Ch 4 Key Concepts Flashcards
Neurotransmitters
Neurotransmitters are chemical messengers that bridge the synaptic gap between neurons to influence the neighbouring cell. When an action potential reaches the presynaptic neuron the neurotransmitters (stored at the terminal of a presynaptic neuron) are released and then move across the synapse and either excite or inhibit the receptors at the postsynaptic neuron. Excitation leads to further action potentials or increase in activity and inhibition suppresses electrical activity. The shapes of neurotransmitters are specific to a particular neuron and indicate what messages can be passed or blocked; they work much like a key and lock, if they don’t ‘fit’ they will be ineffective. Neurons are characterised by the kind of neurotransmitter they store and release. Neurotransmitters are important as malfunctions at the synapse can be associated with low levels of serotonin and are linked to depression. Synapses specific to serotonin may take it back into the same neuron from which it is released, a process known as reuptake. Drugs such as Prozac, known as selective serotonin reuptake inhibitors, inhibit the reuptake of serotonin therefore are used treat depression.
Action potential
An action potential is a brief and sudden change in the resting value of electrical voltage in a cell and is how information is transmitted between neurons. Action potentials travel along a neuron in a fraction of a second; highlighted by how rapidly we respond to tissue damage, e.g., if we touch something hot. Information is encoded in terms of the frequency of an action potential, e.g., coldness in the fingertips is detected by ‘cold’ neurons; these neurons will show more frequent action potentials to a very cold than to a slightly cold stimulus. Action potentials are important in our understanding of the nervous system, as they are a way of measuring how information is transmitted. The accurate measurement of action potentials involves comparing activation with stable values at rest. Information is carried between neurons chemically, using neurotransmitters, and within neurons electrically. In this way, sensory neurons send information, e.g, about tissue damage or tactile stimulation, to the central nervous system (CNS). Tissue damage would usually trigger a series of action potentials in a group of neurons. Motor neurons send information from the CNS to muscles.
Genotype
The genotype is the collection of all an individual’s genes (which influence temperament, body structure, etc.) within each cell of the body. It is the genetic information provided by the parents, at the time of fertilisation by the combination of genes and remains constant throughout life. Genes interact within the fluid environment in the cell, thereby interacting with neighbouring cells and the whole organism interacts with its environment. The result of this interaction, or behaviour/structure, in development of genotype and environment is known as the phenotype. This can vary between genetically identical individuals raised in different environments. For example plants raised in nutritionally rich soil will differ from genetically identical plants raised in poor soil lacking nutrients. The genotype can be seen as potential for development into a number of different phenotypes. Some phenotypes will be better adapted to an environment than others; genotypes which contributed to such a phenotype will increase in frequency in the population, as the basis of evolution. The genotype/phenotype distinction is important since it highlights that although there is a genetic basis for differences in a population, interaction within the environment must be taken into account when investigating development and behaviour.
Phenotype
The phenotype is the behaviour or structure that results from the interaction of an individual’s genotype, the collection of all an individual’s genes within each cell of the body, with the environment. The genotype is the genetic information provided by the parents, at the time of fertilisation by the combination of genes and remains constant throughout life. Genes interact within the fluid environment in the cell, thereby interacting with neighbouring cells and the whole organism interacts with its environment. Features of the phenotype change in response to experience within the environment, e.g. muscle strength is acquired or aggression is learned. This can vary between genetically identical individuals raised in different environments. For example plants raised in nutritionally rich soil will differ from genetically identical plants raised in poor soil lacking nutrients. The genotype can be seen as potential for development into a number of different phenotypes. Some phenotypes will be better adapted to an environment than others; genotypes which contributed to such a phenotype will increase in frequency in the population, as the basis of evolution. The genotype/phenotype distinction is important since it highlights that although there is a genetic basis for differences in a population, interaction within the environment must be taken into account when investigating development and behaviour.
Brain lesions
A brain lesion is damage to a region within the brain, e.g. accident or surgery. Brain lesions are helpful in providing a source of information about how the brain functions. Changes in behaviour after a particular region is damaged can suggest the contribution of that region to normal functioning. For example, Phineas Gage suffered extensive damage to the left prefrontal lobe after an accident with a tamping iron. He became emotionally uninhibited, suggesting that this part of the brain acts to inhibit emotional expression. However, there are problems with this kind of evidence, as the damage is uncontrolled phenomena and can affect more than one area of the brain. Further, there is no control group for comparison. Interpretation is difficult due to the plasticity of the brain as other areas may take over particular functions from the damaged area, or are ‘rewired’. There has been some experimental research using laboratory animals to create selective lesions to investigate the effect; however this raises ethical issues as it is unclear if the info provided would extend to humans. Surgery also offers insight into understanding the structure of the brain, for example, Penfold, while removing diseased tissues from the brain, found that electrical stimulation of parts of the temporal lobe elicited early childhood memories. This was important in providing a basis for biological theories of memory.
