Overview Of The Nervous System Flashcards
What are the components of CNS?
- Brain
- Spinal cord
- Collection of cells bodies called a nucleus
What are synapses ?
- Specialized junctions between neurons that facilitate transmission of impulses
- Axons end as swollen bulbs where they interact with other cells
- Vary in number-few to thousands
- Synapses can occur between axon and dendrite (axodendritic), axon and soma (axosomatic) or between axon and another axon (axoaxonic)
- They could also occur between axons and effector cells e.g. muscle cells (neuromuscular junction), gland cells
What are the types of synapses?
- electrical
- chemical synapse-neurotransmitter- acetylcholine
Explain the chemical synapse
- pre and post synaptic membranes
- Synaptic cleft (extracellular space between membranes). No direct contact between the two membranes.
- Involves the release of chemical substances (neurotransmitters) from vesicles in presynaaptic axon into the synaptic cleft to reach the post synaptic membrane of another cell.
What is the presynaptic element (bouton, knob)?
Where Neurotransmitter (chemical) is produced and packaged into vesicles
What is the synaptic cleft?
The 20-30 nm space- neurotransmitter is released into this space to reach postsynaptic membrane
What is the post synaptic membrane?
Target of neurotransmitters
What are the common types of neurotransmitters?
- acetylcholine
- Catecholamines
- serotonin
- amino acids- GABA, GLY (inhibitory), GLU (excitatory), ASP,
- nitric oxide- synthesized within synapse
- Small peptides- substance P, VIP, CCK, HRH produces by APUD cells
Describe acetylcholine as a common types of neurotransmitters
- neuromuscular junction SNS
- ANS pre- and postsynaptic neurons
- used by cholinergic neurons
- Degraded by acetylcholinesterase
Describe Catecholamines as a common type of neurotransmitter
- precursor tyrosine
- epinephrine (adrenaline)- used in adrenergic drugs
- norepinephrine
- used by catecholaminergic neurons in CNS & ENS
- removed by COMT, MAO
Describe serotonin as a common type of neurotransmitter
Precursor- tryptophan
Used by serotonergic neurons
Describe the neuromuscular junctions (NMJ)- motor end plates
- NMJ contact between terminal ends of axons and muscle fiber
- chemical synapsis occurs here
- Numerous synaptic vesicles are seen at the cleft. No myelin is present at this part of the axon only single Schwann cell layer
- release of the neurotransmitter (acetylcholine) into the post synaptic membrane causes chemically gated sodium channels on this membrane to open and allow influx of sodium ions into the muscle cell creatin an action potential that excites muscle contraction
- remaining acetylcholine in the synaptic cleft is broken down by acetylcholinesterase enzyme and prevents further excitation of the muscle cells.
How do polio, herpes, rabies affect the nerve?
Neuroinvasive viruses via retrograde transport
How does the tetanus toxin affect the neuron?
Block the release of inhibitory neurotransmitters (glycine and gamma- amino acid butyric acid) in. CNS
How does the myasthenia Gravis affect the neuron?
Antibodies against acetylcholine receptors
