Mod 1-Obj6: Biological feedback systems, +&-

Question 1

Feedback mechanisms

Answer 1

A homeostatic control mechanism uses feedback to maintain balance in the internal environment (ECF)

• In a feedback mechanism the response alters the initial stimulus which the alters the response
• Can be negative or positive

Question 2

Negative feedback mechanism

Answer 2

The output shuts off the original effect of the stimulus or reduces its intensity, causing the variable to change in a direction opposite to that of the initial change, returning to homeostatic range

Question 3

Positive feedback mechanism

Answer 3

The response enhances the original stimulus so the response is accelerated, the change proceeds in the same direction as the initial change, causing the variable to deviate further from its original value

Question 4

Body temperature regulated by negative feedback mechanism

Answer 4

Stimulus: Heat
body temperature rises
Receptors: Temperature sensitive cells in skin and brain
afferent pathway
Control centre: thermoregulatory centre in brain
Efferent pathway
Effector: sweat glands
Response-Evaporation of sweat, body temperature falls; stimulus ends

Question 5

Uterine contraction form of positive feedback

Answer 5

1. Head of fetus pushes against cervix
2. Nerve impulses from cervix transmitted in brain
3. Brain stimulates pituitary gland to secrete oxytocin
4. Oxytocin carried in bloodstream to uterus
5. Oxytocin stimulates uterine contractions and pushes fetus towards cervix

Question 6

Why is there negative feedback?

Answer 6

Provides stability and long term control over internal conditions
-Maintains the narrow range of body conditions required for optimal cell function

Question 7

Why is there positive feedback?

Answer 7

Accelerates a process to completion

-Occurs when a potentially dangerous or stressful process must be completed quickly

Question 8

Stimulus-response

Answer 8

The basis of the ability of the body to make appropriate changes

• rely on effective communication
• Receptor detects a stimulus (change in the internal environment) which sends a message via the afferent pathway to the control centre thus via the efferent pathway sends a message to the effector causing a response

Question 9

Two communication systems

Answer 9

Nervous and endocrine systems

Question 10

Nervous impulses

Answer 10

1. Electrical
2. Rapid
3. Short-lived

Question 11

Homones

Answer 11

1. Chemical
2. Slow acting
3. Short lived

Question 12

Two main subdivisions of the nervous system

Answer 12

CNS and PNS

Question 13

Central nervous system

Answer 13

Is the control centre

Question 14

Peripheral nervous system

Answer 14

Nerves carry impulses to and from the CNS

Question 15

Nerves

Answer 15

A peripheral nerve is a bundle of many nerve cells

• Includes afferent and efferent fibres
• Afferent fibres transmit electrical signals to the CNS
• Peripheral targets of efferent fibres include specific muscles or glands

Question 16

The endocrine system

Answer 16

Control responses that require duration through the action of chemical messengers called hormones

• Hormones are released from the cells of endocrine glands, directly into the bloodstream
• Any cell with the appropriate receptor can responds to the hormone

Question 17

Endocrine functions

Answer 17

1. Growth
2. Metabolic rate
3. Reproductive processes
4. Digestive processes

Question 18

Similarities between nerves and hormones

Answer 18

Together, these two systems regulate and control body processes

1. Both are means of cellular communication
2. Both involve stimulus-response mechanisms

Question 19

Differences between nerves and hormones

Answer 19

1. Nature of the message (electrical vs. chemical)
2. Speed and duration of the responses (rapid and short term vs. slower and longer term)
3. Range of targets (specific vs. widespread)