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FSU / Natural science / NSCI 2000 / What are the two methods for measuring receptors in the brain? Do they

What are the two methods for measuring receptors in the brain? Do they

What are the two methods for measuring receptors in the brain? Do they


School: Florida State University
Department: Natural science
Course: Introduction to Brain and Behavior
Professor: Maria greenwood
Term: Fall 2016
Tags: biopsychology and Studyguide
Cost: 50
Name: Chapters 4, 5, 6/7, 8, 12, & 13
Description: Here are the objectives of the first five chapters for Biopsychology. Some of the answers may have periods "...". This means that I am going to update the answer Monday because I currently do not fully understand it. Good luck!!
Uploaded: 10/14/2016
13 Pages 8 Views 19 Unlocks

PSB2000 Study Guide

What are the two methods for measuring receptors in the brain? Do theymeasure RNA or protein?

Chapters 4, 5, 6/7, & 8


Chapter 4

1. Describe the resting membrane potential and its ionic basis?

a. How is it measured?

2. Know the polarization arch of depolarization

3. Describe postsynaptic potentials (PSPs), both excitatory and inhibitory 4. Explain how an AP is triggered, how does it move along axons? a. What factors contribute to conductance?

5. What happens to concentrations of K+ and Na+ during an AP? 6. Be able to define refractory periods

7. Describe different synapses & synaptic transmission

8. Compare and contrast neurotransmitter receptors If you want to learn more check out what is folate?

a. How are NTs “deactivated”?

9. Name and explain the classes of neurotransmitters

Chapter 5

1. What are the two methods for measuring receptors in the brain? Do they measure RNA or protein?

What scanning techniques can be used to measure brain structure?

2. Describe the common psychological batteries and what they test 3. Discuss several biopsychology methods used in the study of nonhuman animal behavior, and know what they measure. If you want to learn more check out what is the meaning of Mens Rea?

4. What scanning techniques can be used to measure brain structure? What about brain activity? Know the differences between them.

Chapters 6 & 7: Part 1

1. Learn & apply the definitions of “sensation” and “perception” to each sensory system. Where does transduction fit in? Don't forget about the age old question of 8) What wittig reagent and carbonyl compound are needed to prepare each alkene?

2. Compare the former hierarchical model with the current hierarchical model. 3. Describe the physical and perceptual dimensions of sound.

4. Know how damage to the cortex, hair cells, or middle ear can affect sound perception.


What happens to concentrations of K+ and Na+ during an AP?

5. Describe the different types of cutaneous receptors & what each is specialized for.

6. Describe the symptoms of congenital analgesia and what research has discovered recently.

7. Describe how the olfactory and gustatory systems may interact. 8. Compare the evidence for and against pheromone communication in humans. 9. What is unique about the human olfactory pathway?

Chapters 6 & 7: Part 2

1. Be able to describe the pathways (from receptors to cortex) for gustation and vision

2. Describe the 5 types of taste and the types of receptors associated with them 3. List the different types of papillae and the basic structure within a papilla 4. List and describe disorders of gustation and olfaction Don't forget about the age old question of What is diamagnetic?

5. Identify the structures of the eye and specific cells within the retina 6. Compare/contrast high acuity and high sensitivity

7. Describe Blindsight and the cells hypothesized to be involved

8. Describe Change Blindness and how it occurs.

9. Define color blindness and what types of cells are involved

Chapter 8

1. List and discuss 3 principles of sensorimotor function. Don't forget about the age old question of Who is Carolus Linneaus?

2. Describe 2 major areas of sensorimotor association cortex and evidence of their functions.

3. List the current areas of secondary motor cortex.

4. Describe mirror neurons.

5. Describe the organization of primary motor cortex. What is somatopy? Know who developed these ideas, and the effect of lesions.

6. Discuss the functions of the cerebellum and basal ganglia.

7. Compare the effect of basal ganglia on movement in normal individuals and patients with Huntington’s Disease.

8. List and explain the 4 descending motor pathways.

9. Discuss central sensorimotor programs and the principles of learning motor sequences.

Chapter 12

1. Explain the 3 phases of energy metabolism.

2. Explain the roles of insulin and glucagon in energy metabolism. 3. Compare set point and positive incentive theories of hunger.

4. Summarize the factors that influence when and how much we eat.We also discuss several other topics like 4) standard of deferred payment - How does the fed measure money?


5. Briefly explain how leptin and ghrelin influence hunger

6. Explain how dopamine behaves in the presence of food, and what variables contribute to this. (Dazzi paper)

7. Compare and contrast osmotic thirst and hypovolemic thirst.

8. Understand the differences between anorexia and bulimia in their presentation of symptoms as well as possible complications.

9. Discuss the Watering Hole Effect, the experiment that demonstrated this, and variables contributing to it. (Krause paper)

Chapter 13

1. Understand the history, classes, and types of hormones.

2. Differentiate between developmental/organization effects and activational effects. Understand examples of each.

3. Discuss examples of behavioral as well as structural dimorphisms. 4. Describe the role of the pituitary and hormones released by the pituitary. 5. Discuss exceptions & challenges to male-female dichotomies in the context of sexual categorization

6. Discuss examples of neural mechanisms of sexual behavior & identity‘ Answers

Chapter 4

1. Resting membrane potential is the difference in electrical charge between the outside and the inside of the cell. This is when the inside of the neuron is negative and the outside of the neuron is positive. (-70mV)

a. It is measured using microelectrodes placed inside and outside of the neuron to compare the voltages.

2. The positive ions flow into the neuron while the negative ions flow out. This increases the voltage and membrane potential making the polarization arch go up. Once the action potential is reached and the arch reaches its peak, hyperpolarization occurs. Hyperpolarization is when the positive ions flow out of the neuron while the negative ions flow in. This is the opposite of depolarization. The arch then continues to decrease, passing the level of the stimulus during its refractory period until it increases again, going back to the level of the stimulus and reaching its resting state.

3. Excitatory postsynaptic potential(EPSP)- neurotransmitter released during postsynaptic neuron during depolarization. (goes above stimulus, -70mV)


Inhibitory postsynaptic potential (IPSP)- neurotransmitter released during hyperpolarization. (goes below stimulus, -70mV)

4. An action potential is triggered by a summation​ (temporal or spatial) and travels down an axon at its node of ranvier​.

a. The diameter of the axon​- wider axons conduct faster than thin. Degree of myelination​- more myelination allows for faster conduction.

5. During the rising phase, the sodium channels open and later on, the potassium channels open. During AP, the sodium channels close. During repolarization, the potassium channels start to close and go into hyperpolarization.

6. Absolute refractory period- Immediately after AP, impossible to initiate another AP - sodium channels cannot open. Relative refractory period- More input need than usual to initiate an AP.

7. Axodendritic- axon terminal connects to another neuron’s dendrite (common), Asosomatic- axon → cell body, Axoaxonic- axon → axon, Dendrodendritic dendrite → dendrite.

8. Ionotropic- receptor that opens an ion channel when NT binds; Metabotropic (G-protein coupled receptors)- utilize a G-protein inside the post-synaptic neuron to induce changes. The effects of metabotropic receptors are slower, long-lasting, more diffuse, and more varied.

a. NT’s are deactivated by either reuptake or enzymatic degradation. Reuptake is when the NT molecule is taken from the transmitter site and recycled through the transporter. Enzymatic degradation is when the NT molecule is broken down by enzymes rather than recycled.

9. The different classes of NT’s are amino acids, monoamines, acetylcholines, and unconventional NT’s. Amino acids- found in the CNS, examples include glutamate (common excitatory NT in the CNS), GABA (common inhibitory), etc.; Monoamines- diffused effects, examples include catecholamines (synthesized from tromine...

Chapter 5

1. Immunocytochemistry- measures proteins and is based on the binding of labeled-protein antibodies. In situ hybridization- measures RNA and uses labeled RNA to locate neurons w/complementary mRNA.

2. … The common psychological batteries measure intelligence, memory, language (problems of phonology, syntax, or semantics), and language lateralization. The test which measures intelligence is the Wechsler Adult Intelligence Scale (WAIS/IQ test). The test which measures memory is the Digit span subtest.

3. Species-common behaviors of animals are tested through open-field tests and traditional conditioning. Open-field tests measure the anxiety, avoidance, and activity of animals through their activity. Traditional conditioning is the conditioning of animals through operant (reinforcement/punishment), Pavlov’s classical (UCS, CS, etc.), and self-stimulation (rat pushing down a lever for food or reinforcement). Semi natural animal learning paradigms include the Morris water maze (Measures spatial learning; the rat must find a hidden platform in an


opaque pool) and conditioned taste aversion (pairing a taste with something that makes an animal ill such as lithium chloride).

4. The scanning techniques which measure brain structure are CT scans and MRIs ( measure waves emitted by hydrogen atoms that have been activated within a magnetic field). The scanning techniques that measure brain activity are Positron Emission Tomography (PET; radiolabeled substance administered → levels of radioactivity in various parts of one horizontal level of brain are shown in the PET image), fMRI (creates an image using the signal created by interaction between oxygen and iron in the blood, also known as a BOLD signal), and EEG (measures gross electrical activity of brain through electrodes placed upon the scalp) . Unlike CT scans and MRIs, PET and MRI show functionality.

Chapters 6 & 7: Part 1

1. Sensation is the process of detecting the presence of stimuli. Perception is the higher-order process of integrating, recognizing, and interpreting patterns of sensations. Sensation occurs through receptors (specialized cells in peripheral tissues in the body). Transduction, the transformation of one form of energy to another, occurs at the receptors of sensory systems during sensation, which leads to perception at the brain.

2. The former hierarchical model is serial and functionally homogeneous. It is not as complex as the current model which is functionally segregated and parallel, with each of the three levels of cerebral cortex containing different areas that specialize in different kinds of analysis.


5. Axons of each auditory nerve lead to the superior olives -> axons project to the inferior colliculi -> medial geniculate nuclei (nuclei of the thalamus)-> primary auditory cortex.

Keep in mind: There is one medial superior olive and one lateral superior olive. The medial tells us the difference in sound arrivals and where the sounds are located. The lateral tells us the difference in sound amplitude (sound is louder in the ear closest). Also, the primary auditory cortex is located in the temporal lobe.


The ear: Sound waves → auditory canal →ear drum (tympanic membrane) vibrates → ossicles (the small bones of the middle ear: malleus, incus, stapes) → oval window → cochlea (hair cells)

6. Damage to the auditory cortex results in temporary complete hearing loss which usually recovers within weeks. There could also be permanent sound localization. The two types of deafness include conductive and sensorineural. Conductive is the damage to the ossicles. Sensorineural is the damage to the cochlea or auditory nerve. Sensorineural deafness is typically due to the loss of hair cells.

7. Cutaneous receptors are receptors in the skin and include two different types: free nerve endings and mechanoreceptors. Free nerve endings are the simplest cutaneous receptors which have no specialized structures on them and include thermoceptors (respond to temperature) and nociceptors (respond to chemical changes in the skin and noxious stimuli). Mechanoreceptors respond to mechanical stimuli and are specialized to detect specific types of touch such as vibration, pressure, etc.

8. Congenital analgesia is a condition where an individual does not feel pain.​ This is caused by an autosomal-recessive trait of a gene that expresses voltage-gated sodium channels on nociceptive neurons. The case study of Miss C., who had congenital analgesia, shows us that pain is important for survival. She did not feel pain when subjected to strong electric shock, ice-baths, burning hot water, etc. She showed no changes in blood pressure, heart rate, or respiration when these stimuli were presented. She later developed infections and extensive skin and bone trauma and died as a result of her condition.

9. The olfactory system is responsible for smell while the gustatory system is responsible for taste. These two systems interact to give us a sense of flavor and monitor the chemical content of the environment.

10.Pheromones are chemicals that influence the physiology and behavior of conspecifics (members of the same species). Findings which support pheromones - menstrual cycles of women living together tend to be synchronized, humans can detect the sex of another by the breath or underarm smell, kin recognition, and the olfactory sensitivity of women is greatest when they are ovulating or pregnant. Findings which refute pheromones - Lack of function vomeronasal organ (VMO). Many also say that it does not fit the definition.

11. The olfactory system is unique for it is the only system which does not first pass through the thalamus.

Chapters 6 & 7: Part 2

1. Cranial nerves → solitary nucleus (nucleus of the solitary tract) → ventral posterior nucleus of the thalamus → primary gustatory


Keep in mind: The afferent neurons leave as part of the 7th, 9th, and 10th cranial nerves. 7th - Chorda tympani, 9th - Glossopharyngeal, and 10th - Vagus.

2. The five types of taste are sweet, bitter, salty, sour, and umami.​ G-protein-linked receptors are in the membranes of the taste receptor cells umami, sweet, and bitter. Salty and sour have ion channels.

3. Taste receptor cells are found on the tongue and in parts of the oral cavity. They typically occur in clusters known as taste buds which are often located around small protuberances called papillae. The four types of papillae are fungiform, foliate, circumvallate, and filiform. Filiform - “fungus or mushroom,” small, 1mm or less in diameter (6 taste buds per papillae); foliate- “folded”, also used for tasting; circumvallate- “around,” very large, also used for tasting (most have 10 on back of tongue); filiform- latin for thread, supports cells (no taste receptors). 4. Olfactory 

Anosmia- the inability to smell.

● Most common cause: blow to the head that causes a displacement of the brain within the skull and shears the olfactory nerves (cracking cribriform plate).

● Hyposmia – reduced ability to detect odors.

● Parosmia (troposmia) – brain perceives odor as an unnaturally unpleasant odor (i.e. flowers smelling like feces or cake frosting smelling like burnt wood).

● Euosmia – brain perceives odor that is normally aversive as pleasant (reverse the above).

● Phantosmia – olfactory hallucination; detecting odors that aren’t there. Can be pleasant or aversive.


● Ageusia- the inability to taste.

○ Rare b/c sensory signals from the mouth are carried via three separate pathways.

5. Iris- regulates the amount of light reaching the retinas.

Cornea- protective outer layer of the eye which refracts (bends) light. Pupil- hole in center of the iris where light enters the eye.

Lens- focuses incoming light on the retina. Refracts light; changes to adjust focal distance (accommodation).

Blind spot- where the optic nerve exits the eye and has no photoreceptors. Retina- neural tissue; where photoreceptors lie.


Specific cells of the retina 

Five layers of diff. types of neurons: receptors, horizontal cells, amacrine cells, and retinal ganglion cells.

Photoreceptors (rods and cones) → Bipolar cells → Retinal ganglion cells → Axons of retinal ganglion cells form optic nerve, which leaves back of eyeball, and goes to brain.

6. Cones- cone-shaped receptors responsible for color vision

Rods- rod-shaped receptors responsible for black/white/grey vision. Duplexity theory- cones and rods mediate different kinds of vision.

a. Cones: Photopic vision- good lighting and provides high-acuity​ colored perceptions of the world, poor sensitivity.

b. Rods: Scotopic vision- dim illumination, high sensitivity ​and poor acuity​.

7. Blindsight is a response to visual stimuli outside conscious awareness of “seeing”. The cells involved in blindsight are place cells, head-direction cells, and border cells. Place cells fire when an animal passes a certain landmark. Head-direction cells track which way the face is pointing. Border cells fire when an animal is close to a wall or boundary of some kind.

8. Change blindness is having no memory of something which an individual was not paying attention to. For example, if you were not paying close attention to something and it disappeared, you would not notice the disappearance of the object.

9. Color blindness is a reduced ability to distinguish between certain colors. Red-green color blindness

a. S​-cones: ​Short ​(~400 nm)

b. M​-cones: ​Medium ​(~525nm)

c. L​-cones: ​Long​ (~700nm)

2 kinds of cones:

● S & L b/c M-cone filled with L opsin. The M-cone becomes red.

● S & M b/c L-cone filled with M opsin. The L cone becomes green.

Chapter 8

1. Three principles of Sensorimotor function:

a. Hierarchical organization- The muscles are at the lowest and are part of the spinal motor circuits which lead to the highest part of the system which is the association cortex.

b. Motor output is guided by the sensory output.


c. Learning changes the nature of the sensorimotor control. Ex: actions can turn from conscious to automatic after repetition over time; the locking of your front door becomes an automatic action and you do not have to consciously think about locking it after doing it for so long repeatedly.

2. The two regions of the Sensorimotor Association cortex are the posterior parietal association cortex and the dorsolateral prefrontal association cortex.

The inputs of the posterior parietal association cortex include visual, auditory, and somatosensory information. The posterior parietal association cortex sends this information to the dorsolateral prefrontal association cortex, secondary motor cortex, and frontal eye fields. It integrates information about body part location and external objects and guides movement. It is also involved in language areas, arithmetic processing, and high-level mathematical thinking.

The dorsolateral prefrontal association cortex receives its input from the posterior parietal cortex and sends its information to the primary motor cortex, secondary motor cortex, and frontal eye fields. It evaluates evaluates external stimuli and initiates voluntary actions.

Note: Both of these association cortices send their information to the secondary motor cortex.

3. The secondary motor cortex is comprised of the premotor cortex (one dorsal one ventral), supplementary motor areas (SMA, preSMA, and supplementary eye field), cingulate motor areas, and the primary motor cortex (output of the cingulate motor areas).

4. Mirror neurons- Neurons that are active when an individual performs an action or is watching another perform the same action.

5. The primary motor cortex is located in the precentral gyrus. It is somatotopic, meaning it devotes larger areas of its cortex to body parts which make complex movements. Ex: the area devoted to the hand is larger than that of the knee.

For the primary motor cortex, small lesions often have minimal effects. Large lesions on the other hand, may disrupt a patient’s ability to move one body part independently of the others and produce stereognosia (inability to identify objects by touch).

6. Cerebellum- coordinates and modulates movement, compares intended movement with movement that occurs and informs cortex of difference to improve.

Basal ganglia- Heterogeneous collection of interconnected nuclei that receive cortical input and send output back via thalamus; modulates motor output and cognitive function, including learning.

7. Huntington’s disease- Loss of neurons in the striatum and globus pallidus → little inhibition on the thalamus and chorea (involuntary movement, writhing)

Normal patients- not too much, not too little inhibition on the thalamus.


8. There are two dorsolateral and two ventromedial motor pathways. These are the corticospinal​ and the corticorubrospinal​.

The dorsolateral​ tracts synapse on interneurons of spinal gray matter. The corticospinal ​descends through the medullary pyramids and then crosses. The corticorubrospinal ​synapses at the red nucleus and crosses before the medulla. These two divisions control distal muscles and limb movements.

The ventromedial​ tracts also include the corticospinal and corticorubrospinal. The corticospinal ​descends ipsilaterally. The ​corticorubrospinal ​descends bilaterally and carries info from both hemispheres. These two divisions control proximal muscles, posture, and whole body movements.

9. All of the levels the sensorimotor system have patterns of activity programmed into them except for the highest levels. When these programs are activated, complex movements are produced. These programs must be stored at a level higher than muscle. Ex: sensorimotor programs may be stored in secondary motor cortex, which is higher than muscle.

These programs can be modified by practice​ which leads to response chunking and/or shifting control to lower levels. Response chunking​ is when the central programs controlling individual response are combined due to practice. Shifting control to lower levels​ allows higher levels to do more complex tasks and promotes in greater speed.

Chapter 12

1. Energy metabolism is the chemical change that makes energy available for use. The three phases include cephalic phase​, absorptive phase​, and fasting phase​. The cephalic phase is the preparation for eating. The absorptive phase is the absorption of energy. The fasting phase is the withdrawing of energy from reserves. The process is then reversed.

2. The two main hormones which regulate glucose and satiety are insulin and glucagon. Both insulin and glucagon are released by the pancreas. … 3. The set point theory states that the body works to maintain a single value (water levels, ion concentration, nutrients, glucose, body temp., fat, etc.) through negative feedback. This means that hunger is a response to an energy need and for survival. The positive-incentive theory states that we are drawn to eat for the pleasure of eating (flavor, learning, social cues, time since last meal, etc.) 4. When we eat is affected by the conditioning to eat rather than energy deficit. How much we eat is affected by the appetizer effect, serving size, social influences, and the sensory specific satiety (less satiety with novel foods).


5. Ghrelin​ comes from the gut and signals hunger. Leptin​ is made by fat cells and signals satiety.

6. Dopamine increase when food is presented.​ Blocking cannabinoid receptors inhibit this increase in dopamine.

7. There are two different ways an individual becomes thirsty: osmotic thirst and hypovolemic thirst. Osmotic thirst is when the water leaves the cell. An example would be the consummation of salty food and an increase in solute concentration, leading to osmotic pressure drawing water out of cells to normalize the solute concentration, thus producing thirst. Hypovolemic thirst is the thirst that results from the loss of fluid from sweating, vomiting, and/or bleeding. It is detected by neurons monitoring blood pressure & by the subfornical organ (SFO).

8. Anorexia Nervosa​ is a disorder where an individual voluntary starves himself or herself. Bulimia​ is a disorder is where an individual binges and purges, commonly with the use of extreme exercise and laxatives. Anorexia involves tiny binges while Bulimia involves huge binges. Anorexia also involves more weight loss than bulimia and compulsive rather than impulsive. These two disorders also have different complications. Anorexia’s complications include bradycardia, hypertension, hypothermia, and anemia. Bulimia’s complications include inflammation of the esophagus, dehydration, vitamin/mineral deficiencies, electrolyte imbalance, and acid reflux.

9. The watering hole effect is tells us how thirst affect our response to stress. The experiment done to answer this question involved administering salt and no salt to rats and exposing them to stressful conditions. Their blood pressure, heart rate, and social interaction were then tested by measuring the blood levels of ACTH, CORT, and Oxt before, during, and after stress. The result was a decrease in blood pressure, heart rate, ACTH, CORT, and an increase in social interaction. This was due to an increase in Oxytocin, which is a stress hormone which helps us cope with stress.

Chapter 13

1. Arnold Adolph Berthold discovered hormones by studying the development of chickens as a result of castration, castration and pre implantation of testes, and


castration and transplantation of testes. This resulted in caponization for the castrated chicken and normal development for the other two chickens whom received pre implantation and transplantation.

The three classes of hormones include amino acid derivatives​, peptides and proteins​, and steroids​. Acid derivatives include Epinephrine, which is from the adrenal medulla. Peptides and proteins have short and long chains of amino acids and include insulin and glucagon from the pancreas, melatonin from the pineal gland, and oxytocin and vasopressin from the pituitary gland. Steroids are synthesized from cholesterol (fat) and fat-soluble and include sex steroids (estrogen, testosterone, etc.) and stress hormones (cortisol, ACTH).

2. Developmental/organizational effects involve influencing the development of anatomical, physiological, and behavioral characteristics that differentiate the sexes. Activational effects involve triggering reproduction-related behavior in mature individuals. These effects, unlike developmental/organizational effects, are temporary​.

3. All humans begin with primordial reproductive tracts: Wolffian ducts​ and Mullerian ducts​. During genital formation (3-4 months in utero), gonads form as either testes or ovaries. Female plan is default. Males have to override this plan with two hormones: Anti-Mullerian hormones​ and androgens (testosterone)​.

Remember: wolffian - males & mullerian - females

When adults are given the hormone, the hormone initiates a behavior which causes activational effects. For these activational effects to occur, the brain must be appropriately organized during development.

4. The pituitary gland is “master gland” of central hormone release. It contains the anterior pituitary and the posterior pituitary. The posterior pituitary contains hormones synthesized in the hypothalamus ( hypothalamic paraventricular and Supra optic nuclei) and receives direct neural input from the hypothalamus. These hormones include vasopressin and oxytocin. The anterior pituitary contains tropic hormones. Tropic hormones are hormones which are not synthesized in the hypothalamus, but influence the release of hormones by other glands. These hormones include the human-growth hormone (HGH),


thyroid-stimulating hormone (TSH), Adrenocorticotropic hormone (ACTH), Luteinizing hormone (LH), etc.

5. Challenges against the female-male dichotomy incle intersex conditions. This is when there is an intermediate/ambiguous sexual development. Sever decades ago, the genitalia would be surgically feminized and the individual would be raised as a female. Today, we identify the basis of the external genitalia and raise consistently. Some specific challenges include the androgenic insensitivity syndrome, congenital adrenal hyperplasia, and Kleinfelter’s syndrome. The androgenic insensitivity syndrome​ is an X-linked recessive disorder which results in androgen production with unresponsive receptors due to genetic mutation. The individual has a female appearance and gender identity and lacks a menstrual cycle. Congenital adrenal hyperplasia​ is when a “tomboyish” XX female individual has too little cortisol and excessively releases adrenal and androgen to compensate. The individual is born with ambiguous genitalia and develops secondary sex characteristic during puberty (deepening voice, descending testicles). Kleinfelter’s syndrome​ involves an XXY karyotype and usually a male gender identity. The individual has low T levels, small testes, low T, low sperm, reduced facial and body hair, increased height, and risk for learning disabilities. Another challenge is the idea that gender identity also involves the brain. Physiology and genetics are not the only factors.

6. An example of a neural mechanism of sexual behavior ​is the correlation of the size of the sexually dimorphic nucleus (SDN) with testosterone levels and aspects of sexual identity. ​Research has shown that the SDN is twice as large in heterosexual men as heterosexual women; homosexual men shift in the female direction. An example of a neural mechanism of sexual identity ​is the bed nucleus of the stria terminalis (BNST, nucleus embedded in axons connecting amygdala with hypothalamus) in transsexuals.​ The BNST is larger in men than in women. For transexual men-to-women, their BNST size matches the BNST size of women rather than men.

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