NBB (Neuron, Brain, Behavior) 1 Flashcards
Explain the concept of localization of function
Specific brain regions have specific functions –> by testing different functions, testing different parts of the brain
can use MRI to visualize neural localization
Define and describe neuroplasticity
List the types of cellular changes that underlie neuroplasticity
Neuroplasticity - potential that the brain has to reorganize to adapt to the environment –> changes in neurons and pathways in response to experience –> regions can take over for others that have been damaged e.g. prosthetics, implants, making new associations
Cellular changes: axon sprouting, dendritic branching synaptogenesis (creating new dendritic spines), neurogenesis, angiogenesis
white matter (axon) plasticity can include myelin formation or remodeling, fiber organization, astrocyte changes, angiogenesis
Explain the difference between a focal and a diffuse lesion
Focal lesion - infection, tumor, or injury that develops at restricted or circumscribed area of neural tissue –> produces focal neurological signs that can be traced to part of the brain eg loss of pain on half the face, loss of vision in one eye
Diffuse lesion - general, such as neurodegenerative diseases, psychiatric disorders, infections, malnutrition, genetic disorders, compression –> diagnosis depends on the beginning symptoms, patterns, and time course
episodic --> migraine, seizures relapsing, remitting --> MS sudden onset, lasting deficits --> Stroke slow, progressive --> PD, Alzheimer's fast, progressive --> tumor, pressure
Describe the morphological classification of neurons and where they are found
1) Pseudounipolar
2) Bipolar
3) Multipolar
1) Pseudounipolar - sensory PNS neuron; cell body migrated out, axon split into two branches - one to spinal cord (CNS) and one to periphery
2) Bipolar - two axons from the cell body; specialized sensory PNS neurons for eyes (sight), ears (hearing), nose (smell)
3) Multipolar - single long axon and multiple dendrites; found in CNS and PNS; most common
Describe general structure of neurons.
PNS: Describe types of neurons and morphological classification
1) Afferents
2) Efferents
CNS: Describe types of neurons:
1) Interneurons
2) Local neurons
3) Projection neurons
Neuron: dendrite (receives input), cell body, axon (sends output via action potentials)
PNS:
(1) Afferents - carry sensory information from periphery –> CNS; usually pseudounipolar
(2) Efferents - CNS –> motor signals to efferent motor neurons whose axons terminate on organs/muscle; multipolar
CNS:
1) Interneurons - ANY neurons that form connections in CNS –> process and integrate info; multipolar
2) Local neurons - connect to cells in immediate region
3) Projection neurons - project to more distant areas of CNS in tracts
Differentiate between the following:
1) CNS convergence vs divergence pathways
2) decussation vs commissure
3) clusters of nuclei vs axons
4) white matter vs gray matter
1A) CNS divergence - multiple outputs from axon terminals via axon collaterals (branches) –> can send info to several pathways/parts of nervous system
B) CNS convergence - multiple inputs to a neuron –> integration of inhibitory and excitatory information eg motor, sensory systems and associative learning
2A) decussation - pathway crosses midline
B) commissure - white matter (Axon) tract that connects structures on the R and L sides of the CNS
3A) cluster of nuclei –> nucleus (CNS), ganglia (PNS)
B) clusters of axons –> tract, nerve, funiculus
4A) White matter - axons
B) gray matter - nuclei/cell bodies and synapses
What are glial cells? Describe the different types and where they are found 1) Astrocytes 2) Oligodendrocytes 3) Microglia 4) Satellite cells 5) Schwann cells
Glial cells - guide neurons, build myelin sheaths, buffer from ions
1) Astrocytes [CNS]- macroglia; physical support, component of blood-brain barrier, K+ metabolism, remove excess neurotransmitter, produce neurtrophic factors and scar tissue post injury, form glial membrane ( called external limiting membrane)
2) Oligodendrocytes [CNS] - macroglia; myelinate multiple axons
3) Microglia [CNS] - phagocytic scavenger cell activated post tissue damage (injury, infection, disease) –> produces growth factors
4) Satellite cells [PNS] - macroglia; provides nutrients and structural support for neurons iN PNS
5) Schwann cells [PNS] - macroglia; myelinate only one axon in PNS
What is the resting membrane potential (RMP)? What are the relative concentrations of Na+ Cl- Ca2+ K+
Resting membrane potential - charge across neuron membrane; usually -65 mV because of osmotic/electrical forces, permeability of neuron, and Na+/K+ pump
Na+, Cl-, and Ca2+ all have higher concentrations OUT»_space; IN
K+ and organic anions have higher concentrations IN»_space; OUT
What are graded membrane potentials?
Graded potentials - changes to resting membrane potential in response to inputs; magnitude varies based on strength of input; arise from summation of individual gated ion channels
A. hyperpolarizing - negative, inhibitory
B. depolarizing - positive, excitatory
Describe the difference between EPSPs and IPSPs
EPSPs = Excitatory Post-synaptic potentials –> depolarizing, graded
usually arise from opening of Na+ or Ca2+ (influx) channels –> make RMP more positive and more likely to have action potential
IPSPs = Inhibitory Post-synaptic potentials –> hyperpolarizing, graded
usually arise from opening of Cl- (influx) or K+ (efflux) channels –> make RMP more negative
whether neurotransmitter evokes EPSP or IPSP depends on the post-synaptic receptor it binds to
Describe importance of temporal and spatial summation with graded membrane potentials
Normally, graded potentials attenuate rapidly with distance
Temporal summation - inputs are in rapid succession so they build on each other
Spatial summation - multiple inputs simultaneously
Describe the molecular processes that underlie action potentials
Describe propagation of action potentials
1) Action potentials occur when membrane potential hits the threshold –> “Trigger zone” usually with lot of Na+ channels
Na+ channels open and Na+ rushes into the cell and depolarizes it –> K+ channels open after (slower) so both channels are open; K+ leaves the cell and makes RMP more negative –> Na+ channel closes while K+ is still open (Refractory period) –> both Na+ and K+ are closed
2) Propagation: local depolarization causes current to flow in both directions –> neighboring voltage gated Na+ channels opens –> continuous repeated process but only in one direction along the axon bc the prior sections are refractory
Explain the function of myelin and axon diameter on conduction velocity
Conduction velocity of action potential increases with:
1) myelination (insulated area with no voltage gated channel underneath) - bc action potential jumps from nodes of ranvier
2) increased axon diameter - bc larger internodal spaces and increased space constants (current can move along further before it attenuates)
Describe 2 diseases related to demyelination
- Multiple Sclerosis - autoimmune inflammatory disorder; demyelination of oligodendrocytes
- Guillan-Barre - viral infection leads to inflammation-induced demyelination of peripheral nerves –> Ascending weakness and elevated protein in CSF
List the steps of synaptic transmission
- Transmitter synthesized and stored in synaptic vesicles
- action potential reaches presynaptic terminal
- depolarization of presynaptic terminal –> opening of voltage gated Ca2+ channels
- Ca2+ influx
- Ca2+ causes vesicles to fuse with presynaptic membrane
- Transmitter released into synaptic cleft
- Transmitter binds to receptor molecules in postsynaptic membrane
- opening/closing of postsynaptic channels
- postsynaptic current causes postsynaptic potential –> changes excitability of postsynaptic cell
- removal of neurotransmitter by glial uptake or enzyme degradation
- retrieval of vesicular membrane from the plasma membrane
Describe the 2 families of postsynaptic receptors:
- Ionotropic
- Metabotropic
- Ionotropic - receptor is linked directly to ion channels - neurotransmitter binds to receptor –> conformational change allows ion flux; v fast
- Metabotropic - receptor does not have a channel - neurotransmitter binds –> G protein messengers released –> causes conformational changes in channel and ion flux; slower, allows for neuromodulation
List the major neurotransmitters that act at ionotropic receptors:
- Excitatory [PNS]
- Excitatory [CNS]
- Inhibitory [CNS]
* NO inhibition in PNS
- Excitatory [PNS] = Acetylcholine
- Excitatory [CNS] = Glutamate –> in ~50% of all neurons; can act at metabotropic (excitatory or inhibitory) or ionotropic (exclusively excitatory) post-synaptic receptors
- Inhibitory [CNS] = GABA or glycine –> opens ligand-gated Cl- channels
Discuss the characteristics and significance of the NMDA receptor.
NMDA - N-methyl-D-aspartate ionotropic receptor
- BOTH voltage gated and ligand-gated channel –> needs both depolarization and glutamate
- at RMP - receptor channel is blocked by Mg2+
- at depolarization - glutamate binds + Mg2+ displaced –> Ca2+ influx
Unique characteristics:
- intracellular signals (kicked off by Ca2+ influx) –> long-term synaptic changes –> regulating neural circuits, learning and memory, changes in dendritic spines, insertion of AMPA receptors
- receptor inhibited by hallucinogenic drugs –> produces hallucinations
long-term potentiation - increased responsiveness of post-synaptic neurons after repeated stimulation
Describe glutamate toxicity
Trauma, diseases –> increased glutamate release/decreased uptake –> glutamate NMDA receptors activated –> Ca2+ influx into cells –> increased Ca2+ causes increased water uptake and stimulation of enzymes –> neurons self-digest
associated with ALS, Alzheimer’s tumors, ischemia, trauma, seizures
Describe the projection origin and functions of the major neuromodulators in the brain:
- Norepi
- Dopamine
- Ach
- Endogenous opioids
- Unconventional neurotransmitters
Neuromodulators - affect neuronal excitability
- Norepi - originates in locus ceruleus (pons); stress hormone, stimulated by amphetamines and Ritalin
- Dopamine - originates in ventral tegmentum and substantia nigra (midbrain); functions in control of movement, reward pathway, and working memory via different pathways (increased in Huntington but decreased in Parkinson, depression)
- Acetylcholine - originates in basal forebrain and pons; functions in arousal and memory (degenerates in Alzheimer’s, Huntington’s)
- Endogenous opioids - originate in spinal cord, brainstem, and forebrain; functions in pain and reward
- unconventional neurotransmitters (not stored) –> A. endocannabinoids (activated by THC) - lipid metabolites that decrease pain signals
B. NO and CO - gases that are involved in neurodegenerative processes
ID the sensory and motor regions of the spinal cord
Spinal cord: foramen magnum –> L1 vertebral body
Bell-Magendie Rule: dorsal (posterior) portion of spinal cord is sensory, ventral (anterior) is motor
Sensory inputs (afferents) from periphery and through dorsal root to the brain Motor outputs (efferents) through ventral root out to periphery
ID the 3 major areas of the brainstem and their functions/associated cranial nerves
Brainstem: transition between spinal cord and brain
- Medulla - regulate body homeostasis and reflexes (vomiting, coughing, swallowing); cranial nerves IX, X, XI, XII (info from taste, skin of head/heart/lungs, digestive system)
- Pons - balance, eye movements, facial expressions, reflexes (eyes, jaw); cranial nerves V, VI, VII, VIII
- Midbrain - control orienting to sound, visual reflexes, motor control; source of dopamine projections to cortex for movement and habit formation; cranial nerves III and IV
What is the reticular formation and where is it found? What is the reticular activating system
Reticular formation - network of nerve pathways (nuclei + neuronal circuits) that run through the core of the brainstem; mediate overall level of consciousness
nuclei are origins of projections to cortex or spinal cord e.g. rostral projections from the midbrain and pons form the reticular activating system –> project to cortex/through thalamus to control attention, arousal, sleep, wakefulness
caudal projections from pons and medulla –> control respiratory rhythms, bp, digestion, reflexes (yawn, swallow, vomit, gag)
Describe the functions of
1) Cerebellum
2) Thalamus
1) Cerebellum - motor control, learning, posture, orientation, balance; damage causes ataxia
2) Thalamus - integrative center for inputs to the cortex eg sensory, motor, reticular formation, limbic; projections go to specific group of nuclei; thalamus is part of diencephalon