Neuro Exam 1

Sensory System

Detect what happens

Associational System

Integrate and interpret events with past experiences (brain cortex not reflexes)

Motor System

Respond with physical action

Gene

Both coding and noncoding DNA sequences

Regulatory DNA

determine what and how much gene is transcribed and translated like a promotor

How many genes expressed in brain out of total?

14,000/20,000 with 6,000 exclusive to the brain

Golgi’s neuron theory

Interconnected reticular system

Golgi stain

Show cell body, dendrites, and axons

Nissi stain

Show many cell bodies and better show density, more zoomed out

Santiago Cajal’s cell theory

Used Golgi staining to show each neuron was distinct but communicate as junctions (neuron doctrine)

Charles Sherrington

Used term synapse for junction between neurons

Electron Microscopy

Generates a beam of electrons, focuses it and a detector records the electrons that pass through

Chemical synapse

Neurotransmitters cross synaptic cleft (space between neurons), has measurable delay and usually one way

Electrical synapse

Ions pass through gap junction channels which is very quick and goes both ways, gap junctions can locally connect cytoplasm keeping membranes separate, cells contribute connexons to create the pores which bridge the synaptic cleft

Dendriites

Recieve synaptic inputs

Cell body

Contains nucleus, biosynthetic machinery, integrates cell demands and inputs

Nucleus

Stores DNA

Axon

Carries output to target cells

Axon terminals

Release transmitters at chemical synapses

Neuron types

Pseudounipolar- one process in soma divides into central and peripheral branches, common in sensory ganglia

Bipolar- one dendrite and one axon, retina

Multipolar- many dendrites and one axon, most common in CNS

Anaxonic- No clear axon, supports local processing, amacrine cells

Neurons

Generate action potentials, communicate with other cells in synapses

Glia

Regulate extracellular environment, form myelin, etc… help neurons do their job, do not generate potentials, almost 1-1 ration with neurons

Astrocytes

(In CNS)Maintain K+, clear and recycle neurotransmitters, help metabolically

Oligodendrocytes

Form mylein around multiple CNS axons

Microglia

Immune cells that survey CNS tissue and respond to injuries

Ependymal Cells

Line ventricles and central canal, circulate cerebrospinal fluid

Schwann cells

In PNS, wrap one segment of one axon with myelin

Satellite glial cells

Form sheath around neuron cell bodies in sensory ganglia, regulate ions

Myelin

Myelin helps with conduction, allowing axons to function better

Oligodendrocyte precursor cells

Generate new oligodendrocytes

Neural stem cells

Can produce neurons and glia but in a very limited fashion

Soma

Contains nucleus, mitochondria, golgi apparatus and rough ER, transcription and protein synthesis happen here

Dendrites

Smooth ER, cytoskeleton, mitochondria

Axon

No nucleus, golgi, or rough ER, have many synaptic vesicles and release machinery

Convergence

Many inputs to one neuron

Divergence

One neuron sends signals to many targets

Signal transmission

1. presynaptic terminal depolarizes- more positive

2. Ca+ floods in

3. Neurotransmitters diffuse across synaptic cleft, initially in vesicles until they reach the cleft and then bind to receptors

4. Receptors respond to the change

Action potential

1. Depolarization, Na+ floods in

2. Repolarization- Na+ channels close while K+ exits

3. Afterhyperpolarization- K+ channels slowly close

Axon Initial Segment

Action potential starts here where Na+ channels are clustered

Types of Neurons

Afferent- send signal towards interneuron

Interneuron- connect neurons together

Efferent neuron- send signal to muscle for physical movement

How to stop muscle from reacting, to relax?

Hyperpolarization- ensures certain cells do not cross action potential to allow reflexes like knee jerk

GFP

Green florescent protein- originally from jellyfish which labels specific cells and gene expression patterns

Cre-lox system

DNA segment is flanked by loxP sites. A specific promoter is used to limit expression of Cre recombinase to a certain type of tissue or muscle. Two different mice/organisms used, one for promoter and one for the gene. As the offspring develops, Cre deletes the flanked DNA segment so it is not expressed in those cells.

Optogenetics

A light sensitive opsin is expressed in a cell population through an adenovirus injection. Light is delivered which activates the opsin and changes the cell activity which can then be measured. Activating one part of cell can result in seeing the changes to other parts of the brain and this the connections between them.

Monosynaptic

Direct excitation

Inhibition

Polysynaptic/disynaptic

Intracellular recording

Electrode accesses one cell and measures membrane potential

Membrane Potential

Voltage difference from inside the cell relative to the outside of the cell, v(inside)-v(outside)

Voltage

Electrical potential

Equilibrium potential

The voltage difference when there is no net movement of ions in and out of a cell

Ion Channels

Provide passive ways for ions to flow down concentration gradient

Active Transporter

Utilizes energy to move ions against concentration gradient/uphill

Relative permeability

How easily an ion can cross cell membrane compared to another, utilized in Goldman equation

Does all the inside and outside of cell need to be overwhelmingly positive or negative?

No, only a thin layer near the membrane

Vm=Ek

Equilibrium, no net K+ movement

Action potential propagation

Local current depolarizes next excitable region working towards threshold along the axon, voltage gated channels regenerate action potentials

Resting membrane potential permeability?

K+ greatest through leak channels
Na+ and Cl- very little

Overshoot after action potential cause?

K+ voltage gated channels take time to close

Action Potential Sequence

Rising: Voltage gated Na+ opens and Na+ enters

Falling: Na+ voltage gated channels close, K+ gated channels open

Hyperpolarization: K+ gated channels remain open as cell voltage goes below resting

Recovery: K+ gated channels close, all channels recover from refractory period

Sustained depolarization causes:

Increased AP firing rate as AP peak cannot get higher than the maximum

Why is Cl- in/out reversed in Goldman equation relative to K+ and Na+

Negative charge

Graded local signals:

Receptor potentials and synaptic potentials

Synaptic potential

Postsynaptic potential which influences whether a cell will be excited or inhibited from an action potential , affects firing probability

Receptor potential

Converts a stimulus into a grade local voltage change

Purpose of Na+/K+ pumps?

Sustains concentration gradient of Na+ and K+