Unit 3 Psychology

Nervous System

A complex, highly organised network of specialised cells that enables the brain to receive information about what is going on from both inside and outside the body and to respond appropriately.

Main roles of the Nervous System

- receive information
- process information
- coordinate a response to information

Central Nervous System (CNS)

Includes the brain and its extension, the spinal cord. Primarily, its roles are to process information received from the body's internal and external environments and to activate appropriate responses.

Brain

A mass of nerve tissue that functions as the main control centre of the nervous system. Many brain functions involve the activation of neural pathways.

Neural Pathway

Comprised of one or more circuits of interconnected neurons that form a communication network. Neural pathways also connect the brain to other parts of the nervous system and the body.

Ascending Tracts

Refers to neural pathways where in which sensory information is carried up to the brain.

Descending Tracts

Refers to neural pathways where in which motor information is carried down from the brain through the spinal cord to the relevant muscles, glands and/or organs.

Spinal Cord

The long, thin bundle of nerve fibres that extends from the base of the brain to the lower back.

Functions of Spinal Cord

- receiving sensory information via the PNS
- sending messages to the brain for processes
- receiving motor information from the brain to send to relative parts of the body via the PNS

Spinal Reflex

An unconscious, automatic response controlled solely by the spinal cord without the involvement of the brain. The immediate response of the spinal cord enables a quicker reaction time compared to the time it takes for sensory information to reach the brain and is therefore believed to be an adaptive response.

Reflex Arc

Another name for spinal reflex. It is referred to as such because the unconscious and automatic response to incoming stimuli is automatically 'reflected back' from the spinal cord without input from the brain.

Examples of Spinal Reflex

- withdrawing your hand after touching the handle of a hot frying pan
- stepping on something sharp and immediately withdrawing the leg that stepped on the sharp object

Peripheral Nervous System (PNS)

The entire network of nerves located outside the CNS. It extends from the top of the head, throughout the body to the tips if the fingers and toes and to all parts of the skin. It's role is to carry information to and from the CNS.

Sub Divisions of the Peripheral Nervous System

- somatic nervous system
- autonomic nervous system

Somatic Nervous System (SNS)

A subdivision of the PNS comprising of the network of nerves that carry sensory information to the CNS and motor information from the CNS to the skeletal muscles.

Afferent Information

Refers to when sensory information goes to the CNS.

Efferent Information

Refers to when motor information leaves the CNS.

Voluntary Movement

Movement controlled through the coordinated actions of both motor and sensory information.

Autonomic Nervous System

A subdivision of the PNS that connects the CNS to the body's internal organs and glands, providing feedback to the brain about their activities as well as increasing or decreasing their respective activities in response to demand placed on the body throughout the day. It is considered 'self-regulating'.

The Sub Divisions of the Autonomic Nervous System

- sympathetic nervous system
- parasympathetic nervous system
- enteric nervous system

Sympathetic Nervous System

Activates internal muscles, organs and glands to prepare the body for vigorous activity or to deal with a stressful or threatening situation. This is initiated by a stressor or fear stimulus and enhances survival by providing an immediate response. Dominant and more active during emotional arousal.

Parasympathetic Nervous System

In the absence of threat and stress, it helps maintain the internal body environment in a steady, balanced state of normal functioning. The parasympathetic nervous system essentially counterbalances the activities of the sympathetic nervous system. Dominant and more active during rest and digestion.

Enteric Nervous System

The nervous system of the gastrointestinal tract. It monitors the physiological conditions of the digestive tract and controls muscle contractions, gastric acid secretion and blood flow.

Enteric Nervous System's Independent Functions

It can function independently from the brain and carry out some of its functions in the digestive process without communicating with the brain.

Conscious Response

A reaction to a sensory stimulus that involves awareness. The response will usually be a voluntary, intentional response that is likely goal directed and a degree of control can be exercised over it.

Examples of Conscious Response

- seeing the sun is shining brightly and choosing to wear sunglasses
- putting a jacket on when it is cold outside

Unconscious Response

A reaction to a sensory stimulus that does not involve awareness. The response is involuntary, unintentional, automatic and we cannot ordinarily control its occurrence.

Reflexive Responses (Autonomic Reflexes)

Bodily responses regulated by the ANS occur automatically without conscious effort, such as: breathing, blinking, digesting food, etc. Other reflexive responses can also help us avoid danger and minimise harm.

Neurons

The building blocks of the brain and the rest of the nervous system. Neurons specialise in the reception and transmission of information throughout the nervous system.

Types of Neurons

sensory, interneurons, motor

Sensory Neuron

Neurons that carry incoming information from the sensory organs, muscles and internal organs to the brain and spinal cord.

Interneurons

Makes the connection between neurons that rarely connect themselves. They relay messages from the sensory to motor neuron.

Motor Neuron

Initiates contraction in muscles causing movement as well as initiating contractions in glands causing hormones.

Neurotransmitter

A chemical substance produced by a neuron that carries a message to other neurons or cells in the muscles, organs or other tissue.

Synapse

It is the site where communication typically occurs between presynaptic and postsynaptic neurons.

Synaptic Gap

Also known as the 'synaptic cleft', it is the small space between the axon terminal of a presynaptic neuron. It is the space that allows neurotransmitters to be transferred from the presynaptic neuron to the post synaptic neuron.

Axon

Transmits messages (electrical/neural impulse) from the soma to the axon terminals.

Axon Terminal

Also known as terminal buttons, they are responsible for storing and secreting neurotransmitters.

Soma

Part of the neuron that contains the nucleus and structures that maintain functioning.

Dendrite

Receives messages (absorbs neurotransmitters) from other neurons and carries it towards the soma.

Myelin

A fatty substance that helps insulate neurons and speeds the transmission of nerve impulses.

Presynaptic Neuron

Sending neuron

Postsynaptic Neuron

Receiving neuron

Reuptake

Refers to the reabsorption of neurotransmitter that have not been bound to receptors in the postsynaptic neuron. The neurotransmitter is reabsorbed into the terminal buttons.

Excitatory Effect

A neurotransmitter effect that allows postsynaptic neurons to fire more easily.

Inhibitory Effect

A neurotransmitter effect that blocks and prevents postsynaptic neurons from firing.

Glutamate (Glu)

The main excitatory neurotransmitter in the CNS. It enhances information transmission by making the postsynaptic neurons more likely to fire.

Functions of Glutamate

It is involved in most aspects of normal brain function such as: learning, memory, perception, thinking and movement.

Effects of Glutamate

- too little glutamate results in poor communication between neurons
- too much can result in over-excitation of receiving neurons, leading to neuronal damage/death

Gamma-Amino Butyric Acid (GABA)

The primary inhibitory neurotransmitter in the CNS. It works throughout the brain to make postsynaptic neurons less likely to fire.

Functions of GABA

Fine-tunes neurotransmission in the brain and maintains neurotransmission at an optimal level.

Effects of GABA

- low GABA levels in the brain has been linked to anxiety symptoms
- without the inhibitory effect of GABA, activation of postsynaptic neurons might get out of control, causing seizures

Neuromodulators

Also known as 'modulatory neurotransmitters', they influence the effects of other neurotransmitters. For example, it can change the reactivity of receptors to another type of neurotransmitter to enhance their excitatory or inhibitory responses.

Dopamine

A neuromodulator that has multiple functions depending on where in the brain it acts. Primarily an excitatory neurotransmitter, it can also have an inhibitory effect depending on the type of receptors that are present.

Functions of Dopamine

It has important roles in voluntary movements, the experience of pleasure, motivation, appetite, reward-based learning and memory.

Effects of Dopamine

- low levels are associated with fatigue, depression, parkinsons disease
- high levels are associated with hallucinations and delusions

Dopamine Reward System

Occurs when two dopamine pathways (mesolimbic and mesocortical) overlap and are strongly associated with rewarding behaviour through the experience of pleasure. Healthy behaviours that may be perceived as rewarding can include: eating when hungry and drinking water when thirsty. Harmful behaviours that involve a loss of impulse control and have caused addiction can include: gambling.

Serotonin

An inhibitory neuromodulator that has a wide range of functions depending on where in the brain it acts. Unlike dopamine, serotonin only has inhibitory effects and so doesn't stimulate brain activity.

Functions of Serotonin

It can affect mood regulation, emotional processing, sleep onset and appetite and pain perception

Effects of Serotonin

- low levels are associated with mood disorders, OCD, anxiety disorders
- excessive amount of serotonin may cause serotonin syndrome, which can be life threatening in some people

Neuroplasticity

The ability of the brain and other parts of the nervous system to change in response to experience.

Synaptic Plasticity

The ability of a synapse to change in response to experience. It enables a flexible, efficient and effectively functioning nervous system and its the biological basis of learning and memory formation.

Sprouting

The creation of new extensions on a neuron to allow it to make new connections with other neurons. This occurs through the growth of nerve endings on axons or dendrites.

Rerouting

Occurs when new connections are made between neurons to create alternate neural pathways. These alternate 'routes' may be entirely new neural pathways or connections to other pathways in the brain.

Pruning

The elimination of weak, ineffective or unused synapses, therefore severing the connections to other neurons. Experience determines which synapses will be retained and those that are not frequently used will decay or disappear.

Long-Term Potentiation

Refers to the long-lasting enhancement of synaptic transmission (excitability) due to repeated strong stimulation. LTP strengthens synaptic connections in a way that enables postsynaptic neurons to be more easily activated.

Long-Term Depression

Refers to the long-lasting decrease in the strength of synaptic transmission (excitability) due to a lack of stimulation of pre- and postsynaptic neurons or prolonged low level stimulation.

Stress

A psychobiological response produced by internal or external stressors.

Stressor

Any stimulus that causes stress. A stressor can be a physical stimulus (loud noise, heavy object, intense light, etc.) or psychological in nature (failing an exam, running late to class etc.).

Internal Stressor

Originates within the individual; e.g. a personal problem that causes worry about future circumstances or the experience of pain that may be perceived as signalling a serious illness (mental).

External Stressor

Originates outside the individual from situations and events in the environment; e.g. having too much homework, being a victim of crime, stuck in traffic (physical).

Acute Stress

Stress that lasts for a relatively short time and is specific to the demands of a particular situation.

Chronic Stress

Stress that continues for a prolonged period of time. This can occur in circumstances such as ongoing financial difficulties, social isolation and loneliness, relationship problems, long-lasting health problems, etc.

Fight, Flight or Freeze

An involuntary and acute stress response, involving physiological changes produced by the sympathetic nervous system.

Fight

Confronting and fighting off a threat.

Flight

Escaping by running away to safety.

Freeze

keeping absolutely still and silent to avoid detection.

First Part of Stress Response

- stress is experienced and detected by the amygdala which sends a signal to the hypothalamus.
- hypothalamus responds to the stressor by activating the sympathetic nervous system which then stimulates the adrenal medulla
- adrenal glands secretes adrenaline and noradrenaline into the blood stream
- the hormones activate various organs that prepare the body for action

Second Part of Stress Response

- hypothalamus stimulates nearby pituitary gland to initiate the HPA axis to secrete additional stress hormones (mostly cortisol)

Adrenaline

A hormone secreted during stress. It prepares the body for action. Often involved with acute stress.

Cortisol

Cortisol is a primary stress hormone secreted in response to an acute stressor and a chronic stressor. It is slower acting compared to other stress hormones but longer lasting. This allows the body to deal with stress for a longer period.

Effects of Cortisol

- increasing blood glucose for energy
- enhancing metabolism
- turns off bodily systems not required to deal with stressor (reproductive functions)
- anti-inflammatory effect, blocking white blood cells that contribute to inflammation
- slows wound healing

Healthy Stress Response

Characterised by a quick rise in cortisol levels, followed by a rapid decline with the termination of the stressful event.

Consequences of Prolonged Stress

- impaired immune system (vulnerability to disease)
- weight gain
- colds, flu, hypertension, digestive problems, atherosclerosis, high blood sugar levels & diabetes
- impaired cognitive performance, learning problems, impaired memory formation, depression, PTSD & other anxiety disorders

Gut Brain Axis

A bidirectional (two-way) communication link between the central and enteric nervous systems, linking cognitive and emotional areas in the brain with the gastrointestinal tract.

Vagus Nerve

Responsible for the communication between the gut and the brain. It is the longest nerve in the body, running from the brain stem to the intestines.

Vagus Nerve Fibres

90% of vagus nerve fibres are afferent (sensory) connections that sends signals up from the gut to the brain. The remaining 10% are efferent (motor) connections.

Microbiota

Refers to the highly diverse and dynamic system of bacteria and micro-organisms that live in the human gastrointestinal tract. The collective term is microbiome. Microbiota can be influenced by diet, infection, disease and lifestyle choices.

Microbiota and Neurotransmitters

Gut bacteria help produce dopamine, GABA and over 80% of the body's serotonin. Disturbances in microbiota can change the production of neurotransmitters in the gut.

Enterotype

A term used to describe each individual's personal composition of microbiota.

Gut Dysbiosis

Refers to the imbalance or lack of diversity in gut bacteria. Gut dysbiosis can reduce the effectiveness of the immune system, cause illnesses and influence the effects of neurotransmitters.

Gut Dysbiosis can cause

- mood disorders
- changes in the production of neurotransmitters in the gut (dopamine, GABA, serotonin)
- digestive disorders
- stress reactivity
- heart disease
- mental health disorders

Selye's General Adaptation Syndrome (GAS)

A three stage physiological response to stress that occurs regardless of the stressor that is encountered. This means that GAS is non-specific and will occur regardless of the source of stressor.

Stages of GAS

alarm (shock/countershock), resistance, exhaustion

Alarm Reaction Stage

The first stage of GAS that occurs when the person first becomes aware of the stressor. This stage involves the shock and countershock stage.

Shock Substage

The body goes into temporary shock and its ability to deal with the stressor falls below normal level. The body reacts as if were injured (e.g. decrease in body temp, blood pressure and muscle tone). The countershock stage combats this.

Countershock Substage

Activates the sympathetic nervous system, triggers fight or flight and increases the body's resistance to the stressor. Adrenaline, noradrenaline, cortisol and other stress hormones are released into the bloodstream. Heart and respiratory system accelerate and muscles are supplied with more energy (glucose & oxygen).

Resistance Stage

If stressor isn't dealt with immediately, the body will enter the resistance stage. It's resistance to the stressor rises above normal but arousal of the alarm reaction stage diminishes through the parasympathetic nervous system. Physiological processes not required to deal with stress decrease.

Cortisol in the Resistance Stage

Cortisol remains in the bloodstream to energise the body and acts as an anti-inflammatory agent and provides fast-acting pain relief. The ability to adapt to the specific stressor increases, but leaves the immune system weak to diseases and illnesses.

Exhaustion Stage

If the stressor isn't dealt with during the resistance stage, the body will enter exhaustion. Alarm reaction changes may reappear but the body cannot sustain resistance against it. As the body has been dealing with the stressor for a long time, stress hormones have been depleted and the immune system becomes vulnerable to mental and physical disorders.