Nervous System

The central nervous system is made of nerve cells in all parts of the body and consists of the brain and spinal cord

It coordinates the response from the stimulus by  detecting a change in the environment from the receptors and then by sending information to an effector

Stimulus --> Receptor --> Sensory neurone --> CNS --> Motor neurone --> Effector --> Response 

Hormones are chemical messengers that are sent in the blood

They are released in various endocrine glands and these make up the endocrine system

The hormones are released directly into the blood and they then affect the target cells and organs

Hormones are slower than nerve impulses but they have a longer effect

Adrenaline is a hormone released by adrenal glands(just above the kidney)

The brain detects stress so it sends nerve impulses so that the adrenal glands release adrenaline

Adrenaline prepares you for "fight or flight" by activating processes that increase your supply of oxygen and glucose

• Adrenaline binds to specific heart receptors and this causes the heart to contract more frequently - this means heart rate and blood pressure increases
• Cells receive more oxygen from this as there is a higher blood pressure
• It also binds to liver receptors which cause the liver to break down supplies of glycogen into glucose
• The blood glucose level increases

Negative feedback can control the hormone level

This means that when the body detects the level of a hormone has gone above or below the normal level, it brings it back to the correct level

Thyroxine regulates metabolism using negative feedback

1. Thyroxine is released by the thyroid gland 

2. Thyroxine is released in response to TSH which is released from the pituitary gland

3. A negative feedback system keeps the amount of thyroxine at the right amount when the level is too high TSH is inhibited so the level then falls

Electrical impulses are sent along the axon of the neurone

The branched endings ( dendrites) connect with other neurones

The myelin sheath acts as an electrical insulator which speeds up the impulse

The long axon speeds up the impulse because it is quicker than lots of short neurones

Synapses are gaps which help speed up the impulse because it triggers chemicals which diffuse across the gap. These then bind to receptor molecules in the membrane of the next nerve cell and sets of an electrical impulse

Reflex actions are automatic responses that are quicker than a normal response because the brain is not involved

The act as a protection

The sensory neurone connects to a relay neurone in the spinal cord which directly links to the motor neurone - this is quicker

Cerebrum - This is responsible for consciousness, memory, intelligence and language

Hypothalamus - Responsible for maintaining body temperature

Medulla - Controls unconscious activities like breathing and heart rate

Cerebellum - Responsible for muscle coordination

Pituitary - A gland that produces many important hormones 

Cornea - refracts light into the eye

Iris - controls how much light enters the pupil

Lens - refracts light onto the retina

Ciliary Body - contains muscles connected to suspensory ligaments to alter lens shape

Retina - contains rods and cones that are sensitive to light

Rod - sensitive in dim light but can't see colour

Cone - sensitive to different colours but not good in dim light

Optic nerve - carries impulse to brain

Distant objects - 

Ciliary muscle relaxes so ligaments pull tight, the lens is less rounded to refract less

Close objects - 

Ciliary muscle contracts which slacken ligaments so lens in more rounded to refract more

Menstrual cycle - 

Stage 1 - day 1, uterus lining breaks down and is released

Stage 2 - lining builds up again, from day 4 to 14 ready for a fertilised egg

Stage 3 - day 14, an egg develops and is released

Stage 4 - Until day 38 the lining is maintained but will break down if there is no fertilised egg

FSH - Causes an egg to mature, stimulates ovaries for oestrogen

OESTROGEN - Causes uterus lining to thicken, stimulates LH and inhibits FSH so only one egg is released

LH - Stimulates egg release, indirectly stimulates PROGESTERONE

PROGESTERONE - Maintains uterus lining and inhibits FSH and LH, low PROGESTERONE allows FSH to increase

Some women have low levels of FSH so the eggs don't mature

FSH and LH can be injected to stimulate ovulation

IVF involves collecting eggs from a woman's ovaries and the male's sperm to grow them in a lab into embryos

The embryos are then transferred to the uterus

Progesterone - 

Stimulates production of thick cervical mucus so sperm are less likely to reach an egg

Thickens uterus lining to reduce the chance of an egg implanting

Prevents ovulation by inhibiting FSH and LH

Progesterone and Oestrogen - 

All progesterone effects plus oestrogen prevents ovulation by secreting FSH

Barrier - try to stop egg and sperm meeting

Condom, Diaphragm

IUD - inserted into the uterus and prevents sperm from surviving, alter lining so eggs can't implant

Sterilisation - surgical procedure to cut tubes in the reproductive system 

Auxins are plant growth hormones

Shoots - 

Positively phototrophic - when exposed to light it accumulates more auxins on the shaded side, this side grows faster and bends towards light

Negatively Gravitropic - More auxins are on the lower side so bends upwards

Roots - 

Negatively Phototrophic - More auxins on the shaded side inhibit elongation so bends downwards

Positively Gravitropic - Auxins are on the lower side so is inhibited and bends downwards