Download Muscular System lecture

Muscular System
Chapter 8
What are functions of the
muscular system?
1.
2.
3.
4.
Gross body movement
Stabilizing body positions – “Tone”
Generate heartbeat
Movement substances within the
body
5. Regulating organ volumes
6. Producing body heat
Properties of Muscle Tissue
1. Electrical Excitability – able to
respond to stimuli and send an
impulse
2. Contractility – ability to contract
forcefully, muscle body shortens
3. Extensibility – ability to stretch
4. Elasticity – ability to return to original
length or shape after contraction
5. Rejuvenation – moderate to poor
What are the 3 types of muscle tissue?
Skeletal
Smooth
Cardiac
Skeletal Muscle
Characteristics:
* Multinucleated
* Striated
* Voluntary control
Appearance:
Smooth Muscle
•Location: Internal organs, blood vessels
Uninucleated cells
•“Peristalsis” movement of digestive tract
Involuntary
•Usually organized into two sheet-like layers:
longitudinal and circular
No striations
•Two types: Visceral and Multiunit
Cardiac
• Striated and uninucleated
• Branching cells
• Intercalated discs
separate cells
• Rhythmicity
• Only found in wall
of heart
• Self-exciting
tissue
• Large transverse
tubules
Aponeurosis, Fascia and Tendons
• Fascia – “gift
wrap” around
muscle body or
found under
skin (spider webs)
• Tendons connect
muscle to bone
• Aponeurosis –
flat/sheet-like
tendon
connects
muscle to CT
Skeletal Muscle Anatomy
The Muscle Fiber (cell)
Structure
•
•
•
•
Sarcolemma
Sarcoplasm
Nucleus(i)
Sarcoplasmic
reticulum
• Mitochondria
• Myofibrils
1. Actin (thin)
2. Myosin (thick)
Skeletal Muscle Fiber Structure
Anatomy of a Myofibril
Sarcomere – smallest contracting
unit
The Sarcomere!
Sarcomere: Single contracting unit within a myofibril.
Striation pattern is caused by the organization of the
myofilaments
• Length = Z line to Z line
Contraction: Z-line
• I band = only actin region
• A band = myosin and actin region moves towards M
line
• H zone = only myosin region
• M line = center of H zone
Muscle Body
Fascicles
Muscle Fibers
Myofibrils
Myofilaments
Largest
to
Smallest
Now that you are familiar with muscle anatomy,
what is the physiology of contraction?
How does muscle contraction happen?
Section 8.3
Structures Involved
in Contraction
Motor Unit:
One neuron and all
the muscle fibers it
connects with.
Stronger contractions
have more motor
units activated.
The Neuromuscular Junction: where the
neuron meets with the muscle fiber.
The Sliding Filament Theory
Video:
“Sarcomere
shortening”
Now, look at how this process really works…
Muscle Contraction
1.
2.
3.
4.
5.
6.
7.
8.
Impulse reaches synaptic
bulb.
Calcium channels open and
calcium enters.
Ca causes vesicles to
migrate to cell membrane to
release neurotransmitter
(Acetylcholine = Ach).
Vesicles fuse with
membrane and release Ach
into synaptic cleft (gap).
Ach diffuses across the
cleft.
Ach binds with receptor
proteins on motor end plate.
Motor end plate depolarizes.
Action potential is generated
in muscle cell.
Video
9. Action Potential moves:
• along the sarcolemma
•down the transverse tubules
Animation
•into the sarcoplasmic reticulum
10. Calcium is released from the sarcoplasmic
reticulum.
Binding site before and after
calcium reaches myofilaments.
VIDEO
Troponin/tropomyosin complex pulled away by
calcium so myosin can bind!
12.
VIDEO
13.
11.
Relaxation Phase…
1. Acetylcholine esterase decomposes Ach and
removes it from synaptic gap.
2. ATP binds to myosin causing linkage to
release from actin.
3. Actin and myosin filaments slide apart.
4. Calcium ions are actively transported back into
the sarcoplasmic reticulum.
5. Muscle fiber relaxes.
So what about Rigor Mortis?
Section 8.4
How does the muscle fiber get ATP for the
contraction?
• Cell Storage
• Creatine phosphate
• Cellular respiration or
fermentation
Creatine Phosphate
• Used when current cell
supply of ATP runs out.
(within 6 sec.)
• Cannot be used
directly as an energy
source.
• Purpose: to transfer
stored energy to ADP
to make ATP.
• Creatine supply is
exhausted in 30 sec.
• Activities that benefit:
100 meter dash and
weight lifting
Aerobic Respiration
• With oxygen
available,
glucose is
converted into
the max amount
of ATP!
Myoglobin:
Oxygen-binding
pigment found
only in muscle
cells.
Anaerobic Method of Acquiring ATP
Occurs by fermentation
Fermentation produces Lactic Acid
Lactic acid is carried to Liver to be converted
back to glucose
Low intensity or moderate exercise can recycle
the lactic acid immediately. (not a lot is
produced)
Can be a good energy source for “stop and go”
sports.
(soccer, tennis, short-term swimming)
***What if you cannot recycle
the lactic acid quickly enough?
Oxygen Debt
• The amount of O2 liver cells require
to convert the lactic acid into glucose +
the O2 muscle cells require to restore
stored ATP and creatine phosphate.
• Training can speed up the process.
O2 Muscle need + O2 Liver need = Oxygen
Debt
For most activities, all systems are used. It’s just
the percentages differ based on the intensity of
the activity.
Activity
% Creatine
Phosphate
% Lactic
Acid
% Aerobic
Respiration
Sprint
95
3
2
Mile
15
55
30
Marathon
5
5
90
Muscle Fiber Types
•
•
•
•
•
Slow
Slow Twitch
Not easily fatigued
Myoglobin – “red”
Use in low intensity
activities – Endurance!
Not a lot of growth – Lean
Lots of mitochondria
•
•
•
•
•
Fast Twitch
Easily fatigued
Little myoglobin – “white”
Used in high intensity
activities – Anaerobic
Power!
Increase filaments with
use – Hypertrophy!
Can be irreversibly
changed into slow twitch!
Fast
Genetically, most people are
50% slow, 50% fast twitch
What if the muscle cannot contract
anymore?
Muscle Fatigue
• Loss of the ability to contract
• Causes:
1. Lactic acid buildup, pH drops
2. Blood supply interruption
3. Lack of acetylcholine
4. Lack of ATP
• Cramps: sudden, involuntary contractions or
spasms in one or more of your muscles.
Possible causes: lack of ATP, dehydration or electrolyte imbalance
Muscular Responses
• Threshold stimulus – minimum
amount of stimulus (Ach) needed to
cause a contraction.
• All-or-None Response – a muscle
fiber will always fully contract no
matter the strength of the stimulus.
If the minimum amount of stimulus
is not met, no contraction will occur.
Muscle contractions can be measured and
recorded by:
The Myogram
Twitch: A single contraction of a
muscle fiber.
Myogram Recording
(Latent)
a)
Shows a series of
twitches with
complete
relaxation before
the next stimulus.
b)
Summation
another stimulus
comes before
complete
relaxation can
occur, thus
increasing the
contraction force.
c)
Tetanus:
Stimulus is held
constant, where
there is no
relaxation.
Recruitment
• Stimulating more motor units in a muscle body to
contract.
• A greater force applied to the muscle or increase
the frequency of stimuli will cause this.
Muscle Tone
• Skeletal muscle fibers constantly being
stimulated by brain. (involuntary)
• Stretch receptors in muscles monitor muscle
health.
• Loss of posture tone = collapse
How Do I Hypertrophy My
Muscles?
1.
2.
3.
4.
Do high intensity activities.
Use the fast-twitch muscles.
Eat protein for building material.
Maintain activity or else: atrophy
By age 80, there is a 50% decrease in muscle
strength!