Module 5 Section 3: Animal Responses

Question 1

What does the cardiac muscle being myogenic mean

Answer 1

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

Question 2

What systems regulate the length of the intervals between the beats

Answer 2

The rate of beating can be regulated by both the nervous system and endocrine system

Question 3

What are the automatic control systems in the body

Answer 3

Nervous response
Controlled by electrical impulses travelling through nerve cells (called neurons)

Chemical response
Controlled by hormones travelling through the bloodstream

Question 4

When may the heart rate increase

Answer 4

Exercise
When we activate fight or flight

Question 5

How can the brain control the heart rate

Answer 5

There is a specific cardioregulatory centre region of the brain called the medulla which controls the heart rate

Question 6

How do nerves and hormones play a part in fight or flight

Answer 6

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.

Question 7

Effects of the sympathetic nervous system during fight or flight

Answer 7

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

Question 8

What examples of hormones that increase heart rate

Answer 8

Noradrenaline
Adrenaline
Thyroxine

Question 9

Nerves that change heart rate

Answer 9

Sympathetic nerves: increases heart rate
Parasympathetic nerves: decreases heart rate

Question 10

How does the nervous system help to control heart rate

Answer 10

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

Question 11

Why do animals alter their heart rate

Answer 11

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

Question 12

How are the internal stimuli that control heart rate detected

Answer 12

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)

Question 13

Pathway of impulses through nervous system to control heart rate

Answer 13

Sensory neurons take action potential from the receptors to the medulla
Medulla processes info and sends action potential to SAN along motor neurons

Question 14

Pathway of change of heart rate when blood pressure is high

Answer 14

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

Question 15

Pathway of change of heart rate when blood pressure is low

Answer 15

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

Question 16

Pathway of change heart rate at high blood O2, low CO2 or high pH levels

Answer 16

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

Question 17

Pathway of change heart rate at low blood O2, high CO2 or low pH levels

Answer 17

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

Question 18

How do hormones increase heart rate and when can this happen

Answer 18

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

Question 19

How are the muscles used in the nervous system

Answer 19

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

Question 20

What is skeletal muscle

Answer 20

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

Question 21

Structure of skeletal muscle

Answer 21

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

Question 22

Function of sarcoplasmic reticulum

Answer 22

The sarcoplasmic reticulum stores and releases calcium ions that are needed for muscle contraction

Question 23

How are muscle fibres specialised

Answer 23

Muscle fibres have lots of mitochondria to provide the ATP that’s needed for muscle contraction.
They are multinucleate (contain many nuclei).

Question 24

What do muscle fibres contain

Answer 24

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

Question 25

Function of transverse (T) tubules

Answer 25

Help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre

Question 26

Structure of muscle fibres going from largest structures to smallest

Answer 26

Muscle Muscle fibres Myofibril Myofilaments

Question 27

What do myofibrils contain

Answer 27

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

Question 28

How to distinguish different myofilaments under the microscope

Answer 28

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.

Question 29

What are the myofibrils made up of

Answer 29

Made up of many short units called sarcomeres

Question 30

Structure of sarcomere

Answer 30

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.

Question 31

How do sarcomeres contract

Answer 31

Myosin and actin filaments slide over one another to make the sarcomeres contract The myofilaments themselves don't contract.

Question 32

How do the contraction of sarcomeres cause the whole muscle to contract

Answer 32

The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract. Sarcomeres return to their original length as the muscle relaxes.

Question 33

Features of relaxed and contracted sarcomeres

Answer 33

Contracted: A bands stay same length I band gets shorter H zones get shorter

Question 34

Structural feature of myosin and actin filaments

Answer 34

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

Question 35

What happens in a myosin filament when at rest

Answer 35

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

Question 36

Process of muscular contraction 1: action potential triggers influx of calcium ions

Answer 36

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

Question 37

Process of muscular contraction 2: ATP provides the energy needed to move the myosin head

Answer 37

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.

Question 38

Process of muscular contraction 3: ATP provides the energy needed to break the cross bridge

Answer 38

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

Question 39

What happens to the myosin myofilaments when excitation stops

Answer 39

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

Question 40

How does aerobic respiration provide ATP for muscular contraction

Answer 40

Most ATP is generated via oxidative phosphorylation in the cell's mitochondria.

Question 41

What is aerobic respiration typically used for and why

Answer 41

Aerobic respiration only works when there's oxygen so it's good for long periods of low-intensity exercise e.g. walking or jogging

Question 42

How does anaerobic respiration provide ATP for muscular contraction and what happens if this occurs over a long period of time

Answer 42

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)

Question 43

What is anaerobic respiration typically used for

Answer 43

Anaerobic respiration is good for short periods of hard exercise, e.g. a 400 m sprint.

Question 44

How does the ATP-Creatine Phosphate (CP) system provide ATP for muscular contraction

Answer 44

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)

Question 45

What is the CP system typically used for

Answer 45

CP runs out after a few seconds so it's used during short bursts of vigorous exercise, e.g. a tennis serve

Question 46

What is a neuromuscular junction

Answer 46

A neuromuscular junction is a synapse between a motor neurone and a muscle cell

Question 47

What neurotransmitter do neuromuscular junctions usually use

Answer 47

Neuromuscular junctions use the neurotransmitter acetylcholine (ACh), which binds to receptors called nicotinic cholinergic receptors.

Question 48

How do neuromuscular junctions work

Answer 48

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

Question 49

When may muscular contraction be stopped by changes at a neuromuscular junction

Answer 49

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.

Question 50

Characteristics of skeletal muscle

Answer 50

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

Question 51

Functions of skeletal muscle

Answer 51

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)

Question 52

What will you see when looking at skeletal muscle under a microscope

Answer 52

Question 53

Characteristics of smooth muscle

Answer 53

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

Question 54

Function of smooth muscle

Answer 54

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

Question 55

Characteristics of cardiac muscle

Answer 55

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

Question 56

What is the hypothalamus

Answer 56

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

Question 57

What is the cerebrum

Answer 57

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

Question 58

What is the pituitary gland

Answer 58

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

Question 59

What is the medulla oblongata

Answer 59

Found at the base of the brain at the top of the spinal cord Automatically controls breathing rate, blood pressure and heart rate

Question 60

Why is the cerebrum highly folded

Answer 60

Increases the surface area and allows greater number of neurons

Question 61

Answer 61

Question 62

How does a full muscle contraction occur from actin-myosin cross bridges forming

Answer 62

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