B1 Unit 2 ~ Co-ordination and Control

The nervous system enables humans to react to their surroundings and coordinate their behaviour.

Information from receptors passes along cells (called neurones) in nerves to the brain.

Nerve impulses are electrical signals that travel along neurones.

Nerve impulses travel at high speed.

Receptors detect stimuli which include light, sound, changes in position, chemicals, touch, pressure, pain and temperature.

Sensory neurones – transmit nerve impulses from the receptors to the CNS when a stimulus is detected.

Motor neurones – transmit nerve impulses from the CNS to effectors, to bring about a response.

Effectors are muscles or glands.

The nervous system can be defined into 2 areas

1. Central nervous system (CNS)  Brain and spinal cord

This coordinates the response

2. Peripheral nervous system (PNS)

Consists of nerves connecting the CNS to the rest of the body (eg the optic nerve and the sciatic nerve)

Nerves are bundles of motor and sensory neurones. Involves sensory nerves and motor nerve cells. Sensory nerve cells detects and Motor neuron cell causes an effect.

Neurones

Sensory neurones ~ carry electrical impulses from receptors to the spinal cord.

Relay Neurons ~ carry electrical impulses in the spinal cord.

Motor Neurons ~ carry electrical impulses from the spinal cord to the effectors.

Synapses

The connections between neurones

When the impulses reaches the end of the axon it causes a chemical to be released.

They are called neurotransmitters.

They diffuse across the gap and stimulate the impulse to continue in the next neurone.

Reflexes

A reflex is a rapid automatic response to a stimulus, which does not involve conscious control.

Functions:

Protection from dangerous stimuli.

Eg hand withdrawal from a hot object.

Maintenance of body processes

eg. Heart rate and breathing

Muscle coordination and posture

Eg knee jerk

A reflex arc is the route taken by a nerve impulse from receptor to effector via the central nervous system to bring about a reflex action.

This involves:  A receptor ,Sensory neurone, Relay neurone {a short connecting neurone in the CNS} , A motor neurone, An effector.

The key point in a reflex arc is that the impulse bypasses the conscious area of your brain. The result is that the time between the stimulus and the reflex action is as short as possible. There is a synapse every time one neurone meets another one!

Many processes within the body are coordinated by chemical substances called hormones.

Hormones are secreted by glands and are transported to their target organs by the bloodstream.

Hormones regulate the functions of many organs and cells.

1) FSH – follicle stimulating hormone

Secreted from: pituitary gland. Effects: causes eggs to mature in ovary. Release of oestrogen from ovary.

2) Oestrogen

Secreted from: ovaries. Effects: inhibits release of FSH , causes the lining of the uterus to develop and thicken. Causes release of a mature egg

3) LH – luteinising hormone

Secreted from: pituitary gland  Effects: stimulates release of egg from ovary

The hormones produced by the pituitary gland and the ovary act together to control what happens in the menstrual. As the oestrogen levels rise they inhibit the production of FSH and encourage the production of  LH by the pituitary gland. When LH levels reach a peak in the middle of the cycle, they stimulate the release of a mature egg.

Increasing fertility

FSH is given as a fertility drug to woman whose own level of FSH is too low to stimulate eggs to mature.

IVF – In Vitro Fertilisation: Fertility drugs are given to increase egg production. Eggs are removed and fertilised with sperm outside the body. These can be allowed to develop into embryos. They may be implanted back into the womb of the mother.

Benefits: Enables infertile couples to have children. Excess embryos can be used for research.

Concerns: Health risks for the mother. Multiple births – some babies may die. People do not like embryos to be used for research.

The pill contains female hormones, particularly oestrogen. The hormones affect women’s ovaries, oreventing the release of any eggs. The pill inhibits the production of FSH so no eggs mature in the ovaries . Without mature eggs, women can’t get pregnant.

Anyone who uses the pill as a contraceptive has to take it regularly. If they forget to take it, the artificial hormones levels drop. Then their bodies own hormones take over very quickly. This can lead to an unexpected release of an egg ~ and an unexpected baby.

Benefits: It can reduce population growth in the developed world.

Concerns: Health problems – eg some increase the risk of blood clots. Religious objections to preventing conception.

The maintenance of a constant internal environment. Constant levels are maintained by negative feedback .

What are the main factors that are controlled?

Internal conditions which are controlled include:

1)The water content of the body

2) Temperature

3)Blood sugar levels

It is important that humans maintain a constant internal enviroment.

Humans respond to change in external temperature in differenet ways.

When hot

Brain detects it. Hairs lowered, sweat and vasodilation {blood supply moves to the surface to increase heat loss}

When cold

Hairs raised {to trap air to heat body}, no sweat {so heat is not lost} and vasoconstriction {the blood supply is away from the skin reducing heat loss}

Osmoregulation The process of water movement into or out of cells is called osmosis. We take in water and salts by drinking. We lose water by breathing, sweating, and urine production by the kidneys. Kidneys regulate the water content.

Blood sugar regulation We take in sugar as carbohydrate in our food. We control blood sugar levels by releasing insulin (a hormone) from the pancreas. Our cells need a constant supply of blood sugar for energy.

Thermoregulation Temperature regulation. Enzymes work best at 37 C. Above and below this by a few degrees, and our cellular reactions stop working. We control our body temperature using our skin, eg by sweating. Controlled by hypothalamus in the brain.

Plants produce hormones and respond to external stimuli, growing towards sources of water and light, which they need to survive.

A tropism is a growth in response to a stimulus and an auxin is a plant hormone produced in the stem tips and roots, which controls the direction of growth. Plant hormones are used in weed killers, rooting powder and to control fruit ripening.

Plants need light and water for  photosynthesis. Plant responses - called tropisms - help make sure that any growth is towards sources of light and water.

There are two main types of tropism: positive tropism – the plant grows towards the stimulus and negative tropism – the plant grows away from the stimulus.Phototropism is a tropism where light is the stimulus. A gravitropism (also called a 'geotropism') is a tropism where gravity is the stimulus. The roots and shoots of a plant respond differently to the same stimuli.

Light Stimulus Shoots ~ positive phototropism (grows towards the light). Light Stimulus Roots ~ negative phototropism (grows away from the light). Gravity Stimulus Shoots~ positive gravitropism  (grows agaisnt the force of gravity). Gravity Stimulus Roots ~ negative gravitropism (grows in the direction of the force of gravity)

Auxins & Photoropism

Auxins are plant hormones that make some parts of a plant grow faster than others. The result is that the plant grows faster than others. The result is that the plant stems bends towards the light. Auxin is produced in the tip of growing shoots. Light destroys the hormone auxin. If a plant is growing towards the light the Auxins that are on the side of the stem that are receiving the light are killed so the growth on that side of the plant shots down casing the plant to bend. On the shaded side of the plant there is more Auxins. So growth on this side speeds up. The result is that the shoots and leaves are turned towards the lights for photosynthesis. If the tips are removed, they cannot produce auxin, so phototropism cannot occur. If the tips are covered, light cannot break down the auxin, so phototropism cannot then occur.

Auxins are also involved in gravitropisms. In a root placed horizontally, the bottom side contains more auxin than the top side. This makes the bottom side grow less than the top side, causing the root to bend in the direction of the force of gravity.

In a shoot placed horizontally, the bottom side contains more auxin than the top side. This makes the bottom side grow more than the top side, causing the shoot to bend and grow against the force of gravity.