Biopsychology (Paper 2)

Question 1

Central Nervous System (CNS)

Answer 1

It consists of the brain and spinal cord. It has two main functions, the control of behaviour and the regulation of the body’s physiological processes. In order to do this the brain must be able to receive information from the sensory receptors (eyes, ears, skin etc.) and be able to send messages to the muscles and glands of the body in response.

Question 2

Brain Division

Answer 2

Cerebrum, Cerebellum, Diencephalon (contains the thalamus and the hypothalamus), Brain Stem

Question 3

Cerebrum

Answer 3

This is the largest part of the brain. It has four lobes, and is spilt down the middle into two halves, called the right and left hemisphere.

Question 4

Cerebellum

Answer 4

Responsible for motor skills, balance and coordinating the muscles to allow precise movements.

Question 5

Diencephalon

Answer 5

Contains the thalamus (regulates consciousness, sleep and
alertness) and the hypothalamus (regulates body temperature, stress response and hunger and thirst)

Question 6

Brain stem

Answer 6

Regulates breathing and heart rate.

Question 7

Spinal Cord

Answer 7

The main function of the spinal cord is to relay information between the brain and the rest of the body. This allows the brain to monitor and regulate bodily processes, such as digestion and breathing, and co-ordinate voluntary movement. The spinal cord is connected to different parts of the body by pairs of spinal nerves, which connect to specific muscles and glands. If the spinal cord is damaged, body areas connected to it by nerves below the damage will be cut off and stop functioning.

Question 8

Peripheral Nervous System (PNS)

Answer 8

The Peripheral Nervous System (PNS) consists of the nervous system throughout the rest of the body (e.g. not the brain or spinal cord). The PNS transmits messages via neurons (nerve cells) to and from the CNS. The PNS has 2 divisions: The somatic nervous system and the autonomic nervous system.

Question 9

Somatic Nervous System

Answer 9

The somatic nervous system controls voluntary movements and is under conscious control. It connects the senses with the CNS and has sensory pathways AND motor pathways. It controls skeletal muscles. The somatic nervous system is controlled by the motor cortex.

Question 10

Autonomic Nervous System

Answer 10

The Autonomic Nervous System (ANS) is involuntary (i.e. not under conscious control). It ONLY has motor pathways and it controls smooth muscles and the internal organs and glands of the body. The ANS is controlled by the brain stem.

Question 11

Sympathetic Nervous System (SNS)

Answer 11

This is activated when a person is stressed. Heart rate and breathing increase, digestion stops, salivation reduces, pupils dilate, and the flow of blood is diverted from the surface on the skin (fight or flight response).

Question 12

Parasympathetic Nervous System (PNS)

Answer 12

This is activated when the body is relaxing and so conserving energy. Heart rate and breathing reduce, digestion starts, salivation increases, and pupils constrict.

Question 13

Neuron

Answer 13

Neurons are specialised nerve cells that move electrical impulses to and from the Central Nervous System (CNS).

Question 14

Cell Body

Answer 14

Control centre of the neuron.

Question 15

Nucleus

Answer 15

Contains genetic material.

Question 16

Dendrites

Answer 16

Receives an electrical impulse (action potential) from other neurons or sensory receptors (e.g. eyes, ears, tongue and skin).

Question 17

Axon

Answer 17

A long fibre that carries the electrical impulse from the cell body to the axon terminal.

Question 18

Myelin Sheath

Answer 18

Insulating layer that protects the axon and speeds up the transmission of the electrical impulse.

Question 19

Schwann cells

Answer 19

Make up the myelin sheath.

Question 20

Nodes of Ranvier

Answer 20

Gaps in the myelin sheath. They speed up the electrical impulse along the axon.

Question 21

Sensory Neuron

Answer 21

Sensory neurons are found in sensory receptors. They carry electrical impulses from the sensory receptors to the CNS (spinal cord and brain) via the Peripheral Nervous System (PNS). Sensory neurons convert information from sensory receptors into electrical impulses. When these impulses reach the brain they are converted into sensations, such as heat, pain etc. so that the body can react appropriately. Some sensory impulses terminate at the spinal cord. This allows reflexes to occur quickly without the delay of waiting for the brain to respond.

Question 22

Motor Neuron

Answer 22

Motor neurons are located in the CNS but project their axons outside of the CNS. They send electrical impulses via long axons to the glands and muscles so they can affect function. Glands and muscles are called effectors. When motor neurons are stimulated they release neurotransmitters that bind to the receptors on muscles to trigger a response, which leads to movement.

Question 23

Relay Neuron

Answer 23

Relay neurons are found in the CNS. They connect sensory neurons to motor neurons so that they can communicate with one another. During a reflex arc (e.g. you put your hand on a hot hob) the relay neurons in the spinal cord are involved in an analysis of the sensation and decide how to respond (e.g. to lift your hand) without waiting for the brain to process the pain.

Question 24

Synaptic Transmission

Answer 24

1. Neurons transmit electrical impulses, known as action potentials, between the pre-synaptic neuron (the neuron transferring the action potential) and the post-synaptic neuron (the neuron receiving the action potential).
2. When the action potential reaches the pre-synaptic terminal it triggers the release of neurotransmitters (chemical messengers) from sacs on the pre-synaptic membrane known as vesicles in a process called exocytosis.
3. The released neurotransmitter will diffuse across the synaptic cleft (physical gap between the pre-synaptic membrane and post-synaptic membrane) where it
   binds to specialised post-synaptic receptor sites.
4. Synaptic transmission takes only a fraction of a second, with the effects terminated by a process called re-uptake. The neurotransmitter is taken back by the vesicles on the pre-synaptic neuron where they are stored for later release.
5. Neurotransmitters can be excitatory or inhibitory. Excitatory neurotransmitters cause an electrical charge in the membrane of the post-synaptic neuron resulting in an excitatory post-synaptic potential (EPSP), meaning that the post-synaptic neuron is more likely to fire an impulse. Inhibitory neurotransmitters cause an inhibitory post-synaptic potential (IPSP), making it less likely that the neuron will fire an impulse.
6. A neuron can receive both EPSPs and IPSPs at the same time. The likelihood that the neuron will fire an impulse is determined by adding up the excitatory and the inhibitory synaptic input. The net result of this calculation, known as summation, determines whether or not the neuron will fire an impulse. If the net effect is inhibitory the neuron will not fire, and if the net effect is excitatory, the neuron will fire.

Question 25

Direction of Synaptic Transmission

Answer 25

The vesicles containing neurotransmitters are ONLY present on the pre-synaptic membrane. The receptors for the neurotransmitters are ONLY present on the post-synaptic membrane. It is the binding of the neurotransmitter to the receptor which enables the information to be transmitted to the next neuron. Diffusion of the neurotransmitters mean they can only go from high to low concentration, so can only travel from the pre-synaptic membrane to the post-synaptic membrane.

Question 26

Endocrine System

Answer 26

Endocrine glands produce and secrete hormones into the bloodstream which are required to regulate many bodily functions. The major glands of the endocrine system include the pituitary gland and the adrenal glands. Each gland produces different hormones which regulate activity of organs/tissues in the body. Although hormones come into contact with most cells in the body, they only affect a limited number of cells, known as target cells. Target cells respond to a particular hormone because they have receptors for that hormone.

Question 27

Pituitary Gland

Answer 27

It produces hormones whose primary function is to influence the release of other hormones from other glands in the body. The pituitary gland is controlled by the hypothalamus, a region of the brain just above the pituitary gland. The hypothalamus receives signals from the body and then sends a signal to the pituitary gland in the form of a releasing hormone. This causes the pituitary gland to send a stimulating hormone into the bloodstream to tell the target gland to release its hormone. As levels of this hormone rise in the bloodstream the hypothalamus shuts down production of the releasing hormone and the pituitary gland shuts down secretion of the stimulating hormone

Question 28

Anterior pituitary gland

Answer 28

The anterior pituitary gland releases the hormone called ACTH which regulates levels of the hormone cortisol.

Question 29

Posterior pituitary gland

Answer 29

The posterior pituitary gland is responsible for releasing the hormone oxytocin which is crucial for infant/mother bonding.

Question 30

Adrenal Cortex

Answer 30

The outer section of the adrenal gland is called the adrenal cortex. It produces the hormone cortisol which is produced in high amounts when someone is experiencing chronic (long-term) stress. Cortisol is also responsible for the cardiovascular system, for instance it will increase blood pressure and causes blood vessels to constrict.

Question 31

Adrenal Medulla

Answer 31

The inner section of the adrenal gland is called the adrenal medulla which produces adrenaline, the hormone that is needed for the fight or flight response that is activated when someone is acutely (suddenly) stressed. Adrenaline increases heart rate, dilates pupils and stops digestion.

Question 32

Sympathomedullary Pathway

Answer 32

The Sympathetic Nervous System (SNS) is triggered by the hypothalamus. The hypothalamus also sends a signal to the adrenal medulla (part of the adrenal glands), which responds by releasing a hormone called adrenaline into the bloodstream. Adrenaline will increase heart rate, constrict blood vessels, increase rate of blood flow, raise blood pressure, divert blood away from the skin, kidneys and digestive system, increase blood supply to the brain and skeletal muscles, and increase respiration and sweating. All of this prepares the body for action and fight or flight by increasing blood supply, and therefore oxygen, to skeletal muscles for physical action and increasing oxygen to the brain for rapid response planning. The Parasympathetic Nervous System - When the threat has passed the parasympathetic nervous system dampens down the stress response. It slows down the heartbeat and reduces blood pressure. Digestion, which is stopped when the SNS is active, restarts.

Question 33

Strengths of Fight or Flight

Answer 33

Studies supports the claim that adrenaline is essential in preparing the body for stress. People who have malfunctioning adrenal glands do not have a normal fight or flight response to stress.

Question 34

Weaknesses of Fight or Flight

Answer 34

Gray (1988) states that the first reaction to stress is not to fight or flight but freeze. This involves the person stopping, looking and listening and being hyper vigilant to danger.

Taylor (2000) found that females tend and befriend in times of stress. Tend and befriend refers to the protection of offspring (tend) and seeking out social groups for mutual defence (befriend). Women have the hormone oxytocin, which means they are more likely to stay and protect their offspring.

Von Dawans (2012) has found that even males also tend and befriend. For example, during the 2001 September 11th terrorist attacks both males and females showed tend and befriend as they tried to contact loved ones and help one another.

Question 35

Visual Centres

Answer 35

The visual cortex processes information such as colour and shape. It is in the occipital lobe of BOTH hemispheres of the brain. Visual processing starts in the retina where light enters and strikes the photoreceptors. Nerve impulses from the retina are transmitted to the brain via the optic nerve. The majority terminate in the thalamus, which acts as a relay station, passing the information onto the visual cortex.

Question 36

Auditory Centres

Answer 36

The auditory cortex processes information such as pitch and volume. It lies within the temporal lobe in BOTH hemispheres of the brain. The auditory pathway begins in the cochlea in the inner ear, where sound waves are converted to nerve impulses, which travel via the auditory nerve to the auditory cortex. Basic decoding occurs in the brain stem, the thalamus carries out further processing before impulses reach the auditory cortex.

Question 37

Motor Cortex

Answer 37

The motor cortex is responsible for voluntary movements. It is located in the frontal lobe of BOTH brain hemispheres. Different parts of the motor cortex control different parts of the body. These areas are arranged logically next to one another. Damage to this area can cause a loss of muscle function/paralysis in one or both sides of the body (depending on which hemisphere/hemispheres have been affected).

Question 38

Broca’s Area

Answer 38

This area is named after Paul Broca who treated patients who had difficulty producing speech. He found that they had lesions to the LEFT hemisphere of the frontal lobe. Damage to the Broa’s Area causes Expressive Aphasia. This disorder affects language production but NOT understanding. Speech lacks fluency and patients have difficulty with certain words which help sentences function (e.g. ‘it’ and ‘the’).

Question 39

Wernicke’s Area

Answer 39

This area is in the LEFT hemisphere of the temporal lobe. Carl Wernicke found that patients with a lesion to this area could speak but were unable to understand language. Wernicke concluded that this area is responsible for the processing of spoken language. The Wernicke Area is connected to the Broca’s Area by a neural loop. Damage to the Wernicke’s Area causes Receptive Aphasia. This disorder leads to an impaired ability to understand language.

Question 40

Weaknesses of Localisation of Function

Answer 40

Some functions are more localised than others. Motor and somatosensory functions are highly localised to specific areas of the cortex. However, higher functions (e.g. personality and consciousness) are much more widely distributed. Functions such as language are too complex to be assigned to just one area and instead involve networks of brain regions.

Equipoteniality theory (Lashley, 1930) holds that higher mental functions are not localised. The theory also claims that intact areas of the cortex take over responsibility for a specific cognitive function following injury to the area normally responsible.

Dronkers et al. (2007) re-examined the preserved brains of two of Broca’s patients. MRI scans revealed that several areas of the brain had been damaged. Lesions to the Broca’s Area cause temporary speech disruption they do not usually result in severe disruption of language. Language is a more widely distributed (and less localised) skill than originally thought.

It may be that how brain areas communicate with each other is more important than specific brain regions. Dejerine (1892) reported a patient who could not read because of damage between the visual cortex and Wernicke’s area.

Bavelier et al. (1997) found that there are individual differences in which brain areas are responsible for certain functions. They found that different brain areas are activated when a person is engaged in silent reading. They observed activity in the right temporal lobe, left frontal lobe and occipital lobe. This means that the function of silent reading does not have a specific location within the brain.

Question 41

Hemispheric Lateralisation

Answer 41

Hemispheric lateralisation refers to the notion that certain functions are principally governed by one side of the brain.

Question 42

What has research shown about the lateralisation of the brain

Answer 42

Systematic research has demonstrated that in most people language centres are lateralised to the left hemisphere. The right hemisphere is dominant for visuo-spatial functions and facial recognition.

Furthermore the right hemisphere of the brain is responsible for the left hand side of the body, and the left hemisphere is responsible for the right hand side of the body. If a patient is experiencing right sided paralysis this means there is lateralised damage to the left hemisphere.

Question 43

How are the two hemispheres connected

Answer 43

The two hemispheres are connected by a bundle of nerve fibres known as the corpus callosum which enables information to be communicated between the two hemispheres.

Question 44

Strengths of Hemispheric Lateralisation

Answer 44

An advantage of hemispheric lateralisation is that it makes sense from an evolutionary perspective. It increases neural processing capacity, which is adaptive. By using one hemisphere to engage in a particular task it leaves the other hemisphere free to engage in another function. Rogers et al. (2004) found that hemispheric lateralisation in chickens is associated with an ability to perform two tasks simultaneously (finding food and being vigilant for predators).

Patients who have extensive damage to their left hemisphere can experience global aphasia (loss of speech production and speech comprehension). This suggests that language is lateralised to the left hemisphere.

Question 45

Weaknesses of Hemispheric Lateralisation

Answer 45

JW (a split-brain patient) developed the capacity to speak using his right hemisphere, with the result that they could speak about information presented in either the left visual field or the right visual field (although he was more fluent if information was presented in the left). It would appear that language is not lateralised entirely to the left hemisphere (Turk et al. 2002).

Lateralisation patterns shift with age (Szaflarski et al 2006) with most tasks generally becoming less lateralised in healthy adulthood.

If one hemisphere is damaged, undamaged regions on the opposite hemisphere can compensate. Danelli (et al. 2013) reported the case of EB, a 17-year-old Italian boy who had virtually his entire left hemisphere removed at the age of two and a half due to a huge benign tumour. EB’s language appeared almost normal in everyday life in terms of vocabulary and grammar. However, systematic testing revealed subtle grammatical problems as well as poorer than normal scores on picture naming and reading of loan words (words adopted from another language e.g. café). Language function can be largely preserved after removal of the left hemisphere in childhood, but the right hemisphere cannot provide, by itself, a perfect mastery of each component of language.

Question 46

Split Brain Research

Answer 46

Sperry and Gazzaniga (1968) investigated split-brain patients. Information from the left visual field goes into the right hemisphere, whereas information from the right visual field goes into the left hemisphere but because in split-brain patients the corpus callosum has been severed there is no way for the information presented to one hemisphere to travel to the other.

Question 47

Split Brain Research Procedure

Answer 47

Split Brain Patients are asked to stare at a dot in the centre of a screen and then information is presented in either the left or right visual field. They are then asked to make responses with either their left hand (right hemisphere), right hand (left hemisphere) or verbally (left hemisphere) without being able to see what their hands were doing. They may be flashed an image of a dog in their right visual field and then asked what they have seen. They will be able to answer ‘dog’ because the information will have gone into their left hemisphere where the language centres are.

Question 48

Split Brain Research Conclusion

Answer 48

If a picture of a cat is shown in a split-brain patient’s left visual field and they are asked what they have seen they will not be able to say because the information has gone into their right hemisphere, which has no language centres. However, they can draw a picture of a cat with their left hand because the right hemisphere controls this hand.

Question 49

Strengths of Split-Brain Research

Answer 49

Split-brain research has enabled discoveries of hemispheric lateralisation.

Experiments on split-brain patients are highly controlled and scientific.

Question 50

Weaknesses of Split-Brain Research

Answer 50

Split-brain patients have often had drug therapy for their epilepsy for much longer than others, which may affect the way in which their brain works. This means the findings of split-brain research cannot be generalised to the target
population.

Many studies using split-brain patients have as few as three participants, making it hard for results to be generalised to the target population.

The data from this research is very artificial. In the real world a severed corpus callosum can be compensated for by the unrestricted use of both visual fields. This means the research lacks ecological validity.

Question 51

Brain Plasticity

Answer 51

Brain plasticity refers to the brain’s ability to change and adapt as a result of experience. Plasticity allows the brain to cope better with the indirect effects of brain damage, such as swelling or haemorrhage following a road accident, or the damage resulting from inadequate blood supply following a stroke.

Question 52

Examples of Plasticity

Answer 52

Life Experience – Nerve pathways that are used frequently develop stronger connections, those that are rarely used eventually die. By developing new connections and reducing weak ones the brain is able to adapt to a changing environment. However, there is also a decline in cognitive functioning with age attributed to these changes. Boyke et al. (2008) taught 60 year olds a new skill (juggling), this increased grey matter in the visual cortex.

Video Games – Kuhn et al. (2014) compared a control group to a group who had been given video game training for at least 30 minutes a day for two months on the game ‘Super Mario’. They found that playing video games caused a significant increase in grey matter in the visual cortex, hippocampus, and cerebellum. Playing video games results in new synaptic connections in brain areas involved in spatial navigation, strategic planning, working memory and motor performance.

Meditation – Davidson et al. (2004) compared eight practitioners of Tibetan meditation with ten students who had no previous meditation experience. An EEG picked up greater gamma wave activity in the monks, even before they started meditating. Gamma waves coordinate neural activity.

Question 53

Strengths of Plasticity

Answer 53

Kempermann et al. (1998) found far more new neurons in the brains of rats in complex environments compared to those housed in basic cages. This increase in neurons was most prominent in the hippocampus, which is involved in the forming of new long-term memories and the ability to navigate.

Maguire et al. (2000) measured grey matter in the brains of London taxi drivers using an MRI scan. The hippocampus in taxi drivers was significantly larger than a control group and this was positively correlated with the amount of time they had spent as a taxi driver (the extent of their life experience).

Question 54

Functional Recovery

Answer 54

Functional recovery is a form of plasticity. Following damage caused by trauma, the brain can redistribute or transfer functions usually performed by damaged areas to other, undamaged, areas. When the brain is still maturing recovery from trauma is more likely (Elbert et al. 2001), however, the brain is capable of plasticity and functional recovery at any age. Studies have suggested that women recover from a brain injury quicker than men do.

Transfer of functions from damaged areas of the brain to undamaged ones can occur, this is called neural reorganisation. Growth of new neurons and/or connections (axons and dendrites) to compensate for damaged areas can also occur, this is called neural regeneration. Axon sprouting is part of neural regeneration, new nerve endings grow and connect with other undamaged nerve cells to form new neural pathways.

Spontaneous recovery from a brain injury tends to slow down after a number of weeks so physiotherapy may be required to maintain improvements in functioning. Techniques can include movement therapy and electrical stimulation of the brain to counter deficits in motor and cognitive functioning that can be experienced following a stroke.

Question 55

Strengths of Functional Recovery

Answer 55

Phantom Limb Syndrome (PLS) can be used as evidence of neural reorganisation. PLS is the continued experience of sensation in a missing limb, as if it were still there. These sensations are often unpleasant and even painful. PLS is thought to be caused by neural reorganisation in the somatosensory cortex that occurs as a result of limb loss (Ramachandran and Hirstein, 1998).

Hubel and Torten Wisel (1963) sewed one eye of a kitten shut and analysed the brain’s cortical response. They found that the visual cortex for the shut eye was not idle (as was predicted) it continued to process information from the open eye. This is further evidence that brain areas can reorganise themselves and adapt their functions.

Question 56

Post-Mortem Examinations

Answer 56

Psychologists may study a person who displays an interesting behaviour while they are alive. When the person dies, the psychologists look for abnormalities in the brain that might explain their behaviour. Post-mortem studies have found a link between brain abnormalities and psychiatric disorders, for instance, there is evidence of reduced glial cells in the frontal lobe of patients with depression.

Question 57

Strengths of Post-Mortem Examinations

Answer 57

Post-mortem studies allow for more detailed examination of anatomical and neurochemical aspects of the brain than would be possible with other methods of studying the brain. They have enabled researchers to examine deeper regions, such as the hippocampus and hypothalamus.

Question 58

Weaknesses of Post-Mortem Examinations

Answer 58

Studies using post-mortems may lack validity because people die in a variety of circumstances and at varying stages of disease. Similarly, the length of time between death and the post-mortem, and drug treatments, can all affect the brain.

Post-Mortem studies have very small sample sizes (as special permission needs to be granted). This means the sample cannot be said to be representative of the target population and so it is problematic to generalise the findings to the
wider population.

Question 59

Functional Magnetic Resonance Imaging

Answer 59

Functional Magnetic Resonance Imaging (fMRI) provides an INDIRECT measure of neural activity. It uses magnetic fields and radio waves to monitor blood flow in the brain. It measures the change in the energy released by haemoglobin, reflecting activity of the brain (oxygen consumption) to give a moving picture of the brain; activity in regions of interest can be compared during a base line task and during a specific activity

Question 60

Strengths of Functional Magnetic Resonance Imaging

Answer 60

fMRIs captures dynamic brain activity as opposed to a post-mortem examination which purely show the physiology of the brain.

fMRIs have good spatial resolution (refers to the smallest feature that a measurement can detect).

Question 61

Weaknesses of Functional Magnetic Resonance Imaging

Answer 61

Interpretation of fMRI is complex and is affected by poor temporal resolution (resolution of a measurement with respect to time), biased interpretation, and by the base line task used.

fMRI research is expensive leading to reduced sample sizes which negatively impact the validity of the research

Question 62

Electroencephalogram

Answer 62

An electroencephalogram (EEG) DIRECTLY measures GENERAL neural activity in the brain, usually linked to states such as sleep and arousal. Electrodes are placed on the scalp and detect neuronal activity directly below where they are placed; differing numbers of electrodes can be used depending on focus of the research. When electrical signals from the different electrodes are graphed over a period of time, the resulting representation is called an EEG pattern. EEG patterns of patients with epilepsy show spikes of electrical activity. EEG patterns of those with brain injury show a slowing of electrical activity.

Question 63

Strengths of Electroencephalogram

Answer 63

An EEG is useful in clinical diagnosis, for instance it can record the neural activity associated with epilepsy so that doctors can confirm the person is experiencing seizures.

EEGs are cheaper than an fMRI so can be used more widely in research.

Question 64

Weaknesses of Electroencephalogram

Answer 64

EEGs have poor spatial resolution.

Question 65

Event-Related Potentials

Answer 65

Electrodes are placed on the scalp and DIRECTLY measure neural activity (below where they are placed) in response to a SPECIFIC stimulus introduced by the researcher. Event-related potentials are difficult to pick out from all the other electrical activity being generated within the brain. To establish a specific response to a target stimulus requires many presentations of this stimulus and the responses are then averaged together. Any extraneous neural activity that is not related to the specific stimulus will not occur consistently, whereas activity linked to the stimulus will.

Question 66

Strengths of Event-Related Potentials

Answer 66

ERPs can measure the processing of a stimulus even in the absence of a behavioural response. Therefore it is possible to measure ‘covertly’ the processing of a stimulus.

ERPs are cheaper than an fMRI so can be used more widely in research.

ERPs have good temporal resolution (unlike fMRIs).

Question 67

Weaknesses of Event-Related Potentials

Answer 67

ERPs have poor spatial resolution (unlike fMRIs).

Only sufficiently strong voltage changes generated across the scalp are recordable. Important electrical activity occurring deeper in the brain is not recorded. The generation of ERPs tends to be restricted to the neocortex.

Question 68

Circadian Rhythms

Answer 68

Circadian rhythms are any cycle that lasts 24 hours. Nearly all organisms possess a biological representation of the 24 hour day. These optimise an organism’s physiology and behaviour to best meet the varying demands of the day/night cycle. Circadian rhythms are driven by the suprachiasmatic nuclei (SCN) in the hypothalamus. This pacemaker (controls the rate at which something occurs) must constantly be reset so that our bodies are in synchrony with the outside world. Natural light provides the input to this system, setting the SCN to the correct time in a process called photoentrainment. The SCN then uses this information to coordinate activity of circadian rhythms throughout the body.

Question 69

The Sleep-Wake Cycle - When are the strongest sleep drives?

Answer 69

Light and darkness are the external signals that determine when we feel the need to sleep and when we wake up. This rhythm dips and rises at different times of the day so that the strongest sleep drives occur between 2:00 - 4:00am and 1:00 - 3:00pm.

Question 70

The Sleep-Wake Cycle - When are the peak releases of melatonin?

Answer 70

The release of melatonin from the pineal gland is at its peak during the hours of darkness. Melatonin induces sleep by inhibiting the neural mechanisms that promote wakefulness. Light supresses the production of melatonin.

Question 71

The Sleep-Wake Cycle - What control is sleep and wakefulness under?

Answer 71

Sleep and wakefulness are also under homeostatic control. When we have been awake for a long time homeostasis tells us that the need for sleep is increasing because of the amount of energy used up during wakefulness. This homeostatic drive for sleep increases gradually throughout the day, reaching its maximum in the late evening.

Question 72

The Sleep-Wake Cycle - Difference between homeostasis and Circadian Rhythms

Answer 72

Circadian rhythms keep us awake as long as there is daylight, prompting us to sleep as it becomes dark. The homeostatic system tends to make us sleepier the longer we have been awake regardless of whether it is night or day. The internal circadian rhythm will maintain a cycle of 24-25 hours, even without natural light.

Question 73

Strengths of Circadian Rhythms

Answer 73

One practical application of circadian rhythms is chronotherapeutics. The time that patients take medication is very important for treatment success. It is essential that the right concentration of drug is released in the target area of the body at the time the drug is most needed. For example, the risk of heart attack is greatest during the early morning hours after waking. Medications have been developed that are taken before the person goes to sleep but are not released until the vulnerable time of 6:00 am.

Question 74

Weaknesses of Circadian Rhythms

Answer 74

Research on circadian rhythms has not isolated people from artificial light, because it was believed only natural light affected circadian rhythms. However, more recent research suggests this might not be true. Cziesler et al. (1999) altered participant’s circadian rhythms down to 22 hours and up to 28 hours by using artificial light alone.

There are individual differences in the length of circadian rhythms. One research study found that cycles can vary from 13 to 165 hours (Czeisler et al, 1999).

Another individual difference in circadian rhythms is when they reach their peak. ‘Morning people’ prefer to rise early and go to bed early whereas ‘evening people’ prefer to rise late.

Question 75

Ultradian Rhythms

Answer 75

Ultradian rhythms span a period of less than 24 hours. An example is the five sleep stages. Human sleep follows a pattern alternating between Rapid Eye Movement (REM) sleep (which is stage five) and Non-Rapid Eye Movement (NREM) sleep (which consists of stages one, two, three and four). The cycle repeats itself every 90 minutes. Each stage shows a distinct EEG pattern. As the person enters deep sleep, their brainwaves slow and their breathing and heart rate decreases. During the fifth stage (REM sleep), the EEG pattern resembles that of an awake person. It is during this stage that dreaming occurs.

Question 76

Kleitman (1969) Basic Rest Activity Cycle (BRAC)

Answer 76

Kleitman (1969) referred to the 90 minute cycle found during sleep as the Basic Rest Activity Cycle (BRAC). He suggested that this 90 minute cycle continues when we are awake. During the day, rather than moving through the sleep stages, we move progressively from a state of alertness into a state of physiological fatigue. Studies suggest that the human mind can focus for about 90 minutes, and towards the end of those 90 minutes the body begins to run out of resources, resulting in loss of concentration, fatigue and hunger.

Question 77

Strengths of Ultradian Rhythms

Answer 77

Ericsson et al. (2006) found support for the ultradian rhythms. They studied a group of elite violinists and found that among this group practise sessions were limited to 90 minutes at a time. Violinists frequently napped to recover from practise, with the best violinists napping more. The same pattern was found among athletics, chess players and writers. This fits with the BRAC.

Question 78

Weaknesses of Ultradian Rhythms

Answer 78

Tucker et al. (2007) suggests that there are individual differences in ultradian rhythms which are biologically determined and may even be genetic in origin. Participants were studied over 11 consecutive days and nights in a laboratory environment. The researchers assessed sleep duration, time taken to fall asleep and the amount of time in each sleep stage. They found differences in all of these characteristics.

Question 79

Infradian Rhythms

Answer 79

Infradian rhythms span a period of longer than 24 hours; they may last weeks, months or even a year. One example of an infradian rhythm is the menstrual cycle, which lasts for about a month. There are considerable variations in the length of this cycle, with some women experiencing a 23 day cycle and others a 36 day cycle (Refinetti, 2006). The average is 28 days. Hormones regulate the menstrual cycle. Ovulation occurs roughly halfway through the menstrual cycle, when oestrogen levels are at their peak, and usually lasts for 16-32 hours. After ovulation, progesterone levels increase in preparation for the possible implantation of an embryo in the uterus

Question 80

Strengths of Infradian Rhythms

Answer 80

Infradian rhythms can affect behaviour. Penton-Voak (1999) found that women express a preference for feminised male faces when choosing a partner for a long-term relationship. However, they showed a preference for masculinised faces during ovulation.

Question 81

Weaknesses of Infradian Rhythms

Answer 81

The menstrual cycle is not only governed by infradian rhythms. When several women of childbearing age live together, and do not take oral contraceptives, their menstrual cycles synchronise. In one study samples of sweat were collected from one group of women and rubbed onto the upper lip of another group of women, their menstrual cycles became synchronised. This suggests that the synchronisation is affected by pheromones. Pheromones are a chemical substance produced and released into the environment by an animal which affects the behaviour of others of the same species.

Question 82

Endogenous Pacemakers

Answer 82

The most important endogenous pacemaker is the suprachiasmatic nuclei (SCN). This is a tiny cluster of nerve cells in the hypothalamus. The SCN plays an important role in generating circadian rhythms. It acts as the master clock, linking other brain regions that control sleep and arousal, and controlling all other biological clocks throughout the body.

Neurons within the SCN synchronise with each other, so that their target neurons in sites elsewhere in the body receive time-coordinated signals. These peripheral clocks can maintain a circadian rhythm, but not for very long, which is why they are controlled by the SCN. This is possible because of the SCN’s built in circadian rhythm, which only needs resetting when external light levels change. The SCN receives information about light levels through the optic nerve. If our biological clock is running slow then morning light shifts the clock. The SCN also regulates the manufacture and secretion of melatonin in the pineal gland via the interconnecting neural pathway.

The SCN sends a signal to the pineal gland, directing it to increase production and secretion of the hormone melatonin at night and to decrease it as light levels increase in the morning. Melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness.

Question 83

Strengths of Endogenous Pacemakers

Answer 83

Folkard (1996) studied a university student, Kate Aldcroft, who spent 25 days in a laboratory. She had no access to the exogenous zeitgebers of light to reset the SCN. However, at the end of 25 days her core temperature rhythm was still at 24 hours. This indicates that we DO NOT need the exogenous zeitgebers of light to maintain our internal biological rhythms.

Question 84

Weaknesses of Endogenous Pacemakers

Answer 84

Kate Aldcroft’s sleep-wake cycle extended to 30 hours, with periods of sleep as long as 16 hours. This suggests that we DO need the exogenous zeitgebers of light to maintain our internal biological rhythms.

Question 85

Exogenous Zeitgebers

Answer 85

The term exogenous refers to anything whose origins are outside of the organism. Exogenous zeitgebers are environmental events that are responsible for maintaining the biological clock of an organism.

The most important zeitgebers for most animals is light. Receptors in the SCN are sensitive to changes in light levels during the day and use this information to synchronise the activity of the body’s organs and glands. Light resets the internal biological clock each day, keeping it on a 24-hour cycle. A protein in the retina of the eye called melanopsin, which is sensitive to natural light, is critical in this system.

When people move to a night shift or travel to a country with a different time zone their endogenous pacemakers try to impose their inbuilt rhythm of sleep (circadian rhythm), but this is now out of synchrony with the exogenous zeitgeber of light. Out of sync biological rhythms lead to disrupted sleep patterns, increased anxiety and decreased alertness and vigilance.

Question 86

Strengths of Exogenous Zeitgebers

Answer 86

The vast majority of blind people who still have light perception have normal circadian rhythms. Blind people without light perception show abnormal circadian rhythms. This shows the vital role that the exogenous zeitgeber of light levels play in maintaining our internal biological rhythms.

Burgess et al. (2003) found that exposure to bright light prior to an east-west flight decreased the time needed to adjust circadian rhythms to local time.

Question 87

Weaknesses of Exogenous Zeitgebers

Answer 87

Studies of individuals who live in Artic regions, where the sun does not set in the summer months, show normal sleeping patterns despite the prolonged exposure to light. This suggests that there are occasions where the exogenous zeitgeber of light may have very little bearing on our internal biological rhythms