BIO 378
Lecture 4: Nervous System

  Nervous System Divisions:

    I. Central Nervous System (CNS): Brain and Spinal Cord; Integration, processing, and coordination of sensory data & motor commands

    II. Peripheral Nervous System (PNS): All nerves outside the CNS; Delivers sensory info to CNS, conducts motor impulses to peripheral tissues
 

         A. Afferent division: Sensory Neurons; send impulses to CNS

                1. Somatic Sensory Neurons: Monitor environment &/or changes in the environment

                2. Visceral Sensory Neurons: Monitor inside of the body

         B. Efferent division: Motor Neurons; send impulses away from CNS

                1. Somatic Nervous System (SNS): System that deals with neurons that effect skeletal muscle (voluntary)

                2. Autonomic Nervous System (ANS): Automatic & involuntary control of smooth muscle, cardiac muscle, some glandular activity
 

                        a. Sympathetic: Fight or flight response
 

                        b. Parasympathetic: Rest & repose response
 
 

Neuron:  a nerve cell - NOT a nerve

    dendrites: Conduct impulses to cell body
 

    cell body: contains nucleus & organelles, maintains metabolism of neuron for growth & repair
 

    axon: conduct impulses away from cell body
 

Nerve: Collection of neurons
 
 

Conducting impulses:

    1.Establish a resting membrane potential (about -70mV).

    2. Stimulate an area of the membrane causing Sodium gates (or channels) to open.  Sodium enters the cell and causes the inside to become positive relative to the outside.

    3.  If the membrane potential reaches the threshhold potential then more Sodium channels open and rapid depolarization occurs.
            Depolarization: Transmembrane potential becomes less negative

            All or none law: If threshold is not reached, no action potential will happen. If it is reached then it will trigger an action potential spike and a chain reaction of action potentials
 

    4. Sodium channels are inactivated and Potassium channels are activated.  Potassium leaves the cell and repolarization occurs.  The membrane potential becomes negative again.
            Repolarization: Transmembrane potential becomes more negative
 
 

    5.  Action potentials move along the membrane.

    5.  When the impulse reaches the end of the axon, neurotransmitters are released and move across to  the dendrites of the next neuron.  This causes the Sodium channels of the next neuron to open and the process repeats itself.

To summarize events occuring during Action Potentials:




 

Useful link:

Human Physiology: Neurons and the Nervous System I

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