Chapter 8 Review

1
Chapter 8 Review

• The Muscular System

2
The Muscles

• Each muscle is an organ, comprised of skeletal
  __________ tissue, several ____________ tissue
  coverings, ____________ tissue to cause it to
  contract, and _______________ to nourish it.

muscle
connective
nervous
blood
3
Connective Tissue Coverings

• Layers of dense connective tissue, called
  ____________, surround and separate each muscle.
• This connective tissue extends beyond the ends of
  muscle and gives rise to cord like ___________
  that are fused to the periosteum of bones.
• Sometimes muscles are connected to each other by
  broad sheets of connective tissue called
  _____________.
• Under the outer layer another layer of connective
  tissue around each whole muscle is called the
  _____________.
• The _______________ surrounds individual bundles
  of fibers called ___________ within each muscle.
• Each muscle cell (fiber) is covered by a
  connective tissue layer called ___________________
  .

fascia
tendons
aponeuroses
epimysium
perimysium
fascicles
endomysium
4
Skeletal Muscle Fibers Structure
sarcolemma

• The muscle fiber membrane is called the
  ____________ which contains the cytoplasm called
  ______________.
• Within the sarcoplasm are many perpendicular
  myofibrils composed of smaller filaments called
  ______________.
• These myofilaments are actually two types of
  filaments, a thicker filament composed of the
  protein __________ and a thinner mostly made of
  the protein ____________.
• The dark stripes are called ____ bands and the
  light bands are called ____ bands.
• A ____________ is defined as a unit extending
  from one _____ line to the next (center of the
  light band).
• T tubules transverse tubules. Where are they
  located? __________________
• Are they open or close to the outside?
• What other tubular structure are they associated
  with?
• What ion does this other tubular structure
  contain?

sarcoplasm
myofilaments
myosin
actin
A
I
Z
sarcomere
Surface invaginations of the sarcolemma
Open
Sarcoplasmic reticulum
Calcium Ions
5
Neuromuscular Interaction

• Neuromuscular junction The site where the motor
  neuron and muscle fiber meet
• The muscle fiber membrane forms a
  _________________ in which the sarcolemma is
  tightly folded and where nuclei and mitochondria
  are abundant.
• Acetylcholine neurotransmitter released from
  the __________________ of the neuron.
• Acetycholinesterase what is its function?
• Where is it found?
• Motor Unit A _________ neuron and the muscle
  __________ it controls make up a motor unit when
  stimulated to do so, the muscle fibers of the
  motor unit contract all at once.

Motor end plate
Quickly breaks down and removes acetylcholine
Axon terminal
synapses between the neuron and the muscle
membrane
motor
fibers
6
Skeletal Muscle Contraction

• Muscle contraction involves several components
  that result in the shortening of sarcomeres, and
  the pulling of the muscle against its
  attachments.
• The protein _________ consists of two twisted
  strands with globular cross-bridges projected
  outward along the strands.
• _________ is a globular protein with myosin
  binding sites. What two proteins are associated
  with it?

myosin
Actin
Troponin and tropomyosin
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What is the sarcoplasmic reticulum?

• A series of channels inside the muscle cell that
  stores calcium ions.

8
Skeletal Muscle Contraction

• According to the sliding filament theory of
  muscle contraction, if allowed to, the myosin
  crossbridge attaches to the binding site of the
  actin filament and bends, pulling on the actin
  filament it then releases and attaches to the
  next binding site on the actin, pulling again.
  What is preventing this from happening
  continuously?
• Energy from the conversion of ATP to ADP is
  provided to the cross-bridges from the enzyme
  ATPase, causing them to be in a cocked position.

Requires calcium ions to be present in order to
occur
ATPase is stored in myosin-filaments
9
Creatine phosphate stores energy that is used to
convert ADP to ATP during muscle contraction
10
Stimulus for Contraction

• The motor neuron must release the
  neurotransmitter acetylcholine from its synaptic
  vesicles into the synaptic cleft in order to
  initiate a muscle contraction.
• Protein receptors in the motor end plate detect
  the neurotransmitters, and a muscle impulse
  spreads over the surface of the sarcolemma and
  into the T tubules where it reaches the
  sarcoplasmic reticulum.

11
When a nerve impulse reaches the end of a motor
neuron,

• Acetylcholine is released!

12
Stimulus for Contraction

• Upon receipt of the muscle impulse, the
  sarcoplasmic reticulum releases its stored
  calcium ions to the sarcoplasm of the muscle
  fiber.
• The high concentration of calcium in the
  sarcoplasm interacts with the troponin and
  tropomyosin molecules, which move aside, exposing
  the myosin binding sites on the actin filaments.
• Myosin heads now bind and pull on the actin
  filaments, causing the sarcomeres to shorten.
• After the nervous impulse has been received, the
  enzyme acetylcholinesterase rapidly decomposes
  the acetylcholine.
• Then, calcium is returned to the sarcoplasmic
  reticulum, and the linkages between myosin and
  actin are broken.

13
Energy Sources for Contraction

• The pigment myoglobin stores oxygen in muscle
  tissue.
• What happens to the respiration rate during
  exercise? It increases.

14
Oxygen Debt

• Oxygen deficiency may develop during strenuous
  exercise, and lactic acid accumulates as an end
  product of anaerobic respiration. This acid
  diffuses out of muscle cells and is carried in
  the bloodstream to the liver.
• When a muscle loses its ability to contract
  during strenuous exercise, it is referred to as
  fatigue.
• This usually arises from the accumulation of
  lactic acid in the muscle causing a lowered pH.
• A muscle cramp occurs due to lack of ATP required
  to return calcium ions back to the sarcoplasmic
  reticulum so muscle fibers can relax.
• Know what causes a muscle strain.

15
Muscle fatigue can be caused by all of the
following except

• Lowering of pH due to lactic acid build-up
• Interruption of blood supply
• Formation of a cramp
• Lack of acetylcholine

16
Muscle Responses

• A muscle fiber remains unresponsive to
  stimulation unless the stimulus is of certain
  strength, called the threshold stimulus.
• When a muscle fiber contracts, it contracts to
  its full extent, it cannot contract partially.
  This is called the all-or-none response.
• Muscle twitch A single, short contraction
  involving only a few motor units is referred to
  as a twitch. Is this considered a very useful
  contraction? No.

17
The strength of a muscle in response to different
levels of stimulation is determined by the

• Number of motor units receiving a threshold
  stimulus

18
Muscle Responses

• A muscle fiber receiving a series of stimuli of
  increasing frequency reaches a point when it is
  unable to relax completely and the force of
  individual twitches combine by the process of
  summation.
• If the sustained contraction lacks any
  relaxation, it is called a tetanic contraction
  (result of summation recruitment together!) NOT
  ALL MOTOR UNITS HAVE BEEN RECRUITED!
• An increase in the number of activated motor
  units within a muscle at higher intensities of
  stimulation is called recruitment. How is this
  done? By activating more motor units.
• Muscle tone is achieved by a continuous state of
  sustained contraction of motor units within a
  muscle.
• Why would this be useful? Useful in maintaining
  posture.

19
Smooth Muscles

• Describe smooth muscle cells.
• They are elongated with tapered ends
• Are they voluntary or involuntary?
• Involuntary
• In multi unit smooth muscle, such as in the blood
  vessels and iris of the eye, fibers occur
  separately rather than as sheets.
• Visceral smooth muscle occurs in sheets and is
  found in the walls of hollow organs these fibers
  can stimulate one another and display
  rhythmically, and are thus responsible for
  peristalsis in hollow organs and tubes.

20
Smooth Muscles

• Smooth muscle contraction How is it like
  skeletal muscle?
• Similar myosin binding to actin mechanism.
• How many neurotransmitters are there that act on
  smooth muscle?
• Two Acetylcholine and norepinephrine
• How is it unlike skeletal muscle?
• Lacks striations (do not have an organized
  arrangement of myosin and actin filaments), have
  relatively underdeveloped sarcoplasmic reticulum

21
Cardiac Muscles

• Describe cardiac muscle cells.
• Rectangular shaped cells with single nucleus in
  each
• How is it like skeletal muscle contraction?
• Involves similar myosin binding to actin process.
• What are the three ways it differs from skeletal
  muscle contraction?
• Involuntary, contracts for longer periods,
  intercalated disks spread impulses of muscle
  (very quickly!).

22
Muscle Terminology

• Origin and Insertion The immovable end of a
  muscle is the origin, while the moveable end is
  the insertion. What does contraction do? Pulls
  the insertion towards the origin, causing
  movement
• Prime mover - the one doing most of the work
• Synergist helper muscles (assist)
• Antagonist opposing muscles (perform opposite
  movements of those of the prime mover)

23
Need to Know Muscles

• Buccinator compresses the cheeks inward
• Muscles of Mastication -
• Temporalis Insertion Coronoid process of
  mandible
• Deltoid abducts upper arm and can flex and
  extend humerus
• Psoas Major flex the thigh
• Iliacus flex the thigh
• Sternocleidomastoid Insertion mastoid process
  of the temporal bone
• Rectus Femoris -
• Fibularis Longus produces plantar flexion
• Rectus abdominis primary flexor of vertebral
  column