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 =