BI0005 - Lecture 1 - nerves

The Central Nervous System - The brain and spinal chord

• The Peripheral Nervous System
• Somatic - controls the musculo-skeletal system
• Visceral - controls the body's organs

The nerve cells that transfer information within the body.

Long-distance electrical signals, and short distance chemical signals.

As an electrical current, consisting of the movement of ions

By large groups of neurons organised into a brain or into simple clusters called ganglia

Neurons which transmit information s from eyes and other sensons that detect external stimuli or internal conditions (blood pressure, blood CO² levels)

Neurons which only make local connections - the vast majority of the neurons in the brain.

Neurons which transmit signals to muscle cells, causing them to contract

In the CNS

In the PNS

In the cell body

The highly branched extensions that receive signals from other neurons - a typical neuron has numerous dendrites

An extension that transmits signals to other cells - a neuron has only one

The cone-shaped region of the axon where it joins the cell body - this is typically where the signals that travel down the axon are generate

The junction where each branched end of an axon transmits information to another cell.

The part of each axon branch that forms a synapse.

Chemical messengers which pass information from the presynaptic neuron to the receiving cell at the synapse. Either excites or inhibits the postsynaptic neuron

The transmitting neuron

The neuron, muscle, or gland cell that receives the signal.

Yes, some interneurons have branched dendrites that take part in about 100,000 synapses whereas other neurons with simpler dendrites have far fewer synapses.

Supporting cells which may nourish neurons, insulate axons of neurons, or regulate extracellular fluid surrounding neurons.

• It is a layer of electrical insulation that surrounds vertebrate axons.
• They are produced by two types of glia - Oligodendrocyctes in the CNS and Schwann cells in the PNS.
• They are made mostly of lipid, which is a poor conductor of electrical current.

• Cell body - size and shape
• Dendrites - number, branching, length
• Axon - length, diameter, branching
• Axon - myelinated or unmyelinated
• Synaptic terminals - number and structure
• Synaptic transmission - chemical or electrical

Not in most cases.

• Synapses which contain gap junctions which do allow electrical current to flow directly from one neuron to another.
• They synchronize the activity of neurons responsible for certain rapid, unvarying behaviors. e.g. escape responses

Synapses which involve the release of a chemical neurotransmitter by the presynaptic neuron. - the majority

Hundreds or even thousands.

They are multiple membrane-bounded compartments into which the neurotransmitters are packaged by the presynaptic terminal after the neurotransmitters are synthesized.

The narrow gap that separates the presynaptic neuron from the post synaptic cell.

• The action potential's arrival depolarizes the plasma membrane, opening voltage gated channels that allow Ca²⁺ to diffuse into the terminal
• The rise in CA²⁺ concentration in the terminal causes some synaptic vesicles to fuse with the terminal membrane, releasing the neurotransmitter.
• The neurotransmitter then diffuses across the synaptic cleft.
• The neurotransmitter binds to the receptor portion of the ligand-gated ion channels in the postsynaptic membrane, opening the channel.
• The neurotransmitter is released from the receptors and the channel closes. 
• Synaptic transmission ends when the neurotransmitter diffuse out of the synaptic cleft, is taken up by the synaptic terminal or by another cell, or is degraded by an enzyme

• Acetylcholine (ACh)
• Glutamate (GLU)
• Noradrenaline (NA)
• GABA (gamma-aminobutyric acid)

• 1. To be stimulated by a neurotransmitter released by another neurone
• 2. To respond to the stimulus, either by being excited or inhibited
• 3. To convey a message, via an action potential, to its terminal
• 4. To release a neurotransmitter from the terminal which will stimulate another neurone (or muscle cell)
• 5. To inactivate the neurotransmitter that it has released.

• 1. A precursor peptide is synthesized in the rough ER.
• 2. The precursor peptide is split in the Golgi apparatus to yield the active neurotransmitter
• 3. Secretory vesicles containing the peptide bud off from the Golgi apparatus
• 4. the secretory granules are transported down the axon to the terminal where the peptide is stored.

• 1. Enzymes convert precursor molecules into neurotransmitter molecules in the cytosol.
• 2. Transporter proteins load the neurotransmitter into synaptic vesicles in the terminal where they are stored.

• Actin filaments - 5nm - Shape of neurone
• Intermediate filaments - 10nm - Axonal 'neurofilaments'
• Tubules - 20nm - axonal neurotubules

• Orthograde transport is movement of molecules/organelles outward, from the cell body (soma) to the synapse or cell membrane.
• Orthograde movement of transport vesicles along the microtubules is mediated by kinesins

• Retrograde transport is movement of molecules/organelles inward, away from the synapse or plasma membrane towards the cell body or soma.
• It is mediated by dynein, and is used to send chemical messages back from the axon back to the cell

Because all the events in neurotransmitter synthesis and release require energy, so neurones need to generate ATP constantly

• 100,000 cells
• 4 kilometers of axon
• 500 metres of dendritess
• 1,000,000 synapses

Glial cells, sometimes called neuroglia or simply glia, are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the brain and peripheral nervous system.

• Oligodendrocytes
• Astrocytes
• Microglia

They form myelin sheaths for several axons

• They control K+, glutamate, and Ca2+ in the extracellular space. 
• Astrocytes adjacent to active neurons cause nearby blood vessels to dilate, increasing blood flow to the area and enabling the neurons to obtain oxygen and glucose more quickly.
• They play important roles in the blood-brain barrier and in local blood flow.

They are Microglia are specialized macrophages, capable of phagocytosis, that protect neurons of the central nervous system.