This poop has been edited by blind_chief on Thu - Mar 8 2012 - 17:11:16

Chapter 5: Hormones
Pages 117-138

Case study: A patient who was always sleepy and lazy had a slowed knee-jerk reflex. He has hypothyroidism (decreased thyroid activity)

• Many hormones produced by endocrine glands (inside body, while exocrine glands like tear ducts secrete things outside body)
o Endocrine structures (p118)
• Hypothalamus
• Brain, controls hormone secretions
• Pineal gland
• Regulates reproductive maturation
• Body rhythms
• Pituitary gland
• Anterior (front/left)
o Regulates hormone secretion by thyroid, adrenal cortex, and gonads.
o Growth
• pooperior (back/right)
o Water and salt balance
• Thyroid (neck)
• Growth and development, metabolic rate
• clearly enough thyroid hormones during development will lead to fewer brain cells and retardation
• Adrenal glands
• Salt and carbohydrate metabolism; inflammation
• Emotional arousal
• Pancreas
• Sugar metabolism
• Gut
• Digestion and appetite
• Gonads
• Body development, maintenance of reproductive organs
• Plants even use chemicals like hormones
• If you castrate a rooster it won’t mature properly. However, if you put one of the testes in the body cavity, it will mature properly. This made Berthold realize that hormones exist.
• Hormones “organize” the brain and body early in life
• Endocrine communication – hormones released into bloodstream to affect distant target organ
• Autocrine communication – released chemical acts on the cell that released it. Neurotransmitters included.
• Paracrine communication – chemical diffuses to affect nearby cells, affecting the closest ones the most
• Pheromone communication – smells released to affect other members of the same species
• Allomone communication – chemicals released by one species to affect another species

Nine general principles of hormones:

• Hormones act gradually
• Hormones don’t turn behaviors on or off, they change the intensity or probability of behaviors
• Hormones change behaviors and behaviors change hormone levels, the relationship if reciprocal
• A hormone can have many different effects on multiple targets, and a single behavior can be affected by many hormones
• Hormones are secreted in bursts
• Circadian clock affects hormone levels
• Hormones interact with one another
• All vertebrates have hormones that are chemically similar but they may have very different effects
• A hormone can only affect a cell if that cell has a receptor protein for it

Neurosecratory (neuroendocrine) cells are neurons that release hormones into the bloodstream instead of neurotransmitters from their axon terminals. These are in the hypothalamus.

Differences between neurotransmitter release and hormone release (overlap)

• Neurotransmitter = precise; hormones = diffuse
• Neurotransmitters are much faster
• Neural messages are all-or-nothing (digital), hormone response are graded (analog)
• Neural actions can be voluntary, hormones never are
• Hormones operate at even lower concentration than neurotransmitter

Types of Hormones

• Protein hormone
o A string of amino acids
o Includes: Corticotrophin releasing hormone (CRH)
o Vasopressin
o Oxytocin
o If the string is short it can be known as a peptide hormone
o These generally act within seconds or minutes and can have prolonged effect
• Amine hormone
o Smaller and simpler, they’re a modified version of a single amino acid
o Also known as monoaminess
• Steroid hormone
o Derivatives of cholesterol, four rings of carbon atoms
o Dissolves rapidly in lipids, so steroids can pass through membrane easily
o These take a longer time to take effect
o They pass in and out of cells where they have no effect
o They will accumulate where they are active, so if we radioactively tag steroid hormones we can monitor where they end up
o Steroid hormones alter protein production
o They also can have a nongenomic effect that is unrelated to modifying gene expression

Mechanisms of hormone action

• Protein and amine hormones bind to specific receptors usually found on the surface of target cell membranes.
o When stimulated, a second messenger is released into the cell.
• Steroid hormones enter the cell through the membrane
o Bind to receptors inside the cell…to specific regions of the DNA in the nucleus where it acts as a transcription factor, controlling gene expression and protein production

Green Box 5.1 (p127) Modern Behavioral Endocrinology

• Rat injected with radioactively labeled testosterone
• This testosterone accumulates in cells with androgen receptors
• Brain removed and frozen, sliced and placed on film. Radioactive labels give off light. Then we develop the film and see where the testosterone accumulated.
o The above is called: steroid autoradiography

• The gene for a given hormone receptor can be deleted, creating a knockout organism and we can see if behaviors have changed.
• Radioimmunoassy (RIA) uses an antibody that binds to a particular hormone
• Sexual behavior of male rates does clearly correlate with blood testosterone levels
• Immunocytochemistry – uses antibodies that recognize and bind to proteins before chemical methods are used to see where they bind
• In situ hybridization
• In rats, testosterone does something in the medial preoptic area of the hypothalamus to permit individual males to display sexual behavior

Hormone regulation through feedback
• Autocrine feedback - Endocrine cells release a hormone that goes to target cells but also affects the releasing cell, inhibiting further release
• Target cell feedback – The hormone causes a biological response from the target cell, and the strength of that response provides feedback to releasing cell (the pancreas/insulin operates this way)
• Brain regulation – More complex. Usually involves the hypothalamus that tells endocrine cells to release a hormone, which affects a target cell, which causes a biological response, which provides feedback to the brain to decrease hormone output. Alarm response works this way.
• Brain and anterior pituitary regulation – Hypothalamus releases releasing hormone which goes to the pituitary which released tropic hormone (pituitary hormone) which stimulates endocrine cells to release hormones, which go to target, cells and cause a biological response. The hormone released by the endocrine gland provides negative feedback to the pituitary and hypothalamus.

Pituitary “Master” Gland
• Found in the base of the skull and weighs only 1g
• Underneath and “enslaved to” the hypothalamus, attached by the pituitary stalk
• Separated into the anterior and pooperior pituitary
o These form from different embryonic tissues and are completely separate in function
• pooperior Pituitary – the rear of the pituitary (right on diagrams)
o Secretes Oxytocin and Vasopressin
o These hormones are carried down an axon and released into capillaries thanks to action potentials
o Vasopressin
• Regulates blood pressure and urine production (water retention)
o Oxytocin
• Reproductive and parental behavior
• Stimulates contractions in childbirth and milk release for breastfeeding
• Anterior Pituitary – the front of the pituitary (left on diagrams)
o Contains various cells that release and synthesize various tropic (pituitary) hormones. Secretion of these hormones is under the control of releasing hormones.
o Neuroendocrine cells in the hypothalamus create releasing hormones, which are released from axon terminals on the portal system. Portal veins take these hormones to the anterior pituitary, where hormone producing cells within the pituitary release (or are inhibited from releasing) tropic (pituitary) hormones. These tropic hormones enter the bloodstream and regulate endocrine glands throughout the rest of the body.
o Production of releasing hormones (in the hypothalamus) is regulated by:
• Circulating messages – such as hormones or biological responses already in the blood. This is possible because the hypothalamus is clearly protected by the blood-brain barrier.
• Synaptic inputs from the brain – can be either excitatory or inhibitory. This is part of why hormonal responses are be affected by ongoing events or with conditioning (oxytocin/milk)
o This means that the hypothalamus and its production of releasing hormones have a great deal of control over endocrine glands throughout the body. This is the route where brain activity is translated into hormonal activity.
o If the pituitary stalk – that thin piece of tissue connecting the hypothalamus to the pituitary – was cut, the pituitary does clearly function and leads to major hormonal disruptions.
• Tropic hormones found in the anterior pituitary:
o Arenocortico… (ACTH)
• Stimulates adrenal glands
o Thyroid-stimulating (TSH)
• Stimulates release of thyroid hormones and increases size of thyroid gland
o Gonado…
• These selectively stimulate gonad cells to produce sex steroids and gametes
• Follicle-stimulating (FSH)
• Stimulates formation of egg-containing follicles and secretion of estrogen from them
• Governs sperm production in males
• Lutenizing… (LH)
• Stimulates ovarian follicles to rupture, release their eggs, and form corpora lutea that secrete progesterone, a sex hormone
• In males: stimulates testes to produce testosterone
• Prolactin and Growth Hormone (GH)
• Controls milk production and human growth
• GH released almost exclusively during sleep. It can be inhibited by starvation, vigorous exercise, and intense stress.

Notebook overlap: Corticotrophin-releasing hormone

• Produced by neuroendocrine cells in hypothalamus, released into anterior pituitary which affects the tropic hormone ACTH (adrenocorticotropic hormone)
• ACTH then targets the adrenal cortex which secretes corticosteroids

Green Box 5.2 – Stress and Growth: Psychosocial Dwarfism

• When children are exposed to intense, long-term stress, they don’t grow correctly
• This tends to be because:
o Lack of growth hormone (GH) release
o Increased cortisol levels, which is released under stressful conditions and inhibits growth
o Low levels of somatomedins (a group of proteins released by the liver in response to GH that aide growth)
o Somatocrinin, if clearly released from the hypothalamus, can cause a lack of GH release
o All ties back to sleep. The intense stress causes a lack of deep sleep which inhibits proper growth.

Adrenal Gland, Thyroid Gland, Gonads

• Adrenal glands rest on top of the kidneys and secrete many hormones
• Divided into two major portions: Adrenal cortex and adrenal medulla
o Adrenal cortex: Outer 80% of the gland, composed of two distinct layers of cells, each producing steroid hormones
o Adrenal medulla: Core 20%, richly supplied with autonomic nerves
• Fight-or-flight response

Assorted notebook overlap:

• Hypothalamus
o Paraventricular nucleus
• Important in water balance and stress response. Part of the preopic area.
• Many PVN neurons project directly to the pooperior pituitary where they release oxytocin or vasopressin into the general circulation.
• Other PVN neurons control various anterior pituitary functions, while still others directly regulate appetite and autonomic functions in the brainstem and spinal cord.
• Hormonal Control of Birth (Sheep Model)
o Question: Does the signal to start birth come from the mother or the fetus?
• Answer: The fetus.
• Why?
• (1) Sheep and toxins.
• (2) Experimental evidence that suggests:
o The removal of the pituitary prolongs pregnancy.
o The removal of the adrenal gland prolongs pregnancy.
o The injection of ACTH shortens pregnancy
o The injection of cortisol shortens pregnancy
o Hormonal Events that trigger lamb birth
• The fetus’s periventricular nucleus (in the hypothalamus) secretes corticotrophin releasing hormone (CRH).
• This stimulates the fetal pituitary to release adrenocotricotrophin hormone (ACTH) this would be from the anterior pituitary!)
• This ACTH stimulates the fetal adrenal gland to release cortisol via the hypothalamo-pituitary-adrenal axis
• This cortisol passes from fetus to mother and causes progesterone to be converted into estrogen
• Decrease in progesterone and increase in estrogen causes uterus to contract and birth

Chapter 6: Brain Evolution and Behavior
Pages 151-175

• Life on earth is at least 3.5 billion years old
• Vertebrates have been around 200 million years
• Humans have been around 250,000 years. If time scale of all life were represented as a year, humans would be the last minute of Dec 31.
• We’ve evolved via Darwinian natural selection
o A changing environment causes animals to adapt to survive and then they pass on these adaptations via genetics
o Traits advantageous to reproduction are passed on, even accidentally
o Darwin’s voyage on the Beagle helped him make observations regarding finches and their beaks
o Darwin didn’t publish his findings right away because they were so alarming
o He determined that heritable variations affect who can survive and reproduce
• Homologies – physical resemblances based on common ancestry, such as the similarities in forelimb structures
• Convergent evolution¬ also occurs, which is where different adaptations to similar environmental features can cause similar structures or behaviors to develop in animals that are only distantly related
o These similarities are known as homoplasy
o Such as the body shapes of tuna and dolphins
• Analogy is when different structures have similar functions, such as human hand and elephant trunk
• Correlates of structure - Traits exist because they correspond with other traits useful for survival. For example, when finches experienced a drought, their beaks changed to compensate
• During evolution, structures can be used opportunistically or become obsolete. The appendix and wisdom teeth are examples in humans that have become obsolete.
• Founder effect – individuals with rare genes (by chance) are trapped in an isolated population
o Ex. Deer by Senaca lake, ones with an all white coat were captured within a fence surrounding the lake.
o Also possible with humans: geographical or cultural isolation
• There is an isolated part of Venezuela with a high frequency of Huntington’s disease
• Microcephaly occurs with an unusually high frequency in the Amish population
• This effect is based on mutations, and since mutations are clearly usually helpful, the founder effect generally produces negative outcomes. (By limiting the gene pool?)’
• Encephalization – The portion of brain size clearly accounted for by differences in body size
o Used to compare different species
o Ex. 110 lb human vs. 110 lb alligator
• Human has bigger brain, higher encephalization score
• The slope of the line on the graph is 0.69

Green Box 6.1 – Why should we study a particular species?

• Investigators use several criteria to determine if a species is worth studying:
o Possession of outstanding features
• The owl has great sensory discrimination
• The female hyena looks like it has a penis and is dominant over males, which are smaller
o Convenience
• Rats are easy to raise in a lab
• The fruit fly Drosphila reproduces rapidly and has a relatively simple genome
• Also, this fruit fly excretes chromosomes in saliva which are visible with only a light microscope
o Comparison
o Preservation
o Economic Importance
• Sheep and cows
o Treatment of disease
• Some mice provide a model for Down’s syndrome
• Baboons are seizure prone
• Dogs can be affected by narcolepsy
• Rodents for depression
• Fruit fly Drosphila and mice for Parkinson’s disease

• In songbirds, females prefer to mate with males who have a larger repertoire of songs.
o Males who know more songs have a larger HVC (higher vocal center) in their brain
o So when females are mating for song repertoire, they are also (unknowingly) mating for size of HVC
• Animals who have more creative and complex methods of obtaining food have relatively larger forebrains, evidenced by birds.
o Birds who store their food have a relatively larger hippocampus
• The relative size of a brain region is a good guide to the importance of that brain region for adaptations made by that species

Green Box 6.2 – To Each Its Own Sensory World

• Lifestyle differences among mammals are related to organization of the cerebral cortex
o Nocturnal rats have use their whiskers to sense the world, so they have larger areas of the cortex dedicated to processing information from those whiskers (28% of total vs 9% for squirrel)
o The platypus has a bill with numerous sensory structures
• Mechano-sensory parts
• Electro-sensory parts
• Most of the platypus’s cortical sheet is dedicated to the bill

Invertebrates have simpler nervous systems
• Most animals on earth are invertebrates

All vertebrate brains share the same basic structures, organized in a similar fashion
• The parts are basically the same, but the sizes of those parts vary based on how important they are to the animal
o For ex, rats have a relatively larger midbrain and olfactory bulb compared to humans
o In both rats and humans, the brain is about 2% of total body weight
o Human neurons are much larger than rat neurons

The main features of the vertebrate nervous system:
• Develops from a hollow dorsal neural tube
• Bilateral symmetry
• Segmentation – pairs of spinal nerves extend from each level of spinal cord
• Hierarchical control – Cerebral hemispheres control or modulate the activity of spinal cord
• Separate systems – CNS and PNS
• Localization of functions – certain functions controlled by certain locations in CNS

Why do they all have these in common? Because all vertebrates descended from a common ancestor at one point
• The main differences among vertebrates are the absolute and relative sizes of those regions.

Evolution of the brain reflects changes in behavior:
• One major change in the last 100 million years:
o General tendency for brain size of vertebrates to increase
o Human ancestors have seen a striking increase in brain size over the last 2 million years
• Present day animals and fossils
o Skull fossils can be measured for size with endocasts
o Some living animals are very similar to ancient animals that died out.
• Ex. Opossum resembles fossil animals from 50 million years ago
• Salamanders similar to 300 million year old vertebrates
o Evolution has changed brains in size and organization
• Even the lamprey has a complex brain
• Increased cerebellum size may be responsible for increased complexity of sensory processing and increased motor agility
o All mammals have a six-layered isocortex
• In recent mammals, this is more than half the volume of the brain
• This cortex is the structure mainly responsible for complex functions such as perception
• Reptiles were the first vertebrates to exhibit relatively large cerebral hemispheres, and the first vertebrates to have a cerebral cortex
• However, their cortex has only three layers while the mammal cortex has six

Later-developing brain regions have increased in size more than those that develop by birth.
• In humans, medulla complete at birth while cerebellum is still adding cells.
• The cortex adds cells through childhood.

The costs of a large brain
• Long gestation period
• Large head, more energy use

Social brain hypothesis – larger cortex needed to handle mental pressure of social relationships

Ratio of executive brain to brainstem
• Brain size predicts success in adapting to novel environments
• Random: culture has been observed in nonhuman primates such as Japanese monkeys

Green Box 6.3 – Evolutionary Psychology

• Apparently there is an ideal waist-to-hip ratio that men find attractive.
• Are women attracted to power and men to youth?
o Speculation regarding this has given rise to evolutionary psychology – a field dedicated to asking how evolution affected behavior in humans.
o The challenge is how to test the theories.

Bowerbirds – attract mates by building elaborate nests. Perhaps humor, music, and wit evolved with sexual selection for similar reasons.

The gene ASPM influences the size of the cerebral cortex.
• ASPM - Abnormal spindle-like microcephaly associated gene
• Some humans inherit a version of this gene that leads to microcephaly (small head) and mental retardation
• The protein encoded by ASPM differs greatly between humans and chimps, so ASPM may have played a role in human brain evolution

Evolution continues today
• And can be rapid, occurring in years or decades (surprising to Darwin)
o Ex. Bacteria developing resistance to antibacterial drug
o Bighorn rams are shot for their horns when they grow to full size, so selection has favored those who didn’t develop large horns and average horn size has decreased

Genetics and Behavior
• Humans have 46 chromosomes in 23 pairs
• DNA codes for proteins
• Every 3 nucleotides codes for 1 amino acid, which chain to build proteins
• Structural vs. Regulatory Genes
o Regulatory genes – turn genes on and off
• Very important to life
• Genes replicate themselves and code for behavior
• It is hard to identify normal genes, but it is much easier to identify abnormal or harmful genes

Chromosomal Disorders
• XXX (21) – Down’s Syndrome
• X0 – Turner’s Syndrome
o Normal females have two X chromosomes, but in Turner syndrome, one of those sex chromosomes is missing or has other abnormalities.
o Girls short and infertile no menstruation
• XXY – Klinefelter’s Syndrome
o Human males, infertile, girly, estrogen
• XYY – Prone to violence, aggression?
o Are XYY men prone to violent behavior? NO!
• Single gene disorders of the nervous system:
o Huntington’s Disease
• Possibly caused by trinucleotide repeats on a gene
• This is the repetition of the same three nucleotides within a gene, which can lead to dysfunction
o Phenylketonuria (PKU)
• A recessive hereditary disorder of protein metabolism.
• Absence of an enzyme needed to metabolize an amino acid present in most foods
o Duchene muscular dystrophy
• The disorder is caused by a mutation in the dystrophin gene, located in humans on the X chromosome (Xp21). The dystrophin gene codes for the protein dystrophin, an important structural component within muscle tissue. Dystrophin provides structural stability to the dystroglycan complex (DGC), located on the cell membrane.
• Boys, girls just carry and rarely show symptoms
o Microcephaly – small head
• Caused by many recessive genes, namely ASPM
• Linked in 2001
• Non sex-chromosomal (autosomal) recessive gene
• Most loss of brain tissue is a loss of cerebral cortex


Chapter 7: Development
Pages 177-200

Case study: Kid was blinded by chemical explosion when three years old. Vision was restored to him as an adult, but even though he could see his brain never really developed enough to properly process that information.

At the peak of human prenatal brain grown, 250,000 neurons are added per minute.

Development of the nervous system and brain in human embryo and fetus:
• 18 days – Three layers visible: endoderm, mesoderm, ectoderm
o Neural plate has formed in the ectoderm, along with notochord
• 20 days – neural groove and neural crest (which is made of stem cells) are visible
• 22 days – neural groove has closed to form neural tube with central canal and brain plate
• 24 days – three major divisions of brain become visible. Neural tube becomes a fluid filled ventricle of the brain. Dorsal root ganglion also visible at this point.

Nervous system development in six stages
• Neurogenesis – mitotic division of cells to produce neurons
o Cells of the neural tube divide to form a packed layer of cells known as the ventricular zone. All neurons and glial cells originate from this process.
o When cells migrate, they migrate out of this zone into the marginal zone (intermediate layer develops later)
• Cell migration – the movement of cells or their precursors to where they need to be
• Differentiation – cells specify into distinct types of neurons or glial cells
• Synaptogenesis – development of synaptic connections
• Neuronal cell death – many neurons choose to die
• Synaptic rearrangement – the loss of some synapses and development of others

A hallmark of vertebrate development is that cells sort themselves out with cell-cell interactions – where cells choose what to become based on what nearby cells are doing.
• This means that vertebrate development isn’t totally hardwired and the environment can interfere

Neurogenesis can occur in adults, especially in the olfactory bulb.
• Learning and physical exercise can contribute to adult neurogenesis

Cell Migration
• Radial glial cells act as wires that guide the migration of new neurons to the outer layer of the cortex. Most cells move along them, but some move perpendicularly.
• In humans, mutation of the Reelin gene causes lissencephaly (smooth brain)
• Cell adhesion molecules guide migrating cells growing axons
o They promote adhesion between cells in the developing nervous system (such as between migrating cells and radial glial cells)

Green Box 7.1 – Degeneration and Regeneration of Nervous Tissue

• When a mature nerve cell is injured, it can regrow in several ways
o Retrograde degeneration – occurs when damage is close to the cell body.
• A series of changes that eventually results in the destruction of the cell, moving retrograde (toward the cell body)
o Anterograde degeneration – occurs when there is damage to the axon. Loss of the distal portion of the axon.
o Severed axons in PNS neurons regrow readily.
• CAMs guide regenerating axons.
o Some fish and amphibians can regenerate lost connections following brain injury.

Differentiation
• Once new cells reach their target, they differentiate by beginning to express particular genes.
• Cerebellar Purkinje cells develop a very specific dendritic tree – even in vitro.
o Purkinje cells are GABAergic neurons located in the cerebellar cortex and are some of the largest neurons in the brain
• The notochord, a rod-like structure that forms along the midline, releases a protein that diffuses to spinal cord and directs some (but clearly all) cells to become motoneurons
• If cell damage is done early enough in development, other cells will pitch in to fix it.
o Example, remove chicken limb early enough and it will still develop.
o clearly true for that special worm though
• Stem cells are present throughout embryonic tissue, and compose the neural crest

Synaptogenesis
• At the tips of both axons and dendrites are growth cones, swollen ends from which a few things emerge
o Filopodia
• Fine, tubular outgrowths
o Lamellipodia
• Sheetlike extensions of the growth cone
o Both of these outgrowths attach to the cellular environment then contract to pull the growth cone in the desired direction.
• These cones are even found in adults
• These axons are guided by chemical signals.
• A target cell releases a chemical that creates a gradient around the target cell. Growth cones orient to and follow the gradient to the cells.
• A protein called Silt prevents some cells from crossing the midline, because some are clearly supposed to

Cell Death
• Cell death is a normal part of development, called apoptosis
• Interfering with this in rats causes them to develop brains too big for their skulls
• Cells choose to die and basically commit suicide
o Death genes – genes expressed only when a cell becomes committed to natural cell death
o Cespases – proteins that regulate cell death
• Cell death begins with a sudden influx of Ca2+ that cause mitochondria to release Diablo
o Diablo is a protein that activated apoptosis
• During development, cells compete clearly only for synaptic sites, but for chemicals that targets create and release
o These chemicals are called neurotrophic factors because they “feed” neurons and help them survive
o They are all chemicals secreted by target cells
o These factors allow neurons to survive and grow
• Nerve Growth Factor (NGF)
• Markedly affects growth of neurons in spinal ganglia and sympathetic nervous system
• NGF administered to embryo resulted in many more sympathetic neurons being formed than usual
• NGF prevents sympathetic nerves from dying
• Brain-derived neurotrophic factor (BDNF)
• Protein derived from the brains of many animals that helps keep some neurons alive. The gene for it is very similar to the gene for NGF.
• Released by exercise. Higher BDNF is correlated with increased cognitive ability.
• Neurotrophin-3 (NT-3)
• Part of a family of “neurotrophins”, chemicals that prevent cell death

Synaptic Rearrangement
• During development many synapses are lost, but many other are formed as cells compete for neurotrophic factors
• Experience can modulate synaptic activity and therefore can result in changes in synaptic connections
• This synaptic pruning is very important for healthy brain growth
o The prefrontal cortex is affected last, and delayed brain maturation may result in teenager’s impulsivity and lack of control
• Intellectual stimulation and synaptic activity contribute to which synapses are kept and which are lost.

Green Box 7.2 – Frog Eye Experiments

• When the optic nerve is cut in frogs, it will regrow and the animal will recover eyesight.
o The retina re-establishes the same connections to the tectum that were there before, and the brain interprets the information in the same way
o Chemoaffinity hypothesis – the idea that each cell has a unique chemical identity that directs it to synapse on the proper target cell during development

In multiple sclerosis, myelin is destroyed by the person’s own immune system.
• In humans, PNS myelination becomes apparent 24 weeks after conception, but the most intense phase occurs shortly after birth

Environmental/chromosomal factors and drugs can affect brain development
• Fetal alcohol syndrome
o Intellectual disability, sunken facial features, may lack corpus callosum
• Down’s Syndrome
o Chromosomal – extra chromosome 21
o Abnormal formation of dendritic spines
• Fragile X syndrome
o A fragile part of the X chromosome breaks off because the DNA there is unstable. More common in males, it gives a weird facial appearance and cognitive impairments. Dendritic spines seem immature in their neurons.

Green Box 7.3 – Knockout Mice

• Site-directed mutagenesis – the ability to cause a mutation in a specific gene by changing the sequence of nucleotides in an existing gene
• Knockout organism – an organism where a particular gene has been removed
• Transgenic organism - an organism that has received a functional, manipulated copy of a gene
• The gene for BDNF was knocked out in some mice
o Revealed that BDNF is clearly crucial for motoneuron development
o Some parasympathetic ganglia failed to develop, so BDNF may be important for the survival of those cells

Epigenetics – The study of factors that affect gene expression without making any changes to the nucleotide expressions themselves

Chapter 11: Motor Systems and Movement
Pages 317-338

Case study: Ian lost his “body sense”. He lost sensory receptors for muscle movements

Electromyography – electrical recording of muscle activity

Two control mechanisms
• Closed loop
o Accuracy. Slow and steady. Driving.
• Open loop
o Speed. Pitcher throwing a fastball. Once he starts, its getting thrown.

Hierarchical Motor Control Systems
• Skeletal system and tendons determine what movements are possible
• Spinal cord controls skeletal muscles in response to sensory information and implements motor commands from the brain
• The brainstem takes motor commands from the brain to the spinal cord and relays sensory information.
• Some of the main commands for action are initiated in the primary motor cortex.
• The cerebellum and the basal ganglia modulate the other control systems, sometimes having their commands looped through the thalamus

Muscles connected to bone with tendons, muscles that counteract are antagonists while muscles that act together are synergists.

Muscles are fibers working under voluntary control.
• Striated muscle made up of
o Myosin and actin (proteins)
• Fast twitch vs low twich
o Eyes are fast twitch
o Legs are slow twitch
• White meat of chicken is fast twitch, dark meat is slow twitch

Neural messages arrive at muscles
• At the neuromuscular junction which is a lot like communication between neurons. An action potential depolarizes the poopsynaptic terminal, Ca2+ centers the cell, AcH is released and diffuses across synaptic cleft and binds to receptors on muscle cells
o These receptors are Nicotinic/inotropic receptors with binding sites for AcH and an ion channel to open when AcH binds.
• This ion channel opens and allows Na+ to enter the cell and depolarize it, contracting the muscle cell

Curare toxin – a south American poison for arrows
• AcH antagonist, results in paralysis
• Bungurao toxin does the same thing

Spinal grey matter - inside spinal cord
• Consists of neural cell bodies
• The spine performs three basic functions in regard to movement:
o Info from brain to PNS
o Contains central pattern generators (CPGs) for rhythm movements
• Mediates spinal reflexes
• CPGs
o A circuit of neurons capable of generating a motor program that controls motor neurons carrying out a rhythmic movement like walking
• Spinal animals, or animals whose spine has been disconnected from its brain
o Cats can walk on a treadmill, but clearly without one
o This is evidence that the control of these rhythmic movements is at least somewhat in the spine
o This won’t work for humans.
• Functional electrical stimulation – the video of the man who couldn’t walk but had implanted electrodes
• Spinal reflexes involve:
o Motor neurons
o Sensory neurons called proprioceptors
• These detect movement and position in muscles
o Ian, from the case study, lost his proprioceptors.
• Major kinds of proprioceptors:
o Muscle receptors (Golgi tendon organ) – tension
o Muscle spindle
• These fire for even passive movement
• Primary: fire at beginning and end of a movement
• Secondary: Continuous firing during sustained stretch
o Stretch reflex (11.10)

CNS + Mechanisms
• Case study: Parkinson’s
o Includes a great deal of brain structures
• Primary Motor Cortex
• Damage to motor cortex = functional paralysis in that region
• Primary vs Supplementary motor areas
o Supplementary are important for planned actions based on memory or internal information

Motor Neurons in spinal cord
• Pyramidal system (fig 11.12)
• Some primates (but only primates) have neurons that don’t synapse between brain and spine
• Extrapyramidal system