Further Biopsychology Flashcards
(30 cards)
Bio: (T1) Divisions of the nervous system: Describe the the nervous system in terms of its major divisions - Outline the central nervous system (CNS).
The central nervous system (CNS) is made up of the brain and spinal cord.
The brain receives information from sensory receptors and sends messages to muscles and glands. It is the centre of all conscious awareness and is divided into different lobes with different functions. It contains the cerebrum which makes up about 85% of the total mass.
The forebrain is divided into 2 parts.
The diencephalon contains the:
Thalamus: concerned with relaying sensory information from the brainstem to the cortex.
Hypothalamus: controls basic functions such as hunger, thirst, sexual behavior; also controls the pituitary gland.
The cerebral hemispheres control higher level cognitive and emotional processes:
The limbic system is involved in learning, memory and emotions
The basal ganglia is involved in motor activities and movement
The neocortex/cerebral cortex is involved with planning, problem-solving, language, consciousness and personality
The spinal cord is an extension of the brain that is responsible for reflex actions. It allows the brain to monitor processes such as breathing and to control voluntary movements.
The hindbrain (pons, medulla, cerebellum) is a continuation of the spinal cord carrying on into the bottom of the brain – the brain stem – mainly composed of sensory and motor neurons. The cerebellum controls movement and motor coordination.
Bio: (T1) Divisions of the nervous system: Describe the the nervous system in terms of its major divisions - Outline peripheral nervous system (PNS) (semocratic and autocratic).
Peripheral (autonomic and somatic):
The portion of the nervous system that is outside the brain and spinal cord. The primary function of the peripheral nervous system is to connect the brain and spinal cord to the rest of the body and the external environment.
The peripheral nervous system transmits information to and from the CNS.
This is accomplished through nerves that carry information from sensory receptors in the eyes, ears, skin, nose and tongue, as well as stretch receptors and nociceptors in muscles, glands and other internal organs.
The PNS is made up of 31 spinal nerves which radiate out from the spinal cord and can be divided into the:
Somatic Nervous System:
The somatic nervous system controls voluntary movements, transmits and receives messages from the senses and is involved in reflex actions without the involvement of the CNS so the reflex can occur very quickly.
Somatic Nervous System (SNS) connects the central nervous system with the senses and is composed of:
Sensory nerve pathways bring information to the CNS from sensory receptors, dealing with touch, pain, pressure, temperature etc.
Motor nerve pathways which control bodily movement by carrying instructions towards muscles
Autonomic Nervous System:
Autonomic Nervous System (ANS) regulates involuntary actions such as bodily arousal (how ‘excited’ or relaxed we are), body temperature, homeostasis, heart rate, digestion and blood pressure. Composed of 2 parts:
The sympathetic nervous system that is involved in responses which help us deal with emergencies. It slows bodily processes that are less important in emergencies such as digestion. The sympathetic ANS leads to increased arousal: e.g. increase in heart rate and blood pressure, pupil dilation, reduction in digestion and salivation.
The parasympathetic nervous system that relaxes the individual once the emergency has passed (eg. slows the heart rate down and reduces blood pressure) and conserves the body’s natural activity by decreasing activity/maintaining it. The parasympathetic ANS leads to decreased arousal.
- note: that the automatic nervous system is divided into the sympathetic nervous system (SNS) and the parasympathetic nervous system (PSNS).
The SNS:
- increases heart rate.
- releases glucose.
- reduces activity within the stomach.
The SNS is the body’s alert system. (Fight or flight response).
The PSNS:
- decreases heart rate.
- increases stomach activity.
- stores glucose.
The PSNS is sometimes referred to as the ‘rest and digest’ system because its role is to relax the body by counteracting the effects of SNS activation.
Bio: (T2) structures and processes: Describe the process of synaptic transmission and neurotransmitters.
The process of synaptic transmission:
Neurotransmitters (excitation and inhibition)
The nervous system is composed of 100 billion cells called neurons. Although different types of neurons vary in size and function they all operate in the same way – passing on messages via electrical and chemical (neurotransmitter) signals.
Neurons lie adjacent to each other but are not connected. When an electrical signal reaches the axon terminals, molecules of neurotransmitters are released across the synaptic gap (the gap separating one neuron from another) and then attach to post-synaptic receptors on the adjacent neuron. This will then trigger an electrical impulse in the adjacent cell.
During synaptic transmission, the action potential (an electrical impulse) triggers the synaptic vesicles of the pre-synaptic neuron to release neurotransmitters (a chemical message).
These neurotransmitters diffuse across the synaptic gap (the gap between the pre and post-synaptic neurons) and bind to specialised receptor sites on the post-synaptic neuron.
The action of neurotransmitters at synapses can be:
Excitatory – make a nerve impulse more likely to be triggered: for example, dopamine or serotonin which produce states of excitement/activity in the nervous system and in our mental state/behavior.
Inhibitory - make a nerve impulse less likely to be triggered: for example, GABA calms activity in the nervous system and produces states of relaxation (as with anti-anxiety medication such as Valium).
Bio: (T2) structures and processes: Describe the influence of the two major systems of biological structures on our behaviour.
Biological structures:
Two major systems of the human body which biological psychologists are interested in are the nervous system and the endocrine system.
The nervous system uses electric currents to pass messages along nerves and chemicals to pass messages from one nerve to the next across a gap called the synapse.
The endocrine system is based on chemicals passing through the blood from one organ to ‘target’ sites. These chemicals are hormones and they are produced in glands. For example, you know of one called adrenaline which is made in the adrenal glands. It is used at synapses where the chemical noradrenaline is being used to pass messages from one neurone to another or to a gland such as the heart etc.
The peripheral nervous system is made up of the somatic nervous system, which communicates between the CNS and the muscles and skin, and the autonomic nervous system (ANS), which involves unconscious control of various glands. Knowledge of the autonomic nervous system will be very important when you go on to study the stress response.
Bio: (T2) structures and processes: Other biological structures required by the specification include: Briefly outline the role of the central nervous system and the endocrine system.
- The central nervous system (CNS) = The section of the nervous system that’s made up of the brain and the spinal chord. Also what causes you to reflexively jerk your hand away from something, such as heat, before you even perceive the temperature.
- Endocrine System = The system that’s made up of a set of glands that secrete hormones into your blood stream. + Pituitary Gland Also known as the ‘“master gland,” it secretes hormones which often signal other glands in the Endocrine System.
Your endocrine system: Makes hormones that control your moods, growth and development, metabolism, organs, and reproduction. Controls how your hormones are released.
Bio: (T2) structures and processes: Outline the role of the neuron and the three specific types.
The neurone = Neurons (also called neurones or nerve cells) arethe fundamental units of the brain and nervous system, the cells responsible for receiving sensory input from the external world, for sending motor commands to our muscles, and for transforming and relaying the electrical signals at every step in between.
The three types of neuron include:
1.Sensory neurons:
Sensory neurons are the nerve cells that are activated by sensory input from the environment - for example, when you touch a hot surface with your fingertips, the sensory neurons will be the ones firing and sending off signals to the rest of the nervous system about the information they have received.
The inputs that activate sensory neurons can be physical or chemical, corresponding to all five of our senses. Thus, a physical input can be things like sound, touch, heat, or light. A chemical input comes from taste or smell, which neurons then send to the brain.
- Motor neurons:
Motor neurons of the spinal cord are part of thecentral nervous system(CNS) and connect to muscles, glands and organs throughout the body. These neurons transmit impulses from thespinal cordto skeletal and smooth muscles (such as those in your stomach), and so directly control all of our muscle movements.
- Relay Neurons:
A relay neuron (also known as an interneuron) allows sensory and motor neurons to communicate with each other. Relay neurons connect various neurons within the brain and spinal cord, and are easy to recognize, due to their short axons.
Alike to motor neurons, interneurons are multipolar. This means they have one axon and several dendrites.
As well as acting as a connection between neurons, interneurons can also communicate with each other through forming circuits of differing complexities.
Bio: (T3) Functions of the endocrine system: Describe the function of the endocrine system, including glands and hormones
The hypothalamus is connected to the pituitary gland and is responsible for stimulating or controlling the release of hormones from the pituitary gland. Therefore, the hypothalamus is the control system which regulates the endocrine system.
The pituitary gland is sometimes known as the master gland because the hormones released by the pituitary gland control and stimulate the release of hormones from other glands in the endocrine system. The pituitary gland is also divided into the anterior (front) and posterior (rear) lobes (see right), which release different hormones.
A key hormone released from the posterior lobe is oxytocin (often referred to as the ‘love hormone’) which is responsible for uterus contractions during childbirth. A key hormone released from the anterior lobe is adrenocortical trophic hormone (ACTH) which stimulates the adrenal cortex and the release of cortisol, during the stress response.
The main hormone released from the pineal gland is melatonin, which is responsible for important biological rhythms, including the sleep-wake cycle.
The thyroid gland releases thyroxine which is responsible for regulating metabolism. People who have a fast metabolism typically struggle to put on weight, as metabolism is involved in the chemical process of converting food into energy.
The adrenal gland is divided into two parts, the adrenal medulla and the adrenal cortex. The adrenal medulla is responsible for releasing adrenaline and noradrenaline, which play a key role in the fight or flight response. The adrenal cortex releases cortisol, which stimulates the release of glucose to provide the body with energy while suppressing the immune system.
Males and females have different sex organs, and in males the testes release androgens, which include the main hormone testosterone. Testosterone is responsible for the development of male sex characteristics during puberty while also promoting muscle growth. In females, the ovaries release oestrogen which controls the regulation of the female reproductive system, including the menstrual cycle and pregnancy.
Bio: (T3) Functions of the endocrine system: Describe the flight or fight response, including the use of adrenaline.
Describe the flight or fight response, including the use of adrenaline.
The fight or flight response including the role of adrenaline:
The fight or flight response is a sequence of activity within the body that is triggered when the body prepares itself for defending or attacking (fight) or running away to safety (flight).
Stress is experienced when a person’s perceived environmental, social and/or physical demands exceed their perceived ability to cope.
The stress response (otherwise known as the ‘fight or flight’ response) is hard-wired into our brains and represents an evolutionary adaptation designed to increase an organism’s chances of survival in life-threatening situations.
The fight or flight response involves two major systems
The Sympathomedullary Pathway – deals with acute (short-term, immediate) stressors such as personal attack.
The Pituitary-Adrenal System – deals with chronic (long-term, on-going) stressors such as a stressful job.
The Sympathomedullary Pathway (SAM):
The hypothalamus also activates the adrenal medulla. The adrenal medulla is part of the autonomic nervous system (ANS).
The ANS is the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These activities are generally performed without conscious control.
The adrenal medulla secretes the hormone adrenaline. This hormone gets the body ready for a fight or flight response. Physiological reaction includes increased heart rate.
Adrenaline lead to the arousal of the sympathetic nervous system and reduced activity in the parasympathetic nervous system.
Adrenaline creates changes in the body such as decreases (in digestion) and increases (sweating, increased pulse and blood pressure).
Once the ‘threat’ is over the parasympathetic branch takes control and brings the body back into a balanced state.
No ill effects are experienced from the short-term response to stress and it further has survival value in an evolutionary context.
Bio: (T4): Localisation of function in the brain and hemispheric lateralisation: Explain what is meant by Localisation of function in the brain and hemispheric lateralisation.
- Localisation of function in the brain:
Localisation of function is the theory that different areas of the brain are responsible for different behaviors, processes or activities. It contrasts with the holistic theory of the brain. If a certain area of the brain becomes damaged, the function associated with that area will also be affected.
The link between brain structures and their functions (e.g. language, memory, etc.) is referred to as brain localisation.
The brain is divided into 2 hemispheres – left and right.
- Hemispheric lateralisation:
Hemispheric lateralisation concerns the fact that the brain’s 2 hemispheres are not exactly alike and have different specialisms. For example, the left hemisphere is mainly concerned with speech and language and the right with visual-motor tasks. Broca (1861) found that damage to the left hemisphere led to impaired language but damage to the same area on the right hemisphere did not.
Investigations into the corpus callosum began when doctors severed patients’ corpus callosum in an attempt to prevent violent epileptic seizures. Sperry (1968) tested such split-brain patients to assess the abilities of separated brain hemispheres.
Bio: (T4): Localisation of function in the brain and hemispheric lateralisation: Localisation of the brain: outline the Somatosensory Area and the Motor Area of the brain.
- The Motor Area:
The motor area is located in the frontal lobe and is responsible for voluntary movements by sending signals to the muscles in the body. Hitzig and Fritsch (1870) first discovered that different muscles are coordinated by different areas of the motor cortex by electrically stimulating the motor area of dogs. This resulted in muscular contractions in different areas of the body depending on where the probe was inserted. The regions of the motor area are arranged in a logical order, for example, the region that controls finger movement is located next to the region that controls the hand and arm and so on.
- The Somatosensory Area:
The somatosensory area is located in the parietal lobe and receives incoming sensory information from the skin to produce sensations related to pressure, pain, temperature, etc. Different parts of the somatosensory area receive messages from different locations of the body. Robertson (1995) found that this area of the brain is highly adaptable, with Braille readers having larger areas in the somatosensory area for their fingertips compared to normal sighted participants.
Bio: (T4): Localisation of function in the brain and hemispheric lateralisation: Localisation of the brain: Localisation of the brain: Describe the different centres of the brain - Incuding visual, auditory and language.
- Visual Centers
Processing of visual information starts when light enters the eye and strikes photoreceptors on the retina at the back of the eye. Nerve impulses then travel up the optic nerve to the thalamus and are then passed on to the visual cortex in the hindbrain.
The right hemisphere’s visual cortex processes visual information received by the left eye and vice-versa. The visual cortex contains different regions to do with colour, shape, movement, etc.
- Auditory Centers:
Processing of auditory information (sound) begins in the inner ear’s cochlea where sound waves are converted into nerve impulses which travel along the auditory nerve to the brain stem (which decodes duration and intensity of sound) then to the auditory cortex which recognises the sound and may form an appropriate response to that sound.
- Language Centers:
Broca’s Area is generally considered to be the main centre of speech production. The neuroscientist after whom this brain area is named found that patients with speech production problems had lesions (damage) to this area in their left hemisphere but lesions in the right hemisphere did not cause this problem. More recent research indicates Broca’s area is also involved with performing complex cognitive tasks (e.g. solving maths problems).
Wernicke’s area is also in the left hemisphere and is concerned with speech comprehension. The neuroscientist after whom this brain area is named found that lesions in this brain area could produce but not understand/comprehend language. Wernicke’s area is divided into the motor region (which controls movements of the mouth, tongue and vocal cords) and the sensory area (where sounds are recognised as language with meaning).
- Broca’s and Wernicke’s areas are connected by a loop which ties together language production and comprehension.
Bio: (T4): Localisation of function in the brain and hemispheric lateralisation: localisation of the brain: outline the key study of Phineas Gage.
Localisation of function is the idea that certain functions (e.g. language, memory, etc.) have certain locations or areas within the brain. This idea has been supported by recent neuroimaging studies, but was also examined much earlier, typically using case studies.
One such case study is that of Phineas Gage, who in 1848 while working on a rail line, experienced a drastic accident in which a piece of iron went through his skull. Although Gage survived this ordeal, he did experience a change in personality, such as loss of inhibition and anger. This change provided evidence to support the theory of localisation of brain function, as it was believed that the area the iron stake damaged was responsible for personality.
Phineas Gage was in an accident which caused him to lose part of his frontal lobe which altered his personality – The frontal lobe may play a role in mood regulation therefore localisation theory is correct.
Severity of the Brain Damage outlined in studies:
In a 1994 study, researchers utilized neuroimaging techniques to reconstruct Phineas Gage’s skull and determine the exact placement of the injury. Their findings indicate that he suffered injuries to both the left and right prefrontal cortices, which would result in problems withemotional processingand rationaldecision-making.
In 2012, new research estimated that the iron rod destroyed approximately 11% of the white matter in Gage’s frontal lobe and 4% of his cerebral cortex.
Phineas Gage’s Impact on Psychology:
Gage’s case had a tremendous influence on early neurology. The specific changes observed in his behavior pointed to emerging theories about the localization of brain function, or the idea that certain functions are associated with specific areas of the brain.
Bio: (T4): Localisation of function in the brain and hemispheric lateralisation: Hemispheric lateralisation: Split Brain Research: Briefly describe the split brain research conducted by Sperry et al.
Sperry (1968)
Aim: To assess the abilities of separated brain hemispheres.
Procedure:
Participants sat in front of a board with a horizontal rows of lights and were asked to stare at the middle point. The lights then flashed across their right and left visual field. Participants reported lights had only flashed up on the right side of the board.
Findings:
When their right eye was covered and the lights were flashed to the left side of their visual field they claimed not to have seen any lights at all. However, when asked to point at which lights had lit up they could do.
Conclusion:
This shows that participants had seen the lights in both hemispheres but that material presented to the left eye could not be spoken about as the right hemisphere (which receives information from the left eye) has no language centre and thus cannot speak about the visual information it has received. It can communicate about this in different non-visual ways, however – e.g. participants could point at what they had seen.
This proves that in order to say that one has seen something the region of the brain associated with speech must be able to communicate with areas of the brain that process visual information.
Bio: (T4): Localisation of function in the brain and hemispheric lateralisation: Briefly provide an evaluation for the Localisation of the brain and hemispheric lateralisation explanations. (+A03).
Summary in support of explanation:
> Research support from case studies – Phineas Gage was in an accident which caused him to lose part of his frontal lobe which altered his personality – The frontal lobe may play a role in mood regulation therefore localisation theory is correct.
> Gender differences have been found with women possessing larger Broca’s and Wernicke’s areas than men, presumably as a result of women’s greater use of language.
Summary in against explanation:
> More recent research has contradicted Sperry’s original claim that the right hemisphere could not process even basic language. For example, the case study of JW found that after a split-brain procedure he developed the ability to speak out of his right hemisphere which means that he can speak about information presented to either his left or his right visual field.
> Because split-brain patients are so rare, findings as described above were often based on samples of 2 or 3, and these patients often had other neurological problems which might have acted as a confounding variable. Also, patients did not always have a complete splitting of the 2 hemispheres. These factors mean findings should be generalised with care.
Bio: (T4+): Other functions of the brain: Explain what is meant by ‘Brain plasticity’.
Brain Plasticity:
Plasticity is the brains tendency to change and adapt (functionally and physically) as a result of experience and new learning. During infancy, the brain experiences a rapid growth in the number of synaptic connections. As we age, rarely used connections are deleted and frequently used connections are strengthened (synaptic pruning).
Although this was traditionally associated with changes in childhood, recent research indicates that mature brains continue to show plasticity as a result of learning.
Learning and new experiences cause new neural pathways to strengthen whereas neural pathways which are used infrequently become weak and eventually die.
Kuhn (’14) found that playing video games for 30+ minutes per day resulted in increased brain matter in the cortex, hippocampus and cerebellum. Thus, the complex cognitive demands involved in mastering a video games caused the formation of new synaptic connections in brain sites controlling spatial navigation, planning, decision-making, etc.
Bio: (T4+): Other functions of the brain: Explisn what is meant by ‘functional recovery of the brain’ after brain trauma.
Functional recovery is the idea that following physical injury or other forms of trauma, unaffected areas of the brain can adapt to compensate for those that are damaged.
- Case studies of stroke victims who have experienced brain damage and thus lost some brain functions have shown that the brain has an ability to re-wire itself with undamaged brain sites taking over the functions of damaged brain sites. Thus, neurons next to damaged brain sites can take over at least some of the functions that have been lost.
Functional recovery is an effect of brain plasticity which is thought to operate in 2 main ways.
Neuronal unmasking. Wall (’77) noticed the brain contained ‘dormant synapses’ – neural connections which have no function. However, when brain damage occurs these synapses can become activated and open up connections to regions of the brain that are not normally active and take over the neural function that has been lost as a result of damage.
Stem cells are unspecialised cells which can become specialised to carry out different types of task: for example, taking on the behavior of neurons in the brain.
There is a negative correlation between functional recovery and age: i.e. young people have a high ability to recover which declines as we age.
Level of education (associated with a more active, neurologically well-connected brain) is positively correlated with speed of recovery from traumatic brain injuries.
Bio: (T5): Ways of studying the brain 1 - scanning techniques: Explain Functional magnetic resonance imaging (fMRI) - and give a strength/ weakness.
Functional magnetic resonance imaging (fMRI):
A brain scanner which measures increased blood flow to brain sites when individuals are asked to perform cognitive/physical tasks. Increased blood flow indicates increased demand for oxygen in that area.
This produces 3D images showing which parts of the brain are involved in a particular mental process, important for our understanding of localisation of function.
Thus, fMRI can help build up a map of brain localisation. For example, an fMRI scan could identify brain sites which received increased oxygen when a participant is asked to solve maths problems.
Strength:
Non-invasive – No insertion of instruments unlike PET and no exposure to radiation – Beneficial to the economy as there is no recovery time so people don’t have to be off work.
Limitation:
fMRI only measures blood flow – it cannot home in on the activity of individual neurons therefore it’s hard to tell exactly what brain activity is being represented on the screen – High likelihood that the findings will be misinterpreted as it doesn’t show activity like EEG/ERP.
Bio: (T5): Ways of studying the brain 2 - scanning techniques: Explain Electroencephalogram (EEGs) - and give a strength/ weakness.
Electroencephalogram (EEGs) Measures electrical activity in the brain using electrodes attached to the scalp, and measures how electrical activity in the brain varies over time/in different states (e.g. waking vs. asleep). EEG readings can detect epilepsy and Alzheimer’s.
4 basic brain wave patterns are (i) alpha – awake and relaxed, (ii) beta – awake and highly aroused or in REM (rapid eye movement sleep), (iii) delta – deep sleep, (iv) theta – light sleep.
Strength:
• Records brain activity over time and can, therefore, monitor changes as a person switches from task to task or one state to another (e.g. falling asleep).
Limitation:
• EEGs only monitor electrical activity in outer layers of the brain, therefore, cannot reveal electrical activity in deeper brain sites.
Bio: (T5): Ways of studying the brain 3 - scanning techniques: Explain Event-related potentials (ERPs) - and give a strength/ weakness.
ERP’s are very small voltage changes in the brain triggered by specific events or stimuli which are measured using an EEG.
Measures small voltages of electrical activity when a stimulus is presented. Because these small voltages are difficult to pick out from other electrical signals in the brain, the stimulus needs to be repeatedly presented, and only signals which occur every time the stimulus is presented will be considered an ERP for that stimulus.
ERPS are of 2 types: (i) sensory ERPS - those that occur within 100 milliseconds of stimulus presentation; (ii) cognitive ERPS – those that occur 100 milliseconds or more after stimulus presentation.
Strength:
• Non-invasive - No insertion of instruments unlike PET and no exposure to radiation – Virtually risk free and is avoidant of any danger to the brain itself.
Limitation:
Lack of standardisation in methodology between studies – Different groups will use varying averages on what neural activity they decide to filter out – Hard to replicate experiments and confirm findings in a peer review study.
Bio: (T5): Ways of studying the brain 4 : Explain Post-mortem examinations and give a strength/ weakness.
Brains from dead individuals who displayed cognitive abnormalities whilst alive can be dissected to check for structural abnormalities/damage: e.g. Broca’s area was discovered after dissections of patients who displayed speech abnormalities, and HM’s (Memory Topic) inability to store new memories was linked to lesions in his hippocampus. Neurological abnormalities have been linked to depression, schizophrenia, anti-social personality disorder, etc.
Strength
• Allow for detailed examinations and measurement of deep brain structures (e.g. the hypothalamus) not measurable by brain scans.
Limitation:
• Ethical issues – Deceased people are not able to provide informed consent such as HM because of his lack of short term abilities – There will be problems with replicability because future ethical guidelines will be stricter.
Bio: (T5): Ways of studying the brain - scanning techniques: list the 4 mentioned ways of studying the brain and recite a brief summary of each.
The 4 mentioned ways of studying the brain include:
- functional magnetic resonance imaging (fMRI).
- electroencephalogram (EEGs).
- Event-related potentials (ERPs).
- Post-mortem examinations.
Bio: (T6): Biological rhythms: provide a brief explanation and outline the differences between Circadian, infradian and ultradian rhythms.
The physiological processes of living organisms follow repetitive cyclical variations over certain periods of time. These bodily rhythms have implications for behavior, emotion and mental processes.
There are 3 types of bodily rhythms:
- Circadian rhythms: follow a 24-hour cycle: e.g. the sleep-waking cycle.
2.Ultradian rhythms: occur more than once a day: e.g. the cycles of REM and NREM sleep in a single night’s sleep.
- Infradian rhythms: occur less than once a day: e.g. menstruation (monthly) or hibernation (yearly).
Bio: (T6): Biological rhythms: Briefly explain the two main controllers of the biological rhythms.
All bodily rhythms are controlled by an interaction of:
- Endogenous pacemakers (EP’s). Internal biological structures that control and regulate the rhythm.
- Exogenous zeitgebers (time givers) (EZ’s). External environmental factors that influence the rhythm.
Bio: (T6): Biological rhythms: Outline the CIRCADIAN RHYTHMS and provide one example of research evidence.
Heart rate, metabolic rate, breathing rate and body temperature all reach maximum values in the late afternoon/early evening and minimum values in the early hours of the morning.
- If we reverse our sleep-waking pattern these rhythms persist. This indicates human bodies are evolved for activity in the day and rest at night and, indeed, being nocturnal or disrupting the circadian cycle is highly stressful and physiologically and psychologically harmful.
The EP controlling the sleep-waking cycle is located in the hypothalamus. Patterns of light and darkness are registered by the retina, travel up the optic nerves to where these nerves join (optic chiasma), and then pass into the superchiasmatic nucleus (SCN) of the hypothalamus. If this nerve connection is severed circadian rhythms become random.
Research evidence:
Ralph bred a group of hamsters to follow a (shortened) 20-hour circadian cycle. SCN cells were removed and transplanted into the brains of rat foetuses with normal rhythms. Once born, these rats adopted a 20-hour cycle. Their brains were then transplanted with SCN cells from 24-hour cycle hamsters and within a week their cycles had adopted this new 24 cycle.
