New Biological Flashcards
The Nervous System
The nervous system is made up of the brain and the spinal cord, whilst the peripheral nervous system (PNS) relays messages from the environment to the CNS, via sensory neurones, and from the CNS to effectors, via motor neurones.
PNS
- The PNS is further subdivided into the autonomic nervous system (which controls involuntary, vital functions of the body, such as maintaining heart rates and breathing rates) and the somatic nervous system (which receives information from sensory receptors belonging to each of the 5 senses, and results in effectors being stimulated by the CNS, via motor neurones).
The Autonomic Nervous System
- The autonomic nervous system is also subdivided into the sympathetic and parasympathetic branches. These branches work as part of an antagonistic pair during the ‘rest and digest’ response, and are crucial in producing the physiological arousal needed to maintain the fight or flight response.
The Endocrine System
- The endocrine system is the main chemical messenger system of the body, where hormones are secreted into the bloodstream from glands, and then are transported towards target cells in the blood, with complementary receptors. The pituitary gland is considered to be the ‘master’ gland because it controls the release of hormones from all other glands in the body. For example, the thyroid releases the hormone thyroxine, which increases heart rate and therefore increases the rate of growth. The adrenal gland releases adrenaline which creates the physiological arousal preceding the fight or flight response, through increasing the activity within the sympathetic branch of the nervous system.
The Fight or Flight response
1.The body senses and becomes aware of a stressor in the environment e.g. the sound of a speeding car.
2.Through sensory receptors and sensory neurones in the PNS, this information is sent to the hypothalamus in the brain which coordinates a response and triggers increased levels of activity in the sympathetic branch of the ANS.
3.Adrenaline is released from the adrenal medulla in the adrenal glands, and is transported to target effectors, via the blood and through the action of the endocrine system.
4. This results in the rectum contracting, saliva production being inhibited and a greater breathing rate. This creates the physiological response needed to sustain the fight or flight response, whose adaptive purpose is to enable us to escape the stressor and so increase the likelihood of our survival.
5. Once the stressor is no longer a threat, as part of an antagonistic pairing, the hypothalamus triggers less activity in the sympathetic branch and more activity in the parasympathetic branch of the ANS. This is also referred to as the rest and digest response, due to the parasympathetic branch decreasing the activity which was originally increased through the action of the sympathetic branch.
Synaptic transmission
Synaptic transmission is a method of neurons communicating with each other relaying information to the CNS across sensory neurons and carrying out responses dictated by the brain through sending information to effectors via motor neurons.
The process of synaptic transmission is as follows:
1.An action potential arrives at the presynaptic membrane, causing depolarisation through the opening of voltage-dependent calcium ion channels, and the consequent influx of calcium ions.
2.The increased concentration of calcium ions within the membrane causes the vesicles, containing neurotransmitter, to fuse with the presynaptic membrane and release their contents into the synaptic cleft through exocytosis.
3. The neurotransmitter diffuses across the synaptic cleft, down a concentration gradient, and binds to complementary receptors on the post-synaptic membrane. This can result in an inhibitory or excitatory effect in the postsynaptic membrane.
4. The resultant action potential will then be transmitted along the axon of the following neuron, resulting in a ‘cascade’ of neurotransmission!
Neurotransmitters
Neurotransmitters can either have an inhibitory or excitatory effect. Inhibitory neurotransmitters (e.g. serotonin) reduce the potential difference across the postsynaptic membrane through the closure of the voltage-dependent sodium ion channels, reducing the likelihood that an action potential will be generated.
Excitatory neurotransmitters
Excitatory neurotransmitters (e.g. dopamine) increase the potential difference across the postsynaptic membrane through triggering the opening of more voltage-dependent sodium ion channels, increasing the likelihood that an action potential will be generated.
Localisation of Function in the Brain
Localisation theory suggests that certain areas of the brain are responsible for certain processes, behaviours and activities.
The motor area
Separated from the auditory area by the central suclus and found in the frontal lobe, this area is involved in regulating and coordinating movements. Lesions or damage in the motor area result in an inability to control voluntary fine motor movements.
The auditory area
An area of the temporal lobe, located on the superior temporal gyrus, which is responsible for processing auditory information and speech. Lesions or damage in the auditory area causes hearing loss, whereas damage to specific parts of the auditory area (Wernicke’s area) results in Wernicke’s aphasia.
The visual area
An area in the occipital lobe which is responsible for processing visual information.
The somatosensory area
An area of the parietal lobe which processes information associated with the senses e.g. touch, heat, pressure etc. “These regions receive neuronal input from specific 1 nuclei of the thalamus that correspond with the handling of sensation along the lines of touch, pain, temperature and limb position”. Lesions in this area result in a loss of ability to denote sensitivity to particular bodily areas.
Wernicke’s Area
Responsible for speech comprehension and located in the temporal lobe (the left temporal lobe for most people). Lesions or damage (e.g. through stroke and trauma) results in Wernicke’s aphasia, which is characterised by the use of nonsensical words (called syllogisms), no awareness of using incorrect words, but no issues with pronunciation and intonation.
Broca’s Area
Responsible for speech production and located in the frontal lobe, usually in the left hemisphere. Lesions or damage results in Broca’s aphasia, characterised by difficulty forming complete sentences and understanding sentences, as well as failing to understand the order of words in a sentence and who they are directed towards i.e. I, you, we, him, me etc.
Localisation of Function in the Brain
Evaluation A03
+ Supporting evidence for localisation of brain function = Tulving et al demonstrated, using PET scans, that semantic memories were recalled from the left prefrontal cortex, whilst episodic memories were recalled from the right prefrontal cortex. This shows that different areas of the brain are responsible for different functions, as predicted by localisation theory. This idea was further supported by Petersen et al (1988) , who found that Wernicke’s area activation is required for listening tasks, whereas Broca’s area is required for reading tasks. This confirms the idea that Wernicke’s area is involved in speech comprehension, whilst Wernicke’s area is responsible for language production.
+ Supporting Case Studies = Phineas Gage was injured by a blasting rod which intersected the left side of his face, tearing through his prefrontal cortex. “The damage involved both left and right 2 prefrontal cortices in a pattern that, as confirmed by Gage’s modern counterparts, causes a defect in rational decision making and the processing of emotion”. Such case studies, particularly those showing marked differences after trauma, demonstrate the idea that some areas of the brain are responsible for specific functions. However, with the use of case studies, the subjectivity of the conclusions drawn and the unusual sample, alongside a lack of control over confounding and extraneous variables, must also be considered.
— Contradictory Theory = The opposite to localisation theory would be a holistic view of brain function, suggesting that each function requires several brain areas to be activated and that these functions are not restricted to these areas. For example, after removing 20-50% of the cortices belonging to rats, found that no specific brain area or lesion was associated with learning how to traverse through a maze. This suggests that intelligence, or even learning, is too complex and advanced a cognitive ability to be restricted to certain areas of the brain. Therefore, this suggests that localisation theory may provide a better explanation for ‘simple’, rather than complex, brain functions.
+ Evidence supporting the link between certain brain areas and symptoms of OCD = Dougherty et al (2002) studied 44 OCD sufferers who’d undergone lesioning of the cingulate gyrus (cingulotomy) in order to control their symptoms. After being assessed using the Structured Clinical Interview for DSMIII-R, the researchers found that “At mean follow-up of 32 months after one or more cingulotomies, 3 32% met criteria for treatment response, and 14% were partial responders. 32-45% of patients previously unresponsive to medication and behavioural treatments for OCD were at least partly improved after cingulotomy”. This suggests that not only are certain brain areas responsible for symptoms of OCD, but that an improved understanding of localisation of brain function has practical applications in the development of more advanced treatments for serious mental disorders.
Plasticity and Functional Recovery of the Brain after Trauma (A01)
Plasticity refers to the brain’s ability to change and adapt in response to experience. When the brain is damaged due to trauma, such as a stroke or traumatic brain injury, plasticity can help the brain to recover function. The brain can adapt by forming new connections between neurons, reorganizing neural networks, and even recruiting different brain regions to perform tasks.
Functional recovery after brain trauma is the process by which the brain restores lost abilities, such as movement, speech, or cognitive functions, after injury. The extent of functional recovery depends on several factors, including the severity and location of the injury, age of the individual, and the amount of rehabilitation received.
Research has shown that the brain’s plasticity and functional recovery can be enhanced through rehabilitation techniques such as physical therapy, cognitive training, and neurofeedback. For example, physical therapy can help to retrain motor skills, while cognitive training can improve memory and attention.
The use of technology, such as brain-computer interfaces and virtual reality, is also being explored as a means of enhancing plasticity and functional recovery. Brain-computer interfaces can help to improve motor function in individuals with paralysis, while virtual reality can provide a realistic environment for cognitive and motor rehabilitation.
Plasticity and Functional Recovery of the Brain after Trauma (A03)
Evaluations
+ Evidence supporting the positive and negative effects of neuroplasticity = Much research has been carried out into the phenomenon of plasticity. For example, Ramachandran et al. has demonstrated negative plasticity through providing an explanation for phantom limb syndrome in terms of cortical reorganization in the cortex and thalamus (particularly, the somatosensory area). Positive plasticity has been demonstrated by the case study of Jodi Miller, who has shown the power of recruiting
homologous areas on the opposite side of the brain, axonal sprouting and the reformation of blood vessels. Therefore, there is evidence supporting not only the existence of, but also the uses of plasticity.
+ Neuroplasticity occurs in animals too = Hubel and Weisel (1970) sutured the right eye of kittens, who are blind from birth, for a period of 6 months, opening the eyes and several points and monitoring brain activity in the visual cortex. The researchers found that, although the right eye was closed, there was still activity in the left visual cortex, corresponding to the development of ocular dominance columns. This was demonstrated by how “during the period of high susceptibility in the 7 fourth and fifth weeks eye closure for as little as 3-4 days leads to a sharp decline in the number of
cells that can be driven from both eyes”. This therefore supports the idea that areas of the brain receiving no input can take over the function of highly stimulated areas, despite originally having different functions.
+ Cognitive reserve may increase the rate of functional recovery = Cognitive reserve is the level of education a person has attained and how long they have been in education. Research suggests that an increased cognitive reserve increases the likelihood of making a disability-free recovery (DFR) after trauma, due to increased rates of neuroplasticity. For example, Schneider et al (2014) found that of the 769 patients studied, 214 achieved DFR after 1 year. Of those, 50.7% had between 12 8 and 15 years of previous education and 25.2% had more than 16 years. This suggests that individuals who have been in education for a longer time may have developed the ability to form neuronal connections at a high rate, and therefore experience high levels of functional recovery, demonstrating positive plasticity.
— There are limits to spontaneous and functional recovery = Although after trauma the brain activates secondary neural circuits which contribute towards reinstating normal function (law of equipotentiality), the brain can only ‘repair’ itself up to a specific point, after which motor therapy or electrical stimulation is needed to increase recovery rates. For example, Lieperta et al (1998) found that after constraint-induced movement therapy, the motor performance of stroke patients improved significantly. Therefore, this suggests that functional recovery cannot be relied upon to reinstate normal function.
Split-Brain Research into Hemispheric Lateralisation (A01)
Split-brain research involves the study of individuals who have undergone a surgical procedure called corpus colostomy, which involves severing the corpus callosum, the bundle of fibres that connects the two hemispheres of the brain. This procedure is typically done to treat severe cases of epilepsy, as it can help to prevent seizures from spreading across the brain.
Split-brain research has been used to investigate hemispheric lateralisation, the idea that the two hemispheres of the brain are specialised for different functions. The left hemisphere is typically associated with language, logic, and analytical thinking, while the right hemisphere is associated with spatial awareness, creativity, and emotion.
One of the most famous split-brain experiments was conducted by Michael Gazzaniga and Roger Sperry in the 1960s. They presented different stimuli to the right and left visual fields of split-brain patients and found that the information presented to the left visual field (which is processed by the right hemisphere) was better at processing nonverbal information, such as visual patterns and faces, while the information presented to the right visual field (which is processed by the left hemisphere) was better at processing verbal information, such as words and numbers.
Other split-brain studies have shown that the two hemispheres can operate independently of each other, with each hemisphere processing information and performing tasks without the other hemisphere’s knowledge. For example, if a split-brain patient is shown a picture of a key in their left visual field (which is processed by the right hemisphere), they may be unable to name the object, but they can use their left hand (controlled by the right hemisphere) to pick up a key.
While split-brain research has provided valuable insights into hemispheric lateralisation, it is important to note that the procedure is not without risks, and ethical concerns have been raised about the use of split-brain patients in research. As a result, researchers have developed non-invasive techniques, such as functional brain imaging, to study hemispheric lateralisation in healthy individuals.
Split-Brain Research into Hemispheric Lateralisation (A03)
Evaluations
— Lack of control with the sample selection = The epileptic patients had been taking anti-epilepsy medications for extended and different periods of time, which may have affected their ability to recognise objects and match words, due to causing cerebral neuronal changes. Secondly, although all patients had undergone a commissurotomy, there may have been differences in the exact procedures e.g. differing extent of the lesioning of the corpus callosum. This would have affected the degree to which the two hemispheres could relay information between themselves. Therefore, these two confounding variables had not been controlled, meaning that the lateralised functions may be examples of unreliable causal conclusions.
+ Clearly demonstrated lateralisation of function = Split-brain research was pivotal in establishing the differences in functions between the two hemispheres, and so opposing the holistic theory of brain function. The left hemisphere was demonstrated as being dominant for language tasks, due to containing language centres, whereas the right hemisphere was demonstrated as being dominant for visuo-spatial tasks. Therefore, this suggests that the left hemisphere is the analyser, whereas the right hemisphere is the synthesiser, and so there are marked differences between the two.
+ Contribution to discussions about lateralisation theories = Such evidence strongly supported the idea of a ‘dual mind’ where the two hemispheres represent two sides of the mind. Pucetti (1980)criticised Sperry and Gazanigga’s work by pointing out that “visual stimuli impinging on the left half 9 of each eye’s retina do not go to the right, but to the left cerebral hemisphere (and vice versa), since the retina is concave and each half retina receives light from the contralateral side of the body”. Therefore, it is clear that split-brain research has sparked much debate about the physiological and theoretical basis of brain function and human abilities.
— The differences in function may not be so clear-cut = With evidence making the drastic distinctions that the left hemisphere is responsible for language (analyser) whilst the right is responsible for visual spatial tasks (synthesiser), this has given the public the false impression that the two hemispheres are ‘opposite’ in function and that they can receive such labels. However, as suggested by Pucetti (1980), there have been cases of split-brain patients who are left-handed but produce and comprehend speech in the right hemisphere, which opposes the predictions made by lateralisation theory.
Therefore, it is important not to jump to conclusions and to appreciate that, through recruitment of homologous areas on the opposite side of the brain, each hemisphere is not restricted to specific functions.
Ways of Investigating the Brain
PET (A01)
PET Scans = These use radioactive isotopes with a long half-life e.g. Nitrogen-13. As the isotope decays, such as through the emission of positrons, these particles interact and are combined with glucose or water molecules, forming radiotracers. An increased number of radiotracers will accumulate in areas of the brain with high levels of activity, due to the haemodynamic response where such areas have a larger requirement for oxygenated blood. Therefore, such highly active areas will appear brightly coloured on the PET scans, as the emitted positron collides with an electron, resulting in the emission of gamma rays which are detected by the scan.
Ways of Investigating the Brain
PET (A03)
— PET scans are very expensive and so are not extensively used in public healthcare systems - only for diagnosis purposes.
— Some people may object to the use of radioactive tracers in their blood, due to exposure to ionising radiation which may lead to cancer. Therefore, only one or two PET scans can be carried out on an annual basis.
+ Very useful for the diagnosis and monitoring of progressive, neurodegenerative diseases, such as
Alzheimer’s (characterised by a reduction in glucose metabolism rates in the brain).
Ways of Investigating the Brain
fMRI (A01)
fMRI scans = These rely on the haemodynamic response. Areas of the brain with high levels of activity have a larger requirement for oxygenated blood, leading to a higher rate of blood deoxygenation. As measured through the bold response, the deoxyhaemoglobin in the blood in these highly active areas absorbs the signal produced by the scan, so such areas appear brightly coloured on the scan.
