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The Biological Basis for
Behavior
The Human Brain
I. Neurons
• A. Three types of
Neurons
– 1. Sensory =
neurons that carry
incoming
information from
the sense receptors
to the CNS also
known as
AFFERENT
NEURONS.
Sensory Neuron
Sensory
Neuron
Brain
Spinal
Cord
Motor
Neuron
• 2. Motor = the neurons that
carry outgoing messages
from the CNS to the muscles
and glands. Also known as
EFFERENT NEURONS.
• 3. Interneurons = CNS
neurons that internally
communicate and intervene
between the sensory inputs
and motor outputs
• B. The structure of the Neuron
– 1. Dendrites = the bushy, branching extensions
of a neuron that receive messages and conduct
impulses forward toward the cell body.
– 2. Axon = the extension of a neuron, ending in
branching terminal fibers, through which
messages are sent to other neurons or to
muscles or glands
3. The Soma = the Cell body – its function is to
support the cell. At the center is the nucleus
4. The myelin sheath = a layer of fatty segmented
tissue that encases the fibers of many neurons
a. Enables vastly greater transmission speed of neural
impulses as
the impulse hops
from one node
to the next
a. The Nodes
of Ranvier =
the nodes along
the myelin sheath
Diagram of a Neuron
– 5. The Synapse = the junction between the axon tip of the sending
neuron and the dendrite or cell body of the receiving neuron – also
called the synaptic gap or cleft
– 6. Neurotransmitters = chemical messengers that transverse the
synaptic gaps between neurons. They create or inhibit the
receiving neuron form generating a neural impulse
The Synapse
https://www.youtube.com/wat
ch?v=m51VFW1m4BQ
II. The Nervous System
• A. The Central Nervous System
– 1. Also known as the CNS
– 2. It consist of the brain and the spinal cord
– 3. Cerebrospinal Fluid (CSF) is a liquid similar
to blood serum found in the ventricles of the
brain and in the central canal of the spinal cord
• B. The Peripheral Nervous System PNS
– 1. The sensory and motor neurons that connect
the CNS to the rest of the body
– 2. It sends sensory input to the brain and relays
commands from the brain to muscles
– 3. Nerves = neural cables containing many
axons which connect the CNS with muscles,
glands, and sense organs
– 4. The PNS consists of
• a. The Somatic System = the division of the
PNS that controls the body’s skeletal
muscles; AKA the skeletal nervous system
• b. Autonomic System = the part of the PNS
that controls the glands and the muscles of
the internal organs such as the heart.
– Parasympathetic
Nervous System =
the division of the
ANS that calms the
body, conserving
its energy
– Sympathetic
Nervous System =
the division of the
ANS that arouses
the body,
mobilizing its
energy in stressful
situations
The Nervous System
III. The Brain
• A. Tools of Discovery
– 1. Lesions and Accidents=
• a. Tissue destruction. A brain lesion is a naturally or
experimentally caused destruction of brain tissue
• b. Used to determine the impact on the brain functioning
• B. The Central Core
– 1. The brain stem
• a. the oldest part and central core of the brain
• b. Begins where the spinal cord swells as it enters the
skull
• c. The brainstem is responsible for automatic survival
functions
• d. The hindbrain is the most posterior part of the brain it
includes the medulla, Pons and cerebellum
– 2. Medulla oblongata
• a. Medulla = the base of the brainstem;
• b. Controls heartbeat and breathing
• c. It lies directly on top of the spinal cord
– 3. Pons
• lies directly above the Medulla
• acts as a bridge between the Medulla and the rest of
the brain, as well as between the cerebral cortex and
the cerebellum
– 4. . Reticular formation = a nerve network in
the brainstem that plays an important role in
controlling arousal
– 5. The Midbrain – located between the
hindbrain and forebrain, it controls and
coordinates some basic sensory and muscle
movements.
– 6. The Thalamus
• a. The thalamus = the brain’s sensory switchboard
• b. Located on top of the brainstem; located in both
hemispheres resembling twin avocados
• c. It directs messages to the sensory receiving areas
of the cortex and transmits replies to the cerebellum
and medulla
– 7. Cerebellum
• a. The “little brain” attached to the rear of the brain
stem, to the side of the pons and medulla
• b. It helps to coordinate voluntary movement and
balance
• D. The Limbic System
– 1. Sometimes referred to as
the forebrain
– 2. The limbic system =
• a. a doughnut shaped system
of neural structures at the
border of the brainstem and
the cerebra hemispheres
• b. Associated with emotions
such as fear and aggression
and drives such as those for
food and sex
• c. Includes the hippocampus,
the amygdala, and the
hypothalamus
– 2. The amygdale = Two almond shaped neural
clusters that are components of the limbic
system and are linked to emotion
– 3. The Hippocampus =
• a. From the Latin word meaning seahorse
• b. Lies between the thalamus and the cerebral
cortex
• .c Is linked with forming new memories
– 4. The Hypothalamus
• a. A neural structure lying below (hypo) the
thalamus.
• b. It directs several maintenance activities (eating,
drinking and body temp), it helps govern to the
endocrine system via the pituitary gland and it is
linked to emotion
https://www.youtube.com/watch?v=6eD6zKpPwVM
IV. The Cerebral Cortex
• A. General Description
– 1. The convoluted portion of our brain where
thinking, memories and our personality are
located.
– 2. Physical description
• a. Convolutions increase the surface area of the
brain
• b. Gyri = rolls that form the folding out portion of
the cerebral cortex
VII. The Cerebral Cortex
• c. Sulci = valleys that form from the folding in
portions of the cerebral cortex.
• d. Seperated by fissures are deeper than valleys
• B. The four lobes
– 1. Frontal lobes
• a. The portion of the cerebral cortex lying just
behind the forehead;
• b. Involved in speaking and muscle movements and
in making plans and judgments, thinking and
creativity
• c. prefrontal cortex receives sensory information
from all senses
– 2. Occipital lobes
– The portion of the cerebral cortex lying at the back of the
head;
– Includes the visual areas, (V1 & V2) which receive visual
information from the opposite visual field and turn it into a
picture
– cortical blindness is a specific type of blindness due to
brain damage
– 3. Parietal lobes
• a. The portion of the cerebral cortex lying at the top
of the head and toward the rear;
• b. Includes the sensory cortex: touch, pain,
temperature
• c. specializes in processing body information such
as touch and body location (memory and location)
– 4. Temporal lobes
• a. The portion of the cerebral cortex lying roughly
above the ears;
• b. Includes the auditory areas, each of which
receives auditory information primarily from the
opposite ear. (hearing and memory)
• c. One of the key areas of speech known as
Wernicke’s Area is located in this lobe (written and
spoken language)
• C. The motor cortex = an area at the rear
of the frontal lobes that controls voluntary
movement
• D. The sensory cortex = the area at the
front of the parietal lobes that registers and
processes body sensations
Motor and Sensory Areas
• E. Association areas = areas of the cerebral
cortex that are not involved in primary motor
or sensory functions. They are involved in
higher mental functions such as learning
remembering, thinking and speaking.
V. Sleep and Dreams
• A. Biological Rhythms
– 1. Biological Rhythms = patterns associated with our
biological clock. These patterns can span days, hours
or even minutes.
– 2. Circadian Rhythms = Biological cycles that occur
about every 24 hours. For example or sleep, blood
pressure, body temperature and urine production
• B. How is our sleep cycle controlled
– 1. The suprachiasmatic nucleus (SCN)lies in
the hypothalamus and is the body’s main
biological clock.
– 2. When light hits the retina it sends a signal to
the SCN which then relays a message to the
pineal glands which in turn secrete melatonin
which is a hormone that plays a key role in
regulating sleep