lecture 2: neurons and major brain areas Flashcards
what are some things your mind and brain does
- sense, perceive, understand the world
- learn and remember
- plan, organize
- love, hate, fear, appreciate music
- protest climate change, play tennis
information processing:
- energy carries information about the world
- sensors on your body capture/transduce that energy
- complex series of “processors” crunch the data, build a model
- other processors generate outputs (move your body, speak)
- all of cognition is the product of your brain state, which
is the product of information processing (computation)
What is the brain made of?
89 billion cells called neurons
& the “wiring” that connects them
& a lot of glial cells (equal to # of neurons,
possibly even more)
Scales of Information Processing from small to large
molecules “neurotransmitters”
cells called “neurons” & collections of neurons
called “assemblies” or “neural circuits”
larger collections of neurons make up “brain areas” & brain areas connect to each other in “networks” forming “neural systems”
Neurons
the fundamental units of the brain and nervous system, the cells responsible for receiving sensory input from the external world, for sending motor commands to our muscles, and for transforming and relaying the electrical signals at every step in between
Brain Structures and Areas
collections of neurons involved in related computations; e.g., “visual areas”, or
“language areas”
dendrite
Dendrites are the structures on the neuron, that function by receiving electrical messages. The functions of dendrites are to transfer the received information to the soma of the neuron. Other biological processes of Dendrites are: Dendrites receive the data or signals from another neuron
How do Neurons “Transmit Information”?
Neural signaling is an electro-chemical process.
The electrical part refers to the flow of ions
(charged particles) in/out of the cell, or through the cell (remember that moving ions carry electrical charge).
The chemical part refers to the flow of
neurotransmitters between neurons
axon
Each neuron in your brain has one long cable that snakes away from the main part of the cell. This cable, several times thinner than a human hair, is called an axon, and it is where electrical impulses from the neuron travel away to be received by other neurons
Membrane Keeps Neuron “Charged” around how many mv
-70mv is resting membrane potential
key ions in neuron
sodium na+
potassium k+
resting membrane potential
the difference in charge across the
membrane at equilibrium (about -70 mv)
na k pump
The sodium–potassium pump is found in many cell (plasma) membranes. Powered by ATP, the pump moves sodium and potassium ions in opposite directions, each against its concentration gradient. In a single cycle of the pump, three sodium ions are extruded from and two potassium ions are imported into the cell.
Three stages of computation in the neuron
RECEIVE
EVALUATE
TRANSMIT (RET)
Stage 1- Input Stage:
many “signals” come in at the
dendrites
Stage 2- “Processing” Stage:
signals summate, adding and
canceling, possibly reaching critical
threshold within the cell body
Stage 3 - Output Stage:
if the input is strong enough (exceeds
threshold) then the neuron passes
the signal along via it’s axon
Synapse
Synapse: where the axon of one
neuron connects to the dendrite of
another neuron
Stage 1: Receiving Signals (input stage)
Action potential in the presynaptic neuron binds vesicles to active zones in presynaptic membrane.
Neurotransmitter gets released into the synaptic cleft.
Neurotransmitter binds with receptors in postsynaptic neuron
depolarized
we say a cell has been depolarized because it ends up with a less negative charge
a cell at rest
negative charge around -70 mv
a cell after an action potential triggers neurotransmitter release is hyperpolarized or depolarized
we say a cell has been depolarized because it ends up with a less negative charge
Excitatory postsynaptic potential (EPSP)
influx of Na+ depolarizes
cell is less polarized
(depolarized) because it has a less negative charge. Depolarization is
excitation, because it makes it more likely the cell will reach threshold
(e.g., -50mv) and trigger an action potential.
Inhibitory postsynaptic potential (IPSP)
influx of Cl- hyperpolarizes
cell can also become more
polarized (hyperpolarized), so it has a more negative charge.
Hyperpolarization is inhibition, because it makes it less likely the cell will
reach threshold and transmit a signal (via an action potential)
Evaluation process happens within
the cell body, region of
cell where axon connects is
axon hillock.
Information Transmission in Neurons
when threshold is reached, voltage sensitive gates open up, triggering a positive spike in voltage (an “action potential” or “spike”)
What we mean by “evaluation stage”
- hundreds or thousands of synaptic inputs
- some are excitatory, some are inhibitory
- e.g., neurotransmitter might open Cl- channel, generating IPSP
- simultaneously, another synaptic input might open Na+ channel, generating EPSP, canceling the hyperpolarization.
more excitatory inputs might lead to depolarization that sums above the critical threshold triggering an “action potential”
- Summing all of the influences together is a simple information processing algorithm,
the one used by cells to determine whether to transmit a signal to other neurons via
an action potential.
threshold
value of membrane potential
(charge inside vs. outside)
at which trigger an action
potential (e.g., -55mv to -
50mv)
action potential
aka “spike”, spikes in voltage
to positive, then below
resting potential, then
back to resting potential
all-or-none:
the value of the action potential is always the same, regardless of the amplitude of the depolarizing current. Spikes do not vary in strength, but they can vary in rate
Transmitting Signals (output stage)
Signals are transmitted along the
axon, until they reach terminal
buttons, where they connect to the
next neuron
myelin sheath
provides electrical
insulation, alters
the flow of current
down the axon;
action potentials
cannot be
generated here
nodes of Ranvier
myelin interrupted;
action potentials
can be generated
here
Saltatory conduction
action potentials “jump” from node to node,
enabling fast propagation of the signal down the axon, with a signal
that never loses strength at any distance
Neurons are the basic units of processing; how
signals come in from other neurons
at the dendrites these signals summate in the cell body if the input is strong enough
(exceeds threshold) an action
potential occurs and the neuron
passes the signal along its axon
resulting in the release of
neurotransmitter into the
synapse and, the process begins again
Cerebral Cortex
(outer areas)
Subcortical Structures
(inner structures)
Brain Stem & Cerebellum
(deep structures)
Ventral
Toward the bottom of the brain or the front of the spinal cord
Dorsal
Toward the top of the brain or the back of the spinal cord
medial
areas of the nervous system that are closer to the midline of the brain or spinal cord
lateral
Lateral is from the side
Gray matter vs white matter
Gray matter is made up of neuronal cell bodies (somas), while white matter primarily consists of myelinated axons.
In the brain, white matter is found closer to the center of the brain, whereas the outer cortex is mainly grey matter
Gray matter is primarily responsible for processing and interpreting information, while white matter transmits that information to other parts of the nervous system
sulci vs gyri
Gyri (singular: gyrus) are the folds or bumps in the brain and sulci (singular: sulcus) are the indentations or grooves. Folding of the cerebral cortex creates gyri and sulci which separate brain regions and increase the brain’s surface area and cognitive ability
Three layers of protective covering called meninges surround the brain and the spinal cord:
The outermost layer, the dura mater, is thick and tough. It includes two layers: The periosteal layer of the dura mater lines the inner dome of the skull (cranium) and the meningeal layer is below that. Spaces between the layers allow for the passage of veins and arteries that supply blood flow to the brain.
The arachnoid mater is a thin, weblike layer of connective tissue that does not contain nerves or blood vessels. Below the arachnoid mater is the cerebrospinal fluid, or CSF. This fluid cushions the entire central nervous system (brain and spinal cord) and continually circulates around these structures to remove impurities.
The pia mater is a thin membrane that hugs the surface of the brain and follows its contours. The pia mater is rich with veins and arteries.
hemispheres of brain
left and right with corpus callosum connecting them
Cross Sections (“Slices”)
0,0,0 is anterior commissure
x-axis increases from
left to right
–y-axis increases from
posterior to anterior
–z-axis increases from
ventral to dorsal
Brodmann’s Map (1909)
helps us map out cerebral cortex: 52 areas, based on cell morphology, density, and layering
major folds of the brain that separate lobes
sylvian fissure, central sulcus, parietooccipital sulcus
Insula or Insular Cortex
awareness of bodily state
(interoception), empathy,
gustatory (taste) cortex,
disgust, pain perception
A map of the body in the motor cortex
Primary Motor Cortex
a.k.a. “M1”
A map of the visual world in occipital cortex
Occipital
Lobe
a.k.a. “primary visual
cortex”
a.k.a. “ V1”
a.k.a. “Brodmann’s Area 17”
homunculus
A cortical homunculus (from Latin homunculus ‘little man, miniature human’) is 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 functions, or sensory functions, for different parts of the body.
what is the name of how we map sound in the auditory cortex
Primary Auditory Cortex
a.k.a. “ A1”
Major Subcortical Structures
Amygdala
Hippocampus
Basal Ganglia
Cingulate Cortex
Thalamus
basal ganglia
a group of structures linked to the thalamus in the base of the brain and involved in coordination of movement
produce dopamine
disorders of basal ganglia tend to be hypokinetic (loss of movement, parkinsons) or hyperkinetic (too much movement, huntingtons)
