SNAB Biology- Topic 8


Nervous and hormonal communications

Responding to the environment helps organisms survive.

1) Animals increase their chances of survival by responding to chnages in their external environment, (avoiding harmful environments such as places too hot or cold)

2) They respond to changes in internal environment to ensure conditions are always optimal for their metabolsim. (chemical reactions that occur inside)

3) Plants also increase their chances of survival by responding to changes in their environment 

4) Any change in the internal or external environment is called a Stimulus.

Receptors, detect stimuli and effectors produce a response:

- Receptors dectet stimuli - can be cells or proteins on cell surface membranes. Loads of different types of receptors that detect different stimuli.

-Effectors are cells that bring a response to a stimulus, to produce an effect. Effectors include muscle cells and cells found in glands (Pancreas)

Receptors communicate with effectors through nervous system or the hormonal system.

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Nervous and hormonal communications

The nervous system sends information as Electrical impulses 

- The nervous system is made up of a complex netwoek of cells called neurones. There are Three main types:

  • Sensory neurones transmit electrical impulses from receptors to the central nervous system (CNS)- the brain and spinal cord
  • Motor neurones transmit electrical impulses from the CNS to effectors.
  • Relay neurons transmit electrical impulses between sensory neurones and motor neurones.

A stimulus is deceted by receptor cells and electrical impulse is sent along sensory neurone.

When an electrical impulse reaches the end of a neurone chemicals are called neurotransmitters takes information acroos to next neurone.

The CNS processes the information and sends impulses along motor neurone to effectors

Electrical impulses are also called nerve impulses or action potentials.

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Nervous and hormonal communications

The hormonal system sends information as chemical signals. The hormonal system is made up of glands and hormones.

  • A Gland is a group of cells that are specialised to secrete a useful substance such as a hormone Eg. Pancreas secretes insulin.
  • Hormones are 'chemical messengers'. Many hormones are proteins or peptides such as insulin.

Hormones are secreted when a gland in stimulated

  • Glands can be stimulated by a change in concentration of a specific substance 
  • They can also be stimulated by electrical impulses

Hormones diffuse directly into the blood, then theyre taken around the body by the circulatory system.

They diffuse out of the blood all over the body but each hormone will only bind to specific receptors for that hormone 

The hormones trigger a response in the target cells 

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Nervous and hormonal communications

Nervous communication:

  • Uses electrical impulses
  • faster responses- electrical impulses are really fast 
  • Localised response 
  • Short-lived response

Hormonal communication:

  • uses chemicals 
  • Slower response - hormones travel at speed of blood 
  • Widespread response 
  • Long-lived response 
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The nervous system - Receptors

  • Receptors are specific- only detect one particular stimulus 
  • There are many different types of receptors that each detect a different type of stimulus 
  • Some receptors are cells (Photoreceptors are receptor clls that connect to the nervous system)
  • Some are proteins on the cell surface membrane (Glucose recpetors are proteins found in the cell membranes of some pancreatic cells.
  • When an nervous system receptor is in its resting stage there's a difference in charge between the inside and the outside of the cell. This means theres a voltage across the mebrane (The membrane is said to be polarised.
  • The votage across the membrane is called the Potential difference.
  • If the change in potenial difference is big enough it will trigger an action potenital - an electrical impulse along a neurone. 
  • An action potential is only triggered if the potential difference reaches a certain level called the threshold.
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The nervous system - Receptors

Photoreceptors are light receptors in your eye 

Light enters the eye through the pupil. The amount of light that enteres is controlled by the muscles of the iris.

Light rays are focused by the lens onto the retina, which lines the inside of the eye . The retina contains photoreceptoe cells - These dectect light 

The fovea is an are of the retina where there are lots of photorceptors 

Nerve impulses from photoreceptor cells are carried from the retina to the brainby the optic nerve (bundle of neurones).

Where the optic nerve leaves the eye is called the blind spot- No photoreceptor cells - Not sensitive to light.

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The nervous system - Receptors

Photoreceptors convert light into an electrical impulse 

Light enteres the eye, hits photorecetors and is absorbed by light-sensitive pigments.

Light bleaches the pigments, causing a chemical change.

This triggers a nerve impulse along a bipolar neurone.

Bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain 

The human eye has two types of photorecteptor - RODS and CONES 

Rods are mainly found in the periphreal parts of the retina, and cones are foud packed together in the fovea.

Rods only give information in black and white (MONOCHROMATIC VISION), cone gives colour information (TRICHROMATIC VSION). There are three types of cones, Red-sensitive, green-sensitive and blue-sensitive. Stimulated in different proportions so you see different colours.

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The nervous system - Receptors

Rod cells Hyperpolarise when stimulated by light. Rods contain a light-sensitive pigment called rhodopsin it is made of two chemicals joined together- Retinal and ospin.

  • Sodium ions (Na+) are pumped out of the cell using active transport
  • Soduim ions diffuse back in to the cell through open sodium channels 
  • Inside of cell only slightly negative compared to outside- cell membraine said to be depolarised
  • Triggers the release of neurotransmitters
  • Neurotransmitters inhibit the bipolar neurone
  • Bipolar neurone can't fire an action potential so no information goes to the brain.
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The nervous system - Receptors

When its light your rod cells are stimulated.

  • Light energy causes rhodopsin to break apart into retinal and opsin, this is called bleaching. Bleaching of rodopsin causes the sodium ino channels to close.
  • Sodium ions are actively transported out of the cell, cant diffuse back in
  • Sodium ions build up on the outside of the cell, making the inside of the membrane much more negative than the outside- the cell membrane is hyperpolarised
  • when rod cell is hyperpolarised it stops releasing neurotransmitters. This means there's no inhibitation of the bipolar neurone.
  • The bipoar neurone is no longer inhibited, it depolarises if the change in potential difference  reaches the threshold, an action potential is transmitted to the brain via optic nerve
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The nervous system- Neurones

  • All neurones have a cell body with a nucles
  • The cell body has extensions that connect to other neurones- dendrites and dendrons carry nerve impulses towards the cell bodt, and axons carry nerve impulses away from the cell body The three different types of neurone have slightly different structures and different functions.

Motor Neurones- many short dendrites carry nerve impulses from the central neurous system (CNS) to the cell body. One long axon carries nerve impulses from the cell body to effector cells 

Sensory Neurones- One long dendron carries nerve impulses from receptor cells to the cell body, which is located in the middle of the neurone, One short axon carries nerve impulses from the cell body to the CNS.

Relay neurones- Many short dendriets carry nerve impulses from sensory neurones to the cel body. An axon carries nerve impulses from the cell body to motor neurones.

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The nervous system- Neurones

Neurone cell membranes are Polarised at rest

  • In a neurone's resting state (not being stimulated), the outside of the mebrane is positively charged compared to the inside. This is because there are more positive ions outside than inside
  • Membrane is polarised - difference in charge 
  • Volatage across membrane when it is at rest is resting potential
  • Resting potenital is created and maintained by sodium-potassium pumps and potassium ions channels in a neurones membrane: Sodium potassium pump use active transport to move three sodium ions (NA+) out of the neurone for every two potassium ions(K+) moved in. ATP is needed for this 
  • Potassium ion channel allow facilitaed diffusion of potassium ions(K+) out of the neurone, down concentration gradient.
  • Sodium-potassium pumps move soidum ions out, membrame is not permeable to sodium ions, so cant get back in. Creates sodium ion electrochemical gradient (concentation gradient of ions) more positive sodium ions outside the cell than inside 
  • Sodium-potassium pumps also move potassium ions in to the neurone, but membrane is permeable to potassium ions so they diffues back out through potassium ion channels
  • Makes outside of the cell positively charged compare to the inside.
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The nervous system- Neurones

Neurone cell membranes become depolarised when they're stimulated. Stimulus trigger ion channels called sodium ion channels to open. If the stimulus is big enough it will trigger a rapid change in potenial difference - Action potential

  • Stimulus- this excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, sodium ions diffuse into the neurone down the sodium ion elctrochemical graident. This mkaes the inside of the neurone less negative.
  • Depolarisation- if the potenital difference reaches the threshold (around -55mV) more sodium ions channels open. More sodium ions diffuse into the neurone.
  • Repolarisation- At potential difference of around +30 mV the sdium ion channels close and potassium ion channels open. The membrane is more permeable to potassium so potassium ions diffuse out of the neurone down the potassium ion concentration gradient. This starts to get membrane back to its resting potential.
  • Hyperpolaristion- Potassium ion channels are slow to close so there's slight 'overshoot' where too many potassium ions diffuse out of the neurone. The potential difference becomes moe negative than resiting potential.
  • Resting potential-  The ion channels are reset. The sodium-potassium pump returns the membrane to its resting potential and maintains it untill the membrane's excited by another stimulus.

After an action potential cell membrane cant't be excited again straight away. Ion channels are recovering and cant open. sodium ion channels are closed during repolarisation and potassium ions channels are closed during hyperplarisation. Period of recovery called refactory period.

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The nervous system- Neurones

The action potential moves along the neurone as a wave of depolarisation.

  • When an action potential happens,some of the sodium ions that enter the neurone diffuse sideways.
  • This causes sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part.
  • This causes a wave of depolarisation to travel along the neurone
  • The wave moves away from the parts of the membrane in the refractory period because these parts can't fire an action potential.
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The nervous system- Neurones

The action potential moves along the neurone as a wave of depolarisation.

  • When an action potential happens,some of the sodium ions that enter the neurone diffuse sideways.
  • This causes sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part.
  • This causes a wave of depolarisation to travel along the neurone
  • The wave moves away from the parts of the membrane in the refractory period because these parts can't fire an action potential.

Bigger stimulus causes more frequent impulses

Once the threshold is reached, an action potential will always fire with the same chnage in voltage, no matter how big the stimulus is.

If threshold isn't reached, an action potential wont fire.

A bigger stimulus won't cause a bigger action potential, but it will cause them to fire more frequently.

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The nervous system- Neurones

Preventing the movement of Sodium ions stops action potential

Local anaesthetics are drugs that stop you from feeling pain in a localised are of your body.

They work by binding to sodium ion channels in the membrane of neurones.

This stops sodium ions from moving into the neurones, their membranes will not depolarise.

This prevents action potential from being conducted along the neurones and stops information about pain reaching the brain.

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The nervous system- Neurones

Action potentials go faster in Myelinated Neurones 

  • Some neurones are Myelinated (They have a myelin sheath)
  • Myelin sheath is an electrical insulator 
  • Its made of a type of cell called a Schwann cell.
  • Between the Schwann cells are tiny patches of bare membrane called the nodes of Ranvier. Sodium ion channels are concentrated at the nodes.
  • In a Myelinated neurone, depolarisation only happens at the Nodes of Ranvier (Where sodium ions can get through the membrane)
  • The Neurones cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse 'jumps' from node to node ( Saltatory conduction and its really fast)
  • In a non-myelinated neurone, the impulse travels as a wave along the whole length of the axon membrane.
  • This is slower than saltatory conduction 
  • The spped at which an impulse moves along a neurone is known as the conduction velocity. A high conduction velocity means that the impulse is traveling quicly 
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The nervous system- Synapses

A Synapse is a junction between a neurone and another neurone or between a neurone and an effector cell

  • The tiny gap between the cells at a synapse is called the synaptic celft.
  • The presynaptic neurone has a swelling called the synaptic knob. Contains Synaptic vesicles filled with chemicals called neurotransmitters.
  • When an action potential reaches the end of a neurone it casues neurotransmitters to be released into the synaptic cleft. These diffuse across to the postsynaptic memebrane and bind to specific receptors.
  • When neurotransmitters bind to receptors they may trigger an action potential, causes a muscle contaction or a hormone to be secreted.
  • Receptors are only on postsynaptic membranes, synapes make sure impulses are undirectional -( only travel one direction)
  • Neurotransmitters are removed from the cleft so the response doesnt keep happening, they are taken back to the presynaptic neurone or broken down by enzymes
  • There are many different neurotransmitters such as actylecholine and dopamine. Actylcholine is involved in muscle contaction and the control of heart rate 
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The nervous system- Synapses

How neurotransmitters transmit nerve impulses between neurones 

1) Action Potential triggers Calcium influx

An action potential arrives at the synaptic knob of the presynaptic neurone. Action potetial stimulates volage-gated calcium ion channels in the presynaptic neurone to open. Calcium ions diffuse into the synaptic knob (Pumped out afterwards by active transport)

2) Calcium influx causes Neurotransmitter Release

Influx of calcium ions into they synaptic knbob causes the synaptic vesicales to move to the presynapic membrane. The fuse with the presynaptic membrane. The vesicles release the neurotranmitters into the synaptic cleft this is called exocytosis.

3) Neurotranmitter triggers an action potential in the postsynaptic neurone

The neurotransmitter diffues across the synaptic cleft and binds to specific receptors on the postsynapic membrane. This causes sodium ion channelsin the postsynapic neurone to open, The influx of sodium ions into the postsynapic membrane cause depolarisation. An action potenital on the postsynaptic membrane is generated if the threshold is reached. The neuronetransmitter is removed from the synaptic cleft so the response does not keep heppening.

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The nervous system- Synapses

Synapses play vital roles in the nervous system

1) Synapese allow information to be dispered or amplified

When one neurone connects to mant neurones information can be dispesed to different parts of the body (Synaptic divergence)

Many neurones connect to one neurone information can be amplifed (Made stronger) - ( Synaptic convergence)

2) Summation at synapses finely tunes the nervous response 

If the simulus is weak only small amounts of neurotransmitters will be relased from neurone to the synaptic cleft. This might not be enough to excite the postsynaptic memebrane to the threshold level to stimulate an action potential.

Summationis where the effect of neurotansmitter released from many neurones is added together ( one neurone is stimulated a lot in a period of time) 

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Responses in Plants

Plants need to repsond to stimuli too 

Plants just like animals increase their chances of survival by responding to changes in their environment 

- They sense the direction of light and grow towards it to maximuse light absorbtion for photosynthesis

- They can sense gravity, so their roots and shoots grow in the right direction.

- Climbing plants have a sense of touch so they are able to find things to climb and reach the sunlight.

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Responses in Plants

A tropism in a plant's groeth response to an external stimulus 

  • A tropism is a response in a plant to a directional stimulus 
  • Plants respond to directional stimuli by regulating their growth
  • A Positive tropism is growth towards the stimulus 
  • A Negative tropism is growth away from the stimulus
  • Phototropism is the growth of a plant in response to light
  • Shoots are positively phototropic and grows towards light 
  • Roots are negativly photoropic and grows away from light
  • Geotropism is the growth of a plant in response to gravity 
  • Shoots are negatively geotropic and grow upwards
  • Roots are positively geotropic and grow downwards
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Responses in Plants

Responses are brought about by growth factors 

Plant do not have a nervous system so they cannot respond using neurones, they do not have a circulatory system so they cannot respond using hormones.

Plants respond to stimuli using growth factors- these are chemicals that speed up or slow down plant growth.

Growth factors are produced in the growing regions of the plant ( Shoot, tips leaves) and thye move to where they are needed in other parts of the plants 

Growth factors called auxins stimulate grwoth of shoots by cell elongation- this is where cell walls become loose and stretchy, so cells get longer 

High concentrations of auxins inhibit growth in the roots

Many other plant growth factors such as:

  • Gibberellins- simulate flowering and seed germination 
  • Cytokinins- stimulate cell division and cell differenatiation 
  • Ethene- stimulates fruit ripening and flowering 
  • Abscisic (ABA) involved in leaf fall
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Responses in Plants

Indoleacetic Acid (IAA) this is an important Auxin That's produced in the tips of shoots in flowering plants. When it enters the nucleus of a cell, its able to regualte transcription of genes related to cell elongation and growth.

IAA is moved around the plant to control tropism (moves by diffusion and active transport over short distances) and via the Phloem in long distances.

This results in different parts of the plants having different amounts of IAA. The uneven distribution of IAA means there's uneven growth of the plant.

Phototropism:  IAA moves to the more shaded parts of the shoots and roots so there is uneven growht 

Geotropism: IAA moves to the underside of shoots and roots so there is uneven growth.

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Responses in Plants

Plant detect light using photoreceptors called phytochromes 

These are found in many parts of a plant including the leaves, seeds, roots and stem

Phytochromes control a range of responses such as plants flower in differnt seasons depending on how much daylight there is at that time of year

Photochromes are molecules that absorb light. They exist in two states Pr state absorbs red light at a wavelength of 660nm amd the Pfr state absorbs far-red light at wavelenghth of 730nm

Daylight contains more red light than far-red light 

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Different areas of the brain

Different areas of the brain control different functions 

The cerebrum

  • The cerebrum is the largest part of the brain
  • Its divided into two halves called cerebral hemispheres
  • Has a thin outer layer called ther cerebrum cortex. Has a large surace area so its highly folded to fit into the skull
  • Involved in the vision, learning, thinking, emotions and movement
  • Back cerebrum involved in vision and the front is involved in thinking

The hypothalamus

  • Found beneath the middle part of the brain 
  • Maintains body temperature at normal level (Thermoregulation) 
  • Produces hormones that control the pituitary gland
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Different areas of the brain

The medulla oblongata

  • Is at the base of the brain at the top of the spinal cord 
  • Automatically controls breating rate and herat rate

The cerebellum

  • Is underneath the cerebrum and it also has a folded cortex
  • Important for coorsingating movement and balance
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Brain structure and function

To investigate the structure and function of the brain and to dignose medical conditions, you need to look inside This can be done with surgery, the brain can be visualised without surgery using scanners

  • 1. Computed Tomography (CT) scanners use Lots of X-rays 
  • CT scanners use radiation (X-Rays) to produce cross-section images of the brain, Dense structures in the brain absorb more radiation than less dense structures so show up as a lighter colour on the scan.
  • If CT scanner shows diseased or damaged brain structure and patient has lost fucntion, the function of that part of the brain can be worked out.

Medical Diagnosis 

  • CT scans can be used to diganose medical problems because they show damaged or disased areas of the brain EG. Bleeding in the brain after a stroke
  • Blood has a different density from brain tissue so it shows up as a lighter colour on a CT scan
  • A scan can show the extent of the bleeding and its location in the brain 
  • Can the work out which blood vessls have been dmaged and what brain functions are likly to be afftected by the bleeding 
  • CT scans are potenially dnagerous using X-Ray- can cause mutations in DNA, which may lead to cancer. Risk of CT scan is VERY LOW
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Brain structure and function

Magnetic resonance imaging (MRI) Scanners use Magnetic fields. MRI use a really strong magnetic field and radio waves to produce cross-section images of the brain.

Investigating brain structure and function

MRI gives higher qulaity images for soft tissue types and better resolution between tissue types for an overall better resolution. MRI shows clearly the difference betwwen normal and abnormal brain tissue. CT scanning, brain function can only be worked out by lokking at dmaged areas.]

Medical diagnosis

MRI scans can also be used to diagnose medical problems as it shows damages or siseased areas of the brain eg Brain tumor 

  • Tumor cells respond differently to a magnetic field than healthy cells so they show up as a lighter colour
  • A scan will show exact size of a tumor and its location in the brain, Doctors use this to decide most effective treatment 
  • work out what brain functions may be affected by the tumour
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Brain structure and function

Functional magnetic resonance imaging (fMRI) scanners show barin activity

  • More oxygenated bloos flows to active areas of the brain 
  • Molecules in oxygenated blood responds differently to a magnetic field than those in deoxygenated blood the singnal returned to the scanner is stonger from the oxygenated blood, which allows more active areas of the brain to be identified.

Investigating brain structure and function

An fMRI scan gives a detailed, high resolution picture of the brain structure, similar to an MRI scan but they can also be used to research the function of the brain. If a function is carried out whilst in the scanner, the part of the brain that is involved with that function will be more active.(Such if a patient moves their left hand, the area of brain involved will be highlighted)

Medical diagonsis 

fMRI scans show damaged or diseased areas of thr brain and allow you to study conditions caused by abnormal activity in the brain. Eg. an fMRI scan can be taken of a patients brain before and during a seizure. This can help to pinpoint which part of the brain is not working properly and can find the cause of the seizure. Patient can recieve mots effective treatment

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Brain structure and function

Positron Emission Tomography (PET) scanners use Radioactive material 

Pet scanners can show how active different area of the brain are

  • A radioactive tracer is introduced into the body and is absorbed into the tissues
  • The scanner sectects the radioactivity of the tracer- building up a map of radioactivity in the body 
  • Different tracers can be used eg. radioactivity labelled glucose can be used to look at glucose metabolism

Investigating brain structure and function 

PET scans are very detailed and can be used to investigate both the structure and the function of the brain in real time.

Medical diagnosis

Pet scans can show is areas in the brain are unusually inactive or active, so they are particulary useful for studying disorders that chnage the brain's activity Eg. Alzheimer's disease.

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Habituation is a type of learned behaviour 

  • Animals including humans increase there chance of survival by responding to stimuli, if the simuli is unimportant (not threatening or rewarding) no point in responding
  • If unimportant stimulis is repeated over time, an animal learns to ignore it (Habituation)
  • Habituation means animals dont waste enegry responding to unimportant stimulis. Alos means thye can spend more time doing other activites for there survival such as feeding 
  • Animals still reamin alert to important stimuli (stimuli which might threathen their survival) 

Fewer Electrical impulses are sent to effectors 

Effectors that carry out the responses to different stimuli are controlled by nervous stimulation. Habituation to a stimulus mean fwewr electrical impulses are sent to the effectors.

  • Repeted exposure to a stimulus decreases the amount of calcium ions that enter the presynaptic neurone
  • This decrease in the influx of calicum ions meaning less neurotansmitters are relased from vesicles into the synaptic cleft, so fewer neurotransmitters can bind to receptors in the postsynaptic membrane
  • As a result, fewer signals are sent to the effector to carry out the response.
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Visual Cortex

The visual cortex is made up of Ocular Dominance Columns. 

  • The visula cortex is an area of the cerebral cortex at the back of your brain
  • THe role of the visual cortex is to receive and process visual information 
  • Neurones in the visual cortex recieve information from either the left or right eye.
  • Neurones are grouped together in columns called Ocular dominace columns. If they recieve from right eye called right ocular dominace columns, if from left- left ocular dominance columns.
  • Columns are same size and they are arranged in an alternating pattern (left, right, left, right) across the visula cortex 
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Visual Cortex

Hubael and Wiesel used animal models to study the visual cortex

  • Some animals have very similar brains to humans, means that scientists can do experiemnets on these animals to investigate brain development
  • Structure of the visual cortex was discovered by Hubael and wiesel they used animal models to study the electrical activity of neurones in the visual cortex 
  • Found that the left ocular dominance columns were stimhlated when an aminal used its left eye, and the right ocular dominance columns were stimulated when used its right eye.

There experiment provise evidence for a critical period in humans 

  • theres a period in early life when it is critical that a kitten is exposed to visual stimuli for its visual cortex ti develop properly. called critical period (same as humans)
  • A cataract makes the lens in the eye go cloudy causing blury vision 
  • If a baby has cataract it is importan to remove it within the first few months of the baby's life otherwise the visual system wont develop properly and vision will be damaged for life
  • If an adult has cataract it is not that serious when the cataract is removed, normal vision comes back straight away, this is because the system is already developed.
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Development of the visual cortex

Visula stimulation organises the nerurones during the critaical period

  • Baby mammals (including humans) are born with lots of neurones in their visual cortex, these neurones need visula stimualtion to become properly organised 
  • Proper organisation of the visual cortex involves the elimination of unnecesary synapes to leave behind those that are needed in processing visual information.
  • During critical period of development, synapeses that recieve stimualtion and pass nereve impulses into the visual cortext are retained.
  • Synapes that dont recieve and visual stimualtion dont pass any on, any nerve impulses to visual cortex are removed.
  • Means if eyes are not stimulated with visual information during critical period, visual cortex will not develop properly as many synapes will be destroyed.
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Brian development

Brain development is how the brain grows and how the neurones connect together 

Mesures of brain development includes ths size of the brain, number of neurones it has and level of brain functions a person has.

Brain develops the way it does due to genes and your environment, brain would develop differently is you had different genes or were brought up in a different environment.

1 Animal experiements

  • Study the effects of different environments on the brain development of animals of same species these are gentically simailar so diffrences in brain developement more likely to be nurture 
  • to study effect of diffrent genes, scientists can genetically engineer mice to lack a particular gene and the raise mice with and without the gene in similar environments.
  • diffrences between the genetically engineered mice and normal mice more likly to me nature 
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Twin studies

  • If identical twins are raised spearately then they will have identical genes but diffrent environments.

Scientists can comapre the brain development of sperated idntical twins any diffrences are due to nurture and not nature and any simailarites are due to nature

Identical twins that are raised together are gentically identical and have similar environments, this means its hard to tell if any diffrences between them are due to nature or nurture. so they comapre them to non-identical twins 

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Cross-culture and New born studies

Children brought up in diffrent cultures have diffrent environmental influences 

Scientists can study the effects of a different uprbringing on brain development by comparing large groups of children who are the same age but from different cultures 

Scientists look for major diffrences in characteristics. Any diffrences in brain development between diffrent cu,tures are due to nurture. 

Newborn studies

The brain of a newborn baby hasn't really been affected by the environment 

Scientists study the brain of newborns to see what functions they are born with and how developed different parts are of the brain. What they are born with is due to nature.

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Brain damage studies

Damage to and adults brain can lead to the loss of brain function eg stroke may cause loss of vision.

If an adult's brain is damaged it cant repair itself so well as it is already fully developed. But a childs brain is still developing - scientists cans study the effects of brain damage on their development.

Scientists compare the development of a chosen function in children with and without brain damage 

If the characteristis still dveelops in children who have brain damage, then brain development is more likely to be nurture for that characteristic 

If it doesnt develop in children who have brain damage, than brain development is more likely to be due to nature because nurture isnt having an effect 

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Imbalances in some neurotransmitters can contribut

Parkinson's disease- is a brain disorder that affects the motor skills of people

  • The neurones in the parts of the brain that control movement are destroyed 
  • Normally produce the neurotransmitter dopamine, so losing them causes a lack of dopamine
  • Less Dopamine is relased into the synaptic clefts, so less dopamine is avaliable to bind to the receptors on the postsynaptic membranes
  • Fewer sodium ions channels on the postsynaptic membrane open, so the postsynaptic cell is less likely to depolarise
  • Fewer action potentials are produced, leading to symptoms like tremors (shaking) and slow movement
  • Scientists know that the symptoms are caused by a lack of dopamine so they've developed drugs (L-Dopa) to increase the level of dopamine in the brain
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Imbalances in some neurotransmitters can contribut


  • Scientists think there's a link between a low level of the neurotransmitter serotonin and depression.
  • Serotonin transmits nerve impulses across syanpatic in the parts of the brain that control mood.
  • Scientits know that depression is linked to a low level of serotonin so they've developed drugs (antidepressants) to increase the level of serotonin in the brain.
  • Some drugs that are used to treat depression (called selective serotonin reuptake inhibitors) increase serotonin levels by preventing its reuptake at synapses.
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Drugs affecting synaptic transmission

L-dopa is a drug that's used to treat the symptoms of Parkinson's disease.

  • Its strucure is very similar to dopamine
  • L-Dopa is given, its absorbed ito the brain and converted into dopamine by the enzyme sopa-secarboxylase (Dopamine can't be given to treat Parkinson's disease because it can't enter the brain). This increases the level of dopamine in the brain 
  • A higher level of dopamine means that more nerve impulses are transmittes across synapses in the parts of the brain that control moevement 
  • This give sufferers of Parkinson's disease more control over their movement

MDMA (Ecstasy)- MDMA increases the level of serotonin in the brain 

  • serotinin is taken back into a presynaptic neurone after triggering an action potenial, to be used again 
  • MDMA increases the level of serotonin by inhibiting the reuptake of serotonin into presynaptic neurones it binds to blocks the reuptake proteins on the presynaptic membrane
  • MDMA also triggers the release of serotinin from presynaptic neurones
  • This means that serotonin levels stay high in the synapse and cause depolarisation of the postsynaptic neurone in parts of the brain that control mood
  • So the effect of MDMA is moos elevation
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Genome Sequencing Projects

Human genome project was a 13 year long project that identified all of the genes found in human DNA 

Information obtained from the HGP is stored in a database, Used databases to identify genes, and proteins, that are involved in disease.

Scientists using information to create new drugs that target the identified proteins- identified an enzyme that helps cancer to spread- a drug that inhibits this enzyme is being developed 

The HGP has also highlighted common genetic variations between people, its know that some of these variations make some drugs less effective.

Drug compaines can use this knowledge to design new drugs that are tailored to people with these variations- these are called personalised medications 

Doctors can also personalise a patient's treatment by using their genetic information to predict how well they will respond to different drugs and only prescribe the ones that will be most effective.

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Social, Moral and Ethical issues

Creating drugs for specific genetic variations will increase research costs for drug companies. These new drugs will be more expensive, which could lead to a two-tier health serice - only wealtheir people could sfford these new drugs.

Some people might be refused an expensive drug because their genetic makeup indicates that it won't be that effective for them- it may be the only drug avaliable though.

The information held within a person's genome could be used by others, Eg. empolyers or insurance companies, to unfairly discriminate agaisnt them.

Reveling that a drug might not work for a person could be psychologically damaging to them Eg i could be there only hope to treat the disease.

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Genetically modified organisms

Genetically modified organisms are organisms that have had there DNA altered.

How genetically engineered to produce drugs:

  • The gene for the protein is isolated using enzymes called restriction enzymes 
  • The gene is copied using PCR
  • Copies are inserted into plasmids (small circular molecules of DNA)
  • The plasmids are transferred into microorganisms 
  • The modified microorganisms are grown in large containers so that they divide an dproduce lots of the useful protein, from the inserted gene.
  • The protein can then be purified and used as a drug
  • Lots of drugs are produce from genetically modified bacteria, for example human insulin.
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Genetically modified plants

The gene for the protein is inserted into a bacterium

The bacterium infects a plant cell 

The bacterium inserts the gene into the plant cell DNA- the plant cell is now genetically modified 

The plant cell is grown into an adult plant - the whole plant contains a copy of the gene in every cell

The protein produced from the gene can be purified from the plant tissues, or the protein could be delievered by eating the plant.

Some drugs have been produced from genetically modified plants such as human insulin 

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Genetically modified animals

The gene for the protein is injected into the nucleus of a fertilised animal egg cell

The egg cell is then implanted into an adult animal- it grows into a whole animal that contains a copy of the gene in every cell

 The protein produced from the gene is normally purified from the milk of the animal

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Benefits and risks associated with using GMO's


  • Agricultural crops can be modified so that they give higher yields or are more nutritious this means these plants can be used to reduce the risk of famine and malnutrition
  • Pest resistance, so fewer pesticides are needed this reduces costs (making food cheeper) and reduces any environmental problems associated with using pesticides.
  • Industrial processes oftern use enzymes. These enzymes can be produced form genetically modified organisms in large quantities for less moeny which reduces costs 
  • Some disorders can be treated with human proteins from genetically engineered organisms insted of with animal proteins. Human proteins are safer and more effective
  • Vaccines produced in plant tissues dont need to be refrigerated. This could make vaccines available to more people in areas where refrigeration isnt avaliable 
  • producing drugs using plants and animals would be very cheap as once the plant or animals are genetically modified they can be reproduced using conventional farming methods. This could make drugs affordable for more people, especially those in porr conditions.
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Risks of GMOs

Some people are concerned about the transmission of genetic material, such as herbicide-resistant crops interbreed with wild plants it could create "superweeds'

Weeds that are resistant to herbicides and if drug crops interbreed with other crops people might end up eating drugs they do not need

Some people are worried about the long term impacts of using GMO's There may be unforseen consequences

Some people think its wrong to genetically modify animals purley for human benefits 

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