P1 Animal Responses

Question 1

What is the nervous system and what is it composed of?

Answer 1

• The nervous system is the network of all the neurones in the body.
• It is composed of the central nervous system (brain and spinal cord - which contains relay, sensory and motor neurones) and the peripheral nervous system (sensory and motor neurones - the remaining neurones).

Question 2

What is the peripheral nervous system composed of?

Answer 2

1. The somatic nervous system (sensory receptor –> CNS –> muscles in limbs) results in voluntary action.
2. The autonomic nervous system (CNS –> internal organs/glands) results in involuntary action eg. controlling heart rate.

Question 3

What is the autonomic nervous system composed of?

Answer 3

1. Sympathetic nervous system, which makes involuntary bodily processes more active.
2. Parasympathetic nervous system, makes involuntary bodily processes less active.

Question 4

What is the largest part of the brain, and what is it’s function?

Answer 4

• Cerebrum
• Controls voluntary actions eg. thinking, memory and speech
• It is divided into two hemispheres, where the left hemisphere controls the right side of the body and the right hemisphere controls the left side.

Question 5

What part of the brain is below the cerebrum, and what is it’s function?

Answer 5

• Cerebellum
• Controls involuntary movements and balance.

Question 6

Where is the hypothalamus located and what is it’s function?

Answer 6

• In the middle of the brain.
• It is an endocrine gland that controls thermoregulation and osmoregulation.

Question 7

What structure of the brain is the hypothalamus connected to, and what is it’s function?

Answer 7

• Pituitary gland (located beneath the hypothalamus and also an endocrine gland).
• The anterior pituitary gland produces and releases hormones eg. FSH.
• The posterior pituitary gland stores and releases hormones from the hypothalamus eg. ADH.

Question 8

What structure is located at the base of the brain and what is it’s function?

Answer 8

• Medulla oblongata
• Regulates functions of the autonomic nervous system eg. heart rate and breathing rate.

Question 9

What is a reflex action?

Answer 9

• An involuntary response to a stimulus.
• The response is a reflex arc, which is very fast and acts to minimise/prevent damage.

Question 10

How does a reflex arc occur?

Answer 10

1. A stimulus is detected by a receptor.
2. The receptor sends impulses to the coordinator (CNS).
3. The CNS sends impulses to an effector, which carries out a response.

Question 11

Describe the knee-jerk reflex (reflex arc).

Answer 11

1. The patellar tendon is knocked (stimulus), causing it to stretch.
2. Stretch receptors in the leg muscles detect this change and send impulses through a sensory neurone.
3. In the spinal cord, this sensory neurone transmits these impulses to a motor neurone.
4. The motor neurone carries these impulses back to the effectors (leg muscles) and cause them to contract, so the leg kicks.

This is fast because the impulse doesn’t travel up to the brain, and it only involves one synapse.

Question 12

Describe the blinking reflex (reflex arc)

Answer 12

1. An object hits the cornea and the cornea receptors/free nerve endings detect this.
2. Receptors send impulses along a sensory neurone to a relay neurone in the brain stem.
3. The relay neurone sends these impulses to a motor neurone, which branches off to the effectors (eyelid muscles).
4. These muscles close the eyelids, which protects the cornea.

Question 13

Describe the fight or flight response.

Answer 13

1. The stimulus is detected by receptors in the body.
2. Impulse are sent along sensory neurones to the hypothalamus.
3. The hypothalamus coordinates a response through the endocrine and nervous system.

Question 14

How does the hypothalamus activate the endocrine system in the flight or fight response?

Answer 14

It activates the adrenal-cortical system (endocrine system) by:
1. Hypothalamus releases a peptide hormone that stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH).
2. ACTH enters the blood stream where it is transported to the adrenal glands, and it stimulates the adrenal cortex to secrete hormones that help us deal with stress, such as cortisol.

Question 15

How does the hypothalamus activate the nervous system in the fight or flight response?

Answer 15

It activates the sympathetic nervous system by:
1. The hypothalamus sends impulses down the sympathetic nervous system to the adrenal glands.
2. This causes the adrenal medulla to secrete the hormones adrenaline and noradrenaline.
3. These hormones have a variety of functions like increasing heart rate. One function of adrenaline is to stimulate glycogenolysis (conversion of glycogen to glucose) in the liver.

Question 16

How does adrenaline stimulate glycogenolysis in the liver?

Answer 16

Second messenger model:
1. Adrenaline (first messenger) binds to a receptor on a liver cell, which activates the enzyme adenylyl cyclase, which converts ATP into cyclic AMP (cAMP).
2. cAMP (second messenger) binds to and activates protein kinase.
3. Protein kinase then phosphorylates another group of enzymes, causing them to convert glycogen to glucose.

Question 17

How is heart rate controlled?

Answer 17

• Heart rate is controlled by the medulla oblongata. It contains two centres that both send impulses down to the sinoatrial node in the heart.
• The acceleratory centre sends impulses through the sympathetic nervous system, increasing heart rate.
• Whereas the inhibitory centre sends impulses through the parasympathetic nervous system, decreasing heart rate.

Question 18

What are the two types of receptors that send impulses to the medulla oblongata (to change heart rate)?

Answer 18

1. Chemoreceptors - detect changes in blood pH.
2. Baroreceptors - detect changes in blood pressure.
   - These receptors are both located in the walls of blood vessels, in the heart and neck.

Eg. chemoreceptors detect a low blood pH, so they send impulses to the medulla oblongata, which sends further impulses down the sympathetic nervous system to the sinoatrial node (SAN). These impulses increase the frequency at which the SAN generates electrical impulses, increasing heart rate. This then increases the rate at which carbon dioxide is exhaled, returning blood pH to a normal level (same happens when baroreceptors detect low blood pressure, and opposite with high pH and high blood pressure).

Question 19

How do adrenaline and noradrenaline increase heart rate?

Answer 19

By increasing activity of the sinoatrial node (SAN).