CBNS 106 Review

Lecture 2

Brain Cells

• Neurons (100 billion)– Process information– Sense environmental changes– Communicate changes to other neurons– Command body response

• Glia (10 times more)– Insulate, support and nourish neurons

Staining

• Nissl Stain– Facilitates study of cytoarchitecture

• Golgi Stain– Shows soma and neurites (dendrites and axon)

Different classes of neurons

Afferent – INFO CNS

ASTROCYTES!!!

CBNS 106

Lecture 3

- Astrocytes buffer excess potassium, cycle it from ecs to bbb

CBNS 106 Review

Lecture 4 and 5

Action Potential

Ideal Actual

“Resting” Cell

During AP

Action Potential ConductionThe entry of positive charge during the action potential causes the membrane just ahead to depolarize to threshold

Orthodromic conduction – action potentials conduct only in one direction

Antidromic conduction – backward propagation

Typical conduction velocity ~ 10 m/sec

Action potentials last ~ 2 msec

Factors Influencing Conduction VelocitySpread of action potential along membrane• Dependent upon axon structure

Path of the positive charge• Inside of the axon (faster)• Across the axonal membrane (slower)

* If the axon is narrow and there are many open membrane pores then most of the current will flow out across the membrane.

* If the axon is wide and there are few open membrane pores, then most of the current will flow down inside the axon

* The farther the current goes down the axon, the farther ahead the action potential will depolarize the membrane and thus the faster the action potential.

Axonal excitability• Axonal diameter (bigger =

faster)

• Number of voltage-gated channels

Myelin: Facilitates current flow• Myelinating cells

– Schwann cells in the PNS– Oligodendroglia in CNS

Factors Influencing Conduction Velocity

Saltatory Conduction – The propagation of an action potential down a myelinated axon

CBNS 106 Review

Lecture 6

Synaptic Transmission• The process of information transfer at a synapse

• Direction of Flow– One direction, Neuron-to-Target Cell

• 1st Neuron called Presynaptic Neuron• Target Cell called Postsynaptic Neuron

• Two Types of synapses– Chemical– Electrical

• Electrical Synapses:- They allow the direct transfer of ionic current from one cell to another- Gap junction- Cells are said to be “electrically coupled”

• Flow of ions from cytoplasm to cytoplasm

Synaptic Transmission

- Very fast transmission• Postsynaptic potentials (PSPs)

- Synaptic integration: Several PSPs occurring simultaneously to excite a neuron (i.e.causes AP)

Synaptic Transmission

Types of Synapses- Axodendritic (a)- Axosomatic (b)- Axoaxonic (c)

- Asymmetrical membrane differentiations (a)

- Symmetrical membrane differentiations (b)

• Chemical Synapses:– Neurotransmitter, the chemical is used to

transfer information from one cell to another- Most synaptic transmission in the mature

human nervous system is chemical.

Synaptic Transmission

Principles of Chemical Synaptic Transmission

• Basic Steps– Neurotransmitter synthesis– Load neurotransmitter into synaptic vesicles– Neurotransmitter Release• Vesicles fuse to presynaptic terminal• Neurotransmitter spills into synaptic cleft– Binds to postsynaptic receptors– Biochemical/Electrical response elicited in postsynaptic cell– Removal of neurotransmitter from synaptic cleft

Synaptic Transmission

Neurotransmitter Release– Exocytosis: Process by which vesicles release their contents; 60 microsec

Mechanisms• Process of exocytosis stimulated by release of intracellular calcium, [Ca2+]i• Proteins alter conformation - activated• Vesicle membrane incorporated into presynaptic membrane• Neurotransmitter released• Vesicle membrane recovered by endocytosis

Synaptic Transmission

Neurotransmitter Recovery and Degradation

– Diffusion: Away from the synapse

– Reuptake: Neurotransmitter re-enters presynaptic axon terminal

– Enzymatic destruction inside terminal cytosol or synaptic cleft

– Desensitization: e.g., AChE cleaves Ach to inactive state

Neurotransmitters• Amino acids: Small organic molecules

• e.g., Glutamate (Glu), Glycine (Gly), gammaaminobutyric acid (GABA)

• Amines: Small organic molecules• e.g., Dopamine (DA), Acetylcholine (Ach), Norepinephrine (NE), Serotonin (5-HT)

• Peptides: Short amino acid chains (i.e. proteins) stored in and released from secretory granules• e.g., Dynorphin, Enkephalins

PSP Generation• EPSP = excitatory postsynaptic potential

– Transient postsynaptic membrane depolarization by presynaptic release of neurotransmitter

• IPSP = inhibitory postsynaptic potential– Transient hyperpolarization of postsynaptic membrane potential caused by presynaptic release of neurotransmitter

Synaptic Integration• Process by which multiple synaptic potentials

combine within one postsynaptic neuron

-Allows for neurons to perform sophisticated computations-Integration: PSPs added together -Spatial: PSPs generated simultaneously in different spaces-Temporal: PSPs generated at same synapse in rapid succession

- Synaptic vesicles: Elementary units of synaptic transmission

- Quantum: An indivisible unit

- Miniature postsynaptic potential (“mini”)

- Quantal analysis: Used to determine number of vesicles that release during neurotransmission

- Neuromuscular junction: About 200 synaptic vesicles, EPSP of 40mV or more

- CNS synapse: Single vesicle, EPSP of few tenths of a millivolt

Synaptic Integration

• IPSPs and Shunting Inhibition– Excitatory vs. inhibitory synapses: Bind different neurotransmitters, allow different ions to pass through channels– Membrane potential less negative than -65mV = hyperpolarizing IPSP

• Shunting Inhibition: Inhibiting current flow from soma to axon hillock

Synaptic Integration

(a) Stimulation of the excitatory input causes inward postsynapticcurrent that spreads to the soma, where it can be recorded as an EPSP.

(b) When the inhibitory and excitatory inputs are stimulated together, the depolarizing currentleaks out before it reaches the soma.

Chemical Synaptic Transmission Principles

Autoreceptors– Presynaptic receptors sensitive to neurotransmitter released by presynaptic terminal– Act as safety valve to reduce release when levels are high in synaptic cleft (autoregulation)