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Coordination and Irritability

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(a) (b) (c) (d)
Figure 4.6: Structural classification of neurones (a) unipolar (b) bipolar (c) pseudo unipolar and (d) multipolar

Exercise 4.1 In an inactive neurone, the axoplasm
is negatively charged with respect
1. How does the structure of the to the conditions outside of the cell.
nervous tissue differ from other
body tissues?. The difference in electrical charge is
2. How are nervous tissues adapted to maintained by active transport of sodium
perform their functions? ions out of axoplasm. A cell in this state
is said to have a resting potential and it
3. Describe the types of neurones. is polarised. At this state, the potential
difference existing across the cell surface
4.1.2 Nerve impulses membrane inside the cell with respect
Task 4.3 to the outside part is negative, which is
Search for information from the library about -70 mV. At this time, the axon does
and internet sources on the nerve not conduct any impulse. The cytoplasm
impulses including resting potential inside the axon has a high concentration of
and phases of action potential. Write K and low concentration of Na . This is
+
+
short notes on the searched information.
contrary to the outside part which has a low
concentration of K and high concentration
+
A nerve impulse is an electrical signal that +
travels along the axon. It is generated when of Na . The resting potential is maintained
by active transport and passive diffusion
the nerve cell is activated. Movement of of ions. It is active transport of ions
ions in and out of the neurone causes a against the electrochemical gradient of
sudden change in the voltage across the sodium/potassium (Na /K ) pump. These
+
+
wall of the axon. This triggers a wave of are carrier substances located in the cell
electrical activity that passes from the cell surface membrane. They are driven by
body along the length of the axon to the energy supplied by ATP (Figure 4.7). The
synapse. rate of diffusion is characterised by the
permeability of the axon membrane to the
Resting potential ion. The K has membrane permeability
+
This occurs when the neurone is at rest. of about 20 times greater than that of Na .
+

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