Neurophysiology and Behaviour - OPTION E Flashcards
1
Q
Neural development
A
= processes that generate, shape, and reshape the nervous system, from the
earliest stages of embryogenesis to the final years of life.
2
Q
Simplified breakdown of human fertilization process
A
zygote –> morula –> (blastocoele) –> blastula,
3
Q
Non-simplified breakdown of human fertilization process
A
After fertilization the zygote divides, soon forming an embryo with a cluster of 16-32 cells called a morula.
After the 64-cell stage, this ball develops an inner cavity, called the blastocoele, thus becoming a blastula, and about 7 to 8 days after fertilization, the embryo becomes implanted in the uterine wall.
During the formation of the gastrula some cells of the blastula soon being moving toward the interior of the blastocoele to form distinct layers – mesoderm, ectoderm and the endoderm. The nervous system is derived from the ectoderm—the outermost tissue layer—of the embryo. The notochord (dorsal cord) – appears – eventually becomes vertebrate.
4
Q
Neurulation =
A
folding process in vertebrate embryos, which includes the transformation of the neural
plate into the neural tube.
The embryo at this stage is termed the neurula.
Around the third week of gestation, the notochord sends a molecular signal that causes the cells of the ectoderm just above it to thicken into a column called the neural plate. The neural plate begins to invaginates (folds inward) to form the neural groove along the back of the embryo which then closes to form the neural tube. This develops into the brain and the spinal nerve cord.
5
Q
Spina bifida =
A
closing of the neural tube = event in the development of the nervous
system –> When the neural tube fails to close correctly, serious birth defects can result.
Spina bifida, which occurs in about 1 of every 1000 births. It is caused by a malformation of the caudal portion of the neural tube. This malformation in turn results in a malformation of the lower vertebrae that
often leaves the spinal cord exposed, makes it vulnerable to injury, and limits use of the legs and feet.
Spina bifida causing a gap higher up the back is more likely to cause paralysis of the lower limbs and mobility difficulties compared with gaps in the middle or at the base of the back. A baby is more likely to have cognitive symptoms if he or she develops hydrocephalus, due to excess spinal fluid in the brain.
6
Q
Spina bifida appears to be associated with …
A
Spina bifida appears to be associated with a deficiency of folic acid. This vitamin should be available in sufficient quantities in the pregnant mother’s food, but if her diet is poor or imbalanced, the resulting shortage of folic acid can be serious enough to interfere with the formation of the neural tube.
7
Q
Development of Neurons and the Central Nervous System
A
- Cell division in the neural tube produces large numbers of cells that differentiate into neurons.
- Axons grow out of immature neurons in response to chemical stimuli.
- Some axons extend beyond the neural tube to reach other parts of the body.
- Some immature neurons migrate to their final location and become sensory or motor neurons.
- Developing neurons form multiple synapses with other neurons.
- It is a use it or lose it approach – if the neurons and synapses are not being used the neural pruning occurs – this is an example of the plasticity of the nervous system throughout life.
Both the brain and spinal cord develop from the neural tube. As the embryo grows the neural tube lengthens. The anterior develops into the brain, the rest forms the spinal cord. This happens before birth.
8
Q
Using Animal Models for research - benefits
A
Some animals commonly used include :
- Caenorhabditis elegans (flatworm),
- Drosophila melanogaster (fruit fly)
- Danio rerio (zebra fish)
- Xenopus laevis (African claw frog)
- Mus musculus (mouse)
Research and experimentation into embryonic development and many aspects of physiology is difficult to do with humans. Model organisms are in vivo models and are widely used to research human disease when human experimentation would be unfeasible or unethical. eg. it may involve damage to the developing embryo or to the adult.
–> made possible by the common descent of all living organisms, and the conservation of
metabolic and developmental pathways and genetics over the course of evolution.
Studying model organisms can be informative, but care must be taken when extrapolating from one organism to another. Animals are
used to build understanding and to research treatments for developmental diseases.
9
Q
Using Animal Models for research - concerns
A
Humans have different biochemical pathways and what may work for a mouse or a frog may not work for humans “if you are a mouse with cancer, we can cure you”
ethics of animal experimentation have resulted in scientists finding alternative methods to test drugs, cosmetics and diseases.
10
Q
Basic overview of the brain
A
The brain is one of the largest organs in the body.
It is protected by the skull, the meninges (membranous coverings), and the cerebrospinal fluid (CSF).
The brain is the control centre for the body.
11
Q
Cerebellum:
A
controls automatic (unconscious) functions such as movement and balance.
It is an ancient part of the brain that we have in common with mammalian brain.
12
Q
Brain Stem:
A
the central trunk of the mammalian brain, consisting of the medulla oblongata, pons, and midbrain, and continuing downwards to form the spinal cord. The autonomic nervous system controls involuntary processes in the body using centres located mainly in the brain stem.
13
Q
Thalamus:
A
main relay centre. All sensory messages enter here before they are sent to the cerebrum.
14
Q
Hypothalamus:
A
maintains homeostasis, such as temperature and blood sugar, and coordinates the nervous
and endocrine systems, controls pituitary gland.
15
Q
Medulla oblongata:
A
controls automatic and homeostatic activities, Such as:
- swallowing involving involuntary muscle contraction, and vomiting,
- breathing rate in response to chemoreceptors in blood vessels responding to carbon dioxide levels,
- heart rate altered by stimulating the heart pacemaker nerve (sino atrial node) to increase or decrease the heart contractions.
16
Q
Pituitary gland:
A
secretes hormones produced by the hypothalamus, regulating many body functions. Eg. FSH, LH, Growth hormone, Prolactin
17
Q
Cerebral cortex (cerebrum)
A
The cerebrum forms a larger proportion of the brain and is more highly developed in humans than other animals. The human cerebral cortex has become enlarged principally by an increase in total area with
extensive folding to accommodate it within the cranium.
Cerebrum is divided into two cerebral hemispheres (left/right).
18
Q
Left and Right Hemispheres
A
The two hemispheres communicate information to each other through the corpus callosum (white matter)
right hemisphere controls the muscles on
the left side of the body, while the left hemisphere controls the muscles on the right side of the human body. Because of cross over wiring, damage to one side of the brain affects the opposite side of the body.
In general, the left hemisphere is dominant in language: logic and exact mathematical computations.
The right hemisphere is mainly in charge of spatial abilities, face recognition and processing music and visual imagery.
19
Q
Hemisphere –> lobes
A
Each is then divided into four lobes: frontal, occipital, temporal and parietal lobes.
Is involved in complex higher order functions such as memory, emotion, language, reasoning and sensory processing.
20
Q
Sensory cortex (Somatosensory)
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receives sensory inputs especially touch. Left somatosensory cortex receives sensory information from right side of body etc.
21
Q
Motor cortex
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controls voluntary muscle contractions. (Left–right cross over)
22
Q
Visual cortex
A
processes visual stimuli by rod and cone receptors in retina of eye. (Left–right cross over). Also includes pattern recognition, speed, direction judgement.
23
Q
Brocas Area
A
controls production of speech.
If a person has damage to this they can not put sounds together to create meaning.
24
Q
Wernickes area
A
controls understanding of written and spoken language
25
Nucleus accumbens
deep in the frontal cortex.
It acts as pleasure or reward centres of the brain. Stimuli such as food, sex, good times cause the release of dopamine that give a feeling of wellbeing.
But, drugs such as nicotine, alcohol, cocaine and heroin also cause the release of dopamine in the nucleus accumbens, and in some cases, these drugs cause much more dopamine release than ‘natural,’ non-drug
rewards.
26
Ventricles:
Cavities containing cerebrospinal fluid, which absorbs shocks and delivers nutrients.
27
Meninges:
membrane covering which protects the brain hemispheres.
28
Body size and Brain size = correlation
There is a strong positive correlation between brain and body mass. The higher above the correlation line the larger brain in relation to body mass.
29
Methods Used to Study the Brain - Animal experiments:
Many experiments are done on animals to determine brain operation. Often primates are used to gain insight into human brain.
The animal is kept alive, its skull is open and various section of the brain are stimulated,
removed, altered etc and the effect on the animal is recorded during and after.
Improved imaging technology is reducing the use of this method in some areas of research.
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Methods Used to Study the Brain - Brain damage - Lesions = Autopsies
Damaged areas of the brain called lesions are caused accident, stroke and tumours.
The loss of brain function gives insight into the areas that are controlled by the brain.
Autopsies after death can locate the areas of
damage and lesions.
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Brain damage - Lesions
Damaged areas of the brain called lesions are caused accident, stroke and tumours.
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Methods Used to Study the Brain - FMRI (functional magnetic resonance imaging)
Active parts of the brain have increased blood flow so a person may be given a stimulus eg. picture of food, and a scan is taken to determine which parts of the brain become active.
Although specific functions can be
attributed to certain areas, brain imagery
shows that some activities are spread in
many areas and that the brain can even
reorganize itself following a disturbance
such as a stroke.
33
stimulus =
is a change in the environment (internal or external) that is detected by a receptor and elicits a response.
34
Human sensory receptors are classified as - Mechanoreceptors:
sensory receptors that respond to mechanical pressure.
Eg. Pacinian corpuscles in the skin and hair cells in the cochlea are the most sensitive mechanoreceptors in transducing air pressure waves into sound. eg, muscles, skin
35
Human sensory receptors are classified as -Chemoreceptors:
sensory receptors that respond to chemicals.
Eg. olfactory receptor neurons in the nose
and taste buds on the tongue. Chemicals in the air are detected by the many different olfactory receptors.
36
Human sensory receptors are classified as - Thermoreceptors:
sensory receptors that respond to relative changes in temperature.
Warm and cold receptors in the skin play a part in sensing environmental temperature.
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Human sensory receptors are classified as - Photoreceptors:
sensory receptors that respond to light,
most commonly referring to a specialized type of neuron found in the retina of vertebrate eyes that is capable of photo transduction
38
nociceptor =
Damaged tissues release prostaglandins, which stimulate a nociceptor pain
neurons.
The passage of impulses from the pain receptors travel to the sensory areas of the cerebral cortex. The feeling of pain is due to these areas of the cerebral cortex
stimulated by: chemical, thermal, or mechanical event that has the potential to damage body tissue,
39
Photoreception - The Structure and Function of the Human Eye
The human eye is essentially a three layered structure comprising an outer fibrous layer (the schlera and cornea), a middle vascular layer (the choroids, ciliary body and iris), and inner retina (neurons and photoreceptor cells).
The shape of the eye is maintained by the
fluid filled cavities (aqueous and
vitreous humors), which also assist in
light refraction.
Eye colour is provided by the pigmented
iris. The iris also regulates the entry of
light into the eye through the contraction
of circular and radial muscles.
40
Vision - two stages (simplified):
formation of the image on the retina and generation and conduction of
nerve impulses.
41
Vision - expanded explination
When light reaches the retina, it is absorbed by the photosensitive pigments associated with the membranes of the photoreceptor cells (the rods and cones). The pigment molecules are altered by the absorption of light in such a way as to lead to the generation of nerve impulses. It is these impulses that are conducted via nerve fibers in the optic nerve to the visual processing centre of the cerebral cortex.
42
Vision - Cells of the Retina
Light falls on the pigment epithelium of the retina at the back of the eye. This stimulates the rods and cones. An impulse (action
potential) is generated which moves through the cells to the optic nerve.
43
Vision - Rods
specialised for vision in dim light.
They sensitive to all visible wavelengths versus three types sensitive to red, blue and green light. The passage of impulses is from a group of rod cells to a single nerve fibre in the optic nerve.
44
Vision - Cones
specialized for colour vision and high visual acuity.
Cone density and visual acuity are greatest in
the central fovea (rods are absent here). Best in bright light.
45
Vision - cones - 3 types = trichromatic colour vision.
There are three classes of cones, each with a maximal response in either short (blue), intermediate (green) or long (yellow-green) wavelength light. The yellow-green cone is also sensitive to the red part of the spectrum and is often called the red cone.
The differential responses of the cones to light of three different wavelengths is called trichromatic colour vision.
46
vision - Colourblindness
inability or decreased ability to see colour or precieve colour differences.
It occurs when one or more of the cone cells are in fewer numbers
The most usual cause is a fault in the development of one or more sets of retinal cones. This type of color blindness is usually a sex-linked condition.
47
vision - Bipolar cells
in the retina combine the impulses from rod or cone cells and send them on to ganglion cells of the optic nerve.
48
vision - Ganglion cells
send messages to the brain via the optic nerve.
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optic chiasma.
The left and right optic nerves meet at a
structure called the optic chiasma. Here, all
the neurons that are carrying impulses from
the half of the retina nearest to the nose
cross over to the opposite optic nerve.
Beyond the optic chiasma, the neurons continue to the thalamus, where the information is processed. It is then carried to the visual cortex at the back of the brain, where further processing leads to formation of images.
50
contralateral processing
the left optic nerve carries information from the right half of the field of vision and vice versa. This is called contralateral processing is due to the optic chiasma, where the right brain processes information from the left visual field and vice versa.
51
The Ear and Hearing (Mechanoreception) - Eardrum:
Eardrum vibrates as sound waves from the air hit and transmits the vibrations to the middle ear.
52
The Ear and Hearing (Mechanoreception) - Bones of the middle ear:
These small bones called ossicles (anvil, hammer and stirrip) act as levers,
amplifying sounds by 20 times and then transmit vibrations to the oval window.
53
The Ear and Hearing (Mechanoreception) - Oval Window:
Transmits sound waves to the fluid filling the cochlea which moves the Round window.
Hence waves can move across the fluid in the cochlea.
54
The Ear and Hearing (Mechanoreception) - Hair cells in the cochlea:
The cochlea is a spiral tube with receptors called hair cells. Sound waves in the
fluid vibrate the hair cells at particular frequencies and wavelengths. This causes the hair cells to send messages via the auditory nerve to the brain.
55
The Ear and Hearing (Mechanoreception) - Auditory nerve:
Impulses caused by sound perception are transmitted to the brain via the auditory nerve.
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The Ear and Hearing (Mechanoreception) - Eustachian tube:
maintains internal pressure the same as outside via throat
57
The Ear and Hearing (Mechanoreception) - Semicircular canals
Hair cells in the semicircular canals detect movement of the head. The sensory hairs are in a swollen area of each semicircular canal which are in three different planes, so can detect motion in any direction.
Due to the inertia of the fluid it lags behind - hence the continued sense of motion when spinning or other fast or prolonged movement.
58
Use of cochlear implants in deaf patients.
Cochlea implants can help people with
non-functional cochlea hair cells.
The external parts are a microphone, a
speech processor and a transmitter.
The internal parts are implanted in bone
behind the ear consists of a stimulator that
converts the sound into electrical impulses
and electrodes that carry the ipulses to the
cochlea. The electrodes directly stimulate
the auditory nerve, by-passing the non
functioning hair cells
59
Neuropharmacology - neurotransmitters
Some neurotransmitters excite nerve impulses in postsynaptic neurons and others inhibit them.
Nerve impulses are initiated or inhibited in post-synaptic neurons as a result of summation of all excitatory and inhibitory neurotransmitters received from presynaptic neurons.
60
Excitory neurotransmitters :
When the neurotransmitter binds to the receptors on the postsynaptic neuron it
causes positively charged ions
eg. Na+ caused to enter the postsynaptic neuron. This causes the post synaptic membrane potential to rise (-70 mV to -50mV).. inducing an excited action potential which travels along the neuron.
61
Inhibitory neurotransmitters :
When the inhibitory neurotransmitter binds to the receptors on the postsynaptic neuron it causes negatively charged ions
eg. Cl- are caused to enter the postsynaptic neuron. This causes the post synaptic membrane potential to drop (-70 mV to -80mV).
This inhibits the action potential.
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Glutamate
Brain Excitory Too much causes excitotoxicity eg. epilepsy, Parkinsons disease
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GABA
Brain Inhibitory Sedative drugs enhance the effects of GABA
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Acetylcholine
Motor nerves (muscles) Brain Excite and inhibit Curare (poison darts) blocks transmission
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Dopamine
Brain Excite and inhibit Affects emotion, reward, motivation. Parkinsons have low dopamine
66
Seratonin
CNS Excite and inhibit Low levels linked to depression
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Adrenaline (epinephrine)
Brain Excites Blood vessel constriction, Alertness
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Slow Acting Neurotransmitters
Some neurotransmitters such as norepinephrine, dopamine and serotonin are slow acting.
They diffuse through surrounding fluid affecting groups of neurons and can affect transmission of days. Eg. dopamine reward feeling may last for hours or days.
Many different slow-acting neurotransmitters modulate fast synaptic transmission in the brain.
Memory and learning involve changes in neurons caused by slow-acting neurotransmitters.
69
Psychoactive Drugs
is a chemical substance that changes brain function and results in alterations in
perception, mood, or consciousness.
Drugs exert their effects on the nervous system by mimicking or blocking the action of neurotransmitters at synapses.
Drugs can act in various regions of the brain to exert their effects, but their ability to alter dopamine neurotransmission in the ventral tegmental area (VTA) and the nucleus accumbens is one of the most important factors that drives continued drug use.
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Psychoactive drugs affect the brain by either - (Stimulants)
increasing postsynaptic transmission
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Psychoactive drugs affect the brain by either - (Sedatives)
decreasing postsynaptic transmission
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Stimulants - Excitory psychoactive drugs. OVERVIEW
Affect the brain and personality by increasing synaptic transmission by mimicing a neurotransmitter or stimulating the release of a neurotransmitter or inhibiting it’s reabsorbtion or opening a neuroreceptor channel.
Stimulant drugs mimic the stimulation provided by the sympathetic nervous system. They are excitory psychoactive drugs that increase synaptic transmission. Most affect dopamine. Dopamine synapses are
responsible for pleasurable feelings.
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Stimulants - Nicotine
binds to receptors in the pre-synaptic neuron leading to depolarization and increased dopamine.
Nicotine is shaped similarly to acetylcholine, it can fit in the same receptors and act just like acetylcholine.
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Dopamine
Dopamine is a neurotransmitter responsible for carrying messages about pleasurable feelings. The result is stimulation of the “reward system” in the brain, which causes feelings of pleasure.
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Stimulants - Cocaine
Cocaine stimulates transmission of synapses that use the neurotransmitter dopamine.
Normally, dopamine is recycled back into the transmitting neuron by a transporter molecule on the surface of the neuron. But if cocaine is present, the drug attaches to
the transporter and blocks the normal recycling of dopamine, causing an increase of dopamine levels in the synapses.
= neurons to continuously fire giving feelings of euphoria, energy and alertness.
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Stimulants - (Amphetamines (MDMA, ecstasy, methamphetamine, P, crystal meth, ice)
Promotes the release of slow acting serotonin and dopamine causing an increase of dopamine and serotonin levels that leads to euphoria.
Methamphetamines actually cause the release of dopamine from the vesicles. This is
independent of the rate of action potentials
and, depending on dose, can cause a relatively quick and prolonged rise of extracellular dopamine levels.
Methamphetamine also blocks the dopamine
transporter from pumping dopamine back into the transmitting neuron. Methamphetamine acts similarly to cocaine in this way
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Sedatives - Inhibitory Psychoactive drugs - OVERVIEW
Affect the brain and personality by decreasing synaptic transmission by blocking a neuro receptor channels or inhibiting the Na + K + pump or blocking the Na + / K + channels.
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Sedatives - Benzodiazepines
(eg. valium (diazepam), rohypnol (date rape drug), xanax) are sedative-hypnotics used as skeletal-muscle relaxants, sleeping pills and to treat anxiety, seizures,
Benzodiazapine drugs bind to an allosteric site on GABA receptors in post synaptic membranes.
GABA is an inhibitory neurotransmitter and when it binds to its receptor a chloride
channel opens, causing hyperpolarisation of the post synaptic neuron.
When benzodiazapines are bound to the receptor the chloride ions enter at a greater
rate – inhibiting nerve impulses.
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GABA
GABA is an inhibitory neurotransmitter and when it binds to its receptor a chloride
channel opens, causing hyperpolarisation of the post synaptic neuron.
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Sedatives - Tetrahydrocannabinol (THC),
Inhibits transmission at cannabinoid synapses in the brain by blocking the release of excitory neurotransmitters.
Cannabinoids also indirectly increase dopamine by blocking the action of another neurotransmitter called GABA. GABA normally acts to dampen the amount of dopamine released in the nucleus accumbens.
However, when GABA is blocked by marijuana compounds, such as THC, the result is an increase in the amount of dopamine released. Hence the feel good effect and addiction.
The effects of THC on mood and behaviour include memory impairment, poor psychomotor control and intoxication.
81
Sedatives - Alcohol
it acts as a depressant by both increasing inhibitory neurotransmission (GABA
systems) and by decreasing excitatory neurotransmission (glutamate). Alcohol also increases dopamine and seratonin secretion.
Alcohol consumption is initially accompanied by decreased attention, alterations in memory, mood changes, reduction of social inhibitions, pleasurable feelings and drowsiness. Continued acute
consumption may result in lethargy, confusion, amnesia, loss of sensation, difficulty in breathing, and death.
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Causes of Addiction - Dopamine secretion:
many addictive drugs affect synapses that use dopamine as a neurotransmitter giving
pleasurable feelings. When the drug is removed, the affect of having much reduced levels of dopamine, and pleasurable feelings make it difficult for addicts to not resume taking the drug.
83
Causes of Addiction - Genetic predisposition:
Addiction has a genetic link. Some genes have been identified that increase the likelihood of a person becoming addicted. This may link to natural dopamine levels which make the drug taking experience more pleasurable or the stopping more unpleasant.
84
Causes of Addiction - Social factors:
Cultural traditions, peer pressure, poverty, life experiences, mental health all contribute to
addiction.
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Painkillers, Analgesics and Anaesthetics -->. Endorphins
Endorphins are natural opiate type compounds produced by the pituitary gland during strenuous exercise/excitement. Endorphins work by binding to the pain receptors (nociceptors) and block the release of neurotransmitters. They also give a sense of well-being as they bind to the body opioid receptors.
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Painkillers, Analgesics and Anaesthetics -->. Analgesics
Analgesics relieve pain without eliminating sensation
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Non-narcotic analgesics
Non-narcotic analgesics such as aspirin, paracetamol and ibuprofen block prostaglandin production at
source of pain, while paracetamol has a similar effect in the brain.
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Narcotic analgesics (opiates)
Narcotic analgesics (opiates) which include morphine, codeine, opium, methadone and diamorphine (heroin), all block opiate receptors, blocking transmission of pain signals in the brain and spinal chord.
The brain’s natural endorphins appear to have a similar action.
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Painkillers, Analgesics and Anaesthetics -->. Anaesthetics
Anaesthetics act by interfering with neural transmission between areas of sensory perception and the CNS.
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General anaesthetics
General anaesthetics cause a reversible loss of consciousness. Eg. Barbituates, Benzodiazapines, Propofol. These only cause unconsciousness, not pain relief so analgesics must be used as well. Sometime muscle relaxants are used.
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Local anaesthetics
Local anaesthetics cause a reversible loss of sensation for a limited region of the body while maintaining consciousness. They act by bonding to Na channels.
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Innate and learned behaviour - OVERVIEW
Behaviours in animals can be attributed to two components: innate behavior that has a genetic basis and learned behavior, which results from the experiences of the animal.
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innate behavior
genetic basis
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learned behavior
results from the experiences of the animal.
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Properties of Innate versus Learned Behaviour - Learned behaviour
Learned behaviour describes the process of acquiring new knowledge or skills (which can be improved with practice). Learned behaviour is dependent on environmental context and can disappear over time if the context is absent
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Properties of Innate versus Learned Behaviour - Innate behaviour
Innate behaviour describes instinctive responses that are ingrained in an animal (it is encoded in the DNA). It can only be modified by genetic change (mutation) which would take place over many generations
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Innate behaviours and Natural selection
Innate behaviour is inherited and is not influenced by the environment, including experiences the organism has during its life.
An organism with the genes for a particular behaviour that increases survival and
reproduction will pass those genes to the offspring.
Many behaviours are innate – even behaviours that seem very complex eg. migration, homing, breeding, courtship, nest building, aggression, feeding.
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Reflexes - OVERVIEW
A stimulus is a change in the environment that is detected by a receptor and elicits a response.
Some responses happen without conscious thought – involuntary responses. Many controlled by the autonomic nervous system.
Autonomic and involuntary responses are referred to as reflexes.
A reflex is a rapid, unconscious automatic response to a stimulus involving a small number of neurons and a central nervous system (CNS) processing point (usually the spinal cord, but sometimes the brain stem). This type of circuit is often called a reflex arc.
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Reflexes - Spinal reflexes
are controlled by the spinal cord:
- The pain withdrawal reflex. Eg. if foot stands on pin, it stimulate a pain receptor in the skin. The pain receptor passes a message to a sensory neuron, which carries it as a nerve impulse to the spinal cord. The message is passed via a linking neuron, called an association neuron to a motor neuron. The
motor neuron carries the message to a muscle in the leg. The message stimulates the muscle to contract, pulling the foot away from the pin. The muscle is called the effector.
- The cross-extensor reflex causes extensor muscles in the other leg to contract, so that it supports the bodys weight.
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Reflexes - Cranial reflexes
Cranial reflexes are controlled by the brain stem:
- The pupil reflex is one example.
If a bright light shines into one eye, the pupils of both eyes constrict. Photoreceptor cells in the retina detect the light stimulus. Nerve impulses are sent in sensory neurons
of the optic nerve to the brain. The brainstem processes the impulses and then sends impulses to circular muscle fibers in the iris of the eye. These muscle fibers contract, causing the pupil to constrict. The pupil reflex is sometimes tested in unconscious patients to help determine whether recovery is
possible. If the pupil reflex and other brainstem reflexes have been lost the patient has probably suffered brain death and will not recover.
- The conjunctival reflex is another example of a cranial reflex.
If the conjunctiva is touched lightly, blinking occurs. The touch stimulus is passed to the brain along sensory neurons in the fifth cranial nerve. Messages are sent along motor neurons in the seventh cranial nerve to stimulate muscles in the upper and lower eyelids to contract and cause blinking.
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Learned Behaviours
result of the conditions that an animal experiences during development. Learned
behaviours include conditioning and imprinting.
Survival chances are increased as a result of learning. If conditions change then animals can adapt to them.
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Classical (Pavlovian) Conditioning = associative learning.
Animals come to associate one stimulus with another. Classical conditioning, founded by Ivan Pavlov, describes a type of associative learning in which behavior that is normally triggered by a certain stimulus comes to be triggered by a substitute stimulus that previously had no effect on the behavior.
Pavlov discovered that the ringing of the bell initially brought about no salivation, but the dogs could be conditioned to relate the ringing of the bell to the presentation of food. Eventually the ringing of the bell elicited the same salivation response as the presentation of food, indicating that the dog was conditioned to associate the two stimuli.
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Imprinting
When animals learn a response to a stimulus during a sensitive age period this is called imprinting.
Konrad Lorenz investigated imprinting in greylag geese. He removed some of the eggs and was present when they hatched. He was the first moving object they saw. The goslings followed him rather than their mother.
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The Role of Inheritance and Learning
Most behaviours in animals combine varying proportions of both genetic (innate) and learned aspects.
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The Role of Inheritance and Learning (example)
The acquisition of birdsong shows these two aspects. Bellbirds use their songs to attract females, to advertise territories and to identify themselves to other birds. The songs in a particular area are specific to each family
of birds that live there. Bellbirds from one area have quite different songs from those in other areas. Young birds are born with the innate ability to sing and call. However they learn the specific songs of the family of
birds in their area. If young birds are taken to other areas they will learn a different song.
Chaffinch studies show that a bird reared in isolation can make a song the correct length and with some notes correct. However the chick must hear an adult male singing within the first few weeks to get the song correct.
Hence some aspects are innate and some learned.
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Ethology
Ethology is the study of animal behaviour in natural conditions.
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animal behaviouralists (1) - Jane Goodall
Jane Goodall (1934- ) is a British ethologist who has spent her life studying chimpanzees in Africa. She famously observed that they have distinct personalities and are capable of behaviour like hugging and tickling each other. Perhaps her most famous observation was that they are capable of using tools.
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animal behaviouralists (2) - Dian Fossey
Dian Fossey (1932-1985) was an American ethologist who studied mountain gorillas in Africa. She lived very closely with them and they became habituated to her. Fossey famously became the first person to be recorded making peaceful contact with a wild gorilla. A photograph (taken in 1969) shows a young male named Peanuts touching her hand. She spent her later years working to prevent poaching.
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animal behaviouralists (3) - Konrad Lorenz
(1903-1989) was a German ethologist who won the Nobel Prize with Nickolaas
Tinbergen He is most famously remembered for his work on imprinting.
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animal behaviouralists (4) - Nikolaas Tinbergen
Nikolaas Tinbergen (1907-1988) was a Dutch ethologist who also won the Nobel Prize. He studied gulls and showed that their chicks instinctively knew to peck at red spots on their parents’ beaks to encourage them to regurgitate food.
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animal behaviouralists (5) - Karl von Frisch
Karl von Frisch Waggle dance in bees showing bee communication and navigation behaviours.
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The three main principles are of ethology
1. Natural selection can change the frequency of observed animal behaviour.
2. Behaviour that increases the chances of survival and reproduction will become more prevalent in a population.
3. Learned behaviour can spread through a population or be lost from it more rapidly than innate behaviour.
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Behaviour and Natural Selection - OVERVIEW
Natural selection is a mechanism of evolution by which the frequency of inherited traits change as a result of environmental selection. (Remember the peppered moth!)
Characteristics which promote survival and reproduction (i.e. beneficial alleles) become more prevalent in a population.
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Behaviour and Natural Selection - EXAMPLE: Blackcaps and Migration
Migratory behaviour in blackcaps as an example of the genetic basis of behaviour and its change by natural selection.
However, studies show that 10% of blackcaps now migrate to the UK instead. Blackcaps are genetically programmed to respond to stimuli (eg. magnet field lines) when they migrate so that they fly in a particular direction. The increase in the numbers of blackcaps migrating to the UK for the winter may be due to warmer winters and greater survival rates in the UK for those birds who have a genetic variation that makes them follow a different
magnet compass to the UK rather than Spain. The blackcap bird breeds during the summer in Germany and, until recently, migrated to Spain or other Mediterranean areas for winter. The migratory behaviours in blackcaps has been demonstrated to have a genetic basis via a number of experiments
= Chicks raised in isolation will follow the migratory routes of their parents (hence it is an innate trait and not learned)
= Hybrid chicks of parents with different migration routes will migrate in a direction between the two parental directions (This suggests heterozygote hybrids exhibit a combination of the migratory tendencies from each homozygous parent) The great tit lays eggs in response to lengthening day length ie. late spring. This is genetically determined.
Some birds have genetic variations that mean they lay earlier. In the past these birds would have reproduced unsuccessfully because of the cold. However many birds are now laying eggs earlier and because the weather is warmer more chicks are surviving.
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Behaviour and Natural Selection - EXAMPLE - Vampire Bats and Altruism
Blood sharing in vampire bats as an example of the development of altruistic behaviour by natural selection.
Altruism is behaviour which benefits another individual at the cost of the performer. Altruism reduces the potential for the altruistic individual passing on their genes however improves the chances of the other
individual passing on genes into the same gene pool (i.e. inclusive fitness) If the individuals are closely related, altruistic genes will persist in the gene pool and be naturally selected Enhancing the reproductive success of relatives who share common genes is called kin selection Organisms that live in social clusters will also promote the conservation of altruistic genes via reciprocal altruism.
Vampire bats commonly regurgitate blood to share with unlucky roost mates who were unable to gain independent sustenance. Vampire bats cannot survive multiple successive days without food, however food
can often be difficult to find The small cost of sharing blood (lost time until starvation) is less than the benefit received (time gained) So sharing blood improves the fitness of the entire brood (via reciprocal altruism), increasing the occurrence of altruism
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Behaviour and Natural Selection - EXAMPLE - Bees and Kin selection
In these colonies, the queen is the only female that reproduces. Throngs of sterile female workers handle nearly every other task in the colony, from scouting and collecting food, to building the hive, and raising the young. Since successive generations of these insects are born from the same mother, they are, in fact, sisters. This may explain the single-minded drive to feed and protect the young at the cost of their own reproduction.
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Survival and Reproduction
Behaviour that increases the chances of survival and reproduction will become more prevalent in a population.
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Foraging Behaviours
Foraging is the act of searching for (and potentially finding) food resources in nature
As availability and abundance of food resources vary, animals must adapt their foraging practices to account for any changes
Animals with optimal foraging strategies will have more available energy with which to survive and reproduce
According to the optimal foraging theory, animals will adopt strategies that:
1. Minimise the cost of foraging (i.e. the amount of energy used to capture and consume prey)
2. Maximise the benefits to the consumer (i.e. the amount of energy yielded by a particular food source)
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Foraging Behaviours - EXAMPLE - Shore Crab
Foraging behaviour in shore crabs as an example of increasing chances of survival by optimal prey choice.
Shore crabs demonstrate selectivity in the type of mussel foraged when the mussel population is abundant:
- Crabs will ignore smaller mussels (as the energy yield is less than that obtained from larger mussels)
- Crabs will also ignore larger mussels (difficult to crush, also risks potential damage to the crab’s claws)
- Crabs will selectively identify and feed on mid-sized mussels (provided the mussel supply is in abundance)
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Foragaing behaviours - EXAMPLE - Bluegill fish
Bluegill fish live in ponds and eat small free swimming crustacea called Daphnia. When food is in short supply, the bluegill eat all sizes sizes of Daphnia to survive. However when there are lots of Daphnia the bluegill select
only the large ones. This means they don’t waste energy catchig small ones and grow much much larger.
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Foragaing behaviours - EXAMPLE - Starlings
Starlings feed their young on insects which they hold in their mouths. Flying using energy. So the greater distance a startling has to travel to find insects the more insects they will hold in their mouths.
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Foragaing behaviours - EXAMPLE - Predators
Predators (eg. lions, cheetahs, crocodiles) selection of weak or young prey maximizes success of hunt and limits injury and energy
expenditure.
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Breeding Behaviours - OVERVIEW
Behaviour that increases the chances of successful reproduction will become more prevalent in a population.
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Breeding Behaviours - Courtship and Mate Selection
Many different types of behaviour are aimed at ensuring successful reproduction.
Courtship behaviours are stereotyped and ritualised and occur as a prelude to mating. Courtship behaviours may include visual displays (inflating pouch, extending wings, copying), grooming, vocalisations (calls), gift giving, feeding, nest building,
touch.
The aims of courtship includes:
Reducing conflict between potential mates Attracting a mate to a breeding site
Assessing the receptivity of a mate Defending chosen mates against other suitors
Assessing the ‘fitness’ of a potential mate Species recognition
Trigger to nest building or ovulation Strengthen pair bond
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Courtship in Birds of Paradise
Females appear drab. Males will have bright plumage and display fancy behaviours to demonstrate their virility
While these features make them a target for predators, they improve chances of attracting female attention (mate selection)
Any exaggerated trait that improves reproductive fitness will become more prominent in future generations
(sexual selection)
Many animals have exaggerated characteristics or behaviours that have evolved as a result of this sexual selection. Sexual selection may leads to the evolution of sexual dimorphism where the male is significantly different from the female.
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Courtship in Peacocks
Peacocks brightly coloured tail feathers make the peacock slow moving, visable to predators and difficult to fly. These are selected by the female peahen as a sign of health and vigor, It
may also be that any individual that can survive despite the disadvantage that the trait has must be well adapted and so is a good choice of mate.
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Mating Systems
These are the ways in which males and females bond during courtship and mating.
1. Polygyny
2. Polyandry
3. Polygynandry
4. Monogamy
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Polygyny
males mate with more than one female eg. most mammals such as deer, horses, seals,
baboons
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Polyandry
females mate with more than one male eg. some birds such as emu
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Polygynandry
several males with several females (promiscuous) eg. pukeko, cats, bonobo chimps
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Monogamy
Breeding pair that forms a partnership for a season or life eg. human, penguins, kiwi
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Mating system - additional = Oviparity
egg laying eg. fish, birds, reptiles
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Mating system - additional = Viviparity
embryo develops inside the body of the mother (eg.placental or marsupial or in some fish, insects)
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Parental Care - OVERVIEW
The success of a species depends on producing enough young that will survive to be able to reproduce.
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Parental Care - R-strategy -
Animals that have little or no parental care:
Produce large numbers of offspring
Low reproductive effort per offspring
Reproductive effort is directed at producing offspring..not caring for them
Eg. fish, insects, frogs
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Parental Care - K-strategy
Animals that have parental care:
Produce few offspring
High reproductive effort per offspring
Reproductive effort is directed at caring for offspring after birth
Eg. humans, elephants, birds
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Breeding Strategies in Coho Salmon
Breeding strategies in Coho salmon populations as an example of behaviour affecting chances of survival and
reproduction.
Male coho salmon form two different breeding populations according to the strategy used for passing on genes:
- All males initially undergo a development phase as juveniles in which they grow within freshwater rivers (~12 months)
- Following that, the males migrate out to the ocean for a period of maturation, whereby they differentiate into two populations"
Some of the male salmon develop into ‘jacks’, while other male salmon will develop into ‘hooknoses
- Jacks are smaller and well camouflaged – they only require ~ 6 months in the seawater to reach maturity
- Hooknoses are larger and brightly coloured – they require ~ 18 months in the seawater to reach maturity
Jacks and hooknoses employ different breeding strategies in order to successfully reproduce with female coho salmon:
- Jacks sneak out from behind rocks or recesses in the riverbed and attempt to stealthily mate with a female
- Hooknoses swim within the open water and fight aggressively amongst one another for the opportunity to mate
Having two breeding pathways improves the rates of successful reproduction and also increases levels of genetic variation
- Jacks have higher rates of survival (as they spend less time in seawater), but have more competition for reproduction
- Hooknoses have lower rates of survival but consequently experience less direct competition for successful mating
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Synchronised Oestrus in Female Lions
Synchronized oestrus in female lions in a pride as an example of innate behaviour that increases the chances of survival and reproduction of offspring. Female lions synchronise their sexual receptiveness
(oestrus) to increase chances of survival and
reproduction of offspring
Lionesses remain in the same pride their entire lives, living with genetic relatives (sisters, aunts, nieces)
Male lions leave their birth group at a young age and in order to reproduce must replace males in existing prides. Upon establishing dominance within a pride, a male lion will kill all cubs already present
The loss of cubs triggers an innate, synchronised response whereby all lionesses enter a period of oestrus
There are many advantages to synchronising oestrus:
= It increases the number of offspring the male lion can produce (risks of displacement are always present)
= It allows for shared lactation and nursing of cubs within the pride (all female lions nurse
indiscriminately)
= It is easier for the lionesses to hunt and defend the pride if all cubs are of a comparable age
