NROSCI 0080 1st Edition Exam 1 Study Guide Topic 1 Development of the Nervous System Structural development can predict behavior How when areas develop similar for similar systems Behavior can be used to predict structure There are factors that influence both structure and behavior injury hormones etc and can be studied both Induce injury see what behaviors are modified Induce behavior see what structures are activated suppressed About 2 weeks after fertilization the blastocyst migrates from the fallopian tube and implants into the uterine wall and forms the embryonic disc This embryonic disc becomes the baby and everything else becomes the amniotic sac and placenta The cells of the embryonic disc differentiate and form 3 distinct layers 1 Endoderm 2 Ectoderm Becomes the nervous system 3 Mesoderm The ectoderm thickens in the center This thickening forms the neural plate The bottom of the neural plate grows much faster than the top causing it the neural plate to curl up This curling forms the neural groove the midline of the structure The curling edges eventually meet and fuse at the top This forms the neural tube This hollow structure becomes the central nervous system and the neural pores at each end remain open for 3 weeks If the anterior pore fails to close anencephaly results fatal condition no brain If the posterior pore fails to close spina bifida results lower spinal nerves cannot reach their destination in the legs loss of motor control and sensation The developing neural tube forms three main bulges that form the various parts of the nervous system 1 Forebrain bulge forms the telencephalon and diencephalon a Telencephalon develops into the cortex and limbic system b Diencephalon develops into the thalamus and hypothalamus c The lateral and third ventricles also develop from the forebrain bulge 2 Midbrain bulge forms the mesencephalon a Mesencephalon develops into the tectum and tegmentum b Cerebral aqueduct 3 Hindbrain bulge forms the metencephalon and myelencephalon a Pons medulla cerebellum b Fourth ventricle The spinal cord regions bud off of the hindbrain bulge and surrounds the central canal As we evolved higher processing abilities our skull size shape does not change Instead our brains evolved to increase its surface area by forming folds These folds form bumps and grooves The bumps are called gyri The grooves are called one of two things depending on their size Sulci are shallow grooves and fissures are deep grooves There are also hollow spaces within the brain called ventricles These have a protective function to absorb force from a blow to the head as to not spread the damage across the entire brain These ventricles are filled with cerebrospinal fluid CSF which also reduces the net weight of the brain due to buoyancy Cell birth each cell starts out as a totipotent stem cell meaning that it has the potential and ability to become any type of cell After some differentiation it becomes a specialized blast cell meaning that it can only become one generic type of cell neuron glial cell cardiac cell etc After even more differentiation the cell becomes one very specific type bipolar sensory neuron oligodendrocyte etc The differentiated cells now have to get to their specific destination we can t have brain cells in our hearts Radial glial cells guide neurons to their final destination Once all the cells are in place the radial glial cells differentiate into other types of glial cells All of this neural division and migration is completed by birth we are born with the same number of neurons we will have our whole lives and they stay in the same place However new connections are constantly being made and old ones are being pruned out New dendrites and more extensive axonal branches are made which contributes to the growing brain size as we mature in the early stages of life Axons know where to branch out to away from due to chemicals produced by other cells The tip of the axon is called the growth cone It is specialized to detect these chemicals Lance Jones and Landmesser conducted an experiment to see how long neurons are able to migrate to their proper destination Mature neurons were unable to reach their proper destination whereas fetal ones were able to There comes a time right before birth where neurons lose the ability to migrate properly and therefore stay put Simple synapses form first then synapses in deep cortical areas Formation of synapses happens at an extremely high rate during the first year of life However not all of these connections are necessary and the brain compensated for this via synaptic pruning Some axons are wrapped with myelin to speed up the speed of conduction This myelin wrapping is fatty and is formed from projections of glial cells In the CNS they are called oligodendrocyes and in the PNS they are called Schwann cells Myelin sheaths are being formed for the first 20 years of life These brain development stages correlate with the different stages of behavior and motor ability that arises in infants Each milestone has a critical period when synapses are being formed If there is a lack of adequate stimuli during the critical period then those connections cannot be formed and the individual will forever experience deficits in that area In summary there are 7 stages of brain development 1 Cell birth 2 Cell migration 3 Cell differentiation 4 Cell maturation 5 Synaptogenesis formation of synaptic connections 6 Synaptic pruning not all synapsis are useful so our bodies cut them out 7 Myelogenesis formation of myelin sheaths Topic 2 Anatomy of the Brain The brain controls our motions and integrates sensory information to create a representation of our surroundings It also has adaptive properties for environmental changes learning response to injury etc The nervous system is broken down as follows Nervous System Central Nervous System Peripheral Nervous System Brain Spinal Cord Somatic Nervous System Voluntary movements Everything outside the skull vertebrae Autonomic Nervous System Involuntary movements Sensory information is afferent information It originates in a body part is relayed up the spinal cord into the hindbrain then up to higher levels of processing Motor information is efferent information exits the brain It originates at higher cortical processes and descends the spinal cord to the destination Directional terms in the brain are different than that in the rest of the body because of the bent axis which is inherent to bipedal walking