin head has one actin-binding site.
Crossbridges form when
the myosin heads of
thick filaments bind to actin in the thin filaments (Fig. 12.3d).
Crossbridges have two states: low-force (relaxed muscles) and
high-force (contracting muscles).
A Z disk runs through the
middle of every I band, so each half of an I band belongs to
a different sarcomere
The proper alignment of filaments within a sarcomere is
ensured by two proteins:
titin and nebulin
titin
Titin is a
huge elastic molecule and the largest known protein, composed of
more than 25,000 amino acids. A single titin molecule stretches
from one Z disk to the neighboring M line. To get an idea of the
immense size of titin, imagine that one titin molecule is an 8-footlong piece of the very thick rope used to tie ships to a wharf. By
comparison, a single actin molecule would be about the length and
weight of a single eyelash
functions of titin
) it stabilizes the position of
the contractile filaments and (2) its elasticity returns stretched
muscles to their resting length
nebulin def and what does it do
Titin is helped by nebulin, an
inelastic giant protein that lies alongside thin filaments and
attaches to the Z disk. Nebulin helps align the actin filaments
of the sarcomere.
At the molecular level, a contraction-relaxation cycle can
be explained by
the sliding filament theory of contraction. In intact
muscles, one contraction-relaxation cycle is called a muscle twitch
the sliding filament theory explains
how a muscle can contract and create force without creating movement. For example,
if you push on a wall, you are creating tension in many muscles
of your body without moving the wall. According to the sliding
filament theory, tension generated in a muscle fiber is directly proportional to the number of high-force crossbridges between the
thick and thin filaments
power stroke
In muscle, myosin heads bind to actin molecules, which are
the “rope.” A calcium signal initiates the power stroke, when
myosin crossbridges swivel and push the actin filaments toward the
center of the sarcomere. At the end of a power stroke, each myosin
head releases actin, then swivels back and binds to a new actin molecule, ready to start another contractile cycle
During contraction,
the heads do not all release at the same time or
the fibers would
slide back to their starting position, just as the mainsail would fall
if the sailors all released the rope at the same time.
do power strokes repeat
The power stroke repeats many times as a muscle fiber contracts.
The myosin heads bind, push, and release actin molecules over and
over as the thin filaments move toward the center of the sarcomere
troponin and tropomyosin
The answer is found in troponin (TN), a calcium-binding complex of three proteins. Troponin controls the positioning of an
elongated protein polymer, tropomyosin {tropos, to turn}.
what was the first piece of evidence suggesting that calcium acts as a messenger inside cells
The discovery that Ca2+, not the action potential, is the signal
for muscle contraction
rigor mortis
. In the condition known as
rigor mortis, the muscles “freeze” owing to immovable crossbridges.
The tight binding of actin and myosin persists for a day or so after
death, until enzymes released within the decaying fiber begin to
break down the muscle proteins.
g. E-C coupling
has four major events:
Acetylcholine (ACh) is released from the somatic motor neuron.
2. ACh initiates an action potential in the muscle fiber.
3. The muscle action potential triggers calcium release from the
sarcoplasmic reticulum.
4. Calcium combines with troponin to initiate contraction
endplate potential (EPP
The addition of net positive charge
to the muscle fiber depolarizes the membrane, creating an endplate potential (EPP). Normally, end-plate potentials always reach
threshold and initiate a muscle action potential (F
what has been implicated in fatigue
ion imbalances
Fast-twitch muscle fibers (type II) develop
tension two to three
times faster than slow-twitch fibers (type I). The speed with which
a muscle fiber contracts is determined by the isoform of myosin
ATPase present in the fiber’s thick filaments. Fast-twitch fibers split
ATP more rapidly and can, therefore, complete multiple contractile cycles more rapidly than slow-twitch fibers. This speed translates into faster tension development in the fast-twitch fibers
myoglobin
n, a red oxygen-binding pigment with a high affinity
for oxygen. This affinity allows myoglobin to act as a transfer molecule, bringing oxygen more rapidly to the interior of the fibers.
Because oxidative fibers contain more myoglobin, oxygen diffusion
is faster than in glycolytic fibers. Oxidative fibers are described
as red muscle because large amounts of myoglobin give them their
characteristic color
summation
If the interval of time between action potentials is
shortened, the muscle fiber does not have time to relax completely
between two stimuli, resulting in a more forceful contraction (Fig.
12.16b). This process is known as summation and is similar to
the temporal summation of graded potentials that takes place in
neurons [p. 261]
tetanus - what it is and when is it reached
If action potentials continue to stimulate the muscle fiber
repeatedly at short intervals (high frequency), relaxation between
contractions diminishes until the muscle fiber achieves a state of
maximal contraction known as tetanus
two types of tetanus
There are two types of
tetanus. In incomplete, or unfused, tetanus, the stimulation rate of the muscle fiber is not at a maximum value, and consequently the fiber
relaxes slightly between stimuli (Fig. 12.16c). In complete, or fused,
tetanus, the stimulation rate is fast enough that the muscle fiber does
not have time to relax. Instead, it reaches maximum tension and
remains there (Fig. 12.16d).
motor unit
The basic unit of contraction in an intact skeletal muscle is a
motor unit, composed of a group of muscle fibers that function together and the somatic motor neuron that controls them
(FIG. 12.17). When the somatic motor neuron fires an action potential, all muscle fibers in the motor unit contract.
Note that although
one somatic motor neuron innervates multiple fibers, each muscle
fiber is innervated by only a
single neuron.
recruitment
The force of contraction in a skeletal muscle can be increased
by recruiting additional motor units. Recruitment is controlled
by the nervous system and proceeds in a standardized sequence.
asynchronous recruitment
One way the nervous system avoids fatigue in sustained contractions is by asynchronous recruitment of motor units. The
nervous system modulates the firing rates of the motor neurons so
that different motor units take turns maintaining muscle tension.
The alternation of active motor units allows some of the motor
units to rest between contractions, preventing fatigue
isometric contractions
Contractions that create force without moving a load are called
isometric contractions {iso, equal + metric, measurement} or
static contractions
is skeletal muscle relatively uniform or different throughout the body
relatively uniform
theres a good chapter summary on pg 447 if u wanna see (u dont have to i dont think)
ok lol
