neuronal communication Flashcards
1
Q
Why is coordination needed?
A
Organisms need to coordinate the
function of different cells and
systems to operate effectively
2
Q
What is homeostasis?
A
The maintenance of a stable equilibrium in the conditions inside the body e.g. digestive organs such as exocrine pancreas, duodenum, and ileum along with the endocrine pancreas and the liver work together to maintain a constant blood glucose concentration
3
Q
Through the process of cell
signalling, nervous and
hormonal systems can…
A
• Transfer signals locally, e.g. between neurones and synapses. Here the signal is used for a neurotransmitter • Transfer signals across large distances, using hormones, e.g. the cells of the pituitary glad secrete ADH, which acts on cells in the kidneys to maintain water balance in the body
4
Q
Describe coordination in plants
A
Unlike animals, plants do not have a nervous system However, they still respond to internal and external changes in their environment in order to survive
5
Q
What is a neurone?
A
A specialised cell which transmits
impulses in the form of action
potentials
6
Q
Describe the structure of a
neurone
A
• Cell body - contains the nucleus surrounded by the cytoplasm. The cytoplasm contains large amounts and endoplasmic reticulum and mitochondria which are involved in the production of neurotransmitters • Dendrons - short extensions which come from the cell body. Divide into smaller branches called dendrites. Transmit electrical impulses towards the cell body • Axons - singular, elongated nerve fibres that transmit impulses away from the cell body. Cylindrical in shape consisting of a narrow region of cytoplasm surrounded by a cell membrane
7
Q
Describe the 3 different types
of neurone
A
• Sensory neurones - transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain. One dendron and one axon • Relay neurones - transmit impulses between e.g. sensory and motor neurones. Many short axons and dendrons • Motor neurones - these neurone transmit impulses from a relay or sensory neurone to an effector. One long axon and many short dendrites
8
Q
What are myelinated
neurones?
A
A neurone where the axon is covered in a myelin sheath (made up of many layers of plasma membrane) • Schwann cells produce these layers of membrane by growing around the axon many times • Myelinated neurones transmit impulses much faster than nonmyelinated neurones
9
Q
What are sensory receptors?
A
Cells/sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and can create action potentials. • Most are energy transducers that convert one form of entry to another
10
Q
What are Pacinian corpuscles?
A
A pressure sensor found in the skin • Oval-shaped structure that consists of a series of concentric rings of connective tissue wrapped around the end of a nerve cell • When pressure on the skin changes, this deforms the rings of connective tissue, which push against the nerve ending • The corpuscle is sensitive only to changes in pressure that deform the rings connective tissue • Therefore when pressure is constant, they stop responding
11
Q
How is mechanical pressure
converted into an impulse?
A
1. Normal state (resting state) the stretch-mediated sodium channels are too narrow to allow sodium ions through 2. Pressure applied the Pacinian corpuscle changes shape (membrane around neurone stretches) 3. This causes the stretchmediated channels to widen and sodium ions diffuse in 4. This influx of positive ions causes a change in the potential difference across the membrane and it depolarise, resulting in a generator potential 5. The generator potential creates an action potential (an impulse) which is passed along the sensory neurone into the CNS
12
Q
What is resting potential?
A
The potential difference across the membrane while the neurone is at rest • The outside is more positively charged than the inside of the axon (-70mV) • The membrane is said to be polarised as there is a potential difference
13
Q
How are resting potentials
maintained?
A
• Na+ ions actively transported out of the axon, and K+ actively transported into the axon • 3 Na+ ions pumped out for every 2K+ pumped in • Gated Na+ ions channels are kept closed, but some of the K+ channels are open, so membrane is more permeable to K+ • K+ diffuses out of cell • Cell cytoplasm also contains large organic anions • Therefore inside of the cell has negative potential compared to outside • The cell membrane is said to be polarised • The potential difference is about -70mV
14
Q
What is action potential?
A
A brief reversal of the potential
across the membrane of a neurone
causing a peak of +40mV compared
to the resting potential of -60mV
15
Q
What happens when a stimulus
is detected by a sensory
receptor?
A
• The energy of the stimulus temporarily reverses the charges on the axon membrane • As a result, the potential difference across the membrane rapidly changes and becomes positively charged at approximately +40mV • This is known as depolarisation - a change in potential difference from negative to positive • The neurone returns to its resting potential
16
Q
When does an action potential
occur?
A
• When protein channels in the axon membrane change shape as a result of the change voltage across its membrane • The change in protein shape results in the channel opening or closing • These channels are known as voltage-gated ion channels
17
Q
What are the stages of an
action potential?
A
1. The membrane starts in its resting state - polarised with the inside of the cell being -70mV compared to the outside. There is a higher concentration of Na+ ions outside than inside, and a higher concentration of K+inside than outside 2. Na+ ions channels open and some Na+ ions diffuse into the cell 3. The membrane depolarises - it becomes less negative with respect to the outside and reaches the threshold value of -50mV 4. Positive feedback causes nearby voltage-gated Na+ ions channels open, and many Na+ ions flood in. As more Na+ ions enter, the cell becomes positively charged inside compared with outside 5. The p.d. across the plasma membrane reaches +40mV. The inside of the cell is positive compared with the outside 6. The Na+ ions channels close and potassium channels open 7. K+ ions diffuse out of the cell, the p.d. inside the cell goes back to negative compared with the outside - this is called repolarisation 8. The p.d. overshoots slightly, making the cell hyperpolarised 9. The original p.d. is restored so that the cell returns to its resting state
18
Q
What are the stages in the
propagation of action
potentials?
A
1. When an action potential occurs, the Na+ ions channels open at that point in the neurone 2. Localised increase in concentration of Na+ ions inside the neurone - action potential 3. Na+ ions diffuse sideways along the neurone, away from the increased region of concentration. The movement of charged particles is a current called a local current 4. The local current causes a slight depolarisation further along the neurone which affects voltagegated Na+ ion channels 5. Na+ ion gate, which was initially closed will now open because of the movement of sodium ions, allowing the action potential to move along the neurone as more Na+ ions enter and set up another action potential 6. The region of the membrane which has been depolarised as the action potential passed along now undergoes repolarisation and to return to its resting potential
19
Q
What is the refractory period?
A
A short period of time when the axon cannot be excited again • Voltage-gated Na+ remain closed, preventing the movement of Na+ ions into the axon • No
20
Q
Why is the refractory period
important?
A
• It prevents the propagation of an action potential backwards along the axon • Makes sure action potentials are unidirectional • Ensure that action potential do not overlap and occur as discrete impulses
21
Q
What does saltatory
conduction mean?
A
• Na+ and K+ cannot diffuse through the fatty layer of the myelin sheath • The ionic movements that create an action potential can only occur at the nodes of Ranvier • The local currents are elongated and Na+ ions diffuse along the neurone from one node of Ranvier to the next • This means that the action potential appears to jump from one node to the next • This is called saltatory conduction • Therefore a myelinated neurone can conduct action potentials more quickly than non-myelinated neurones
22
Q
Give two other factors that
affect the speed at which
action potential travels
A
Axon diameter • The bigger the diameter, the faster the impulse is transmitted • Because there is less resistance to the flow of ions in the cytoplasm, compared with those in smaller axon Temperature • The higher the temperature, the faster the nerve impulse • Because ions diffuse faster at higher temperatures
23
Q
What is the all-or-nothing
principle?
A
Nerve impulses are all-or-nothing responses • If a stimulus reaches the threshold value it will always trigger a response and an action potential • No matter how large the stimulus, the same sized action potential will always be triggered • The larger the stimulus, the more frequently the action potentials will be generated
24
Q
What is a neurotransmitter?
A
A chemical involved in communication across a synapse between adjacent neurones, or a neurone and a muscle cell • Used as a signalling molecule between two neurones in a synapse
25
What is a synapse?
```
The junction (small gap) between
two neurones, or a neurone and an
effector
• A cholinergic synapse uses
acetylcholine as its
neurotransmitter
```
26
What are the key features in
| the pre-synaptic bulb?
```
The pre-synaptic neurone ends in a
swelling called the pre-synaptic bulb
• many mitochondria - indicating
that an active process needing
ATP is involved
• A large amount of smooth
endoplasmic reticulum, which
packages the neurotransmitter into
vesicles
• Large numbers of vesicles
containing molecules of a
chemical called acetylcholine, the
transmitter that will diffuse across
the synaptic cleft
• A number of voltage-gated
calcium ion channels on the cell
surface membrane
```
27
Describe the post-synaptic
| membrane
```
• Contains specialised sodium ion
channels that can respond to the
neurotransmitter
• These channels consist of 5
polypeptide molecules. 2 of these
have a special receptor site that is
specific to acetylcholine
• The receptor sites have a
complementary shape to that of
the acetylcholine molecule
• When acetylcholine is present in
the synaptic cleft, it binds to the 2
receptor sites, and causes the
sodium ion channel to open
```
28
Describe the transmission of a
| signal across the synaptic clef
```
1. An action potential arrives at the
synaptic bulb
2. The voltage-gated calcium ion
channels open
3. Calcium ions diffuse into the
synaptic bulb
4. The calcium ions cause the
synaptic vesicles to move to,
and fuse with, the pre-synaptic
membrane
5. Acetylcholine is released by
exocytosis, and the molecules
diffuse across the cleft
6. Acetylcholine molecules bind to
the receptor sites on the sodium
ion channels in the post-synaptic
membrane
7. The sodium ion channels open,
and sodium ions diffuse across
the post-synaptic membrane
into the post-synaptic neurone
8. A generator potential or
excitatory post-synaptic
potential (EPSP) is created
9. If sufficient generator potentials
combine, then the potential
across the post-synaptic
membrane reaches the threshold
potential
10. A new action potential is created
in the post-synaptic neurone
```
29
What is acetylcholinesterase?
It’s an enzyme found in the synaptic
| cleft
30
What are the roles of
| synapses ?
```
• They ensure that impulses are
unidirectional (go in one direction)
because the neurotransmitter
receptors are only present on the
postsynaptic membrane
• Allow an impulse from one
neurone to be transmitted to
multiple neurones at multiple
synapses
• Allow a number of neurones to
feed into the same synapse with a
single postsynaptic membrane
```
31
What is spatial summation?
When many presynaptic neurones
connect to one postsynaptic
neurone
32
What is temporal summation?
When a single presynaptic neurone
releases a neurotransmitter to a
postsynaptic neurone
33
What is the structural
organisation of the mammalian
nervous system?
```
Central Nervous System (CNS) -
your brain and spinal cord. Relay
neurones
• Peripheral Nervous System (PNS) -
all the neurones that connective
CNS to the rest of the body.
Sensory neurones and motor
neurones
```
34
What is the functional
organisation of the mammalian
nervous system?
* Somatic nervous system
| * Autonomic nervous system
35
Describe the somatic nervous
| system
```
• Under conscious control
• Used when you voluntarily decide
to do something e.g. moving a
muscle to move your arm
• Carries impulses to the body’s
muscles
```
36
Describe the autonomic
| nervous system?
```
• Works constantly and is under
subconscious control
• e.g. causes the heart to beat,
digestion of food
• Carries nerve impulses to glands,
smooth muscle (e.g. walls of small
intestine), and cardiac muscle
```
37
How is the autonomic nervous
| system divided?
* Sympathetic system
| * Parasympathetic system
38
Describe the sympathetic
| system
```
• Many nerves leading out of CNS,
each to a separate effector
• Ganglia just outside the CNS
• Short pre-ganglionic neurones
• Long post-ganglionic neurones
• Noradrenaline as neurotransmitter
• Increases activity - prepares body
for activity
• Most active at times of stress
• Increases heart rate, dilates pupils,
increases ventilation rate
• Reduces digestive activity
```
39
Describe the parasympathetic
| system
```
• A few nerves leading out of the
CNS which divide up and lead to
different effectors
• Ganglia in the effector tissue
• Long pre-ganglionic neurones
• Short post-ganglionic neurone
• Acetylcholine as neurotransmitter
• Decreases activity - conserves
energy
• Most active during sleep or
relaxation
• Decreases heart rate, constricts
pupils, reduces ventilation rate,
increases digestive activity
```
40
Describe the structure of the
| brain
```
• Cerebrum - controls voluntary
actions e.g. learning, memory,
personality, and conscious thought
• Cerebellum - controls
unconscious functions e.g.
posture, balance and nonvoluntary movement
• Medulla oblongata - used in
autonomic control, e.g. controls
heart rate and breathing rate
• Hypothalamus - regulatory centre
for temperature and water balance
• Pituitary gland - stores and
releases hormones that regulate
many body functions
```
41
Describe the cerebrum
```
• Highly convoluted, which
increases its surface area, and
therefore its capacity for complex
activity
• Split into left and right halves
known as the cerebral
hemispheres. Each hemisphere
controls one half of the body
• The outer layer of the cerebral
hemispheres is known as the
cerebral cortex (2-4mm thick)
• Reasoning and decision-making
occur in the frontal and prefrontal
lobe of the cerebral cortex
```
42
Describe the cerebral cortex
```
• Sensory areas receive action
potential indirectly from sensory
receptors. Size of regions
allocated to receive input from
different receptor are related to the
sensitive of there that inputs are
received from
• Association areas compare
sensory inputs with previous
experience, interpret what the init
means, and judge an appropriate
response
• Motor areas send action potential
to effectors. Sizes of regions
allocated to deal with different
effectors are related to the
complexity of the movement
needed in the parts of the body
• Motor areas on the left side of the
brain control the effectors on the
right side of the body and vice
versa
```
43
Describe the cerebellum
```
• Concerned with the control of
muscular movement, body
posture, and balance
• Doesn’t initiate movement, but
coordinates it
• Receives information from the
organs of balance in ears, and
information about the tone of
muscles and tendons
• It then relays this information to
the areas of the cerebral cortex
that are involved in motor control
• The cerebrum and cerebellum are
connected by the pons
```
44
Describe the medulla
| oblongata
```
• Contains many important
regulatory centres of the
autonomic nervous system
• The cardiac centre, which
regulates heart rate
• The vasomotor centres, which
regulates circulation and blood
pressure
• The respiratory centre, which
controls the rate and depth of
breathing
• Also controls activities e.g.
swallowing, peristalsis and
coughing
```
45
Describe the hypothalamus
```
Main controlling region for the
autonomic nervous system
• Two centres - one for the
parasympathetic and one for the
sympathetic nervous system
• Controlling complex patterns of
behaviour e.g. feeding, sleeping
and aggression
• Monitoring the composition of
blood plasma - therefore it has a
very rich blood supply
• Producing hormones - it is an
endocrine gland
• Regulates body temperature
```
46
Describe the pituitary gland
```
Found at the base of the
hypothalamus
• Anterior pituitary (front section) -
produces 6 hormones including
FSH, which is involved in the
reproduction and growth of
hormones
• Posterior pituitary (back section) -
stores and releases hormones
produced by the hypothalamus,
e.g. ADH involved in urine
production
```
47
Describe the components of
| the reflex arc
```
• Receptor - detects stimulus and
creates an action potential in the
sensory neurone
• Sensory neurone - carries impulse
to spinal cord
• Relay neurone - connects the
sensory neurone to the motor
neurone within the spinal cord or
brain
• Motor neurone - carries impulse to
the effector to carry out the
appropriate response
```
48
Describe the spinal cord
```
A column of nervous tissues running
up the back
• It is surrounded by the spine for
protection
• At intervals along the spinal cord,
pairs of neurones emerge
```
49
Describe the knee-jerk reflex
```
Spinal reflex
1. The leg is tapped just below the
kneecap (patella)
2. This stretches the patellar
tendon and acts as a stimulus
3. This stimulus initiates a reface
arc that causes the extensor
muscle on top of the thigh to
contract
4. At the same time, a relay
neurone inhibits the motor
neurone of the flexor muscle,
causing it to relax
5. This contraction, coordinated
with the relaxation of the
antagonistic flexor hamstring
muscle, causes the leg to kick
The absence of this reflex may
indicate nervous problems, and
multiple oscillation of the leg may be
a sign of cerebellar disease
```
50
Describe the blinking reflex
```
Cranial reflex
1. When the cornea of the eye is
irritated by a foreign body, the
stimulus triggers an impulse
along a sensory neurone (5th
cranial nerve)
2. The impulse then passes
through a relay neurone in the
lower brain stem
3. Impulses are then sent along
branches of the motor neurone
(7th cranial nerve) to imitate a
motor response to close the
eyelids
4. Consensual response i.e. both
eyes are closed
```
51
What are the 3 types of muscle
| in the body?
```
• Skeletal muscle - skeletal muscles
make up the bulk of body muscle
tissue. These are the cells
responsible for movement e.g. the
biceps and triceps
• Cardiac muscle - cardiac muscle
cells are found only in the heart.
These cells are myogenic,
meaning they contract without the
need for a nervous stimulus,
causing the heart to beat in a
regular rhythm
• Involuntary muscle (aka smooth
muscle) - these muscle cells are
found in many parts of they body,
e.g. in the walls of hollow organs
such as the stomach and bladder.
Also found in the walls of blood
vessels and the digestive tract,
where through peristalsis they
move food along gut
```
52
Describe skeletal muscle
```
• Fibre appearance: Striated
• Control: Conscious (voluntary)
• Arrangement: Regularly arranged
so muscle contracts in one
direction
• Contraction speed; Rapid
• Length of contraction: Short
• Structure: Muscles showing cross
striations are known as striated or
striped muscles. Fibres are tubular
and multinucleated
• Fatigues quickly
```
53
What is the structure of
| skeletal muscle made up of ?
```
• Bundles of muscle fibres (muscle
cells) enclosed in a plasma
membrane known as the
sarcolemma
• Myofibrils
```
54
Describe muscle fibres
```
Contain a number of nuclei and
are much longer than normal cells,
as they are formed as are result of
many individual embryonic muscle
cells fusing together
• This makes the muscle stronger,
as the junction between adjacent
cells would be a point of weakness
• The shared cytoplasm within a
muscle fibre is known as
sarcoplasm
• Parts of the sarcolemma fold
inwards (aka transverse or T
tubules) to help spread electrical
impulses through the sarcoplasm
• This ensures the whole fibre
receives the impulse to contract at
the same time
• Lots of mitochondria to provide
the ATP needed for muscle
contraction
• Modified version of the
endoplasmic reticulum known as
the Sarcoplasmic reticulum. This
extends throughout the muscle
fibre and contains calcium ions
required for muscle contraction
```
55
What are myofibrils?
```
Long cylindrical organelles made of
protein and specialised for
contraction
• Provide almost no force alone, but
collectively are very powerful
• Lined up in parallel to provide
maximum force when they all
contract together
```
56
What are myofibrils made up
| of?
```
Two types of protein filament
• Actin - the thinner filament. Two
strands twisted around each other
• Myosin - the thicker filament. Long
rod-shaped fibres with bulbous
heads that project to one side
```
57
What causes the striped
| appearance of myofibrils?
```
Light bands (aka isotopic or Ibands):
Appear light as they are
the region where actin and myosin
filament don’t overlap
• Dark bands (aka anisotropic or Abands):
Appear dark because of
the presence of thick myosin
filaments. Edges are especially
dark as the myosin is overlapped
with actin
• Z-line: Line found at the centre of
each light band. The distance
between adjacent Z-lines is a
sarcomere. Sarcomere is the
functional unit of the myofibril.
When a muscle contracts, the
sarcomere contracts
• H-zone: Lighter coloured region at
the centre of each dark band. Only
myosin present. When muscle
contracts, H-zone decreases.
```
58
Describe cardiac muscle
```
• Fibre appearance: Specialised
striated
• Control: Involuntary
• Arrangement: Cells branch and
interconnect resulting in
simultaneous contraction
• Contraction speed: Intermediate
• Length of contraction:
Intermediate
• Structure: Shows striations, but
they are much fainter than those in
skeletal muscle. Fibres are
branched and uninucleated
• Doesn’t fatigue easily
```
59
Give more detail about the
structure of cardiac muscle
cells
```
• Individual cells form long fibres
which brand to form cross-bridges
between the fibres
• Cross-bridges help ensure that
electrical stimulation spreads
evenly over the walls of the
chambers
• The cells are joined by intercalated
discs - specialised cell surface
membranes fused to produce gap
junctions that allow free diffusion
of ions between the cells
• Doesn’t fatigue quickly
```
60
Describe involuntary muscle
```
Fibre appearance: Non-striated
Control: Involuntary
arrangement: No regular
arrangement - different cells can
contract in different directions
Control: Slow
Contraction speed: Can remain
contracted for a relatively long time
Structure: Muscles showing no
cross striations are called nonstriated or unstriped muscles. Fibres
are spindle shaped and uninucleated
```
61
What is neuromuscular
| junction?
The structure at which a nerve
meets the muscle; it is similar in
action to a synapse
62
How is a contraction
stimulated at the
neuromuscular junction?
```
1. Action potentials arriving at the
end of the axon open calcium
ion channels in the membrane.
Calcium ions flood into the end
of the axon
2. Vesicles of acetylcholine move
towards and fuse with the end of
the membrane
3. Acetylcholine molecues diffuse
across the gap and fuse with
receptors in the sarcolemma
4. This opens sodium ion channels,
which allow sodium ions to enter
the muscle fibre, causing
depolarisation of the
sarcolemma
5. A wave of depolarisation
spreads along the sarcolemma
and down transverse tubules (ttubules) into the muscl
```
63
What is a motor unit?
```
• Some motor neurones stimulate
single muscle fibres
• However, many motor neurones
divide and connect to several
muscle fibres
• All these muscle fibres contract
together, providing a stronger
contract together, providing a
stronger contraction
• This is called a motor unit
```
64
Describe the structure of
| myosin
```
Myosin filaments have globular
heads that are hinged, which
allows them to move back and
forth
• On the head is a binding site for
each of actin and ATP
• The tails of several hundred
myosin molecules are aligned
together to form the myosin
filament
```
65
Describe the structure of actin
```
• Actin filaments have binding sites
for myosin heads (actin-myosin
binding sites)
• These binding sites are often
blocked by tropomyosin, which is
held in place by troponin
```
66
What happens when a muscle
| is in a resting state?
```
• The actin-myosin sites are blocked
by tropomyosin
• The myosin heads cannot bind to
the actin, and the filaments cannot
slide past each other
```
67
What happens when a muscle
| is stimulated to contract?
```
• The myosin heads form bonds
with actin filaments known as
actin-myosin cross-bridges
• Myosin heads then flex (change
angle) in unison, pulling the actin
filament along the myosin filament
• The myosin then detaches from
the actin and its head returns to its
original angle, using ATP
• The myosin then reattaches further
along the actin filament and the
process occurs again
• This is repeated up to 100 times
per second
```
68
Describe the sliding filament
| model
```
During contraction the myosin
filaments pull the actin filaments
inwards towards the centre of the
sarcomere. This results in:
• the light band becoming narrower
• The Z lines moving closer together,
shortening the sarcomere
• The H-zone becoming narrower
• During contraction, the thick and
thin filaments slide past one
another
```
69
Describe the mechanism of
| contraction
```
• The sliding action is caused by the
movement of the myosin heads
• When the muscle is stimulated, the
tropomyosin is moved aside,
exposing the binding sites on the
actin
• The myosin heads attach to the
actin and move, causing the actin
to slide past the myosin
```
70
How is contraction controlled?
```
1. When the muscle is stimulated,
the action potentials passes
along the sarcolemma and down
the T-tubules into the muscle
fibre
2. The action potential is carried to
the sarcoplasmic reticulum,
which stores calcium ions, and
causes the release of calcium
ions into the sarcoplasm
3. The calcium ions bind to the
troponin, which alters the shape
pulling the tropomyosin aside.
This exposes the binding sites
on the actin
4. Myosin heads bind to the actin,
forming cross-bridges between
the filaments
5. The myosin heads move, pulling
the actin filament past the
myosin filament
6. The myosin heads detach from
the actin and can bind again
further up the actin filament
7. Once contraction has occurred,
the calcium ions are rapidly
pumped back into the
sarcoplasmic reticulum, allowing
the muscle to relax
```
71
How is energy applied during
| muscle contraction?
```
• The hydrolysis of ATP into ADP
and phosphate
• The energy is required for the
movement of the myosin heads
and to enable to sarcoplasmic
reticulum to actively reabsorb
claim ions from the sarcoplasm
• The 3 main ways ATP is generated
are: aerobic respiration, anaerobic
respiration, certain phosphate
```
72
How is ATP generated during
| aerobic respiration?
```
1. Tropomyosin molecule prevents
myosin head from attaching to
the binding site on the actin
molecules
2. Calcium ions released from the
sarcoplasmic reticulum cause
the tropomyosin molecule to pull
away from the binding sites on
the actin molecules
3. Myosin head now attaches to
the binding site on the actin
filament
4. Head of myosin changes angle,
moving the actin filament along
as it does so. The ADP molecule
is released
5. ATP molecule fixes to myosin
head, causing it to detach from
the actin filament
6. Hydrolysis of ATP to ADP by
myosin provides the energy for
the myosin head to resume its
normal position
7. Head of myosin reattaches to a
binding site further along the
actin filament and the cycle is
repeated
```
73
How is ATP generated by
| anaerobic respiration?
```
In very active muscle, oxygen is
used up more quickly than the
blood supply can replace it
• ATP has to be generated
anaerobically
• ATP is made by glycolysis but, as
no oxygen is present, the pyruvate
which is also produced is
converted into lactate (lactic acid)
• This can quickly build up in the
muscles resulting in muscle fatigue
• Anaerobic respiration is used for
short periods of high-intensity
exercise
```
74
How is ATP generated by
| cretaine phosphate?
```
Cretaine phosphate is a chemical
stored in muscle
• Cretaine phosphate acts as a
reserve supply of phosphate,
which is available immediately to
combine with ADP, reforming ATP
• This system generates ATP rapidly,
but the store of phosphate is used
up quickly
• Used for short bursts of vigorous
exercise e.g. a tennis serve
• When the muscle is relaxed, the
cretaine phosphate store is
replenished using phosphate from
ATP
```
