ns conduction and neurotransmission
TRANSCRIPT
Conduction & NeurotransmissionConduction & Neurotransmission
Marieb & Hoehn pp388Marieb & Hoehn pp388--421421
PC1001 / PP2101Dr Nicole [email protected]
• 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
NeuronNeuron
• 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: FunctionTypes of Neurons: Function
Marieb & Hoehn Figure 11.1 with modifications
Sensory/afferent neurons
Motor/efferent neurons
Interneurons
Types of Neurons: Types of Neurons: StructureStructure
Rhoades & Pflanzer Figure 7-8
Marieb & Hoehn Figure12.32
NeurogliaNeuroglia
Marieb & Hoehn Figure 11.3
Nerve Impulse ConductionNerve Impulse Conduction
• Irritability
• Conductivity
• Nerve impulse = moving action potential
Rhoades & Pflanzer Figure 7-19
Speed of transmissionSpeed of transmission
• speed of impulse transmission varies due to:– axon diameter
• less resistance to current flow
– degree of myelination
MyelinationMyelination
• 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 75 30 2
1.5512
• Multiple Sclerosis– Loss of myelin
– Axon scarring
– Slowed impulse transmission
NeurotransmissionNeurotransmission• 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
NeurotransmissionNeurotransmission
• neurotransmitters are stored in axon terminals of presynapticneuron (in vesicles)
• Neurotransmitter released from presynaptic neuron
• diffuses into synaptic cleft
• interacts with receptor on postsynaptic terminal
• Chemical Synapse
Marieb & Hoehn Figure 11.18
NeurotransmittersNeurotransmitters
– Acetylcholine (ACh) • cholinergic synapses• Alzheimer’s disease
– Norepinephrine (noradrenaline)• adrenergic synapses
– Dopamine
– Serotonin
– Glutamate
• Excitatory vs Inhibitory neurotransmitters
Graded Potential Graded Potential vsvs Action PotentialAction 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 ProcessingInformation 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