- Created by: 06eprice
- Created on: 12-08-19 14:04
The Nervous System
The nervous system coordinates voluntary and involuntary movements of an animal - receiving, responding to and transmitting signals around the body. It consists of two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS).
CNS = the processing centre:
- Brain - processes thoughts, emotions and is involved in main activities.
- Spinal chord - sends impulses to and from the brain.
PNS = connects the CNS to limbs and organs:
- Somatic nervous system - voluntary movement, skeletal muscles, etc.
- Autonomic nervous system - involuntary, digestion, respiration, heartrate, etc.
The autonomic NS = controls vital muscles and glands to maintain homeostasis:
- Sympathetic - releases adrenaline to coordinate the fight or flight response.
- Parasympathetic - slows down/reverses effects of sympathetic and restores homeostasis.
Stage 1) Nerve impulses are sent down the axon ending, causing vesicles to release neurotransmitters into the synapse.
Stage 2) These neurotransmitters bind onto receptors of the next dendrite.
Stage 3) Summation occurs, in which neurotransmitters are either excited or inhibited - EPSP or IPSP. EPSP will excite the body, these are more likely to be refired (eg, adrenaline). IPSP will relax the body and calm it down, these are less likely to be refired (eg, seretonin).
Stage 4) Once summation has occured, neurotransmitters are released back into the synapse. They will either be re-uptaken or diffused into the synapse.
The Fight or Flight system
1) Our receptors detect a dangerous stimulus; this causes us stress and the information is sent to the hypothalamus.
2) The hypothalamus communicates our stress to the sympathetic nervous system.
3) The sympathetic system prepares us for a Fight or Flight situation by signalling to the adrenal medualla to release adrenaline into the bloodstream.
4) Adrenaline causes:
- Increased heart/breathing rate to supply oxygenated blood to our muscles
- Triggers the release of glucose to give us energy to run away or attack the threat
- Inhibits digestion to prevent any inconvenient urges whilst under threat
- Diverts blood from our stomach to our muscles to provide us with energy to fight or run
5) Once the threat has passed the parasympathetic system acts to reverse the effects of the sypathetic. Heart/breathing rate slows, digestion restarts and homeostasis is restored.
Gender differences in the Fight or Flight system
- Fight and flight research has only been carried out on males as women do not produce the response.
- Women 'tend and befriend' as they have higher levels of the bonding hormone, oxytocin.
- Not only does oxytocin reduce fear, but it programmes a women to protect her offspring: the best way to do this is to 'befriend' an enemy.
- Men too have been shown to become friendlier in stressful situations: human connections help in times of crisis so they become more cooperative.
Problems encountered when studying gender differences in a fight or flight situation:
Gender bias = some research only considers men and women as a whole, differences aren't taken into account. / Alpha bias = sometimes gender differences are exagerated, making findings invalid.
Not all women are nurturing and not all men are agressive, it is subjective on the person and generalisations shouldn't be made.
Long term stress - fight or flight
During long term periods of stress, a second systems called the HPA begins working more slowly. The system releases cortisol.
Cortisol provides energy and increases pain threshold. However, it also weakens the immune system and has negative long term affects.
Some work places have introduced meditation breaks, that allow stress levels to reduce so less cortisol is present in the bloodstream.
Hypothalamus = CRH ---> Pituitary glad = ACTH ---> Adrenal glands = Cortisol
The Endocrine System
Sends molecules (hormones) through the blood stream. Molecules are produced in glands around the body.
Hypothalamus = A brain region controlling the pituitary gland. Releases Leptin and CRH. Regulates body temp and ensures adequate food intake. Leptin gene released signals to hypothalamus to tell us to stop eating. Some overweight have a mutation in this gene so the hypothalamus cannot detect any Leptin, hence over-eating occurs.
Pituitary Gland = The 'master gland'. Releases FSH and ACTH. Secretes hormones that act upon other glands, such as growth hormones and oxytocin.
Thyroid Gland = Regulates internal conditions by releasing Thyroxin. Metabolism, growth and tempurature.
Parathyroids = Regulate calcium in the blood. Releases Parathyroid Hormone (PTH). Raises blood calcium by breaking down the bone.
Adrenal glands = Prepares body for fight or flight situations. Releases Cortisol and adrenaline. Provides body with energy, increases heart/breathing rate, etc.
Pancreas = Regulates blood sugar levels. Releases Insulin and Glucagon. Too high - Insulin released to convert Glucose into Glycogen. Too low - Glucagon released to convert Glycogen into Glucose.
Testis/Ovaries = Release either testosterone, or Oestrogen and Progesterone. Sperm production / voice breaking / sex drive / muscle strength / the menstural cycle.
Localisation in the brain
Localisation = certain areas of the brain are responsible for specific functions.
Frontal Lobe = personality, decision making, problem solving and emotions.
Motor Cortex = controls voluntary movement.
Sensory Cortex = processes sensory information (eg, smell, touch, taste).
Parietal Lobe = perception and making sense of the world.
Occipital Lobe = processes visual information.
Temporal Lobe = involved in hearing, memory and language.
Cerebellum = balance, posture and coordination.
Brainstem = signals between brain and body. Controls breathing, heart rate, swallowing, blood pressure and consciousness.
Wernicke's Area = language comprehension. Located left temporal.
Broca's Area = speech production. Located left frontal.
Localisation of function
Broca and Wernick:
During post mortem found damage to their patients left temporal lobes (Wernick's area - language comprehension) and left frontal lobes (Broca's area - speech production). The damage was evidence that these seperate areas in the brain served different functions.
Localisation of cortical functioning:
When reading, we use the visual cortex to see words and Wernick's area to understand them. If the connection between these two is broken, reading difficulties will emerge. This shows that seperate parts of the brain can also function together to carry out a task.
Gender and localisation:
Gender differences in localisation can explain the differences in our behaviours. Women have larger larger Broca's and Wernick's areas, meaning they overthink, talk more and are better at English than men (although womens language skills may be more advanced because they are social creatures, not the other way around). Men tend to be more logical and better at maths because of this.
Lateralisation of function
Lateralisation = certain hemispheres control specific functions.
Left hemisphere = controls right side of body, speech and language comprehension.
Right hemisphere = controls left side of body, creativity, spacial awareness and facial recognition.
Sperry's Split Brain research - intro
Investigated hemispheric lateralisation in split-brain patients.
1) The patients had epilepsy and under-went a corpus callosotomy in which the two hemispheres were seperated.
2) Due to the corpus callosum communication line being broken, Sperry was able to see the extent to which the hemispheres functioned by themselves.
3) He could then also analyse what functions they were specialised to.
Sperry's Spilt Brain research - method and results
Method 1 - pictures/info seperately presented to the left and right visual fields. Patients would be asked to describe it.
If shown to the right VF (left hemisphere), the patients would be able to describe it easily. If shown to the left VF (right hemisphere), the patient would not be able to produce a description.
Method 2 - an object placed in the patient's left or right hand and asked to describe what they felt.
Objects in right hand (left hemisphere) could be easily described. Those in the left hand (right hemisphere) couldn't be described.
Method 3 - image shown to left and right VF and patients asked to re-draw what they saw.
Images shown to left VF (right hemisphere) images would be neat and clear. Right VF (left hemisphere) images were poor.
Method 4 - shown initial image, followed by several more (one was identicle to initial image) then asked to identify which image was the identicle one.
Left VF (right hemisphere) patient would correctly identify it straight away. Right VF (left hemisphere) took much longer.
Conclusion - The two hemispheres have individual functions, but work together to carry out tasks. The left hemisphere (right VF) dominates in language and speech tasks, the right (left VF) excelled in visual tasks due to facial recognition, etc.
Evaluating Sperry's Spilt Brain research
- demonstrates the existance of hemispheric lateralisation through the dominance of each individual hemisphere in certain tasks.
- very controlled conditions (Standardisation) meaning results are highly reliable and replicable, giving us confidence in the findings.
- sample only consisted of 11 people so results are ungeneralisable and unrepresentative.
- the experimental group were compared to a control group with no history of epilepsy, so we cannot be sure if behaviours are due to epilepsy or having a split brain (control should have contained people with epilepsy and no split brain).
- controlled conditions mean the results lack external validity, making them inaccurate as they don't reflect how we would respond in a realistic environment.
The brains ability to alter its structure and function in response to new learning or trauma.
- Brain structure changes with environmental input, so everytime we learn something new synaptic connections and neural pathways are formed.
- The more you use a neural pathway the stronger it gets. The less you use it the weaker it gets, until it is deleted through synaptic pruning.
- The brain is malleable and constantly changes from birth, it is most malleable during infancy.
Research into Neuroplasticity - Maguire et al (2000):
- Examined the brain structure of London taxi drivers.
- MRI scanned 16 taxi drivers and 16 non-taxi drivers.
- The cab drivers had larger hippocampuses than the control group.
- In addition, the longer the subject had been a taxi driver, the larger his hippocampus was.
- This shows that the brain is plastic; the stucture physically adapts as new information regarding London driving routes are learnt.
- The taxi drivers are required to remember the names of roads meaning that neural pathways are constantly forming and growing stronger.
Functional recovery of the brain after trauma
The brain can adpat and repair itself after suffering damage. It does this through:
Neural unmasking = activating dormant synapses to open connections that compensate for a nerby damaged area and take over its function.
Axon sprouting = the growth of new axons to help repair damaged connections.
Recruitment of homologous areas = similar areas of the brain (but in the opposite hemisphere) will take over the function of damaged areas. Eg, if the Broca's area in the left frontal lobe was damaged, then corresponding tissue in the right hemisphere will take over its function over time and 'learn to talk'.
Factors affecting recovery of the brain
Age = the brain is most malleable during infancy so this is when functional recovery is most efficient. Studies have shown that patients over the age of 40 take longer to recover from trauma because their brains are less plastic.
EB - a 2 year old boy who had his left hemisphere removed due to a tumour. He was left unable to produce or understand speech. By 17 he could speak almost fluently, as his right hemisphere had taken over the function of his left.
Gender = women are more able to recover from trauma than men because their brains are less lateralised.
Ratcliffe et al (2007) - studied 300 patients with brain injuries. He tested patients responses to rehabilitation during the injury and a year after. Women did better in attention and language tests, men did better in visual tasks.
Education = people with higher levels of education are more likely to recover from trauma as their brains are used to change. They are likely to retain function due to increased cognitive capacity.
Schenider et al (2014) - 39% who had a qualification recovered. Only 10% of those who did not have a qualification made a recovery.
Extra studies to support Brain Plasticity
Costa et al:
Found that those who knew a second language had increased amounts of grey matter in their brain in comparison to those who were monolingual.
Davidson et al:
Found that Buddhist monks who meditated frequently had a greater activation of gamma waves in their brains, than those who didn't meditate.
Were shown to increase grey matter in the brain after participants played 30 minutes a day for 2 months.
The increased levels of gamma waves and grey matter, provide evidence for physical, structural changes to the brain as the environment changes and we learn new information: proving that our brains are plastic and adapt to our surroundings.
After trauma, the brain will heal itself through Spontaneous Recovery. When this process slows down, neurorehabilitation is required to help a patient make a full recovery.
Constraint Induced Movement Therapy (CIMT):
- Typically used for those recovering from strokes, or who have lost function of their limbs.
- It prevents patients from using their functioning limbs, forcing them to have to use their paralysed ones.
- This causes the brain to re-learn how to work the limbs, so each hemisphere can take over the function of the corresponding damaged tissue, or recover itself.
Wolf and Winstein et al (2008) - patients required to use paralysed limbs 6 hours a day for 2 weeks. Their brain function was measured before and after the therapy. All patients made improvements, proving that CIMT aids recovery of the brain.
Evaluating neuroplasticity and functional recovery
- research and studies have had practical applications in developing neurorehabilitation therapies.
- these therapies help to cure patients with brain damage, improving their quality of life and the economy (as more people are back in work and less using expensive healthcare).
- general info obtained from these studies give us more insight into how the brain functions, leading to extensive practical applications in therapy, etc.
- a lot of research is carried out on animals, which is unethical and cannot be accurately extrapolated to humans.
- in most studies brain function is measured after injury, not before, so we cannot be sure of the actual extent of recovery of the brain.
- these procedures have been done on very few people and so results cannot be accurately generalised: age, gender and the extent of brain damage should be taken into account.
- Neuroplasticity has negative maladaptiveconsequences such as phantom limb syndrome. This causes distressing sensations in missing limbs due to cortical reorganisation.
Our bodies have biological clocks called endogenous pacemakers. These synchronise with exogenous zeitgebers, which help to reset and regulate our clocks, allowing our bodies to coordinate with the outside world.
Biological rhythms are evolutionary functions. We are adapted to sleep at night and be conscious during the day. This is because there is better visiblility during the day: ideal hunting conditions. We also benefit from the vitamin D from the sun.
Endogenous pacemakers and exogenous zeitgebers regulate our biological rhythms.
There are 3 main rhythms:
1) Circadian - 24 hour cycle. Eg, sleep/wake cycle.
2) Ultradian - under 24 hour cycle, can occur several times a day. Eg, the stages of sleep.
3) Infradiun - over 24 hour cycle, weekly, monthly or annually. Eg, menstual cycle or SAD.
Internal body clocks that control our sleep cycle.
The Suprachiasmatic Nucleus (SCN):an example of an endogenous pacemaker. Known as the 'master clock', it is a bundle of cells in the hypothalamus that controls our sleep/wake cycle in a 24 hour rhythm.
How do EPs work?
1) light levels send signals to our optic nerves, where melanopsin is stored.
2) here, the melanopsin absorbs visible light and then communicates this info to the SCN.
3) the SCN responds to light signals and sends the info to the pineal gland.
4) the pineal glad can then recognise whether it is night or day and release or inhibit melatonin on this basis.
(Melatonin is a sleeping hormone. If light levels are high, the pineal gland inhibits its release to ensure we stay awake. If light levels are low, the pineal gland assumes it is night time, and will secrete the hormone to make us sleep).
An external cue that works alongside endogenous pacemakers to regulate our body clocks.
- acts as a reset to our body clock, by signalling that it is day time.
- it is absorbed by melanopsin to cause a decrease in melatonin levels: this wakes us up.
- food, meal times and social activities help to let our bodys know what time of day it is.
- for example, when people are jet lagged they still stick to normal routine as a way to re-sink their body clock.
Artificial light and melatonin pills are also zeitgebers. This is because they help to regulate when someone feels tired or alert, without the presence of natural light.
- Body clocks that function in a 24hour rhythm.
- An example of a circadian rhythm is the sleep/wake cycle.
- It dips and rises throughout the day. Our sleep drives are strongest at 1-3pm and 2-4am. These dips become more intense the more sleep deprived we are.
If we are awake for too long then homeostasis will make us sleep regardless of external cues (EZ), it will always override an imbalance of sleep to ensure our bodies are recharged. Likewise, if we have had enough sleep then homeostasis will wake us up.
Jet lag and overnight shift work are examples of interruptions to circadian rhythms. They cause tiredness and lack of concentration by putting endogenous pacemakers out of synch with exogenous zeitgebers (eg, working in the dark will cause issues with melatonin production).
Examples of other circadian rhythms: our core body temp (lowest at 4.30am and highest at 6pm) / our hormone production (melatonin released or inhibited from pineal gland as light levels change).
Circadian rhythms - case study
Michel Siffre, 1962:
Procedure = subjected himself to long periods of time in an underground cave. He had no external cues, and simply woke, ate and slept when he naturally felt the urge.
Findings = the first time he spent 61 days in the cave, resurfacing in September thinking it was August. The second time he spent 6 months in the cave, his natural circadian rhythm settled to 24 hours with occasional dramatic variations, sometimes stretching to a 48 hour cycle.
Conlusion = the study empahsises the importance of exogenous zeitgebers (external cues) in regulating our body clocks correctly. It shows that endogenous pacemakers can come out of synch without the presence of light and social cues.
Evaluation = results aren't generalisable as it was a sample of one person / Siffre wasn't isolated from artificial light which alters the s/w cycle, so results may not be accurate due to confounding variables / individual differences in rhythms and sleep/wake cycles make results hard to generalise / the knowledge from this study in relation to body rhythms has practical applications, showing that timing affects the success of drug treatments. Eg, heart attacks more likely in the morning so treatments can be taken then.
- Happen in cycles of under 24 hours, and can occur several times a day.
- An example of an ultradian rhythm is the stages of sleep, that repeats every 90-100 minutes.
The stages of sleep:
1) Light sleep. Theta waves produced. Eye movement and muscle activity decreases by 50%.
2) Light sleep. Theta waves produced. Eye and muscle movement stops, brain waves slow down and sleep spindels (sudden bursts of activity) begin.
3) Deep sleep. Delta waves produced. No eye or muscle movements, difficult to wake up.
4) Very deep sleep. Delta waves produced. No eye or muscle movement, sleeper disorientated when woken.
5) REM sleep. Heart, breathing rate and blood pressure increase, eye movement becomes irregular, muscles become paralysed, the sleeper will dream.
Ultradian rhythms - BRAC
Basic Rest Activity Cycle:
- A 90 minute alert cycle in which we go from alert to fatigued within the period.
- This occurs multiple times through out the day.
Knowledge of the BRAC has practical applications in...
- Education - determining the length of lessons based on the amount of time we can stay alert for without becoming fatigued.
- Improving the economy - we now have a better understanding of how the sleep cycle works, and how to become well rested, which we can use to improve peoples sleep. This will aid their concentration and hence they will become more productive and produce a better quality of work in contribution to the economy.
Ultradian rhythms - case study
Dement and Klietman:
Procedure = participants were woken at several points throughout the night whilst in different stages of sleep. They were asked to recall the dream they were having, and say how long it lasted. The descriptions were then compared to the participants EEG readings to see if they matched up.
Findings = when woken in REM sleep, 80% of dreams were correctly recalled. When woken in non-REM sleep, only 7% were recalled.
Conclusion = the findings support the idea that there are stages of sleep, and that dreaming only occurs in REM sleep.
Evaluation = this knowledge has practical applications in improving quality of life and the economy by helping people to sleep better by sleeping for longer (to ensure you sleep through all the stages and become well rested) / self-report technique whilst recalling dreams is inaccurate, participants can easily lie / sleep may be poor in the artificial environment anyway, so results lack external validity.
- Longer than 24 hours; weekly, monthly or annually.
- An example of an infradian rhythm could be the menstrual cycle or SAD.
The Menstrual Cycle:
A 28 day cycle. Day 1-5 the lining is shed and bleeding starts. Day 6-14 bleeding stops and the lining becomes thicker, enriched in blood and nutrients. Day 14-25 an egg is released into the uterus from the ovaries, if sperm are present the egg can be fertilised. Day 25-28 if not fertilised, hormonal changes signal for the egg to break down and the lining of the uterus is shed.
Seasonal Affective Disorder:
This is an annual IR, in which individuals become depressed through the winter and recover through summer. It is caused by low light levels during winter months, which result in the release of melatonin, making us feel drowsy and tired. Eastmen et al 1998, introduced phototherapy, a mood light that helps to regulate melatonin levels. The therapy relieved symptoms in 60% of suffers.
Infradian rhythms - case studies
A women who spent 3 months in a cave with only dim lighting, found that her menstrual cycle shortened to 25 days. This shows that the absence of exogenous zeitgebers can cause rhythms to become out of synch.
Found that women in all-girls halls of residence synched menstural cycles. This is said to be caused by pheremones. This has evolutionary benefits as it means women will be fertile at the same time and hence have children at the same time, so childcare can be shared. Again, this demonstrates how IR are influenced by external factors.
Found that cycles synched through exposure to body odour. Sweat samples from seperate groups rubbed on one anothers top lips. The womens' cycles synchronised despite their seperation. This provides evidence that IR are sychronised by external factors.
Infradian rhythms - evaluation
- Studies have provided us with insight into how internal rhythms function and that they are affected by external factors. The knowledge helps us to change our lifestyle as a way to regulate our cycles.
- Therapies such as phototherapy have been developed to help cure disorders such as SAD. This improves quality of life and the economy.
- The studies have small samples, making results ungeneralisable.
- Every woman experiences a different length of menstrual cycle, making most findings unrepresentative of a wider population due to individual differences.
- Most studies use self-report techniques which means results lack credibility and accuracy.
- Menstrual cycles fluxuate anyway, it may not have been Reinberg's cave or external factors causing this.