Exam 2 Review

Chapter 5: Synapses and Neurotransmission

Synapse Types: Similarities and Differences

  • Electrical Synapses: Direct transmission via gap junctions; faster, bidirectional.

  • Chemical Synapses: Use neurotransmitters; slower but allow signal modulation; unidirectional.

  • Similarities: Both facilitate communication between neurons.

  • Differences: Electrical synapses use ions, while chemical synapses use neurotransmitters.

Components of the Synapse (Fig 5.4)

  • Presynaptic terminal

  • Synaptic cleft

  • Postsynaptic membrane

  • Synaptic vesicles

  • Receptors

Chemical Neurotransmitter Release (Fig 5.12)

  1. Action potential arrives at the presynaptic terminal.

  2. Voltage-gated Ca2+ channels open.

  3. Ca2+ influx triggers synaptic vesicle fusion.

  4. Neurotransmitter is released into the synaptic cleft.

  5. Neurotransmitter binds to postsynaptic receptors.

  6. Postsynaptic response occurs.

  7. Neurotransmitter is degraded or reabsorbed.

Quantal Release of Neurotransmitter

  • Definition: Neurotransmitters are released in discrete packets (quanta).

  • Significance: Provides insight into synaptic function and neurotransmitter availability.

  • Measurement: Patch-clamp recordings, electrophysiology.

Types of Synapses (pp. 111-115)

  • Axodendritic

  • Axosomatic

  • Axoaxonic

  • Dendrodendritic

Three Classes of Neurotransmitters

  1. Amino Acids: Fast-acting (e.g., Glutamate, GABA)

  2. Amines: Modulatory (e.g., Dopamine, Serotonin)

  3. Peptides: Slow-acting (e.g., Substance P, Endorphins)

Neurotransmitter Synthesis and Storage (Fig 5.11)

  • Amino acids and amines: Synthesized in the axon terminal.

  • Peptides: Synthesized in the soma, transported to the terminal.

Function in the Synapse

  • Amino acids: Direct ion channel effects.

  • Amines: Modulate synaptic activity.

  • Peptides: Long-lasting effects on neuronal circuits.

Transmitter-Gated Ion Channels vs. G-Protein Coupled Receptors

  • Transmitter-Gated: Fast, direct ion flow.

  • G-Protein Coupled: Slow, indirect signaling via second messengers.

G-Protein Sequence of Events (Fig. 5.17, 5.22)

  1. Neurotransmitter binds to receptor.

  2. G-protein is activated.

  3. G-protein interacts with ion channels or enzymes.

  4. Ion channel opens or second messenger pathway is activated.

Second Messengers

  • Definition: Molecules that relay signals inside the cell.

  • Example: cAMP.

Autoreceptors

  • Function: Regulate neurotransmitter release via negative feedback.

Neurotransmitter Recovery and Degradation

  • Reuptake

  • Enzymatic breakdown

  • Diffusion

Axon Synapse Targets (Fig 5.6, 5.7)

  • Dendrites

  • Soma

  • Axons

Shunting Inhibition (Fig 5.21)

  • Inhibitory inputs reduce membrane resistance, preventing depolarization.

PSP, EPSP, IPSP

  • PSP: Postsynaptic potential.

  • EPSP: Excitatory postsynaptic potential.

  • IPSP: Inhibitory postsynaptic potential.

Charge Spread in the Cell

  • Passive diffusion and active propagation.

Chapter 6: Neurotransmitters and Receptors

Neurotransmitter Classification and Release

  • Fast vs. Slow: Amino acids (fast), peptides (slow).

  • Vesicle vs. Granule Release: Synaptic vesicles for amino acids/amines, dense-core granules for peptides.

Excitatory vs. Inhibitory Neurotransmitters

  • Ach: Excitatory

  • GABA: Inhibitory

  • Glutamate: Excitatory

Neurotransmitter Criteria

  1. Synthesized and stored in presynaptic neurons.

  2. Released upon stimulation.

  3. Evokes a response in the postsynaptic neuron.

Receptor Binding

  • One neurotransmitter can bind to multiple receptor types.

Identifying Receptor Subtypes

  1. Pharmacology

  2. Ligand-binding studies

  3. Molecular cloning

Membrane-Spanning Proteins

  • Channel proteins

  • Ion pumps

Four Channel Types

  • Gap junctions: Always open.

  • Voltage-gated: Open via membrane potential changes.

  • Transmitter-gated: Open via neurotransmitter binding.

  • G-protein-coupled: Open via intracellular signaling.

Neurotransmitter Synapse Locations

  • Ach: Neuromuscular junctions.

Neurotransmitter Degradation

  • Ach: Broken down by acetylcholinesterase.

  • Catecholamines: Degraded by monoamine oxidase (MAO); blocked by cocaine.

  • Serotonin: Removed via reuptake; degraded by MAO; blocked by SSRIs.

Receptor Subtypes and Function

  • Ach: Nicotinic, Muscarinic.

  • Glutamate: AMPA, NMDA, Kainate.

G-Protein Coupled Receptors

  • Signal transduction via second messenger cascades.

G-Protein Steps (Fig. 6.30, p. 175)

  1. Binding of ligand.

  2. Activation of G-protein.

  3. Activation of effector protein.

  4. Second messenger activation.

  5. Cellular response.

Chapter 7: Neuroanatomy

Directional Terms

  • Anterior, Rostral, Dorsal, Ventral, Posterior, Caudal.

  • Sagittal, Midsagittal, Horizontal, Coronal.

  • Ipsilateral, Contralateral.

  • Efferent, Afferent.

CNS vs. PNS

  • CNS: Brain, spinal cord.

  • PNS: Cranial/spinal nerves, autonomic system.

Dorsal vs. Ventral Roots

  • Dorsal: Sensory (with ganglia).

  • Ventral: Motor.

Meninges and CSF Circulation

  • Layers: Dura mater, Arachnoid mater, Pia mater.

  • CSF Flow: Lateral ventricles → Third ventricle → Fourth ventricle.

Brain Imaging Techniques

  • CT: X-rays.

  • MRI: Magnetic fields.

  • PET: Radioactive glucose.

  • fMRI: Oxygen levels.

Embryonic Development

  • Neural tube → CNS.

  • Neural crest → PNS.

Brain Regions and Functions

  • Forebrain: Cortex, thalamus, hypothalamus.

  • Midbrain: Tectum, tegmentum.

  • Hindbrain: Cerebellum, pons, medulla.

Lobes of the Brain

  • Frontal (Motor)

  • Parietal (Somatosensory)

  • Temporal (Auditory)

  • Occipital (Visual)

Chapter 5: Synapses and Neurotransmission

Synapse Types: Similarities and Differences

  • Synapse: The junction between two neurons where communication occurs.

  • Electrical Synapse: A type of synapse where ions pass directly between neurons through gap junctions, allowing for fast, bidirectional signaling.

  • Chemical Synapse: A synapse where neurotransmitters transmit signals from one neuron to another, making the process slower but allowing for modulation.

Components of the Synapse

  • Presynaptic Terminal: The end of the neuron that releases neurotransmitters.

  • Synaptic Cleft: The small gap between the presynaptic and postsynaptic neurons.

  • Postsynaptic Membrane: The surface of the receiving neuron that contains receptors for neurotransmitters.

  • Synaptic Vesicles: Small sacs in the presynaptic terminal that store neurotransmitters.

  • Receptors: Proteins on the postsynaptic membrane that bind neurotransmitters and trigger a response.

Chemical Neurotransmitter Release

  • Action Potential: A rapid electrical signal traveling along a neuron.

  • Voltage-Gated Ca²⁺ Channels: Channels that open when the action potential arrives, allowing calcium ions to enter.

  • Ca²⁺ Influx: The entry of calcium ions into the presynaptic terminal, triggering neurotransmitter release.

  • Neurotransmitter Binding: The process where neurotransmitters attach to receptors on the postsynaptic membrane.

  • Postsynaptic Response: The change in the receiving neuron due to neurotransmitter binding.

  • Neurotransmitter Degradation/Reuptake: The removal of neurotransmitters from the synaptic cleft, either by breakdown or reabsorption.

Quantal Release of Neurotransmitter

  • Quanta: Discrete packets of neurotransmitter released in fixed amounts.

  • Patch-Clamp Recording: A technique to measure ion flow and neurotransmitter release.

  • Electrophysiology: The study of electrical properties of biological cells and tissues.

Types of Synapses

  • Axodendritic: A synapse between an axon and a dendrite.

  • Axosomatic: A synapse between an axon and a soma (cell body).

  • Axoaxonic: A synapse between two axons.

  • Dendrodendritic: A synapse between two dendrites.

Three Classes of Neurotransmitters

  • Amino Acids: Fast-acting neurotransmitters (e.g., glutamate, GABA).

  • Amines: Modulatory neurotransmitters that affect mood and arousal (e.g., dopamine, serotonin).

  • Peptides: Slow-acting neurotransmitters that influence long-term neural circuits (e.g., endorphins, Substance P).

Neurotransmitter Synthesis and Storage

  • Amino Acid & Amine Synthesis: Occurs in the axon terminal.

  • Peptide Synthesis: Takes place in the soma and is transported to the terminal.

Transmitter-Gated Ion Channels vs. G-Protein Coupled Receptors

  • Transmitter-Gated Ion Channels: Directly allow ion flow when a neurotransmitter binds, leading to a fast response.

  • G-Protein Coupled Receptors (GPCRs): Activate intracellular signaling pathways, leading to slower but more complex effects.

G-Protein Signaling Sequence

  1. Neurotransmitter binds to receptor.

  2. G-protein is activated.

  3. G-protein interacts with ion channels or enzymes.

  4. Ion channel opens or second messenger pathway is triggered.

Second Messengers

  • Definition: Molecules that relay signals inside the cell after receptor activation.

  • Example: cAMP (cyclic adenosine monophosphate).

Autoreceptors

  • Function: Regulate neurotransmitter release through negative feedback.

Neurotransmitter Recovery and Degradation

  • Reuptake: Neurotransmitters are reabsorbed into the presynaptic neuron.

  • Enzymatic Breakdown: Enzymes break down neurotransmitters in the synaptic cleft.

  • Diffusion: Neurotransmitters move away from the synapse.

Shunting Inhibition

  • Definition: Inhibitory signals reduce membrane resistance, preventing depolarization and signal transmission.

PSP, EPSP, IPSP

  • PSP (Postsynaptic Potential): A change in the electrical charge of the postsynaptic neuron.

  • EPSP (Excitatory Postsynaptic Potential): A depolarizing potential that increases the likelihood of neuron firing.

  • IPSP (Inhibitory Postsynaptic Potential): A hyperpolarizing potential that decreases the likelihood of neuron firing.

Chapter 6: Neurotransmitters and Receptors

Neurotransmitter Classification and Release

  • Fast Neurotransmitters: Amino acids such as glutamate and GABA.

  • Slow Neurotransmitters: Peptides such as endorphins.

Excitatory vs. Inhibitory Neurotransmitters

  • Acetylcholine (Ach): Excitatory.

  • GABA (Gamma-Aminobutyric Acid): Inhibitory.

  • Glutamate: Excitatory.

Neurotransmitter Criteria

  1. Synthesized and stored in presynaptic neurons.

  2. Released upon stimulation.

  3. Evokes a response in the postsynaptic neuron.

Receptor Binding & Subtypes

  • Pharmacology: Studying drug interactions with receptors.

  • Ligand-Binding Studies: Examining molecules that bind receptors.

  • Molecular Cloning: Identifying receptor genes.

Membrane-Spanning Proteins & Channel Types

  • Gap Junctions: Always open, allowing ion flow.

  • Voltage-Gated Channels: Open when membrane potential changes.

  • Transmitter-Gated Channels: Open when a neurotransmitter binds.

  • G-Protein Coupled Channels: Open via intracellular signaling.

Neurotransmitter Degradation

  • Ach: Broken down by acetylcholinesterase.

  • Catecholamines (Dopamine, Epinephrine, Norepinephrine): Degraded by monoamine oxidase (MAO); blocked by cocaine.

  • Serotonin: Removed via reuptake; degraded by MAO; blocked by SSRIs.

G-Protein Coupled Receptors (GPCRs)

  • Function: Signal transduction via second messenger cascades.

Chapter 7: Neuroanatomy

Directional Terms

  • Anterior/Rostral: Toward the front.

  • Dorsal: Toward the back.

  • Ventral: Toward the belly.

  • Posterior/Caudal: Toward the rear.

  • Ipsilateral: Same side of the body.

  • Contralateral: Opposite side of the body.

  • Efferent: Carries signals away from the CNS.

  • Afferent: Carries signals to the CNS.

CNS vs. PNS

  • CNS (Central Nervous System): Brain and spinal cord.

  • PNS (Peripheral Nervous System): Cranial/spinal nerves and autonomic system.

Brain Imaging Techniques

  • CT (Computed Tomography): X-ray imaging.

  • MRI (Magnetic Resonance Imaging): Uses magnetic fields for detailed imaging.

  • PET (Positron Emission Tomography): Measures brain activity using radioactive glucose.

  • fMRI (Functional MRI): Detects brain activity via oxygen levels.

Brain Regions

  • Forebrain: Controls complex functions (cortex, thalamus, hypothalamus).

  • Midbrain: Coordinates movement and sensory input.

Hindbrain: Controls basic survival functions (cerebellum, pons, medulla).