Neurons, Neurotransmission, and Communication in the Nervous System

1. Chapter 1 Neurons, Neurotransmission and Communication

2. Organization of the nervous system • The central nervous system (CNS), which consists of the brain and spinal cord • Surrounded by the peripheral nervous system (PNS)

3. Central nervous system • Spinal cord • Simple reflex actions • Transmission of information to and from brain & spinal cord • Brain • Control and response of behaviour

4. Peripheral nervous system (PNS) • Two functions • Detecting external information • Transmitting information to CNS • Two divisions of PNS • Somatic nervous system • Autonomic nervous system (ANS) • parasympathetic nervous system • sympathetic nervous system

5. Functional types of nerve cells Sensory neuron Interneuron Motor neuron

6. Basic nerve cell structure

7. Inside the neuron

8. Glial cells (Greek for glue) • These non-neural cells help maintain homeostasis • Involved in cortical development and the guidance of neurons • Astrocytes (star shaped)• Largest of the glial cells form BBB • Microglia (mobile)• Immune system – remove debris • Myelin formation • Oligodendrocytes – in CNS • Schwann – in PNS

9. Information transmission • Axon to dendrite – axodendritic exchange • Axon to cell body – axosomatic exchange • Axon to axon – axoaxonic exchange • Dendrite to dendrite – dendrodendritic exchange

10. Resting potential

11. The sodium-potassium pump • Active process to transport Na+ ions out of neuron & K+ into the neuron • Three Na+ leave the cells for for every two K+ that enter the cell • Require energy supplied by ATP

12. The action potential • Transmits information • All or nothing principal

13. Repolarization & refractory period • Absolute refractory period • Neuron is totally resistant to additional stimulation • Relative refractory period • Neuron can be stimulated by another impulse but the stimulus must be of greater intensity than normal • Repolarization • Restoration of the resting potential to -70 mV

14. Saltatory conduction • Myelin sheath is the insulation segment that covers axons • Junction between segments are called the nodes of Ranvier • Action potential appears to jump along the length of an axon at the nodes of Ranvier – saltatory conduction • Disorder of the myelin sheath is Multiple Sclerosis (MS)

15. Synaptic transmission • On arrival of the action potential at the presynaptic terminal Ca++ ion channels open, which causes… • A variable number of vesicles to move to release sites • Neurotransmitter diffuses across synaptic cleft and…. • Attaches to the receptor sites on postsynaptic membrane

16. Summation effects • The additive effects of events occurring at the same time from different locations on the neuron

17. Non-synaptic chemical communication • Neuromodulators • Have a more widespread effect than neurotransmitters • Usually peptides • Hormones • Chemicals released by the endocrine system which have an effect on target cells and organs • E.g. testosterone – aggression

18. Endocrine system • Adrenal glands • Secrete hormones that influence the metabolism of the body and influence the body's response and defence against stress • Hypothalamus • Activates and controls the part of the nervous system that controls involuntary body functions. Involved in regulating sleep and stimulating appetite • Ovaries and testicles • Ovaries secrete hormones that influence female characteristics. Testicles secrete hormones that influence male characteristics • Pancreas • Secretes a hormone (insulin) that controls the use of glucose by the body

19. Endocrine system • Parathyroid glands • Secrete a hormone that maintains the calcium level in the blood • Pineal body • Involved with sleep cycles and the daily biological cycles • Pituitary gland • Produces a number of different hormones that influence various other endocrine glands • Thymus gland • Plays a role in the body's immune system • Thyroid gland • Produces hormones that stimulate body heat production, bone growth, and the body's metabolism

20. Receptor types • There are two types of neurotransmitter receptor • Ionotropic receptors (channel-linked receptors ) • Metabotropic (G protein-linked receptors) • Features of Ionotropic receptors are: • Ligand-gated ion channels • Action is immediate and brief • Features of Metabotropic receptors are: • Responses are indirect, slow, complex and often prolonged and widespread

21. Neurotransmitters • Direct action • Neurotransmitter binds to channel-linked receptor and opens ion channels • Promotes rapid responses • Examples: ACh and amino acids • Indirect action • Neurotransmitter binds to a G protein-linked receptor and acts through an intracellular second messenger • Promotes long-lasting effects • Examples: biogenic amines, neuropeptides and soluble gases

22. Neurotransmitter: GABA • Main inhibitory neurotransmitter • Created from glutamate via the enzyme glutamate decarboxylase • GABA’s activity ends with re-uptake, just like with any other amino acid neurotransmitters • Dysfunction with this inhibitory neurotransmitter can cause seizures

23. Neurotransmitter: glycine • Inhibitory neurotransmitter • Mainly in the spinal cord, brain stem and retina • It is a simple amino acid, both in structure and function • Formed of an amino group and a carboxyl (acidic) group attached to a carbon atom • One glycine antagonist is strychnine

24. Neurotransmitter: glutamate • Most commonly found excitatory neurotransmitter • The NMDA glutamate receptor is one of the subtypes of the glutamate receptors • The amygdala and basal ganglia also contain high concentration of NMDA receptors • NMDA receptors have a role to play in the process known as LTP

25. Neurotransmitter: aspartate • Excitatory neurotransmitter, stimulating NMDA receptors • Opens ion-channels and is primarily in the ventral spinal cord • Inactivated when reabsorbed into the presynaptic membrane

26. Neurotransmitter: serotonin • Serotonin is referred to also as 5-hydroxytryptamine (5HT) • Serotonin is synthesized via the amino acid tryptophan • Important role in the central nervous system in regulating emotions • Pathways spread widely all over the brainstem, the cerebral cortex and the spinal cord • Stopped mainly by the uptake of 5-HT from the synaptic cleft • Selective serotonin re-uptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs) are used for treating depression

27. Neurotransmitter: melatonin • Derived from serotonin within the pineal gland and the retina • Plays a role in the sleep/wake cycle • Also functions as an inhibitor of the synthesis and secretion of dopamine and GABA

28. Neurotransmitter: noradrenaline • Is an excitatory neurotransmitter • Found in the locus coeruleus, the pons and the reticular formation • Pathways are thought to play a key role in behaviours like attention and arousal

29. Neurotransmitter: dopamine • Monoamine neurotransmitters • Four pathways in the brain: the nigrostriatal, mesocorticolimbic, mesocortical and the tuberoinfundibular pathways • A shortage of cells that produce dopamine in the substantia nigra contributes to the development of Parkinson’s disease • Excessive dopamine may be involved in the development of schizophrenia

30. Neurotransmitter: acetylcholine • First neurotransmitter ever to be identified • ACh is present both in the peripheral and central nervous systems • Cholinergic pathways play a role in cognitive functions, especially memory • Alzheimer's patients have a noticeable acetylcholine deficiency in their brains • There are two primary kinds of acetylcholine receptors: nicotinic acetylcholine receptors (nAChR) and muscarinic acetylcholine receptors (mAChR)

31. Neuropeptides and neuromodulators • Neuropeptides are made up of short amino acid chains and act as neurotransmitters • Neuromodulators, as their name suggests, do not directly excite or inhibit the postsynaptic cell, but increase or decrease the release of neurotransmitter or modify the reaction of postsynaptic cells

32. Neurotransmitter: soluble gases • Certain soluble gases also act as neurotransmitters • Nitric oxide (NO) is produced by many cells in the body and is thought to play a role in memory and learning

33. Summary – nervous system

34. Summary – neurotransmitters

35. Readings • Barnes, J. (2011). Essential Biological Psychology (Chapter 1). London: Sage. • The Essentials • Roger, B., & Barasi, S. (2008). Neuroscience at a Glance. Chichester: Wiley-Blackwell. • Next Steps Gazzaniga, M.S., Ivry, R.B., & Mangun, G.R. (2008). Cognitive Neuroscience: TheBiology of the Mind. New York: W.W. Norton & Co. • Delving Deeper Stone, J.M., Morrison, P.D., & Pilowsky, L.S. (2007). Glutamate and dopamine dysregulation in schizophrenia: a synthesis and selective review. Journal of Psychopharmacology, 21(4), 440-452.