Psychobiology

Psychobiology (also known as Behavioural Neuroscience), applies biological principles to the behaviour of humans and other animals. It typically involves the study of neurons, nerves, neurotransmitters and basic biological processes that underlie normal/abnormal behaviour.

Galvani and Volta

Galvani's study of bioelectricity and frogs led to the replacement of the 'balloonist' belief that air/fluid carried signals and led to animation.

Volta invented the battery to prove that Galvani's findings were caused by electricity, rather than heat or the like. He worked in electrochemistry.

Batteries

Batteries work by a chemical process that leaves more ions at the anode; as these repel themselves, the ions flow down the conductor, assuming it is attached to the cathode or ground (positive/neutral charge, hence less ion dense than the anode).

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The Neuron

Neurons are electrically excitable cells that provide a means for information transfer throughout the nervous system.

Golgi Method for Staining Brains

Golgi developed a method of staining brain tissue that led to the acceptance and adoption of neuron theory, by allowing scientists to view individual neurons.

His method involved fixing silver chromate particles to the neuron membrane, leading to a black deposit on a yellow background.

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Different staining techniques reveal the distribution of different neuron types in the brain.

Types of Neurons

There are many different types of neurons (or brain cells, as they are referred to in lay-terms). For instance:

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Anatomy of a Neuron

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  • Dendrites receive information from terminals of other cells
  • The soma (cell body) contains the nucleus (keeps the cell alive and functioning).
  • The axon conducts electrical signals away from the cell body/soma - determines whether or not the cell fires by summating excitatory and inhibitory inputs.
  • The myelin sheath is a type of glial cell that protects the axon. It speeds the electrical conduction down said axon.
  • The Nodes of Ranvier (gaps in the myelin sheath) allow the jumping of charge from node to need, speeding conduction.
  • The terminals pass electrical signal to the dendrite of the next/target cell (through contact).
  • Schwann cells form part of the myelin sheath around the axon.

Action Potentials

Action potentials are also known as nerve impulses, and neurons that emit action potentials are said to have "fired".

They occur where the electrical membrane potential of a cell rapidly rises and falls; when placing an electrode tip inside the cell membrane reveals a negatively charged internal state of -70 mV - as the potential changes different 'gates' are opened and closed, leading to different flows of current.

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Initially, positively charged sodium ions enter the cell, before being pumped outside causing a polarity shift. These cells are then followed out by some positively charged potassium ions, leaving it in a negatively charged repolarization state.

An action potential can travel 1m of axon in 7ms.

Synaptic Communication

Neurons communicate through the synapse. Between the terminal buttons and the dendrites exists a space ('cleft') through which the two must communicate. The terminal buttons release transmissions, which then join onto the dendrites.

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Changes in neurotransmission at the synaptic cleft are the basis for learning, which we will explore in a later lecture.

There are three forms of communication:

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Reuptake

Reuptake is the process by which the sending neuron reabsorbs excess neurotransmissions, to clear the synapse.

Neurotransmitters

Neurotransmitters are chemicals used to transmit signals from neurons across the synaptic cleft.

Excitatory vs Inhibitory ([EI]PSP)

There are two types of neurotransmitters; inhibitory/excitatory post-synaptic potential. EPSPs bind to NA+ gates, whereas IPSPs bind to K+ channels; they counteract each other, meaning that the threshold of activation is being moved closer to and further away from depending on which neurotransmitters are released.

Types of Neurotransmitters

There are many major neurotransmitters, the two we'll look at are:

  • Glutamate is a key excitatory neurotransmitter.
  • GABA is a key inhibitory neurotransmitter.

Whether a cell fires reflects the summation of the excitatory (glutamate) and inhibitory (GABA) inputs.

PET

PET involves binding a radioactive atom to a molecule that has the same shape as a neurotransmitter and injecting this into the person.

When the neurotransmitter binds to its receptor the radioactive atom is released and this is detected by the scanner and translated into the images shown.

From imaging GABA and glutamate, we can tell they are densely distributed throughout the brain.

Neuromodulation

Neuromodulation is the more general, background-level, modulation and regulation of brain signalling; instead of transmitting a specific signal from a presynaptic cell to a postsynaptic partner, one neuron uses different neurotransmitters to signal several different neurons, and play a general role in moderating activation levels of neighbouring cells.

Neuromodulator Systems

There are 4 systems that each express different types of neurotransmitters; the dopamine, serotonin, cholinergic and noradrenaline systems.