Basic units of the nerve system are called the neurons. These cells receive, integrate, and
transmit information in the nervous system. They form neural networks which are not
random or arbitrary. The entire nervous system is divided into two functional units:
1. The central nervous system (CNS) which consists of the brain and the spinal
cord which consist of nerve cells.
2. The peripheral nerve system (PNS) which consists of all other nerve cells in the
rest of the body.
These two units are anatomically separate but their functions are highly interdependent.
The PNS transmits signals to the CNS where the CNS organizes and evaluates the
information and then direct the PNS to perform specific behaviours and make movements.
Nerve cells are excitable (unlike other cells) and are specialized for communication.
They’re powered by electrical impulses and communicate with other nerve cells through
Reception phase: take up chemicals from other neighbouring cells
Integration phase: assess incoming signals
Transmission phase: pass their signals to another receiving neurons
Three basic types of neurons:
1. sensory neurons – detect information from neighbouring neurons and pass
information to the brain usually via the spinal cord (aka afferent neurons)
2. motor neurons – direct muscles to contract or relax thereby producing movement
(aka efferent neurons which means they transmit information from the brain to the
3. interneurons communicate within local or short-distance circuits. They integrate
neural activity within a single area rather than transmitting information or signal to
Together, sensory and motor neurons control movement.
Reflexes are automatic.
- dendrites: short, branchlike appendages that increase the neuron’s receptive field
and detect chemical signals from their neighbours
- cell body: also known as the soma, the information received from thousands of
other neurons is collected and integrated
- axon: where electrical impulses travel
- nerve: is a bundle of axons
- terminal buttons
- synapse: where chemical communication occurs between neurons
- synaptic cleft: tiny gap
- myelin sheath allows the electrical signals to travel quickly; it encases the neuron;
made up of glial cells or neuroglia
- Nodes of Ranvier: gaps of exposed neuron where there are ion channels
The resting membrane potential is negatively charged.
Action potentials cause neuronal communication. Two types of signals are: excitatory and inhibitory.
Excitatory signals depolarize cell membranes, increasing the likelihood that a neuron will
Inhibitory signals hyperpolarize cells, decreasing the likelihood that the neuron will fire.
When a neuron fires, the sodium channels open and depolarize the neuron. The influx of
sodium makes the neuron positively charged. After, potassium channels open to let the
potassium rush out. Through natural restoration, the membrane repolarizes itself.
Earliest symptoms of MS include blurry vision and numbness in limbs. This neurological
disorder is characterized by the myelin sheath deterioration, which in turn slows down
action potentials. Motor actions become jerky and people lose the ability to coordinate
motor movements. Over time, movement, sensation, and coordination are severely
Neuron either fires or it does not which implies the all or none principle. It is the sum of
inhibitory and excitatory signals received by the neuron which determines whether the
neuron fires or not.
Neurotransmitters bind to receptors across the synapse.
The three major events that terminate the neurotransmitter influence in the synaptic cleft
1. reuptake – neurotransmitter is taken back into the presynaptic terminal buttons
2. enzyme deactivation – occurs when an enzyme destroys the neurotransmitter in the
3. autoreception – monitor how much neurotransmitter has been released into the
synaptic cleft, when excess is detected, the autoreceptors signal the presynaptic
neuron to stop releasing neurotransmitter.
Drugs and toxins can alter a neurotransmitter’s action in 3 ways:
1. can alter how a neurotransmitter is synthesized
2. they can raise or lower the amount of neurotransmitter released from the terminal
3. by blocking reuptake, they can change the way a neurotransmitter is deactivated in
the synaptic cleft and therefore can affect the concentration of the neurotransmitter
Drugs that enhance the actions of neurotransmitters are called agonists. They essentially
increase how much neurotransmitter is made, so there is more inside each vesicle and
can block the reuptake of neurotransmitters.
Drugs that inhibit these actions are called antagonists. They decrease the amount of
neurotransmitters, so there are fewer in each vesicle and they also help destroy
neurotransmitters in the synapse.
Drugs and toxins can also mimic neurotransmitters and bind with their receptors. Heroin
and cocaine act similarly to the neurotransmitters.
Acetylcholine Motor control over muscles, learn