Neuron

Lecture 1: The Neuron

Neuroscience- study of the body’s nervous systems

The nervous system controls every aspect of human behaviour. E.g. curiosity, pain, pleasure, movement, reasoning, learning, memory, emotion and madness.

CNS- brain and the spinal cord

PNS- Everything else.

Neuroscience

Levels of analysis:

-          Molecular- look at the important chemicals involved

-          Cellular- understand what the cells do

-          Systems- how the cells and the chemicals come together to make systems

-          Behavioural

-          Cognitive

Neurons

-          Process information

-          Can communicate with themselves and with other parts of the body (not neurons)

-          Sense environmental changes (weather/ temperature changes)

-          Communicate changes to other neurons

-          They communicate by expressing unique chemicals, and neurotransmitters and by being electrically excitable

-          Command body response

-          Can fire action potentials

Glia – Insulates, supports, nourishes, and contributes to regulating neurons. They are largely the support players. Are not electrically excitable and cannot fire action potentials

The Neuron Doctrine

-          The neuron is the basic functional unit of the brain

-          Brain function and thus human behaviour arises from communication between different types of neurons

Neurons communicate using:

-          Electrical signals

-          Chemical signals

To understand how the brain works, you need to understand how neurons function

The neuron

Is composed of:

-          Soma (cell body)

-          Dendrites

-          Axon

All these different compartments of neurons have specialised functions

·       Is a cell that has a number of appendages-  which help to receive and transmit signals

·       Within one cell you can have that same cell doing a number of different things

·       Cells are segregated to do different things

·       Dendrites are the antenna- can listen to what other neurons are saying

·       Cell body- the engine- ensures all the proteins are being made

·       depending on the message of the cell- 1 axon so there is 1 coherent message that leaves that service compared to the number of different dendrites that can listen in its environment.

·       Compare with other non-neuronal cells in the body which are mainly round/spherical

·       The structure of neurons allows for the cell type to process

Sometimes, the spine, which is not smooth, has other cells making contact on our surface. The spine increases the surface area, allowing more contact.

Neurons are social beings they are never on their own

 The Soma

Composed of:

-          The cytosol: watery fluid inside the cell

-          Organelles: membrane-enclosed structures within the soma

-          Cytoplasm: contents within a cell membrane (e.g. organelles, excluding the nucleus)

Organelles

The Nucleus

Responsible for:

-          Gene expression

-          Transcription

-          RNA processing

Neuronal DNA gets turned on- causes MRNA to be made then protein synthesis

A major site for protein synthesis- Rough endoplasmic reticulum

Smooth ER and Golgi Apparatus

-          Sites for preparing/ sorting proteins for delivery to different cell regions (trafficking) and regulating substances.

-          All proteins are made here but the proteins that endow dendrites with their function will be trafficked to the dendrites

-          Golgi is unique. Every cell has one but in terms of the neuron, it is really important in terms of packaging and targeting cargo.

The brain is highly energy-dependent

 If Neurons are deprived of energy for a few minutes they begin to die- neurons do not regenerate

The neurons you are born with are the ones you will have for the rest of your life

Mitochondrion

-          Generates energy

-          Site of cellular respiration (inhale and exhale)

-          Krebs cycle

-          ATP- cells energy source

The neuronal membrane

-          Barrier that encloses cytoplasm

-          ~5nm thick

-          Protein concentration in the membrane varies

-          Structure of discrete membrane regions influences neuronal functions

-          The difference between the neuronal membrane and all other membranes is what is expressed within your plasma membrane.

-          Neurons don’t have flowing electrons instead they have ion channels- protein structures which are selectively permeable for inorganic ions- the basis of neuronal excitability. Non-excitable cells do not have them

Electrons generate electricity- whenever you get an electrical charge you get electricity

The cytoskeleton

-          Not static (constantly changing)

-          Internal scaffolding of neuronal membrane

-          Three “bones”

·       Microtubules

·       Microfilaments

·       Neurofilaments

The axon

Axons are responsible for relaying/sending information from one neuron to the next

-          Axon hillock (beginning)- where the action potential starts

-          Axon proper (middle)

-          Axon terminal (end)

Differences between the axon and the soma

-          ER does not extend into the axon

-          Protein composition: Unique

The Axon terminal

Differences between the cytoplasm of the axon terminal and axon

-          Presence of synaptic vesicles- not found in any other cells which store the neurotransmitter and store the chemicals that carry the information.

-          These cannot be free-flowing because the enzymes may degrade them which they are unable to do in the presynaptic terminal.

-          Allows to release of a certain amount of neurotransmitter

-          Abundance of membrane proteins

-          Large number of mitochondria- energy

The Synapse

-          Point of communication between neurons

-          Axon is referred to as the presynaptic location of the neuron

-          Occurs by synaptic transmission

-          Electrical to chemical to electrical transformation

-          Synaptic transmission dysfunction- mental disorders

Types of Synapses

Chemical synapses- communicate with chemicals (neurotransmitters)

Electrical synapses- communicate with electricity

The flow of information between neurons

Afferent and Efferent Axons

-          Afferent (carry to): carry information toward a particular point

-          Efferent (carry from): carry information away from a point

Dendrites

-          Act as the ‘antennae’ of neurons since they receive information relayed from the axons.

-          Dendrites are responsible for receiving & processing information sent from the axon/s of other neurons- they are endowed with specific proteins (receptors)

-          Unlike axons which are normally single fibres, dendrites have numerous branches

-          Dendritic tree

-          The majority of all the synapses & receptors are located on dendrites -> dendrites referred to as the postsynaptic location of the neuron

-          Dendrites can be ‘smooth’ or ‘spiny’- postsynaptic (receives signals from axon terminal)

Classification based on the number of neurites

-          Single neurite- unipolar These are usually sensory neurons, neurons in your periphery that are there to sense any information

-          Two or more neurites- bipolar (two), multipolar more than two

Classification based on dendritic and somatic morphologies

-          Stellate cells- Star shaped

-          Pyramidal cells- pyramid-shaped

-          Spiny or aspinous

Neuron’s structure correlates with function

An extraordinary diversity of neurons within the brain allows for many brain functions e.g.

-          Thought processes

-          Motor activity

-          Pain

-          Senses (hearing, sight)