1.Part Function

CELLBODY Receive messages from dendrites and transmit

them through axons.

DENDRITE Receives an impulse f,rom an axon.

AXON Transmits an impulse away from the cell body.

NODE OF RANVER Jumping points for the nerve impulse along an

axon membrane. Part of the axon or dendrite not

surrounded by a myelin sheath.

MYELIN SHEATH A fatty-like insulating substance formed by Schwann

cells, found around nerve fibres and which promote

faster transmission of nerve impulses.

SYNAPTIC ENDINGS Release of transmitter substances which will carry

an impulse from dendrites to nerve cell bodies

across a synapse.

3. A neuron is a nerve cell, consisting of a cell body from which projects dendrites and an axon.

1. (a) An electrical (polarity) change in a neuron.

(b) The state of an axon when it is not conducting a nerve impulse.

(c) A change in the ion (Na+/K+) distribution such as occurs in an axon during transmission of a nerve impulse.

2. (a) The neuron is not transmitting an impulse.

(b) The neuron is transmitting an impulse.

3. Because there is a difference in ion distribution on either side of the membrane, with a high concentration of Na+ on the outside and a high concentration of K+ and large negative ions on the inside.

4. The "sodium/potassium pump" ( active transport).

5. A reversal in the ion distribution inside and the outside of the axon.

6. The "sodium/potassium pump" is stopped: positive sodium ions move into the axon and

add themselves to the already present positive potassium ions

7. (a) The neuron becomes negative on the outside and positive on the inside.

(b) The neuron once again becomes positive on the outside and negative on the inside.

8. An impulse travels along an axon by means of a progressive wave of depolarization/ polarization (a wave of negativity) caused by the movement of sodium and potassium ions

in and out of the axon as the axon undergoes stimulation from resting potential to action

potential.

9. Because neuro-transmitter substances which cause an action potential to be initiated are

found only at the ends of the dendrites, the impulse is in a one-way direction from axon to

dendrites through the cell body.

10. Myelinated nerve fibres are surrounded by a sheath of myelin which acts an an insulator; the sheath is interrupted by nodes of Ranvier which are "jumping gaps" for the nerve impulse; both the myelin sheath and the nodes provide for faster transmission in myelinated nerve fibres than in unmyelinated fibres.

11. a. The time following an action potential when the neuron cannot be triggered to carry another impulse. The "pump" is restoring the original ion concentrations.

b. A neuron either fires and carries an impulse or does not. Increasing stimulus intensity can cause a neuron to fire more frequently but it cannot change the characteristics of an individual impulse.

1. (a) AXON To transmit a nerve impulse away from the cell body of a neuron.

(b) SYNAPTIC ENDING To cause release of neurotransmitter substanes.

(c) PRESYNAPTIC MEMBRANE Release of neurotransmitter sustances.

(d) SYNAPTIC VESICLES Contain neurotransmitter substances

(e) SYNAPT1C CLEFT To conduct neurotransmitter substances from axon to dendrite.

(f) NEUROTRANSMITER SUBSTANCE To transmit the action potential across a synaptic deft.

(h) DENDRlTE Transmission of an impulse towards the cell body of the neuron.

2. (a) The impulse travels along the axon from the cell body to the synapse.

(b) At the synaptic ending there is a release of neurotransmitter substances from synaptic vesicles as well as the release of calcium ions to flow into the synaptic ending.

(c) Calcium ions promote the release of neurotransmitter substances into the synaptic cleft.

(d) By acting on the postsynaptic membrane, the neurotransmitter substances excite (or inhibit) the transmission of a nerve impulse from one neuron to another across the synaptic cleft.

(e) The synaptic cleft "conducts" the neurotransmitter substances between two neurons.

(f)The postsynaptic membrane becomes depoparized by the neurotransmitter substances fitting into specific receptor sites on the postsynapffc membrane.

(g) Because enzymes destroy (and recycle) them.

(h) Acetylcholine is one of a number of transmitter suhtances which set up (initiate) an action potential in dendrites.

1. To provide an instant, unconscious response to a potentially dangerous stimulus.

2. (a) RECEPTOR Generates an afferent nerve impuloe

(b) SENSORY NEURON Transmits nerve impulse from receptor to the central nervous system (nerve cord).

(c) INTERNEURON Transmits the sensory (afferent) nerve impulse from the sensory neuron to the motor (efferent) neuron.

(d) MOTOR NEURON Transmits the nerve impulse from the interneuron to an effector (a muscle or a gland).

(e) EFFECTOR ORGAN Receives the motor (efferent) impulse and reacts.

3. (a) Skin receptor is stimulated.

(b) Axon of sensory neuron carries the sensory (efferent) impulse.

(c) Sensory impulse goes through the dorsal root ganglion.

(d) Sensory impulse goes through dorsal root of spinal nerve.

(e) Synapse between the sensory neuron axon and dendrite of interneuron in the dorsal horn of the grey matter in nerve cord.

(f) Impulse travels through interneuron.

(g) Synapse between Interneuron axon and motor neuron dendrite.

(h) Motor neuron in ventral horn of grey matter carries the impulse

(i) along the axon of the motor neuron (now an efferent impulse)

(j) out through a ventral root of the spinal nerve.

(k) The effector (muscle) receives the efferent (motor) impulse and contracts

Sample Exam Questions

1. A a nerve impulse arrives at the synaptic ending of an axon where calcium ions enter, causing vesicles to move to the presynaptic membrane. This releases a neurotransmitter substance from the synaptic vesicles; the transmitter substances move across the presynaptic membrane and into the synaptic cleft and across to receptors in the postsynaptic membrane which then becomes depolarized, setting up an action potential in the dendrite.

2. A stimulus sets up a nerve impulse in a receptor. This impulse is carried via a sensory nerve (.afferent nerve) through a dorsal root ganglion and the dorsal horn of a spinal nerve into the grey matter of the nerve cord. Here there is a synapse to an interneuron which carries the impulse to another synapse, Ws one to a motor neuron in the ventral horn of the nerve cord. The impulse goes on through the ventral root of a spinal nerve and on through a motor nerve (-efferent nerve) to reach and set up a response in an Effector.

3. The nerve impulse is propagated along a nerve fibre as a "wave of negativity" caused by sodium ions flowing rapidly into the axon as a result of the opening of sodium gates.

Depolarization occurs, and an action potential is generated. This action potential becomes a

resting potential by a reversible outflow, flrst of potassium ions and then of sodium ions.

This changa the polarity of the interior of the axon relative to its exterior. In myelinated

nerva the impulse arcs across noda of Ranvier on its way towards the effector.

4. Both action potential and resting potential involve differences in potassium/sodium and organic ion concentrations inside and outside the the nerve fibre. An action potential is set up a result of this difference in polarity. During an action potential there is an inflow of positive sodium ions; enough to cause the outside of the nerve fibre to become negative relative to the inside. After the action potential has passed a given point, the nerve fibre retums to neutral., i e., a resting potential. The resting potential is caused by the retum of the positive potassium ions to the inside as well as the reinstatement of the "sodium/potassium pump" moving sodium ions to the outside. The result is that the outside of the nerve fibre becomes positive again.