CNS Flashcards
CNs made up of?
Brain(Cerebrum,cerebellum,brainstem and spinal cord)
Functions of CNS
Patterns of action potentials encode information leading to:
1.Sensory perception
2.Information processing, 3.integration, & storage
Motor and Behavior
Required terms
White matter: High density of myelin covering axon pathways (and very few neurons)
Gray matter: High density of neurons and dendrites (Axons also present).
Nucleus: cluster of neurons within the CNS
Ganglion: cluster of neurons outside the CNS
Cortex: dense layers of neurons
Tract: axons within the CNS traveling as a group/usually named based on region of origin & termination (i.e. spinocerebellar tract)
Pathway: similar to tract however it relates more to synaptically connected neurons performing a function
grey matter externally,white matter internally
Cytology of the CNS
Neuron…cell to cell communication or signaling
Neuroglia….
CNS
Astrocytes…maintain extracellular environment…buffer…glutamate
Oligodendroglia…myelin sheaths
Microglia (latent phagocytes)…..removing infectious agents
Ependymal cells (line ventricles/CSF production)
PNS
Schwann cells
Satellite cells…similar to astrocytes
BAsic functional unit of the neuron
Dendrite,cell body,axon,synapses,spinal cord,
What does Excitatory synapses focus on dendrites or Axon?
Dendrites
Axonal dendritic communications
What does Inhibitory synapses focus on dendrites or Axon?
Axosomal communication
Contents of the Axon Hilux is
High density of sodium Chanel that moves in 1 direction after Excitation(its activated a refractory phase)…greatest probability of generating an action potential
Characteristics of Uni-polar cell type
invertebrates have these.
axon and a dendrite coming out as a sngular process
Characteristics of pseudo-uni-polar cell type
Primary sensory neurons.
cell body,axon and bifurcates to receive sensory inputs and the other end to spinal cord
Characteristics of bipolar cell type
Sensory organs to the eyes, dendritic sites at the and
internurones
middleman
Characteristics of Multi-polar cell type
cell body and 2 ends of dendrite sites
Axonal Transports
powered by ATP:
Kinesin: anterograde Dynein: retrograde
Motor Neurone-axon to the toe.
.presynaptic terminal relies on generation of protein in the cell body…
active axonal transport allow for energy and ca use for movement of substance from soma to the axon and synaptic terminal
Micro filament and neuro filament
Atp and calcium used by protein for transport..
A lot Atp calcium dependent….
Kinesin…antegrade…to the presynaptic region
Dynein..retrograde..from the presynaptic neurone
expensive
lysosomal degradation as an example.
Neuroglia components
Astrocytes --projection everywhere. Epindymal cells….produce csf… Astrocytes may regulate csf production since its connected to Epindymal cells Can pick up potassium ions Management of glutamate concentration
Oligodendrocyte…produces myelin
AP
they are the same size,needs frequency altered to be able to use more or less
Myelination
produced by Oligodencrocytes
Greater conduction velocity
Increases the effective membrane resistance (length constant)
Decreases the capacitance
Restricts action potential generation to the Nodes of Ranvier
Nodes are rich in sodium and potassium channels
+ and – forces attract each other ,blocks the charges from seeing each other so capacitance is decreased.
Ap regeneration does not need to happen throughout the axonal length.
Minimize Atp,conduction at nodes of Ranvier
Myelination benefits
Fast reflexes
“Complex mental processing”
Metabolic Advantage
Types of fibres
A fibers (myelinated) 1 to 22 microns Subdivided into: α β γ δ in order of decreasing
B fibers (myelinated) 1 to 3 micrometers C fibers (unmyelinated fibers) 0.1 to 2.5 micrometers
Peripheral nerve fibres and thier reactions
A-alpha fibers: motor & proprioception
A-beta fibers: motor, touch, pressure
A- gamma fibers: motor/muscle tone (muscle spindle)
A-delta fibers: pain, temperature,touch
B-fibers: PREganglionic autonomic
C- fibers: dull pain, temperature, touch, POSTganglionic autonomic– NO MYELIN
Synaptic Signaling
-Classic Neuron-Neuron Junction
Electrical ..found in brain astrocytes neurons,fast signal transmission
Gap Junctions(cell to cell communication through open channels) -Chemical
Neurotransmitter mediated
-Neuron-Glial(neurons and astrocytes)
-Extra-synaptic – we now know NT released at a synapse can have actions at locations distal to the original synapse.
Receptors outside synapse
Electrical synapses/Gap junctions
found in brain astrocytes neurons,fast signal transmission
Low-resistance pathway between cells that allows current to flow directly from one cell to another
Allows the exchange of small molecules between cells.
Fast & bidirectional
Synchronization of network activity/Electronically coupled neurons
Gap junctions regulated by voltage, intracellular pH, Ca++, and G protein—coupled receptors
Chemical synapsis
ACh—nicotinic(NMJ)
Nicotinic(GAnglia site)
Neuropeptide
Neuropeptides. In Neuron dense vesicles…co released with something else
Gaseous transmitter
nitric oxide…Direct transmission.
Characteristics of a neurotransmitter
Criteria
Present in presynaptic terminal
Cell must be able to synthesize the substance
Released upon depolarization of presynaptic membrane
Specific receptor on the postsynaptic membrane (+/- extrasynaptic locations) to respond to it
Differencies between peptide and non peptide neuro transmitters
Non peptide or classic neurotransmitter/Peptide transmitter.
Synthesized and packaged in the nerve terminal/Synthesized and packaged in the cell body; transported to the nerve terminal by fast axonal transport
Synthesized in active form/Active peptide formed when it is cleaved from a much larger polypeptide that contains several neuropeptides
Usually present in small, clear vesicles/Usually present in large, electron-dense vesicles
Released into a synaptic cleft/May be released some distance from the postsynaptic cell
There may be no well-defined synaptic structure
Action of many terminated because of uptake by presynaptic terminals via Na+-powered active transport/Action terminated by proteolysis or by the peptide diffusing away
Typically, action has short latency and short duration (msec)/Action may have long latency and may persist for many seconds
Classic neurotransmitters examples(small molecules)
Class I Acetylcholinexx Class II: Biogenic Amines Norepinephrine xx Epinephrine Dopamine Serotonin Histamine Class III: Amino Acids Gamma-aminobutyric acid (GABA) Glycine…inhibitory….spine Glutamate….excitate…brain Aspartate
Classes of neuro peptides and peptide transmitters
- Hypothalamic-releasing hormones…Luteinizing hormone
- Pituitary peptides
- Peptides that act on gut and brain…Substance P…increase the number of pain signal coming to brain .opiod will reduce that signal.
- Other tissues…
Examples Gaseous Neurotransmitters
Are NOT released from “vesicles”
Nitric oxide (NO)(Blood vessels and in the Brain)
Carbon monoxide
Nmda stimulate NO production(Brain)…….Ca from NMDA…calmodulin….activates endothelial nitric oxide synthase which promotes…arginine to convert into….NO
Cerebral vessel tone influenced
Glutamate Activity
major excitatory….
Brought into the vesicle by Vglut…..
Glutamatergic neuron stimulated by AP…
after VGCC opens and releases calcium.
..
Glutamate released and stimulates a lot of other receptors
Ligand gated ion channels(NMDA,AMPA, Kainate and gprotein coupled receptors
Metabotropic glutamate receptors.
Glutamate levels are controlled by EAAT1,2,3,4,5(Excitatory Amino Acid transporters)
Excitotoxicity happens because we have glutamate hanging around for too long ..
Major TBI release glutamate into the brain and stimulate glutamate receptors to release calcium too much calcium may cause Apoptosis.
Astrocytes(express these transporters EAAT 1 and 2 that take up glutamate and they contain an enzyme called glutamine synthase which convert glutamate to glutamine that is not active at glutamate receptors.
Glutamine can be excreted from cell and taken back up by presynaptic terminals and in the presynaptic terminal there is an enzyme glutaminase which will convert glutamine back to glutamate.
Post-synaptic responses to neurotransmitter
EPSP (or IPSP) occurs when neurotransmitter binds to a post-synaptic receptor
ligand gated ion channel (“fast” transmission)
G-protein coupled receptor (“slow” transmission)
Gaba is main Inhibitory
EPSP…depolarize…….Glutamate NeurotransmitTer(AMpA receptor)…..passess …na and will depolarise
IPSP…
hyperpolarize…….Gaba NT(Gaba receptor) ..passes chloride for increase chloride conductance which then comes in and hyper polarize the cell and cause IPSP
between excitation and inhibitory, the one the happens depends on the membrane potential
the nernst potential of the ions involved..
EPSP excitatory response
Increased Na+ influx
Decreased Cl- influx or K+ efflux
Change in receptor expression or enzymatic/metabolic activity (delayed effect)
potassium channel closes or potassium stays in the cell.
IPSP inhibitory response
Increased Cl- influx or K+ efflux
pre-synaptic
post-synaptic
Change in receptor expression or enzymatic/metabolic activity (delayed effect)
in IPSP 1 synapse chnahges membrane potential by how much
*Each EPSP changes membrane potential by 0.5-1mV at most for <15ms.
What magnitude of change is generally required to reach threshold?
so we need multiple synapse to reach threshold easily by multiple firing
must be done with 15Ms
Spatial and Temporal Summation is Required to Reach the Threshold Potential
It is the sum total of all synaptic activity that determines if threshold is reached and and if an action potential is triggered
Facilitation (sub-threshold stimulation)
Function of reverbatory circuit
used for short term memory
Most synaptic events occur at the ?
Dendrites.
Majority of Synapses are dendritic.
ALkalosis and acidosis does what to neuronal excitability
Alkalosis greatly increases neuronal excitability
Acidosis greatly depresses neuronal activity;
What does Hypoxia do to neuronal excitability
Decreases.
Drugs can increase or decrease excitability.T or F
T
Cerebral cortex
Cranial nerve 1 Fine tune lower brain functions Sensory perception Cognition Learning Large “memory storehouse” Motor planning & voluntary movement Language Essential for “higher level thought”
2 hemispherer connected by the Corpus Colusum
Fontal lobe
Planning and carrying out motor behavior (motor, premotor, cingulate motor, and supplementary motor areas, frontal eye field)
Speech (Broca’s area, inferior frontal gyrus of the dominant hemisphere)
“Intellectual activities”
Personality and emotional behavior (rostral frontal lobe)
MOTOR
Broca’s area
Parietal Lobe
Sensory perception and processing (somatosensory cortex/parietal association cortex)
Projections to the frontal lobe carrying somatosensory information modulates voluntary motor behavior
Parietal association cortex processes visual information from the occipital lobe and then sends projections to the frontal lobe to influence motor behavior.
In dominant hemisphere sends somatosensory information to Wernicke’s area.
Establishment of spatial context (non-dominant hemisphere)