Chapter 2c Flashcards
Neural synapse
the region that includes the axon terminals of the presynaptic neuron, the synaptic gap, and the dendrites of the postsynaptic neuron
Presynaptic neuron
the neuron that releases neurochemicals into the neural synapse
Axon terminal or terminal buttons
the end of a neuron that releases neurochemicals into the neural synapse
Synaptic gap
the space between the presynaptic neuron and the postsynaptic neuron
Postsynaptic neuron
the neuron that receives neurochemicals from the neural synapse
Dendrites
a branched extension of a neuron on which receptor sites are located
Receptor sites
a protein molecule on the dendrites of a neuron that receives neurochemicals
Neural chemical
a chemical substance that transmits neural information within the nervous system
Synaptic transmission
the chemical conveyance of neural information between two neurons across a neural synapse
Enabling and steps of synaptic transmission
Neurochemicals are released by the presynaptic neuron and affect the postsynaptic neuron. In this way, these chemical substances enable synaptic transmission, which is the chemical conveyance of neural information between two neurons across a neural synapse.
In other words, neurons communicate with one another through the release of neurochemicals. The process of synaptic transmission is as follows:
1. Neurochemicals are produced in the axon terminals of the presynaptic neuron.
2. Neurochemicals are released from the axon terminals of the presynaptic neuron into the
synaptic gap.
3. Neurochemicals bind to receptor sites on the dendrites of the postsynaptic neuron.
4. Neurochemicals affect the postsynaptic neuron, either triggering or inhibiting a response.
Binding
Each neurochemical has a distinct molecular structure that corresponds to a specific receptor site. A neurochemical can only bind to the corresponding receptor site that matches its specific molecular structure. It cannot bind to the receptor sites of other neurochemicals because these receptor sites do not match its specific molecular structure, just as other neurochemicals cannot bind to its receptor site.
Chemical and electrical transmission
This lesson focuses on synaptic transmission, which involves the release of neurochemicals into the neural synapse to chemically transmit neural information. However, the transmission of neural information along neural pathways is an electrochemical process, meaning it involves electrical signals and chemical signals. While the VCAA study design only requires you to know about the chemical signals, also learning about the electrical signals may help you understand the complete process of neural transmission.
Neurochemicals bind to receptor sites and have an effect on the postsynaptic neuron (chemical transmission). The postsynaptic neuron becomes either more or less likely to fire an action potential, which is an electrical impulse that travels down the axon of a neuron (electrical transmission). The firing of an action potential triggers the release of neurochemicals from the axon terminals of this neuron, which is now the presynaptic neuron, into the synaptic gap (chemical transmission). This electrochemical transmission continues along the neural pathway, as electrical signals are transmitted within neurons and chemical signals are transmitted between neurons.
Types of beurochemicals
Neurotransmitters
Neuromodulators
Neurotransmitter
Neurotransmitters are extremely important for normal brain functioning, despite being small in size and affecting only one or two postsynaptic neurons. You will learn about neurotransmitters in this section of the lesson.
Theory details
Neurotransmitters are chemical molecules that have an effect on one or two postsynaptic neurons. This type of neurochemical enables rapid communication between two neurons across the neural synapse.
Types of neurotransmitters
Excitatory neurotransmitters, which have an excitatory effect on the postsynaptic neuron.
• Inhibitory neurotransmitters, which have an inhibitory effect on the postsynaptic neuron.
Both inhibitory and excitatory neurotransmitters bind to their corresponding receptor sites on the dendrites of the postsynaptic neuron. The difference is the effect that they have on the postsynaptic neuron. Inhibitory and excitatory neurotransmitters have different influences on the likelihood of the postsynaptic neuron firing an action potential, which is an electrical impulse that travels down the axon of a neuron.
Action potential
Electric impulse that travels down the axon of a neuron
Excitatory effect
when the neurotransmitter increases the likelihood of the postsynaptic neuron firing an action potential
Glutamate
the main excitatory neurotransmitter in the nervous system
Excitatory effect info and main type
Excitatory effects occur when an excitatory neurotransmitter binds to receptor sites on the dendrites of the postsynaptic neuron. They enhance neural transmission along neural pathways by activating postsynaptic neurons.
Glutamate is the main excitatory neurotransmitter in the nervous system.
Effect: Increases the likelihood of the postsynaptic neuron firing an action potential
Role in fubctioning: Glutamate has an important role in learning and memory. Specifically, the excitatory effects of glutamate form and strengthen synaptic connections between neurons that are repeatedly activated during learning. These strong synaptic connections represent memories of what has been learnt. In this way, glutamate enables synaptic plasticity, which you will learn about in the next lesson of this chapter. Glutamate also has an important role in thought and movement.
Inhibitory info and main type
Inhibitory effects occur when an inhibitory neurotransmitter binds to receptor sites on the dendrites of the postsynaptic neuron. They suppress neural transmission from occurring along neural pathways by regulating the activation of postsynaptic neurons.
GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the nervous
Effect; Decreases the likelihood of the postsynaptic neuron firing an action potential
Role in function: GABA has an important role in regulating postsynaptic activation in neural pathways, preventing the overexcitation of neurons. In this way, GABA reduces anxiety, which is a physiological and psychological response that involves general feelings of worry and apprehension, by inhibiting excitatory neural signals that contribute to anxiety. Furthermore, by inhibiting the uncontrolled firing of action potentials, GABA has an important role in preventing seizures.
Neurotransmitters effect
It is a common misconception that inhibitory effects are negative because they slow the transmission of neural information. However, it is important to understand that both excitatory and inhibitory effects are important for optimal brain functioning.
Postsynaptic neurons in neural pathways would fire
uncontrollably without the inhibitory effects of GABA
counterbalancing the excitatory effects of glutamate,
potentially causing anxiety and seizures. Conversely,
postsynaptic neurons in neural pathways would not be
adequately stimulated and activated without the excitatory GABA effects of glutamate counterbalancing the inhibitory effects
of GABA, potentially causing learning and concentration difficulties, and mental exhaustion. Figure 5 demonstrates the importance of neurotransmitter levels remaining balanced for optimal brain functioning.
Neuromodulators
a chemical molecule that has an effect on multiple postsynaptic neurons
As the name suggests, neuromodulators have a modulatory role in the brain, influencing neural activity on a larger and slower scale than neurotransmitters. You will learn about neuromodulators in this section of the lesson.
Theory details
Neuromodulators are chemical molecules that have an effect on multiple postsynaptic neurons. This type of neurochemical modulates neural activity on a larger scale than neurotransmitters. This is because neuromodulators are released into multiple neural synapses and consequently affect multiple postsynaptic neurons, unlike neurotransmitters,
as demonstrated in figure 6. Therefore, neuromodulators have widespread modulatory effects as they can influence large areas of brain tissue. Furthermore, the action of neuromodulators produces relatively long-lasting effects, as they modulate neural activity more slowly than neurotransmitters. However, like neurotransmitters, neuromodulators must bind to their specific receptor sites to have an effect on groups of postsynaptic neurons.
Neuromodulators can also modulate the effect of neurotransmitters by
changing the responsiveness of the receptor sites of a particular neurotransmitter, enhancing the excitatory or inhibitory effects of neurotransmitters.
• changing the neurotransmitter release pattern of the presynaptic neuron.
Neuromodulators types
Dopamine
Seratonin
Dopamine
a neuromodulator primarily responsible
for voluntary motor movement, the experience of pleasure, and reward- based learning
Pathways: There are pathways in the brain along which dopamine is transmitted. These pathways originate from regions that produce dopamine, including:
• the substantia nigra, which is located in the midbrain.
• the ventral tegmental area, which is located in the midbrain.
Effect: Dopamine can have excitatory and inhibitory effects on the postsynaptic neuron. The effect dopamine has depends on the type of receptor sites present at the particular brain location.
Role in functioning: Dopamine has an important role in coordinating voluntary motor movement. Dopamine produced in the substantia nigra transmits neural information that enables smooth, coordinated muscle movement.
• Dopamine has an important role in reward-based learning. When a person is rewarded for doing a behaviour, dopamine produced in the ventral tegmental area is released, which is associated with the experience of pleasure. Behaviours that may cause the release of dopamine include any behaviour that receives a reward. Examples of rewards include money, food, sex, and virtual prizes in an online game.
• Dopamine also has a role in motivation, given its role in reward-based learning. Rewarding behaviours that trigger the release of dopamine have
a pleasurable consequence for the person and are therefore more likely to be repeated. In this way, dopamine can motivate the person to engage in rewarding behaviours to experience pleasure once again. This explains why the release of dopamine is associated with addiction. Addictive behaviours, such as gambling or drug use, often provide an intensely pleasurable reward to the person, motivating them to repeat the behaviour, which consequently contributes to addiction.
Contribution to Parkinson’s disease
As you have learnt, dopamine produced in the substantia nigra has an important role in coordinating voluntary motor movement. When the loss of neurons occurs in the substantia nigra, dopamine production, and therefore dopamine levels in the brain, are reduced. This contributes to the development of Parkinson’s disease, which is a neurodegenerative disease that impacts neural messages related to voluntary motor movement. Motor symptoms of Parkinson’s disease include:
• slowness of movement
• muscle rigidity
• uncontrollable and involuntary shaking (tremors)
• difficulty starting and stopping body movements
• difficulty balancing
• stooped posture.
This impeded motor function that is characteristic of Parkinson’s disease can be treated by medication that artificially increases levels of dopamine in the brain, given that dopamine is the neuromodulator that functions to coordinate voluntary motor movement.
Seratonin
a neuromodulator primarily responsible for the regulation of mood and sleep
Pathway: There are pathways in the brain along which serotonin is transmitted.
These pathways originate from the raphe nuclei, which are masses of neurons in the brainstem that produce serotonin.
Effect: Serotonin has inhibitory effects on the postsynaptic neuron.
Role in functioning; Serotonin has an important role in mood regulation and stabilisation. Appropriate levels of serotonin in the brain enable a person to experience positive and stable moods, promoting wellbeing. Low levels of serotonin
in the brain are associated with mental disorders, including depression. Depression is characterised by prolonged negative moods, diminished interest or pleasure in daily activities, and feelings of worthlessness and inappropriate or excessive guilt (American Psychiatric Association, 2013). This demonstrates the role of serotonin in regulating mood and explains why some medications used to treat depression increase serotonin levels or target serotonin receptors in the brain.
• Serotonin has an important role in regulating the sleep-wake cycle, which is the 24-hour period comprising time spent asleep and time spent awake. In this way, serotonin influences your quality and quantity of sleep at night, as well as feelings of alertness and wakefulness during the day.
• Serotonin has various other roles depending on the receptor types it binds to and the brain area it acts upon, including appetite, digestion, and arousal.
