B 10 THE HUMAN NERVOUS SYSTEM

• Homeostasis is the regulation of the conditions inside your body to maintain a stable internal environment, in response to changes in both internal and external conditions.

• It is really important for maintaining the right conditions for your cells to funtion properly and for enzyme action.

• In the human body, homeostasis includes control of:
  - blood glucose concentration
  - body temperature
  - water levels

All control systems in the body include receptors, coordination centres and effectors:

• Receptors- cells that detect changes in the environment, called stimuli, and turn them into electrical impulses. Receptors are often located in the sense organs such as the... and are sensitive to...
  - Ear- sound and position of head
  - Eye- light
  - Skin- touch, pressure, pain, temperature
  
  
• Coordination centres- areas that receive and process the information from the receptors. They send out signals and coordinate the response of the body.
  
  
• Effectors- muscles or glands that produce a response. 
  E.g. - muscle contracting to move an arm
           - muscle squeezing saliva from the salivary gland
           - gland releasing a hormone into the blood

• The nervous system uses electrical impulses to enable you to react quickly to your surroundings and coordinate your behaviour.
  
  
• Nerve = group of neurones that transmit information to various parts of the body
• Neurones = individual nerve cells that conduct impulses
  
  
• Central nervous system = consists of the brain & spinal cord.
  
  
• Stimuli = changes in the environment.
• Receptors = cells that detect stimuli
• Sensory Neurone = carry electrical impulses from the receptors (sense organs) to the CNS
• Relay Neurone = neurone in the central nervous system
• Motor Neurone = carry electrical impulses from the CNS to the rest of the body
• Effector- a muscle or gland, which responds to nervous impulses
• Response.

• Nervous system summed up as:
  STIMULUS --- RECPETOR --- COORDINATOR (CNS) --- EFFECTOR
  
  

  
  

• Synapses = junctions between nerve cells.
• When a nerve impulse arrives at the end of a neurone, chemicals are released. 
• These diffuse across the synapse, and cause a new nerve impulse in the next neurone. 

EFFECT OF CAFFEINE ON REACTION TIME:

1.) 50cm ruler- get person to rest their arm on table with hand off the side of table with hand open

2.) get someone else to hold the ruler so the 0 end is just above the top of their hand 

3.) Drop ruler unexpectantly for them to catch it by closing their hand around the rule asap

4.) Record results by measuring what point is at the top of the hand once caught. Repeat twice more.

5.) Get the tester person to drink 100ml/32mg of caffiene and wait 10-15 mins 

6.) Repeat steps 1- 4

•  Reflex actions (arc) are rapid and automatic (don’t involve thinking). For example, you would pull your hand away from a hot flame without thinking. 
• Reflexes involve sensory, relay and motor neurones;

This is what happens:
1. receptor detects a stimulus ie a change in the environmen
2. sensory neurone sends a signal to a relay neurone
3. motor neurone sends a signal to an effector
4. effector produces a response

The way the iris in our eye adjusts the size of the pupil in response to bright or dim light is a reflex action.

• The brain is made up of billions of interconnected neurones that control complex behaviour 
• It is important for controlling all behaviour, actions, thoughs and feelings

• Cerebral Cortex - conciousness, intelligence, memory and language
• Cerebellum - coordination of muscular activity and balance 
• Medulla - unconcious activities, e.g. heartbeat and breathing

• Brain damage

By studying patients with brain damage, scientists can learn which parts of the brain are responsible for doing different jobs.

• Electrical stimulation

Scientists have stimulated different parts of the brain with a weak electrical current and then asked patients to describe what they experienced and the effects. 
+ can discover more about brain     - could be damaging brain without realising 

• MRI brain scans

Modern imaging methods such as MRI (Magnetic Resonance Imaging) scans can show details of brain structure and function. Patients are asked to perform various tasks and, by looking at the scan, scientists can see which parts of the brain are active when the task is carried out.
+ develops better understanding of how bain works, safe, painless- no ionising radiation
- patient must lie absolutely still, claustrophobia, no metal inc pacemakers etc.