Psychology: The Biology of Mind
September 23, 2013
Module 4: Neural and Hormonal Systems
• Biology, Behaviour and Mind
Every idea, mood, urge is a biological happening.
Plato correctly located the mind in the spherical head.
Aristotle, his student, believed the mind was in the heart.
In the early 1800s, German physician Franz Gall proposed that phrenology, which was studying
bumps on the skill to reveal a person's mental abilities and character traits.
Although it proved to be false, it focused attention to localization of function - the idea that
various brain regions have particular functions.
• Neural Communication
Neurons = nerve cells
Neurons differ, but have the same theme
Each neuron consists of a cell body and its branching fibers.
The bushy dendrite fibers receive information and conduct it toward the cell body.
From there the cell's lengthy axon fiber passes the message through its terminal branches to
other neurons or to muscles or glands.
Dendrites listen, Axons speak.
Some axons are encased in a myelin sheath, a layer of fatty tissues that insulates them and
speeds their impulses.
Neurons transmit messages when simulated by signals from our senses or when triggered by
chemical signals from neighbouring neurons. In response, a neuron fires an impulse, called the
action potential - a brief electrical charge that travels down its axon.
Depending on the fiber type, a neural impulse travels at speeds ranging from a sluggish 2 miles
per hour to a breakneck 180 miles per hour.
Neurons generate electricity from chemical events.
In the neurons chemistry-to-electricity process ions (electricity charged atoms) are exchanged.
How Neurons Communicate
Neurons interweave intricately
British physiologists Sir Charles Sherrington (1857-1952) noticed that neural impulses were
taking an unexpectedly long time to travel a neural pathway, inferring that there must be a brief
interruption in the transmission.
Sherrington called the meeting point between neurons a synapse.
The axon terminal of one neuron is in fact separated from the receiving neuron by a synaptic
When an action potential reaches the knob-like terminals at an axon's end, it triggers the release
of chemical messengers called neurotransmitters
Within 1/10,000 of a second, the neurotransmitter molecules cross the synaptic gap and bind to
receptor sites on the receiving neuron.
For an instant, the neurotransmitter unlocks tiny channels at the receiving site, and electrically
charged atoms flow in, exciting or inhibiting the receiving neuron's readiness to fire.
In the process called reuptake, the sending neuron reabsorbs the excess neurotransmitters.
How Neurotransmitters Influence Us
Aparticular brain pathway may use only one or two neurotransmitters, and a specific
neurotransmitter may affect specific behaviour and emotions.
Acetylcholine (ACh) plays a role in learning and memory, and it is the messenger at every
junction between motor neurons and skeletal muscles.
WhenACh transmission is blocked, the muscles cannot contract and we are paralyzed. Dopamine influences movement, learning, attention, and emotion. Oversupply is linked to
schizophrenia and undersupply is linked to tremors.
Serotonin affects mood, hunger, sleep and arousal. Undersupply can be linked to depression.
• The Nervous System
The nervous system is the body's speedy electrochemical communication network, consisting of
all the nerve cells of the peripheral and central nervous systems.
The brain and the spinal cord form the central nervous system (CNS) which is the body's
The Peripheral Nervous System (PNS) is responsible for gathering information and for
transmitting CNS decisions to other body parts.
Nerves, electrical cables formed of bundles of axons, link the CNS with the body's sensory
receptors, muscles and glands.
Sensory Neurons carry messages from the body's tissues and sensory receptors inward to the
brain and spinal cord for processing.
Motor Neurons carry instructions from the CNS out to the body's muscles.
Information is processed in the brain's internal communication system via its interneurons.
The Peripheral Nervous System
Two components - somatic and autonomic.
Somatic Nervous System enables voluntary control of our skeletal muscles.
The Autonomic Nervous System controls our glands and the muscles of our internal organs,
influencing glandular activity, heartbeat, and digestion.
The Sympathetic Nervous System arouses and expands energy - if something alarms or
challenges you, your sympathetic nervous system will accelerate your heartbeat, raise your blood
pressure, slow your digestion raise your blood sugar and cool you with perspiration to make you
alert and ready for action.
When the stress sub-sides, your Parasympathetic Nervous System will produce the opposite
effects, conserving energy as it calms you by decreasing your heartbeat, lowering your blood
sugar and so forth.
The Central Nervous System
The brains neur