Cells of the Nervous System Flashcards
Main structures of neurons
- Soma (cell body)
- Dendrites (branches)
- Axon
- Terminal buttons (terminals, bouton)
Divisions of neurons according to function
- Sensory neurons- detect changes in external and internal environment (CNS and PNS, light, sound, odours, touch…).
- Motor neurons- controls muscle contraction and also gland secretion (CNS and PNS).
- Interneurons- lie entirely within the CNS and are involved in cognition (i.e.,perceiving, learning, remembering and executive functioning such as decision making).
Divisions of neurons according to structure
- Multipolar neuron – neuron with one axon and many dendrites attached to its soma.
- Bipolar Neuron – neuron with one axon and one dendrite attached it its soma.
- Pseudo-Unipolar Neuron– neuron with one axon attached to its soma; the axon divides, with one branch receiving sensory information and the other sending the information into the central nervous system.
Describe the function of astrocytes
- “Star cells”
- Provide physical support to neurons
- Provide nourishment
- When neurons die they clean up debris and form scar tissue, providing structure where damaged neuron was. However, they cannot take the function of the neuron.
- Control chemical composition of fluid surrounding neurons
- help form the blood-brain barrier
- Secrete neurotrophic factors
Take up K+ & neurotransmitters
Describe the function of oligodendrocytes
- Support axons and produce the myelin sheath -insulation, lipids
- Nodes of Ranvier – bare portion of axon
- wraps around several adjacent axons in the CNS
- single schwann cell wrapped around the PNS axon
Describe the blood brain barrier
A semipermeable barrier between the CNS and circulatory system, which helps to regulate the flow of nutrient rich fluid into the brain.
Describe the Area Postrema
a region of the medulla (hind brain) where the blood-brain barrier is weak.
This allows toxins in the blood to stimulate this area, which initiates vomiting – poison expelled from the body
Describe the stages of the action potential graph
Action Potential – brief electrical impulse that provides the basis for conduction of information along an axon.
Threshold of Excitation –The value of the membrane potential that must be reached to produce an action potential
Hyperpolarization – increase in the membrane potential of a cell
How can Na+ be found outside of the cell, when both forces (diffusion and electrostatic pressure tend to push it inside?
- Protein in the membrane that pushes Na+ out of the cells
- Active mechanism in the membrane that extrudes Na+ out and transports K+ in
Describe the generation and propagation of the action potential.
- As depolarisation starts and the threshold of excitation is reached, Na channels open and Na+ ions move into cell changing the membrane potential from – 70 to +40 mV.
- The K+ channels open after a slight delay and K+ begins to leave the cell
- The sodium channels become blocked when the action potential reaches its peak (+40mV). No more Na+ ions can enter.
- K+ ions move out of the cell, bringing the membrane potential back towards its resting potential.
- Potassium channels close and sodium channels re-set.
- The membrane potential overshoots its resting –70mV and hyperpolarization occurs as a result of extra K+ ions outside the axon. As they diffuse away the resting membrane potential is restored.
Define Neuronal Integration
The process by which inhibitory and excitatory postsynaptic potentials summate and control the rate of firing of a neuron
What are the two postsynaptic potentials
- Excitatory Postsynaptic Potential (EPSP) – excitatory depolarization of the postsynaptic membrane.
Inhibitory Postsynaptic Potential (IPSP) – inhibitory hyperpolarization of the postsynaptic membrane.
What determines the nature of postsynaptic potentials?
- The nature of PSP is determined by postsynaptic receptors – which ion channels they open
○ 3 major types of ion channels: Na+, K+ and Cl-
How does each major type of iron channel cause a postsynaptic potential.
- Neurotransmitter that open Na+ channel = (+) Na+ charge causes depolarisation. = excitatory post synaptic potential.
- Potassium leaves the cell if K+ channel is opened = inhibitory post synaptic potential
- Chloride ion channel opens = C- ions move into cell = hyperpolarisation = inhibitory post synaptic potential
Describe how metabotropic receptors work.
Indirect opening of ion channel.
- Molecule of transmitter substance bind with receptor
- Receptor activates G protein
- Alpha-subunit breaks away, binds with ion channel and opens it
- Ions into the cell, produced postsynaptic potential
