CH 10 – Nervous System
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Transcript of CH 10 – Nervous System
Major Organs
• Central Nervous System (CNS)– Brain– Spinal Cord
• Peripheral Nervous System (PNS)– Connect brain to the rest
of the body
Generalized Model of a myelinated neuron.
Tissue made of these kinds of cells appear white: “white matter” of brain and spinal cord.
(Nissl Bodies)
Electrochemical
• Chemicals (neurotransmitters) cause an electric charge (action potential) to travel through a nerve
• Calcium and sodium ions are essential to the process
• Lead (Pb) will replace calcium ions in the body and interfere with neurotransmitter release
Peripheral Nervous System
• Sensory = afferent • Motor = efferent– Somatic (voluntary)– Autonomic (involuntary)
Autonomic Functions
• Parasympathetic– Rest and Digest
• Stimulates peristalsis• Lowers blood pressure• Slows breathing• Stimulates anal sphincter
• Sympathetic– Fight or Flight
• Blood vessels constrict• Heart beats faster• Breathing quickens• Peristalsis stops
Types of Neuroglial Cells
• Astrocyte Star-shaped cells that provide physical and nutritional support for neurons
• Microglia: digest parts of dead neurons.• Oligodendroglia: Provide the insulation (myelin)
to neurons in the central nervous system.• Ependymal: line the central canal• Schwann Cells: Provide the insulation (myelin)
to neurons in the peripheral nervous system.
Neuroglial Fun Facts
• Neuroglial cells account for half the brain’s volume
• Most brain tumors are from neuroglial cells that divide too often
• Researchers are trying to develop implants of neuroglial cells that secrete chemicals to treat Alzheimers, MS and Parkinson disease
Neuron Not-so-Fun Fact
• Mature neurons in CNS do not divide• What you got, is what you got– Unless neural stem cells are stimulated to
proliferate• Axons may regenerate
Stimuli disrupt homeostasis
• Light, temperature or pressure cause ion channels to open and the voltage changes
• If stimuli reaches a certain threshold, it generates an action potential
• Several sub-threshold potential stimuli can can generate an action potential via summation
1) Neuron stimulation causes sodium channels to open
2) Sodium flows in and makes the local area positive
3) Positive charge triggers same action further down the axon
4) Behind the action potential Potassium channels open to let K+ ions flow out and reestablish polarization
Low on Ca+ ?
• It takes calcium ions to close voltage gated channels
• If there aren’t enough Ca+, the gates may be stuck in the open position. (Tetany)
Neurotransmitters
• 30 different kinds!!• Synthesized in cytoplasm of synaptic knobs• Release is triggered by calcium ions diffusing
IN through voltage gated ion channels
Neurotransmitter SamplerNeurotransmitter What it does
Acetylcholine Triggers skeletal muscle action
Histamine Promotes alertness
Endorphins Reduce pain (our natural opiate)
Epinephrin Mood enhancer
Dopamine Mood enhancer
Drugs can alter neurotransmitter levels
• Tryptophan affects serotonin (makes you sleepy)• Nicotine tricks neurons into releasing dopamine• Curare blocks acetylcholine