The human NS is a complex network of nerve cells and fibres that enables the brain to receive information about the environment and to command responses.
Nerves are cylindrical bundles of several thousand neuron axons (fibres)
Neurons are specialised cells in the brain and NS that transmit electrical impulses, enabling thought, speech, movement etc.
The CNS is the major division of the NS that includes all nerves in the central system. Its 2 main processes are controlling behaviour and regulating the body’s physiological processes.
The brain and the spinal column/ cord are the 2 main components of the CNS, but the brain stem is often included too. The brain is responsible for the integration and co-ordination of information received and decision making in response, whereas the spinal column is a column of nerves that links the brain stem with the PNS.
The PNS includes all the nerves external to the CNS. The Somatic NS carries both sensory information about the internal and external environment to the CNS and motor instructions from the CNS to the PNS. This means it can control skeletal (voluntary) muscle movements. The Autonomic NS works with smooth (organ) muscle to affect action and control involuntary bodily processes.
The Sympathetic NS is responsible for explosive action, and the fight/freeze/flight response to perceived threats. Whereas the Parasympathetic NS works to rest and digest to preserve homeostasis. These work on a principle of reciprocal inhibition.
Neurons communicate through the process of synaptic transmission, where the electric action potential is briefly carried by chemical neurotransmitters. When the action potential reaches the axon terminal of the pre-synaptic neuron, neurotransmitters in the vesicles are released to diffuse across the synaptic gap to the post synaptic neuron. If an inhibitory neurotransmitter is received at the specialised receptor cells, IPSP is generated, which leads to a decrease in voltage. Whereas if the neurotransmitter is excitatory, EPSP is generated and the resting pd increases.
Whether the post-synaptic cell fires is determined by the summation or calculation of these charges.
Spatial summation is where EPSPs are generated from many different pre-synaptic neurons, while temporal summation is the high frequency action potentials of a single pre-synaptic neuron. If the membrane potential reaches -55mV (from its resting potential of -70mV) the post-synaptic neuron fires an action potential and the process continues.
This graph demonstrates the membrane potential of a post-synaptic neuron before, during and after an action potential is generated.
Similarities:
Differences:
The pituitary gland is seen as the main gland in the endocrine system, however this is controlled by the hypothalamus. The hypothalamus is significant because it can create instructions in both the endocrine and nervous systems (it brings the systems together).
The pituitary gland is responsible for the release of hormones from glands in the body. These hormones travel through the blood stream and bind to the receptors at their target organs or glands, to influence behaviour.
The endocrine system uses a negative feedback loop (this means the system responds when the conditions are no longer ideal) to maintain homeostasis (the regulation of internal bodily functions in an optimal state).
Note: I need to be able to give an example of a hormone - not adrenaline
Gland Hormone
The hypothalamus releases CRH in the brain, which travels to the pituitary gland and instructs it to release ACTH. ACTH then travels through the blood stream, when it reaches the adrenal cortex, the cortex is instructed to secrete cortisol.
Cortisol release is generally used as a second fight or flight wave: it is referred to as chronic stress (plan C) or the HPA axis.
Cortisol release evolved because of its adaptive nature, so cortisol in the short term can have many benefits:
However, in the long term, this can become dangerous and lead to many problems:
Stress can either be acute or chronic. Chronic (plan C - there is no plan B) is explained with the release of cortisol, and is not 100% necessary.
Plan A demonstrates how the NS can work with endocrinal back up.
Localisation of function is the theory that particular regions of the brain are responsible for specific functions such as language. It means that behaviours originate from specific, discrete regions. The antonym of this is that function is distributed.
FM (radio - the motor cortex is in the frontal lobe)
PS (play station - the somatosensory cortex is in the parietal lobe)
wTAf (teaching assistant/ wtf - Wernicke’s area in the auditory cortex in the temporal lobe can cause fluency aphasia)
OV (ovulation - visual cortex is in the occipital lobe)
Visual information is received as light energy in the photoreceptors in the retina, before being translated in the ganglion cells in the retina. It travels along the optic nerve as an impulse before being received in the thalamus (relay station). Then it is directed and interpreted in the visual cortex in the occipital lobe.
Auditory information is received in the cochlea in the inner ear, and is translated in the Organ of Corti. It travels along the auditory nerve and is first received in the brain stem (where basic decoding takes place), then the thalamus then the auditory cortex in the temporal lobe.
The somatosensory cortex is the part of the brain that receives and interprets information relating to touch, whereas the motor cortex is the part of the cortex with motor origin. Both cortices have the whole body represented, but it is represented contralaterally, upside down and not proportionally. The size of the body part on the cortex is due to the sizes of sensory receptors and muscle effectors, not the actual size of the body part.
Note: the somatosensory has some features that the motor doesn’t because you cannot move them e.g. gums or head.
This is called the somatosensory and motor homunculus.
There are two main language centres in the brain: Broca’s area and Wernicke’s area.
Broca’s area is responsible for the production of language and is found in the posterior portion of the left frontal lobe. It was theorised by Paul Broca who studied patients who could understand but not produce language, during post-mortem analyses it was found that these patients had lesions in one specific area. There are two regions of Broca’s area: language and demanding cognitive tasks (Fedorenko et al, 2012).
Wernicke’s area is responsible for the understanding and comprehension of language. It is located in the posterior portion of the left temporal lobe. Wernicke suggested that language involves separate motor and sensory regions located in different cortical regions. This was supported when there was a neural loop found which ran between Broca’s and Wernicke’s areas (the arcuate fasiculus).
When either of these areas become damaged, a person can develop aphasia. This is a language deficit. There are 3 types:
Hemispheric lateralisation is the theory that each hemisphere is specialised for distinct ways of processing and particular functions. Even though the two hemispheres are separate, they are connected by the corpus callosum, which is a bundle of nerve fibres which allows the communication of signals between the two hemispheres.
There are somatosensory, auditory and visual cortices in both hemispheres, and the control of movement and reception is contralateral. However there are some differences in the functions associated with each hemisphere:
Remember that piece of research where there was damage to one of the hemispheres, and then the patient was asked to draw shapes e.g. M made of zs or triangles etc.
There are more similarities than differences between the brains of XX and XY individuals, but note that XX individuals tend to have more connected brains whereas XY are more likely to be “left-oriented”.
Split-brain research refers to the studying of individuals who have had split-brain surgery, in order to understand more about the individual specialisms of each hemisphere. In this surgery the corpus callosum is severed or burned in order to minimise the frequency and intensity of epileptic seizures (to stop them spreading between the two hemispheres). However, using split brain patients is difficult because the surgery is rare, so it has the same limitations as case studies.
Sperry’s research into SB patients contained 11 participants with commissurotomies (severing of the CC) and a control group that did not have any hemispheric disconnection. It was a natural experiment with elements of case-studies (due to a small sample size) where participants were measured on their performance of certain tasks in a laboratory.
Participants were asked to look at a focal point in the screen and there was a brief showing of a visual stimulus in either the left or right field of vision. If it was in the left FoV (RH), the participant was unable to name it (sometimes they even claimed they couldn’t see anything), but could identify it from a list of words, or draw it with their left hand then name it. When a stimulus was shown to the right FoV (LH), participants could name the stimulus.
The two hemispheres appeared to work independently, e.g. if a stimulus was shown to the LH, then the RH, it would not be recognised and was perceived to be new. Similarly when an object was “shown” to each hand then placed in a grab bag, each hand would often pick up and reject the object the other hand was looking for - they worked completely separately.
Later research showed that when the L FoV (RH) was shown an Arcimboldo fruit face, it saw the face first, but when the same painting was shown to the R FoV (LH), it only recognised the fruit.
Evaluation of SB research:
Plasticity refers to the brain’s ability to adapt in response to experience. Any experience or change in the environment can lead to plasticity, but a key one is learning: neural challenge.
When an individual practises a skill, or revises, neural networks in the brain can be established and each time this behaviour is repeated, this pathway is strengthened. Neurons in these pathways can have preferences for connections (they like to keep doing the same thing), which can lead them to adapt e.g. strengthen or change pathways to make a skill more efficient. Even accidental interaction between neurons (it doesn’t need to be an intentional practising of a skill) can demonstrate plasticity. Going through life provides the brain with many opportunities to adapt.
Functional recovery is when the brain can restore skills or behaviours after damage has occurred. This can happen because of the plasticity of the brain and it often works with structural reorganisation by moving the functions of areas damaged by trauma to other undamaged areas.
Ways the brain can reorganise:
Congenital damage is when brain damage resulted from development so it was present at birth.
Acquired damage is whem brain damage results from later trauma or insult.
PM: post-mortem examinations involve studying the actual, physical brain of a deceased individual to look for lesions or causes for any phenomenological afflictions or mental health disorders an individual may have struggled with e.g. Broca’s work with Tan. They are used to find the underlying neurobiology of a particular behaviour. It is useful for learning about the ways that certain psychiatric disorders can physically affect the brain e.g. increased ventricular size in schizophrenic patients.
To analyse brains, the brain of a patient can be compared to a neurotypical control.
fMRI: functional magnetic resonance imaging measures changes in brain activity by looking for changes of blood flow to certain areas. This allows researchers to create a visual map of activity in the brain, rather than just anatomy, to deduce that certain regions are involved in task performance.
EEG: Electroencephalograms measure electrical activity in the brain using electrodes on the scalp. Signals are graphed over a period of time and abnormal patterns or arrhythmias (no particular rhythm) can be used to diagnose disorders e.g. epilepsy. Data is gathered and summated or superposed to create a graph where different types of waves (alpha, beta, delta and theta) can be identified by their frequency.
From this data you get rhythmic patterns of neural oscillations because the neurons are in synchrony. It provides generalised information on the activity of many neurons.
ERP (event-related potentials): this relies of EEG data to pinpoint/ time-lock certain spikes or troughs of brain activity to specific stimuli. It is difficult to detect, but after a stimulus is shown it is possible to see tiny voltage changes which must be averaged together to see the impact. These responses can be divided into 2 categories: sensory responses (signals are generated before the first 100ms) or cognitive responses (signals are generated after the first 100ms).
Note: the strengths and limitations of each of these methods can often offset each other.
Clarity of data:
Note: you could have an essay on 1 or more bio rhythms, or even circadian. But for infradian and ultradian by themselves, it shouldn’t be more than 8 ish marks.
Biological rhythms are patterns of physiological processes that occur and recur with a predictable regularity. They govern the activity of cells and organs.
There are 3 types of biological rhythm:
In the exam you must stress the rhythmicity.
Circadian rhythms are any bodily cycle that lasts about 24 hours, even in the absence of environmental stimuli (if there are no environmental cues, a rhythm is said to be free running). Circadian rhythms influence so many aspects of our body including sleep-wake cycles, body temperature and hormone secretion.
Irregular rhythms, or when the CR is not in sync with the environment (e.g. jet lag or shift work), can lead to things like low mood and motivation, poor cognitive functioning, or other more serious conditions such as heart health, diabetes or bipolar disorder.
Circadian rhythms are governed by the suprachiasmatic nucleus which sits close to the hypothalamus. The SCN is entrained (synchronised to stimuli) by light signals from the brain: when the SCN receives signals of light in the morning, the “master clock” is reset in a time-dependent manner. When the SCN is reset, it sends signals to the peripheral oscillators (other cells in the body, each with their own body clock) to ensure there is synchrony.
Note: sleep and wakefulness are not governed by circadian rhythms alone, homeostatic sleep pressure is what makes us want to sleep more and more the longer we have been awake.
An example of an ultradian rhythm is the BRAC: Basic Rest Activity Cycle - a 90 minute cycle of alertness and sleep stages (Kleitmann).
#ladder of sleep cycles diagram
Sleep progresses through 5 (sometimes 4 because stage 4 is difficult to distinguish from 3) key stages in a ladder process. The evolutionary benefit of this is that is someone was woken up early, they will have had the benefits of each stage of sleep.
NREM sleep: non-REM sleep. It is slow-wave sleep (stages 1-4)
REM sleep: Rapid Eye Movement sleep. This is significant because it is paradoxical (the EEG of someone in REM sleep looks almost indistinguishable from someone who is awake), and desynchronised (there is no predictable pattern of electrical activity over the cortex). Humans dream when they are in REM sleep, this is also where emotional processing occurs. Heart rate increases and breathing gets shallower.
Stage 1: light sleep where we feel drowsy and muscle activity slows down: the brain has alpha waves
Stage 2: slightly deeper sleep, breathing and heart rate slows. Neural activity is characterised by theta waves
Stage 3: deep sleep where theta waves begin to turn into delta waves
Stage 4: very deep sleep where healing and repair occur. This is also where sleep-walking occurs
As the night progresses, the length of stage 4 sleep decreases, while the time spent in REM increases. This is also true of a lifespan.
There is some (slightly sketchy) evidence for weekly infradian cycles, but this is limited so we focus on the menstrual cycle instead.
Make sure you focus on the fact that this is a biological rhythm for reproduction, not just a period thing.