The Biological Explanation
The Central Nervous System (CNS)
The CNS consists of the brain and spinal cord. Neurons are nerve cells that pass information around the brain and communicate with the
rest of the body through nerve cells. Neurons connect by using synapses. Motor neurones carry information out from the brain; Sensory neurones carry information inward to the CNS
E.g. touching a hot pan – sensory neurones detect the heat and pass on this message through a relay in the spinal cord, this then sends a message through the motor neurones to the muscles which contract, leading you to move your hand
The CNS is therefore used for decision making and coordination. Incoming information needs to be understood and then appropriate action can be taken. For simple responses the brain is not needed and the spinal cord can generate the response. For more detailed information the brain takes over the processing role.
Neurotransmitters are chemicals which carry messages across the synaptic cleft/gap and pass on the message from one neuron to another from the terminal button of one neuron to the dendrite of the receiving neuron. By telling the next neuron whether to fire or not is whether the message is passed on. If the neuron receives more excitatory responses than inhibitory it is likely to fire.
Examples of neurotransmitters we will study in more detail next year include serotonin and dopamine.
The role of Genes
Genes are made up of DNA. This is found on our chromosomes. We inherit 23 chromosomes from each parent which are responsible for characteristics such as eye colour, hair colour and height. These are examples of phenotypes as they are the behaviours/characteristics shown. The genotype would be the genetic material that is not observed. Some genes are recessive and two copies are required for the characteristics to be shown. Others are dominant and only one copy is needed.
Genes and Gender
One pair of genes are responsible for gender – if the chromosomes are XX it is a female, if XY a male. The female always passes on a X chromosome whereas males may pass on an X or Y. All foetuses begin development the same in the first 6 weeks however depending on whether the Y chromosome is present, development of the gonads differs after this due to the role of hormones released from the Y
chromosome. SRY is a gene on the Y chromosome which releases testis determining factor. This turns the gonads into testicles and stops them developing into ovaries.
Abnormalities
There are two genetic abnormalities that can occur. Turner syndrome is a genetic disorder where a female has an abnormality on one of the X chromosomes where they are missing all or part of the chromosome. This results in them being shorter than average and having under developed ovaries leading to infertility. Turner syndrome is represented as XO.
Klinefelter’s syndrome is a genetic condition that affects males. This is where they inherit an extra X chromosome – making them XXY. Males with Klinefelter's syndrome have small testes and lack testosterone, meaning they lack many of the secondary sexual
characteristics.
Hormones and Gender
Hormones carry messages around the body in the blood stream. This makes them slower than neurotransmitters. Female hormones are oestrogen and progesterone and testosterone is the male hormone.
H-Y antigen is a horrmone released from the Y chromosome which also works on stopping the ovaries developing and the testes developing. If the testes are developed enough by 12 weeks, the first hormone they release is called anti-mullerian hormone which prevents
female development and leads to the Wolffian system to develop into male sex organs. The testes are responsible for producing androgens
which masculinise the foetus. This includes testosterone. At puberty these are released again in the form of testosterone
which is responsible for secondary sexual characteristics.
Abnormalities
Androgenital syndrome is when a female (XX) is exposed to androgens results in male rather than female sex hormones.
Androgen insensitivity syndrome is when there is a lack male hormones results in a baby with a female appearance but chromosomally male (XY).
Brain Lateralisation
This refers to the extent which hemisphere is involved in which activity. Male brains are said to be more lateralised – this means showing a
preference for one hemisphere, this is the right hemisphere. This can explain why they are better at spatial tasks than females e.g. map reading, mental rotation tasks and parking a car.
Females show greater bilateral activity and use both hemispheres equally. This is said to be due to females having a larger corpus callosum which connects both hemispheres. This suggests if females suffer brain injury they will be less affected than males.
Evidence to support this comes from patients with brain damage; lab experiments which have found women do better on language, verbal fluency and speed of speaking tasks while men are better at spatial tasks such as maze performance and mental rotation tasks; and also scans which show males who have had less exposure to androgens in the womb tend to use their brain more similarly to females, and use both hemispheres.
Also male to female transsexuals have been found to be better at verbal tasks and worse at spatial tasks. This suggests there is a biological reason from them wanting to change sex.
The Central Nervous System (CNS)
The CNS consists of the brain and spinal cord. Neurons are nerve cells that pass information around the brain and communicate with the
rest of the body through nerve cells. Neurons connect by using synapses. Motor neurones carry information out from the brain; Sensory neurones carry information inward to the CNS
E.g. touching a hot pan – sensory neurones detect the heat and pass on this message through a relay in the spinal cord, this then sends a message through the motor neurones to the muscles which contract, leading you to move your hand
The CNS is therefore used for decision making and coordination. Incoming information needs to be understood and then appropriate action can be taken. For simple responses the brain is not needed and the spinal cord can generate the response. For more detailed information the brain takes over the processing role.
Neurotransmitters are chemicals which carry messages across the synaptic cleft/gap and pass on the message from one neuron to another from the terminal button of one neuron to the dendrite of the receiving neuron. By telling the next neuron whether to fire or not is whether the message is passed on. If the neuron receives more excitatory responses than inhibitory it is likely to fire.
Examples of neurotransmitters we will study in more detail next year include serotonin and dopamine.
The role of Genes
Genes are made up of DNA. This is found on our chromosomes. We inherit 23 chromosomes from each parent which are responsible for characteristics such as eye colour, hair colour and height. These are examples of phenotypes as they are the behaviours/characteristics shown. The genotype would be the genetic material that is not observed. Some genes are recessive and two copies are required for the characteristics to be shown. Others are dominant and only one copy is needed.
Genes and Gender
One pair of genes are responsible for gender – if the chromosomes are XX it is a female, if XY a male. The female always passes on a X chromosome whereas males may pass on an X or Y. All foetuses begin development the same in the first 6 weeks however depending on whether the Y chromosome is present, development of the gonads differs after this due to the role of hormones released from the Y
chromosome. SRY is a gene on the Y chromosome which releases testis determining factor. This turns the gonads into testicles and stops them developing into ovaries.
Abnormalities
There are two genetic abnormalities that can occur. Turner syndrome is a genetic disorder where a female has an abnormality on one of the X chromosomes where they are missing all or part of the chromosome. This results in them being shorter than average and having under developed ovaries leading to infertility. Turner syndrome is represented as XO.
Klinefelter’s syndrome is a genetic condition that affects males. This is where they inherit an extra X chromosome – making them XXY. Males with Klinefelter's syndrome have small testes and lack testosterone, meaning they lack many of the secondary sexual
characteristics.
Hormones and Gender
Hormones carry messages around the body in the blood stream. This makes them slower than neurotransmitters. Female hormones are oestrogen and progesterone and testosterone is the male hormone.
H-Y antigen is a horrmone released from the Y chromosome which also works on stopping the ovaries developing and the testes developing. If the testes are developed enough by 12 weeks, the first hormone they release is called anti-mullerian hormone which prevents
female development and leads to the Wolffian system to develop into male sex organs. The testes are responsible for producing androgens
which masculinise the foetus. This includes testosterone. At puberty these are released again in the form of testosterone
which is responsible for secondary sexual characteristics.
Abnormalities
Androgenital syndrome is when a female (XX) is exposed to androgens results in male rather than female sex hormones.
Androgen insensitivity syndrome is when there is a lack male hormones results in a baby with a female appearance but chromosomally male (XY).
Brain Lateralisation
This refers to the extent which hemisphere is involved in which activity. Male brains are said to be more lateralised – this means showing a
preference for one hemisphere, this is the right hemisphere. This can explain why they are better at spatial tasks than females e.g. map reading, mental rotation tasks and parking a car.
Females show greater bilateral activity and use both hemispheres equally. This is said to be due to females having a larger corpus callosum which connects both hemispheres. This suggests if females suffer brain injury they will be less affected than males.
Evidence to support this comes from patients with brain damage; lab experiments which have found women do better on language, verbal fluency and speed of speaking tasks while men are better at spatial tasks such as maze performance and mental rotation tasks; and also scans which show males who have had less exposure to androgens in the womb tend to use their brain more similarly to females, and use both hemispheres.
Also male to female transsexuals have been found to be better at verbal tasks and worse at spatial tasks. This suggests there is a biological reason from them wanting to change sex.