The Brain and the CNS

I thought this coral looked like brain tissue (Daniel Hjalmarsson)

Located at the top of the body, the brain is protected by the skull as it is a muscle that's very susceptible to damage. There are four main aspects to the brain:

• The cerebrum makes up a large majority of the brain as a whole. The outer layer is called the cerebral cortex (which is more well known). The cerebrum consists of two hemispheres (halves) which are responsible for intelligence, personality and our conscious mind. They are also responsible for language and skill-set memory.
• The hypothalamus is responsible for our body's control of temperature and water levels. We often talk about the thermoregulatory centre (temperature control) in the hypothalamus when discussing homeostasis.
• The medulla is responsible for unconscious activities (that we don't control) such as heart rate and breathing
• The cerebellum is responsible for control of movements such as balance, muscle movement and co-ordination of our body.

 (BBC Bitesize)

Even though we know a lot about the brain, there is still a significant proportion of the brain we know little to nothing about. To find out more about the brain, we need to try non-invasive methods of experimentation. Often scientists will use small electrical frequencies to stimulate different parts of the brain. We can develop EEGs (electroencephalograms) to detect electrical frequencies in the brain. Scientists can also use MRI (magnetic resonance imaging) scans and study people with brain damage.

So how is the brain linked to the CNS? Well, without the brain we wouldn't function! The central nervous system consists of the brain and the spinal chord.  In the nervous system, receptors are inside and outside your body and these detect stimuli e.g. pain, temperature, pressure. The senses are due to different receptors;

• Touch- Pain receptors, pressure receptors, temperature receptors
• Taste- Chemical receptor cells
• See- Light receptor cells
• Hear- Sound receptor cells
• Smell- chemical receptor cells

Some receptors detect changes (stimuli) in the external environment like pressure when something touches you. Other receptors are internal and detect changes inside your body like the pancreas detecting glucose levels. Some receptors are single celled (e.g. pain receptors). Other receptors are groups of cells that work together in a more complex formation (e.g. the eye receptor cells).

The co-ordination centre in the brain is where, in a conscious response, it receives information and co-ordinates a response. Effectors carry out a response when the body needs to react. Effectors can be muscles or glands. 

1. Muscle responses are carried out via nerve communication. They are fast responses carried by neurones and their messages are carried out via electrical impulses. They are short lived.
2. Glandular responses are those carried out via hormonal communication. They are generally slower (with some exceptions like adrenaline) and their messages are carried in the blood. These are generally longer lived as they are in the bloodstream.

Along with the CNS (central nervous system) our body has a PNS (peripheral nervous system) which allows the rest of the body (like out arms and our legs) to be connected to the CNS. Nervous impulses allow different parts of the body to communicate with each other (a bit like a group chat run by the brain!).

So lets talk about our neurones. Nerve impulses are carried around the body via billions are neurones. Sensory neurones carry the impulse from the receptors to the CNS. Motor neurones carry the impulse from the CNS to the effector. Here is what you need to know about neurones:

• At one end is the cell body of the neuron with the nucleus.
• The axon is a long extension of the cytoplasm surrounded by cell membrane
• The axon is surrounded by a fatty sheath which insulates the neuron and subsequently increases the speed of the nerve impulse
• The branched endings make connections with other neurones or effectors
• Impulses are transmitted through a synapse (gap between two neurons) using neurotransmitter chemicals

So how do we get messages across this synapse?

1. The impulse reaches the end of the sensory neuron
2. The impulse causes the release of neurotransmitter messenger chemicals which diffuses across the synapse
3. The transmitter chemicals bind to specific, complimentary receptors on the next neurons surface. This causes an impulse to be created in the motor neuron.
4. Excess transmitter is taken back up into the sensory neuron through re-uptake channel. This prevents further, unwanted stimulation of the motor-neuron

Me trying to post this quickly so I can go to bed(Filip Mroz)

The more synapses in a response pathway, the slower the reaction will be because there are more synapses for the chemicals to diffuse across which means there will be a slower reaction time.

A reflex is co-ordinated by a reflex arc. The nerve impulse generated doesn't go to the brain (most) and it just enters the spinal chord before going to the effector. Reflexes are unconscious responses because they are involuntary. In reflexes, the relay neurones link the nervous system together. Instead of passing from the sensory neurone to the co-ordination centre, they skip the co-ordination centre and pass through the relay neurone and back to a motor neurone to carry out a response. Here's what an involuntary response roughly consists of:

• Receptor cells detect a stimuli (e.g. pain)
• The sensory neurone generates an impulse and transmits this across other nerves and into the spinal chord
• The impulse travels into synapses in the CNS and then travels into the relay neurone (Not the brain!)
• The relay neurone passes this impulse into the motor neurone and an effector (muscle) carries out a response