Biopsychology

Question 1

describe the CNS

Answer 1

• CNS is made up of the brain, and spinal cord
• Controls the behaviour and regulation of the bodies physiological functions
• Receives information from sensory receptors and sends messages to the muscles and glands of the body this involves the spinal cord

Question 2

describe the spinal cord

Answer 2

• Main function is to relay information between the brain and the rest of the body
• Allows brain to monitor and regulate the rest of the body and change conditions according to the environment
• Connected to different parts of the body by pairs of spinal nerves which connect with specific muscles and glands, for example spinal nerves that branch off from the thoracic region of the spinal cord carry messages to and from the chest and other parts of the abdomen
• Contains circuits of nerve cells that enable us to perform simple reflexes without direct involvement of the brain e.g. pulling hand away from something that is hot

Question 3

what are the parts of the brain

Answer 3

• cerebrum
• cerebellum
• diencephalon
• brain stem

Question 4

describe the cerebrum

Answer 4

largest part of the brain and is divided into four different lobes which each have a different primary function, the frontal lobe produced speech and thought, the occipital lobe is involved in the processing of visual images. It is spilt down the middle into two halves called cerebral hemispheres these are specialised for particular behaviours and two halves communicate with each other through the corpus callosum

Question 5

describe the cerebellum

Answer 5

sits beneath the cerebrum, it is involved in controlling a persons motor skills and balance, coordinating muscles to allow precise movement, when this section does not work properly it can induce problems such as speech and motor problems as well as epilepsy

Question 6

describe the diencephalon

Answer 6

lies beneath the cerebrum and on top of the brain stem, this contains then hypothalamus and thalamus. The thalamus is a relay station for nerve impulses coming from the senses routing them to the appropriate part of the brain where they can be processed. Hypothalamus regulates body temperatures and has some other important factors, it acts as a link between the endocrine system and the nervous system and controls the release of hormones from the pituitary gland

Question 7

describe the brain stem

Answer 7

responsible for regulating the automatic functions that are essential for life, such as breathing, heartbeat and swallowing, motor and sensory neurones travel through the brain stem and allow impulses to pass between the brain and spinal cord

Question 8

describe the peripheral nervous system

Answer 8

• The nervous system outside the CNS make up the peripheral nervous system, this systems job is to relay nerve impulses from the CNS to the rest of the body and from the body back to the CNS
• Two main divisions of the peripheral nervous systems such as the somatic nervous system and the autonomic nervous system

Question 9

describe the somatic nervous system

Answer 9

• Made up of 12 pairs of cranial nerves and 31 pairs of spinal nerves
• These nerves both have sensory neurons and motor neurons
• Sensory neurons relay messages to the CNS and motor neurone relay messages from the CNS to other parts of the body
• Reflex action without the involvement of the CNS

Question 10

describe the automatic nervous system

Answer 10

• Involuntary actions are performed such as heart beat and intestine digesting food
• Bodily functions would not work as efficiently if you had to think about them
• It has two parts the sympathetic and the parasympathetic they regulate the same organs but have opposite effect due to the neurotransmitters that they used
• Sympathetic uses noradrenaline which has stimulating effects
• Parasympathetic uses acetylcholine which has inhibiting effects

Question 11

describe the sympathetic nervous system

Answer 11

• It is involved in responses that help us deal with emergencies such as increasing heart rate and blood pressure
• Neurons from the SNS travel to every organ and gland in the body this prepares the body for rapid action when the individual is under threat

Question 12

describe the parasympathetic nervous system

Answer 12

• Relaxes them once the emergency has past, it slows the heart rate and decreases blood pressure
• Digestion begins under PNS influence
• Involved in energy conservation and digestion therefore referred to as the bodies rest and digest system

Question 13

describe the structure and function of neurones

Answer 13

• Neurons are cells that are specialised to carry neural information throughout the body
• Three types – sensory, relay, motor
• Consist of a cell body, dendrites and an axon
• Dendrites – at one end of the neuron they receive signals from neuron or from sensory receptors they are connected to the cell body
• From the cell body the impuse is carried along the axon where it terminates at the axon terminal
• Myelin sheath is the insulating layer that forms around the axon, allows the nerve impulses to transmit more rapidly along the axon, length of neuron can vary

Question 14

describe sensory neurones

Answer 14

• Carry nerve impulses from sensory receptor to the spinal cord and the brain
• Found in various locations in the body
• Convert information from these sensory receptors into neural impulses
• When the impulses reach the brain they are translated into sensations so that the organism can react
• Not all sensory neurons travel as far as the brain with some ending in the spinal cord, allowing reflex actions to occur quickly

Question 15

describe relay neurons

Answer 15

• They lie between the sensory input and motor output, they allow sensory neurons to communicate with motor neurons
• Lie wholly in the brain and the spinal cord

Question 16

describe motor neurons

Answer 16

• Located in the CNS that project their axons outside the ACNS and directly or indirectly control muscles
• Form synapses with muscles and control their contractions
• When stimulated it reaches neurotransmitters that bind to the receptors on the muscle and triggers a response which leads to muscle movement
• When the axon of a motor neuron fires the muscle contracts
• Strength of the muscle contraction depends on the rate of firing of the aons of motor neurons that control it
• Muscle relaxation is caused by inhibition of the motor neurons

Question 17

describe the synaptic transmission

Answer 17

• Once an action has arrived at the terminal button at the end of the axon it needs to be transferred to another neuron or tissue
• Must cross a gap between the presynaptic neuron and postsynaptic neuron, this area is known as the synapse this includes the end of the presynaptic neuron, the membrane of the postsynaptic neuron and the gap in between
• Physical gap between pre and postsynaptic cell membrane is known as the synaptic gap
• At the end of the axon of the nerve cell are sacs known as synaptic vesicles – contain chemical messengers that assist in the transfer of the impulse
• When action reaches synaptic vesicles it causes them to release contents through exocytosis
• Released neurotransmitter diffuses through the gap and binds to specialised receptors on the surface of the cell that recognise it and are activated by that particular neurotransmitter
• Once activated they produce excitatory or inhibitory neurotransmitters
• Takes less than a second
• Effects terminated by a process called re-uptake, this is when the neurotransmitter is re-taken up by the presynaptic neuron where it is stored and used later
• How quickly the neurotransmitter is taken up again determines how prolonged its effects will be
• Some antidepressants inhibit the re-uptake therefore prolonging it and leaving the neurotransmitter in the synapse for longer
• Can be turned off after they have stimulated the postsynaptic neuron this is done through enzymes

Question 18

what are excitatory neurotransmitters

Answer 18

are the nervous systems on switches, they increase the likelihood that an excitatory signal is sent to the postsynaptic cell which is then more likely to fire

Question 19

what happens when an excitatory neuron binds to an postsynaptic receptor

Answer 19

it causes an electrical change in the membrane of the cell that results in an excitatory post-synaptic potential (EPSP) this means that the postsynaptic cell is more likely to fire

Question 20

what is an inhibitory neurotransmitter

Answer 20

are off switches, they decrease the likelihood that a neuron fires and calm the mind and body, induce sleep and filter out unnecessary excitatory neurons

Question 21

what happens when an inhibitory neurotransmitter binds with a postsynaptic receptor

Answer 21

results in a inhibitory postsynaptic potential (IPSP) making it less likely that the cell will fire

Question 22

what is the likelihood of a cell firing determined by

Answer 22

• Nerve cell can receive both ESPS and IPSP at the same time, therefore the likelihood of the cell firing is therefore determined by adding up the excitatory and inhibitory synaptic output

Question 23

how can the strength of EPSP be increased

Answer 23

• Strength of the EPSP can be increased in two ways – spatial summation is a large number of EPSP are generated in many different synapses on the same postsynaptic neuron at the same time or temporal summation this is when a large number EPSP are generated at the same synapse by a series of high frequency action potentials on the presynaptic neuron, the rate at which a particular cell fires is determined by what goes on in the synapses

Question 24

if excitatory are more active it …

Answer 24

fires at a higher rate

Question 25

if inhibitory are more active then…

Answer 25

they fire at a slower rate

Question 26

describe endocrine

Answer 26

• Produce and secrete hormones
• Majority include the pituitary gland, adrenal glands and reproductive organs
• Each gland produces different hormones
• Regulated by feedback, signal sent to hypothalamus who sends to endocrine who sends hormones to target organ which then causes change, change sensed by hypothalamus which shuts down secretion of hormones and slows down secretion of target organ hormones

Question 27

describe hormones

Answer 27

• Chemicals that circulate in the blood stream and carried to target sites
• They usually only affect a given number of target cells as they have receptors that are specific to that hormone
• When enough receptor sites are stimulated by hormones this results in physiological reaction in the target cell
• Timing of hormone release is critical for normal functioning as too little or too much released at the wrong time could lead to dysfunction

Question 28

describe pituitary gland

Answer 28

• Releases hormones who influence the release of hormones from other glands regulating many of the body functions
• Controlled by the hypothalamus, this receives information from many sources about the basic functions of the body and then regulates these functions
• Produces hormones which travel in the bloodstream and directly causes changes in physiological processes in the body or stimulate other glands to produce other hormones
• High levels of hormones in other endocrine glands can stop the hypothalamus and pituitary gland releasing more of their own hormones this is called negative feedback

Question 29

what are the main parts of the pituitary gland

Answer 29

• the anterior pituitary and posterior pituitary

Question 30

what does the anterior pituitary do

Answer 30

releases ACTH to respond to stress, it stimulates the adrenal glands to produce cortisol, the anterior also produces LH and FSH which is important in reproductive functioning, stimulate the ovaries to produce oestrogen and progesterone and in males that stimulate the testes to produce testosterone and sperm

Question 31

what does the posterior pituitary

Answer 31

• Posterior releases oxytocin which stimulates the contraction of the uterus during childbirth and is important in mother infant bonding

Question 32

describe the adrenal glands

Answer 32

• Two adrenal glands sit on top of the kidneys, made up of two parts, the outer part is called the adrenal cortex and the inner is known as the adrenal medulla
• Different in functions, hormones released by the cortex are essential for life whereas those released by the medulla are not

Question 33

describe the adrenal cortex hormones

Answer 33

produces cortisol which supports bodily functions, increased in response to stress, If cortisol is low then individual has low blood pressure and poor immune function and cannot deal with stress, It produces aldosterone which maintains blood volume and blood pressure

Question 34

describe the adrenal medulla hormones

Answer 34

releases adrenaline and noradrenaline that prepare the body for fight or flight, helps respond to stressful situations

Question 35

describe the fight or flight response

Answer 35

The amygdala and hypothalamus
- When individual is faced with a threat the amygdala responds, this associates sensory signals with emotions such as fear and anger
- Then sends a distress signal to the hypothalamus which communicates with the rest of the body
- Bodies response to stressors are two options – acute stressors such as personal attack, the second is chronic stressors such as a stressful job
Response to acute sudden stressors
The sympathetic nervous system
- It begins to prepare the body for rapid action necessary for fight or flight
- Sends a signal to the adrenal medulla which increases the hormone adrenaline
Adrenaline
- Goes through the body and causes physiological changes, causes heart beat to increase, and blood pressure to increase
- Breathing becomes more rapid and is deeper to increase the amount of oxygen
- Amount of energy increases in the body so it can reply to the fight or flight
The parasympathetic nervous system
- When the threat has past the parasympathetic branch of the ANS decreases the stress responses
- Causes the heartbeat and blood pressure to drop again
- Digestion happens again
Response to chronic stressors
- If the brain continually sees something as threatening then it uses a second system, this causes the adrenaline to decrease and the hypothalamus activates a stress response system called the HPA axis which consists of the pituitary gland and the adrenal gland
- H – this is the hypothalamus, relies on a series of hormonal signals to keep the SNS working and it releases a series of chemical messengers CRH which is released into the blood stream in response to a stressor
- P – this is the pituitary gland, when CRH arrives at the pituitary gland is causes it to produce and to release ACTH which is transported in the bloodstream to the adrenal glands
- A – the adrenal glands, the ACTH causes the adrenal cortex to release various stress related hormones including cortisol, which is responsible for some of the fight or flight responses, they can be positive meaning that it causes an increase in energy and a decrease in pain or negative as it causes impaired cognitive performance and a lowered immune system
- Feedback – this is efficient at regulating itself as both hypothalamus and pituitary glands have special receptors that monitor cortisol levels if they rise above normal then they initiate a reduction in CRH and ACTH levels

Question 36

describe localisation of function

Answer 36

Motor and somatosensory areas
The motor cortex
- Responsible for voluntary movement
- Located in the frontal lobe along the precentral gyrus
- Both hemispheres have a motor cortex and they control opposite sides of the body, they are arranged next to each other
The somatosensory cortex
- Detects sensory events arising from different regions in the brain
- Located in the parietal lobe of the brain along the postcentral gyrus, this is the area of the cortex which processes sensory information in regards to touch, it localises this area
- In both hemispheres receiving information from opposite sides of the body
Visual and auditory centres
Visual centres
- Located in the visual cortex in the occipital lobe of the brain
- Visual processing begins in the retina where light enters and strikes the photoreceptors, nerve impulses from the retina are then transmitted to the brain via the optic nerves
- Some nerve impulses from the retina travel to areas of the brain involved in coordination of the circadian rhythms but the majority end in the thalamus which acts as a relay station and passes information into the visual cortex
- Spans both areas of the hemisphere, right hemisphere receive input from the left hand side whiles the left receives input from the right
- Visual cortex has several different areas which process different types of visual information
Auditory centres
- Lies within the temporal lobes on both sides of the brain
- Begin in the cochlea in the inner ear this is where sound waves are converted to nerve impulses which travel via the auditory nerves to the auditory cortex in the brain
- First stops at the brainstem this is where the decoding takes place then next is the thalamus which acts as a relay station and also processes the information, last stop is the auditory cortex acts as a response
Language centres
Broca’s area
- Named after a French neurosurgeon who treated a patient who he referred to as tan as this was the only syllable that the patient could say
- Tan was able to understand language but not able to speak it, therefore Broca studied 8 other patients who had similar deficits along with lesions in their left frontal hemisphere, patients with damage to the right area did not have the same language problems therefore he identified a language centre in the frontal lobe in the left hemisphere which is critical for speech
- Other neuroscientists have found evidence of activity in the area when people perform cognitive tasks which have nothing to do with speech
- Fedorenko et al, discovered two regions of Brocas area one involved in language and the other to do with cognitive tasks
Wernicke’s area
- Discovered an area of the brain that was involved in understanding language, this was in the left temporal lobe
- Patients could speak but not understand language
- Therefore he proposed that language involves separate motor and sensory regions which are located in different cortical regions
- The motor region is near the area which controls the mouth therefore it control the mouth and tongue
- Sensory region is close to the regions that are responsible for auditory and visual input
- Neural loop that runs between Brocas and Wernickes area

Question 37

describe lateralisation and split brain research

Answer 37

Hemispheric Lateralisation
- Laternalisation refers to the two halves of the brain being not alike
- Each hemisphere is different, for example neural mechanisms for some functions of the brain such as language is primarily in one half of the brain. Broca established that damage in a particular area of the left brain hemisphere led to speech deficits whereas damage to the right hemisphere in the same place did not have the same effect
- Important question is if that language is in the left hemisphere then how can we talk about things in the right hemisphere, thereof ore the two hemispheres are connected this allows connection through a bundle of nerve fibres such as the corpus callosum
- In treatment for serve epilepsy surgeons cut the bundle of nerves that formed the corpus callosum this was done to prevent the violent electrical activity that accompanies electrical seizures this split their brain
Split brain research
Sperry and Gazzaniga’s research
- Sperry and Gazzaniga studied split brain patients, to test separated hemispheres they were able to send visual information to one hemisphere at a time in order to study hemispheric lateralisation
- As there was no corpus callosum the information can only be processed in the hemisphere that it is received in, in a typical study the split brain patient would focus on a dot in the centre of the screen while information was presented to either the left or right visual field, they were then asked to make responses with their left or right hand which is controlled by opposite hemispheres or verbally which is controlled by the left hemisphere without seeing what their hands were doing
- For example if the patient was flashed a picture of a dog on their right visual field they were asked what they were seen and they would reply dog but if they saw this on the left visual field then they would say that they see nothing as the information from the left visual field is processed by the right hemisphere which can see the picture but it has no language centre so cannot reply verbally
What have we learnt from split brain research
- Working with split brain patients have discovered a number of differences between the two hemispheres
- Left is responsible for speech and language
- And the right specialises in visual-spatial processing and facial recognition
- Split brain has not shown that the brain is organised into specific regions for specific tasks instead it suggests a connectivity between different regions

Question 38

describe plasticity and functional recovery of the brain

Answer 38

Neural organisation is changed as a result of experience, there are many types of experience that can do this
Plasticity as a result of life experience
- As people gain life experiences nerve pathways are used to develop stronger connections whereas neurons that are not used die out
- Therefore the brain can adapt to situations and changing environments
- Natural decline in cognitive functioning with age can be attributed to changes in the brain and this had led to evidence to look for ways in which new connections can be made to reverse this effect
- For example Boyke et al – found evidence of brain plasticity in 60 years old taught a new skill and this caused increases in grey matter in the visual cortex when the practising stopped changes are reversed
Playing video games
- Kuhn et al – they compared a control group with a video game training group that was trained for two months for at least 30 minutes a day on the game super Mario. They found increase in grey matter in various brain areas including the cortex hippocampus and cerebellum this is not evident in the control group who did not play the video game
- Caused new synaptic connections in brain areas involved in spatial navigation, planning, working memory and motor performance
Meditation
- Researchers working in Tibetan monks have been able to demonstrate that meditation changes the inner workings of the brain.
- Davidson et al – compared 8 monks who meditated with 10 volunteers who had no meditation experience, they were fitted with electrical wires and asked to meditate, electrodes picked up greater activity of gamma waves in the monks while the students only had a shorter increase of gamma waves
- Therefore meditation changes the workings of the brain in the short term and permeant as the monks had more gamma rays then before they started to meditate
Functional recovery after trauma
Using stroke patients it was found that the brain could re wire itself over time so that some level of function can be regained, although some parts are damages others take over the functions that were lost, neurons can make new circuits
Mechanisms for recovery
- Regenerative developments in brain functions arise from brains plasticity this is the ability to change structurally and functionally after trauma, it does this in two ways this is neuronal unmasking and stem cells
- Neuronal unmasking – Wall 1997, this identified dormant synapses in the brain, they exist anatomically but their function is blocked, as the rate of neural input is too low for them to be activated but increasing the rate of activity can cause them to work again and open connections this creates a spread of activation which leads to the development of new structures
- Stem cells – unspecalised cells that can differentiated and specialise they can become nerve cells therefore replacing damaged cells or neurodegenerative disorders, can be placed in the brain or transplanted that could rescue injured cells or they could form a new neural network

Question 39

describe ways of studying the brain

Answer 39

Post – mortem examinations
- Used to establish the underlying neurobiology of a particular behaviour
- May study behaviour while they are alive that suggest possible underlying brain damage, they can look for abnormalities which explain their behaviour
- Used for Brocas Tan to prove the brocas area
- Made it possible to identify parts of the brain that are to do with memory for example HM – his inability to memorise was shown by lesions in the hippocampus
Scanning techniques
Functional magnetic resonance imaging (fMRI)
- This measures changes in brain activity whole a person performs a task, measures change in blood flow in particular areas of the brain which indicates increased neural acitivity in that area, when brain activity increases in a particular area then the amount of oxygen supplied to that area increases and the change in blood flow is what the researchers measure
- Can be used to see a matching pattern of change and therefore results can be concluded
Electroencephalogram (EEG)
- Measures electrical activity in the brain as electrodes detect small electrical charges in the brain and this is recorded on a EEG
- This can be used to detect various types of brain disorder or diagnose other disorders that influence such as Alzheimer’s
- Four basic EEG patterns are alpaha waves, beta waves, delta waves and theta waves, when a person is awake but relaxed the alpha waves are recoreded when they are physiologically aroused their EEG patterns show a low amplitude and fast frequency beta waves, they are also found in REM sleep when eyes move back and forth, delta and theta occur when the person is asleep
Event – related potentials (ERPs)
- Small voltage changes in the brain that are triggered by specific events or stimuli, difficult to pick out from all the other electrical acitivity being generated at once
- Many presentations of the stimulus have to happen to established one particular average, has to cancel out background noise
- Can be divided into two categories – waves within the first 100 milliseconds are sensory ERPs as they reflect initial responses and those after the first 100 reflect how the individual evaluates the stimulus

Question 40

describe circadian rhythms

Answer 40

The nature of circadian rhythms
- Circadian rhythms are driven by our body clocks and are found in all cells of the body they are synchronised by the master circadian pacemaker – the suprachiasmatic nuclei which is found in the hypothalamus
- Pacemaker is constantly reset so that our bodies are in synchrony with the outside world
- Light is the primary input to the system, setting the body clock to the correct time is a process termed photoentrainment
- In mammals light sensitive cells within the eye act as brightness detectors and send messages to the SCN about the light levels, the SCN then use this information to coordinate the activity of the entire circadian system
The sleep wake cycle
- The circadian rhythm not only dictates when we should be sleeping but when we should be awake, light and darkness are the external signals that determine when we need to sleep and when we need to wake up
- Dips and rises happen at different times of the day, they usually occur between 2-4am and 1-3 pm this is where we feel more sleepy this is less intense if we have had sufficient sleep
- Sleep and wakefulness is also determined by the homeostatic control, when we are awake for a long time then it tells us that we need more sleep due to the energy used in wakefulness, gradually decreases during the day and then in late evening when most people fall asleep
- The circadian system keeps us awake as long as its daylight, promoting us to sleep as it becomes dark, the homeostatic system tends to make us sleepier as time goes on throughout the waking period regardless of night or day
- The internal circadian system keeps us awake and maintains a clock for about 24-25 hours a day even in the absence of external cues
- Major alternations in sleep and wake schedules because this causes the biological clock to become out of balance
Other circadian rhythms
- Core body temperature – best indications of the circadian rhythm, it is at its lowest at 36 degrees which is at 4:30am and at its highest 38 degrees which is at 6:00 pm, sleep occurs when the core body temperature drops and the body temperature rises in the last hours of sleep this promotes the feeling of alertness
- Hormone production – hormone release follows a circadian rhythm for example the production and release of melatonin from the pineal gland in the brain and follows a circadian rhythm, peak levels occur in the dark and by activating chemical receptors in the brain it encourages feelings of sleep

Question 41

describe ultradian and infradian rhythms

Answer 41

Ultradian rhythms
- The sleep portion of this cycle follows a type of rhythm called an ultradian rhythm, this is a biological rhythm that is referred to as ultradian as it lasts less than 24 hours
Sleep stages
- Ulradian rhythm found in human sleep follows a pattern of alternating REM (rapid eye movement) and NREM (non rapid eye movement) this consists one through 4 stages
- Cycle repeats itself every 90-100 minutes with stages having different duratiosn
- Cycle consists of a progression through the 4 stages of NREM sleep before entering a final stage of REM sleep then the whole cycle starts again
- Stage 1- 4-5%, this is light sleep, muscle activity slow down, occasional muscle twitching
- Stage 2 – 45-55% breathing pattern and heart rate slows, slight decrease in body temperature
- Stage 3- 4-6% deep sleep begins, brain begins to generate slow delta waves
- Stage 4-12-15% very deep sleep rhythmic breathing, limited muscle acitivty and brain produces delta waves
- Stage 5 – 20-25% - rapid eye movement, brainwaves speed up and dreaming occurs, msucles relax and heart rate increases, breathing is rapid and shallow
The basic rest activity cycle
- Kleitman 1969 – referred to the 90 minute cycle found during sleep as the best rest acitivty cycle (BRAC), but he suggested that the 90 minutes occur during the day, but rather than moving through sleep stages we move progressively from a state of alertness into a state of sleep stages
- Human can focus for 90 minutes and towards the end they loos concentration, fatigue and hunger
Infradian rhythms
- Rhythms that are longer than 24 hours, they may last days, weeks months or even may be annual
- Like the female menstrual cycle in humans
Weekly rhythms
- Lots of weekly rhythms confined to 7 days a week for example male testosterone levels increase at the weekends as they are more likely to have sex than during the weekdays, frequency of births on weekends is lower than on weekdays
- Halberg et al – reported 7 day rhythms of blood pressure and heart rate but evidence is weak
Monthly rhythms – human menstrual cycle
- Women’s reproductive cycle lasts about 1 month and is regulated by hormones which either promote ovulation or stimulate the uterus for fertilisation
- Ovulation occurs halfway through when the oestrogen level peaks and lasts for 16 to 32 hours, after the ovulatory phase progesterone levels increase in preparation for the possible implantation of an embryo in the uterus
Annual rhythms
- Annual rhythms are related to the seasons for example migration
- Research suggests a seasonal variation in mood in humans some people become depressed in the winter and this is also associated with an increase in heart attacks which varies seasonally and peaks in the winter, most deaths occur in January

Question 42

endogneous pacemakers and exogenous zeitgebers

Answer 42

Endogenous pacemakers
- Refer to the organs that are within the organism
- Products of inherited genetic mechanisms and allow us to keep pace with changing environment
- Most important pacemaker is the superchiasmatic nucleus – SCN
The superchiasmatic nucleus
- SCN is main pacemakers and lies in the hypothalamus
- Generates the circadian rhythm, links to other regions in the brain which control sleep
- Neurons within the SCN synchronise with each other so that their target neurons in sites elsewhere in the body receive correctly time co-ordinated signals, these peripheral clocks maintain a circadian rhythm but not for long as they must be controlled by the SCN
- Possible because the SCN built in circadian rhythm which only needs resetting when external light levels change, SCN receives light levels via the optic nerve, this happens when our eyes are shut as eyes penetrate the eyelids, if our biological clock is running slow then morning light automatically adjusts the clock putting it in rhythm with the world outside
The pineal gland
- SCN sends information to the pineal gland in order to make it increase production and secretion of the hormone melatonin at night and to decrease it as light levels increase in the morning
- Pineal and SCN jointly function as endogenous pacemakers in the brain
- Sensitivity to light means it must be synchronised with the light dark rhythm outside
Exogenous zeitgebers
- Refers to anything that are outside the organism
- Environmental events that are responsible for entraining the biological clocks
Light
- Receptors in the SCN are sensitive to changes in light levels
- Keeps body on a 24 hour clock
- Retina and rods detect light in visual images
- Protein called melanopsin is sensitive to natural light which is critical in this system
Social cues
- Aschoff et al showed that individuals are able to compensate for the absence of zeitgebers such as natural light by responding to social zeitgebers
- Early stucies of jet lag found that circadian rhythms of air travellers adjusted more quickly if they went outside more at their destination as they are exposed to social cues of their new time zone
- Blind peoples circadian rhythms are no different to sighted people as both groups are exposed to the same social cues as there are still connections between the eye and the SCN