The Normal Brain

Written by Julie Taylor

The Normal Brain...

Teenage Brain and Brain Plasticity

Here are some normal brain facts so that you know what each part is called and you can make better sense of what the doctors tell you.  There's also a very interesting video which you can link to at the end of this page.

Brain Facts

• Brain size = approx. 3 pounds - it reaches full size by age six. From birth, the number of brain cells does not increase, but the size of the cell does and the number of connections between brain cells increases. Some connections are not made until late teens or early 20’s, which accounts for what parents knowingly call 'the teenage brain'.

• Consistency = jello

• It has a convoluted surface - lots of folds, which increases the surface area of the brain.

Neuron

• A neuron = a brain cell. There are 100 billion neurons in the brain. Neurons don’t touch each other, instead they communicate using electrical signals that require specific chemicals to allow the signal to jump from neuron to neuron. (These chemicals are called neurotransmitters).

• Grey matter (40%) = cell bodies.

• White matter (60%) = the axons.
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Blood Supply

The brain needs a lot of oxygen. Oxygen is carried to the brain by the blood. The blood supply is extensive throughout the brain. (20% of the blood flow, 20% of the oxygen). If brain cells do not get oxygen for 3 to 5 minutes, they begin to die.

Natural Protection for the Brain

The brain is naturally protected in many ways, including:

• 1. Skull: also called the cranium

• 2. Meninges: the brain and spinal cord are covered by a tough, translucent membrane, made up of three layers.

• 3. Blood brain barrier: Protects the brain from chemical pollution from the rest of the body. Blood flowing into the brain is filtered so that many harmful chemicals cannot enter the brain.

• 4. Cerebro Spinal Fluid (CSF): This fluid bathes the brain and spinal cord. It cushions the brain from jolts and is nutritive.

Parts of the Brain

The brain is very complex…these notes are very simplified and abbreviated.

1.Brain Stem:

• Connects the spinal cord and brain.

• Motor (movement) and sensory (feeling) pathways to/from body and face travel through the brain stem.

• Contains vital centers for cardiac (heart), respiratory (breathing) and vasomotor. This is essential for automatic functions, necessary for life and for arousal (being awake and alert).

2.Cerebellum:

• Involved in balance and posture. Coordination.

3.Cerebrum (Cerebral cortex) - which is divided into LOBES:

3a. Frontal Lobe

The front part of this lobe is called the PREFRONTAL LOBE - which is involved in higher level thinking and personality.

The back part of the lobe consists of the “premotor” and “motor” areas which produce and modify movements.

• Behaviour
• Judgement
• Inhibition
• Libido/Sexual Urges
• Emotion
• Creative thought
• Personality
• Intellect
• Executive Function: abstract thinking, problem solving, initiation, planning and organizing, insight, self-monitoring
• Language expression (talking, expressing yourself) is usually on the LEFT side in an area called “Broca’s area”.

3b. Parietal Lobe

• Primary sensory area - which controls sensation, including tactile (touch), sterognosis (appreciation of form through touch), and proprioception (joint sensation).
• Putting all sensory information together and making sense of it.
• Some language and reading function (usually on the LEFT side), spelling and math.
• Some visual perceptual functions (usually on the RIGHT side), topographical, memory (making sense of what we see).

3c. Temporal Lobes

• Some hearing
• Involved in short and long term memory. (RIGHT side - visual memory and LEFT side - verbal memory).
• Some vision pathways travel through this lobe.
• Music
• Some language and speech: understanding language is in the back part of this lobe, in an area called “Wernicke’s area”.
• Some behaviour and emotions, including fear.

3d. Occipital Lobe

• Vision - visual reception, plus association area that help in visual recognition

The Two Hemispheres of the Brain

The 2 hemispheres are joined by a thick bundle of nerve fibres (200-250 million nerve fibres), called corpous callosum. There are some differences between the two sides of the brain:

The Left Side

• Controls movements and sensation on the right side of the body.
• Always involved in language - expression and comprehension in right handed people.
• Math
• Logic

The Right Side

• Controls movements and sensations on the left side of the body.
• Visual perception
• Temporal (time) and spatial relationships
• Communicating emotion
• Analyzing non-verbal information
• Facial recognition
• Music
• Visual imagery

Exception: some left handed people have different organization of language in their brain.

Specific pathways/functions

Visual pathways - there is a complex system, involving all areas of your brain for different aspects of vision and visual perception. Because the pathways are long and are in many different areas, this system can be damaged with a stroke or an acquired brain injury.

Vestibular system - This is also a complex system, involving the inner ear; 8th cranial nerve, cerebellum and brainstem. Disruptions in the system are common after the brain injury.

Brain Plasticity - Recently there has been a lot of evidence to support the fact that whilst the 'normal' state may be that the right side of the brain has certain functions and the left side of the brain has its own, each side is capable of 'picking up' tasks that the other side can no longer do...  There's a very interesting video about Rasmussen's disease and hemispherectomy  available at the bottom of the attached page - Click Here.