Neural Conduction and Action Potential

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Neural Conduction

• Neural conduction involves electrical signals moving along the axon.
• Synaptic transmission depends on neurotransmitters to facilitate communication between neurons.

Structure of a Neuron

• Dendrites receive incoming signals.
• The axon transmits signals away from the cell body.
• Terminal buttons send signals to other neurons.
• Nerves are a bundle of axons transmitting information over long distances.

Membrane Potential

• Membrane potential is the electrical voltage difference between the inside and outside of a cell, caused by ion distribution.
• Crucial ions include Sodium (Na+), Potassium (K+), and Chloride (Cl-).
• The sodium-potassium pump actively transports 3 Na+ out and 2 K+ in, maintaining the resting potential at -70mV.

Action Potential

• The threshold voltage is -55mV.
• All-or-nothing principle dictates that an action potential occurs if the threshold is reached.

Stages of Action Potential

• Resting state is -70mV, characterized by high Na+ outside and high K+ inside, maintained by the sodium-potassium pump.
• Depolarization occurs at +30mV, with Na+ channels opening, enabling Na+ to enter the neuron, making the membrane potential positive.
• Repolarization occurs at -70mV, with Na+ channels closing and K+ channels opening, restoring negativity.
• During hyperpolarization, the state is below -70mV, where K+ channels close slowly, causing excess K+ efflux.
• This phase ensures no immediate re-firing.
• The sodium/potassium pump restores original ion distribution to return to the resting potential.

Refractory Periods

• No action potential can occur during the absolute refractory period.
• A stronger stimulus is needed to trigger an action potential during the relative refractory period.

Saltatory Conduction

• Action potentials in myelinated axons jump between Nodes of Ranvier, speeding up transmission.
• Glial cells, including Schwann cells (PNS) and oligodendrocytes (CNS), support this process.

Synaptic Transmission

• Synapses are junctions between two neurons where signals are transmitted.
• The synaptic cleft is a tiny gap (~40nm) between neurons.

Process of Synaptic Transmission (VRRERR)

• Vesicles contain neurotransmitters.
• The action potential causes vesicles to release neurotransmitters into the synaptic cleft.
• Neurotransmitters bind to receptors on the postsynaptic neuron.
• Enzymes break down excess neurotransmitters in the synapse.
• Neurotransmitters are reabsorbed into the presynaptic neuron during reuptake.
• Vesicles are refilled for the next signal during the replenishment.

Effects on the Postsynaptic Neuron

• The excitatory effect increases the likelihood of an action potential.
• The inhibitory effect decreases the likelihood of an action potential.

Summary of Neural Events

• A key function of a sodium-potassium pump is the maintenance of membrane potential.
• Neuron sequence: Resting → Depolarization → Repolarization → Hyperpolarization → Resting.
• Synaptic processes involve neurotransmitter release, receptor binding, and enzymatic or reuptake termination.

Research Methods in Biopsychology

• Biopsychology analyzes the correlation between biological processes and behavior, using invasive and non-invasive methods.

Invasive Research Methods

• Involve direct physical access to the brain.

Ablation Methods

• Surgical removal of brain tissue to observe how behavior changes, pinpointing brain regions tied to specified functions.

Lesion Techniques

• Damage precise brain regions to study its consequence on behavior through electrolytic, chemical, or aspiration.

Non-invasive Research Methods

• Avoid the necessity for direct brain entry, typically employed in research.

Psychophysiological Recordings

• Records electrical activity within the brain by using scalp electrodes.

Electroencephalography (EEG)

• Explores brain wave patterns linked to sleep, seizures, and cognition.

Magnetoencephalography (MEG)

• Identifies the magnetic field generated by neural activities.
• Accurately measures timings of brain capabilities to support epilepsy research.

Electromyography (EMG)

• Assesses function of motor control and neuromuscular diseases, measuring muscle activity with electrodes targeting muscles.

Electrooculography (EOG)

• Eye movements are recorded to determine voltage changes within the eyeball.
• Useful in sleep studies and cognitive research.

Electrodermal Activity (EDA)

• Measures skin conductance to study the effects on stress and emotion.

Electrical Stimulation

• Stimulate specific brain areas to watch the consequence on behavior.
• The oscilloscope displays real-time electrical activity.
• The ink-writing Oscilloscope - Rolls paper along with use of ink to record evoked potentials.
• Computers are used to store and analyze electrical signals.

Neuroimaging Techniques (Structural Imaging)

• An X-ray is a basic method, yet limited to detect detailed brain structures.
• Computerized Tomography (CT Scan) constructs cross-sectional images through computer processing of X-ray data.
• Detects abnormal structures such as tumors and brain injuries.
• Magnetic Resonance Imaging (MRI) uses magnetic fields and radio waves that produce detailed brain images.
• Detects brain lesions for anatomical studies.

Functional Imaging Techniques

• Records metabolic changes through radioactive glucose to determine active brain regions involved in different activities, using a Positron Emission Tomography (PET Scan).
• Detects neural activity measuring blood flow change with the use of Functional MRI (fMRI).
• Commonly used in cognitive neuroscience and diagnosis in the medical field.
• With a Diffusion Tensor Imaging (DTI), orientation of neural axons are determined.
• It maps path along with water diffusion in the brain.
• The Transcranial Magnetic Stimulation (TMS) temporarily turns off some brain regions with magnetic fields for operational reasons.

Neuropsychological Assessments

• Evaluate cognitive and behavioral functions.
• The Wechsler Intelligence Test assess intelligence and cognitive abilities in adults.
• The Dichotic Listening Test uses non-invasive test to examine hemispheric lateralization of language processing.

Summary of Research Methods

• Lesions and ablations produce data on brain functions but are only used on animals; which provides direct insight into the function within the brain of those animals.
• Non-invasive approaches (EEG, MRI, fMRI) are reliable to humans; it allows researchers to examine the human brain.
• PET, CT, and MRI helps researchers visualize brain structure and activity.

Early Development of the CNS

• Derives from the ectoderm that specifically originates from the neural plate.
• Neural folds elevate and merge to give the neural tube.
• Neural plate establishes the neural crest.

Neurulation Process (Week 4 of Development)

• Process starts in the cervical region and proceeds in the cranial (head) and caudal (tail) directions.
• Neural tube starts to form blood vessels (vascularize) when the neuropores gets closed.

Key Genes Involved in CNS Development

• Shh is used as a very important factor for structuring the CNS.
• Pax is employed in brain & spinal cord segmentation.
• BMPs controls formation of the neural crest.
• TGF-β gives rise to dorsal structuring.

Development of Neurons and Glial Cells

• Neuroepithelial cells in the ventricular zone creates neuroblasts.
• Glioblasts change into supportive brain cells.
• Brain microglia is scattered around in the brain.

Spinal Cord Myelination

• Begins during the late phase of gestation and can last until first year after the birth.
• Oligodendrocytes produce myelin sheaths surrounding the spinal cord neurons.

Development of the Brain

• In week 3-4, the primary brain vesicles will emerge.
• Prosen cephalon will give rise to the forebrain.
• The midbrain will emerge though the mesescephalon.
• The hindbrain will form from a rhombencephalon.

Primary Brain Vesicles (Week 5)

• The telencephalon forms the cerebral hemispheres.
• The thalamus, hypothalamus, and retina come from the diencephalon.
• With the mesencephalon, the midbrain forms, containing the tectum, and tegmentum.
• The metencephalon becomes the pons and cerebellum.

Hindbrain Development

• The pontine flexure divides the hindbrain.
• Parts of metencephalon and the medulla oblongata become the cerebrum in later development.

Midbrain Development

• The area consist of substantia nigra, which makes dopamine.
• Sylvius' cerebral aqueduct enables CSF streams betwixt third/fourth ventricles.

Forebrain Development

• The forebrain produces optic vesicles, which help establish the optic nerves/retina thereafter.
• The corpus striatum starts as week 6, as is essential for monitoring movements.