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NS Conduction and Neurotransmission

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Conduction & NeurotransmissionMarieb & Hoehn pp388-421

Dr Nicole Reinke [email protected]

PC1001 / PP2101

Objectives Describe the different types of nerve cells Describe the structure of a typical neuron and the functions of the components Describe the different types of glial cells and their functions Discuss the factors that affect the speed with which action potentials are propagated Understand the process of neurotransmission

Neuron Highly specialised to transmit messages

Cell body (soma) Organelles Incoming signals

Dendrites Incoming signals

Axon Outgoing signals Axon hillock

Axon terminals

Rhoades & Pflanzer Figure 7-8

Types of Neurons: Function

Sensory/afferent neurons


Motor/efferent neurons

Marieb & Hoehn Figure 11.1 with modifications

Types of Neurons: Structure

Rhoades & Pflanzer Figure 7-8

Marieb & Hoehn Figure12.32


Marieb & Hoehn Figure 11.3

Nerve Impulse Conduction Irritability Conductivity Nerve impulse = moving action potential

Rhoades & Pflanzer Figure 7-19

Speed of transmission speed of impulse transmission varies due to: axon diameter less resistance to current flow

degree of myelination

Myelination Schwann cells (PNS), Oligodendrocytes (CNS) Nodes of Ranvier myelin insulates axon & prevents charge leakage

Marieb & Hoehn Figure 11.5

Rhoades & Pflanzer Figure 7-20

20 120

12 75

5 30

1.5 2

Multiple Sclerosis Loss of myelin Axon scarring Slowed impulse transmission

Neurotransmission how nerves communicate with each other and with body structures communication occurs at the synapse. presynaptic neuron postsynaptic neuron synaptic cleft

Marieb & Hoehn Figure 11.17

Synaptic cleft

Neurotransmission neurotransmitters are stored in axon terminals of presynaptic neuron (in vesicles) Neurotransmitter released from presynaptic neuron diffuses into synaptic cleft interacts with receptor on postsynaptic terminal

Chemical Synapse

Marieb & Hoehn Figure 11.18

Neurotransmitters Acetylcholine (ACh) cholinergic synapses Alzheimers disease

Norepinephrine (noradrenaline) adrenergic synapses

Dopamine Serotonin Glutamate Excitatory vs Inhibitory neurotransmitters

Graded Potential vs Action Potential Postsynaptic potentials = Graded potentials Local changes in membrane potential More positive (depolarization) or more negative (hyperpolarization)

Action potentials All-or-none once threshold is reached

Postsynaptic potentials Excitatory postsynaptic potentials (EPSP)

Inhibitory postsynaptic potentials (IPSP)

Information Processing Information decoding Sum of the activity of inhibitory and excitatory synapses

Information encoding Generation of impulses proportional to overall intensity of incoming stimuli

Marieb & Hoehn Figure 11.17

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