Download Muscular System - s3.amazonaws.com

Muscular System
Chapter 9
Objectives:
Identify three types of muscle tissue
Describe the structure from a whole muscle to a single
muscle fiber
Describe the Sliding filament theory
Describe the events at the neuromuscular junction (NMJ)
Explain the role of calcium and adenosine triphosphate
(ATP) in muscle contraction
Trace the sequence of events from nerve stimulation to
muscle contraction
•
Types and functions of
muscles
Skeletal
•
Voluntary, striated
Smooth
•
Involuntary
•
non-striated
Cardiac
•
Involuntary, striated
Skeletal Muscle
•
Voluntary
•
Attached to bone
•
Produce movement
•
Maintain body posture
•
Stabilize joints
•
Produce heat (shivering)
Micro: skeletal muscles are - long, cylinder shaped (tubes),
composed of protein arranged to look striated (striped)
Smooth Muscle
(Visceral muscle)
Involuntary, non-striated
Found: walls of viscera - stomach, bronchioles,
intestines, blood vessels,...
Contraction of smooth muscles enable the
viscera to perform its function
EX. contraction of the stomach smooth
muscles mixes solid into paste and pushes it
into the intestines for digestion/absorption
Cardiac Muscle
Involuntary
Found: only in the heart
Function: to pump blood throughout the body
Micro: cardiac cells are long branching cells that
fit together tightly at junction called intercalated
discs which promote rapid electrical signals
through the hearts
Structure of the whole
muscle
“Belly” of muscle is the large fleshy body of the
between two slender points of attachment
muscle
Composed of thousands of muscle fibers
Fascia - layers of tough connective tissue around large skeletal muscle
Extends at each end of the muscle to form tendons, strong, cordlike structure
Muscle attaches to bone in 3 ways:
•
Tendon attaches muscle to bone
•
Muscles attach directly to bone/soft tissue
•
Aponeurosis - flat sheet-like fascia connects muscle to muscle/muscle to
bone
Fascia
Epimysium - most outer layer of fascia
Perimysium - layer of connective tissue that surrounds smaller bundle
bundles of muscle fibers (fascicles)
Fascicles - bundles of fibers
Endomysium - layer of connectives that covers individual muscle fibers
Muscle - to - Filament
Fascia
Fascia - separates the muscle into isolated compartments
Each compartment receives blood vessels and nerves necessary for muscle function
Issues: Compartment Syndrome
Muscle sustains a crush injury, muscle is damaged inflammation, edema inside the compartment limited
space)
Increase in pressure inside fascia - compresses
nerves/blood supply - decreased oxygen
perfusion/nourishment - muscles and nerves can begin to
die
Immediate treatment = Fasciotomy, slicing fascia
lengthwise to relieve pressure inside muscle to prevent
permanent muscle and nerve damage
Compartment Syndrome
Single Muscle Fiber
Micro: muscle cell is elongated, has more than 1 nucleus
Sarcolemma - muscle cell membrane
Transverse tubule (T-tubule) - several points on the
sarcolemma where the membrane penetrates into the muscle
fiber
Sarcoplasmic reticulum - specialized endoplasmic reticulum,
stores calcium and ATP
Sarcolemma, T-Tubules,
Sarcoplasmic Reticulum
Myofibrils & Sarcomere
Each muscle fiber (cell) is
composed of long cylindrical
structures... myofibrils
Each Myofibril is made up of a
series of contractile
units...sarcomeres
Sarcomeres extend from Z-line
to Z-line, formed by a unique
arrangement of 2 contractile
proteins...Actin and Myosin
Sarcomeres
Each sarcomere extends from z-line to z-line
Formed by unique arrangement of 2 contractile
proteins (filaments), Actin and Myosin
Muscle contraction occurs at these contractile proteins
When a crossbridge is formed (connection of the Actin
and Myosin) the muscle is contracting ...when the
crossbridge is broken the muscle relaxes
When the crossbridge is formed the sarcomere shorten
- because actin/myosin filaments slide past eachother...
“Sliding Filament Theory”
When stimulated...myosin heads make contact
with actin form a “crossbridge”
Once achieved the myosin head rotates pulling the
actin towards the center of the sarcomere
Rotation of the myosin head forces the actin to
slide past the myosin
Muscle relaxation occurs when the crossbridge is
broken
Like a Trombone!!!!
Role of Calcium and ATP
ATP helps myosin heads form a crossbridge but only in
the presence of Calcium
When muscle is relaxed calcium is stored in the
sarcoplasmic reticulum (away from the actin and
myosin)
Calcium is released from sarcoplasmic reticulum and
causes actin/myosin and ATP to interact...muscle
contraction occurs!
Calcium is then pumped back into sarcoplasmic
reticulm away from actin/myosin and ATP ....
crossbridge is broken and muscle relaxes!
Skeletal Muscles and
Nerves
•
Muscle fibers need to be stimulated by a nerve !!!
•
Motor Nerve (somatic nerve) = type of nerve that
supplies skeletal muscles with an action potential
(nerve impulse)
•
nerves exit through the spinal cord and
supplies muscle fibers with stimulation, they
innervate the muscles
•
NMJ - neuromuscular junction is the point
where the motor nerve meets the muscle
NMJ (neuromuscular
junction)
•
Structures of the NMJ:
•
Membrane at end of each nerve (axon terminal)
•
Space between the nerve ending and muscle
membrane (synaptic cleft)
•
Receptor site on the cell membrane (sarcolemma)
What happens at the
NMJ?
•
4 steps involved in the transfer of information
from the nerve to the muscle @ the NMJ
•
Stimulated nerve causes release of a chemical
substance (neurotransmitter) that diffuses across
the NMJ and stimulates the muscle membrane.
4 Steps @ NMJ
1. Stimulation of nerve causes electrical signal (nerve impulse) which moves to
the nerve ending...nerve ending has has vesicles (pouches) filled with a
chemical substance (neurotransmitter)
Acetycholine (ACh) is the neurotransmitter @ NMJ
2. Impulse causes the vesicle to move toward the nerve ending...vesicle fuses
with nerve ending and ACh is released from vesicle into the space between
nerve ending and muscle fiber membrane
3. ACh (acetylcholine) diffuses across synaptic cleft and binds to receptor sites
on the muscle membrane (sarcolemma)
4. ACh stimulates receptors... causes electrical signal to develop along muscle
membrane
• ACh then unbinds from receptor and is immediately destroyed by an
inhibitor (acetylcholinesterase)
• This makes the receptor sites available for additional ACh when the nerve
is stimulated again
So What happens to the
electrical signal in the muscle
membrane?
•
Electrical signal travels along the muscle membrane and
triggers a series of events...
• Electrical signal penetrates into the fiber via the T-Tubules
• Signal stimulates the sarcoplasmic reticulum to release
calcium
• Calcium floods sarcomeres
• Calcium interacts with Actin/Myosin/ATP = muscle
• Eventually the calcium is pumped back into sarcoplasmic
reticulum...causing muscle relaxation!
“Rigor Mortis”
Stiffness of Death
•
When a person dies ATP production ceases
•
+ crossbridge = contraction
•
- crossbridge = relaxation
•
Deficiency in ATP prevents detachment of the
crossbridge - muscle remains contracted, stiff
•
Onset 2 hours after death, Peak 12 hours after
death - subsides by 36 hours
Disorders of NMJ
Myasthenia Gravis - affects the NMJ
•
Symptoms from damaged receptor sites
on muscle membrane
•
Disease process alters receptor site to ACh can’t
bind...muscle contraction is impaired, weak
•
“Myasthenia” means weak
•
Slow onset of symptoms, low tolerance to
exercise, can eventually progress to affecting
breathing muscles (skeletal muscle)
NMJ Disorders...
NMJ Disorders...
Neurotoxins - chemical substance produced by bacteria that disrupts normal
function of the nervous system
•
•
•
Clostridium tetani “tetanus” - bacteria that secretes a neurotoxin that
overstimulates ACh by excess firing of motor neuron - severe muscle spasm
(tetanic contraction)
•
usually jaw muscles are affected first
•
incidence of tetany is low, but mortality is high - reason for tetanus booster
every ten years
Clostridium Botulinum “botulism”
•
rare but serious bacterial spores that entire the body either through
wounds or food (symptoms 8-36 hours after ingestion)
•
produces a neurotoxin that prevents the release of ACh from the ends of
the nerves w/in the NMJ...without ACh muscle fibers can’t
contract, including breathing muscles!!
•
NOTE: small injections of neurotoxin (botox) has been used
to treat severe muscle spasm and erase muscle induced wrinkles
cosmetic reasons
for
Neurotoxins..
.
Neuromuscular Blockade (curare)
•
•
Curare - a classification of medicine, a skeletal
muscle blocker, used in sx to promote muscle
relaxation
•
medication binds and occupies the ACh
receptors - inhibiting ACh from
binding...muscle relaxation is prevented
•
History: used in hunting - arrow tips were
dipped in medicine to paralyze prey
Receptor Terminology
Somatic motor neuron - is a cholinergic fiber
•
receptor on the muscle membrane is a cholinergic receptor called Nm receptor
(nicotinic muscle receptor)
•
somatic motor neuron secretes ACh - acetylcholine (neurotransmitter)
•
Blocking Nm receptors: Curare is an example of medication that blocks
skeletal (Nm receptors)
•
Activating Nm receptors: stimulates muscle contraction
•
•
Neostigmine is an example of a medication that inactivates cholinesterase,
decreases enzyme that destroys ACh, there is an increase in amount of ACh
available to bind to the Nm receptors
•
Called Anti-cholinesterase because it inactivates cholinesterase
NOTE: try to understand why anti-cholinesterase agents improve symptoms of
Myasthenia Gravis!!!
Response of a Whole
Muscle
•
The contractile response of a whole muscle differ from that
of a single muscle fiber, ALL or Nothing!
•
Muscle fibers contract maximally all the time - never
partially contract.
•
Whole muscles can increase contraction (force,strength) to
lift a child verses a pencil
•
Whole muscles only utilize what is needed to get the job
done - Recruitment!
•
Recruitment - is the process in which muscle fibers use,
recruit additional fibers to increase force of contraction
Twitch and Tetanus
•
Terms used to describe whole muscle contraction
•
Twitch - single stimulus delivered to a muscle, contract and relax
quickly - not useful physiologically
•
Tetanus - repeated stimulus to a muscle, muscle is unable to
relax , sustained muscle contraction
• muscles that sustain our posture undergo tetanus
•
Muscle tone (tonus) - refers to a normal continuous state of
partial muscle contraction. Tone is due to the contraction of
different groups of muscle fibers w/in a whole muscle
• Maintaining tone - one group contracts first - as these
fibers begin to relax - a second group contracts
• Important role in smooth muscle of blood vessel, vascular
tone helps maintain blood pressure
Energy Source for
Muscle Contraction
•
Muscle contraction requires a rich supply of ATP. ATP is
consumed by the contracting muscle and is replaced in three ways:
1. Aerobic Metabolism: in the presence of oxygen, fuel (glycogen,
glucose, fat) is broken down to yield ATP
2. Anaerobic Metabolism: when body metabolized fuel in absence
of oxygen, complete breakdown of fuel is not possible
• Lactic Acid is produced, responsible for soreness that
accompanies heavy exercise
3. Metabolism of Creatine Phosphate: creatine phosphate
contains energy that the body can use to replenish ATP quickly
during contraction. Is a storage form of energy that ensures
muscles operate for long periods
Muscle Terms
•
Origin - the origin of a muscle attaches to the stationary bone
•
Insertion - attaches to the moveable bone
•
Prime Mover - “chief muscle” single muscle generally responsible w/ helper movers
•
Synergists - muscles that assist movement
•
Antagonists - opposing force of chief muscle
Muscle Terms ...
Hypertrophy - overused
muscles increase in size
•
•
Intentional - body builders
•
Unintentional - over work to
cardiac muscle...
cardiac hypertrophy
Muscle Terms...
Atrophy - wasting away of
muscle that are not used
•
•
•
Disuse atrophy - a fx leg is
casted for a few weeks unable to
exercise - muscle will atrophy can be restored
Contracture - if a muscle is
immobilized for prolonged
periods of time, abnormal
formation of fibrous tissue w/in
the muscle, “freezes” in a flexed
position and restricts mobility
Naming Skeletal Muscles
•
Size
•
Shape
•
Orientation of Fibers
•
Location
•
Number of Origins
•
Identification of Origin/Insertion
•
Muscle Action
Size and Shape of
Muscles
•
Size:
Shape:
•
Vastus - huge
•Deltoid
•
Maximus - large
•Latissims
- wide
•
Longus - long
•Trapezius
- trapezoid
•
Minimus - small
•Rhomboideus
•
Brevis - short
•Teres
- triangular
- round
- rhomboid
Location:
•
Direction:
•
Rectus - straight
•Gluteus
•
Oblique - diagonal
•Brachii
•
Transverse - across
•
Circularis - circular
•Pectoralis
•Supra
•Infra
•Sub
- chest
- buttock
- arm
- above
- below
- underneath
•Laterals
- lateral
•
Number of Origins
Muscle Action of• Adductor
Muscle
moves limb towards
Biceps - 2 sites
muscle is anchored
•
Triceps - 3 sites
muscle is anchored
•
Quadricep - 4 sites
muscle is anchored
midline
•
Abductor Muscle moves limb away from
midline
•
Flexor Muscle flexion
•
Extensor Muscle extension
•
Levetor Muscle elevates structure
Review in Text
Muscles Head
to Toe
Shoulder/Upper
•
arm
Head
•
•
Facial Muscles
•
Chewing Muscles
Neck
•
•
Sternocleidomastoid
•
Trapezius
•
•
Lower Arm
•
Hands/Fingers
Trunk
•
•
•
•
Flexors/Extensors
•
Carpal Tunnel
Breathing Muscles
Abdominal Wall
rotator cuff
Thigh/Leg/Foot
•
•
Hamstrings