Human responses

Role of the nervous system

Coordination and regulation of body functions.

CNS

Central nervous system.

What makes up the CNS?

The brain and spinal cord.

PNS

Peripheral nervous system.

What makes up the PNS?

Nerves outside the brain and spinal cord.

How do electrical impulses travel through the nervous system?

Along neurons.

Three main types of neuron

Sensory neurons relay neurons and motor neurons.

Function of a sensory neuron

Carries impulses from receptors towards the CNS.

Function of a relay neuron

Connects neurons within the CNS.

Function of a motor neuron

Carries impulses from the CNS to an effector.

Five senses

Sight hearing smell taste and touch.

What detects stimuli?

Receptors.

Stimulus

A change in the internal or external environment that can be detected by receptors.

What happens when a receptor detects a stimulus?

It triggers an electrical impulse in a sensory neuron.

Reflex action

A rapid automatic response to a stimulus.

Purpose of a reflex action

To rapidly coordinate a response without requiring conscious thought.

Effector

A muscle or gland that produces a response.

Sequence of a simple reflex arc

Receptor → sensory neuron → relay neuron → motor neuron → effector.

Why are reflex actions rapid?

They use a short neural pathway and are automatically coordinated by the nervous system.

Synapse

A junction between two neurons.

Synaptic gap

The small gap between neurons at a synapse.

Neurotransmitter

A chemical substance released by one neuron that transmits a signal across the synapse.

Where are neurotransmitters stored?

In vesicles in the presynaptic neuron.

What happens when an impulse reaches the presynaptic terminal?

Vesicles release neurotransmitter molecules into the synaptic gap.

What happens to neurotransmitters after they are released?

They diffuse across the synaptic gap.

What do neurotransmitters bind to?

Receptor proteins on the postsynaptic neuron.

What happens when neurotransmitters bind to receptors?

An impulse is stimulated in the next neuron.

What happens to neurotransmitters afterwards?

They may be reabsorbed into the presynaptic neuron or diffuse into the surrounding fluid.

Why do synapses ensure one-way transmission?

Neurotransmitter release occurs from the presynaptic neuron and receptors are located on the postsynaptic neuron.

Endocrine system

A system of glands that produce and release hormones.

Hormone

A chemical substance produced by a gland and carried by the blood that alters the activity of one or more specific target organs.

How do hormones travel around the body?

Through the bloodstream.

Target organ

An organ whose cells respond to a particular hormone.

Main difference between nervous and hormonal control

Nervous control is generally faster and shorter-lasting while hormonal control is generally slower and longer-lasting.

Hormone secreted during fight or flight situations

Adrenaline.

Effect of adrenaline on breathing rate

It increases breathing rate.

Effect of adrenaline on heart rate

It increases heart rate.

Effect of adrenaline on pupil diameter

It increases pupil diameter.

Effect of adrenaline on blood glucose concentration

It increases blood glucose concentration.

Why does adrenaline increase blood glucose?

To make more glucose available for respiration and energy release.

Homeostasis

Maintaining a relatively stable internal environment despite changes in external or internal conditions.

Set point

The desired or reference value around which a physiological condition is maintained.

Negative feedback

A control mechanism where a change from the set point triggers responses that oppose the original change.

Basic structure of a negative feedback loop

Change from set point → detection → corrective response → condition moves back towards set point.

What happens when body temperature increases above the set point?

Vasodilation and sweating increase heat loss and lower body temperature.

Vasodilation

Widening of blood vessels near the skin surface.

How does vasodilation cool the body?

More blood flows near the skin surface increasing heat loss.

How does sweating cool the body?

Evaporation of sweat removes heat from the skin.

What happens when body temperature decreases below the set point?

Vasoconstriction and shivering help conserve and generate heat.

Vasoconstriction

Narrowing of blood vessels near the skin surface.

How does vasoconstriction reduce heat loss?

Less blood flows near the skin surface reducing heat transfer to the environment.

How does shivering warm the body?

Rapid muscle contractions increase metabolic activity and heat production.

Why is thermoregulation important for enzymes?

Enzymes work best within a particular temperature range.

What happens to enzymes at excessively high temperatures?

They can denature changing the shape of their active site.

What happens to enzyme-controlled reactions at low temperatures?

Reactions become slower.

Two antagonistic hormones controlling blood glucose

Insulin and glucagon.

What does antagonistic mean?

Having opposing effects.

What does insulin do?

Lowers blood glucose concentration.

What does glucagon do?

Raises blood glucose concentration.

What happens when blood glucose rises above the set point?

Insulin is released causing blood glucose to decrease.

What happens when blood glucose falls below the set point?

Glucagon is released causing blood glucose to increase.

Role of the liver in blood glucose control

It stores glucose as glycogen and can break glycogen down to release glucose when blood glucose is low.

Why is it important to regulate blood glucose?

Cells need a suitable supply of glucose for respiration while chronically high blood glucose can contribute to disease.

Type 1 diabetes

A condition where the body does not produce enough insulin because insulin-producing cells are destroyed.

Type 2 diabetes

A condition involving reduced responsiveness to insulin and often insufficient insulin production.

Treatment for Type 1 diabetes

Insulin replacement alongside management of blood glucose.

Treatment for Type 2 diabetes

Management may include lifestyle changes and medication and some people may also require insulin.

Why is controlling blood glucose important for people with diabetes?

It helps reduce the risk of complications caused by prolonged abnormal blood glucose levels.

Sugar tax

A tax placed on foods or drinks containing added sugar intended to reduce consumption.

How could a sugar tax potentially reduce diabetes incidence?

Higher prices may reduce consumption of sugary products potentially reducing excessive sugar intake and associated health risks.

Why might a sugar tax not completely solve the diabetes problem?

Diabetes has multiple contributing factors so reducing sugary product consumption alone may not eliminate the risk.

What should you consider when evaluating a sugar tax?

Its effectiveness changes in purchasing or consumption unintended effects and whether it addresses the wider causes of diabetes.