1
Q
The nervous system
A
- Network of specialised cells in the body
- Consists of the central nervous system and the peripheral nervous system.
- It is our main internal communication system whose main functions are to collect, process and respond to information in the environment and to co-ordinate the workings of the organs and cells within the body.
2
Q
Central nervous system (CNS)
A
consists of the brain and the spinal cord
3
Q
The brain
A
- Centre of all conscious awareness
- Involved in all psychological processes
4
Q
The spinal cord
A
- Transfers messages to and from the brain and body
- Responsible for simple reflex actions
5
Q
The peripheral nervous system
A
- Responsible for relaying messages to and from the CNS and rest of the body via neurones (nerve cells)
6
Q
Somatic nervous system
A
- Facilitates communication between the central nervous system and the outside world.
- It is made up of sensory receptors that carry information to the spinal cord and brain, and motor pathways that allow the brain to control movement.
- Controls voluntary muscle movements and some involuntary, eg reflex arc.
7
Q
Automatic nervous system
A
- Maintains internal bodily processes like body temperature, heart rate and blood pressure.
- Works largely unconsciously and involuntarily.
- Subdivided into the parasympathetic nervous system and the sympathetic nervous system.
8
Q
Sympathetic nervous system
A
- Prepares the body for ‘fight or flight’ response.
- Impulses travel from the sympathetic nervous system to organs in the body to help us prepare for action, e.g. quickens heart rate, inhibits less important processes like digestion and need to urinate.
9
Q
Parasympathetic nervous system
A
- Its role is to relax the body and return it to its normal resting state.
- It slows down our heart rate and breathing rate and reduces blood pressure.
- It also restarts any functions (e.g. digestion) that were inhibited during the fight-or- flight response.
10
Q
Neurons
A
Nerve cells that process and transmit information (messages) throughout the human nervous system through electrical and chemical signals.
11
Q
Fill in the gaps:
Neurons can ____ in size but they all _____ the ____ structure.
A
Neurons can vary in size but they all share the same structure.
12
Q
Dendrites
A
Branch-like structures that extend from the cell body that receives and carry signals from neighbouring neurons or sensory receptor cells towards the cell body
13
Q
Axon
A
Carries an electrical signal (called an action potential) away from the cell body, along the axon, to the terminal buttons.
14
Q
Myelin sheath
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Covering that insulates and protects the axon and speeds up the transmission of the electrical signal along the axon.
15
Q
Terminal button
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Communicates with the next neurone in the chain across a gap called the synapse (or synaptic cleft), through a process of synaptic (chemical) transmission.
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Q
Cell body
A
Control centre of the neuron
17
Q
Nucleus
A
Contains genetic material
18
Q
What are the three types of neurons?
A
Sensory
Relay
Motor
19
Q
Function of a sensory neuron
A
Carry messages from sensory receptors in the peripheral nervous system (found in skin, tongue etc) to the central nervous system.
20
Q
Why do some neurons stop at the spinal cord?
A
To allow quick reflex actions
21
Q
Structure of a sensory neuron
A
Long dendrites and short axons
22
Q
Function of a relay neuron
A
- Connect sensory neurons to motor neurons and other relay neurons.
- Involved in the analysis of sensations.
23
Q
Where are relay neurons found?
A
In the brain and spinal cord
24
Q
Structure of a relay neuron
A
Short dendrites and short axons
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Function of a motor neuron
Connect the central nervous system to effectors such as muscles and glands. Therefore, they allow the CNS to control movement.
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Structure of a motor neuron
Short dendrites and long axons
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Nodes of ranvier
Gaps that divide up (segments) the myelin sheath. These speed up the transmission of the impulse by forcing it to 'jump' across the gaps along the axon.
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Why does the myelin sheath have gaps (nodes of ranvier)?
If the myelin sheath was continuous this would have the reverse effect and slow down the electrical impulse.
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How do neurons transmit signals?
Through electric transmission and synaptic (chemical) transmission
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Where does electrical transmission occur?
Within a neuron
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Process of electrical transmission
At rest, a neuron is negatively charged inside the cell body (-70V) i.e., the inside of the cell is negatively charged compared to the outside of the cell. When a neuron receives a signal from a neighbouring neuron, the inside of the cell body becomes momentarily positively charged (becomes depolarised) causing an action potential (which is an electrical signal) to travel down the axon.
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Where does synaptic (chemical) transmission occur?
Between neurons
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Synaptic (chemical) transmission
The process by which neighbouring neurons communicate with each other by sending chemical messages across the gap (the synapse) that separates them.
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Process of synaptic transmission
When the action potential (electrical signal) reaches the axon terminal at the end of the neuron, it triggers the release of neurotransmitters from tiny sacs called synaptic vesicles. Once the neurotransmitter crosses the gap, it is taken up by a postsynaptic receptor on the postsynaptic neuron and here the chemical signal is converted back into an electrical signal in the postsynaptic neuron and the process of transmission begins again in this other neuron.
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Neurotransmitters
Brain chemicals that are released from the synaptic vesicles that relay signals across the synapse to the next neuron in the chain.
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Neurotransmitters- Lock and key
Each neurotransmitter has it’s own molecular structure, which means it will only fit to a particular postsynaptic receptor- much like a lock and key.
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Examples of specialist functions of neurotransmitters
Dopamine - pleasure
(Imbalance in dopamine causes schizophrenia)
Serotonin - mood
(Imbalance in serotonin causes depression)
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Why can neurons only transmit information in one direction at a synapse?
Neurotransmitters are released by the presynaptic neuron and received by the postsynaptic neuron- so it can’t go the other way!
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What are the two effects that neurotransmitters can have on neighbouring neurons?
Excitatory or inhibitory effect
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Excitation
Excitation occurs when excitatory neurotransmitters stimulate the postsynaptic receptor resulting in an increase in the positive charge of the postsynaptic neuron.
This increases the likelihood of the postsynaptic neuron firing and passing on the electrical signal.
This is known as a excitatory postsynaptic potential (EPSP).
41
Inhibition
Inhibition occurs when inhibitory neurotransmitters stimulate the postsynaptic receptor resulting in an increase in the negative charge of the postsynaptic neuron. This decreases the likelihood of the postsynaptic neuron firing and passing on the electrical signal. This is known as a inhibitory postsynaptic potential (IPSP).
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Summation
Summation is the addition of the EPSPs and the IPSPs.
Neurons can receive both EPSPs and the IPSPs, so these are summed.
If the net effect on the postsynaptic neuron is inhibitory (a very negative charge), the neuron is less likely to fire.
If the net effect on the postsynaptic neuron is excitatory ( a very positive charge), the neuron is more likely to fire.
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Endocrine system
The body’s major information system that instructs glands to release chemical substances called hormones directly into the bloodstream. These hormones travel towards target organs in the body and regulates its activity.
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Hypothalamus
Hypothalamus is connected to the pituitary gland and is responsible for controlling the release of hormones from the pituitary gland - so it’s the control system that regulates the endocrine system.
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Pituitary gland
Pituitary gland in the brain is often called the ‘master gland’ because it controls the release of hormones from all other glands.
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Pineal gland
Secretes melatonin, which is responsible for important biological rhythms, including the sleep-wake cycle.
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What is the adrenal gland divided into?
Adrenal cortex and adrenal medulla
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Adrenal cortex
Secretes cortisol which stimulates the release of glucose.
Suppresses immune system
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Adrenal medulla
Secretes adrenaline and noradrenaline which results in physiological changes related to the fight or flight response.
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Androgens
Androgens include the main hormone testosterone and are released by the testes.
Testosterone is responsible for the development of male sex characteristics, muscle growth and aggressive behaviours.
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Oestrogen
Oestrogen is secreted from the ovaries in the female body.
It controls regulation of the female reproductive system, including the menstrual cycle and pregnancy.
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Thyroid Gland
Releases thyroxine which is responsible for regulating metabolism
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Why do people with fast metabolism struggle to put on weight?
Metabolism is involved in the chemical process of converting food into energy
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Fight or flight response
When something is perceived as a stressor or a threat, the amygdala is activated which sends a distress signal to the hypothalamus. The hypothalamus then activates the sympathetic medullary pathway- this is the pathway running to adrenal medulla and the sympathetic nervous system. The sympathetic nervous system then activates the adrenal medulla, which releases adrenaline and noradrenaline into the bloodstream. Adrenaline triggers physiological changes in the body (e.g. increased heart rate, increased breathing rate, increased blood pressure) which create the physiological arousal needed to either stand your ground and fight or run away very quickly (flight) for example, a faster heart and breathing rate.
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What happens once the threat has passed?
The parasympathetic nervous system brings the body back to its resting state. It slows down the heart rate and brings the blood pressure back to a normal level. It also restarts the inhibited processes such as digestion.
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Weakness of fight or flight response
While the fight or flight response may have been a useful survival mechanism for our ancestors, who faced genuinely life-threatening situations (e.g. from predators), modern day life rarely requires such an intense biological response. Furthermore, the stressors of modern day life can repeatedly activate the fight or flight response, which can have a negative consequence on our health. For example, humans who face a lot of stress and continually activate the sympathetic nervous system will continually increase their blood pressure which can cause damage to their blood vessels and result in a heart disease. This suggests that the fight or flight response is a maladaptive response in modern-day life.
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What is the outer layer of the brain called?
Cerebral cortex
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Localisation of function theory
The theory that different parts of the brain are responsible for different functions.
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Corpus callosum
A bundle of fibres which form a communication pathway between the two hemispheres and helps exchange information
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Holistic theory (equipotentiality)
The brain works as a single entity and there is no specific part for specific jobs
[opposite to the theory of localisation]
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What are the four different lobes of the brain?
Frontal lobe
Temporal lobe
Parietal lobe
Occipital lobe
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Posterior
back
63
anterior
front
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Where is the motor area?
Back of frontal lobe
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What does the motor area do?
Controls voluntary movement on the opposite side of the body.
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What happens if there is damage to the motor area?
Result in loss of fine motor movements on the opposite side of the body to where the injury is i.e. left motor cortex injury results in movement problems in the right hand side of the body
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Where is the somatosensory area located?
front of both parietal lobes
68
What does the somatosensory area do?
Receives incoming sensory information from the skin to produce different sensations of pressure, pain and heat.
69
Effect of damage to the somatosensory area
Numbness or tingling in certain parts of the body depending on where the damage was
70
Where is the visual centre located?
Occipital lobe
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What does the visual centre do?
Receives and processes visual information. Information from right-hand side of visual field is processed in the left hemisphere, and information from the left-hand side of the visual field is processed in the right hemisphere.
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Effects of damage to the visual centre
Damage to the left hemisphere can cause blindness of right-hand side of visual field in both eyes.
Damage to the right hemisphere can cause blindness of left-hand side of visual field in both eyes.
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Where is the auditory centre located?
Temporal lobe
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What does the auditory centre do?
Receives and processes speech-based acoustic information.
Information from right ear goes to left hemisphere and information from left ear goes to right hemisphere.
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Effect of damage to the auditory centre
Partial or extensive hearing loss depending on extent of damage
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Where is Broca’s area located?
Left frontal lobe
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Function of broca’s area
Responsible for speech production
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Effect of damage to broca’s area
Broca’s aphasia: slow and inarticulate but meaningful speech
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Where is wernicke’s area located?
Left temporal lobe
80
Function of wernicke’s area
Involved in language processing and comprehension
81
Effect of damage to wernicke’s area
Wernicke’s aphasia: produce fluent but meaningless speech, with neologism (nonsense words)
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Localisation evaluation
Supporting evidence: Case Study on Phineas Gage
One strength of the localisation theory is that there is supporting evidence from a case study.
For example, in 1848 Phineas Gage suffered a unique neurological injury during an accident whilst he was working on the railways.
A metre-length pole shot through Gage’s left cheek, exiting his skull and taking a portion of his left frontal lobe with it. He survived but was left with significant personality changes; Gage turned from someone who is calm and reserved to someone who was quick-tempered and rude.
This suggests that the frontal lobe may be responsible for functions that determine our personality, such as impulse control and regulating mood, which provides supporting evidence for the localisation theory, where different parts of the brain are responsible for different functions.
83
Localisation evaluation
Supporting evidence: Brain Scans
One strength of the localisation theory is that there is evidence from brain scans to support it.
For example, Peterson (1988) used brain scans to demonstrate how Wernicke’s area was active during a listening task, which is the area responsible for comprehension of language, and Broca’s area was active during a reading task which is the area responsible for speech production.
These objective methods for measuring brain activity, that are not open to experimenter bias, suggest that localised areas of the brain have specific functions
84
Localisation evaluation
Conflicting evidence: Lashley (1950)
One weakness of the localisation theory is that there is conflicting evidence from neurosurgery on rats that challenges its claims.
For example, Lashley (1950) removed areas (between 10-50%) of the cortex in rats who were learning the route through a maze. He found that no area was more important than any other area in terms of the rats’ ability to learn the route and that the process of learning seemed to require every part of the cortex.
This research suggests that higher cognitive processes, such as learning, are not localised but distributed throughout the brain in a more holistic way in the brain (termed equipotentiality theory), which undermines the credibility of the localisation of function theory.
However, it is difficult to make meaningful generalisations from the findings of animal lesion studies to humans. This is because the human brain is more complex. This reduces the external validity of the findings from Lashley’s study.
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Localisation evaluation
Conflicting evidence: Trembley (2016)
One weakness of the localisation theory is that there is conflicting neuroimaging evidence that questions whether language is localised to just Broca’s and Wernicke’s areas.
For example, recent advancements in neuroimaging techniques, such as fMRI, means that neural process can be studied with more accuracy. Trembley (2016) found using these imaging techniques that language function is distributed far more holistically in the brain than first thought, as language centres were also found in the right hemisphere and subcortical regions whereas previously, these were considered to only be located in the left temporal lobes in Broca’s and Wernicke’s areas.
This highly objective evidence questions the claim that language is localised and confined to a couple of key areas in the brain, but rather it is organised more holistically in the brain, which contradicts the localisation theory that language is processed in specific regions of the brain.
86
Describe the localisation of function in the human brain (6 marks)
Localisation of function is the idea that certain functions, such as memory, hearing or sight etc, have a certain area in the brain in which they are essentially found.
For example, the motor area is located in the posterior frontal lobe, it is responsible for voluntary movement by sending signals to muscles in the body. The right hemisphere controls the left half of the body and the left hemisphere controls the right half of the body. If this area is damaged, an individual loses fine motor movements in the opposite side of the body to where the injury is. For instance, injury to the left motor cortex would result in body movement issues in the right half of the body.
Broca’s area is located in the left frontal lobe. It is involved in speech production. Damage to this area results in Broca’s aphasia, where speech is slow and not fluent.
Wernicke’s area, located in the left temporal lobe, is involved in language processing and comprehension. Damage to this area results in Wernicke’s aphasia, in which an individual would produce fluent but meaningless speech.
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What is hemispheric lateralisation?
The idea that two halves of the brain are functionally different and that each hemisphere has functional specialisations. E.g left = language, right = visual-motor tasks
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Left hemisphere = ‘analyser’
What does ‘analyser’ refer to?
Breaking things into components ie language production and language comprehension
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Right hemisphere = ‘synthesiser’
What does ‘synthesiser’ refer to?
Combining of different things to make the whole.
90
Give 3 examples of functions/ areas in the brain that are not lateralised
Vision, motor and somatosensory areas
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Contralateral
Cross - wired / opposite side
(Left hemisphere processes information from the right side of the body and the right hemisphere deals with the left side of the body)
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Ipsilateral
Same side
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Why is vision both contralateral and ipsilateral?
Each eye receives visual information from the right visual field (RVF) and left visual field (LVF).
The RVF of both eyes is connected to the left hemisphere.
The LVF of both eyes is connected to the right hemisphere.
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Corpus callosum
Nerve fibres that connect the two hemispheres and facilitates inter-hemispheric communication ie communication between the two hemispheres.
95
Who were the first to investigate hemispheric lateralisation in their split-brain research?
Sperry and Gazzaniga (1967)
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Split brain patients
Individuals who have undergone a surgical procedure where the corpus callosum, which connects the two hemispheres, is cut.
This procedure, which separates the two hemispheres, was used as a treatment for severe epilepsy.
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What happens when the corpus callosum is cut?
Information presented to one hemisphere can not be transferred to the other hemisphere.
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Aim of Sperry’s split brain research
To examine the extent to which the two hemispheres are specialised for certain functions (hemispheric lateralisation).
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Method of Sperry’s split brain research
An image/word was projected to the patient’s left visual field (which is processed by the right hemisphere) or the right visual field (which is processed by the left hemisphere).
Two variations where patients were asked:
1. Visual: ‘describe what you see’
2. Tactile: ‘select a similar object to the one presented’ or ‘describe what has been placed in your hand’
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Sperry’s split brain research: Results of the visual test (LVF)
Participants could not describe what they saw if the picture was presented on the LVF, showing that messages could not be relayed from the right hemisphere to the language centres in the left hemisphere, resulting in them saying ‘nothing was there’.
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Sperry’s split brain research: Results of the visual test (RVF)
Participant could describe what they saw on the RVF, showing the superiority of the left hemisphere when it comes to the language production.
102
Sperry’s split brain research: Results of the visual test - LVF with a pinup picture
If a pinup picture was shown to the LVF, there was an emotional reaction (e.g. a giggle) but the participants reported usually seeing nothing or just a flash of light.
This supports the view that the left hemisphere is verbal and the right hemisphere is ‘silent’ but emotional.
103
Sperry’s split brain research: Results of the tactile test
Participants could select and identify a test object presented in the LVF from a series of alternate objects using their left hand.
This is due to the right hemisphere being dominant in terms of visual motor tasks.
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Conclusion of Sperry’s split brain research
There are key differences between the two hemispheres and certain functions are lateralised in the brain:
1. Left = speech and language
2. Right = visual-motor task and providing emotional context
