Psych U3 AOS1

The role of a neuron

A neuron is an individual nerve cell that is specialised to receive, process and/or transmit information

• They carry information in the form of action potential to the appropriate part of the nervous system to interpret the message and enable a response

• There are 3 different types; motor, sensory and inter

Parts of a neuron

• Dendrite

• Cell body/soma (contains nucleus)

• Axon

• Myelin

• Myeline sheath

• Axom terminal

• Terminal button

• Synaptic vesicles

Dendrite

An extension of a neuron that detects and receives information from other neurons

Cell body/soma

Contains the nucleus and integrates the incoming information from other neurons. It is then transmitted along the axon in the form of action potential.

Axon

A single tubelike extension that transmits neural information to other neurons.

Myelin/myelin sheath

A white fatty substance that surrounds and insulates the axon.

Axon terminals

At the end of each axon are branches called axon terminals, each axon terminal has a small knob-like swelling at its tip called a terminal button that secretes chemicals called neurotransmitters from from small sacs called synaptic vesicles.

Central nervous system (CNS)

Comprises the brain and its extension, the spinal cord

• Its main function is to receive and process information from the body’s internal and external environments and to activate appropriate responses and transmit these messages in order to control human functioning.

The brain

Continuously receives, processes and transmits information to and from the body, playing a crucial role in almost everything we think, feel and do.

Neural pathway

Comprises one or more circuits of interconnected neurons that form a communication network.

The spinal cord

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

Two main functions

• Receive sensory information from the PNS and send these signals to the brain for processing

• Receive sensory information from the brain and send it to the PNS

Peripheral nervous system (PNS)

The entire network of nerves located outside the CNS

It carries information from the CNS from the body’s muscles, organs and glands (about the internal environment) and from the sensory organs (about external environment) and carries information from the CNS to the body’s muscles, organs and glands.

Divisions of the PNS

Somatic, autonomic, sympathetic, parasympathetic, enteric

Somatic nervous system

A network of nerves that carries sensory information from sensory receptors in the body to the CNS and motor information from the CNS to skeletal muscles.

Afferent vs Efferent information

Afferent information is sensory information coming into the CNS, whereas efferent information leaving the CNS

Autonomic nervous system

Subdivision of the PNS that connects the CNS to the body’s visceral organs (heart, stomach and liver) and glands (sweat, salivary and adrenal) to regulate their function.

Sympathetic nervous system

Prepares the body for action by increasing the activity of most visceral muscles, organs and glands in times of vigorous activity, stress or threat.

Parasympathetic nervous system

Responsible for decreasing the activity of most visceral muscles, organs and glands, and restoring body functioning to its normal state (homeostasis)

Enteric nervous system

Is embedded within the walls of the gastrointestinal tract that is dedicated to regulating its functioning.

Conscious response

response to a sensory stimulus is a reaction that involves awareness. You will have paid attention to the stimulus and therefore know about it. 

• The response will usually be a voluntary, ‘intentional’ reaction. 

• The reaction, even if momentary, is also likely to be goal-directed (have a purpose), and you will be able to exercise some degree of control over it. 

• A conscious response may occur in response to both external and internal stimuli.

Unconscious response

Response to a sensory stimulus is a reaction that does not involve awareness. 

It is involuntary, unintentional, automatic, and we cannot ordinarily control its occurrence. Bodily responses regulated by the ANS occur automatically without conscious effort.

Spinal reflex

is an unconscious, involuntary and automatically occurring response to certain stimuli without any involvement of the brain. 

It is often referred to as a reflex arc because the response to an incoming stimulus is automatically ‘reflected back’ from the spinal cord without any initial input from the brain and before the brain has even processed or is conscious of the stimulus.

Synaptic plasticity

The ability of the synapse to change in response to experience. 

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 (‘sprouts’) on axons or dendrites, thereby enabling new links to be made, including rerouting of existing connections.

Rerouting

Occurs when new connections are made between neurons to create alternate neural pathways. The rerouting may involve the existing synaptic connections and/or new connections from the sprouts.

Pruning

The elimination of weak, ineffective or unused synapses (and therefore connections to other neurons).

Long-term potentiation (LTP)

Refers to the long-lasting strengthening of synaptic connections, resulting in enhanced or more effective synaptic transmission. 

• LTP improves the ability of two neurons to communicate with one another at the synapse, and this improvement is stable and enduring. 

• LTP strengthens synaptic connections, which enables postsynaptic neurons to be more easily activated in the future.

Process of LTP

• The postsynaptic neurons become more and more responsive to the presynaptic neurons as a consequence of repeated stimulation by neurotransmitters. 

• The more that the connection is activated, the more it is strengthened. The more the connection is strengthened, the more the relevant neural pathway is strengthened, increasing the efficiency in transferring information along the pathway and decreasing the likelihood that what has been learned will be forgotten. 

• In addition, the more we use the information being remembered, the more the LTP process strengthens the pathway, making it easier to retrieve that information.

Long-term depression (LTD)

Is the long-lasting decrease in the strength of synaptic transmission and neuronal response (which is the opposite of LTP).

Process of LTD

• This results from a lack of stimulation of pre- and postsynaptic neurons or prolonged low-level stimulation. 

• Generally, a postsynaptic neuron becomes less responsive to the neurotransmitter released by a presynaptic neuron, and the effect is to weaken the synaptic connection and therefore weaken or even silence communication at the synapse.

• It is believed that LTD may be just as important for learning and memory as LTP. The weakening or elimination of unused synapses through LTD may prune unimportant or unwanted connections, leaving behind the important connections that have been strengthened through repeated use by LTP. 

• LTD may, for example, enable old memories or unused connections and pathways for previously learned information or skills to be cleared out. 

• LTD may be what allows us to correct our thinking when solving a problem, or to adjust our movements when learning a new motor skill.

• It may also provide the basis of blocking or erasing unwanted, inappropriate or incorrect thoughts, feelings and behaviours.

How does communication work?

When neurons communicate with one another, most do so by sending neurotransmitters across the tiny space between the terminal buttons of one neuron, which release the neurotransmitter, and the dendrites of another, which receive the neurotransmitter. 

This tiny space, called the synaptic gap (or synaptic cleft) is one component of the synapse.

The neural synapse is the site where communication typically occurs between adjacent neurons. 

The other two components of the synapse are the terminal buttons of the presynaptic (‘sending’) neuron and the dendrites of the postsynaptic (‘receiving’) neuron.

Neurotransmitters

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

Effects of neurotransmitters

• Some neurotransmitters have an excitatory effect and consequently stimulate or activate postsynaptic neurons to perform their functions.

• Other neurotransmitters have an inhibitory effect and block or prevent postsynaptic neurons from firing. 

Some neurotransmitters also occur as hormones, so they may be referred to as neurohormones. For example, noradrenaline (also called norepinephrine) is a neurotransmitter and a hormone. It is secreted as a hormone by the adrenal glands into the blood, and as a neurotransmitter from neurons.

Glutamate

The main excitatory neurotransmitter in the CNS. This means that glutamate enhances information transmission by making postsynaptic neurons more likely to fire. 

• It is the second most common neurotransmitter in the brain and is involved in most aspects of normal brain function, including perception, learning, memory, thinking and movement. 

• Glutamate has crucial roles in the synaptic changes that occur during learning and memory. Its excitatory effects promote the growth and strengthening of synaptic connections between neurons within a neural pathway that subsequently represents the memory of what has been learned.

Gamma-Aminobutyric Acid (GABA)

The primary inhibitory neurotransmitter in the CNS. It works throughout the brain to make postsynaptic (‘receiving’) neurons less likely to fire (so it ‘inhibits’ firing). 

• One of its roles is to fine-tune neurotransmission in the brain and maintain neurotransmission at an optimal, or ‘best possible’, level. 

• Without the inhibitory effect of GABA, activation of postsynaptic neurons might get out of control. Their uncontrolled activation could spread throughout the brain, causing seizures similar to those of epilepsy and other problems. 

• Anxiety symptoms like those experienced by people with phobias have been connected to a low level of GABA in the brain, thereby impacting on the regulation of neuronal transmission in the brain.

Role of neuromodulators

• Can change the reactivity of receptors to another type of neurotransmitter to enhance their excitatory or inhibitory responses.

• Can also team up and work together with another neurotransmitter in a synapse to make the other more or less potent.

• Do not release their chemical messengers into a single synapse. Instead, they are released into far broader areas, where they can affect a large number of neurons at once (100 000 or more). Therefore, an entire neural tissue, brain area, pathway or multiple pathways may be influenced by exposure to a neuromodulator’s action.

Dopamine

A modulatory neurotransmitter known to have multiple functions depending on where in the brain it acts.

• For example, it has important roles in voluntary movements, the experience of pleasure, motivation, appetite, reward-based learning and memory. It has also been implicated in various mental conditions, including Parkinson’s disease, addiction and schizophrenia.

• Although primarily an excitatory neurotransmitter, dopamine can have either an excitatory effect at one location or an inhibitory effect at another, depending on the type of receptors that are present.

Seratonin

A modulating neurotransmitter that has a wide range of functions, depending on where in the brain it acts. For example, it has important roles in mood, emotional processing, sleep onset, appetite and pain perception.

• Serotonin is widely described as a mood stabiliser, with low levels associated with mood disorders such as depression and seasonal affective disorder.

• It seems that the right amount of serotonin is required for us to feel positive, calm and have a stable mood

• Reduced levels of serotonin in the brain have also been associated with a number of anxiety disorders, particularly obsessive-compulsive disorder (OCD).

• Serotonin also seems to play an important role in the regulation of the daily sleep–wake cycle, including when we fall asleep, how much we sleep and when we wake, as well as our feeling of wakefulness throughout the day.

Stressor

Stimuli that cause or produce stress and challenge our ability to cope.

Internal stressor

originates within the individual (illness, pain, lack of sleep, thoughts and emotions (low self-esteem)

External stressor

originates outside the individual from situations and events in the environment (getting stuck in a queue, having too much homework, being nagged by parents, someone not following the rules, overcrowded environment, being physically threatened)

Stress

A state of physiological and psychological arousal (tension) produced by internal or external stressors that challenge an individual’s ability or resources to cope.

Acute stress

• Is brief and specific to the demands of a particular situation, it produces a very high level of arousal for a relatively short time. 

  • Eg. A deadline, a performance, fight/flight/freeze response.

Episodic acute stress

• When acute stress is encountered over and over again, the cumulative effect is more significant on our physical and psychological health. 

  • Eg, Your pet dies, you get the flu, you fall behind at school, you miss SACs.

Chronic stress

• Involves ongoing demands, pressures and worries that are long-lasting and produce an increased arousal level that persists over a relatively long time, negatively effecting health (physical) and wellbeing (psychology.)

  • Eg, Money trouble, abusive partner, chronic illness

Eustress

•  A positive psychological response to a stressor that is short-term and not harmful to the body. Eustress typically provides the motivation and energy we need to perform at an optimal level. 

  • Characterised by positive psychological states: Enthusiasm, motivation, excitement, heightened alertness

  • Common causes: Stage performance, a first date, riding on a roller-coaster, doing well on an exam.   

Distress

• A negative psychological response to a stressor that can be short-term, but if long-term, has harmful effects on the mind and body. 

  • Characterised by negative psychological states: Anger, anxiety, nervousness, irritability, tension.

  • Common causes: Lining up in a queue when you are in a hurry, relationship problems, and financial pressure.

The fight-flight-freeze model

an involuntary response to a sudden and immediate threat (or stressor) in readiness to:

Fight – confront and battle the threat

Flight – escape and run away to safety

Freeze – keep absolutely still and silent to avoid detection

The fight-flight-freeze model is described as

• A survival mechanism - These physical changes enable our bodies to react effectively to stressful events that threaten our wellbeing, therefore enhancing our chances of survival and reproduction of our species.

• Situation dependent - Which of the three reactions that occur, depends on the situation. (# limitation – Do you think it also depends on the individual?) 

• Involuntary - The biological processes underlying each reaction occur before the brain’s visual information processing areas have had a chance to fully interpret what is happening. Hence, they are involuntary.

  • Eg. Fight - We can catch a ball we see out of the corner of our eye before we think about it and actually register that it is tennis ball flying at our face.

Biological processes of FFF reactions

• The brain-body pathway that activates the FFF reaction is called the sympathetic adreno-medullary system (SAM.) Because both the sympathetic nervous system and the endocrine (hormone) system are involved in this response.

• Collectively the sympathetic NS and the adrenaline and noradrenaline released from the endocrine system:

  • Increase heart rate and blood pressure

  • Redistribute blood supply from the skin and intestines to the muscles (which explains why digestion slows and you go pale.)

  • Increase respiration rate (to increase oxygen supply)

  • Increase glucose secretion by the liver (for energy)

  • Dilate pupils (so the eyes can take in as much light as possible - aiding visual acuity)

  • Suppress functions that are not immediately essential in order to conserve energy, such as digestion and sexual drive.

• Once the threat has passed, the parasympathetic nervous system dominates again calming and restoring normal functioning.

Freeze reaction

• is often physically described as a ‘stop, look and listen’ behavioural response because, often, before immobility sets in, there is a reflexive, orienting response of the head or eyes towards the direction of the threat. 
  
  

• This is followed by:

  • hypervigilance – being on guard, watchful, or extremely alert.

  • No vocalisations 

  • Tonic immobility - tense muscles collapse and become still so no body movements occur

  • The racing heart slows significantly 

  • Blood pressure drops quickly 

• The biological processes involved in enabling the freeze state are not completely understood. 

  • Partial dominance by the parasympathetic nervous system. A state characterised by both energy-conservation and mobilisation ready for action ensues (You’ve stopped with one foot on the brake and one on the accelerator.)

The General Adaptation Syndrome (GAS)

Proposes a three stage explanation of the physiological stress response that occurs regardless of the stressor that is encountered. This model includes an explanation of the short (acute) and long term (chronic) consequences for stress exposure:

Stage 1: Alarm Reaction Stage (with Shock and Counter Shock)

Stage 2: Resistance 

Stage 3: Exhaustion

Stage 1 of GAS model

Alarm Reaction Stage (with Shock and Counter Shock sub-stages) - occurs when the organism first becomes aware of the stressor

Shock – a temporary state where the organism’s ability to deal with the stressor falls below its normal level. 

• Characterised by a drop of blood pressure, body temperature and muscle tone

Counter shock – the sympathetic nervous system dominates allowing the body to rebound, increasing its resistance to the stressor.  

• Characterised by a heightened level of arousal and alertness to help fight the stressor

• Immediate release of adrenaline and noradrenaline as well, cortisol will also start to be slowly released.

• The SNS and stress hormones accelerate the heart rate & respiratory rate, supplying the muscles with more glucose and oxygen to allow the body to action a fight or flight response.

Stage 2 of GAS model

Resistance – the body’s resistance to the particular stressor rises above normal for a prolonged period, maximising resources to cope and adapt. 

• The intense arousal of the alarm reaction stage diminishes, but physiological arousal remains at a level above normal for a prolonged period, due to:

  • The continued release of the stress hormone cortisol.

  • Cortisol continues to assist in the activation of the sympathetic nervous system. Together, they re-route energy away from nonessential bodily processes such as digestion, growth, sex drive, menstruation, testosterone and sperm production to essential body processes such as increased heart rate.   

• Generally, if the effort to deal with the initial stressor during the resistance stage is successful, the organism will have adapted to the stressor and the body eventually returns to its normal ‘balanced’ (homeostatic) state of functioning.

The role of cortisol

• Cortisol takes significantly longer to release than adrenaline; its effects can be sustained for much longer.

• The level of cortisol in the bloodstream is commonly used as a measurable indicator of prolonged stress. 

• Cortisol is released by the adrenal cortex (the outer layer of the adrenal gland) into the bloodstream. 

• Cortisol increases metabolism, for example, aiding the liver to release glucose into the bloodstream, for muscles to use as energy.  

• Cortisol has an anti-inflammatory effect by blocking the activity of white blood cells (#problem) that contribute to inflammation. 

• Retards tissue repair – slowing wound healing 

• Suppresses the immune system, making an individual vulnerable to disease. 

• Cortisol increases appetite - Increasing weight gain > cardiovascular disease. 

• High Cortisol levels have been associated with physical health problems:  Increased illness (colds/flus), hypertension (high blood pressure), digestive issues, obesity, hyperglycemia (high blood sugar), which is linked to diabetes, cardiovascular disease, and stroke. 

• High Cortisol levels have been associated with cognitive impairment: impaired memory recall, learning problems, impaired concentration and problem-solving ability. As well as mental illness: anxiety, depression.

Stage 3 of GAS model

Exhaustion – The level of resistance to the stressor falls below normal due to depleted resources and prolonged activation of the physiological stress response system which has caused wear and tear (harm) to physical and mental health. 

• The exhaustion stage occurs when the individual, despite huge effort, has not been able to adapt and deal with the stressor and they are unable to cope.

• The Exhaustion stage is characterised by: 

• extreme fatigue

• high levels of anxiety

• Symptoms of depression

• nightmares

• impaired sexual performance

• impaired memory recall

• hypertension (high blood pressure)

• gastrointestinal problems (IBS)

• heart disease

• in extreme cases, death

The gut-brain axis

A paradigm that explains the two-way directional relationship between the brain and the gastrointestinal system (which is controlled by the enteric nervous system) and how they influence each other via the vagus nerve.

Microbiota

Are living microorganisms that live in the gastrointestinal tract and maintain gut health and functioning.

Impact of microbiota imbalance

• Recent research on humans has centred on antibiotic use (which reduces good gut bacteria or microbiota) as well as chronic stress studies on people with high cortisol levels (which also reduces good gut bacteria and microbiota). 

• These studies reveal that unhealthy gut microbiota is linked to changes in the production of the neurotransmitter GABA, as well as dopamine (a pleasure-producing neuromodulator) and particularly serotonin (a mood-stabilising neuromodulator) because 90% of the body’s serotonin levels are produced in the gut. This is why an unhealthy microbiome can:

• Impair our mental processes such as our response or resilience to stressors, making us feel more stressed. 

• Impair our cognitive capacity to problem-solve and our overall memory capacity. 

• Increase stress levels, as well as the diagnosis of mental and physical disorders such as Anxiety Disorders, Autism and Parkinson’s disease.

Parts of the gut brain axis

It consists of the brain, spinal cord, autonomic nervous system (sympathetic, parasympathetic, enteric), the Hypothalamic-pituitary-adrenal (HPA) axis and the gut.

The brain is included because our mental processes, particularly our moods, emotions and stress (our worries and anxieties) influence our gut health, and our gut can influence our moods (who doesn’t get irritable and have lower concentration when they have an upset stomach!)

The HPA axis is part of the endocrine system and is specifically responsible for the release of cortisol from the adrenal glands. Cortisol and other stress hormones have a significant impact on decreasing gut health. Poor gut health is also linked to higher stress levels, which cause higher cortisol.

The spinal cord and autonomic nervous system (sympathetic and parasympathetic, and enteric) are included because they provide the neural communication pathways that maintain the activity of the organs, muscles and glands that make up the gut or gastrointestinal system.

The transactional model of stress and coping

Richard Lazarus and Susan Folkman’s Model for explaining the response to stress focuses on stress as a psychological process ONLY. They propose that stress is the outcome of a transaction between the individual and their external environment. Key to this model is that the individual determines through their own appraisal (evaluation) if they experience stress - it is not a given; they have an element of control and influence

Primary appraisal

Primary appraisal is an individual’s assessment of the situation

• Is it positive (benign), irrelevant, or stressful

• If stressful, what kind of stress?

• Harm/loss = has happened - involves an assessment of how much damage has already occurred (e.g. ‘I have lost my job)

• Threat = could happen - involves an assessment of harm/loss that may not have occurred yet but could occur in the future (e.g. ‘I might not be able to afford rent’)

• Challenge = potential for personal growth - involves an assessment of the potential for personal gain or growth from the situation (e.g. ‘ I'll get any other job I can and will learn to budget and save money’)

Secondary appraisal

An individual's assessment of the coping resources available to deal with demands

• Internal resources = personality and character (e.g. strength and determination)

• External resources = support networks (family, money, time)

Coping flexibility

Refers to the ability to effectively modify or adjust one’s coping strategies according to the demands of different stressful situations. It includes the abilities to:

• Recognise whether the use of a flexible coping strategy is appropriate for the specific situation

• Select a coping strategy that suits the situational circumstances

• Recognise when the coping strategy being used is ineffective

• Discontinue an ineffective coping strategy

• Produce and implement an alternative coping strategy when required

High coping flexibility

Individuals who readily adjust their coping strategies if a particular strategy they are using is proving to be ineffective. They also tend to use different types of coping strategies across a variety of stressful situations, and there tends to be a good fit between the coping strategies they deploy and the characteristics of the specific situational demands.

Low coping flexibility

Individuals that consistently use the same type of coping strategies across different stressful situations, and persist in their use of the coping strategies they deploy, even if ineffective. Essentially, these individuals aren’t very adaptable and almost always approach coping much the same way, almost habitually.

Approach coping strategies

Involve efforts to confront a stressor and deal directly with it and its effects. Activity is focused towards the stressor, its causes and a solution that will address the underlying problem and minimise or eliminate its impact.

Avoidance coping strategies

Involve efforts that evade a stressor and deal indirectly with it and its effects. Activity is focused away from the stressor, and there is no attempt to actively confront the stressor and its causes.