Exam I (Revised) Flashcards
Phrenology
By touching the skull, you can make assessments on personality
Brain would be bigger/smaller (convexities, concavities) depending on the functions you possess
Franz Gall
Jean Pierre Flourens
Critique of phrenology/Gall’s presumption of localization
Would lesion animals in localized spots –> a lesion did impair brain functioning, but a lesion anywhere would do so, not in just one area –> concluded that all regions of cortex contributed equally to behavior
Equipotentiality
Flourens’ lesioning work
Over time, lesioned animals recovered normal cortical functioning without tissue damage being repaired
–> Assumed intact areas of brain took over functioning
Equipotentiality asserts that any brain region has the potential to support any given brain function
Jacksonian March
John Hughlings Jackson
During seizures, noticed there was a specific sequence of body parts that correlate with seizure activity traveling along motor cortex
Paul Broca
Lesion –> Could only say “Tan”
Localized area for language production
Left frontal cortex = Broca’s Area
Broca’s Area
Left frontal cortex
Localized area for language production
Paul Broca and “tan” patient
Neuron
Cells in the brain that generate electrical and chemical signals that control all other systems of the body
Camillo Golgi
Developed a silver stain that allowed for the visualization of individual neurons
Golgi believed the brain was a continuous mass of tissue with a common cytoplasm –> referred to as a syncytium
Golgi’s obsolete scientific theory stated that the brain existed as one continuous network
Cytoplasm
Protoplasm within a living cell, excluding the nucleus; fills remaining space in cell outside of nucleus and enclosed by membrane
Axoplasm is the cytoplasm within the axon of a neuron
Synctium
A cellular network containing several nuclei and cytoplasmic continuity
Ramon y Cajal
Used Golgi’s stain to show that the brain was made up of individual nerve cells linked together by long extensions
Neuron Doctrine
Ramon y Cajal
Neuron Doctrine: nervous system made up of discrete individual cells (neurons)
Ramon y Cajal used Golgi’s stain to show that the brain was made up of individual nerve cells linked together by long extensions
Soma
Cell body
Integrates
Axon
Transmitting Process
Conducts
Dendrite
Receiving Process
Collects
Synapse
Gap between neurons where transmission takes place
Axon Hillock
Region of cell body where axon emerges; the membrane is rich with voltage gated Na+ channels, which can generate action potential
Myelin Sheath
Cholesterol-laden sheath that insulates axons; composed of oligodendrocites
Node of Ranvier
Gap between myelin sheaths, between Schwann cells
Axon Terminal
Terminal Bouton
Outputs information
Button-shaped endings on neurons where neurons form into vesicles before being released into synaptic cleft (synapse)
Vesicle
Release is regulated by voltage-gated calcium channel
Stores of neurotransmitters in the presynaptic terminal that are released into the synapse via calcium-triggered exocytosis
Resting Membrane Potential
- Electrical charge: -70 mV
- Neurons maintain life by maintaining electrical and chemical disequilibrium (neg inside relative to outside)
- ELECTRICAL: neuron will maintain negative -70 mV voltage relative to extracellular space
- CHEMICAL: neuron will hold high concentration of K+ and low concentration of Na+ relative to extracellular space
Action Potential
The change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell
Voltage across a neuron suddenly reverses and then, about 1 ms later, is abruptly restored
- all or nothing
- only forward
- require refractory period
Depolarization
Cell becomes more positive
If the number of EPSPs is much higher than number of IPSPs, the cell will depolarize. If threshold level is reached (-55mV), an action potential will be initiated by axon hillock.
Na+ leaks into axon (-70 mV —> -55 mV) Na+ voltage gated ion channel opens, allowing sodium to flow into axon (-55mV —> +40 mV)
Hyperpolarization
Cell becomes more negative, overshooting resting level
At +40 mV, Na+ channels close and K+ channels open. As potassium exits axon, the cell begins to repolarize. The cell “undershoots” in which membrane potential dips lower than resting state (+40 mV —> -100 mV), known as hyperpolarization.
Electrical Force, Diffusion Force
Ions flow into and out of the neuron under the forces of electricity (electrical, voltage) and concentration gradients (diffusion)
Electrical: neuron maintains -70 mV relative to extracellular space
Chemical: neuron will hold higher concentration of potassium inside and lower concentration of sodium inside relative to extracellular space
Transporter Pumps
A transmembrane protein that moves ions across a plasma membrane against their concentration gradient through active transport
Na+/K+ Pump: Removes 3 Na+ for every 2 K+ admitted
Electrical Gradient
Concentration Gradient
Electrical: neuron maintains -70 mV relative to extracellular space
Chemical/concentration: neuron will hold higher concentration of potassium inside and lower concentration of sodium inside relative to extracellular space
Neuron begins at rest (-70mV), maintaining life through an electrical and chemical disequilibrium (slightly negative inside relative to extracellular space)
Voltage Gated Channel, Chemical Gated Channel
Chemical: these open in response to a specific chemical stimulus (E.g: neurotransmitter, such as acetylcholine, or a hormone); these are specifically important a synapses
Voltage: these open in response to a change in the membrane potential; these are important in conducting action potentials along axons
Postsynaptic Potential (PSP)
Small changes in voltage (about 1 mV)
Regenerative Spike
The action potential spreads just far enough down membrane for neighboring voltage-gated channels to open up, causing the cycle to start again, moving progressively down axon (action potential propagation).
Salutary Conduction
Jumping, AP regenerated at each node
Inhibitory Postsynaptic Potential (IPSP)
When positive ions, such as potassium, flow out of cell or negatively charged ions, such as chloride, flow into cell, the neuron becomes hyperpolarized
Excitatory Postsynaptic Potential (EPSP)
When positive ions, such as sodium, flow into cell (slightly reducing the negativity, depolarizing it)
Temporal Summation
Small voltage changes are collected in dendrites and travel along dendritic membrane to soma, where all the branches come together
Temporal: high frequency stimulation by one presynaptic neuron; signals arrive at soma at same time
The total voltage of the cell is determined by the overall pattern of incoming signals (+EPSP, -IPSP)
Spatial Summation
Small voltage changes are collected in dendrites and travel along dendritic membrane to soma, where all the branches come together
Spatial: simultaneous activation by many presynaptic neurons; signals arrive on different branches and converge at the soma
The total voltage of the cell is determined by the overall pattern of incoming signals (+EPSP, -IPSP)
Neurotransmitter
Transmit signals between neurons
Exciting/inhibiting specific postsynaptic neurons
Glutatmate
EPSP
Excitatory neurotransmitter
Opening of Na+
Acetylcholine
Excitatory neurotransmitter in the peripheral nervous system
Excitatory neurotransmitter
opening of Na+
Acetylcholine: facilitates learning and memory
• affected in Alzheimer’s Disease
GABA
IPSP
inhibitory neurotransmitter
influx of Cl- ions, hyperpolarizing cell /or K+
Agonist
agonist: molecule that occupies receptor and activates
antagonist: molecule that occupies receptor and blocks
Antagonist
agonist: molecule that occupies receptor and activates
antagonist: molecule that occupies receptor and blocks
Neurology
Function and pathology of the nervous system
Neuroscience
Mechanisms of the nervous system
- neuroanatomy
- neurophysiology
- neurochemistry
Cognitive Psychology
How the mind processes information
Dorsal
Top
Ventral
Bottom
Anterior
Front
Posterior
Back
Rostral
Front
Caudal
Back
Medial
Middle
Lateral
Side
Brain Slices
Axial/Transversal: top and bottom
Sagittal: Side/side
Coronal: front and back
Transverse
(aka Axial)
Top and bottom
Axial
Top and bottom
Saggital
Side and side
Coronal
Front and back
Neuron Communication
Electrical: Electrical impulses carry signals within a neuron, propagating down axon
Chemical: Carry signals between neurons, crossing the synapse from presynaptic axon terminal to postsynaptic dendrite
Grey Matter, White Matter
Grey = border, cell bodies White = majority of middle, axons
Gyrus, Sulcus
Gyrus = top Sulcus = bottom
GS in alphabetical order, top to bottom
Fundus is very bottom concavity
Fundus
Concavity of gyrus/sulcus
Precentral Sulcus
Sulcus
Precentral gyrus = primary motor cortex
Central Sulcus
Boundary of motor and sensory cortices
Separates frontal lobe from parietal lobe
Separates primary motor cortex from primary somatosensory cortex
Postcentral Sulcus
Sulcus
Postcentral gyrus = primary somatosensory cortex
Sylvian Fiissure
Separates temporal lobe from frontal and parietal
Insula buried deep within it
Central Fissure
Separates frontal lobe from parietal lobe
Separates primary motor cortex from primary somatosensory cortex
Parieto-Occipital Sulcus
Separates parietal and occipital sulci
Involved in planning
Angular Gyrus
In parietal lobe, near superior edge of temporal lobe
Angular is below supra, parietal lobe
Transfers visual information to Wernickle’s area, in order to make meaning from visually perceived words
Supramarginal Gyrus
Language perception and processing
Supra is on top of angular, parietal lobe
Lesion = aphasia (making sense of words)
Gross Dissection
Since gross anatomy is the study of brain anatomy at the visible level, I am assuming gross dissection is simply dissecting brain regions at the macroscopic level.
Golgi Stain
Silver staining reveals the entirety of one neuron but not all neurons in total
Nissi Stain
Aniline dye dark blue staining reveals every cell body in total picture, allowing an estimate of total
Cortical Layers
The cerebral cortex is made up of 6 cortical layers
Layer 4: Main input layer, receives input from thalamus (V1)
Layer 2/3: Send info to higher levels of cortex [feed-forward] (V2 –> V4)
Layer 5/6: Send feedback projections to earlier levels of cortex [feedback] and project to thalamus [feed-forward] or other subcortical structures
- Cell bodies located layer have dendrites that extend to another layer
- Many project to the neurons in the layer(s) above and below (in addition to many already sending ff and fb projections)
- Neurons “stacked” on top of one another forming cortical columns
LAYER 4 = MAIN INPUT LAYER
LAYER 5 = MAIN OUTPUT LAYER
Line of Gennari
Striate Cortex
Band of myelinated neurons, forming a thick white stripe in cross-sectional views of the cortex lining the calcarine fissure.
Fundus of the calcarine sulcus of the occipital lobe
Composed of axons bringing visual information into the layer 4 of visual cortex
Cytoarchitecture
Brodmann
52 layers, based on cell morphology, density, and layering
Circuitry
?
Brain Activation
Ways of examining circuitry
Using heat map
Myelination
DTI - white matter tracts
Topographic Organization
Spatially adjacent stimuli on sensory receptor surfaces are represented in adjacent positions in cortex
Retinotopy
From the 3D reality, lower area visual neurons form a visual image on the retina such that neighboring regions of visual space are represented by neighboring regions of neurons
Concave shape of retina on back of eyeball means anything perceived below the point of fixation will be projected onto upper retina, and left projected to right
So everything in the primary visual cortex is “flipped” with respect to the visual field
Tonotopy
Tones close to each other in terms of frequency are represented in topologically neighboring regions in the brain
Homunucleus
A distorted representation of the human body, based on a neurological “map” of the areas and proportions of the human brain dedicated to processing motor function
Discrimination ability –> more neurons coding for adjacent areas
Functional Division
Brain is divided into different subsections according to function.
Electrophysiology
Measures the electrical activity of neurons, and, in particular, action potential activity
Fixation Point
Fixation or visual fixation is the maintaining of the visual gaze on a single location
Receptive Field
The particular region of a visual field in which the onset of a particular stimulus will drive the firing of a correlated neuron
Movement Field
Neurons from primary motor cortex have a preference for the orientation of movements
Broadly tuned, very little specificity
Rate Coding
Frequency coding
As the frequency or rate of action potentials (or “spike firing”) increases
action potentials/time
Tuning Curve
Used to characterize the responses of sensory neurons to external stimuli
Orientation can be decoded by changes and spike rates
Offers a way to describe the preferences a neuron reacts to
A neuron’s role is to encode the stimulus at the tuning curve peak, because high firing rates are the neuron’s most distinct responses
Population Coding
Summation of input from thousands of units firing
“wisdom of the masses”
Temporal Coding
When precise spike timing or high-frequency firing-rate fluctuations are found to carry information
Angelo Mosso
Discovery that brain blood supply pulsates
From his findings that these pulsations change during mental activity, he inferred that during mental activities blood flow increases to the brain.
Brain diverts more blood to that part of brain during mental processing
Brainin balancing device: Mosso reasoned his volunteer’s brain would have to process the sound, requiring more blood, making it weigh more, which would tip the scale toward the head’s side. According to his manuscripts, that’s exactly what happened.
PET
Injected with tracer, pick up on distribution
Localization of brain activity
MRI
Structural imaging
Uses magnetic field and radio frequency
fMRI
BOLD blood oxygen level dependent
Blood level = correlate for brain activity
Blood oxygen-level dependent
Neural correlate for brain activity
Hemodynamic signal driven by metabolic need of cell
BOLD
Blood oxygen-level dependent
Neural correlate for brain activity
Hemodynamic signal driven by metabolic need of cell
Hemodynamics
Hemodynamic response (HR) allows the rapid delivery of blood to active neuronal tissues
fMRI imaging technique used to measure the haemodynamic response of the brain in relation to the neural activities
slow compared to direct neural recordings
Subtraction Logic
The idea behind cognitive subtraction is that, by comparing the activity of the brain in a task that utilizes a particular cognitive component (e.g. the visual lexicon) to the activity of the brain in a baseline task that does not, it is possible to infer which regions are specialized for this particular cognitive component
fMRI and PET
Spikes
Neuron firing
Exitotoxins
Exitocins: chemicals that overstimulate neuron receptor
Overexciting neurons causing tissue damage and cell death
Neurotoxins
Neurotoxins are toxins that are poisonous or destructive to nerve tissue through inhibition
By inhibiting the ability for neurons to perform their expected intracellular functions, or pass a signal to a neighboring cell, neurotoxins can induce systemic nervous system arrest as in the case of botulinum toxin or even nervous tissue death
Cyrogenic Depression
Cooling
Reversible
Inhibitory Neurotransmitter
INHIBITORY NEUROTRANSMITTER
Hyperpolarizes neurons and drastically reduce probability of firing
They inactivate neuronal cell bodies, where the receptors are located and NOT passing axons.
When an inhibitory NT activates the receptor site, it causes additional potassium channels to open which may cause potassium ions to flow out of the cell and if additional positively charged potassium ions flow out of the cell, the inside of the cell will become more negative.
In other words, inhibitory neurotransmitters cause an opening of ligand-gated potassium ion channels which leads to a local hyperpolarization (more negative than normal). This is known as a Inhibitory Postsynaptic Potential (IPSP) because it’s going to be LESS likely to throw off an action potential.
ex: GABA and Glycline, or GABA agonists
Contusion
Brain damage common in specific area
Orbitofrontal and anterior temporal
Holbourn
Orbitofrontal and Anterior Temporal Contusions
Neuropsychology
Neuropsychology is the study of the structure and function of the brain as they relate to specific psychological processes and behaviors
Single Dissociation, Double Dissociation
A “single dissociation”: a single dissociation happens when a patient has an impaired competence X but a normal (or a less impaired) competence Y
A “double dissociation”: a pattern of results in which damage to area A affects performance on task X, but not on task Y; whereas damage to area B affects performance on task Y, but not on task X.
Establishing a single dissociation between two functions provides limited and potentially misleading information, whereas a double dissociation can better demonstrate that the two functions are localized in different areas of the brain
TMS
Measure activity and function of specific brain circuits in humans
Connection between the primary motor cortex and a muscle to evaluate damage from stroke
Coil magnetic field is used to cause electric current to flow in a small region of the brain via electromagnetic induction.
Retinogeniculate Visual Pathway
- Visual stimuli is inverted top to bottom and flipped left to right when projected to retina
- Information in left visual field is detected by right sides of eyes (left nasal, right temporal) and processed by right LGN/hemisphere
- Information in right visual field is detected by left sides of eyes (left temporal, right nasal) and processed by left LGN/hemisphere
- Information leaves the eye by way of the optic nerve
- Optic nerves cross at optic chiasm (nerves from temporal side remain lateral, nerves on nasal side cross over)
- After optic chiasm, axons are called optic tracts
- Optic tracts terminates at lateral geniculate nuclei, the visual part of the thalamus that functions as the primary relay system for visual processing
- Axons from the LGN fan out through optic radiations, myelinated fibres between the thalamus and primary visual cortex
Fovea
Region of the retina most densely packed with photoreceptors, and thus supporting highest resolution vision
Center of eye
Optic Chiasm
The part of the brain where the optic nerves partially cross
Lateral Geniculate Nucleus (LGN)
Receives a major sensory input from the retina
Visual part of thalamus, primary relay nucleus for visual processing
Left LGN receives right visual input from left sides of eyes
Right LGN receives left visual input from right sides of eye
The LGN is the main central connection for the optic nerve to the occipital lobe, particularly the primary visual cortex
Optic Radiation
Myelinated fibers between the thalamus and primary visual cortex (V1)
Contralateral Retina
Contralateral Nasal Retina
Contra = opposite side
Ipsilateral Retina
Ipsilateral Temporal Retina
Ipsi = same side
Center-Surround Receptive Field
There are two types of retinal ganglion cells: “on-center” and “off-center”
On-center cell is stimulated when the center of its receptive field is exposed to light, and is inhibited when the surround is exposed to light
Off-center/surround cells stimulated when surround is exposed to light, inhibited in center
Magnocellular, Parvocellular
MAGNOCELLULAR NEURONS
- receive input from larger retinal ganglion cells (larger receptive field)
- input from LGN layers 1,2 and output to top of V1 layer 4
- Magnocellular layers of LGN: detection of motion and location (bigger picture); larger receptive field
M retinal ganglion cells (RGCs) sample larger space, have larger receptive field and do not carry color specific information; faster axonal conduction velocities; project to orientation-selective V1 areas; good temporal resolution
PARVOCELLULAR NEURONS
- receive input from smaller retinal ganglion cells (smaller receptive field)
- input from LGN layers 3-6, output to lower of V1 layer 4
Input from small retinal ganglion cells
Smaller receptive field
Parvocellular neurons in LGN project to color-selective blobs in V1; good spatial resolution
Detection of color and form (finer details)
Calcarine Sulcus
Where the primary visual cortex (V1) is concentrated
Simple Cell, Complex Cell
Simple cells in V1 respond preferentially to specific orientations, and complex cells can signal the termination of lines
Hypercolumns
Hubel and Weisel’s perpendicular penetrations found that neurons within the same cortical column responded to the exact same orientation
Parallel penetrations found that adjacent columns tended to be tuned to slightly rotated orientations
A hypothesized grid of orientation columns that, together, represented every possible orientation that could fall within a receptive field.
Represent
- Stereo (depth)
- Color
- Line orientation
Feature Channel
- Stereo (depth)
- Color
- Line (edge) orientation
Separate cortical channels for the processing of form, color, movement and depth of visual stimuli
Color and form = P pathways
Depth and movement = M pathways
Quadranopsia
Can only view one quarter of the visual field
Hemianopsia
Decreased vision or blindness (anopsia) in half the visual field
Scotoma
A partial loss of vision or a blind spot in an otherwise normal visual field
Objectivist
Our senses precisely, and accurately, reflect the physical world. They provide us with a true, complete, and accurate representation.
J.J. Gibson (Cornell)
Direct Perception
Subjectivist
There is no inherent organization to the world, but rather, our brain organizes our perceptions, and we therefore believe the world is, itself, organized.
Gestalt
Binocular Rivarly
Phenomenon of visual perception in which perception alternates between different images presented to each eye
Motion Selectivity
Magnocellular layers of LGN: detection of motion and location (bigger picture)
input from large retinal ganglion cells
larger receptive field
MT has a columnar architecture of direction selectivity for visual motion perception, area IT has a columnar architecture of complex shape/feature selectivity for object recognition.
Direction Selectivity
Some V1 cells are also direction selective meaning that they respond strongly to oriented lines/bars/edges moving in a preferred direction
MT has a columnar architecture of direction selectivity for visual motion perception, area IT has a columnar architecture of complex shape/feature selectivity for object recognition.
PPA
Parahippocampal place area (PPA)
Encoding and recognition of environmental scenes
Inferior temporo-occipital cortex
FFA
Fusiform face area (FFA)
Inferior temporal cortex (IT)
Codes for faces
Extrastriate Cortex
Areas outside of V1 but that V1 projects to
Foveal Vision
Center of gaze
BOLD Signal v. Spikes
SPIKES = electrical, EEG, HIGH temporal resolution
BOLD = hemodynamics, PET/fMRI, HIGH spatial resolution
Heeger Study: Spikes v. BOLD
Imply a proportional relationship between fMRI response and average firing rate
fMRI Bold Signal
- oxygenated hemoglobin and deoxygenated hemoglobin have different magnetic profiles
- neuronal activity creates increased need for blood to that area –> this results in an increased hemodynamic response (rapid delivery of blood to active neuronal tissue)
- this HR serves as a proxy for neural activity
- baseline is subtracted from changed values
- time lag (neural activity….fMRI bold signal evoked)
Hemodynamic response
The rapid delivery of blood to active neural tissue
Serves as a proxy for neural activity
Hemineglect
right temporal parietal damage
failure to be aware of one side of space
Brain Regions
Chart
Optic Nerve
Carries visual information from eye until optic chasm
Optic Tract
After chiasm, axons are called optic tract
Contralteral Retina, Ipsalateral Retina
Contralateral nasal retina
Ipsilateral temporal retina
Retinal Ganglion Cells
Neuron located near the inner surface (the ganglion cell layer) of the retina of the eye
Also compose optic nerves, etc.
Cortical Magnification
Cortical magnification = disproportionate representation of high-acuity portions of a sensory system
Cortical representation of the fovea, with its many more columns of neurons, covers a large area relative to the cortical representation of the periphery, with its relatively fewer columns of neurons
80% of V1 is devoted to processing information from the central 10% of the retina
The fovea is the region of the retina most densely packed with photoreceptors, and thus supporting highest resolution vision
Foveal Receptive Fields
In V1, receptive fields are smallest at regions receiving input from the fovea, and largest at regions receiving input from the periphery
Hubel and Wiesel
Discovered orientation selectivity of V1 neurons
Found that neurons responded preferentially to orientations
A neuron responded with bursts of action potentials in given angle
Utility of V1 Orientation Selectivity
Orientation selectivity allows for the detection of edges, direction selectivity necessary for motion
Stereoscopic information
Depth
V1 Organizational Structure
Pinwheel
Orientation-insensitive blob at the center and several “petals” made up of orientation-selective columns of neurons emanating from it
Sodium-Potassium Pump
During refractory period (when cell unable to generate AP) Na+/K+ pump expels 3NA+ ions for every 2K+ ions admitted, returning cell to resting state (-100 mV —> -70 mV)
Electrochemical Gradient
The active transport of ions across the cell membrane causes an electrical gradient to build up across this membrane. The number of positively charged ions outside the cell is usually greater than the number of positively charged ions in the cytosol (neg inside)
difference in charges creates voltage; voltage across membrane =membrane potential
neg inside, pos outside
mem potential favors outflux of positive ions in, and neg ions out
a chemical force (the ions’ concentration gradient), and an electrical force (the effect of the membrane potential on the ions’ movement). These two forces working together are called an electrochemical gradient.
Excitatory Neurotransmitters
glutamate, acetylcholine
Inhibitory Neurotransmitters
GABA, glycine
Neuronal Communication
Neuronal Communication
Neuron begins at rest (-70mV), maintaining life through an electrical and chemical disequilibrium (slightly negative inside relative to extracellular space)
- Electrical: neuron maintains -70 mV relative to extracellular space
- Chemical: neuron will hold higher concentration of potassium inside and lower concentration of sodium inside relative to extracellular space
Small voltage changes are collected in dendrites and travel along dendritic membrane to soma, where all the branches come together
- Temporal: high frequency stimulation by one presynaptic neuron; signals arrive at soma at same time
- Spatial: simultaneous activation by many presynaptic neurons; signals arrive on different branches and converge at the soma
- The total voltage of the cell is determined by the overall pattern of incoming signals (+EPSP, -IPSP)
If the number of EPSPs is much higher than number of IPSPs, the cell will depolarize. If threshold level is reached (-55mV), an action potential will be initiated by axon hillock.
Na+ leaks into axon (-70 mV —> -55 mV) Na+ voltage gated ion channel opens, allowing sodium to flow into axon (-55mV —> +40 mV) At +40 mV, Na+ channels close and K+ channels open. As potassium exits axon, the cell begins to repolarize. The cell “undershoots” in which membrane potential dips lower than resting state (+40 mV —> -100 mV), known as hyperpolarization.
The action potential spreads just far enough down membrane for neighboring voltage-gated channels to open up, causing the cycle to start again, moving progressively down axon (action potential propagation).
During refractory period (when cell unable to generate AP) Na+/K+ pump expels 3NA+ ions for every 2K+ ions admitted, returning cell to resting state (-100 mV —> -70 mV)
Action potential propagates down axon until it reaches axon terminal.
As the signal begins to reach the presynaptic terminal, Ca++ voltage-gated channels open, flooding Ca++ ions into cell.
The influx of Ca+ ions acts as the signal for signal-mediated exocytosis of vesicles containing neurotransmitters. Neurotransmitters diffuse across the synaptic space, binding to receptors on postsynaptic neuron.
