Cognitive neuroscience
H2. Introducing the brain
Structure and function of the neuron; 3 components
● Cell body
● Dendrites
● Axon
● Neuron: cell that makes up nervous system + supports cognitive function
Cell body
● Contains nucleus → contains genetic code for protein synthesis
Dendrites
● Branch from cell body
● Enable communication with other neurons
● Receive info from neurons close by
● Number and structure varies with place in the brain (type of neuron)
Axon
● Each neuron has 1 axon (may be divided into branches → collaterals
● Sends info to other neurons
● Transmits an action potential
Synapse; Pre- postsynaptic
● Disc-shaped, at the terminal of an axon
● Small gap between neurons, in which neurotransmitters(chemical signals) are released
● Two neurons forming the synapse
○ Presynaptic: before synapse
○ Postsynaptic: after synapse
○ Reflects direction of info flow
● Some synapses signal electrically not chemically
Axon hillock
● Start of an axon
● Electrical current is large enough: action potential initiated
Action potential
● Presynaptic neuron is active: action potential sent through axon
● When reaches axon terminal, neurotransmitters released into synaptic cleft
Neurotransmitters
● Bind to receptors on dendrites or cell body of postsynaptic neuron
● Create a synaptic potential → conducted passively (without creating action potential) through
dendrites of postsynaptic neuron
● Passive current strong enough at beginning of axon in postsynaptic neuron → action potential
triggered in this neuron
Passive/active conduction
● Passive conduction → short range. Electrical signal impeded by resistance of surrounding
matter
● Active conduction → long range, between neurons by action potentials
Cell membrane
● Barrier for certain chemicals
● Protein molecules act as gatekeepers; allow certain chemicals in/out under certain conditions
,Chemicals going in/out membrane + balance
● Charged sodium ion: Na+
● Charged potassium ions: K+
● Balance between these in/outside membrane: normally at resting potential of -70mV across
membrane (inside negative relative to outside)
Important for generation of an action potential
● Voltage gated ion channels: only found in axons, so only axon can produce an action potential
Sequence of events in generating action potential
1. Strong enough passive current across axon membrane: opens sodium (Na+) channels
2. Sodium enters cell, cell depolarizes → becomes less negative on inside
○ At -50mV: membrane becomes penetrable → charge on inside momentarily reverses →
sudden depolarization + following repolarization in membrane = action potential
3. Negative potential of cell restored via potassium flowing out and sodium not flowing back in
4. Brief period of hyperpolarization → inside more negative than when at rest: more difficult for axon
to depolarize + prevents AP from travelling backwards
How AP moves progressively down the axon
● AP in one part of axon opens adjacent Na+ channels, so it can move from cell body to axon
terminal
● Goes faster if axon is myelinated
Myelin
● Fat substance around axon of some cells (mostly those that carry motor signals)
● Blocks normal Na+/K+ transfer, so AP jumps via passive conduction down axon where there’s no
myelin (nodes of Ranvier)
● Destruction of myelin: MS
Protein receptors in membrane of postsynaptic neurons
● They bind to neurotransmitters
● Many set up a localised flow of Na+, K+ or chloride → creates the synaptic potential
Neurotransmitters inhibitory & excitatory effects on postsynaptic neuron
● Inhibitory effects → makes it less likely to fire
○ Achieved by making inside of neuron more negative than normal → harder to depolarize
● Excitatory effects → makes it more likely to fire
○ Synaptic potentials are then passively conducted
How neurons code info
● Size AP doesn’t vary, the number of AP’s per second does
● This ‘spiking rate’ (rate of responding) depends on info the neuron is carrying
○ Some may have high spiking rate in some situations: during speech, but not others (during
vision)
● Neurons responding to similar type of info often grouped together → specialization of brain
regions
Type of info a neuron carries
● Depends on input/output it receives/sends to other neurons
● Input/output determines function of a region
Gray + white matter
● Gray matter: neural cell bodies
● White matter: axons and support cells (glia)
● Folded sheet of grey matter: cerebral cortex
● Center of brain, grey matter subcortex: basal ganglia, limbic system, diencephalon
Association tracts + Commissures + Projection tracts
● Association tracts: white matter tracts project between different cortical regions in same
hemisphere
,● Commissures: white matter tracts project between different cortical regions in different
hemispheres
○ Most important commissure: corpus callosum
● projection tracts: white matter tracts project between cortical and subcortical structures
Ventricles
● Hollow chambers filled with cerebrospinal fluid CSF
○ Non-cognitive functions: carries waste metabolites, transfers messenger signals, provides
protective cushion for brain
Brain evolution
● Adding additional structures onto older ones
4 ventricles
● 2 lateral ventricles: in each hemisphere
● One around subcortical structures
● One in brainstem (hindbrain)
Directions for navigating the brain
● Anterior (rostral) → towards the front
● Posterior (caudal) → towards the back
● Superior (dorsal) → towards the top
● Inferior (ventral) → towards the bottom
● Lateral (medial) → outer part
● Medial → in/toward the middle
Central nervous system
Coronal cross-section
● Slice in vertical plane through both hemispheres
● Brain appears round
Sagittal section
● Slice in vertical plane through one of hemispheres
● When sagittal section is between hemispheres: called midline or medial section
Axial section
● In horizontal plane
Cerebral cortex
● Two folded sheets of grey matter; L/R hemisphere
, ● High surface area to volume ratio; efficient packaging
● 3mm thick + has different layers; reflect grouping of different cell types
● 6 main cortical layers: neocortex (new cortex)
Lateral surface cortex - 4 lobes per hemisphere
● Frontal, parietal, temporal, occipital lobes
Insula
● Island of cortex beneath temporal lobe
3 different ways to divide regions of cerebral cortex
● Regions divided by pattern of gyri and sulci
○ Same pattern in everyone
● Regions divided by cytoarchitecture
○ Broadman’s areas: 52 areas (BA1-BA52), based in distribution of cell types across cortical
layers
● Regions divided by function
○ Only for primary sensory and motor areas
○ Higher cortical regions harder to ascribe unique functions to
Subcortex
● Collection of grey matter beneath cortical surface
● Divided in different systems
Basal ganglia
● Large round mass in each hemisphere
● Regulates motor activity, programming / termination of action
● Learning of rewards, skills, habits
● Disorders hypokinetic (poverty of movement) or hyperkinetic (excess of movement) -
Parkinson - Huntingtons
Basal ganglia main structures
● Caudate nucleus (tail-like structure)
● Putamen (lie more laterally)
● Globus pallidus (lie more medially)
Limbic system
● Region of subcortex involved in relating organism to its present and past environment
● Involved in detection/expression of emotional responses
● Include; amygdala, hippocampus, cingulate cortex, mammillary bodies
Amygdala
● Detection of fearful or threatening stimuli
Cingulate gyrus
● Detection of emotional and cognitive conflicts
Hippocampus
● For learning and memory
Mammillary bodies
● 2 small round projections(uitsteeksels) implicated in memory
Olfactory bulbs
● Under frontal lobes
● By connections to limbic system → importance of smell for stimuli and
● Influence on mood and memory
Diencephalon, 2 main structures
● Thalamus + hypothalamus
H2. Introducing the brain
Structure and function of the neuron; 3 components
● Cell body
● Dendrites
● Axon
● Neuron: cell that makes up nervous system + supports cognitive function
Cell body
● Contains nucleus → contains genetic code for protein synthesis
Dendrites
● Branch from cell body
● Enable communication with other neurons
● Receive info from neurons close by
● Number and structure varies with place in the brain (type of neuron)
Axon
● Each neuron has 1 axon (may be divided into branches → collaterals
● Sends info to other neurons
● Transmits an action potential
Synapse; Pre- postsynaptic
● Disc-shaped, at the terminal of an axon
● Small gap between neurons, in which neurotransmitters(chemical signals) are released
● Two neurons forming the synapse
○ Presynaptic: before synapse
○ Postsynaptic: after synapse
○ Reflects direction of info flow
● Some synapses signal electrically not chemically
Axon hillock
● Start of an axon
● Electrical current is large enough: action potential initiated
Action potential
● Presynaptic neuron is active: action potential sent through axon
● When reaches axon terminal, neurotransmitters released into synaptic cleft
Neurotransmitters
● Bind to receptors on dendrites or cell body of postsynaptic neuron
● Create a synaptic potential → conducted passively (without creating action potential) through
dendrites of postsynaptic neuron
● Passive current strong enough at beginning of axon in postsynaptic neuron → action potential
triggered in this neuron
Passive/active conduction
● Passive conduction → short range. Electrical signal impeded by resistance of surrounding
matter
● Active conduction → long range, between neurons by action potentials
Cell membrane
● Barrier for certain chemicals
● Protein molecules act as gatekeepers; allow certain chemicals in/out under certain conditions
,Chemicals going in/out membrane + balance
● Charged sodium ion: Na+
● Charged potassium ions: K+
● Balance between these in/outside membrane: normally at resting potential of -70mV across
membrane (inside negative relative to outside)
Important for generation of an action potential
● Voltage gated ion channels: only found in axons, so only axon can produce an action potential
Sequence of events in generating action potential
1. Strong enough passive current across axon membrane: opens sodium (Na+) channels
2. Sodium enters cell, cell depolarizes → becomes less negative on inside
○ At -50mV: membrane becomes penetrable → charge on inside momentarily reverses →
sudden depolarization + following repolarization in membrane = action potential
3. Negative potential of cell restored via potassium flowing out and sodium not flowing back in
4. Brief period of hyperpolarization → inside more negative than when at rest: more difficult for axon
to depolarize + prevents AP from travelling backwards
How AP moves progressively down the axon
● AP in one part of axon opens adjacent Na+ channels, so it can move from cell body to axon
terminal
● Goes faster if axon is myelinated
Myelin
● Fat substance around axon of some cells (mostly those that carry motor signals)
● Blocks normal Na+/K+ transfer, so AP jumps via passive conduction down axon where there’s no
myelin (nodes of Ranvier)
● Destruction of myelin: MS
Protein receptors in membrane of postsynaptic neurons
● They bind to neurotransmitters
● Many set up a localised flow of Na+, K+ or chloride → creates the synaptic potential
Neurotransmitters inhibitory & excitatory effects on postsynaptic neuron
● Inhibitory effects → makes it less likely to fire
○ Achieved by making inside of neuron more negative than normal → harder to depolarize
● Excitatory effects → makes it more likely to fire
○ Synaptic potentials are then passively conducted
How neurons code info
● Size AP doesn’t vary, the number of AP’s per second does
● This ‘spiking rate’ (rate of responding) depends on info the neuron is carrying
○ Some may have high spiking rate in some situations: during speech, but not others (during
vision)
● Neurons responding to similar type of info often grouped together → specialization of brain
regions
Type of info a neuron carries
● Depends on input/output it receives/sends to other neurons
● Input/output determines function of a region
Gray + white matter
● Gray matter: neural cell bodies
● White matter: axons and support cells (glia)
● Folded sheet of grey matter: cerebral cortex
● Center of brain, grey matter subcortex: basal ganglia, limbic system, diencephalon
Association tracts + Commissures + Projection tracts
● Association tracts: white matter tracts project between different cortical regions in same
hemisphere
,● Commissures: white matter tracts project between different cortical regions in different
hemispheres
○ Most important commissure: corpus callosum
● projection tracts: white matter tracts project between cortical and subcortical structures
Ventricles
● Hollow chambers filled with cerebrospinal fluid CSF
○ Non-cognitive functions: carries waste metabolites, transfers messenger signals, provides
protective cushion for brain
Brain evolution
● Adding additional structures onto older ones
4 ventricles
● 2 lateral ventricles: in each hemisphere
● One around subcortical structures
● One in brainstem (hindbrain)
Directions for navigating the brain
● Anterior (rostral) → towards the front
● Posterior (caudal) → towards the back
● Superior (dorsal) → towards the top
● Inferior (ventral) → towards the bottom
● Lateral (medial) → outer part
● Medial → in/toward the middle
Central nervous system
Coronal cross-section
● Slice in vertical plane through both hemispheres
● Brain appears round
Sagittal section
● Slice in vertical plane through one of hemispheres
● When sagittal section is between hemispheres: called midline or medial section
Axial section
● In horizontal plane
Cerebral cortex
● Two folded sheets of grey matter; L/R hemisphere
, ● High surface area to volume ratio; efficient packaging
● 3mm thick + has different layers; reflect grouping of different cell types
● 6 main cortical layers: neocortex (new cortex)
Lateral surface cortex - 4 lobes per hemisphere
● Frontal, parietal, temporal, occipital lobes
Insula
● Island of cortex beneath temporal lobe
3 different ways to divide regions of cerebral cortex
● Regions divided by pattern of gyri and sulci
○ Same pattern in everyone
● Regions divided by cytoarchitecture
○ Broadman’s areas: 52 areas (BA1-BA52), based in distribution of cell types across cortical
layers
● Regions divided by function
○ Only for primary sensory and motor areas
○ Higher cortical regions harder to ascribe unique functions to
Subcortex
● Collection of grey matter beneath cortical surface
● Divided in different systems
Basal ganglia
● Large round mass in each hemisphere
● Regulates motor activity, programming / termination of action
● Learning of rewards, skills, habits
● Disorders hypokinetic (poverty of movement) or hyperkinetic (excess of movement) -
Parkinson - Huntingtons
Basal ganglia main structures
● Caudate nucleus (tail-like structure)
● Putamen (lie more laterally)
● Globus pallidus (lie more medially)
Limbic system
● Region of subcortex involved in relating organism to its present and past environment
● Involved in detection/expression of emotional responses
● Include; amygdala, hippocampus, cingulate cortex, mammillary bodies
Amygdala
● Detection of fearful or threatening stimuli
Cingulate gyrus
● Detection of emotional and cognitive conflicts
Hippocampus
● For learning and memory
Mammillary bodies
● 2 small round projections(uitsteeksels) implicated in memory
Olfactory bulbs
● Under frontal lobes
● By connections to limbic system → importance of smell for stimuli and
● Influence on mood and memory
Diencephalon, 2 main structures
● Thalamus + hypothalamus
