Nerves and Hormones

The nervous system allows the body to respong to changes in the enviroment. Reflex actions are extra rapid responses to stimuli; this process also involves the nervous system and the brain.

Receptors:

• Eyes- Light
• Ears- Sound and posistion of head
• Tongue- Chemicals in food
• Nose- Chemicals in the air
• Skin- Touch, Pressure, Pain and temperature.

Cells:

• Light recpetors have a necleus, cytoplasm and cell membrane
• The Human Central nervous system (CNS) consists of the brain and spinal cord.
• When a recpetor is stimulated is sends a signal along the nerve cells, also called neurones to the brain. 

Nerve cells that carry information as tiny electrical signals. 

• Sensory- Neurons carry signals from receptors to the spinal cord and brain.
• Relay- Neurons carry messages from one part of the CNS to another.
• Motor- Neurones carry sinals from the CNS to to effectors.

Simple Reflex action:

• Receptor > Sensory Neuron > Relay Neurone > Motor Neurone > Effector (Synapse) 

1) Receptor detects a stimulus - a change in enviroment

2) Sensory Neurone sends impulses to relay neurone

3) Motor neurone send impulses to effector

4) Effector produces an impulse

• Synapse- A gap between neurons where the transmission of informationis chemical rather than electrical. One neurone realeases the chemical into the gap. Chemical diffuses across the gap and next neurone transmits a electrical signal.

Hormones are chemical substances that regulate processes in the body. 

Control of internal conditions:

The internal enviroment of the body is controlled by the nervous system and hormones, The maintenance of a constant internal enviroment is called homeostasis. 

Water content in the body

• The Lungs- When we exhale
• The Skin- Through sweating
• Passing urine- Produced by the kidneys

Ion content of the body

Ion leves are controlled to protect cells from too much water entering/leaving. Ion content is controlled by the loss of ions from

• The skin- Through sweating
• Passing urine- Produced by the kidneys

Temperature of the body

This is controlled to keep the temperature that enzymes work best. 

• Sweating
• Shivering
• Controlling blood flow to the skin

Blood Sugar Levels

Controlled to provide cells with constant supply of energy. Blood sugar level is controlled by the release and storage of glucose and controlled by insilin.

Hormones are chemicals secreted by glands in the body. Different hormones affect different target organs. The bloodstream usually transports the hormones from the gland to the organs. Hormones regulate the functions of many organs and cells. 

The Menstrual Cycle

A recurring monthly process in which the living of the uterus is prepared for pregnany. If pregnancy does not hapen the lining is shed at menstruation.

Follicle stimulating hormone (FSH)

• The hormone FSH is secreted by the pituitary gland.
• Causes the egg to mature in the ovary
• It stimulates the ovaries to release the hormone oestrogen

Oestrogen

• Secreted by the Ovaries
• Stops FSH being produced- so that only one egg matures in a cycle
• Stimulates the pituitary gland to realise Luteinizing hormone (LH) which triggers ovulation (release of mature egg from ovary)

Human fertility is controlled by hormones. This means that knowledge of hormones can be used to decide to increase or reduce the chances of fertilisation and pregnancy.

Contraceptives

• The oral contraceptive, (the pill) greatly reduces the chances of mature eggs being produced. 
• Contains oestrogen and progestrone
• These hormones inhibit the production of FSH which stops eggs maturing in the ovaries

Benefits and risks

• Oral contraceptives allow couples to choose the time they start a family, and choose the time they stop having children
• The first birth-control pills contained a lot more oestrogen than the pills today. This caused big side-effects. Such as...Changeds in weight, mood and blood pressure.