1. Neurons Aims: Must be able to describe and label neuron.
Should be able to relate the structure of neurons to the functions they perform.
Could be able to outline the process by which a nerve impulse is passed along a neuron.

2. Nerve cell (neuron)
Nerve cells are the basic unit of the nervous system.
Axons and dendrites may vary in length.
A number of neurons bound together is called a nerve.

3. Types of Neurons Sensory (Affector) neurons PNS to CNS
Motor (Effector) neurons
CNS to PNS
Inter/connecting neurons
Found in CNS

4. Activity
Answer the questions from pages 95 and 96 in Biozone book.

5. Communication between neurons
The cells (receptors) of a sensory nerve detect an environmental disturbance.
Sensory neurons generate a signal that is passed as an electrical message between neurons to particular effector cells.
Adjacent neurons do not actually touch each other.
There is a gap between them called the synaptic cleft.
The connection between the axon of one neuron and the dendrite of another is called a synapse.

6. The Synapse
As the impulse reaches the axon terminal the terminal produces chemicals known as neurotransmitters.
Neurotransmitters diffuse across the synaptic space.
Neurotransmitters bind to the dendrites of the next neuron.
Neuron then generates and carries an electrical impulse to it’s axon terminals.

7. Neurotransmitters
Neurotransmitters are specialised chemical messengers:
produced by nerve cells
transported in the axon
released at the synapse
cause chemical and electrical changes in adjacent cells.
Most neurotransmitters play different roles throughout the body, many of which are not yet known.

8. Activity
Answer the questions from page 101 in Biozone book.

9. Neurohormones
A neurohormone is any hormone secreted by or acting on a part of the nervous system.
Neurohormonal activity is distinguished from that of classical neurotransmitters as it can have effects on cells distant from the source of the hormone.

10. Neurohormone action:

11. Neurohormone action:
Neurons in the hypothalamus in the brain secrete neurohormones into blood capillaries that become associated with the pituitary.
Signals received by cells of the pituitary are transduced and the pituitary responds by producing a hormone as instructed.
This hormone enters the bloodstream and is transported to its target cells.

12. The Receptors
Sensory neurons serve as the body’s receptors as they are able to detect disturbances in the environment:
Chemoreceptors:
chemicals
Mechanoreceptors:
pressure
Photoreceptors:
light
Thermoreceptors:
temperature
Pain receptors:
pain

13. The Nerve Impulse Cell membrane of an axon is polarised:
(difference in charge between the inside and outside of the cell).
An axon at rest (not transmitting an impulse) negatively charged on the inside relative to the outside.
This is called a resting potential. K Na Na K

14. The Nerve Impulse
To become polarised: sodium – potassium pumps actively pump sodium ions out of the cell and potassium ions into the cell.
Three sodium ions are expelled for every two potassium ions pumped in. K Na Na K

15. The Nerve Impulse Na+ accumulates outside and K+ inside.
They are both positive ions - but more ++ outside – so: negative inside and positive outside. K Na Na K

16. The Nerve Impulse
As the impulse moves along the axon, the permeability of the membrane changes…
… positive ions – Na+ move into the cell –
This results in the outside being more negative than the inside… K Na Na K

17. The Nerve Impulse
A nerve impulse involves a change in the charge across the axon membrane.
A nerve impulse is a wave of electrical change (an action potential) that passes rapidly along an axon.
After the nerve impulse has been transmitted – the distribution of ions across the cell membrane is restored. K Na Na K

18. Action Potential

19. Activity
Video:
Answer the questions from pages 100 in Biozone book.

20. After Nerve Impulses
After the nerve impulse has been transmitted along the axon of one neuron it is transmitted further to:
Another neuron
An effector - Muscle
An effector - Gland

21. Neuron pathways
A neuron cell body may have hundreds of axon terminals synapsing with it.
Two kinds of pathways:
Diverging pathway
Converging pathway

22. Diverging Pathway Single axon links to several postsynaptic neurons
One cell can influence many others.

23. Converging Pathway Several axons link to few postsynaptic neurons
One cell can be influenced by many others.

24. Neurotoxins.
Homeostatic mechanisms, hormonal and nervous, can be brought to a halt by adverse event.
Toxins often act on the nervous system, causing paralysis and pain, even death, unless treatment is obtained immediately…

25. Reflex Arc Happens in situations with extreme stimulus.
Not enough time to involve the brain without serious injury.
Relay neurones in the spinal cord pass message from sensory neuron straight to motor neuron, they also transmit a pain signal to the brain.
React to the stimulus – Then feel pain after.

26. Sensory (afferent) nerves
Comparing Responses
Reflex Arc
Voluntary Response
Involuntary Response
Receptors Involved
General Pain
Any
Transmission to CNS
Sensory (afferent) nerves
CNS Involved
Spinal Cord
Brain
Brain - Hypothalamus
Transmission from CNS
Motor Neurons
Autonomic Nerves

27. Activity
Answer the questions from page 99 in Biozone book.