Module 5 Section 3: Animal Responses Flashcards
What does the cardiac muscle being myogenic mean
It does not require any external stimuli to initiate contraction, contraction is initiated by the muscle itself.
This allows the heart to beat at its own regular intervals
What systems regulate the length of the intervals between the beats
The rate of beating can be regulated by both the nervous system and endocrine system
What are the automatic control systems in the body
Nervous response
Controlled by electrical impulses travelling through nerve cells (called neurons)
Chemical response
Controlled by hormones travelling through the bloodstream
When may the heart rate increase
Exercise
When we activate fight or flight
How can the brain control the heart rate
There is a specific cardioregulatory centre region of the brain called the medulla which controls the heart rate
How do nerves and hormones play a part in fight or flight
Nerve impulses from sensory neurones arrive at the hypothalamus, activating both the hormonal system and the sympathetic nervous system.
The pituitary gland is stimulated to release a hormone called ACTH.
This causes the cortex of the adrenal gland to release steroidal hormones.
The sympathetic nervous system is activated, triggering the release of adrenaline from the medulla region of the adrenal gland.
Effects of the sympathetic nervous system during fight or flight
Adrenaline is released
Heart rate increases - blood pumped round body faster
Muscles around bronchioles relax so breathing is deeper
Glycogen converted into glucose - more glucose available for muscles to respire
Smooth muscle in the arterioles supplying the skin and gut constrict
Smooth muscle in arterioles supplying heart, lungs and skeletal muscles dilate - means blood is diverted to these
Erector pili muscles in the skin contract - makes hair stand on end and animal looks bigger
What examples of hormones that increase heart rate
Noradrenaline
Adrenaline
Thyroxine
Nerves that change heart rate
Sympathetic nerves: increases heart rate
Parasympathetic nerves: decreases heart rate
How does the nervous system help to control heart rate
SAN generates electrical impulses that cause the cardiac muscles to contract
The rate at which the SAN fires (the heart rate) is unconsciously controlled by a part of the brain called the medulla
Why do animals alter their heart rate
It allows them to respond to internal stimuli
E.g. to prevent fainting due to low blood pressure or to make sure the heart rate is enough to supply the body with enough oxygen
How are the internal stimuli that control heart rate detected
Pressure receptors (baroreceptors) in the aorta and the vena cava
Stimulated by high and low blood pressure
Chemical receptors (chemoreceptors) in the aorta, the carotid artery (in the neck) and in the medulla
They monitor oxygen level in the blood, CO2 and pH (indicators of O2 level)
Pathway of impulses through nervous system to control heart rate
Sensory neurons take action potential from the receptors to the medulla
Medulla processes info and sends action potential to SAN along motor neurons
Pathway of change of heart rate when blood pressure is high
High blood pressure
Baroreceptors detect blood pressure
Impulses sent to medulla, which sends impulses along the vagus nerve
This secretes acetylcholine, which binds to receptors on the SAN
Cardiac muscles cause heart rate to slow down to reduce blood pressure back to normal
Pathway of change of heart rate when blood pressure is low
Baroreceptors detect low blood pressure
Impulses sent to medulla which sends impulses along accelerator nerve
This secretes noradrenaline which binds to receptors on SAN
Cardiac muscles cause heart rate to speed up to increase blood pressure back to normal
Pathway of change heart rate at high blood O2, low CO2 or high pH levels
Chemoreceptors detect chemical changes in the blood
Impulses are sent to medulla which sends impulses along the vagus nerve
This secretes acetylcholine which binds go receptors on SAN
Cardiac muscles cause heart rate to decrease to return O2, CO2 and pH levels back to normal
Pathway of change heart rate at low blood O2, high CO2 or low pH levels
Chemoreceptors detect chemical changes in the blood
Impulses are sent to medulla which sends impulses along the accelerator nerve
This secretes noradrenaline which binds to receptors on SAN
Cardiac muscles cause heart rate to increase to return O2, CO2 and pH levels back to normal
How do hormones increase heart rate and when can this happen
During fight or flight response
Adrenaline binds to specific receptors in the heart
Causes cardiac muscle to contract more frequently and with more force so heart rate increases and heart pumps more blood
How are the muscles used in the nervous system
The CNS (brain and spinal cord) receives sensory information and decides what kind of response is needed
If the response needed is movement, the CNS sends signals along neurones to tell skeletal muscles to contract
What is skeletal muscle
Skeletal muscle (also called striated, striped or voluntary muscle) is the type of muscle you use to move
e.g. the biceps and triceps move the lower arm
Structure of skeletal muscle
Skeletal muscle is made up of large bundles of long cells, called muscle fibres.
The cell membrane of muscle fibre cells is called the sarcolemma.
Areas of the sarcolemma fold inwards across the muscle fibre and stick into the sarcoplasm (a muscle cell’s cytoplasm).
These folds are called transverse (T) tubules
A network of internal membranes called the sarcoplasmic reticulum runs through the sarcoplasm
Function of sarcoplasmic reticulum
The sarcoplasmic reticulum stores and releases calcium ions that are needed for muscle contraction
How are muscle fibres specialised
Muscle fibres have lots of mitochondria to provide the ATP that’s needed for muscle contraction.
They are multinucleate (contain many nuclei).
What do muscle fibres contain
Muscle fibres have lots of long, cylindrical organelles called myofibrils.
They’re made up of proteins called actin and myosin and are highly specialised for contraction
Function of transverse (T) tubules
Help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
Structure of muscle fibres going from largest structures to smallest
Muscle
Muscle fibres
Myofibril
Myofilaments
What do myofibrils contain
Myofibrils contain bundles of thick and thin myofilament that move past each other to make muscles contract
Thick myofilaments are made of the protein myosin.
Thin myofilaments are made of the protein actin
How to distinguish different myofilaments under the microscope
You may see a pattern of alternating dark and light bands:
Dark bands contain the thick myosin filaments and some overlapping thin actin filaments - these are called A-bands.
Light bands contain thin actin filaments only - these are called I-bands.
What are the myofibrils made up of
Made up of many short units called sarcomeres
Structure of sarcomere
The ends of each sarcomere are marked with a Z-line.
In the middle of each sarcomere is an M-line.
The M-line is the middle of the myosin filaments.
Around the M-line is the H-zone.
The H-zone only contains myosin filaments.
How do sarcomeres contract
Myosin and actin filaments slide over one another to make the sarcomeres contract
The myofilaments themselves don’t contract.
How do the contraction of sarcomeres cause the whole muscle to contract
The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract.
Sarcomeres return to their original length as the muscle relaxes.
Features of relaxed and contracted sarcomeres
Contracted:
A bands stay same length
I band gets shorter
H zones get shorter
Structural feature of myosin and actin filaments
Myosin filaments have globular heads that are hinged, so they can move back and forth.
Each myosin head has a binding site for actin and a binding site for ATP.
Actin filaments have binding sites for myosin heads, called actin-myosin binding sites.
Two other proteins called tropomyosin and troponin are found between actin filaments.
These proteins are attached to each other and they help myofilaments move past each other
What happens in a myosin filament when at rest
In a resting (unstimulated) muscle the actin-myosin binding site is blocked by tropomyosin, which is held in place by troponin.
So myofilaments can’t slide past each other because the myosin heads can’t bind to the actin-myosin binding site on the actin filaments
Process of muscular contraction 1: action potential triggers influx of calcium ions
When an action potential from a motor neurone stimulates a muscle cell it depolarises the sarcolemma.
Depolarisation spreads down the T-tubules to the sarcoplasmic reticulum
Causes the sarcoplasmic reticulum to release stored calcium ions into the sarcoplasm.
Calcium ions bind to troponin, causing it to change shape
This pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament.
This exposes the binding site, which allows the myosin head to bind.
The bond formed when a myosin head binds to an actin filament is called an actin-myosin cross bridge
Process of muscular contraction 2: ATP provides the energy needed to move the myosin head
Calcium ions also activate the enzyme ATPase
This breaks down ATP (into ADP + Pi) to provide the energy needed for muscle contraction.
The energy released from ATP moves the myosin head, which pulls the actin filament along in a kind of rowing action.
Process of muscular contraction 3: ATP provides the energy needed to break the cross bridge
ATP also provides the energy to break the actin-myosin cross bridge
So the myosin head detaches from the actin filament after it’s moved.
It is now ready to attach to another binding site to carry on contraction
What happens to the myosin myofilaments when excitation stops
Ca2+ leave their binding sites on troponin molecules
Moved by active transport back to sarcoplasmic reticulum (needs ATP)
Troponin molecules return to original shape
This pulls the attached tropomyosin molecules with them
Means tropomyosin molecules block the actin myosin binding sites again
Muscles aren’t contracted because no myosin heads are attached to actin filaments (so there are no actin-myosin cross bridges).
The actin filaments slide back to their relaxed position, which lengthens the sarcomere
How does aerobic respiration provide ATP for muscular contraction
Most ATP is generated via oxidative phosphorylation in the cell’s mitochondria.
What is aerobic respiration typically used for and why
Aerobic respiration only works when there’s oxygen so it’s good for long periods of low-intensity exercise
e.g. walking or jogging
How does anaerobic respiration provide ATP for muscular contraction and what happens if this occurs over a long period of time
ATP is made rapidly by glycolysis.
The end product of glycolysis is pyruvate
Pyruvate is converted to lactate by lactate fermentation.
Lactate can quickly build up in the muscles and cause muscle fatigue (where the muscles can’t contract as forcefully as they could do previously)
What is anaerobic respiration typically used for
Anaerobic respiration is good for short periods of hard exercise, e.g. a 400 m sprint.
How does the ATP-Creatine Phosphate (CP) system provide ATP for muscular contraction
ATP is made by phosphorylating ADP.
This is done by adding a phosphate group taken from creatine phosphate (CP).
CP is stored inside cells and the ATP-CP system generates ATP very quickly.
The ATP-CP system is anaerobic (it doesn’t need oxygen) and it’s alactic (it doesn’t form any lactate)
What is the CP system typically used for
CP runs out after a few seconds so it’s used during short bursts of vigorous exercise, e.g. a tennis serve
What is a neuromuscular junction
A neuromuscular junction is a synapse between a motor neurone and a muscle cell
What neurotransmitter do neuromuscular junctions usually use
Neuromuscular junctions use the neurotransmitter acetylcholine (ACh), which binds to receptors called nicotinic cholinergic receptors.
How do neuromuscular junctions work
They release neurotransmitters
This triggers depolarisation in the postsynaptic cell
Depolarisation of a muscle cell always causes it to contract (if the threshold level is reached).
Acetylcholinesterase (AChE) stored in clefts on the postsynaptic membrane is released to break down acetylcholine after use
When may muscular contraction be stopped by changes at a neuromuscular junction
Sometimes a chemical (eg. a drug) may block the release of the neurotransmitter or affect the way it binds to the receptors on the postsynaptic membrane.
This may prevent the action potential from being passed on to the muscle, so the muscle won’t contract
This can be fatal if it affects the muscles involved in breathing,
E.g: the diaphragm and intercostal muscles.
If they can’t contract, ventilation can’t take place and the organism can’t respire aerobically.
Characteristics of skeletal muscle
Also called voluntary muscle
Skeletal muscle contraction is controlled consciously (you have to voluntarily decide to contract it).
Made up of many muscle fibres that have many nuclei.
The muscle fibres can be many centimetres long.
You can see regular cross-striations (a striped pattern) under a microscope
Functions of skeletal muscle
Some muscle fibres contract very quickly they’re used for speed and strength but fatigue quickly (fast twitch muscle fibres)
Some muscle fibres contract slowly and fatigue slowly - they’re used for endurance and posture (slow twitch muscle fibres)
What will you see when looking at skeletal muscle under a microscope
Characteristics of smooth muscle
Also called involuntary muscle
Involuntary muscle contraction is controlled unconsciously (it’ll contract automatically without you deciding).
It’s also called smooth muscle because it doesn’t have the striped appearance of voluntary muscle
Each muscle fibre has one nucleus.
The muscle fibres are spindle-shaped: with pointed ends, and they’re only about 0.2 mm long.
Muscle fibres contract slowly and don’t fatigue
Function of smooth muscle
It’s found in the walls of your hollow internal organs, e.g. the gut, the blood vessels
Your gut smooth muscles contract to move food along (peristalsis) and your blood vessel smooth muscles contract to reduce the flow of blood
Characteristics of cardiac muscle
Also called heart muscle
Contracts on its own - it’s myogenic (but the rate of contraction is controlled involuntarily by the autonomic nervous system).
It’s found in the walls of your heart.
It’s made of muscle fibres connected by intercalated discs, which have low electrical resistance so nerve impulses pass easily between cells
Muscle fibres are branched to allow nerve impulses to spread quickly through the whole muscle.
Each muscle fibre has one nucleus.
The muscle fibres are shaped like cylinders and they’re about 0.1 mm long.
Can see some cross-striations but the striped pattern isn’t as strong as it is in voluntary muscle
Muscle fibres contract rhythmically and don’t fatigue
What is the hypothalamus
Found beneath the middle part of the brain
Automatically maintains body temperature at the normal temperature
Regulates water balance
The hypothalamus produces hormones that controls pituitary gland
What is the cerebrum
Largest part of the brain
Divided into two halves called cerebral hemispheres
Has thin outer layer which is highly folded
The cerebrum is involved in voluntary actions like vision, hearing, learning, memory and thinking
What is the pituitary gland
Found beneath hypothalamus
Controlled by hypothalamus
Separated into anterior and posterior pituitary gland
Releases hormones and stimulates other glands to regulate body functions
E.g. adrenal glands
What is the medulla oblongata
Found at the base of the brain at the top of the spinal cord
Automatically controls breathing rate, blood pressure and heart rate
Why is the cerebrum highly folded
Increases the surface area and allows greater number of neurons
How does a full muscle contraction occur from actin-myosin cross bridges forming
First actin-myosin cross bridge breaks
The myosin head then reattaches to a different binding site further along the actin filament.
A new actin-myosin cross bridge is formed and the cycle is repeated (attach, move, detach, reattach to new binding site.).
Many cross bridges form and break very rapidly, pulling the actin filament along - which shortens the sarcomere, causing the muscle to contract.
The cycle will continue as long as calcium ions are present and bound to troponin
