Nerves and Hormones

Nervous system allows u to:

• react to surroundings
• coordinate behaviour

Nervous system consists of:

• brain
• spinal cord
• nerves (neurones)
• receptors

information from receptors in sense organs passes along neurones (nerve cells) to ur brain or spinal cord (CNS). CNS then coordinates ur response by sending instructions to effectors

Effectors are either muscles or glands:

• muscles respond by contracting
• glands respond by releasing chemical substances 

cells called receptors in ur sense organs detect stimuli (changes in ur environment). Different stimuli are detected by different receptors:

• receptors in eyes sensitive to light 
• receptors in ears sensitvie to sounds & changes in position, which help balance
• receptors in nose & on ur tongue sensitive to chemicals, helping u smell & taste 
• receptors in skin sensitive to touch, pressure, pain & temperature changes 

Light receptors have a nucleus, cytoplasm and cell membrane 

Neurones are specially adapted cells that carry electrical signals. Three types of neurone, each with slightly different function:

• sensory neurones carry impulses from receptors to the CNS
• motor neurones carry signals from CNS to effectors
• relay neurones carry impulses from one part of the CNS to another 

Neurones don't touch each other, tiny gap between them called a synapse

Reflex actions designed to prevent ur body from being harmed. Reflex actions automatically quick. They speed up ur response time because they by-pass ur brain. They involve sensory, relay and motor neurones. Ur spinal cord acts as the co-ordinator. 

1. ur receptor cells detects a stimulus

2. an impulse travels along a sensory neurone

3. the impulse is passed along a relay neurone in the spinal cord in the CNS

4. the impulse travels along a motor neurone 

5. thr impulse reaches the organ (effector) that causes a response

Humans need to keep their internal environment relatively constant. Body must control:

• temperature - to maintain temperature at which enzymes work best (37degees celcius)
• water content - 70% of body mass is water, vital for chemical reactions to take place properly
• ion content - if we don't have correct balance of ions, cells can become shrivelled, swollen or even burst
• blood sugar (glucose) levels - to provide cells with constant supply of energy

Body controls temperature by:

• shivering to increase temperature 
• sweating to lower temperature 

Water leaves body in three ways:

• from lungs when breathe out 
• from skin when body sweats to cool down (also ions lost)
• via kidneys in urine (excess water only) (also ions lost) 

Glucose is used up when its converted to energy. Glucose, ions & water gained by drinking & eating

Hormones - chemicals produced by glands. They; coordinate many processes within ur body, regualte functions of many organs & cells and usually travel to target organs in the bloodstream. Several hormones involved in menstrual cycle of women. These hormones cause; an egg to be released every month from the ovaries and changes in thickness of womb liningThese hormones produced by pituitary gland in brain & ovaries.

1. follicle stimulating hormone (FSH) from pitituary gland causes:

• an egg to mature in the ovaries
• the ovaries to produce oestrogen

2. oestrogen from the ovaries

• inhibits further production of FSH
• causes production of LH

3. LH from pitituary gland

• stimulates the release of an egg in middle of menstrual cycle

Hormones can be given to women to:

• increase fertility - women who don't produce enough FSH naturally can be given FSH & LH in a 'fertility drug' to stimulate eggs to mature
• reduce fertility - oestrogen and progestorone can be given in birth control pills to prevent FSH production so eggs don't mature

The first birth control pills contained large amounts of oestrogen, which made women suffer side effects. Pills that only contain progesterone tend to have fewer side effects. Birth control pills now contain much lower doses of oestrogon or are progesterone only. 

Using fertility drugs increases the chance of multiple births, which increases risk of complications during pregnancy

IVF treatment is given to women who have difficulty becoming pregnant

The main stages of IVF are:

1. the mother is given FSH and LH to make several eggs mature

2. the eggs are collected from the mother

3. the eggs are fertilised in a laboratury using the father's sperm

4. the fertilised eggs develop into embryos

5. one or two embryos are inserted into the mother's uterus (womb) to develop