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
Interneurons
Motor/efferent neurons
Marieb & Hoehn Figure 11.1 with modifications
Types of Neurons: Structure
Rhoades & Pflanzer Figure 7-8
Marieb & Hoehn Figure12.32
Neuroglia
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
