Neurobiology Midterm

Types of Glial cells and functions

astrocytes - support, regulate, generally maintain homeostasis

oligodendrocyte - produce myelin for CNS axons, can myelinate multiple cells

schwann cells - produce myelin for PNS axons, can only myelinate one cell

microglia - immune cells of brain, help mitigate inflammation and damage

Role of myelin

myelin speeds up action potentials when traveling down the axon because the action potential jumps from node to node

nodes of ranvier are gaps in myelin

without myelin action potentials leak through membrane

Cells involved in neuronal repair after injury

microglia - macrophages in brain, mitigate inflammation, mitigate damage, clear debris, modulate inflammatory response

astrocytes - support, regulate, maintain homeostasis for neurons, clear debris, modulate inflammatory response

Schwann cells and oligodendrocytes - repair axons and myelin in PNS and CNS, respectively

action potential steps

1. Threshold - the critical level of depolarization that must be reached for an action potential to occur in a neuron.

2. rising phase - Na+ rushes into cell, rapidly depolarizing cell, making cell more positive

3. overshoot - the part of the action potential where the membrane potential exceeds 0 mV, leading to a positive interior.

4. falling phase- voltage gated sodium channels close, while voltage gated potassium channels open, creating an outward flow of K+, leading to a negative interior

5. undershoot - hyperpolarization occurs because the voltage gated potassium channels stay open for just a little too long

6. absolute refractory period - sodium channels inactivate when the membrane becomes strongly depolarized. They can’t open again until the membrane potential is negative.

action potential extra info

firing rate depends on strength of current

the threshold, shape, frequency, firing pattern, resting membrane potential, and membrane resistance are all different for different types of cells

fixed in size and duration

what makes the conduction of an action potential faster?

myelination - faster speed bc action potential hops from node of raniver to node of ranvier, can’t leak out in between

larger axonal diameter - faster speed bc more of the electric current goes down the axon instead of leaking out - wide hose with few leaks vs narrow hose with many leaks, wide hose allows for more water to flow down it instead of out across membrane

What mV for each phase of action potential?

resting = -65 mv to -80 mv

threshold = -55 mv

depolarization = 40 mv

hyperpolarization = -90 mv

Ion pumps

sodium potassium pump - helps ensure negative membrane potential by pushing an unequal ratio of Na+ out to K+ in - actively transports against natural concentration gradient, so it needs ~ 70% of brain’s ATP - for every 3 sodium leaving, 2 potassium enter

calcium pump - helps maintain low levels of calcium inside cell so the cell can fully function

types of synapses

electrical synapses - neurons are connected by gap junctions for fast communication - Ex: escape, breathing, heartbeat, etc - lets ions and small molecules pass freely in both directions

chemical synapse - transmitter gated ion channels (receptor receives neurotransmitter and opens, causing depolarization) and protein coupled receptors (receptor receives neurotransmitter and causes G-proteins to activate, which then activate second messengers which can go and do other things, etc, basically causes chain of events instead of simple action potential)

Types of neurotransmitters

Amino acids - Ex: GABA, Glutamate, Glycine

Amines - Ex: Serotonin, Dopamine, Norepinephrine

Peptides - Ex: neurotensin

EPSP vs IPSP

EPSP - makes neuron more likely to fire action potentials, excitatory - if the transmitter gated channels let in Na+ or if the cell depolarizes in response to a neurotransmitter, its EPSP

IPSP - makes neuron less likely to fire action potentials, inhibitory - if the transmitter gated channels let in Cl- or if the cell hyperpolarizes in response to a neurotransmitter, its IPSP

types of neurotransmitter receptors

Neurotrasmitter-gated Ion Channels

• AMPA Receptors - quick, first to respond - EPSP

• NMDA Receptors - slower, crucial for plasticity - EPSP

• Kainate Receptors

• GABAA Receptors - IPSP

• Glycine Receptors - IPSP

• Nicotinic ACH Receptors - EPSP

G-Protein-Coupled Receptors/Metabotropic Receptors

• dopamine receptors

• G Protein gated ion channels

• muscarinic ACh Receptors (heart)

• Serotonin receptors

• ‘Adrenergic receptors

• endocannabinoid receptors

Receptor agonists vs receptor antagonists

Inhibitors are drugs that inhibit the function of proteins needed for the action potential to happen

receptor agonists bind to receptors and mimic normal neurotransmitters, which can make it more effective or stay open for longer or many other things

receptor antagonists bind to receptors and block their normal function

both are usually drugs of some kind

Optogenetics

scientists can control neurons using light

first they insert a specific gene that creates light-sensitive ion channels, so they can then shine a blue light on the neurons and open those channels, causing action potentials

the gene is channel rhodopsin

immunohistochemistry

Immunohistochemistry uses antibodies in order to color and visually observe expression of specific proteins in fixed cell tissues. An example of this technique is using primary and secondary antibodies to the GFAP protein which is expressed in astrocytes, in order to see where astrocytes occur in a brain tissue sample through immunofluorescent imaging.

Experimental models used in neuroscience research

In vivo - in a living organism, usually rodents, fruit flies, zebrafish, nematodes, etc

In vitro - in artificial environment outside living organism

Ex vivo - outside living organisms but tissue is intact

In silico - computer simulation

Neuronal structure and function

Neuronal membrane - encloses everything, keeps cytosol contained, ~ 5mm thick

soma - central body of neuron, contains nucleus and other organelles and cytoplasm

nucleus - contained in nuclear envelope, contains chromosomes made of DNA

Axon - contains synapses, which are made of postsynaptic neuron, presynaptic neuron and synaptic cleft

dendrite - full collection of dendrites are called dendritic tree, each dendrite is a dendritic branch, each dendritic branch has smaller dendritic spines - works like an antenna, covered in synapses to receive signals from other axons - can synthesize proteins locally

Classifying neurons

Unipolar - 1 dendrite/axon - speedy - for reflexes

Bipolar - 1 dendrite and 1 axon

Multipolar - 1 axon multiple dendrites - most common

• stellate cell - start shaped dendritic trees - spiny neurons

• pyramidal cell - pyramid shaped dendritic trees

• spiny neurons - have spines

Role of calcium in neurotransmitter release

1. action potential reaches the axon terminal

2. voltage-gated calcium channels open, allowing Ca2+ to enter

3. Ca2+ triggers exocytosis of synaptic vesicles. (synaptic vesicles fuse with membrane )

4. Neurotransmitter is released into the synaptic cleft.

5. Neurotransmitters bind to postsynaptic receptors.

Ion Channels vs Ion pumps

Ion Channels:

• passive diffusion

• goes with gradient

• can be gated (ex: voltage gated sodium channels)

• important for rapid changes in ion concentration

Ion pumps:

• active diffusion

• require ATP

• move ions against gradient

• maintain long-term ion gradients, like the resting membrane potential

Spatial summation vs Temporal summation

Summation is basically a neuron choosing whether it should fire an action potential or not

Spatial is basing it off of many signals from many different axons telling the dendrites to fire an action potential

Temporal is basing it off of one axon repeatedly and rapidly telling the dendrites to fire an action potential

Steps in chemical synaptic transmission

neurotransmitter synthesis, loading into synaptic vesicles, exocytosis, binding and activation of receptors, reuptake and degradation

DNA and Gene expression

Chromosomes are made of DNA

Sections of DNA are genes, which contain instructions on how to make proteins

DNA —transcription—> mRNA —translation—> proteins

Organelle functions

Nucleus - stores DNA, controls growth and metabolism

Ribosomes - make proteins from amino acids, receive instructions to make proteins through DNA—>mRNA

Mitochondria - create ATP through cellular respiration

Endoplasmic Reticulum - synthesizes, modifies and transports proteins and lipids - Rough ER has ribosomes attached, smooth ER does not

Golgi Apparatus - processes and packages proteins and lipids for transport

Vacuoles - storage of water, nutrients, waste, etc

Cytoskeleton - protein filaments that provide structure and support and facilitate movement and transport