Chapter 11 Muscle Tissue

1
Chapter 11Muscle Tissue

• Muscles can only do two things contract and
  ________.
• Study of muscles myology

2
Introduction to Muscle

• Movement is a fundamental characteristics of all
  living things
• Types of muscle
• skeletal
• cardiac
• Smooth

3
5 Characteristics of Muscle

• 1. Responsiveness
• capable of response to chemical signals, stretch
  or other signals being able to respond
• 2. Conductivity
• electrical excitation travels along the muscle
  fiber
• 3. Contractility -- shortens when stimulated
• 4. Extensibility -- capable of being stretched
• 5. Elasticity -- returns to its original resting
  length after being stretched

4
(No Transcript)
5
MICROSCOPIC MUSCLE

• 1. Skeletal muscle consists of fibers (cells)
  covered by a sarcolemma and contain sarcoplasm,
  nuclei, sarcoplasmic reticulum, and transverse
  tubules.
• These are involved in the pathway of the
  excitation-contraction mechanism.
• 2. Each fiber contains thin and thick
  myofilaments.
• The filaments are compartmentalized into
  sarcomeres

6
Micro Muscles (Cont.)

• 3. Thin filaments are composed of actin,
  tropomyosin, and troponin thick filaments
  consist of myosin.
• a. Actin and myosin are the two contractile
  proteins in muscle.
• b. Tropomyosin and troponin are muscle's
  regulatory proteins.
• c. Projecting myosin heads are called cross
  bridges and contain actin- and ATP-binding sites.

7
CONTRACTION OF MUSCLE

• Sliding Filament Mechanism
• 1. During muscle contraction, myosin cross
  bridges pull on thin filaments, causing them to
  slide inward toward the H zone
• a. Z discs come toward each other and the
  sarcomere shortens, but the thick and thin
  filaments do not change in length.
• b. The sliding of filaments and shortening of
  sarcomeres causes the shortening of the whole
  muscle fiber and ultimately the entire muscle.
• Note Muscles do not fold

8
StrIAtions

• Dark A bands alternating with lighter I bands
  give muscle its striated appearance
• A band is thick filament (Thick letter)
• I band is thin filament (Thin letter)
• Found in ______ and ______
• Not found in ________

9
Neuromuscular Junction (Synapse) I

• The Neuromuscular Junction (NMJ)
• 1. A motor neuron transmits a nerve impulse
  (action potential) to a skeletal muscle where the
  nerve impulse serves as a stimulus for
  contraction.
• 2. Excitable cells (neurons and muscle fibers)
  make contact and communicate at specialized
  region called a synapse.
• At the synapse electrical energy from the neuron
  is converted to chemical energy (Ach) and finally
  resulting in mechanical energy of the muscle

10
Neuromuscular Junction II

• 3. A neuromuscular junction (NMJsynapse) refers
  to an axon terminal of a motor neuron and the
  portion of the muscle fiber sarcolemma in close
  approximation with it (motor end plate)
• (NO TOUCHING, PLEASE!)
• 4. Acetylcholine (ACh), released by the synaptic
  vesicles of a motor neuron in response to an
  action potential, triggers a muscle action
  potential.

11
Muscle Contraction

• When a nerve impulse (nerve action potential)
  reaches an axon terminal
• The synaptic vesicles of the terminal release
  acetylcholine (ACh),
• 1) that diffuses across the cleft and binds to
  chemically gated Na channels on the sarcolemma,
• 2) Plasma membranes exhibit voltage changes in
  response to stimulation
• ion gates open allowing Na to rush into cell and
  then K to rush out of cell (quick up-and-down
  voltage shift is called action potential)

12
Muscle Contraction (Cont.)

• This then travels into the transverse tubules and
  causes some of the Ca2 stored in the
  sarcoplasmic reticulum to be released into the
  sarcoplasm.
• 1) This causes the relaxed filaments to interact
  and start pulling.
• 2) The released calcium ions that combine with
  troponin, causing it to pull on tropomyosin to
  change its orientation, thus exposing
  myosin-binding sites on actin.
• 3) This allows the myosin head to bind to actin.

13
Muscle Contraction/ Relaxation

• The source of energy for muscle contraction is
  ATP (Adenosine triphosphate)
• ATPase splits ATP into ADP P and the released
  energy activates myosin cross bridges.
• Relaxation is brought about when ACh is broken
  down by the enzyme acetylcholinesterase (AChE)

14
Motor Unit

• A motor neuron the muscle fibers it innervates
• Fine control
• small motor units contain as few as 20 muscle
  fibers per one nerve fiber
• eye muscles
• Strength (gross) control
• gastrocnemius muscle has 1000 fibers per one
  nerve fiber

15
Stretching

• Muscle Over-contracted causes weakness
• thick filaments cant slide
• The longer the stronger
• Muscle over-stretched causes weakness
• No overlap of filaments- does not allow for cross
  bridges to form
• Remedy
• Stretch after exercise

Neuromuscular Junction
16
Recruitment

• According to the all-or-none principle,
  individual muscle fibers contract to their
  fullest extent they do not partially contract.
• Muscle as a whole can have graded contractions to
  perform different tasks i.e lift a glass of milk
  versus a whole gallon of milk
• The process of increasing the number of active
  motor units is called recruitment.

17
Isometric Isotonic Contractions

• Isometric muscle contraction
• develops tension without changing length
• Isotonic muscle contraction
• tension development while shortening concentric
• tension development while lengthening eccentric

18
ATP Sources

• All muscle contraction depends on ATP
• Pathways of ATP synthesis
• anaerobic fermentation (ATP production limited)
• occurs without oxygen, but produces toxic lactic
  acid
• aerobic respiration (far more ATP produced)
• requires continuous oxygen supply, produces H2O
  CO2

19
Muscle Fatigue and Soreness

• The inability of a muscle to maintain its
  strength of contraction or tension is called
  muscle fatigue.
• 1. It occurs when a muscle cannot produce enough
  ATP to meet its needs.
• Microscopic muscle damage appears to be a major
  contributing factor to muscle soreness which
  follows bouts of strenuous exercise.
• Skeletal muscle fibers cannot divide and have
  limited powers of regeneration

20
Muscle Tone and Arnold

• Hypotonia decreased or lost muscle tone flaccid
  muscles.
• Atrophy is a wasting away of muscles and may be
  caused by disuse or severing of the nerve supply
• Hypertonia increased muscle tone and may be
  expressed as either spasticity (stiffness) or
  rigidity
• Hypertrophy refers to an increase in the diameter
  of muscle fibers resulting from very forceful,
  repetitive muscular activity. (Arnold)

21
Muscular Dystrophy

• Group of hereditary diseases in which skeletal
  muscles degenerate are replaced with adipose
• Mainly a disease of males
• rarely live past 20 years of age
• Diagnosis from myogram which is a record of a
  muscle contraction

22
Myasthenia Gravis

• Autoimmune disease where antibodies attack NMJ
  and bind ACh receptors
• drooping eyelids and double vision
• difficulty swallowing
• weakness of the limbs
• respiratory failure
• Treated with cholinesterase inhibitors, thymus
  removal or immunosuppressive agents

23
Myasthenia Gravis
Drooping eyelids (ptosis) and weakness of muscles
of eye movement
24
DANGER

• The use of anabolic steroids by athletes to
  increase muscle size, strength, and endurance has
  been shown to have very serious side effects,
  some of which are life-threatening.

25
Toxins Paralysis

• Pesticides contain cholinesterase inhibitors that
  bind to acetylcholinesterase prevent it from
  degrading ACh
• spastic paralysis possible suffocation
• Tetanus or lockjaw is spastic paralysis caused by
  toxin of Clostridium bacteria
• causes overstimulation of the muscles
• Flaccid paralysis with limp muscles unable to
  contract caused by curare that competes with ACh
• respiratory arrest

26
Rigor Mortis

• Stiffening of the body beginning 3 to 4 hours
  after death.
• peaks at 12 hours after death diminishes over
  next 48 to 60 hours
• Muscle relaxation requires ATP. True or False?
• Why does ATP production stop with death?
• Fibers remain contracted until myofilaments decay

27
ABNORMALS

• Abnormal contractions of skeletal muscle include
• 1. spasm- involuntary contraction
• 2. cramp- painful spasm
• 3. tremor- rhythmic, involuntary, purposeless
  contraction
• Intension tremor
• Non-intension tremor
• 4. fasciculation- involuntary, brief twitching,
  not associated with movement
• ALS, MS, or normal
• 5. tic- involuntary, brief movement