6 - Neurons & Information Flow

Neurons

Basic signalling units of the nervous system (carry signals)

Glial cells

Support cells (support neurons)

• Not just physical supports, they also help with info processing + movement

Oligodendrites

Supports + insulates axons by forming myelin

• Glial cell part of the CNS

Astrocytes

• Large portion of cells in the brain

• Forms the blood-brain-barrier

  • Star shaped - lots of branches (has plugs @ their ends to block + monitor movement of molecules)

• Provides neuron with substrates for ATP production

• Helps maintain homeostasis by taking up H₂O + K⁺

Blood-Brain-Barrier

Highly selective semi-permeable membrane of cells that lines the cells in the brain (heavily moderates what enters brain cells - prevent harmful substances from entering the cells and damaging the brain)

Microglia

specialized immune cells in CNS; remove damaged cells and invaders

• Exists in the CNS, but not apart of it

Ependymal Cells

creates the lining of the ventricles and make cerebrospinal fluid

• glial cell apart of CNS

Schwann Cells

insulates (wraps around) axons by forming myelin (speeds up signals)

• Gaps between myelin = Nodes of Ranvier

• glial cell apart of PNS

Satellite cells

form supportive capsules around nerve cell bodies in ganglia (collection of nerve cell bodies outside CNS)

• Non-myelinating

• glial cell apart of PNS

Sensory Neurons

conduct signals/messages to the spinal cord and the brain

Motor Neurons

conduct signals/messages from the brain and spinal cord

Interneurons

neurons completely contained within the CNS; transmits impulses between other neurons

• Part of a reflex arch

Soma (cell body)

contains genetic info and organelles

• integrates postsynaptic potentials

Dendrites

receives messages from other neurons or sensory receptors

Axon

conduct electrical signals from the axon hillock to the terminal buttons

Mechanically-gated ion channels

open in response to physical forces (ie. pressure and stretch)

• Found in sensory neurons

Voltage-gated ion channels

open in response to changes in the cell’s membrane potential

• Amount of voltage (potential) to open the channel depends on the channel type

• Voltage gated Na⁺ + K⁺ channels are important in the initiation and the conduction of electrical signals along the axon

Saltatory Conduction

the process of an action potential jumping to the unmyelinated parts of the axon

Synapse

the region where an axon terminal meets its target cell

Presynaptic cell

the neuron that delivers a cell signal to the synapse

Postsynaptic cell

the cell that receives the signal from the synapse

Electrical synapses

Electrical signals passed from the cytoplasm of one cell to another through pores of gap junctions proteins

• Synchronizes activity within a network of cells

• Found in the CNS, smooth muscle, cardiac muscle + some non-excitable cells

  • Allows for muscles/organs to work at a similar pace, not randomly (heart beating the same)

Chemical synapses

neurocrine molecules carry signals from one cell to the next; electrical signal of presynaptic cell converted to a chemical signal

• Signal molecules cross synaptic cleft + bind to a receptor on the target cell

• Majority of synapses

Steps of Synaptic Transmission

1. Synthesis

2. Transportation and Storage

3. Release

4. Binding

5. Reuptake

6. Degreation

Neurotransmitter

act on receptors in target cells close to the neuron that secretes them

• Most can bind to more than just one type of receptor

• Can have a different effect depending on the type of tissue