Module 1 The Nervous System

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Reflect and Connect

Reflect on the Big Picture

From the Big Picture scenario, your rapidly beating heart, your increased breathing rate, and the simple walking across the room take on a whole new meaning. In this lesson, you have examined how the information communicated through neurons can then be transmitted across the gap between neurons, or between a neuron and a muscle. You have examined the various types of neurotransmitter substances found naturally in the body, and you should now understand how they can speed up or slow down communication. You have also looked at the effect of drugs on the synaptic gap.

Lesson Summary

In this lesson, you have explored the following focusing questions:

• How does the anatomy and function of the synaptic gap and neuromuscular junction facilitate the transmission of nerve impulses between neurons, and between neurons and effectors?
• How do chemicals that we take into our body and disorders such as Parkinson’s Disease compromise synaptic transmission?

The parts of the nervous system: neurons, neural pathways, receptors, effectors and synapses all fir together like the pieces of a puzzle. If one piece fails to fit, the system doesn’t work right. Disorders such as Parkinson’s Disease and chemical substances such as drugs can interrupt the function of the system.

 

Glossary

acetylcholine: one of the most common neurotransmitters of both the somatic nervous system and the parasympathetic nervous system; functions by binding to receptors on the postsynaptic membrane and either depolarizing or hyperpolarizing the membrane

 

cholinesterase: an enzyme necessary to decompose acetylcholine in the synaptic cleft so that the products (choline and ethanoic acid) can be reabsorbed by the presynaptic membrane; also called acetylcholinesterase

 

dopamine: generally an excitatory neurotransmitter in the CNS

 

excitatory neurotransmitter: neurotransmitters that promote nerve impulse transmission in the postsynaptic membrane by opening sodium channels

 

GABA (gamma aminobutyric acid): an inhibitory neurotransmitter in the CNS

 

glutamate: an excitatory neurotransmitter in the CNS

 

inhibitory neurotransmitter: neurotransmitters that hinder nerve impulse transmission in the postsynaptic neuron by hyperpolarizing it

 

neuromuscular junction: tiny gap located between an axon terminal and a muscle cell

 

neurotransmitters: chemical messengers released from the synaptic knob of a neuron at a synapse that diffuse across the synaptic cleft, bind to specially shaped protein receptors on the postsynaptic membrane, and stimulate the postsynaptic neuron

 

norepinephrine: neurotransmitter released by sympathetic neurons of the autonomic system to produce an excitatory effect on target muscles; also called noradrenalin

 

postsynaptic neuron: the receiving neuron

 

postsynaptic membrane: the cell membrane of the cell body, or  the dendrite on the other side of the synapse

 

presynaptic neuron: the sending neuron

 

presynaptic membrane: the surface membrane surrounding the synaptic knob and facing the synaptic cleft

 

receptor proteins: protein molecules located on the postsynaptic membrane that have complementary shapes to certain neurotransmitters, allowing the neurotransmitter to fit into them

 

serotonin: an inhibitory neurotransmitter in the CNS

 

synapse: the location or junction in a neural pathway where one neuron communicates with another neuron; a tiny gap between the synaptic terminal of an axon and the signal receiving dendrite or cell body of another neuron or an effector, such as a muscle

 

synaptic cleft: a tiny space separating the synaptic knob of a transmitting neuron from a receiving neuron or effector cell

 

synaptic knob: the tiny enlarged ending on an axon terminal

 

vesicles: tiny membranous sacs that, in this case, contain neurotransmitters; also called synaptic vesicles