Chapter 3 - Biology and Behaviour
Q: How Does the Nervous System Operate?
3.1 Neurons Are the Basic Units of the Nervous System
Neurons receive, integrate and transmit information, and communicate through neural
networks. These networks develop through genetic influence, mutation and experience, and
repeated firing.
Nerve cells are excitable: they are powered by electrical; impulses and communicate
with other nerve cells through chemical signals. This happens in three phases: reception,
integration, and transmission.
Sensory neurons detect information from the physical world and pass that
information along the brain. Somatosensory neurons provide information from the skin and
muscles. Motor neurons direct muscles to contract or relax, thereby producing movement.
Interneurons act as relay stations facilitating communication between sensory and motor
neurons.
Messages are received by dendrites, processed in the cell body, transmitted along
the axon, and sent to other neurons via chemical substances released from the terminal
buttons across the synapse.
3.2 Action Potentials Produce Neural Communication
An action potential, also called neural firing, is the electrical signal that passes along the
axon. This signal causes the terminal buttons to release chemicals that transmit signals to
other neurons.
When a neuron is resting, the electrical charge inside the neuron is slightly more
negative than the electrical charge outside. This difference is the resting membrane potential
and occurs because the ratio of negative to positive ions is greater inside the neuron than
outside it. The neuron is described as being polarised when it has more negative ions inside
than outside. Sodium and potassium ions contribute to the resting membrane potential. The
flow of ions through each channel is controlled by a gating mechanism, and the
sodium-potassium pump.
A neuron receives chemical signals from a nearby neuron through its dendrites.
These chemical signals impact local ion channels, thus influencing the polarisation of the
neuron. By affecting polarisation, the chemical signals tell a neuron whether to fire. There
are two types of signals: excitatory (depolarising the cell, increasing the likelihood a
neuron will fire) and inhibitory (hyperpolarising the cell, decreasing the likelihood a neuron
will fire). A neuron is barraged by thousands of excitatory and inhibitory signals, and its firing
is determined by the number and frequency of those signals. If the sum of excitatory and
inhibitory signals leads to a positive change in voltage that surpasses the neuron’s firing
threshold, an action potential (the change from a negative charge to a positive one) is
generated.
After an action potential is generated (i.e., when a neuron is depolarised past its firing
threshold), the membrane potential is slightly more negative than the resting potential, and it
would require an even more excitatory input to trigger another action potential (relative
,refractory period). The all-or-none principle dictates that a neuron fires with the same
potency each time.
When a neuron fires, the cell membrane’s depolarisation moves along the axon like a
wave. A myelin sheath insulates the axons and is made up of glial cells. Between the
segments are small gaps of exposed axons called the nodes of Ranvier.
3.3 Neurotransmitters Influence Mental Activity and Behaviour
The neuron that sends the signals is called the presynaptic neuron, and the one that
receives the signals is called the postsynaptic neuron. Inside each terminal button of the
presynaptic neuron are neurotransmitters, chemicals that are made in the axon or cell
body and stored in vesicles, and that bind with specific receptors. After an action potential
travels to the terminal button, it causes the vesicles to attach to the presynaptic membrane
and release their neurotransmitters into the synapse. Receptors are specialised protein
molecules located on the postsynaptic membrane that specifically respond to the chemical
structure of the neurotransmitter available in the synapse. The binding can cause ion
channels to open or to close more tightly, producing an excitatory or inhibitory signal in the
postsynaptic neuron.
The three major events that terminate the neurotransmitter’s influence in the synapse
are reuptake (the neurotransmitter is taken back into the presynaptic terminal buttons for
recycling), enzyme deactivation (an enzyme breaks down the neurotransmitter), and
autoreception (monitoring how much neurotransmitter has been released in the synapse
and signaling to stop releasing the neurotransmitter).
Drugs that enhance the actions of neurotransmitters are known as agonists, while
those that inhibit these actions are known as antagonists.
Q: What are the Basic Brain Structures and Their Functions?
3.5 The Cerebral Cortex Underlies Complex Mental Activity
The largest part of the human brain is the forebrain, made up of the cerebral cortex and
the underlying subcortical areas, and consists of two hemispheres. Each cerebral
hemisphere has four lobes: the occipital (vision), parietal (touch, spatial relations),
temporal (hearing, memory), and the frontal lobes (thought, planning, movement).
The outer layer of the cerebral cortex exists of gray matter (neurons’ cell bodies,
dendrites, and nonmyelinated axons that communicate only with nearby neurons), and
underneath white matter (myelinated axons that travel between brain regions). The corpus
callosum exists of white matter and allows information to flow between the hemispheres. The
right hemisphere is better with spatial relationships, while the left hemisphere is better with
language. Split brain is a condition that occurs when the corpus callosum is surgically cut
and the two hemispheres of the brain do not receive information directly from each other.
3.8 The Insula and Subcortical Structures Contribute to Taste, Emotions, Memory, and
Reward
Below the outside surface of the cerebral cortex lie the insula and subcortical regions. The
insula is part of the cerebral cortex that lies deep within folds of the lateral fissure.
, Subcortical structures include the thalamus, hypothalamus, hippocampus, amygdala,
and the basal ganglia.
The insula houses the primary gustatory cortex, which is necessary for the sense of
taste. Other parts of the insula play a role in the ability to be aware of bodily states related to
emotion.
The thalamus receives almost all incoming sensory information, organises it, and
relays it to the cortex (except for smell).
The hypothalamus is the brain’s main regulatory structure and receives input from
and projects its influence to almost everywhere in the body and brain. It affects the functions
of many internal organs, regulating body temperature, rhythms, blood pressure, and blood
glucose levels. It is also involved in many motivated behaviours.
The hippocampus plays an important role in the formation of new memories
(seeming to do so by creating new interconnections within the cerebral cortex with each new
experience).
The amygdala is involved in learning about biologically relevant stimuli, such as
those important for survival.
The basal ganglia are a system of subcortical structures crucial for planning and
producing movement. They receive input from the entire cerebral cortex, and send that input
back to the motor planning area of the cerebral cortex.
3.9 The Brain Stem and Cerebellum House Basic Programs for Survival and
Movement
Below the cerebral cortex and subcortical structures lie the spinal cord and brain stem. The
spinal cord is a rope of neural tissue and one of its functions is the coordination of reflexes.
Its most important function is to carry sensory information up to the brain and carry motor
signals from the brain to the body parts below to initiate action.
The brain stem consists of the medulla oblongata, the pons, and the midbrain. It also
contains a network of neurons known collectively as the reticular formation. This network
projects up into the cerebral cortex and affects general alertness. It is also involved in
inducing and terminating different stages of sleep. The cerebellum is important for motor
function.
Q: How Does the Brain Communicate With the Body?
3.11 The Peripheral Nervous System Includes the Somatic and Autonomic Systems
The peripheral nervous system (PNS) transmits a variety of information to the central
nervous system (CNS). It also responds to messages from the CNS to perform specific
behaviours or make bodily adjustments. In the production of psychological activity, both of
these systems interact with a different mode of communication within the body: the
endocrine system.
The PNS has two primary components: the somatic nervous system (SNS) and the
autonomic nervous system (ANS). The SNS transmits sensory signals to the CNS via
nerves. Specialised receptors in the skin, muscles, and joints send sensory information to
the spinal cord, which relays it to the brain. The CNS sends signals through the SNS to
muscles, joints, and skin to initiate, modulate, or inhibit movement. The ANS regulates the
body’s internal environment by stimulating glands and maintaining internal organs.
Q: How Does the Nervous System Operate?
3.1 Neurons Are the Basic Units of the Nervous System
Neurons receive, integrate and transmit information, and communicate through neural
networks. These networks develop through genetic influence, mutation and experience, and
repeated firing.
Nerve cells are excitable: they are powered by electrical; impulses and communicate
with other nerve cells through chemical signals. This happens in three phases: reception,
integration, and transmission.
Sensory neurons detect information from the physical world and pass that
information along the brain. Somatosensory neurons provide information from the skin and
muscles. Motor neurons direct muscles to contract or relax, thereby producing movement.
Interneurons act as relay stations facilitating communication between sensory and motor
neurons.
Messages are received by dendrites, processed in the cell body, transmitted along
the axon, and sent to other neurons via chemical substances released from the terminal
buttons across the synapse.
3.2 Action Potentials Produce Neural Communication
An action potential, also called neural firing, is the electrical signal that passes along the
axon. This signal causes the terminal buttons to release chemicals that transmit signals to
other neurons.
When a neuron is resting, the electrical charge inside the neuron is slightly more
negative than the electrical charge outside. This difference is the resting membrane potential
and occurs because the ratio of negative to positive ions is greater inside the neuron than
outside it. The neuron is described as being polarised when it has more negative ions inside
than outside. Sodium and potassium ions contribute to the resting membrane potential. The
flow of ions through each channel is controlled by a gating mechanism, and the
sodium-potassium pump.
A neuron receives chemical signals from a nearby neuron through its dendrites.
These chemical signals impact local ion channels, thus influencing the polarisation of the
neuron. By affecting polarisation, the chemical signals tell a neuron whether to fire. There
are two types of signals: excitatory (depolarising the cell, increasing the likelihood a
neuron will fire) and inhibitory (hyperpolarising the cell, decreasing the likelihood a neuron
will fire). A neuron is barraged by thousands of excitatory and inhibitory signals, and its firing
is determined by the number and frequency of those signals. If the sum of excitatory and
inhibitory signals leads to a positive change in voltage that surpasses the neuron’s firing
threshold, an action potential (the change from a negative charge to a positive one) is
generated.
After an action potential is generated (i.e., when a neuron is depolarised past its firing
threshold), the membrane potential is slightly more negative than the resting potential, and it
would require an even more excitatory input to trigger another action potential (relative
,refractory period). The all-or-none principle dictates that a neuron fires with the same
potency each time.
When a neuron fires, the cell membrane’s depolarisation moves along the axon like a
wave. A myelin sheath insulates the axons and is made up of glial cells. Between the
segments are small gaps of exposed axons called the nodes of Ranvier.
3.3 Neurotransmitters Influence Mental Activity and Behaviour
The neuron that sends the signals is called the presynaptic neuron, and the one that
receives the signals is called the postsynaptic neuron. Inside each terminal button of the
presynaptic neuron are neurotransmitters, chemicals that are made in the axon or cell
body and stored in vesicles, and that bind with specific receptors. After an action potential
travels to the terminal button, it causes the vesicles to attach to the presynaptic membrane
and release their neurotransmitters into the synapse. Receptors are specialised protein
molecules located on the postsynaptic membrane that specifically respond to the chemical
structure of the neurotransmitter available in the synapse. The binding can cause ion
channels to open or to close more tightly, producing an excitatory or inhibitory signal in the
postsynaptic neuron.
The three major events that terminate the neurotransmitter’s influence in the synapse
are reuptake (the neurotransmitter is taken back into the presynaptic terminal buttons for
recycling), enzyme deactivation (an enzyme breaks down the neurotransmitter), and
autoreception (monitoring how much neurotransmitter has been released in the synapse
and signaling to stop releasing the neurotransmitter).
Drugs that enhance the actions of neurotransmitters are known as agonists, while
those that inhibit these actions are known as antagonists.
Q: What are the Basic Brain Structures and Their Functions?
3.5 The Cerebral Cortex Underlies Complex Mental Activity
The largest part of the human brain is the forebrain, made up of the cerebral cortex and
the underlying subcortical areas, and consists of two hemispheres. Each cerebral
hemisphere has four lobes: the occipital (vision), parietal (touch, spatial relations),
temporal (hearing, memory), and the frontal lobes (thought, planning, movement).
The outer layer of the cerebral cortex exists of gray matter (neurons’ cell bodies,
dendrites, and nonmyelinated axons that communicate only with nearby neurons), and
underneath white matter (myelinated axons that travel between brain regions). The corpus
callosum exists of white matter and allows information to flow between the hemispheres. The
right hemisphere is better with spatial relationships, while the left hemisphere is better with
language. Split brain is a condition that occurs when the corpus callosum is surgically cut
and the two hemispheres of the brain do not receive information directly from each other.
3.8 The Insula and Subcortical Structures Contribute to Taste, Emotions, Memory, and
Reward
Below the outside surface of the cerebral cortex lie the insula and subcortical regions. The
insula is part of the cerebral cortex that lies deep within folds of the lateral fissure.
, Subcortical structures include the thalamus, hypothalamus, hippocampus, amygdala,
and the basal ganglia.
The insula houses the primary gustatory cortex, which is necessary for the sense of
taste. Other parts of the insula play a role in the ability to be aware of bodily states related to
emotion.
The thalamus receives almost all incoming sensory information, organises it, and
relays it to the cortex (except for smell).
The hypothalamus is the brain’s main regulatory structure and receives input from
and projects its influence to almost everywhere in the body and brain. It affects the functions
of many internal organs, regulating body temperature, rhythms, blood pressure, and blood
glucose levels. It is also involved in many motivated behaviours.
The hippocampus plays an important role in the formation of new memories
(seeming to do so by creating new interconnections within the cerebral cortex with each new
experience).
The amygdala is involved in learning about biologically relevant stimuli, such as
those important for survival.
The basal ganglia are a system of subcortical structures crucial for planning and
producing movement. They receive input from the entire cerebral cortex, and send that input
back to the motor planning area of the cerebral cortex.
3.9 The Brain Stem and Cerebellum House Basic Programs for Survival and
Movement
Below the cerebral cortex and subcortical structures lie the spinal cord and brain stem. The
spinal cord is a rope of neural tissue and one of its functions is the coordination of reflexes.
Its most important function is to carry sensory information up to the brain and carry motor
signals from the brain to the body parts below to initiate action.
The brain stem consists of the medulla oblongata, the pons, and the midbrain. It also
contains a network of neurons known collectively as the reticular formation. This network
projects up into the cerebral cortex and affects general alertness. It is also involved in
inducing and terminating different stages of sleep. The cerebellum is important for motor
function.
Q: How Does the Brain Communicate With the Body?
3.11 The Peripheral Nervous System Includes the Somatic and Autonomic Systems
The peripheral nervous system (PNS) transmits a variety of information to the central
nervous system (CNS). It also responds to messages from the CNS to perform specific
behaviours or make bodily adjustments. In the production of psychological activity, both of
these systems interact with a different mode of communication within the body: the
endocrine system.
The PNS has two primary components: the somatic nervous system (SNS) and the
autonomic nervous system (ANS). The SNS transmits sensory signals to the CNS via
nerves. Specialised receptors in the skin, muscles, and joints send sensory information to
the spinal cord, which relays it to the brain. The CNS sends signals through the SNS to
muscles, joints, and skin to initiate, modulate, or inhibit movement. The ANS regulates the
body’s internal environment by stimulating glands and maintaining internal organs.
