The genetic message is contained in chromosomes (which are threadlike structures found in the nucleus of every cell). Each chromosome carries many genes. Chromosomes are made of DNA (which contains the genetic blueprint for each individual). A gene is a section of a DNA.

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Module 2a- Biological & Developmental Bases of Behaviour
Genetic Principles
1. The genetic message is contained in chromosomes (which are threadlike structures found in
the nucleus of every cell). Each chromosome carries many genes. Chromosomes are made
of DNA (which contains the genetic blueprint for each individual). A gene is a section of a
DNA.
2. Genes control the characteristics of the body, e.g. eye colour & height etc.,
3. Human cells (except for sex cells (sperm and egg) consist of 23 pairs of chromosomes, half
contributed by the mother's egg, half by the father's sperm
4. The 23rd pair of chromosomes which determine a person’s sex, male or female. X female; Y
male is determined by the father.
I. THE NERVOUS SYSTEM
Have two main branches, the Central Nervous system and the Peripheral Nervous system.

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A. The Central Nervous System
a. Its Function :--receives, processes, interprets, and stores incoming information; sends out
messages to muscles, glands, internal organs
b. Consist of :--brain and spinal cord
– The central nervous system acts as the central executive of the body; decisions are made
here, and messages are communicated to the rest of the body via nerves (bundles of
axons); the nerves outside the brain and spinal cord form the peripheral nervous system
B. The Peripheral Nervous System--nervous system outside brain and spinal cord
a. Its Functions
i. Sensory nerves (afferent neurons)--bring input from skin, muscles, and organs
ii. Motor nerves—(efferent neurons)--carry output to muscles, glands, and organs
– Afferent nerve pathways move information toward the brain and spinal cord; efferent
pathways carry central nervous system messages to muscles and glands.
b. Divisions of the Peripheral Nervous System
1. Somatic nervous system
a) Nerves connected to sensory receptors
b) Nerves connected to skeletal muscles--voluntary action
– The somatic system consists of nerves that bring sensory information to the brain and
nerves that connect to muscles needed to initiate movement
2. Autonomic nervous system--works automatically- involuntary action e.g. breathing &
digestion.
Functions--regulates blood vessels, glands, organs (heart, stomach, bladder & lungs)
I. Divisions of the Autonomic Nervous system
(a) Sympathetic--mobilizes the bodily resources and increases the output of energy during
emotion, stress and emergencies. (Increases the heart rate)
(b) Parasympathetic—conserves the body’s resources and allows the body to relax and store
energy (decreases the heart rate)
II. COMMUNICATION IN THE NERVOUS SYSTEM
A. Components of the nervous system
– Glial cells—cells that hold neurons in place; they also nourish and insulate neurons
(create the myelin sheath for the neurons)
– Neurons--cells that communicate to, from, or within the CNS. They are the basic units of
the nervous system.
The structure of the neuron
a) Dendrites--receive messages from other neurons, transmit to cell body
b) Cell body--keeps the neuron alive, determines whether to fire

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c) Axon--transmits messages away from cell body to other neurons:
 Ends in branches or axon terminals
 Many axons are insulated by a fatty material (myelin sheath)
 Bundles of axons in the peripheral nervous system form nerves
The basic building blocks of the nervous system are neurons. There are three main types
i. Sensory neurons make the initial contact with the environment, carrying signals to the
brain
ii. Interneurons, the most plentiful type, convey information from one internal processing
site to another
iii. Motor neurons carry messages and commands away from the central nervous system to
the muscles and glands
B. How neurons communicate
Neurons communicate across Synapse = axon terminal + synaptic cleft (small space
between one axon and next dendrite) + covering membrane of receiving dendrite or cell
body
– Many thousands of neurons may communicate at a synapse
– Wave of electric voltage, called action potential, moves down axon to end of axon
terminal, called synaptic end bulb
– Action potentials travel more rapidly in myelinated axons than in unmyelinated axons
– Synaptic end bulb releases chemical neurotransmitters (transmitters) which have been
stored in synaptic vesicles (sacs in the end bulb)
– Transmitters cross the synaptic cleft and briefly lock onto receptor sites on the receiving
dendrites
– They can increase or decrease the likelihood that the receiving neuron will generate an
action potential
– Receiving neuron averages the excitatory and inhibitory incoming messages to
determine if it reaches firing threshold
– Neurons either fire or do not fire (all or none); the strength of firing does not vary
C. Chemical messengers in the nervous system (Neurotransmitters)
Neurotransmitters exist throughout the body
Cell
body

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Some better understood neurotransmitters and some of their effects
(1) Serotonin--sleep, mood, eating
(2) Dopamine--movement, learning, memory, emotion [pleasure]
(3) Acetylcholine--muscle action, memory, emotion
(4) Norepinephrine--heart rate, learning, memory
III. A TOUR THROUGH THE BRAIN
Forebrain
 forward most part of the brain containing thalamus, hypothalamus, limbic system and the
cerebrum.
 Thalamus: relay station for sensory stimulation.
 Hypothalamus: vital for body temperature regulation, concentration of fluids, storage of
nutrients, aspects of motivation and emotion.
 Limbic System: Includes the amygdala, hippocampus, and parts of the hypothalamus.
Involved in memory, emotion and in the drives of hunger, sex and aggression.
 Amygdala: connected with aggression, fear response, and vigilance.
 Cerebrum: responsible for thinking and language.
I. Cerebrum--responsible for higher forms of thinking--divided into two halves or cerebral
hemispheres and connected by band of fibers called corpus callosum
II. Right hemisphere in charge of left side of the body
III. Left hemisphere in charge of right side of the body
IV. Lateralization --each hemisphere has somewhat different tasks and talents
• Outer layer of the Cerebrum about 1/8 of an inch thick.
Involved in most bodily activities, sensations, and responses. It is divided into four regions

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(1) Occipital lobes--contain the visual cortex (vision)
(2) Parietal lobes--contain somatosensory cortex, that receives information about pressure,
pain, touch, and temperature from all over the body
(3) Temporal lobes--contain auditory cortex (hearing)
(4) Frontal lobes--contain the motor cortex (movement); responsible for making plans, taking
initiative, and thinking creatively
VI. THE TWO HEMISPHERES OF THE BRAIN
A. Corpus callosum, connects the cerebral hemispheres (the two halves of the brain)
1. Left hemisphere handles:
– language for nearly all right-handed people and a majority of
– more active than right side during some logical, symbolic, and sequential tasks, such as
math
– the left side is dominant because cognitive skills, including rational and analytic abilities,
originate here.
2. Right hemisphere handles:
– visual and spatial abilities,
– ability to recognize faces,
– appreciation of art and music;
– some researchers claim it is intuitive
In real life, the two hemispheres cooperate automatically in most activities.
V. THE ENDOCRINE SYSTEM
– The endocrine system is an integrated system of small organs that involve the release of
extracellular signaling molecules known as hormones.
– The endocrine system consists of a set of glands, such as the thyroid, gonads, adrenal
and pituitary glands, and the hormones they produce,
– The pituitary gland is called the “master gland” but it is under the control of another
gland called the hypothalamus, it controls growth.
– A gland is cell or group of cells that produce and release substances used nearby or in
another part of the body.
– The endocrine system is instrumental in regulating metabolism, growth, pregnancy,
development and puberty, tissue function, and also plays a part in determining mood.
– Hormones: Long-distance messengers (part of the Endocrine System)
– The Substances produced in one part of the body but affect another
– Originate primarily in endocrine glands that release hormones into the bloodstream,
which carries them to other organs and cells
– Examples of hormones
– Androgens (e.g., testosterone)--masculinizing, influence sexual arousal in both sexes

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– Estrogen--feminizing, influence menstrual cycle, may contribute to improved learning and
memory

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– Estrogen--feminizing, influence menstrual cycle, may contribute to improved learning and
memory