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Anatomy & Physiology I Unit Seven. Nervous System Function. The general purpose of the nervous system is to coordinate the function of all body cells and maintain homeostasis using electrical and chemical means. Nervous System Function. Integrating Center. Sensor. Effectors. Stimulus.
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Anatomy & Physiology I Unit Seven
Nervous System Function The general purpose of the nervous system is to coordinate the function of all body cells and maintain homeostasis using electrical and chemical means
Nervous System Function Integrating Center Sensor Effectors Stimulus Response
Anatomy of the Human Nervous System Neuron – a nerve cell Nerve – a bundle of neuron axons wrapped in fibrous connective tissue Ganglion – a mass of neuron cell bodies found in the PNS
Neuron Properties and Classes Neuron properties: ~ excitability – respond to stimuli ~ conductivity – sending electrical impulses ~ secretion – release of neurotransmitters
Neuron Properties and Classes Neuron classes: ~ afferent (sensory) neurons * detect a variety of stimuli and send messages to the CNS
Neuron Properties and Classes Neuron classes: ~ interneurons * found only in the CNS * receive signals from afferent neurons * carry out integrative functions * approximately 90% of all neurons
Neuron Properties and Classes Neuron classes: ~ efferent (motor) neurons * send messages from CNS to effectors (muscles or glands) in response to stimuli
Neuroglia Neuroglia - support cells that aid in the functions of neurons > four types are found in the CNS * astrocytes * oligodendrocytes * microglia * ependymal cells
Neuroglia Neuroglia - support cells that aid in the functions of neurons > two types are found in the PNS * Schwann cells * satellite cells
Action Potentials • Resting membrane potential: • + polarization of neuron due to • differences in external & internal • ion concentrations • + typical RMP is -70mV (more • anions on the inside than outside)
Action Potentials Action potential: + a nerve (electrical) impulse + generated by chemically mediated channels + propagated by charge mediated channels
Action Potential Propagation Saltatory conduction
The Neural Synapse A synapse is junction at the end of a neuron axon where it stimulates another cell by way of chemical messengers called neurotransmitters
The Neural Synapse The most common synapse types are: ~ neural synapse – junction between one neuron and another ~ myoneural synapse – junction between a neuron and a muscle cell
The Neural Synapse Presynaptic membrane Synaptic cleft Postsynaptic membrane
The Neural Synapse Neurotransmitters are chemical messengers that are released by an axon presynaptic membrane Some neurotransmitters will excite postsynaptic membranes while others will inhibit them
Neurotransmitters Neurotransmitter classes: + acetylcholine + amino acids + monoamines + neuropeptides
Neurotransmitters Acetylcholine: + released in myoneural synapses & in most ANS synapses + excites skeletal muscle + inhibits cardiac muscle + excites & inhibits smooth muscle and glands depending on location
Neurotransmitters Amino acids: + four types that excite or inhibit activity in the CNS + excitatory – glutamate & aspartate + inhibitory – glycine & GABA (gamma aminobutyric acid)
Neurotransmitters Amino acids: + glutamate is the principle excitatory neurotransmitter of the brain, while aspartate is the principle one in the spinal cord
Neurotransmitters Amino acids: + GABA is the most common inhibitory neurotransmitter in the brain, while glycine is the most common in the spinal cord
Neurotransmitters Monoamines: + found mainly in the brain, but also in the spinal cord and ANS + can exhibit excitatory or inhibitory effects depending on location
Neurotransmitters Monoamines: + catecholamines are a group of commonly known monoamines ~ norepinephrine is found in the brain, spinal cord & ANS causing excitation & inhibition
Neurotransmitters Monoamines: + catecholamines are a group of commonly known monoamines ~ epinephrine is found in the brain & spinal cord causing excitation & inhibition
Neurotransmitters Monoamines: + serotonin is found in the CNS and is secreted by platelets + its effects are usually excitatory
Neurotransmitters Monoamines: + histamine is found in the brain and is secreted by basophils + its effects are as a potent vasodilator
Neurotransmitters Neuropeptides: + found mainly in the CNS, but also in the digestive tract + they are mainly inhibitory in nature, playing major roles in pain suppression and digestion
Neurotransmitters Neuropeptides: + beta endorphin suppresses pain and fatigue + cholecystokinin (CCK) suppresses appetite and aids in digestion
The Neural Synapse Cholinergic receptors
The Neural Synapse Adrenergic receptors
Postsynaptic Response As has been noted, postsynaptic responses can be excitatory or inhibitory Neurotransmitters that elicit an excitatory response do so by producing excitatory postsynaptic potentials (EPSPs)
Postsynaptic Response Neurotransmitters that elicit an inhibitory response do so by producing inhibitory postsynaptic potentials (IPSPs) Both EPSPs and IPSPs are necessary for proper function in the nervous system