THE CENTRAL NERVOUS SYSTEM
A stimulus is a change in an organism's environment.
We respond to stimuli in order to survive.
This respone is made by the central nervous system which includes the brain and spinal cord.
The CNS is connected to the body by the peripheral nervous system. Which consists of sensory neurons and motor neurons.
SENSORY neurons: carry impulses from receptors to the CNS.
MOTOR neurons: carry impulses from CNS to the effectors.
RECEPTORS AND EFFECTORS
Receptors and effectors form parts of organs such as:
muscle cells, receptor cells in the retina and hormone secreting gland cells.
Muscles cells in a muslce- impulses go along MOTOR neurons and cause the muscles to CONTRACT.
Light receptors-lens focuses light onto receptor in retina. Cells are then stimulated and send impulses to the brain along sensory neurons.
Hormone-secreting gland cells- impulses travel along a motor neuron and this triggers a release of hormone into the bloodstream.
NEURONS AND SYNAPSES
Neurons are specially adapted and carries an electrical signal.
When stimulated: they elongate and connect parts of the body and the have branched endings so that a neurons can act on many others.
In motor neurons cytoplasm forms fibres to surround the membrane called axon.
Some axons are found in fatty sheath that insulates the neuron and increases the speed that the nerve impluse is transmitted
SYNAPSES are gaps between neurons.
The impulses are transferred between neurons by; first a nerve impulse reaches a synapse and the impulse triggers the relase of chemical called neurontransmitters which diffuse into the gap and binds the receptor of a motor neuron. The the nerve impulse is sent through the motor neuron. But they only bind with certain chemicals.
REFLEX ACTIONS AND SIMPLE REFLEXES
Reflexes are fast, automatic involuntary responses to a stimulus.
A receptor is stimulated - maybe by a sharp pin etc- and causes an impulse to go along a sensory neuron to the spine. The sensory neuron synapses with a relay neuron by-passing the brain and this relay neuron synapses with a motor neuron to send impulses to the effector. The effector responds. eg by taking the had off the pin.
Babies learn simple reflexes such as: stepping- when held, they can learn to walk, startle- a baby shoots out its legs and arms when startled, grasping reflex- they hold tight of fingers in their hands, rooting-they turn their head and open their mouths when the cheek is stroked, sucking- baby sucks on a finger that's in its' mouth.
Adults also have reflexes such as the pupil of our eyes; it gets smaller when there is a bright light to protect the eye. Our iris controls the amount of light by contracting various muscles; in dim light the pupil gets bigger,in high key lighting the pupil gets smaller.
CONDITIONED AND MODIFYING REFLEXES
New responses to stimuli can be learnt by building association betweent eh stimulus and the new stimulus. This is a conditioned reflex.
A Russian Scientist named Pavlov discovered that dogs create saliva when there is food around. He then experimented through repetition to create a new stimulus for the creation of saliva and so he rang a bell (secondary stimulus ) everytime meat was shown to the dog and eventually when the bell rang, the dog created saliva without seeing any food.
Some conditioned reflexes help animals survive for example birds learn not to eat specific caterpillars by learning the patterns and colours of the caterpillar.
Sometimes, the brain can modify a reflex by sending a signal via a neuron to a motor neuron in the relfex arc. For example keeping hold of a hot plate is a modification.
Neuron pathways are formed through new experiences. As each neuron matures at birth, it sends out branches and so the amount of synapses increases.
Each time you have a new experience a different neuron pathway is stimulated.
Everytime the experience is repeated after taht, the pathway gets stronger.
Pathways that do not get used very often are deleted and only the pathways that are used the most are preserved.
This is why repetition helps us to learn things; because it strengthens our pathways and keeps them preserved.
CHILDREN AND DEVELOPMENT
feral children have been isolated from society in some way and so they don't go through the same development stages and normal children; this is because alot of developemtn at early stages is through social activities. Sometimes this isolation can be delierate and other times it's accidental.
And so, because these children have never communicated with any other humans, they do not learn to talk and therefore just 'grunt'. At a later age, feral children may learn to talk when they are no longer isolated by at a later time, learning language is much harder.
when a baby is born, there are development milestones in place; if these milestones are missing then the child may be lacking in stimulation or there are neurological problems.
A three month baby should be able to lift their head when help to someone's shoulder and at 12 months the baby should be able to hold a cup and drink from it.
ADAPTING/COORDINATION OF SENSES/MEMORY
pathways in the brain mean that it is easier for animals to adapt to new environments; dogs can be trained to follow commands and dophlin captivity can be trained to collect food from a persons' hand.
COORDINATION OF SENSES.
the cerebral cortex part of the brain that helps us to learn this. It is concerned with; intelligence, memory, language, consciousness.
MEMORY is the ability store and retrive information.
verbal memory can be divided into short term and long term memory: short-term can only store a limited amount of information for a limited amount of time whereas long-term stores unlimited amounts of information.
We're more likely to remember things if its repeated, there's a stronger stimulus for example colour smell or sound, or there's a pattern to it. For example learning planets.
MAPPING THE CORTEX
the cerebral cortex can be mapped in 3 differnt ways:
in physiological techniques, damage to different parts of the brain can produce different problems such as memory loss and studying these effects has led to an understanding of which parts do what.
in electronic techinques, a electroencephalogram is a visual record of the electrical activity generated by neurons. Electrodes and placed on the scalp and these pick up the electrical signals. By stimulating the patient's receptors, the parts of the brain which respond can be mapped.
magnetic resonance imaging scanning- this is relatively new and can be used to produce images of different cross sections. the pictures that are made us colour to represent different level of electrical activty. the activity in the brain changes depending on what the person is oding or thinking
Drugs affecft the nervous system by changing the travelling speed of nerve impulses.
send false signals
prevent nerve impulses from travelling across synapses and overload the nevrous system with impulses.
Serotonin is a chemical transmitter us in the CNS and can enhance a mood to make you feel happy. It passes along the brains' synapse and lands on receptors. if it doesn't land on a receptor, it is reabsorded back into transmitting neurons by transporter molecules.
ecstasy (mdma) blocks the transporters causing a build up of serotonin in the synapse which can lead to serotonin concerntrations in the brain to increase and feelings of elation
the neurons can be harmed and this means that there may be memory loss in the long run.