Nervous system Flashcards
Divisions of the functional nervous system
Somatic and autonomic (visceral) nervous system
Somatic nervous system innervation
Skin and most skeletal muscles
Autonomic nervous system
Innervates visceral and smooth muscles and glands. Includes sympathetic and parasymphathetic divisions.
Formation of Neural tube
Thickening/elongation of neural plate, Lateral folding, fusion of opposing folds and separation from overlying ectoderm (Neural crest cells).
Lateral folding of the neural plate
Neural groove formed, Median hinge point formed, and lateral hinge points formed.
Neural crest cell formation
Fusion of neural tube allows overlying cells to seperates and become neural crest cells.
Where are molecular signals for brain development initiated?
Neural crest plate
BPM molecular signals
Neural crest signals that established brain sensory regions
SHH molecular signals
Neural crest signals that establish brain motor regions.
At day 26, what are the brain segments?
Proscencephalon, Mesencephalon, Rhombencephalon
What are the primary CNS segments?
Three brain segments, spinal cord, flexures.
What segment makes up the midbrain vesicle?
Mesencephalon
What brain segment Makes up the forebrain vesicle?
Prosencephalon
What Brain segment makes up the hindbrain vesicle?
Rhombencephalon
What happens at week 5 to the brain segments?
The three segments further divide into 5 segments.
What segments does the prosencephalon differentiate into?
Telencephalon and diencephalon
What segments does the rhombencephalon differentiate into?
Metencephalon and myelencephalon
What brain segment doesn’t differentiate?
Mesencephalon.
What becomes of the five brain segments?
They each differentiate into specific parts of the brain.
Where does the cell lineages within the CNS come from
Pseudostratified epithelium made of neuroepithelial cells. Dividing neuroepithelial cells are at the lumen of neural tube while external limiting cells at basement membrane are undergoing DNA synthesis.
What is the primary cell lineage of CNS cells?
neuroepithelium -> multipotential stem cells -> bipotential progenitor cells -> neuronal lineage or glial lineage progenitor cells.
What do neuronal lineage cells become?
Mature Neuron or microglial cell
What do glial lineage cells become?
Oligodendrocytes, astrocytes, special glial cells, or ependymal cells.
What is a neurite outgrowth?
Axons and dendrites. Growth cones extend filopodia into environment to test local environment.
Forebrain segmentation structures
Prosomeres and ventral forebrain
What happens if ventral forebrain is not induced?
Holoprosencephaly and cyclopia
What does the midbrain become?
Isthmic organizer
What does the hindbrain become
Rhombomeres and isthmic organizer
What does the spinal cord differential into?
Bilateral pairs of spinal nerves which is determined by somitic mesoderm
Telencephalon becomes?
Cerebrum
Diencephalon becomes?
Thalamus, hypothalamus, pineal body, pituitary gland, eyes
Mesencephalon becomes
Auditory colliculi, Cerebral aqueduct
Metencephalon becomes
Pons and cerebellum
Myelencephalon becomes
Medulla oblongata
What cells form all symphathetic/parasymphathetic ganglia?
Neural crest cells.
T/F:motor Neuroblast forms their axons as outgrowths in the basal plate
True
How do neural crest cells form spinal ganglion
The neural crest growth of the dendrites toward the periphery; the axon growth towards the dorsal horn.
What are schwann cells?
Neural crest cells that wrap around the nerve process in the peripheral nerve system. Many schwann cells for one neuron. The schwann cell spirals around the neuron.
Neuron filopodia
From neurons that extend and retract to test environment. If environment is favorable, then filopodia will adhere.
What is a neurite?
An axon or dendrite that is capped by a growth cone.
How is axon outgrowth achieved?
If environment is favorable, the pioneering axon grows out before the others follow. Many then follow forming fasciculation by fasciles.
What is neuron stabilization?
Interaction between axon and target determine connection type and number. Apoptosis occurs if connection issues of need to reduce number of neurons.
Where do neural crest cell originate from?
Lateral margins of neural plate.
How do neural crest cell migrate?
As mesenchymal cells. They change shape by loosing cell adhesion molecules (CAM) and gain integrins. Integrins allow for travel through well defined pathways. CAM’s re-expressed at new locations.
What are the two neural crest cell differentiation hypothesis?
Equal development potential-differentiation determined by environment.
Preprogrammed before migration-determined by internal factors.
Both are true.
Three major divisions of neural crest cell?
Cranial, circumpharyngeal, and Trunk NCC.
What are the cranial NCC?
Responsible for tissues of facial region.
What are the circumpharyngeal NCC?
Makes up gut and heart. Two pathways: Vagal crest cells and cardiac crest cells.
What are the trunk NCC?
Makes adrenal chromaffin cells (adrenal cortex), melanocytes, sensory ganglia, sympathetic ganglia/neurons.
What makes up the motor nervous system?
The somatic and autonomic divisions. Autonomic division has sympathetic and parasympathetic divisions.
What are the three types of neurons?
Sensory (afferent), Motor (efferent) and interneurons (most abundant).
What are neuroglial cells?
Provide neuronal support and nutrition, maintain homeostasis, forms myelin, and participates in transmission. More neuroglial cells than neurons.
What is the cell body of a neuron?
A soma and contains the grey matter
What is the name of a RER in a neuron?
Nissl body
Are are the name of cell clusters in the CNS? The PNS?
CNS is nuclei, PNS is ganglia.
What are the role of dendrites?
To receive signals and carry to soma. Have leaky sodium channels.
What are the role of axons?
Carry action potential away from soma that originated from axon hillocks. Axon may have collateral.
What are the structures of a synapse.
Presynaptic neuron with vesicles, synaptic cleft, postsynaptic neuron with receptors.
What is the resting potential inside a neuron?
It is negative inside the cell (-70mV) compared to the outside of the cell.
Neuron sodium/potassium pump?
3 sodium out, 2 potassium inside cell keeps resting potential.
What is the graded potential?
Stimulus at the dendrite of a neuron. Occurs when leaky channels open in dendrites causing depolarization. If GP sufficient, then potential spreads to axon hillocks. Must overcome threshold potential in order to transmit signal down axon hillock/axon.
What are the three neuron structural classifications?
Bipolar (symmetrical), unipolar, and multipolar neuron.
What are the types of glial cells?
Six types: astrocytes, oligodendrocytes, microglia, ependymal, schwann, and satellite cells.
Astrocyte cells
Largest and most numerous, control environment, assist in migration of new neurons, maintains blood-brain barrier.
Oligodendrocytes cells
Produce/maintain neurons with myelin sheaths that surround many neurons.
Microglia cells
Immune cells of CNS from WBC that act as macrophages. Clear unwanted debris by CNS lesions.
Ependymal cells
Circulates CSF, forms linings of fluid ventricles, source of CSF fluid in brains.
Satellite cells
In PNS, surround neuronal cells and provide support/insulation.
Schwann cells
In PNS, form mylein sheaths in PNS. only cell for a small portion of neuron.
How many cranial nerves and spinal nerves in PNS?
12 pair of cranial and 31 pair of spinal nerve pairs.
Divisions of the ANS of the motor division?
Sympathetic and parasympathetic system.
What is the resting potential?
When there is no net movement of ions across the cell membrane.
Sodium potassium ATPase
Carries 3 sodium out and transports 2 potassium in. Balances passive forces of diffusion.
Which ion is can easily pass through membrane of neuron?
Its highly permeable to potassium and low permeability to sodium.
What do leak potassium channels in neurons do?
They allow potassium to passively leave neurons
What do leak sodium channels do in neurons?
They allow sodium to passively enter neurons.
What type of ion channels are in neurons?
Passive and active (gated) channels. Active channels include chemical, voltage, and mechanical gated channels.
What happens during depolarization?
A shift in transmembrane potential toward 0mV. Movement of Na through channel into cell.
What happens during repolarization?
Movement back to resting potential. Sodium gated channels close and potassium channels open allowing potassium to leave cell.
What happens during hyperpolarization?
Increasing negativity of the resting potential
What is refractory period?
The time period from beginning of action potential to resting state.
Absolute refractory potential
Sodium channels open or inactivated. No action potential possible.
Relative refractory potential
Membrane potential almost normal. Large stimulus can activate it.
How many groups of axons fibers?
Three groups of axon (A, B, C).
Group A axon fibers
Mylinated, large diameter, high speed, carry rapid information to/from CNS
Group B axon fibers
Myelinated, medium diameter, medium speed, carry intermediate signals.
Group C axon fibers
Unmyelinated, small diameter, slow speed.
What are the two types of synapses?
Electrical and chemical synapses.
Electrical synapse
Direct physical contact with cells
Chemical synapse
Signal transmitted across gap via chemical neurotransmitters.
What do excitatory neurotransmitters do at post-synaptic membranes?
They activate post-synaptic by depolarization
What do inhibitory neurotransmitters do to post synaptic membranes?
The hyperpolarize the post synaptic membrane to inhibit response.
Synaptic delay
Occurs at arrival of action potential at synaptic terminal and effect post-synaptic terminal. Less terminals means faster response. Reflexes may involve only one synapse.
What causes synaptic fatigue?
Occurs when neurotransmitter are depleted and cannot send stimulus until replenishment.
What are the five neurotransmitters?
Norepinephrine (NE), dopamine, serotonin, gamma aminobutyric acid (GABA).
What are neuromodulators?
Similar to neurotransmitters but have longer effects and take longer to appear. Require multiple steps and often an intermediate.
What are the ways neurotransmitter/neuromodulators work at the synapse?
Direct effect (ACh, glycine, aspartate), indirect via G protein (E, NE, dopamine), and indirect via intracellular enzyme (lipid soluble gases, NO, CO).
How does indirect G protein work at synapse?
Work through second messenger. Enzyme complex binds GTP and activates adenylate cyclase, produces cAMP (second messenger). cAMP opens ions channels to depolarize.
How does indirect intracellular enzyme synapse activation work?
Lipid soluble gas activates intracellular enzyme that opens channels and changes cell activity.
How is information processed at individual neuron?
It is a net effect on axon. Individual neuron receives both excitation and inhibitory signals, but works on net effects.
Temporal summation
Rapid, repeated stimuli at on synapse, occurs multiple times.
Spatial summation
From multiple locations, many stimuli received at multiple synapses.
Chain of autonomic neurons
Two motor neurons; pre-ganglionic and post-ganglionic
What is the physiology of sympathetic neuron chains?
Pre-ganglionic: short, myelinated, high branches
Post-ganglionic: long, non-myelinated, few branches
T1-L2, called the thoracolumbar division.
What does the sympathetic chain ganglia innervate?
Innervates effectors in the thoracic cavity, head, and limbs. (eyes, salivary gland, heart, lung)
What does the sympathetic collateral ganglia innervate?
Anterior to vertebrae. Innervate organs in abdominopelvic region (liver, stomach, GI, kidney, adrenal medulla).
What organ is activated by sympathetic system that releases neurotransmitters into blood?
The adrenal medullae.
Parasympathetic neuron chains physiology
Pre-ganglionic chains: Myelinated, long, few branches
Post-ganglionic chains: myelinated, short, few branches.
Origin: Brainstem, sacral spinal cord. Called craniosacral division.
What neurotransmitters are used by the sympathetic system?
Pre-ganglionic used ACh,
Post-ganglionic release NE, Epi.
What neurotransmitters are used by the parasympathetics system?
Pre-ganglionic used ACh,
post-ganglionic use ACh or NO.
Alpha sympathetic receptors
For smooth muscle contraction, G protein
Beta sympathetic receptors
Smooth muscle relaxation, heart muscle contraction. G protein.
Cholinergic (ACh) sympathetic receptors
Innervates sweat glands, blood vessels of muscles and brain. Stimulates sweat glands and vaso-dilation.
Nitroxidergic sympathetic synapses
NO as neurotransmitter. Produce vaso-dilation to increase blood flow to brain, muscles.
Nicotinic parasympathetic synapses
On ganglionic cells to excite (depolarize) post-ganglionic neurons by ACh.
Muscarinic parasympathetic synapses
At target organ, use G protein. Effects last longer than nicotinic receptors. Can excite or inhibit.
