Neuroanatomy Flashcards
Voltage changes during Action Potential - draw chart
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WHAT ARE EPSPS ANS IPSPS?
EPSPs and IPSPs are graded (they may have different intensities). They spread and collect in the hillock, where they add up (= neural summation)
If the sum of EPSPs and IPSPs crosses a certain threshold (e.g. -50 mV),
an ACTION POTENTIAL will occur.
(the membrane depolarizes) EXCITATORY POST-SYNAPTIC POTENTIAL (EPSP)
(the membrane hyperpolarizes) This is called an INHIBITORY POST-SYNAPTIC POTENTIAL (IPSP).
DISTRIBUTION OF IONS ACROSS MEMBRANE
When the neuron is “at rest” (no inputs), ions are NOT evenly distributed across the membrane.
Na+ and Cl- are more highly concentrated outside the cell, whereas K+ is more highly concentrated inside the cell.
WHAT IS CYTOARCHITECTONICS?
Even though all neocortex is composed of 6 cortical layers, neurons in different areas of cortex (and elsewhere) have different structure (size shape, etc.)
The study of the structure of neurons is called cytoarchitectonics (cyto = cell)
Cells within a particular functional region tend to have similar cytoarchitecture.
One important aim of cytoarchitectonics is to identify potential functional regions by looking at the cytoarchitecture of neurons.
Major subcortical structures
WHAT ARE THEY (LIST)
THEY ARE ALL ______
Consist of gray matter nuclei beneath the cortex (a nucleus is a
cluster of densely packed neurons)
They include:
- Basal ganglia
- Limbic system
- Dienchephalon (Thalamus + Hypothalamus)
- Cerebellum
- Brainstem
•Pattern of gyri & sulci
–e.g., inferior frontal gyrus
HOW DO NEURONS COMMUNICATE?
The most common way in which neurons communicate with one another is by sending a chemical signal, known as neurotransmitter.
Intro to Neuronal Communication
•The primary purpose of the brain is to sense, interpret and ultimately act upon the environment.
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•This is achieved through the interaction of neurons in neural circuits.
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•For neurons to interact they need to communicate with each other.
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•Neurons have evolved ways of communicating with one another by generating electrical and chemical signals.
Voltage gated ion channels
(See slides) Voltage gated and ???? Gated?
How does it get back to the resting membrane potential?
Remember that at rest, there’s more Na+ outside the cell than inside, whereas for K+ the opposite is true…
But at the end of the action potential, lots of Na+ have entered the cell and lots of K+ have exited, so the proportions have reversed.
How do we return to the resting-potential concentrations?
Na+/K+ pumps!
Human Cortex contains:
dips/infoldings (Sulci), if very deep, called Fissures
raised surfaces/convolutions (Gyri)
LIMBIC SYSTEM
Major structures:
Amygdala
Hippocampus
Cingulate Gyrus
Mammilary bodies
Major functions
relating the organism to present and past environment
Emotion
Memory
Useful terms to refer to sections (slices) of the brain -
- Horizontal (or Axial)
- Coronal
- Sagittal
Put it all together: what are all the different ways we can talk about one brain region
Brodmann areas (cytoarchitectonic maps)
Gross anatomy
Function
•There are several ways to describe the anatomy of the brain
–Gross neuroanatomy
–Cytoarchitecture
–Functional divisions
•As a result, the same brain region may be described in different ways
Sodium Potassium Pump - Draw diagram!
– Sympathe)c
• Responds to stress, mediates fight-flight response (heart races, dilate muscle blood vessels, hormones are released)
Function
–e.g., primary visual cortex
–Difficult for higher cortical regions
Glia
• support cells; around the same glia cells-to-neurons proportion
Produce Myelin:
Fatty substance surrounding axons of many neurons; speeds electrical transmission of output along the axon
CEREBELLUM
Cerebellum (“little brain”)
2 lobes
attached to hindbrain
Major functions
integrates information about motor commands with sensory feedback
enables smooth movement and dexterity
Medial vs. lateral
WHAT IS ACTION POTENTIAL?
When an action potential occurs (AC), we say the neuron “fires”.
What it means is that the neuron has itself “decided” to send a signal to other neurons downstream.
The AP consists of a quick wave (≈2 ms) of depolarization (immediately followed by repolarization) that propagates (spreads) down the axon.
Unlike EPSPs and IPSPs, which are graded, APs either occur or not (we say the AP is an “all-or-none” event, because it either occurs fully o not at all)
sodium potassium pump (Na+/K+ pumps)
Works against the concentration gradient and therefore requires energy.
Na+/K+ pumps not only make the concentration of Na+ and K+ ions different across the membrane, but also create a difference in electrical potential across the membrane (voltage).
Ions carry positive or negative charge
- Na+ and K+ carry positive charge
- Cl- carries negative charge
We say we have a membrane electric potential when the distribution of positive and negative charges across the membrane is different (e.g. the inside of neuron is more negative than the outside)
Efferent
Info from CNS to PNS - info E xits the CNS
• COGNITIVE NEUROSCIENCE:
– How the brain supports cogniBve funcBons – How dysfuncBon of neural mechanisms relates to various cogniBve disorders – What tools cogniBve neuroscienBsts use
Afferent
Info A rrives in the CNS
Cortex - Why is it wrinkled?
To fit more grey matter into the skull.
GROSS NEUROANATOMY STRUCTURES AND SUBCORTICAL STRUCTURES
- Cortex
- Subcortical structures
–Basal ganglia
–Limbic system
–Thalamus and hypothalamus
–Brainstem
–Cerebellum
VOLTAGE-GATED CHANNELS?
Crossing of the threshold opens voltage-gated channels at the hillock (part of the axon closest to the soma), which in turn let more Na+ ions into the neuron, further depolarizing that section of the membrane.
Once the first voltage-gated channels open up, the voltage change (depolarization) they cause around them will in turn open other neighboring voltage-gated channels along the axon, leading to further depolarization. The cyclic mechanism allows for the spread of depolarization down the axon (all the way to the axon terminal).
Major fissures and sulci
NEURONS MEMBRANE - SIMILAR TO OTHER CELLS? WHY?
A neuron’s membrane shares many features in common with other kinds of cells. It consists of a lipid bi-layer that is semipermeable, i.e., most ions and molecules cannot freely enter or exit the neuron (although there’s some leakage)
STRUCTURE OF A NEURON
NAME THE LOBES
ONE MORE LOBE! (HIDDEN)
Cortex (Cerebral Cortex)
Cortex = “Bark” (as in Tree Bark).
It’s a thin layer of gray matter (1/8 in)
Underlying white matter: connections between neurons
WHAT ARE THE Functional divisions (cortex) AND WHAT DO THEY DO??
- Primary functional regions
- Receive direct input from sensory organs (via thalamus) OR send direct output to the body (via thalamus)
- Process only one kind of information
- e.g. “primary visual cortex”
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- Secondary functional regions
- Still process just one kind of information, but don’t get direct input/send direct output (elaboration)
- E.g. “secondary visual cortex”
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- Association regions
- Process more than one kind of information
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What we’re going to be doing here is asking what parts of the brain are associated with different functions
Like what parts of the brain are associated with vision
Talking about functional regions, can divide them up into three types: primary, secondary and association
– Soma%c
- Innervate skin, joints, muscles
- sense of touch, movement feedback, pain
Sulcus / Sulci
Not as deep as fissures - dips
Basal ganglia
Major structures:
Caudate Nucleus
Putamen
Globus Pallidus
Major functions
motor control
skill learning
PROPOGATION DOWN THE AXON
(Golgi staining)
• Cell bodies & processes
DIENCEPHALON
Thalamus: relay between all the sensory organs (except smell) and the cortex
Hypothalamus:
regulates bodily functions
temperature
eating and drinking
sexual activity
regulation of endocrine functions
NEURONAL MEMBRANE
A neuron’s membrane shares many features in common with other kinds of cells. It consists of a lipid bi-layer that is semipermeable, i.e., most ions and molecules cannot freely enter or exit the neuron (although there’s some leakage)
Major fissures and sulci
Rostral vs. Caudal or Anterior vs. Posterior
HODGKIN-HUXLEY CYCLE
NEURONS MEMBRANE - ‘RESTING’
When a neuron is at rest (no inputs), the distribution of all ions is such that the outside of the membrane is more positive than the inside. NEGATIVELY POLARIZED
(Nissl staining)
• Mostly cell bodies
APs either occur or not (we say the AP is an “all-or-none” event, because it either occurs fully o not at all)
So how does it work?
- Rising phase (3 in picture): Na+ channels open along the axon, letting Na+ into the cell and depolarizing (+30 mV) the axonal membrane.
- Falling phase (4 in picture): K+ channels open along the axon, letting K+ out of the cell, and repolarizing the membrane.
- Undershoot phase (5 in picture): K+ channels continue to be open, further letting K+ out of the cell, and leading to hyperpolarization of the membrane (refractory period: the neuron cannot fire during this phase)
SUMMARY OF VOLTAGE CHANGES DURING AP (DRAW WITH NUMBERS)
BRAINSTEM MAJOR FUNCTIONS/ structures
Major structures
Midbrain
Hindbrain
Pons
Medulla oblongata
Major functions
Connects brain & spinal cord
Vital functions such as breathing and heart rate (hindbrain)
ACTION POTENTIAL / THRESHOLD
How does the action potential accomplish what it accomplishes?
The arrival of AP at the axon terminal opens up voltage-gated Ca+ channels
Ca+ influx causes vesicles storing NT to fuse with the pre-synaptic membrane, releasing NT into the synaptic cleft.
What does the action potential accomplish?
The release of neurotransmitters at the axon terminals
MEMBRANE GATES?
Transport of ions in and out of the membrane is controlled by gates that can open at particular moments and close again.
We refer to these gates as ion channels, and examples include Na+, Cl-, K+ channels.
TYPES OF NEURONS
We’re now in a position to understand what happens when a neurotransmitter binds to a receptor in the post-synaptic membrane.
I mentioned earlier that this binding causes changes in the electrical potential of the membrane, which can excite, inhibit, or modulate the activity of the post-synaptic neuron.
BUT HOW?
Let’s take the case of an excitatory neurotransmitter.
Dorsal vs. ventral or Superior vs. Inferior
(myelin staining)
•Myelinated axons
(grey matter, white matter, ventricles – Label)
EXCITATORY EFFECTS
make the postsynaptic neuron more likely to release neurotransmitters in turn. These effects are initiated by changes in the membrane’s electric potential that take place when the neurotransmitter binds with the receptor.
Major fissures and sulci
