THE NERVOUS SYSTEM Introduction B. The nervous system is divided into two parts: 1. Central Nervous System (CNS) - brain and spinal cord 2. Peripheral Nervous System (PNS) peripheral nerves through the body - includes _______ pairs of spinal nerves - includes _______ pairs of cranial nerves Three Basic Functions 1. Sensory Function 2. Integrative Function 3. Motor Function – - Somatic Nervous System- Autonomic Nervous SystemNeurons: Nerve cells. - cell body with many extensions or processes (nerve "fibers") which conduct impulses 1. Dendrites 2. Axons Neuroglial Cells (neuroglia) - supportive tissue of the nervous system (more numerous than neurons). Five types Microglial Cells Oligodendrocytes Astrocytes Schwann cells *Myelin Sheaths Neurons A. Neurons = masses of nerve cells that transmit information to other nerves, tissues or cells (nerve impulses) 1. ___________________ - contains the nucleus and two extensions 2. ___________________ - shorter, more numerous, receive information 3. _________ - single, long fiber which conducts impulses away from the cell Myelin Nodes of Ranvier Myelinated (_____________) vs Unmyelinated (________________) Classification of Neurons 1. _____________________(sensory neurons, motor neurons, interneurons) 2. _____________________(multipolar, bipolar, unipolar) Interesting Info: Cell Membrane Potential Resting Potential / Threshold Potential / Action Potential 1. Neuron membrane maintains _______________________________________ 2. Threshold stimulus is received 3. _______________________________________channels open 4. Sodium ions diffuse inward, depolarizing the membrane 5. _______________________________________ channels open 6. Potassium ions diffuse outward, repolarizing the membrane 7. The resulting action potential causes a local ________________________ current that stimulates adjacent portions of the membrane. 8. Wave of a______________________________ travel the length of the axon as a nerve impulse Nerve Impulse *Propagation of action potentials along a nerve axon Impulse Conduction – speed of an impulse proportionate to ____________________of axon (greater diameter = faster impulse) Myelinated axons conduct ________________________________than unmyelinated axons The Synapse Synapse = Nerve pathway – nerve impulse travels from neuron to neuron Dendrite >> cell body >> along axon >> synapse (gap) To complete the signal, a _______________________________ is released at the gap to signal the next neuron _________________________________ – increase membrane permeability, increases chance for threshold to be achieved Inhibitory – decrease membrane permeability, decrease chance for threshold to be achieved Types of Neurotransmitters Acetylcholine – stimulates ______________________________________ Monoamines – Norepinephrine & Dopamine (sense of feeling good, low levels = depression) Serotonin = ________________________________________________ Endorphins = ______________________________________________ Synapses are highly susceptible to drugs and fatigue Impulse Processing Neuronal pool – groups of neurons that make hundreds of synaptic connections and work together to perform a common function Types of Nerves Sensory Nerves – conduct impulses into ______________________________ Motor Nerves – carry impulses to ________________________ Mixed Nerves - contain both sensory and motor nerve Nerve Pathways Reflex arc – simple pathway, includes only a few neurons (_____________________________) Reflex Behavior – automatic, subconscious responses to stimuli Knee-jerk reflex = Withdrawal reflex =