NS Conduction and Neurotransmission

Conduction & NeurotransmissionConduction & Neurotransmission

Marieb & Hoehn pp388Marieb & Hoehn pp388--421421

PC1001 / PP2101Dr Nicole Reinkenicole.reinke@jcu.edu.au

• 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