Internal and external stimuli

Question 1

Outline what happens in a simple reflex arc.

Answer 1

receptor detects stimulus → sensory neuron → relay neuron in CNS coordinates response → motor neuron
→ response by effector

Question 2

Give the advantages of a simple reflex.

Answer 2

1. Rapid response to potentially dangerous stimuli since only 3 neurons involved
2. Instinctive

Question 3

Suggest a suitable statistical test to determine whether a factor has a significant effect on the movement of an animal in a choice chamber.

Answer 3

Chi squared

Question 4

What features are common to all sensory receptors?

Answer 4

● Act as energy transducers which establish a generator potential.
● Respond to specific stimuli.

Question 5

Describe the basic structure of a Pacinian corpuscle.

Answer 5

● Single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule.
● Stretch-mediated Na+ channels on plasma membrane.
● Capillary runs along base layer of tissue.

Question 6

What stimulus does a Pacinian corpuscle respond

to? How?

Answer 6

1. Pressure deforms membrane, causing stretch-mediated Na+ ion channels to open.
2. If influx of Na+ raises membrane to threshold potential, a generator potential is produced.
3. Action potential moves along sensory neuron.

Question 7

Define myogenic.

Answer 7

Contraction of heart is initiated within the muscle itself rather than by nerve impulses.

Question 8

State the name and location of the 2 nodes involved in heart contraction.

Answer 8

● Sinoatrial node (SAN): within the wall of the right atrium.
● Atrioventricular node (AVN): near lower end of right atrium in the wall that separates the 2 atria.

Question 9

Describe how heartbeats are initiated and coordinated.

Answer 9

1. SAN initiates wave of depolarisation (WOD).
2. WOD spreads across both atria= atrial systole.
3. Layer of fibrous, non-conducting tissue delays impulse while ventricles fill & valves close.
4. AVN conveys WOD down septum via Bundle of His, which branches into Purkinje fibres along ventricles.
5. Causes ventricles to contract from apex upwards.

Question 10

State the formula for cardiac output.

Answer 10

cardiac output (CO) =
stroke volume (V) x heart rate (R)

Question 11

What is the autonomic nervous system?

Answer 11

● System that controls involuntary actions of glands and muscles.
● 2 subdivisions: sympathetic & parasympathetic.

Question 12

State the difference between the sympathetic and

parasympathetic nervous system.

Answer 12

Sympathetic involved in ‘fight or flight’ response: stimulates effectors to speed up activity.
Parasympathetic involved in normal resting conditions: inhibits effectors to slow down activity.

Question 13

Name the receptors involved in changing heart rate and state their location.

Answer 13

Baroreceptors (detect changes in blood pressure): carotid body.
Chemoreceptors (detect changes in pH e.g. due to increase in CO2 concentration): carotid body & aortic body.

Question 14

How does the body respond to an increase in blood

pressure?

Answer 14

1. Baroreceptors send more impulses to cardioinhibitory centre in the medulla oblongata.
2. More impulses to SAN down vagus nerve via parasympathetic nervous system.
3. Stimulates release of acetylcholine, which decreases heart rate.

Question 15

How does the body respond to a decrease in blood

pressure?

Answer 15

1. Baroreceptors send more impulses to cardioacceleratory centre in the medulla oblongata.
2. More impulses to SAN via sympathetic nervous system.
3. Stimulates release of noradrenaline, which increases heart rate and strength of contraction.

Question 16

How does the body respond to an increase in CO2

concentration?

Answer 16

1. Chemoreceptors detect pH decrease and send more impulses to cardioacceleratory centre of medulla oblongata.
2. More impulses to SAN via sympathetic nervous system.
3. Heart rate increases, so rate of blood flow to lungs increases = rate of gas exchange and ventilation rate increase.