NEUR200 Exam 1 Outline

Unit 1: The Nervous System

I. The Nervous System

A. Nervous System Division and Subdivisions

  1. Parts of the CNS

    • The Central Nervous System (CNS) consists of the brain and spinal cord, serving as the main control center for processing information and coordinating responses.

  2. Divisions of the PNS

    • The Peripheral Nervous System (PNS) includes all neural elements outside the CNS. It is further divided into:

      • Somatic Nervous System: Controls voluntary movements.

      • Autonomic Nervous System: Regulates involuntary functions (subdivided into sympathetic and parasympathetic systems).

B. Neural Anatomy

  1. Meninges

    • Three protective membranes covering the brain and spinal cord: Dura mater, Arachnoid mater, and Pia mater.

  2. Blood Supply and the Blood Brain Barrier (BBB) a) What types of molecules can pass through the BBB?

    • Lipid-soluble molecules, small molecules, and certain proteins can cross the BBB. Larger hydrophilic molecules mostly cannot pass.

  3. Grey vs. White Matter, Ventricles

    • Grey Matter: Contains neuronal cell bodies.

    • White Matter: Composed of myelinated axons.

    • Ventricles: Fluid-filled cavities in the brain that contain cerebrospinal fluid (CSF).

  4. Tracts vs. Nerves

    • Tracts: Bundles of axons in the CNS.

    • Nerves: Bundles of axons in the PNS.

C. Parts of the Brain (Know General Locations)

  1. Cerebral Cortex: Responsible for higher-level functions such as thought and action.

  2. Brain Stem: Controls basic life functions (breathing, heart rate).

  3. Cerebellum: Involved in coordination and balance.

  4. Corpus Callosum: Connects the left and right cerebral hemispheres.

  5. Thalamus: Relay station for sensory information.

  6. Hypothalamus: Regulates homeostatic functions such as temperature and hunger.

D. Anatomical Referencing

  1. Dorsal, Ventral, Anterior, Posterior

    • Dorsal: Toward the back

    • Ventral: Toward the belly

    • Anterior: Toward the front

    • Posterior: Toward the back

Unit 2: Neurons

I. Neurons

A. Parts of a Neuron

  1. Soma: Cell body that contains the nucleus.

  2. Dendrites: Branch-like structures that receive signals from other neurons.

  3. Axon: Long projection that transmits electrical impulses away from the soma.

  4. Axon Terminals: End points where neurotransmitters are released.

B. Neurons are Polarized! Why?

  • Neurons maintain a difference in charge across their membranes due to the distribution of ions, contributing to the resting membrane potential (RMP).

C. Myelin, Nodes of Ranvier

  • Myelin is a fatty substance that insulates axons, speeding up signal transmission. Nodes of Ranvier are gaps in the myelin sheath where ion channels are concentrated.

D. Synapse, Synaptic Cleft

  • The synapse is the junction between two neurons where communication occurs. The synaptic cleft is the gap between the axon terminal of one neuron and the dendrite of another.

Unit 3: Neuronal Diversity

I. Neuronal Diversity

A. Afferent vs. Efferent

  • Afferent neurons carry sensory signals to the CNS.

  • Efferent neurons carry motor signals from the CNS to effectors (muscles/glands).

B. Types of Neurons

  • Multipolar: Multiple dendrites, one axon (most common).

  • Unipolar: One process that branches into two (sensory neurons).

  • Bipolar: One dendrite and one axon (found in sensory organs).

Unit 4: Interneuron Connections

I. What are the 3 Basic Steps?

  1. Integration: Processing sensory input.

  2. Output: Generating a response.

  3. Transmission: Sending signals to effectors.

II. Gradients

A. Electrical Gradient

  1. Like charges repel, opposites attract

    • Ions move in response to electrical forces.

B. Concentration/Chemical Gradient

  1. Passive Diffusion: Movement of ions from high to low concentration without energy.

  2. Active Diffusion: Movement against the concentration gradient requiring ATP, often mediated by pumps known as ATPases.

C. Effect of Permeable Membranes on Electrochemical Gradients

  • Semi-permeable membranes regulate ion flow, influencing electrochemical gradients critical for signal propagation.

Unit 5: Resting Membrane Potential

I. Resting Membrane Potential

A. Definition

  • Membrane Potential/Voltage refers to the charge difference across a membrane, dependent on ion concentrations.

    • Inside the cell, the resting membrane potential is approximately -70 ext{ mV}, primarily due to ionic pumps and channels.

B. Important Ions

  1. Sodium (Na⁺): Higher concentration outside the cell.

  2. Potassium (K⁺): Higher concentration inside the cell.

  3. Neurons are most permeable to K⁺, with K⁺ channels being integral to maintaining RMP.

C. Key Channel in Maintenance of RMP

  • Sodium-Potassium Pump (Na⁺/K⁺ ATPase): Actively transports Na⁺ out and K⁺ in, crucial for maintaining RMP.

Unit 6: How Membrane Potentials Change

I. Cell Membrane Permeability to Ions

A. Ion Channels

  1. Ligand-gated Channel: Opens in response to binding of a neurotransmitter.

  2. Voltage-gated Channel: Opens in response to changes in membrane potential.

  3. Mechanoreceptive Channel: Opens in response to mechanical pressure or distortion.

B. Definitions

  1. Permeability: The ability of ions to cross the membrane.

  2. Conductance: The ease with which electric current flows through the membrane.

  3. Flux: The rate of ion movement across the membrane.

Unit 7: Nernst and Goldmann Equations

I. Nernst Equation

A. Purpose

  • Used to calculate equilibrium potentials for specific ions across a membrane.

B. Equilibrium Potentials

  • The Nernst equation provides the potential at which there is no net movement of a particular ion into or out of the cell, taking into account the concentration gradient.

II. Goldmann Equation

A. Purpose

  • Provides an estimate of the entire neuron's membrane potential when considering the relative permeability of different ions.

Unit 8: Changes from the RMP

I. EPSPs and IPSPs

  • Excitatory Postsynaptic Potentials (EPSPs) and Inhibitory Postsynaptic Potentials (IPSPs) lead to depolarization or hyperpolarization of the neuron respectively.

A. Propagation

  • Signals can be propagated by multiple similar stimuli.

II. Summations

A. Temporal vs Spatial Summation

  1. Temporal Summation: Accumulation of stimuli over time at the same synapse.

  2. Spatial Summation: Accumulation of stimuli from multiple synapses.

    • All-or-none threshold: Summations must reach a certain threshold to initiate an action potential.

    • Once the threshold is reached, the action potential is generated and fully propagates down the axon.

Unit 9: Neurotransmitters

I. Relevant Neurotransmitters

A. Types

  1. Glutamate: Major excitatory neurotransmitter, acts on AMPA receptors.

  2. GABA: Major inhibitory neurotransmitter, acts on GABA receptors, crucial for reducing neuronal excitability.

Unit 10: Action Potential

I. Stages of Action Potential

  1. Depolarization: Rapid influx of Na⁺ due to open voltage-gated Na⁺ channels.

  2. Repolarization: K⁺ channels open, K⁺ exits the cell, returning the potential to resting state.

  3. Hyperpolarization: K⁺ channels remain open longer, leading to temporary overshoot below RMP.

A. Refractory Periods

  1. Absolute Refractory Period: No action potential can be initiated, due to inactivation of Na⁺ channels.

    • The ball-and-chain mechanism of voltage-gated Na⁺ channels prevents Na⁺ influx.

  2. Relative Refractory Period: A stronger than normal stimulus is needed to initiate an action potential, as some Na⁺ channels recover but K⁺ channels are still open.

B. Direction of Action Potential

  • Action potentials do not propagate backwards due to the inactivation of Na⁺ channels in the previously activated segment of the axon.

II. Myelin

A. Functions of Myelin

  1. Insulation: Prevents ion leakage, enhancing conduction speed.

  2. Saltatory Conduction: Action potentials jump from Node to Node (Nodes of Ranvier), increasing the speed of neural signal transmission.

III. Neurotransmitter Vesicle Release

A. Process of Release

  • Neurotransmitters are stored in vesicles at axon terminals. When an action potential arrives, it opens voltage-gated Ca²⁺ channels which allow Ca²⁺ influx. This Ca²⁺ influx initiates a cascade that ultimately leads to the release of neurotransmitters into the synapse, allowing communication between neurons.

Unit 11: Definitions and Methods of Neural Representation

I. Definitions

A. Neural Representation

  • Refers to the pattern of neural activity that corresponds to an internal or external stimulus.

B. Coding Techniques

  1. Rate Coding: Neural information is conveyed by the firing rate of neurons.

  2. Temporal Coding: Information conveyed through the timing of spikes.

  3. Population Coding: Information is represented by the collective activity of a group of neurons, differing slightly from rate/temporal coding in the emphasis on collective response rather than individual rates.

II. Methods of Neural Monitoring

A. Monitoring/Recording Techniques

  1. Single Unit Recording: Measures the activity of individual neurons, providing high spatial and temporal resolution.

  2. EEG/MEG: Measures electrical/magnetic fields generated by neural activity, useful for mapping brain activity but with less spatial resolution.

    • ECoG: Particularly invasive recordings used for research and clinical purposes closer to the cortex.

  3. MRI/fMRI: Imaging techniques for visualizing brain structure/function. Resting state fMRI detects functional connectivity between brain regions.

  4. PET: Positron Emission Tomography, used for imaging brain metabolism and function, with good spatial resolution but limited temporal resolution.

B. Interference Techniques

  1. Brain Lesions: Studying damaged areas to infer function.

  2. Optogenetics: Using light to control neurons genetically modified to express light-sensitive ion channels, providing precise control over neuronal activity.

  3. DREADDs: Designer Receptors Exclusively Activated by Designer Drugs, allowing control of specific neuronal populations via synthetic drugs.

  4. TMS: Transcranial Magnetic Stimulation, non-invasive technique stimulating the brain with magnetic fields.

  5. DBS: Deep Brain Stimulation, invasive technique implanting electrodes to modulate brain activity.