Nervous-system coordination

• The nervous system senses changes in both internal conditions and the external environment.

• Information about a stimulus is detected and communicated so that an appropriate response can be coordinated.

• Responses enable the body’s different physiological systems to work together effectively.

• Coordination allows body functions to be adjusted when conditions or physical demands change.

  

  The brain and spinal cord form the central pathway for coordination, while branching nerves connect this pathway to the rest of the body. This arrangement allows information and responses to pass between physiological systems.

Sensory receptors

• Receptors are specialised cells that respond to particular stimuli and initiate nervous-system responses.

• Proprioceptors detect information about body position and movement.

• Baroreceptors detect changes in pressure, particularly changes associated with blood pressure.

• Chemoreceptors detect changes in chemical conditions, including oxygen, carbon dioxide and acidity.

• For examinations, identify the stimulus detected and the resulting nervous response; the receptors’ internal workings are not assessed.

Autonomic balance

• The autonomic nervous system regulates involuntary functions without requiring conscious control.

• Its two divisions are the sympathetic and parasympathetic nervous systems.

• Sympathetic activity generally prepares physiological systems for increased demand, including an increased heart rate.

• Parasympathetic activity generally supports recovery and decreases heart rate when demand falls.

• Their contrasting effects allow functions such as cardiac activity to be adjusted as conditions change.

  

  The two autonomic divisions usually produce contrasting adjustments. Their balance enables involuntary functions to match periods of greater activity or recovery.

Epinephrine and norepinephrine

• Epinephrine and norepinephrine are hormones involved in widespread physiological adjustment.

• They cause changes in blood pressure.

• They cause changes in heart rate.

• They also cause changes in blood sugar levels.

• In an examination response, connect both hormones with all three specified effects.

Reproductive hormones

Nervous-system divisions

Physiological control

• Cardiac function is controlled through cooperation between intrinsic cardiac mechanisms and extrinsic nervous influences.

• Intrinsic mechanisms establish the heart’s rhythm, while extrinsic factors adjust heart rate according to the body’s requirements.

• The autonomic nervous system coordinates changes in breathing and ventilation when physiological demands change.

• This coordination adjusts the movement of air into and out of the lungs.

• The nervous system detects thermal conditions and coordinates responses involved in temperature control.

• These examples demonstrate how nervous communication coordinates several physiological systems simultaneously.

Endocrine communication

• The endocrine system consists of the body’s glands and hormones.

• It helps regulate biological processes throughout the body.

• Hormones are mediator molecules released in one part of the body.

• They regulate the activity of responsive cells located in other parts of the body.

• Different hormones regulate cardiovascular function, blood sugar, water retention, health and athletic performance.

  

  The endocrine system contains glands distributed throughout the body. Hormones released from these locations regulate cells and biological processes elsewhere.

Blood sugar and water retention

• Insulin and glucagon regulate blood sugar concentration through opposing effects.

• Insulin acts when blood sugar concentration must be reduced.

• Glucagon acts when blood sugar concentration must be increased.

• Together, these hormones regulate the availability of sugar in the blood.

• Antidiuretic hormone regulates the retention of water by the kidneys.

• Do not confuse blood-sugar regulation by insulin and glucagon with water regulation by antidiuretic hormone.

  

  Insulin lowers elevated blood sugar, whereas glucagon raises reduced blood sugar. The diagram emphasises that the two hormones regulate blood sugar in opposite directions.