How Does the Brain Develop?

How is the brain organized? Everything we do, feel and say from infancy to the end of life reflect the functioning of our brain How is the brain organized?

The Neuron The neuron is the basic building block of the nervous system They are often grouped in bundles called nerves. There are billions and billions of neurons throughout the body

4 parts of the neuron Dendrites are specialized to receive signals from neighboring neurons and carry them back to the cell body Thin, bushy-like structures that receive information from outside the neuron Relays the information into the cell body

The Neuron The Cell body contains the cell nucleus The cell body relays the information down to the axon

The structure of a neuron Axon: A thin, long structure that transmits signals from the cell body to the terminal buttons. The axon is wrapped in myelin, a fatty sheath that allows it to transmit information more rapidly.

Once the information hits the Terminal button, it is transmitted outside the cell by neurotransmitters, which reside in the axon terminal.

The Neuron

Fun Facts Average number of neurons in the human brain 100 billion Average number of neurons in an octopus brain 300 million Rate of neuron growth during development of a fetus (while in the womb) 250,000 neurons per minute

The information shoots from one end of the neuron to the other. How do neurons communicate?

Electrical Communication Action potential is an electrical current sent down the axon initiates the release of neurotransmitter. The activity within the neurons is electrical. This current causes the neuron to “fire” When an action potential moves down the axon, it causes the release of neurotransmitters

Synaptic transmission The neurons don’t actually touch each other, there is a gap between one neuron and the next called Synapses. The space between neurons Information must be transmitted across the synapse to other neurons via the neurotransmitters.

Presynaptic Neuron Postsynaptic Neuron

Neurotransmitters Neurotransmitters are chemical substances that reside in the axon terminals They communicate to other neurons by binding to receptors on neighboring neurons

What observations can you make about the brain?

Brain Development The wrinkled outer area of the brain is called the Cerebral Cortex- The cortex regulates many of our functions that we think of distinctly human. Your personality, ability to carry out plans, certain types of thinking, memory, sensory activity.

Looking at the Brain The exterior covering (cortex) of the brain is wrinkled which increases the surface area of the brain The brain is divided into 2 hemispheres Right and left hemispheres

The Corpus Callosum connects these hemispheres and allows communication from one side of the brain to the other.

Corpus Callosum The structure that connects the two cerebral hemispheres. Damage to the corpus callosum affects communication between the two hemispheres. Severing the C.C. was a treatment for epilepsy. For almost 60% of left-handed and almost all right-handed people, the brain areas controlling speech are located in the left hemisphere. When the C.C. is severed, behavioral oddities emerge: A woman who grasps something in her right hand that she cannot se, she can name it but not if it is placed in her left hand – the information goes to the less linguistic right hemisphere. The right hemisphere is not totally “illiterate” but it is more sensitive to the emotional content of speech

The beginning of the brain can be traced to the period of the zygote Approximately 3 weeks after conception a groups of cells form a flat structure called the neural plate

The neural plate folds to form a tube that ultimately becomes the brain and spinal cord 3 week old zygote

Early Brain Development In the months after birth the brain grows rapidly, producing billions of neurons, dendrites and axons, as well as synapses reaching its peak around the infant’s first birthday. -In the first 2 years the brain increases in size from 25% to 75% of its adult weight Soon after synapses soon to gradually disappear a phenomenon known as synaptic pruning. -This process is the brain’s way of “weeding out” the unnecessary connections between neurons.

Brain growth and development There is a fivefold increase in the number of dendrites in cortex from birth to age 2 years, as a result approximately 15,000 new connections may be established per neuron. This is called “Transient exuberance” These connections are necessary because thinking and learning require many connections between many parts of the brain Experience is vital for brain formation

If cells are unused they atrophy and are rededicated to other senses If cells are unused they atrophy and are rededicated to other senses. Underused neurons, like synapses are inactivated by pruning process

When children suffer brain damage, cognitive processes are usually impaired; these processes often improve gradually showing the brain’s plasticity The brain’s organization is somewhat flexible and if damaged the brain can make new connections