Module 5: Animal Responses

Question 1

What are the 2 main structural system that the nervous system is split into?

Answer 1

1) The central nervous system (CNS)

2) The peripheral nervous system. (PNS)

Question 2

What is the CNS and PNS made up of?

Answer 2

The CNS is made up of the brain and spinal cord.

The PNS is made up of neurones that connect the CNS to the rest of the body.

Question 3

What are the 2 main functional systems that the PNS can split into?

Answer 3

1) The somatic nervous system (SNS)

2) The autonomic nervous system (ANS)

Question 4

What does are the roles of SNS and PNS?

Answer 4

The somatic nervous system controls conscious activities. e.g. running and playing video games.

The autonomic nervous system controls unconscious activities e.g. digestion and heart rate.

Question 5

What is the autonomic nervous system split into?

Answer 5

1) Sympathetic nervous system

2) Parasympathetic nervous system.

Question 6

What is the role of the parasympathetic and sympathetic nervous system.

Answer 6

The sympathetic nervous system stimulates the ‘flight or fight’ response. It releases the neurotransmitter noradrenaline.

The parasympathetic system is the ‘rest and digest’ system that calms the body down. Parasympathetic neurones release the neurotransmitter acetylcholine.

Question 7

What are the 5 main brain structures called?

Answer 7

1) Cerebrum

2) Hypothalamus

3) Medulla Oblongata

4) Cerebellum

5) Pituitary gland.

Question 8

Describe the Cerebrum.

Answer 8

It is the largest part of the brain. It is divided into two halves called cerebral hemispheres.

The cerebrum has a thin outer layer called the cerebral cortex, which is highly folded, giving it a large surface area.

The cerebrum is involved in vision hearing, learning, thinking and processing language.

Question 9

Describe the Hypothalamus.

Answer 9

It is found beneath the middle part of the brain.

It is involved in homeostatic responses such as maintaining body temperature (thermoregulation).

It also produces hormones that control the pituitary gland.

Question 10

Describe the Medulla oblongata.

Answer 10

This is at the base of the brain, at the top of the spinal cord.

It is involved in unconscious processes such as automatically controls breathing and heart rate.

Question 11

Describe the cerebellum.

Answer 11

The cerebellum is a leaf-shaped structure found towards the back of the brain. It is positioned underneath the cerebrum and is highly folded.

It is important for muscle coordination, posture and coordination of balance.

Question 12

Describe the pituitary gland.

Answer 12

It is found beneath and is controlled by the hypothalamus.

It releases hormones and stimulates other glands to release their hormones.

Question 13

What is a reflex action?

Answer 13

Reflexes are rapid, unconscious actions that protect the body from harm.

This is because the pathway of communication doesn’t involve conscious parts of the brain- instead it goes through unconscious parts of the brain or the spinal cord, which stops us from having to think about the action, which would waste time.

Question 14

Explain the eye reflex.

Answer 14

To prevent damage to the eye, you automatically blink if something touches it.

Sensory receptors in the cornea are stimulated when something touches the eye, sending an electrical impulse along a sensory neuron to the central nervous system (CNS).

In the CNS, a relay neuron passes the impulse between the sensory neuron and a motor neuron, which passes the impulse to the orbicularis oculi muscles in the eyelids. These contract and cause the eyelid to close.

Question 15

Explain the knee-jerk reflex.

Answer 15

If your quadriceps muscle stretches suddenly, you automatically straighten your leg to help keep your balance.

Stretch receptors in the quadriceps muscle detect that the muscle is being stretched and send an electrical impulse along a sensory neuron to the spinal cord.

In this case, the impulse is passed directly onto a motor neuron, which carries the impulse to the quadriceps muscle. The muscle contracts and causes the leg to straighten.

Question 16

What is the ‘fight or flight’ response?

Answer 16

It prepares our body for action in response to a threat.

Question 17

Describe the neural process of the ‘fight or flight’ response.

Answer 17

Nerve impulses from the sensory neurone arrive at the hypothalamus, activating both the hormonal endocrine system and the sympathetic nervous system.

The pituitary gland is simulated to release a hormone called ACTH which acts on the adrenal glands, stimulating the release of steroid hormones (e.g. cortisol) from the adrenal cortex.

Then, the sympathetic nervous system is activated which signals to the adrenal glands to release adrenaline from the adrenal medulla.

Question 18

What are the effects of the sympathetic nervous system and adrenaline when activated?

Answer 18

1) Heart rate is increased.

2) Breathing rate increases

3) Glycogen is hydrolysed into glucose via glycogenolysis.

4) Increased muscle tension

5) Decreased digestion

6) Decreased salivation

7) Pupils dilate

8) Erector pili muscles in the skin contract- this makes the hair stand on end so the animal looks bigger and scarier.

Question 19

How is heart rate controlled via the nervous system?

Answer 19

The medulla oblongata is a brain region found at the bottom of the brain, in the brain stem. It is involved in unconscious processes, such as controlling heart rate and breathing rate.

A part of the medulla oblongata called the cardiovascular control centre is responsible for changing heart rate according to our body’s needs.

It works by sending impulses along sympathetic or parasympathetic neurones which release different neurotransmitters onto the sino-atrial node (SAN) - the SAN then modifies its rate of firing to slow down or speed up the heart rate.

Question 20

What are the two types of receptors found in the heart?

Answer 20

1) Baroreceptors

2) Chemoreceptors

Question 21

What are the roles of baroreceptors and chemoreceptors?

Answer 21

Baroreceptors: these are pressure receptors in the aorta and the carotid arteries. they are stimulated by high and low blood pressure.

Chemoreceptors: are chemical receptors in the aorta, carotid arteries and in the medulla oblongata. they monitor the oxygen level in the blood and also carbon dioxide and pH.

Question 22

Explain the control of heart rate in response to high blood pressure.

Answer 22

The baroreceptors detect high blood pressure and send impulses along sensory neurones to the cardiovascular centre, which sends impulses along parasympathetic neurones.

These secrete acetylcholine, which binds to receptors on the SAN. This causes the heart rate to slow down in order to reduce blood pressure back to normal.

Question 23

Explain the control of heart rate in response to low blood pressure

Answer 23

Baroreceptors detect low blood pressure and send impulses along sensory neurones to the cardiovascular centre, which sends impulses along sympathetic neurones.

These secrete noradrenaline, which binds to receptors on the SAN. This causes the heart rate to speed up in order to increase blood pressure back to normal.

Question 24

Explain the control of heart rate in response to high blood O2, low CO2 or high blood pH levels.

Answer 24

Chemoreceptors detect chemical changes in the blood and send impulses along sensory neurones to the cardiovascular centre, which sends impulses along parasympathetic neurones.

These secrete acetylcholine, which binds to receptors on the SAN. This causes the heart rate to decrease in order to return oxygen, carbon dioxide and pH levels back to normal.

Question 25

Explain the control of heart rate in response to low blood O2, CO2 or low blood pH levels.

Answer 25

Chemoreceptors detect chemical changes in the blood and send impulses along sensory neurones to the cardiovascular centre, which sends impulses along sympathetic neurones.

These secrete noradrenaline, which binds to receptors on the SAN. This causes the heart rate to increase in order to return oxygen, carbon dioxide and pH levels back to normal.

Question 26

Explain the control of heart rate in response to a stressor.

Answer 26

When an organism is threatened, the adrenal glands release adrenaline.

Adrenaline binds to specific receptors in the heart. This causes the cardiac muscle to contract more frequently and with more force, so the heart rate increases and the heart pumps more blood.

Question 27

What are the 3 types of muscle?

Answer 27

1) Skeletal muscle

2) Smooth muscle

3) Cardiac muscle

Question 28

Describe the structure and function of skeletal muscle.

Answer 28

Skeletal muscle is made up of bundles of long muscle cells, called muscle fibres.

The cell membrane of muscle cells is called the sarcolemma and the cytoplasm of muscle cells is called the sarcoplasm.

The sarcolemma folds into the sarcoplasm, creating something called transverse (T) tubules which help to spread electrical impulses throughout the cell.

A network of internal membranes called the sarcoplasmic reticulum runs through the sarcoplasm, which stores calcium ions for muscle contraction.

Muscle cells also differ from other cells in that they contain many nuclei (they are multinucleate) and lots of mitochondria to generate ATP for muscle contraction.

In addition, muscle fibres contain long cylinders of protein called myofibrils, which enable the muscle fibre to contract.

Question 29

What are myofibrils?

Answer 29

It is made up of short units called sarcomeres that contain bundles of thick and thin myofilaments that move past each other to make muscles contract.

The thick myofilaments are made of the protein myosin and the thin myofilaments are made of the protein actin.

Question 30

Describe the components of a Sarcomere.

Answer 30

Myosin is a thick myofilament and appears as a dark band (called the A band) under the microscope.

Actin is a thin myofilament and appears as a light band (called the I band) under the microscope.

At the end of each sarcomere is a Z-line. Sarcomeres are joined together lengthways at the Z-line.

Right in the middle of the sarcomere is a region called the M-line.

The H-zone refers to the portion of the A-band which only contains myosin filaments (and not the portions where actin overlaps with myosin).

Question 31

State what the sliding filament theory is.

Answer 31

A nerve signal triggers calcium to release to the muscle fibres.

Calcium binds to troponin moving tropomyosin and exposing binding sites on the actin.

Myosin heads attach to the actin, forming crossing bridges and myosin heads pivot.

This pulls actin filaments to the centre powered by ATP.

ATP binds to the myosin causing it to release from actin.

Myosin resets by hydrolysing and ATP is ready for another cycle.

Question 32

What are the three sources of ATP

Answer 32

1) Aerobic respiration: Oxidative phosphorylation generates most of the ATP in aerobic respiration. This takes place in the mitochondria. Can only take place when oxygen is plentiful e.g. low-intensity exercise.

2) Anaerobic respiration: Small amounts of ATP are produced in glycolysis. Takes place in the cytoplasm. Produces lactic acid which leads to muscle fatigue. Suitable for short bouts of high-intensity exercise.

3) ATP- creatine phosphate (ATP_CP) system: In muscles, ATP be made by taking a phosphate group from phosphocreatine and phosphorylating ADP. In this reaction, phosphocreatine is converted into creatine, which is removed from the body via the kidneys. Phosphocreatine is stored in muscle cells and can generate ATP very quickly (but soon runs out). Used for very short bursts of vigorous exercise. It is anaerobic (does not use oxygen) and alactic (does not produce lactic acid).

ADP + CP - ATP + C (creatine)

Question 33

What are the properties of skeletal muscle (voluntary muscle)?

Answer 33

Striated (striped) appearance

Under conscious (voluntary) control

Contains fast-twitch fibres which contract quickly but fatigue quickly and slow-twitch fibres which contract and fatigue more slowly – fast-twitch are used for rapid movements (like sprinting) while slow-twitch are used for posture and endurance sports

Muscle fibres have multiple nuclei and can be several centimetres long

Question 34

What are the properties of smooth muscle?

Answer 34

Cells are spindle-shaped (pointy at the ends) with no stripes

Under unconscious (involuntary) control

Contract slowly and do not fatigue

Each fibre has a single nucleus and is around 0.2 mm long

Found in blood vessels and in the walls of internal organs

Question 35

What are the properties of cardiac muscle?

Answer 35

Contains cross-striations (striped appearance) – but not as many as skeletal muscle

Fibres are connected by intercalated discs – these have low resistance so electrical activity easily passes between fibres

Fibres are branched at the ends

Contracts on its own accord (myogenic) but the rate of contraction is controlled by the autonomic nervous system.

Contracts rhythmically and does not fatigue.

Each fibre has a single nucleus and is around 0.1 mm long

Found in the walls of the heart.

Question 36

Explain Neuromuscular junctions.

Answer 36

Neuromuscular junctions (NMJs) are the fancy name for a synapse between a motor neuron and a muscle cell. NMJs use the neurotransmitter acetylcholine and contain receptors called nicotinic cholinergic receptors. Unlike typical synapses:

The postsynaptic membrane in NMJs is folded into clefts which store the enzyme acetylcholinesterase, which breaks down acetylcholine.

Acetylcholine always acts as an excitatory neurotransmitter.

The postsynaptic membrane contains a higher number of receptors.

Question 37

Describe the investigation in detecting electrical activity to measure muscle fatigue.

Answer 37

You can measure the muscle fatigue by recording the electrical activity of skeletal muscles. The electrical activity represents the brain telling the muscles to move – the greater the electrical signal, the more tired the muscle is, since the brain is having to recruit more muscle fibres to help lift the weight.

Method:

Attach two electrodes to the muscle e.g. biceps

Attach a third electrode on a part of the body that isn’t moving – this is the control

Turn off any electrical equipment in the room to reduce ‘noise’ in the signal

Connect the electrodes to an amplifier – this increases the electrical signal to make it easier to read. Connect the electrodes and amplifier to a computer.

A straight line should appear on the electromyogram when the muscle is relaxed.

Fluctuating lines will appear when the muscle contracts e.g. flexing the biceps

Lift a weight – the amplitude of the lines increases with time because more motor units are required to lift the weight. As the muscle fatigues, the amplitude increases further as even more motor units are recruited to lift the weight.