Chapter 4: The brain and Behaviour
building blocks of the nervous system
estimated 100 billion nerve cells in the brain and spinal cord
Structure of a Neuron: Each has three main parts: a cell body, dendrites and an axon. (P.93)
Soma (cell body): contains biochemical structures needed to keep the neuron alive and its nucleus carries
the genetic information that determines how the cell develops and functions.
Dendrites: receive and collect messages from neighboring neurons and send them to cell body
Axon: conducts electrical impulses away from the cell body to other neurons, muscles or glands
Axon branches out at its end to form axon terminals, as many as several hundred in some cases. Each AT may
connect with dendrites from numerous neurons, making it possible for a single neuron to pass messages to as
many as 50,000 other neurons.
Myelin Sheath: Fatty insulation layer derived from glial cells.
Interrupted by nodes of Ranvier, where myelin is extremely thin.
If damaged, it will interrupt the timing for action potential.
Glial Cells: support Neurons. They do not send or receive
nerve impulses, but surround neurons and hold them in place.
Also manufacture nutrient chemicals that neurons need and
absorb toxins and wastes.
Two Types: ○ Astrocyte ○ Oligadendrocyte
Neuron Function #1: Electrical Impulses (p.94)
Outside: Na (Sodium) and Cl (Chloride)
Inside: K+ (potassium) and A- (or anions, protein molecules)
Cell membrance have ion channels (potassium and sodium)
Membrane potential – difference in charge between inside and
outside of a cell
1. Resting potential:
10:1 concentration of sodium (Na+) ions outside the neuron and
the negative protein (A-) inside contribute to a resting potential
Inside of cell is more negative
neuron is in a state of polarization
2. Action potential (Nerve Impulse)
if stimulated = shift in electrical charge from -70mV to +40mV
Lasts approximately 1 millisecond
Na+ channels open, and Na+ flood into axon (Inside is more positive, cell is depolarized)
To restore resting potential, the cell closes its Na+ and K+ channels on membrane open, K+ flows out of cell
(Inside of cell restores negative state, cell is repolarized)
After impulse passes a point along the axon, there is an Absolute refractory period: while the cell is
restoring negative state, the membrance is not excitable and cannot discharge another impulse.
Impulse (Na+) flows down axon to axon terminals and escaped K+ ions are recovered.
All or Nothing : action potentials occur at maximum intensity, or they do not occur at all. Only occurs if neuron is
sufficiently stimulated. Neuron Function #2: Synaptic Transmission (p.96)
Neurons do not actually touch each other.
Synaptic space: a tiny gap between the axon terminal and the next neuron.
They communicate via neurotransmitters: chemical substances that carry messages cross the
synaptic space to other neurons
FIVE STEPS: Synthesis → Storage → Release → Binding → Deactivation or Reuptake
1. In the synthesis stage, the transmitter molecules are formed inside neuron.
2. The neurons are stored in synaptic vesicles: chambers within the axon terminals.
3. When action potential comes down the axon, these vesicles move to surface of the axon terminal and the
molecules are released into the fluid-filled space between the axon of the presynaptic (sending) neuron and the
membrane of the postsynaptic (receiving) neuron.
4. The molecules cross the synaptic space and bind themselves to receptor sites: large protein molecules
embedded in the receiving neron’s cell membrane. Each receptor site has a specifically shaped surface
that fits a specific transmitter molecule, like a lock and key.
When transmitter molecule binds to a receptor site, a chemical reaction occurs. This reaction can have two
different effects on the receiving neuron.
When an excitatory transmitter is at work, the chemical reaction causes the receiving neuron’s sodium
channels to open, ions flow through and depolarize, creating action potential
An inhibitory neurotransmitter will do opposite. Cause positive K+ to flow out of neuron, increasing
negative potential and making it harder to fire the neuron.
5. Once binded to receptor, it continues to excite/inhibit the neuron until it is shut off. Can happen in two ways:
Some transmitter molecules are deactivated by other chemicals located in the synaptic space that
breaks them down into their chemical components.
the deactivation mechanism is reuptake in which the transmitter molecules are taken back into the
presynaptic axon terminals. Specialized Neurotransmitter Systems (p.97)
Excite postsynaptic neuron - Depolarization Inhibits postsynaptic neuron - Increases negative membrane
Serotonin Endorphin (neuromodulator)
Acethcholine (ACh): a neurotransmitter involved in muscle activity and memory.
Alzheimer’s disease (undersupply), paralysis (absence), violent muscle contrations (oversupply)
Dopamine: E: involved in voluntary movement, emotional arousal, learning, memory and experiencing pleasure/pain
Parkinson’s disease and depression (undersupply), schizophrenia (overactivity)
Serotonin: E/I in mood, sleep, eating and arousal, and may be an important transmitter underlying pleasure and pain.
Depression, sleeping/eating disorder (undersupply), OCD (overactibity)
Norepinephrine: E/I functions are various sites; controlling learning, memory, wakefulness and eating
Depression (undersupply), stress/panic (overactivity)
GABA: inhibitory transmitter in motor system
Destruction of GABA-producing neurons in Huntington’s disease produces tremors and loss of motor control, as well as
Endorphin: inhibits transmission of pain impulses
Insentivity to pain (oversupply), pain hypersensitivity (undersupply)
Most neurotransmitter have their effects only on specific neurons that have receptors for them. Others are called
neuromodulators: have a more widespread and generalized influence on synaptic transmission. Eg endorphin
Psychoactive Drugs (p.99)
chemicals that produce alternations in consciousness, emotion, and behavior.
Alter the synthesis, storage, release, binding, or deactivation of neurotransmitters.
Agonist: a drug that increase activity of neurotransmitters Antagonist: a drug that inhibits or decreases the action of
Enhances synthesis, storage, release a neurotransmitter
Mimic a neurotransmitter by binding with and Reduces synthesis, storage, release, or binding
stimulating postsynaptic receptor sites Prevents binding by blocking receptor sites on
Bind to/stimulate postsynaptic sites postsynaptic neuron
make it more difficult for neurotransmitters to be
deactivated, eg inhibiting reuptake
Depressant Caffeine an agonist for Acetylcholine.
GABA agonist an Adenosine anatognist (excites neurons)
Glutamate antagonist Adenosine inhibits stimulates Dopamine
overall neural slow-down excitatory transmission (increase energy and
and By reducing adenosine, pleasure), which explains
Inhibits: Rational thinking, excitation is increased, more addiction
Emotional control, Motor energy is available.
increase Dopamine and Norepinephrine activity by:
o cause presynaptic neurons to release more also increases Dopamine and Norepinephrine activity
o Inhibit reuptake, allowing excitatory o Inhibit reuptake of neurotransmitter
neurotransmitters to keep stimulating Causes feelings of excitation, increased muscular
postsynaptic neurons strength, and euphoria
Boost arousal and mood
Date Rape Drugs (Rohypnol, GHB)
Enhance the activity of GABA
Causes: Respiratory slowing, Loss of consciousness, Coma, Death, Loss of memory Psychology 100
Chapter 4: The brain and Behaviour
N ERVOUS S YSTEM
Sensory neurons: carry input message from the sense organs to the spinal cord and brain
Motor neurons: transmit output impulses from the brain and spinal cord to the body’s muscles and organs
Interneurons: perform connective or associative function within the nervous system
Summary: The major divisions are the CNS and PNS. The peripheral system is divided into the somatic system
(responsible for sensory and motor functions) and the autonomic nervous system (which directs the activity of
the body’s internal organs and glands).
PERIPHERAL NERVOUS SYSTEM (p101)
Contains all the neural structures that lie outside of the brain and spinal cord.
1. Enables us to sense events in and out of the body (input functions) eg hunger
2. Enables us to responds to events with muscles and glands (output functions)
1. Somatic Nervous System (sense and respond to environment)
transmit messages from sensory organs to brain (Sensory nerves)
send messages from the CNS to the muscles that control voluntary movements (Motor nerves)
2. Autonomic Nervous System
Regulate body’s internal environment
Controls involuntary functions eg respiration, circulation and digestion, stress responses
a) Sympathetic nervous system: activation or arousal function, mobilizes body, and tends to act as total unit
b) Parasympathetic nervous system: slows down bodily processes, reduce arousal, more specific in its action
o Together they maintain equilibrium or homeostasis: a delicately balanced or constant internal state
E.g. Fight-or-flight response (p102 chart)
Under stress, system will: Speed up heart rate (more blood to muscles, increase oxygen); Dilates
pupils (enhanced vision); Slows down digestive system (more blood to muscles); Increase respiration
rate (more oxygen); Contract vessels (increased blood pressure)
After stress, system will: Contract pupils, constricts bronchi (lungs), slows heartbeat, stimulates
activity in stomach, dilates vessels
CENTRAL NERVOUS SYSTEM (p102)
Contains the brain and spinal cord, which connects most of the PNS with the brain
1. Spinal Cord
Conducts spinal reflexes (do not require brain)