Neural Development

Creation of a structural and functional mechanism that can respond to changes in the organism's external or internal environment

• Recieve signals from the internal and external environments
• Integrate the input
• Respond to stimuli

Capability of recalling a thought at least once and usually again and again

remember, use, forget

reversible chemical changes in the brain

permanent chemical changes in the brain

Capability of the nervous system to integrate and store memories

brain and spinal cord

nerves connecting brain to head

nerves that branch from the spinal cord

• cylinder of nerve tissue that runs down the center canal in the spine
• handles some automatic motor responses to sensory information by itself

handles involuntary jobs

stimulates the "fight or flight" response to threating situations

relaxes the body

• Length of fibers: long dendrites and short axon
• Location: cell body and dendrites are outside of the spinal cord; the cell body is located in a dorsal root ganglion
• Function: conduct impulse to the spinal cord
• moving away from a central organ or point

• Length of fibers: short dendrites and long axons
• Location: dendrites and the cell body are located in the spinal cord; the axon is outside of the spinal cord
• Function: conduct impulse to an effector (muscle or glad)
• moving toward a central organ or point

• aka connector neurons, relay neurons
• Length of fibers: short dendrites and short or long axon
• Location: entirely within the spinal cord or CNS
• Function: interconnect the sensory neuron with appropriate motor neuron
• smaller cells
• form complex chains or circuits

stimulus, receptor, sensory neuron, coordinator, motor neuron, effector, response

the formation of new neurons ( can take place in the adult brain, unknown how functional these neurons are)

areas of necrosis resulting from obstruction of local circulation

• decrease in volume and weight
• widening of grooves on the surface of the brain
• enlargement of the ventricles (open spaces)
• acculation of lipofuscin (pigment in the cells)
• neurofibrillary tangles
• senile plaques
• small infarcts

• separates blood and cerebrospinal fluid (CSF)
• physical isolation for the CNS (not the PNS)
• allows glucose, oxygen, vitamins, and some amino acids to pass through
• causes differential drug sensitivity

general barrier and choroid plexus

the juction beween the endothelial cells lining the capillaries are much tighter in the CNS than in most other areas of the body

leaky capillary endothelium but tight junctions between choroids epithelial cells (found in ventricles of the brain)

• multiple elongated processes specialized in receiving stimuli
• usually covered by a large number of throny spines (gemmules) - site of synapses

• aka soma
• contains cytoplasm and nucleus (mono- or bi- nucleated)
• can also recieve stimuli

single process specialized in generating or conducting nerve impulses to other cells

• based on size and shape
• Multipolar: 1 axon, multiple dendrites, most common type
• Bipolar: 1 axon, 1 dendrite
• Pseudounipolar: 1 process close to the cell body but which divides into 2 branches froming a T shape

• specialized, localized regions of contact between 2 cells
• typical neuron has between 100-1000 synapses

• alter membrane potential of neurons by chemical or electrical means
• Chemical: release neurotransmitters
• Electrical: via gap junctions

• Terminal membrane: presynaptic membrane, i.e. axon terminal buds that contain neurotransmitters
• Region of extra cellular space: synaptic gap, space between the presynaptic and postsynaptic endings
• Postsynaptic membrane: membrane of effector organ, contains receptor sites for neurotransmitters

chemical-gated ion channels in membrane of post-synaptic cell

vesicles containing neurotransmitters in pre-synaptic cells

• Excitatory ion channel synapses
• Inhibitory ion channel synapses
• Non channel synapses
• Neuromuscular junctions
• Electrical synapses

• sodium channel neuroreceptors
• when channels open positive ions flow in, causing a local depolarization, making an action potential more likely

• chloride channel neuroreceptors
• when channels open negitive ions flow in, causing a local hyperpolarisation, making an action potential less likely
• an impulse in one neuron can inhibit an impulse in the next

• No channels
• Have membrane-bound enzymes
• When activated by a neurotransmitter, enzymes catalyse the production of a mesenger chemical inside the cell

• synapses formed between motor neurons and muscle cells
• always use neurotransmitter acetylcholine
• always excitatory

• the membranes of the two cells actually touch and share proteins
• allows for an action potential to be passed directly from one membrane to the next
• found only in the heart and eye

• Make sure that impulses only flow in one direction
• Allow for integration to occur
• Allow for summation to occur
• Allow for the filtering out of continual unnecessary or unimportant background stimuli

several pre-synaptic neurons converge at a synapse with a single post-synaptic neuron

one pre- and post-synaptic neuron but the frequency of impulses reaching the synapse differs

dendrites and axons

• epineurius
• perineurium
• endoneurium

aggregation of nerve cell bodies in the PNS

aggregation of nerve cell bodies in the CNS

many layers of modified glial cell membrane wrapped around axons (white matter)

enveloped within glial cell clefts or not at all (grey matter)

• united layers of the membranes of the sheath cell forming a lipoprotein complex
• consists of many layers of modified cell membranes
• made up of 70-80% lipid and 20-30% protein

Formed by the edges of glial cell groove coming together over a developing axon

• begins at 16-20 weeks of gestation
• continueing into early twenties
• demyelination of adult nerve fibers seriously imparis impulse conduction

• spaces inbetween adjacent glial cells along the length of the axon
• allows ions to flow with ease between the extracellular fluid and the axon
• electrical impulses spread from node to node

• Outside: positive charge (more Na, less K)
• Inside: negative charge (more K, less Na)

• output through the axon
• sum of all the excitatory and inhibitory potentials from all that cell's synapses

• temporary reversal of the electrical potential along the membrane
• sequence of changes in polarity of the membrane
• results from the propagation of the nerve impulse along the membrane

• electrical stimulation of the membrane
• chemicals in contact with the membrane
• mechanicle damage to the membrane
• heat and cold

• depolarization
• repolarization

• At rest the outside of the membrane is more positive than the inside
• Depolarization: cell becomes permiable toNa, positive ions flow into the inside of the cell
• Repolarization: cell once again becomes impermeable to Na, cell returns to normal charges
• action potential spreads through membrane (can't move backward)

.1-100 m/s

• Temperature: higher temperature = faster speed
• Axon diameter: larger diameter = faster speed
• Myelin sheath: increases speed

• action potential jumping from node of ranvier to node of raniver
• makes action potential propagate faster

new neurons interact with existing brain cells to recreate the function of damaged brain cells

• ectodermal origin
• provide passive support
• help maintain neurons
• regulate neurite extention and patterning
• form myelin sheath
• 10 glial cells per neuron

• start shaped
• cleand up brain debris
• transport nutrients to neurons
• hold neurons in place
• digest parts of dead neurons
• regulate content of extracellular space
• control blood flow to neurons

provide insulation (myelin) to neurons in CNS

digest parts of dead neurons

lines canal of spine and brain

provide insulation (myelin) to neurons in the PNS

physical support to neurons in the PNS

• Waves of cellular proliferation: 1. neuron proliferation 2. glial proliferation
• Rate of birth mass acretion maximum at birth
• Brain approximatelly 1/3 to 1/2 of adult size by 1 month post-partum
• Brain weight plateau by 18 months of age
• Decrease in brain volume and weight after age 50: 1. loss of neurons 2. shrinkage of neurons 3. changes in dendrites and synapses
• With advancing age: 1. accumulation of lipofuscin 2. neurofibrillary tangles 3. senile plaques 4. small infarcts

• Major pathways: DNA
• Minor pathways: environmental ques

• Mesoderm forms the notochord which triggers neural induction via chemicals
• Ectoderm (above the mesoderm) forms the neural plate
• Neural plate folds to form a tube, neural tube first closes in the center, moving outward in both directions; anterior portion forms 3 outpouchings which will become the brain
• Neural crest then moves outward forming the PNS

When the neural tube doesn't close all the way

Incompelete closure of the posterior portion of the neural tube

• Ependyma: inner layer
• Gray matter: central layer
• White matter: outer layer

• brain tissue growth factors
• produced as a result of brain ctivity

• response to induction signals
• peak neuronal progenitor cell proliferation occurs early in gestation and stops shortly after birth
• peak glial proliferation occurs later in gestation and after birth
• neural stem cells continue to proliferate throughout life

• guidance dependent on physical cues
• movement via amoebpoid activity
• movement facilitates by cilia
• 96-97% of the neuroblasts arrive at appropriate target tissues

• neurons which aggregate don't migrate anymore
• influenced by cell/substrate adhesion molecules
• during aggregation neurons become aligned

• capacity to synthesize neurotransmitters
• development of distinct processes

• initial microenvironment influences
• specific neuronal receptors
• remodeling of dendritic trees

• coincides with the arrival of axons at their target fields
• ranges from 15-85% with an average of 40-50% of the initial population
• occurs in both CNS and PNS

• developmental errors
• overproduction of neurons that can't find target tissue
• competition for essential maintenance factor from target tissue cells

• occurs after apoptosis
• reduction in the extent of innervations to various tissues
• occurs in both the CNS and PNS
• regulated by functional activity

progressive development of integrated patterns of neuronal function

• Cell proliferation
• Migration of young post-mitotic neurons
• Aggregation of relevant cells
• Cytodifferentiation
• Synaptogenesis
• Apoptosis
• Process and synapse elimination

• Forebrain: cerebral cortex; responsible for thought, voluntary movement, language, reasoning, perception
• Midbrain: responsible for vision, audition, eye movement, body movement
• Hindbrain: contains the cerebelium; responsible for movement, balance, posture

brain folds

brain rooves

series of tough membranes covering the brain and spinal cord

bundle of nerve fibers

• proliferation occurs inside the tube and migrates outward
• creates 6 layers -outer layer is the youngest
• glial cells create a latter for the migrating cells to "climb"