Chapter 3: Biological Foundations of
Studies the connection between the brain, the mind, and behaviour
Only relatively recently the brain was considered important for thought, feeling, personality
CHAPTER 3: Learning Objectives – The Nervous System
Understanding of neural communication:
Structure of the neuron
Electrical transmission and the action potential
Chemical transmission and neurotransmitters
Differentiate different levels of the nervous system
Peripheral nervous system
o Somatic nervous system
o Autonomic nervous system
Sympathetic nervous system
Parasympathetic nervous system
Central nervous system
o Spinal cord
Neurons transmit information
Interneurons connect neurons together
Glial cells outnumber neurons 10:1, and support neurons by:
o Protecting brain from toxins
o Forming blood-brain barrier
o Getting rid of neuron waste
o Creating myelin
TYPES OF NEURONS
Afferent neurons (sensory)—relay information from the senses to the brain and spinal cord.
Efferent neurons (motor)—send information from the central nervous system to the glands and
muscles, enabling the body to move.
Interneurons—carry information between neurons in the Central Nervous System. PARTS OF A NEURON Axon transmits information to as many as 50,000 other neurons
Axon terminals are at the end of axons and form synapses with other neurons
Myelin sheath, made of fatty substance produced by glial cells, acts as insulator so impulses are
sent more efficiently.
o Not completely formed at birth.
o Filling in of myelin helps account for cognitive abilities, improved movement
o Multiple sclerosis is a disease where the immune system attacks and destroys the
myelin… results in uncoordinated movement, paralysis
Dendrites are branches that extend from the cell body and receive most of the information from
Neurons generate electricity and release chemicals. In the neuron’s resting state, the resting potential, we call the neuron polarized. Its resting
potential’s charge is 70 mv.
Graded potentials happen as a result of the negative charge of the neuron changing, but not
enough to set off an action potential.
An action potential is a neural impulse: the neuron becomes active, it fires.
o The threshold for a neuron firing at action potential is -55 mv.
Synapses are subject to the all-or-nothing law: the neuron either fires or it doesn’t; it cannot
HOW THE ACTION POTENTIAL OCCURS
The permeability of the cell membrane increases
This process allows IONS (electrically charged atoms or molecules) to easily move into
and out of the axon
Inside the axon, there are normally more negative than positive ions. When at rest (not
firing), a neuron carries a negative electrical potential (or charge) relative to the fluid
outside the cell. This slight negative charge is the neuron’s resting potential.
Depolarization: When a neuron is sufficiently stimulated by an incoming signal, ion
channels open in the cell membrane, allowing positive sodium ions to go INTO the axon.
o When polarized, the charge of the neuron is -70
o When depolarized, the charge of the neuron is +40 o This inflow of positive ions causes the membrane potential (charge) to change to
a positive value
This sudden and brief reversal is called the action potential
After the action potential, the potassium ions are pumped back out and sodium comes
back in. The neuron is ready again for action potential.
Absolute refractory period: recovery period when K+ flows out of the membrane. The
membrane is not excitable at this time.
If neurons fire in the same way, how do we discern between dim light and strong light?
What changes is the rate of firing (frequency) and the number of neurons firing.
SUMMARY OF ELECTRICAL TRANSMISSION
Neuron generates electrical impulse
Action potential caused by changes in concentration of negative and positive ions
Electrical impulse travels down myelin-covered axon until it reaches the axon terminals
Synapse: the junction where the axon of a sending neuron communicates with a receiving
neuron across the synaptic cleft
Presynaptic neurons send messages; postsynaptic receive them
Lock-and-key effect: Receptor sites have specialized spaces where only certain
EFFECTS OF NEUROTRANSMITTERS
Excitatory neurotransmitters increase likelihood of action potential
Inhibitory neurotransmitters decrease likelihood of action potential (make the neuron more
negative inside rather than depolarizing to positive)
Excitatory postsynaptic potential (EPSP) is a temporary depolarization of
postsynaptic membrane potential caused by the flow of positively charged ions into the
postsynaptic cell. Makes the neuron more likely to fire.
DEACTIVATION OF NEUROTRANSMITTERS
Breakdown: Chemical breakdown of neurotransmitters into chemical components
Reuptake: Neurotransmitters taken back into presynaptic neuron to be used after their
excitatory or inhibitory effect
TYPES OF NEUROTRANSMITTERS
Acetylcholine (ACh) Serotonin
Memory Mood disorders
Muscle activity Depression (low)
Low ACh related to Alzheimer’s
Parkinson’s disease (low) Painkiller
Schizophrenia (high) Natural “high”
Motor control DRUGS
Bind to receptors and imitate neurotransmitters
o Opium binds to endorphin receptors, you feel a high
o Antidepressants bind to serotonin receptors, imitate serotonin
“CUSTOM DESIGNED NEURONS”
Relevant to stem cell research
Stem cells are “starter cells” from fetuses; they can become anything
Stem cells can be put in the brain and they will become the cells around them
This can help treat Parkinson’s
o Stem cells become neurons that produce dopamine, which is needed with Parkinson’s
o Brains are very receptive to transplant, unlike heart/lung transplants
o Treatment takes many years to develop, take effect, gain approval
THE NERVOUS SYSTEM
PERIPHERAL NERVOUS SYSTEM
SOMATIC NERVOUS SYSTEM
Sensory neurons send messages from senses to brain
Motor neurons control our movement, voluntary actions
Consists of things of which we are constantly aware and over which we have control
AUTONOMIC NERVOUS SYSTEM
Involuntary functions – blood vessels, heart, things we’re not aware of
Sympathetic nervous system: Arouses or increases function (e.g: dilates pupil, accelerates
o Takes over during “fight or flight,” or under stress
Parasympathetic, contrastingly, slows things down to regain equilibrium
o Homeostasis: a state of balance
CENTRAL NERVOUS SYSTEM
Connects brain with the rest of the body
Neurons in spinal cord are protected by vertebrae
Interneurons connect sensory neurons to motor neurons
o Spinal reflex: behaviour that occurs with no input from the brain at all. (E.g: Touch a hot
stove, nerve impulses connect with interneurons and then motor neu