5.1.5 (g-l) Animal responses

Question 1

Describe the simple structure of a skeletal muscle. (3)

Answer 1

Composed of a bundle of fibres.

These fibres are composed of myofibrils.

Myofibrils are composed of protein filaments: myosin and actin.

Question 2

Describe the skeletal muscle cells. (5)

Answer 2

Long, tubular cells which a multinucleated.

Enclosed in a membrane- sarcoplasm.

Contains specialised endoplasmic reticulum: sarcoplasmic reticulum which releases calcium ions for contraction.

Abundant mitochondria which releases many ATP for muscle contraction.

Myofibrils like actin and myosin; specialised protein used in contraction.

Question 3

Describe the skeletal muscle.

Answer 3

Responsible for voluntary movement as it s controlled my the somatic nervous system.

Straited fibres which are regularly arranged, therefore contractions occur in one direction.

Contractions that occur are short and rapid.

Question 4

Describe the cardiac muscle. (3)

Answer 4

Myogenic cells, so are under involuntary control.

Branched interconnecting cells that cause simultaneous contractions.

Fibres are uninucleated and have fair straitions.

Question 5

Describe the smooth muscles. (4)

Answer 5

Non-straited, spindle shaped, uninucleated fibres generally found hollow organs like the stomach and digestive tract.

Under involuntary control.

Due to no regular arrangement in cells, contractions occur in different directions.

Contractions can occur for a relatively long period compared to the other muscles.

Question 6

Describe actin.

Answer 6

Thin protein filament composed of two strands wound around each other.

Overlapping areas contain binding sites for myosin.

Forms the ‘light band’ in the sacromere.

Question 7

Describe myosin.

Answer 7

Thick, rod shaped protein filament, with bulbous heads.

These heads attach to overlapping actin during contraction.

Forms the ‘H-zone’ in the sacromere.

Question 8

Describe the sacromere. (5)

Answer 8

This is the region between two z lines.

Z lines: Separates the light band. The distance between adjacent z lines is the sacromere, which decreases during contraction.

Light band (I-band): region that is only composed of actin filaments.

Dark band (A-band): region that is only composed of thick, filament, myosin, overlapping the thin filament, actin.

H-zones: Occurs in the middle of the dark band. Here, it is only composed of thick filament, myosin.

Question 9

Name the 5 gross structures of the brain.

Answer 9

Cerebrum

Cerebellum

Medulla oblongata

Hypothalamus

Pituitary gland

Question 10

Cerebrum

Answer 10

The largest structure in the brain, divided into lobes:

Frontal
Occipital
Temporal
Parietal

Cerebrum is responsible for many functions mainly including:

Conscious thought
Learning and memory
Controlling speech

Question 11

Hypothalamus (5)

Answer 11

Located in the centre of the brain and conducts many functions:

Control of osmoregulation: produces ADH
Thermoregulation
Control of circadian rhythms
Produces releasing factors.

Question 12

Medulla oblongata

Answer 12

Located in the hindbrain. This structure links the brain to the spinal cord.

Contains centres for controlling breathing, heart rates and blood pressure

Question 13

Cerebellum

Answer 13

Located in the hindbrain:

Controls muscular movement and co-ordination.
Regulates balance and posture.

Question 14

Pituitary gland

Answer 14

An endocrine gland that is a protrusion of the bottom of the hypothalamus.
Split up into the anterior and posterior:
Anterior- produces hormones including FSH
Posterior- stores and releases hormones produced by the hypothalamus, including ADH.

Question 15

Reflex

Answer 15

Involuntary response to a stimulus:

Allows a fast response that minimises damages to the body, which is an evolutionary advantage.

Basic pathway of a reflex:
Receptor receives stimulus —> Sensory neurone receives impulse from receptor —-> Relay neurone —-> Motor neurone —> effector muscle/ gland

Question 16

Knee jerk reflex

Answer 16

Spinal reflex (L2, L3 and L4) : Impulse bypasses the brain.

A kick occurs when pressure is exerted on the lower patella.

1. Stimulus: Tapping below the patella stretches the patella tendon.
2. Impulse travels to the spine via a sensory neurone
3. An interneurone inhibits an impulse being sent to the hamstring
4. There is no relay neurone that connects sensory and motor neurone to the quadricep which contracts.

The reflex helps to maintain posture and balance.

Question 17

Blinking reflex

Answer 17

Cranial reflex (5th and 7th cranial nerve): bypasses spinal cord.

Occurs when the cornea is stimulated or when light is very bright (optical reflex).
Also occurs when sounds 40-60 dB are heard.

Pathway:

1. Stimulus: cornea is stimulated eg. contact with foreign body.
2. Sensory neurone (5th cranial nerve) receives impulse from receptor.
3. Relay neurone is lower brain stem receives impulse from sensory neurone.
4. Motor neurone (7th cranial nerve) receives impulse which causes ‘closing of eyelids’.

This reflex is used to evaluate damage to the lower brain stem especially in unconscious patients.

Question 18

Advantages of reflexes (4)

Answer 18

Avoids the body being harm/ reduces the severity, if the body is harmed.

Prevents overloading of the brain when the response is always the same.

Does not have to be learned, so protection is provided from birth.

Very rapid as reflex arcs contain as few as 1/2 synapses.

Question 19

Describe the ‘fight or flight’ response (7)

Answer 19

Occurs when there is a perception of a threat/ danger. This is controlled by the sympathetic nervous system.

1. Receptors eg. auditory or visual, receives and impulse.
2. Sensory neurone sends impulse to hypothalamus which increases the stimulation of the SNS.
3. This triggers the release of adrenaline from the adrenal medulla into the blood. This causes physiological changes.
4. Hypothalamus also releases corticotropin-releasing factor (CRF) into the pituitary gland.
5. Release of CRF stimulates the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary gland.
6. ACTH stimulates the release of many corticosteroids from the adrenal cortex, which also causes physiological responses.

Question 20

Describe the action of adrenaline. (6)

Answer 20

Adrenaline binds on the plasma membrane of a hepatocyte and activates a G protein.

This triggers the activation of the enzyme, adenylyl cyclase.

Adenylyl cyclase converts ATP into cAMP, which acts as a secondary messenger.

cAMP activates other enzymes, protein kinases.

Protein kinases activate other enzymes by phosphorylating them.

The enzyme activated hydrolyses glycogen into glucose.

Question 21

Describe the action of the “secondary messenger model”

Answer 21

One hormone, the primary messenger, is able to cause a ‘cascade’ of effects.

For example, adrenaline can cause many cAMP molecules to be formed. This activates many more enzymes.

Question 22

How does the nervous system and endocrine system work in synergy to respond to changes in blood pH. (6)

Answer 22

The brain contains two control centres in the medulla oblongata that are linked to the Sino-atrial node in the heart.

Increase in CO2= Increase in carbonic acid = DECREASE in pH (more acidic)

Detected by chemoreceptors in: carotid artery and aorta.

• Increased frequency in impulses is sent to the medulla
• More impulses to the SAN via the sympathetic nervous system: accelerator nerve.
• More noradrenaline and adrenaline released
• Increases the frequency of depolarisation from the SAN
• Heart rate is increased.

An increase in pH:

• Less frequent impulses to be sent from the medulla via the vagus nerve (parasympathetic) to the SAN.
• Less adrenaline and noradrenaline released
• Heart rate decreases.

Question 23

How does the nervous system and endocrine system work in synergy to respond to changes in blood pressure. (6)

Answer 23

There are baroreceptors located in the walls of the carotid artery and the aorta.

A change is pressure is detected which sends an impulse to the medulla.

An increase in pressure:

• less frequent impulses sent from the medulla to the vagus nerve (parasympathetic).
• less impulses to the SAN
• Less adrenaline and noradrenaline released
• heart rate decreases.

A decrease in pressure:

• More impulses to the medulla
• More impulse sent from medulla down the accelerator nerve (sympathetic).
• More impulses sent to the SAN.
• More noradrenaline and adrenaline released
• Heart rate increases.

Question 24

Explain the sliding filament theory.

Answer 24

This is the mechanism for skeletal muscle contraction:

1. An action potential from the neuromuscular junction, reaches the sarcoplasmic reticulum and causes voltage gated calcium ions to open.
2. Calcium ions diffuse down its concentration gradient and bind to troponin.
3. Troponin changes shape and causes tropomyosin to move and uncover the actin binding site.
4. Myosin head in now able to bind to form an actin-myosin crossbridge. ADP is attached to myosin.
5. Once Myosin binds, it changes angle and releases ADP.
6. ATP binds to the myosin head which causes myosin to unbind from actin.
7. Myosin contains ATPase which hydrolyses ATP back to ADP. This returns the myosin head to its original position.

Question 25

Compare the parasympathetic and sympathetic nervous system. (8)

Answer 25

• Sympathetic (S) puts the body under stress whereas parasympathetic (P) makes the body to rela.
• S uses noradrenaline, P uses acetylcholine.
• S contains short preganglionic neurones but a long postganglionic one.
  P contains long preganglionic neurones but short post ganglionic one.
• S causes an increase in heart and breathing rate whereas P causes a decrease in this.
• S causes an increase in blood flow to skeletal muscles. P causes in increase in blood flow to the gut.
• S causes pupil dilation, P causes pupil constriction.
• S causes bronchi to dilate, P causes bronchi to constrict.
• S increases glycogenolysis, P increases glycogenesis.