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BIOLOGICAL BASES OF BEHAVIOR

THE HUMAN BRAIN

The influence of biology (sometimes called the neuroscience or biopsychological perspective) is growing. Some researchers predict that someday psychology will be a specialty within the field of biology. An understanding of the biological principles relevant to psychology is needed to understand current psychological thinking.


The human brain consists of three major divisions; hindbrain, midbrain, and forebrain

Major Division

Subdivision

Structures

Prosencephalon
(Forebrain)


Telencephalon

Neocortex; Basal Ganglia; Amygdala; Hippocampus; Lateral Ventricles

Diencephalon

Thalamus; Hypothalamus; Epithalamus; Third Ventricle

Mesencephalon
(Midbrain)


Mesencephalon

Tectum; Tegmentum; Cerebral Aqueduct

Rhombencephalon
(Hindbrain)


Metencephalon

Cerebellum; Pons; Fourth Ventricle


Myelencephalon

Medulla Oblongata; Fourth Ventricle

Brain Structure

1. Hindbrain- structures in the top part of the spinal cord, controls basic biological functions that keep us alive.  Medulla- controls blood pressure, heart rate, and breathing; Pons- connects the hindbrain with the mid and forebrain, also involved in the control of facial expressions; Cerebellum- portion of the lower brain that coordinates and organizes bodily movements for balance and accuracy.

2 Midbrain-between the hind and forebrain, coordinates simple movements with sensory information.

3 Forebrain- controls what we think of as thought and reason.   Thalamus- portion of the lower brain that functions primarily as a central relay station for incoming and outgoing messages from the body to the brain and the brain to the body  Hypothalamus- portion of the lower brain that regulates basic needs (hunger, thirst) and emotions such as pleasure, fear, rage, and sexuality
Amygdala and Hippocampus- two arms surrounding the thalamus, important in how we process and perceive memory and emotion


NOTE: The three parts above are grouped together and called the limbic system because they all deal with aspects of emotion and memory.

What is a neuron?

A neuron is a nerve cell. The brain is made up of about 100 billion neurons.

Neurons are similar to other cells in the body in some ways such as:


  1. Neurons are surrounded by a membrane.

  2. Neurons have a nucleus that contains genes.

  3. Neurons contain cytoplasm, mitochondria and other "organelles".

However, neurons differ from other cells in the body in some ways such as:

  1. Neurons have specialized projections called dendrites and axons. Dendrites bring information to the cell body and axons take information away from the cell body.

  2. Neurons communicate with each other through an electrochemical process.

  3. Neurons form specialized connections called "synapses" and produce special chemicals called "neurotransmitters" that are released at the synapse.

It has been estimated that there are 1 quadrillion synapses in the human brain. That's 1015 or 1,000,000,000,000,000 synapses! This is equal to about a half-billion synapses per cubic millimeter. (Statistic from Changeux, J-P. and Ricoeur, P., What Makes Us Think?, Princeton: Princeton University Press, 2000, p. 78)

How big is the brain? How much does the brain weigh?

The adult human brain weighs between 1300 g and 1400 g (about 3 lbs). A newborn human brain weighs between 350 and 400 g. For comparison:

elephant brain = 6,000 g
chimpanzee brain = 420 g
rhesus monkey brain = 95 g
beagle dog brain = 72 g
cat brain = 30 g

rat brain = 2 g


The picture to the right is a human brain.
(Image provided by Dr. Wally Welker, Univ. of Wisconsin Brain Collection)

Ways of studying the brain

Accidents, Lesions, Electroencephalogram, Computerized axial tomography, Magnetic resonance imaging (MRI), Positron emission tomography, Functional MRI

 
Neuroanatomy  



Neuron – a nerve cell, which transmits electrical and chemical information throughout the body 
dendrite
- part of the neuron that receives information from the axons of other nerve cells
Axon
- part of the neuron that carries messages away from one neuron to the dendrites of another Cell body, or soma- contains the nucleus and other parts of the cell needed to sustain its life  
Myelin sheath- a fatty covering around the axon that speeds neural impulses  
Terminal buttons- the branched end of the axon that contains neurotransmitters  
Vesicles
– bubblelike containers of neurotransmitters, located at the end of an axon Neurotransmitters-– chemicals in the endings of nerve cells that send information across the synapse Acetylcholine – neurotransmitter that regulates basic bodily processes such as movement  
Dopamine – a neurotransmitter involved in the control of bodily movements ( involved in Parkinson’s disease, and Alzheimer’s)  
Endorphins
– neurotransmitters that relieve pain and increase our sense of wellbeing 
Serotonin- mood control

Synapse- the junction point of two or more neurons; a connection is made by neurotransmitters.




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