Transcript Effectors MUSCLES

Effectors
MUSCLES
3 Types of Muscles
• Smooth Muscle- Contracts without conscious
control. Its found in walls of internal organs
(apart from the heart) e.g. Stomach, intestine and
blood vessels.
• Cardiac Muscle- contracts without conscious
control, like smooth muscle but its only found in
the heart.
• Skeletal Muscle- is the type of muscle you use to
move, e.g. Biceps and triceps move the lower
arm.
How do muscles work?
• Skeletal muscles cause the skeleton to move at joints.
• They are attached to the skeleton by tendons, which transmit the
muscle force to the bone and can also change the direction of the
force.
• Tendons are made of collagen fibres and are very strong and stiff
(i.e. not elastic).
• The skeleton provides leverage, magnifying either the movement
or the force.
• Muscles are either relaxed or contracted.
• In the relaxed state muscle is compliant (can be stretched)
• In the contracted state muscle exerts a pulling force, causing it to
shorten or generate force.
• Since muscles can only pull (not push), they work in pairs called
antagonistic muscles. The muscle that bends (flexes) the joint is
called the flexor muscle, and the muscle that straightens (extends)
the joint is called the extensor muscle.
Skeletal Muscle
• Made up of large
bundles of cells
called muscle fibres.
• Sacrolemma folds
inwards across the
muscle fibre, these
folds are called
transverse (T)
tubules, they help
spread electrical
impulses throughout
the sarcoplasm.
The structure of skeletal muscle
• A single muscle contains around 1000 muscle fibres
running down the length of the muscle and joined
together.
• Each fibre is actually a single muscle cell. They
contain many nuclei, their cytoplasm is packed full of
microfibrils, bundles of protein filaments that cause
contraction, they also contain ATP for contraction.
Myofibirls Structure
Sliding Filament Theory
• Muscle contraction is explained by the sliding
filament theory. This is where myosin and
actin filaments slide over one another to make
sarcomeres contract. The simultaneous
contraction of lots of sacromeres means the
myofibrils and muscle fibres contract.
Sacromeres return to their original length as
the muscle relaxes.
The sarcomere – structure to function
Hansen and Huxley realized that the interlocking structure of the
thick and thin filaments allows them to slide past one another. This
reduces the length of the sarcomere.
contraction
At the same time the banding pattern of the sarcomere changes;
light bands, formed by actin, shrink as the filaments become more
interlocked.
The sliding filament theory
Practice Questions
troponin
tropomyosin
myosin
complex
ADP
Pi
actin
filament
myosin
filament
• At rest, the actin-myosin binding site is
blocked by tropomyosin, held in place by
troponin
• Myosin heads cannot bind to actin filaments
Ca2+
• Ca2+ binds to troponin, changing its shape
• Tropomyosin is pulled out of the binding site
• Myosin head can bind – bond is an actinmyosin cross bridge
• Ca2+ activates ATPase, breaking down ATP to
ADP + Pi
• Energy provided moves myosin head, pulling
acting filament along in a ratchet motion
• Free ATP binds to head, changing shape
• Actin-myosin cross bridge breaks
• ATP is hydrolysed, and head returns to original
shape
• With continued stimulation the cycle is
repeated
• If stimulation ceases, Ca2+ is pumped back into
sarcoplasmic reticulum
• Troponin and tropomyosin return to original
positions
• Muscle fibre is relaxed
Energy for Muscle Contraction
So much energy is needed when muscles
contract that ATP gets used up very quickly.
ATP has to be continuously generated so
exercise can continue-this happens in 3 main
ways
Aerobic Respiration
• Most ATP is generated via oxidative
phosphorylation in the cell’s mitochondria.
Aerobic respiration only works when there’s
oxygen so its good from long periods of lowintensity exercise, e.g. A long walk.
Anaerobic Respiration
• ATP is rapidly made by glycolysis. The end
product of glycolysis is pyruvate which is
converted to lactate by lactate fermentation.
Lactate can quickly build up in the muscles
and cause muscle fatigue. Anaerobic
respiration is good for short periods of hard
exercise, e.g a 400m sprint.
ATP- Phosphocreatine (PCr) System
• ATP is made by phosphorylating ADP. The
equation for this is
ADP + PCr
ATP + Cr (Creatine)
• PCr is stored inside cells and the ATP-PCr system
generates ATP very quickly. PCr runs out after a
few seconds so its used during short bursts of
vigorous exercise, e.g. A tennis serve. The ATPPCr system is anerobic and its alactic.
Slow and Fast Twitch Muscle Fibres
• Skeletal muscles are made up of two types of
muscle fibres- slow twitch and fast twitch.
Different muscles have different proportions
of slow and fast twitch fibres.
Slow Twitch
Fast Twitch
SLOW TWITCH FIBRES
FAST TWITCH FIBRES
Appearance
__________
__________
Characteristics
•Rich in _________ (a red-coloured
protein that stores oxygen).
•A rich supply of blood vessels to deliver
_________ and glucose.
•Numerous _____________to produce
ATP.
•A supply of glycogen to provide a
source of metabolic energy but can also
use fat stores.
•High concentration of enzymes that
regulate ________ cycle.
•Low ____________ content (can’t store
much oxygen).
•Thicker and more numerous
____________ filaments.
•A high concentration of enzymes that
control _____________.
•Few ________________ and blood
vessels.
•Has a store of _______________ to
rapidly generate ATP.
•Has a higher concentration of
_____________ than slow twitch to
hydrolyse ATP quickly.
How they work
•Muscle fibres contract __________
•Produce less powerful contractions that
can be sustained over a long period of
time – high resistance to ____________
•Energy released through __________
respiration.
•Muscle fibres contract _________
•Produce powerful contractions ONLY
over a short period of time – _______
resistance to fatigue.
•Energy released through ____________
respiration using glycogen (stored
glucose).
Uses
•Good for _____________ activities E.g.
Maintaining posture,
_________________________
•Good for short bursts of _________and
power E.g. Eye movement,
____________.
SLOW TWITCH FIBRES
FAST TWITCH FIBRES
Appearance
Red
White
Characteristics
•Rich in myoglobin (a red-coloured
protein that stores oxygen).
•A rich supply of blood vessels to
deliver oxygen and glucose.
•Numerous mitochondria to produce
ATP.
•A supply of glycogen to provide a
source of metabolic energy but can
also use fat stores.
•High concentration of enzymes that
regulate Krebs cycle.
•Low myoglobin content (can’t store
much oxygen).
•Thicker and more numerous myosin
filaments.
•A high concentration of enzymes
that control glycolysis.
•Few mitochondria and blood vessels.
•Has a store of phosphocreatine to
rapidly generate ATP.
•Has a higher concentration of ATPase
than slow twitch to hydrolyse ATP
quickly.
How they work
•Muscle fibres contract slowly.
•Produce less powerful contractions
that can be sustained over a long
period of time – high resistance to
fatigue
•Energy released through aerobic
respiration.
•Muscle fibres contract rapidly.
•Produce powerful contractions ONLY
over a short period of time – low
resistance to fatigue.
•Energy released through anaerobic
respiration using glycogen (stored
glucose).
Uses
•Good for endurance activities E.g.
Maintaining posture, long-distance
running.
•Good for short bursts of speed and
power E.g. Eye movement, sprinting.