Exam I (Revised) Flashcards Preview

Cognition and the Brain > Exam I (Revised) > Flashcards

Flashcards in Exam I (Revised) Deck (153):
1

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

2

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

3

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

4

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

5

Paul Broca

Lesion --> Could only say "Tan"
Localized area for language production
Left frontal cortex = Broca's Area

6

Broca's Area

Left frontal cortex
Localized area for language production
Paul Broca and "tan" patient

7

Neuron

Cells in the brain that generate electrical and chemical signals that control all other systems of the body

8

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

9

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

10

Synctium

A cellular network containing several nuclei and cytoplasmic continuity

11

Ramon y Cajal

Used Golgi's stain to show that the brain was made up of individual nerve cells linked together by long extensions

12

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

13

Soma

Cell body
Integrates

14

Axon

Transmitting Process
Conducts

15

Dendrite

Receiving Process
Collects

16

Synapse

Gap between neurons where transmission takes place

17

Axon Hillock

Region of cell body where axon emerges; the membrane is rich with voltage gated Na+ channels, which can generate action potential

18

Myelin Sheath

Cholesterol-laden sheath that insulates axons; composed of oligodendrocites

19

Node of Ranvier

Gap between myelin sheaths, between Schwann cells

20

Axon Terminal

Terminal Bouton

Outputs information

Button-shaped endings on neurons where neurons form into vesicles before being released into synaptic cleft (synapse)

21

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

22

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

23

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

24

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)

25

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.

26

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

27

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

28

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)

29

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

30

Postsynaptic Potential (PSP)

Small changes in voltage (about 1 mV)

31

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).

32

Salutary Conduction

Jumping, AP regenerated at each node

33

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

34

Excitatory Postsynaptic Potential (EPSP)

When positive ions, such as sodium, flow into cell (slightly reducing the negativity, depolarizing it)

35

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)

36

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)

37

Neurotransmitter

Transmit signals between neurons

Exciting/inhibiting specific postsynaptic neurons

38

Glutatmate

EPSP
Excitatory neurotransmitter
Opening of Na+

39

Acetylcholine

Excitatory neurotransmitter in the peripheral nervous system

Excitatory neurotransmitter
opening of Na+

Acetylcholine: facilitates learning and memory
• affected in Alzheimer’s Disease

40

GABA

IPSP
inhibitory neurotransmitter
influx of Cl- ions, hyperpolarizing cell /or K+

41

Agonist

agonist: molecule that occupies receptor and activates

antagonist: molecule that occupies receptor and blocks

42

Antagonist

agonist: molecule that occupies receptor and activates

antagonist: molecule that occupies receptor and blocks

43

Neurology

Function and pathology of the nervous system

44

Neuroscience

Mechanisms of the nervous system
- neuroanatomy
- neurophysiology
- neurochemistry

45

Cognitive Psychology

How the mind processes information

46

Dorsal

Top

47

Ventral

Bottom

48

Anterior

Front

49

Posterior

Back

50

Rostral

Front

51

Caudal

Back

52

Medial

Middle

53

Lateral

Side

54

Brain Slices

Axial/Transversal: top and bottom
Sagittal: Side/side
Coronal: front and back

55

Transverse

(aka Axial)

Top and bottom

56

Axial

Top and bottom

57

Saggital

Side and side

58

Coronal

Front and back

59

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

60

Grey Matter, White Matter

Grey = border, cell bodies
White = majority of middle, axons

61

Gyrus, Sulcus

Gyrus = top
Sulcus = bottom

GS in alphabetical order, top to bottom

Fundus is very bottom concavity

62

Fundus

Concavity of gyrus/sulcus

63

Precentral Sulcus

Sulcus
Precentral gyrus = primary motor cortex

64

Central Sulcus

Boundary of motor and sensory cortices

Separates frontal lobe from parietal lobe
Separates primary motor cortex from primary somatosensory cortex

65

Postcentral Sulcus

Sulcus
Postcentral gyrus = primary somatosensory cortex

66

Sylvian Fiissure

Separates temporal lobe from frontal and parietal

Insula buried deep within it

67

Central Fissure

Separates frontal lobe from parietal lobe
Separates primary motor cortex from primary somatosensory cortex

68

Parieto-Occipital Sulcus

Separates parietal and occipital sulci
Involved in planning

69

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

70

Supramarginal Gyrus

Language perception and processing

Supra is on top of angular, parietal lobe

Lesion = aphasia (making sense of words)

71

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.

72

Golgi Stain

Silver staining reveals the entirety of one neuron but not all neurons in total

73

Nissi Stain

Aniline dye dark blue staining reveals every cell body in total picture, allowing an estimate of total

74

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

75

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

76

Cytoarchitecture

Brodmann
52 layers, based on cell morphology, density, and layering

77

Circuitry

?

78

Brain Activation

Ways of examining circuitry

Using heat map
Myelination
DTI - white matter tracts

79

Topographic Organization

Spatially adjacent stimuli on sensory receptor surfaces are represented in adjacent positions in cortex

80

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

81

Tonotopy

Tones close to each other in terms of frequency are represented in topologically neighboring regions in the brain

82

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

83

Functional Division

Brain is divided into different subsections according to function.

84

Electrophysiology

Measures the electrical activity of neurons, and, in particular, action potential activity

85

Fixation Point

Fixation or visual fixation is the maintaining of the visual gaze on a single location

86

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

87

Movement Field

Neurons from primary motor cortex have a preference for the orientation of movements

Broadly tuned, very little specificity

88

Rate Coding

Frequency coding

As the frequency or rate of action potentials (or "spike firing") increases

# action potentials/time

89

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

90

Population Coding

Summation of input from thousands of units firing
"wisdom of the masses"

91

Temporal Coding

When precise spike timing or high-frequency firing-rate fluctuations are found to carry information

92

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.

93

PET

Injected with tracer, pick up on distribution
Localization of brain activity

94

MRI

Structural imaging
Uses magnetic field and radio frequency

95

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

96

BOLD

Blood oxygen-level dependent

Neural correlate for brain activity

Hemodynamic signal driven by metabolic need of cell

97

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

98

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

99

Spikes

Neuron firing

100

Exitotoxins

Exitocins: chemicals that overstimulate neuron receptor

Overexciting neurons causing tissue damage and cell death

101

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

102

Cyrogenic Depression

Cooling
Reversible

103

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

104

Contusion

Brain damage common in specific area
Orbitofrontal and anterior temporal
Holbourn

Orbitofrontal and Anterior Temporal Contusions

105

Neuropsychology

Neuropsychology is the study of the structure and function of the brain as they relate to specific psychological processes and behaviors

106

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

107

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.

108

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

109

Fovea

Region of the retina most densely packed with photoreceptors, and thus supporting highest resolution vision

Center of eye

110

Optic Chiasm

The part of the brain where the optic nerves partially cross

111

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

112

Optic Radiation

Myelinated fibers between the thalamus and primary visual cortex (V1)

113

Contralateral Retina

Contralateral Nasal Retina

Contra = opposite side

114

Ipsilateral Retina

Ipsilateral Temporal Retina

Ipsi = same side

115

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

116

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)

117

Calcarine Sulcus

Where the primary visual cortex (V1) is concentrated

118

Simple Cell, Complex Cell

Simple cells in V1 respond preferentially to specific orientations, and complex cells can signal the termination of lines

119

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

120

Feature Channel

1.Stereo (depth)
2.Color
3.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

121

Quadranopsia

Can only view one quarter of the visual field

122

Hemianopsia

Decreased vision or blindness (anopsia) in half the visual field

123

Scotoma

A partial loss of vision or a blind spot in an otherwise normal visual field

124

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

125

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

126

Binocular Rivarly

Phenomenon of visual perception in which perception alternates between different images presented to each eye

127

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.

128

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.

129

PPA

Parahippocampal place area (PPA)

Encoding and recognition of environmental scenes

Inferior temporo-occipital cortex

130

FFA

Fusiform face area (FFA)

Inferior temporal cortex (IT)

Codes for faces

131

Extrastriate Cortex

Areas outside of V1 but that V1 projects to

132

Foveal Vision

Center of gaze

133

BOLD Signal v. Spikes

SPIKES = electrical, EEG, HIGH temporal resolution

BOLD = hemodynamics, PET/fMRI, HIGH spatial resolution

134

Heeger Study: Spikes v. BOLD

Imply a proportional relationship between fMRI response and average firing rate

135

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)

136

Hemodynamic response

The rapid delivery of blood to active neural tissue

Serves as a proxy for neural activity

137

Hemineglect

right temporal parietal damage

failure to be aware of one side of space

138

Brain Regions

Chart

139

Optic Nerve

Carries visual information from eye until optic chasm

140

Optic Tract

After chiasm, axons are called optic tract

141

Contralteral Retina, Ipsalateral Retina

Contralateral nasal retina
Ipsilateral temporal retina

142

Retinal Ganglion Cells

Neuron located near the inner surface (the ganglion cell layer) of the retina of the eye

Also compose optic nerves, etc.

143

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

144

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

145

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

146

Utility of V1 Orientation Selectivity

Orientation selectivity allows for the detection of edges, direction selectivity necessary for motion

147

Stereoscopic information

Depth

148

V1 Organizational Structure

Pinwheel

Orientation-insensitive blob at the center and several “petals” made up of orientation-selective columns of neurons emanating from it

149

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)

150

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.

151

Excitatory Neurotransmitters

glutamate, acetylcholine

152

Inhibitory Neurotransmitters

GABA, glycine

153

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.