- Created by: Alan Nguyen
- Created on: 19-11-17 15:22
It is a complex network of nerve cells to and from the brain and spinal cord to different parts of the body.
Helps the different parts of the body communicate with each other. The CNS receives information from the senses and controls behaviour and the regulation of the body’s physiological processes.
Divided into 4 main areas: the cerebrum, cerebellum, diencephalon and the brain stem.
Responsible for coordinating sensation, intellectual and nervous activity by receiving information from the sensory receptors (eyes, nose, ears) and sends messages to the muscles and glands of the body.
Largest part of the brain and is further divided into 4 lobes such as the frontal lobe and the occipital lobe. The cerebrum split down the middle into cerebral hemispheres and communicate through the corpus callosum.
The frontal lobe is involved in thought and production of speech whilst the occipital lobe is involved in processing visual images.
Lies beneath the cerebrum and above the brainstem. The diencephalon has 2 structures: the thalamus and the hypothalamus.
The thalamus acts as a relay station for nerve impulses from the senses. The hypothalamus regulates body temperature, hunger and thirst and controls the release of hormones from the pituitary gland.
Beneath the diencephalon and adjacent to the cerebellum. Connects the brain to the spinal cord.
Is responsible for regulating automatic functions that are essential for life such as breathing, heartbeat and swallowing. Motor and sensory neurons travel through the brain stem to allow impulses to pass between the brain and spinal cord.
A collection of nerve cells that are attached to the brain and run the length of the spinal column. The spinal cord is connected by pairs of spinal nerves.
The spinal cord relays information between the brain and the rest of the body to allow the brain to monitor and regulate bodily processes such as digestion, breathing and to coordinate voluntary movements.
Made up of all the nerves outside the CNS. It consists of 2 main divisions: the somatic nervous system and the autonomic nervous system.
The PNS relays nerve impulses from the CNS to the rest of the body and back to the CNS.
Comprised of 12 pairs of cranial nerves and 31 pairs of spinal nerves which both have sensory and motor neurons.
The somatic nervous system is involved in reflex actions because it does not involve the brain therefore is quick and rapid.
Sensory: relay messages to the CNS
Motor: relay information from the CNS to other areas of the body.
Divided into further 2 parts: the sympathetic and parasympathetic nervous system.
Involved in regulating involuntary actions without our conscious awareness such as heartbeat and digestion, it is necessary because these vital bodily functions would not work efficiently.
This system is involved in responses that deal with emergencies by neurons travelling from SNS to every organ and gland to prepare for rapid action.
Some responses include:
Increased pupil size = more light for better vision
Bronchial tubes in lungs dilate = greater oxygen intake
Increase in heart rate = greater blood flow to muscles and organs
Sweat glands stimulated to produce more sweat = cools the body
Glycogen stories in liver is converted to glucose = energy boost
Dilating blood vessels = increase blood pressure
Slows digestion and urination (less important
Generally, uses the neurotransmitter acetylcholine, which has inhibitory effects.
Calming and relaxing the body once the threat has passed by slowing down heartbeat and blood pressure.
Referred to as ‘rest and digest’ because it conserves energy and reactivates digestion.
Is a network of glands throughout the body.
They manufacture and secrete hormones delivered using blood vessels to target sites
The body’s chemical messengers that circulate in the bloodstream and affect target cells because they have receptors for that specific hormone.
Hormones travel through the bloodstream to regulate the activity of cells/organs and can influence mood.
Timing is vital as too much/little at the wrong time can result in dysfunctions such as too high a level of cortisol can lead to Cushing’s disease.
Consists of the hypothalamus which controls the pituitary gland; the pituitary gland secretes many hormones some of which stimulate other glands; adrenal glands help trigger the fight or flight response and the reproductive organs. The system is regulated by a feedback system. For example, a signal sent from the hypothalamus to the pituitary in the form of a releasing hormone causes the pituitary to secrete a stimulating hormone into the bloodstream. This hormone then sends a signal to target glands to secrete its hormone.
As levels of secreting hormone rises in the blood the hypothalamus shuts down secretion of releasing hormone and the pituitary gland shuts down secretion of the stimulating hormone. As a consequence, slows down secretion of the target glands hormone therefore resulting in a stable concentration of hormones circulating in the bloodstream.
The pituitary gland
Referred to as the ‘master gland’. Comprised of an anterior and a posterior.
Influence the release of hormones from other glands. It is controlled by the hypothalamus. The hypothalamus receives information from sources then uses this information to regulate bodily functions.
The anterior releases ACTH (adrenocorticotrophic hormone) as a response to stress by stimulating the adrenal glands to make cortisol, also produces LH and FSH and produces testosterone and sperm in the testes; the posterior releases oxytocin which is important for mother-infant bonding. It also stimulates contraction of the uterus during childbirth.
The adrenal glands
The 2 glands sit on top of the kidneys and comprised of 2 distinctive parts in each of them: The adrenal cortex and the adrenal medulla.
The adrenal cortex (outer part) which produces cortisol to regulate and support functions such as cardiovascular and anti inflammatory. Cortisol is increased in response to stress. Low cortisol means low blood pressure, poor immune function and inability to deal with stress. The cortex also produces aldosterone to maintain blood pressure.
The second part (inner part) releases adrenaline and noradrenaline which prepare the body for fight or flight. Adrenaline helps the body respond to a stressful situation by increasing heart rate and blood flow to the muscles and brain. Additionally, it helps with the conversion of glycogen to glucose for energy. Noradrenaline constricts blood vessels which increase blood pressure.
Consist of the ovaries and testes.
The ovaries are responsible for the production of eggs and hormones, oestrogen and progesterone.
The testes produce testosterone which causes the development of facial hair deepening of voice and growth spurt during puberty, sperm production and muscle strength. The hypothalamus instructs the pituitary gland on how much testosterone to produce and the pituitary gland passes this message onto the testes.
Specialised cells that carry neural information throughout the body.
Neurons typically consist of dendrites, axons, myelin sheath and a cell body.
Help in receiving, processing and transmitting information by moving electrical impulses to and from the central nervous system. There are 3 types of neurons: the sensory, relay and motor.
Dendrites = At one end of the neuron receive signals from other neurons/sensory receptors and are connected to the cell body.
Myelin sheath = is an insulating layer that forms around the axon to allow nerve impulses to transmit more rapidly along the axon – if damaged, impulses slow down so affects signal speed.
Axon = Receives outgoing signals from cell body.
Cell body = Is the control centre of the cell in which impulses are carried along the axon from the cell body.
Types of neurons
Sensory neuron = carry nerve impulses from sensory receptors to the spinal cord and brain (found in sense receptors) Convert info from these receptors into neural impulses and is then translated into sensations when it reaches the brain.
Relay neuron = (found within the brain and spinal cord) allows sensory and motor neurons to communicate with each other.
Motor neuron = forms synapses with muscles and control their contractions by projecting their axons outside the CNS. When stimulated, it releases neurotransmitters that bind to receptors on the muscle and triggers muscle movement. When the axon of a motor neuron fires, the muscle with which it has formed synapses with contracts – strength of muscle contraction depends on rate of firing muscle relaxation is caused by inhibition of motor neuron.
An electrical signal caused by neurons transmitting information from neurons.
The dendrites receive information from sensory receptors/neurons and is passed down to the cell body and onto axon (travels its length).
Synaptic transmission process
Once an action potential has arrived at the terminal button at the end of the axon, it crosses the synaptic gap between the presynaptic neuron and the postsynaptic neuron. As the action potential reaches the synaptic vesicles (found at the end of the nerve cell) it causes the vesicle sacs to release their contents through exocytosis. The released neurotransmitter diffuses across the gap and binds to specialised receptors on the surface of the cell that recognise it and are activated. Once activated the receptor molecules produce either excitatory or inhibitory.
Are chemical messengers that carry nerve impulses across the synaptic to the receptor site on the post synaptic neuron.
There are 2 types of neurotransmitters:
Excitatory – such as acetylcholine are stimulating so they increase the likelihood of the excitatory signal sent to the postsynaptic cell which is more likely to fire.
Inhibitory – such as serotonin and GABA calms so they decrease the likelihood of the inhibitory signal sent to the postsynaptic and of the neuron firing. They also induce sleep and filter excitatory signals.
Binding of a neurotransmitter
When a neurotransmitter binds with a postsynaptic receptor:
An excitatory binding with a postsynaptic receptor causes an electrical change in the membranes of that cell resulting in an excitatory post synaptic potential (EPSP) therefore is more likely to fire.
An inhibitory binding with a postsynaptic receptor results in an inhibitory postsynaptic potential (IPSP) therefore is likely to fire.
The net result of adding up the excitatory and the inhibitory synaptic input determines whether the cell fires or not.
Spatial summation = large number of EPSPs generated at many different synapses on the same postsynaptic neuron at the same time.
Temporal summation = large number of EPSPs generated at same synapse by a series of high frequency action potentials on the same presynaptic neuron.
Fight or flight response
Is a sequence of activity within the body that is triggered when the body prepares itself for defending or attacking or fleeing due to a threatening or stressful situation. This response evolved as a survival mechanism.
When an individual is faced with a threat, the amygdala is mobilised which associated the sensory signals (hear or smell) with emotions associated with the situation for example fear/anger. The amygdala sends a distress signal to the hypothalamus which communicates with the body through sympathetic nervous system. There are two responses: acute and chronic.
Acute (sudden) stressors
When the sympathetic nervous system is triggered, it begins the process of preparing the body for rapid action.
The SNS sends a signal to the adrenal medulla to release adrenaline which causes the heart to beat faster pushing more blood to the muscles and other organs. Blood pressure also increases, breathing is more rapid to take in more oxygen. Adrenaline also triggers release of blood sugar and fats to supply energy. Blood vessels divert from digestion to the muscles to make it tense. When the threat has passed, the parasympathetic nervous system reduces the stress response by slowing down heartbeat and reduce blood pressure. Digestion is inhibited when SNS was stimulated but returns to rest and digest because the parasympathetic nervous system is activated.
Chronic (ongoing) stressor
If the brain continues to perceive something as threatening, the hypothalamus activated a stress response called the HPA axis: hypothalamus, pituitary gland and adrenal cortex.
In response to the continued threat, the hypothalamus releases CRH (corticotrophin releasing hormone) into the bloodstream. CRH causes pituitary to produce and release ACTH (adrenocorticotrophic hormone) and is then transported in the blood to the adrenal glands. ACTH stimulates the adrenal cortex to release cortisol to release a quick burst of energy and a lower sensitivity to pain but can cause impaired cognitive performance and a lowered immune response.
Cortisol levels are monitored in the HPA axis (chronic) by the hypothalamus and pituitary gland that have special receptors.
These hormones are inhibited and reduced if cortisol levels get too high, monitored by negative feedback.
Criticism of Fight or Flight (negative effects)
There are numerous negative effects on the body.
For example, long term increase in blood pressure can damage the blood vessels and lead to heart disease.
In addition, too much cortisol suppresses the immune response.
This increases the likelihood that the person will become ill.
Criticism of the Fight or Flight (freeze response)
Another criticism, according to Gray is that most animals and humans initially ‘freeze’ in response to a threat.
The first reaction of avoiding confrontation enables them to assess the threat before responding.
Adrenaline and cortisol promote this hyper vigilant state, where the individual is alert to danger, focusing attention on relevant sensory inputs.
This phase allows the subject to adapt to the threat and choose the best response to that threat.
Evaluation of fight or flight (tend and befriend)
Taylor et al discovered that the ‘tend and befriend’ response seems to be more characteristic for the coping method of females.
This is because women’s responses have evolved to be a maternal instinct, as they were the primary caregiver of children therefore adhere to a more passive nature to not risk putting children in danger.
This behaviour could be linked to the release of the hormone oxytocin, which increases relaxation (decreases anxiety) and reduces the fight or flight response.
This means that males and females have different responses to coping with stress, as females respond differently due to hormones.
Evaluation of fight or flight (SRY gene)
There is evidence of a genetic basis for gender differences in the fight or flight response.
Lee and Harley found that the SRY gene, found on the male Y chromosome, promotes the development of male aggression.
This might prime males to release more adrenaline when threatened.
This shows that males and females respond differently to stress because females do not have a Y chromosome.
Is a region of the brain responsible for the generation of voluntary motor movements.
Located in the frontal lobe of the brain, along a bumpy region known as the precentral gyrus. Both hemispheres of the brain have a motor cortex, with one on one side of the brain controlling muscles on the opposite side of the brain.
Different parts of the motor cortex exert control over different parts of the body and are arranged logically to one another.
A region of the brain that detects sensory events and processes input from sensory receptors in the body sensitive to touch.
Located in the parietal lobe of the brain along the postcentral gyrus (processing of sensory info related to touch).
Uses sensory info to produce sensations of touch, pressure, pain and temp which is then localised to specific body regions.
Both hemispheres have a somatosensory cortex, with the cortex on one side of the brain receiving info from the opposite side of the brain.
Primary visual centre is located in the visual cortex in the occipital lobe but visual processing occurs in the retina where light enters and hits the photoreceptors.
Nerve impulses are then transmitted from the retina to the brain via optic nerve, the majority of the nerve impulses terminate in the thalamus, acting as a relay station to pass the info onto the visual cortex.
Visual cortex spans both hemispheres, with the right hemisphere receiving its input from the left hand side of the visual field vice versa.
Contains different areas involved in processing colour, shape, movement.
Concerned in the temporal lobes on both sides of the brain, where we find the auditory complex.
The auditory pathways begin 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.
Cochlea travels to brain stem where a basic decoding occurs like duration and intensity of sound then travels to the thalamus which acts as a relay station which further processes the auditory stimulus. The last stop is the auditory cortex where it is recognised.
Broca’s area (language centre)
Broca studied patient Tan, who was able to understand spoken language, but was unable to speak of express his thoughts in writing. Broca also studied 8 other patients with similar language deficits and found that they all had lesions in the same area of the left frontal lobe.
This lead to him proposing Broca’s area a language centre in the posterior portion of the frontal lobe of the left hemisphere. This area is believed to be critical for speech production.
Research has discovered 2 regions of Broca’s area, one selectively involved in language, the other involved in response to demanding cognitive tasks.
Wernicke’s area (language centre)
Found in the posterior portion of the left temporal lobe involved in understanding language. Patients with a lesion in this area could speak but were unable to understand language.
Wernicke proposed that language involves separate motor and sensory regions located in different cortical regions; Motor region (in Broca’s area) is close to the area controlling mouth, tongue and vocal cords; Sensory region (in Wernicke’s) is close to auditory and visual input of the brain.
Input from these regions is thought to be transferred to Wernicke’s area where it is recognised as language and associated with meaning.
A neural loop known as the arcuate fasciculus between Broca and Wernicke.
One end is for the production of language and the other end is responsible for processing of spoken language.
Evaluate strength of localisation (aphasia & lesio
Support for localisation comes from studies of patients with aphasia due to lesions.
Broca researched nine patients with similar speech deficits, and found they all had lesions in a particular part of their left frontal lobe.
In addition, Wernicke researched patients who could still speak but had problems understanding language. He found they all had lesions in a similar area in the left temporal lobe.
This shows that there are specific areas in the brain that are specialised for language production and comprehension.
Evaluate strength of localisation (take over funct
Research believed that if a brain area was damaged, other intact areas of cortex could take over their function.
The effect of brain damage would depend on its existent rather than its location.
This is supported by the discovery that people can regain some cognitive abilities after brain damage.
This supports the idea that basic motor and sensory functions are localised, but higher mental functions are not.
Evaluate criticism of localisation (affect several
One problem with this study is that lesions often affect several brain areas.
Research examined the preserved brains of 2 of Broca’s patients using MRI, and found other areas were damaged, not just Broca’s area.
In fact, lesions that only affect Broca’s area generally only result in temporary speech disruption.
This suggests that language involves networks of brain regions, not just a few specific areas.
Evaluate criticism of localisation (individual dif
Patterns of activation of brain areas during language tasks vary between individuals.
For example, research has observed activation in the right temporal lobe as well as the left frontal, temporal and occipital lobes during silent reading.
Other studies have shown that women, who use language more than men, have larger Broca’s and Wernicke’s areas.
This suggests that localisation of function may develop differently depending on use.
Refers that some mental processes in the brain are mainly specialised to either the left or right hemisphere, the two halves are not exactly alike.
Research has found that the left hemisphere is dominant for language and speech whereas the right excels at visual-motor tasks.
Broca established that damage in a particular area of the left hemisphere led to language deficits unlike damage to the right hemisphere which did not have the same consequences.
The 2 hemispheres are connected through the corpus callosum allowing info received by one hem to be sent to the other hem.
Split brain patients in surgery had severe epilepsy, surgeons cut the bundle of nerve fibres that formed the corpus callosum. The aim was to prevent violent electrical activity accompanied by epileptic seizures from one hemisphere to the other.
Split brain research
Took advantage of the fact that info from the left visual field goes to the left hemisphere. Because the corpus callosum is cut in split brain patients, the info presented to one hemisphere has no way of travelling to the other hemisphere and can be processed only in the hemisphere that received it.
The split brain patient would fixate on a dot in the centre of a screen while information was prevented to either the left or right visual field and would then be asked to make responses with either their left hand (right hem) or right hand or verbally (left hem).
If the patient was flashed a picture of a dog to the right visual field and asked what they saw, they would answer dog. However if a picture of a cat was flashed to the visual field, the patient would say they saw nothing.
This is because from the left visual field info is processed by the right hemisphere, which can see the picture, but as it has no language centre, cannot respond verbally.
The left hemisphere, which does have a language centre, does not receive info about seeing the pic therefore cannot say that they have seen it.
Split brain continued
Sperry and Gazzaniga were the first to study the capabilities of split brain patients. To test the capabilities of the separated hemispheres, they were able to send visual info to just one hemisphere at a time in order to study hemispheric lateralization.
Left hemisphere is responsible for speech and language, and the right hemisphere is responsible for visual-spatial processing and facial recognition.
Evaluate strength of split brain (new abilities)
Split-brain patients may develop new abilities.
For example, a patient known as J.W. developed the capacity to speak about information presented to either hemisphere.
This shows that his lateralisation was not fixed.
This supports the idea that lateralisation is determined by use and the brain can adapt to new requirements.
Evaluate criticism of split brain (rare)
Split brain research has limitations as patients who have had this procedure are rare.
The procedure is rarely carried out nowadays, and many studies only included a few participants or even just one.
These patients may have had underlying physical disorders, or there may have been some intact nerve fibres remaining.
This means the results of studies are not always replicated, and it may be unwise to draw general conclusions from them.
Evaluate criticism of lateralisation (age)
However, lateralisation is not fixed but changes with age for many types of tasks.
Healthy older adults have less lateralisation of function, using both hemispheres more as they get older.
Research found that language lateralisation increased during childhood and adolescence, but decreased steadily after age 25.
This suggests that older people’s brains recruit both hemispheres to increase their processing power, perhaps to compensate for age related cognitive decline.
Evaluate criticism of lateralisation (RH/LH)
Language may not be restricted to the left hemisphere but differs between individuals.
Right handed people generally develop their language centres in the left hemisphere, but left-handed people may have them on either side or both.
For this reason neurosurgeons find out which hemisphere is dominant and contains language centres in an individual patient before carrying out treatment to minimise cognitive side effects.
This means we shouldn't generalise or make assumptions about the lateralisation of language centres in individuals.
refers to the brain’s ability to modify its own structure and function as a result of experience. Researched used to believe that changes in the brain only took place during infancy and childhood but recent research has demonstrated that the brain continues to create new neural pathways and alter existing ones to adapt to new experiences.
Plasticity as a result of life experience
People gain new experiences, nerve pathways that are used frequently develop stronger connections, whereas neurons that are rarely or never used eventually die.
Brain is able to constantly adapt to a changing environment. However, there is also a natural decline in cognitive functioning with age that can be attributed to changes in the brain.
60 year olds taught juggling skills found an increase in grey matter in visual cortex, when practicing stopped, these changes were reversed.
Playing video games
Makes many different complex cognitive and motor demands.
Research compared a control group with a video game training group that was trained for 2 months for at least 30 mins per day on super mario.
Found a significant increase in grey matter in various brain areas including the cortex, hippocampus and cerebellum.
This increase was not evident in the control group that did not play super mario.
Researchers concluded that video game training had resulted in new synaptic connections in brain areas involved in spatial navigation, strategic planning, working memory and motor performance.
Research compared 8 practitioners of Tibetan meditation with 10 student volunteers with no previous meditation experience.
Both groups were fitted with electrical sensors and asked to meditate for short periods.
Electrodes picked up much greater activation of gamma waves in the monks.
Students only showed a slight increase in gamma wave activity while meditating.
Research concluded that meditation not only changes the workings of the brain in the short term by the monks having greater gamma rays even before they started.
refers to the recovery of abilities and mental processes that have been compromised as a result of brain injury or disease. Moving functions from a structurally damaged area of the brain after trauma to other undamaged areas.
Wall first identified what he called ‘dormant synapses’ in the brain.
These are synaptic connections that exist anatomically but their function is blocked.
Under normal conditions these synapses may be ineffective because the rate of neural input to them is too slow for them to be activated.
However, increasing the rate of input to these synapses, as would happen when a surrounding brain area becomes damaged, can then open or unmask these dormant synapses.
The unmasking of dormant synapses can open connections to regions of the brain that are not normally activated, creating a lateral spread of activation which, in time gives way to development of new structures.
Are unspecialised cells that have the potential to give rise to different cell types that carry out different functions, including take on the characteristics.
3 views on how stem cells might work to provide treatments for brain damage caused by injury or dying cells.
First view is that stem cells implanted into the brain would directly replace dead or dying cells.
A second possibility is that transplanted stem cells secrete growth factors that somehow rescue the injured or dying cells.
Transplanted cells form a neural network, which links an uninjured brain site, where new stem cells are made, with the damaged region of the brain.
Evaluate criticism of FP (age)
Functional plasticity reduces with age so adults need to develop compensatory behavioural strategies to deal with cognitive deficits, such as writing lists of seeking social support.
However, adults can still show functional recovery with intense restraining and extensive practice.
But the capacity for neural reorganisation is much greater in children than adults.
Evaluate strength of plasticity (animal studies)
Animal studies support plasticity in response to an enriched environment.
Kemperman found that rats kept in complex environments developed more new neurons than rats kept in lab cages.
In particular, they showed an increase in neurons in the hippocampus, which is associated with learning and navigation.
This supports the idea that the number of new neurons can change in adult animals in response to environmental stimulation.
Evaluate strength of plasticity (taxi drivers)
London taxi drivers also demonstrate plasticity.
Research measured the grey matter in taxi drivers brains using MRI scanning, and found a positive correlation between the size of their posterior hippocampus and how long they had worked as a taxi driver.
This was a way of operationalising their navigational experience.
So it seems the more navigational experience the drivers had, the larger their posterior hippocampus had become, supporting plasticity in response to experience.
Evaluate strength of Recovery (rats TBI)
Stem cells have helped rats to recover from traumatic brain injury TBI.
In a controlled experiment, rats given transplants of stem cells into their brains developed more neuron-like cells in the area of the injury than control rats.
Also, stem cells were observed to have migrated to the area of injury.
This suggests that stem cells could be actively involved in recovery from TBI, at least in rats.
A pattern of behaviour that occurs or recurs approximately every 24 hours, which is set and reset by environmental light levels. It is described as free running. An example is sleep wake cycle; alternating states of sleep and waking dependent on the 24 hour circadian cycle.
- circadian rhythms are driven by our body clocks, found in all of the cells of the body, and synchronised by the master pacemaker, the suprachiasmatic nuclei found in the hypothalamus.
- light provides the primary input to the system, setting the body clock to the correct time known as photoentrainment.
- mammals have light sensitive cells within the eye acting as brightness detectors; sending messages input light levels to the SCN.
- SCN then coordinates the circadian systems activity.
- light and darkness are the external signals that determine when we feel the need to sleep and when to wake up.
- Circadian rhythm dips and rises at different times of the day with the strongest sleep drive at 2-4am, 1-3pm
- sleepiness we experience during these dips is less intense if there is sufficient sleep, more intense when we are sleep deprived.
sleep and wakefulness are also determuned by homeostatic control
- when awake for a long period of time, homeostasis tells us that the need for sleep is increasing due to the amount of energy used up during wakefulness. This homeostatic drive for sleep increases gradually throughout the day.
- Circadian systems keeps us awake as long as there is daylight, when dark we fall asleep.
Other circadian rhythms
core body temp is at its lowest around 36 degrees celsius at about 4.30am and at its highest about 38 degrees celsius around 6pm.
- sleep occurs when the core temp begins to drop and body temp starts to rise during last hours of sleep promoting a feeling of alertness in the morning.
- Many feel sleepy in the afternoon because there is a small dip in body temp around 2pm and 4pm.
- production and release of melatonin from the pineal gland in the brain follows a circadian rhythm, with peak levels occurring during the hours of darkness.
- Activating chemical receptors in the brain, melatonin encourages feelings of sleep. When it is dark, more melatonin is produced when it is light, the production of melatonin drops and the person wakes.
Case study: Siffre
- subjected himself to long periods of time living underground to study his own circadian rhythms
- had no external cues, no daylight or clocks.
- woke and ate and slept when he felt appropriate to
- internal body clock influenced his behaviour
Evaluate strength of CR (drugs)
A real world application of circadian rhythms is chronotherapeutics.
To be most effective, drugs need to be released into the body at the optimal time.
For example, the risk of heart attack is greatest in the early morning.
This has prompted development of novel drug delivery systems so that the drug is released into the bloodstream during the vulnerable period.
Evaluate strength of CR (siffre age)
Evidence for a free running circadian rhythm comes from studies by cave explorer siffre.
During 6 months in a cave in texas with no daylight, clocks or radio, his circadian rhythm settled to just over 24 hours, but with some dramatic variations
At age 60, his circadian rhythm had slowed down, sometimes stretching to 48 hours.
This shows that the circadian rhythm is not dependent on light or social cues and can vary with age.
evaluate criticism of CR (individual diff)
There are individual differences in circadian rhythms.
The cycle length can vary from 13 to 65 hours.
Also morning people prefer to rise early and go to bed early, whereas evening people prefer to wake and go to bed later.
So individuals seem to have innate differences in their cycle length and onset.
evaluate criticism of CR (temp)
Temperature may be more important than light in setting the body clock.
It seems the SCN transforms info about light levels into neural messages that set the body’s temperature.
Research found that fluctuations in body temperature cause tissues to become active or inactive.
So, although the SCN responds to light, the circadian fluctuation of body temperature may actually control the other biological rhythms.
Are cycles that last less than 24 hours, such as the cycle of sleep stages occurring throughout the night, or BRAC
- A pattern of alternating rapid eye movement and non rapid eye movement sleep, consisting of stages 1 through to 4.
- This cycle repeats itself about every 90-100 minutes throughout the night.
- A complete cycle consists of a progression through the 4 stages of NREM sleep before entering final stage of REM.
- Recorded from electrical activities of the brain, with each stage showing a different EEG pattern.
- As the person enters deep sleep, their brainwaves slow and breathing and heart rate increases. During stage 5 REM, the EEG resembles that of an awake person adn dreaming occurs most here.
Outline the sleep stages
- stage 1= light sleep, muscle activity slows down with occasional muscle twitching.
- stage 2= breathing pattern and heart rate slows. Slight decrease in body temp.
- stage 3= deep sleep begins, brain begins to generate slow delta waves.
- stage 4= very deep sleep, rhythmic breathing, limited muscle activity, brain produces delta waves.
- stage 5= REM. Brainwaves speed up and dreaming occurs, muscles relax and heart rate increases. Breathing is shallow and rapid.
Basic Rest Activity Cycle
- Kleitman referred to the 90 minute cycle found during sleep as the BRAC. However, kleitman also suggested that this rhythm cycle also continues during the day, even when we are awake.
- The difference during the day, rather than moving through sleep stages is we move progressively from a state of alertness into a state of physiological fatigue every 90 minutes.
- Research suggests that the himan mind can focus for a period of about 90 minutes and towards the end of these 90 minutes the body begins to run out of 90 resources, resulting in loss of concentration, fatigue and hunger.
- For example, coffee breaks allows workers to divide sessions into 90 minute phases and is repeated in the afternoon with cat naps more likely in the afternoon.
rhythms that have a duration of over 24 hours, and may be weekly, monthly or even annually like the monthly menstrual cycle in women.
- male testosterone levels are elevated at weekends and young couples report more sexual activity at weekends than on weekdays, the frequency of births is lower at weekends than on wednesdays
- A woman's menstrual cycle lasts about one month
- however, there are variety in the length of this cycle with some women experiencing a relatively short 23 day cycle whereas others have a cycle as long as 36 days. The average is around 28 days.
- This cycle is regulated by hormones, which either promote ovulation or stimulate the uterus for fertilisation. Ovulation occurs roughly halfway through the cycle and lasts for 16-32 hours.
- After the ovulatory phase, progesterone levels increase in preparation for the possible implantation of an embry in the uterus.
- In most animals the rhythms are related to the seasons for example migration as a response to lower temperatures and decreased food sources in winter.
- In humans research suggests a seasonal variation in mood in humans especially in women, with some people becoming severely depressed during the winter months (seasonal affective disorder).
- The winter is also associated with an icnrease in heart attacks, which varies seasonally and peaks in winter. Mosr deaths occuring in january according to a recent study.
Evaluate strength for ultra (performers)
Research support for the BRAC comes from studies of elite performers.
Research found that elite violinists generally practice for 90 minutes at a time, and often nap between practice sessions.
Research found the same pattern among other musicians, athletes, chess players and writers.
This supports the existence of a 90 min ultradian cycle of alertness and fatigue.
Evaluate strength for infra (finding mates)
The menstrual cycle affects mate choice around ovulation, as women prefer more 'masculinised' faces.
These may represent good genes for short term liaisons, with mroe likelihood of conception.
In contrast, women generally prefer slightly 'feminised' male faces when picking a partner for long term relationships, as they may represent kindness and cooperation.
This shows how a hormonally controlled rhythm may also impact behaviour.
Evaluate weaknesses of infra (regulated by exog)
The menstrual cycle can also be controlled by exogenous cues.
When several women of childbearing age live together and do not take oral contraceptives, their menstrual cycles tend to synchronise.
Studies applied daily sweat samples from one group of women to the upper lips of women in a separate group, and their menstrual cycles become synchronised.
This suggests that a woman's menstrual cycle can be regulated by pheromones from other women as well as her own pituitary hormones.
Evaluate weakness of ultra (different sleeps)
Individual differences in sleep patterns may be biologically determined.
Research found large differences between individuals' sleep patterns, which were consistent over 11 nights in a controlled sleep lab.
Individuals also respondedvery differently to 36 hour periods of sleep deprivation.
This suggests that sleep patterns may be at least partially determined by genes.