1. sgs-psychology.org.uk Structure and Function of the Nervous System An introduction to Physiological Psychology

2. sgs-psychology.org.uk Structure and Function of Nervous System Organisation of Nervous System: The peripheral nervous system connects the CNS with the sensory receptors, muscles and glands. Brain Spinal Cord Somatic Nervous System Central Nervous System Peripheral Nervous System Sympathetic Branch Parasympathetic Branch Autonomic Nervous System

3. sgs-psychology.org.uk Structure and Function of Nervous System The peripheral nervous system: –Subdivided into: Somatic nervous system: Consists of sensory and motor neurons that bind together to create nerves to transmit messages to sensory receptors Autonomic nervous system: Controls glands and smooth muscles in bodily organs –Sympathetic nervous system: arouses the body –Parasympathetic nervous system: slows down body processes

4. sgs-psychology.org.uk Structure and Function of Nervous System How signals travel through the system: –The nervous system is made up of nerves – bundles of cells called neurones. Myelin Sheath Node of Ranvier Cell body Nucleus Dendrites Axon

5. sgs-psychology.org.uk Structure and Function of Nervous System Three types of neurone: –Sensory: Carry input messages from the sense organs to the spinal cord and brain –Motor: Transmit impulses from the brain and spinal cord to the muscles and organs –Interneuron: Perform connective or associative functions in the nervous system

6. sgs-psychology.org.uk Structure and Function of Nervous System Conduction of a nerve impulse: –Neurons are surrounded by a salty liquid environment which has a high concentration of sodium ions (Na+) –The inside of the neuron has some positively charged potassium ions (K+) and many other negatively charged ions –The combination creates the resting potential at -70 millivolts.

7. sgs-psychology.org.uk Structure and Function of Nervous System The action potential: –When a neurone is stimulated sodium floods into the cell making it more positive. This is called depolarisation. –In order for the signal to be sent, depolarisation much reach -0.65 millivolts. –If this happens then the neuron ‘fires’ according to the all-or-nothing rule. –The sodium is then pumped back out, readying the cell for the next signal.

8. sgs-psychology.org.uk Structure and Function of Nervous System The action potential: 1 + + + + + + + - - - - - - - The polarised membrane at resting potential. Na + K+K+

9. sgs-psychology.org.uk Structure and Function of Nervous System The action potential: 2 - - + + + + + + + + + + + + + + - - - - - - - - - - - - When stimulated sodium ions rush in to the cell causing depolarisation

10. sgs-psychology.org.uk Structure and Function of Nervous System The action potential: 3 + + - - + + + + + + + + + + - - + + - - - - - - - - - - As the wave of depolarisation flows along the axon, the cell is repolarised behind it.

11. sgs-psychology.org.uk Structure and Function of Nervous System The action potential: 4 + + + + - - + + + + + + + + - - - - + + - - - - - - - - The arrow shows the direction of the action potential as it travels down the axon.

12. sgs-psychology.org.uk Structure and Function of Nervous System Neurotransmitters: –When a signal reaches the end of the neuron it comes to a gap called the synapse. Here the message goes from being an electrical signal to a chemical one. –The electrical signal reaching the end of the neuron releases a chemical into the gap. This is known as a neurotransmitter and there are more than 40 in the human body.

13. sgs-psychology.org.uk Structure and Function of Nervous System The roles of neurotransmitters: –Excitatory neurotransmitters depolarize the postsynaptic cell membrane by stimulating the inflow of sodium ions. –Other neurotransmitters hyperpolarize the membrane by stimulating ion channels to allow K+ ions to flow out, thus inhibiting neuron firing.

14. sgs-psychology.org.uk Structure and Function of Nervous System What happens once the neurotransmitter has done its job? –Breakdown Other chemicals in the synapse break down neurotransmitters into their chemical components –Reuptake Neurotransmitters are taken back into the pre-synaptic axon terminal

15. sgs-psychology.org.uk Structure and Function of Nervous System Some important neurotransmitters: –Acetylcholine (ACh) - Involved in memory and muscle activity –Dopamine - An excitatory transmitter –Serotonin - Enhances mood, eating, sleep, and sexual behaviour –Endorphins - Reduce pain and increase feeling of well-being