Overview of the Nervous System Neurons and Neuroglia Physiology of Nerve Conduction Synapse and Synaptic Transmission

Central nervous system Peripheral nervous system Autonomic nervous system Somatic nervous system Parasympathetic Nervous system Sympathetic nervous system Afferent nerves Efferent nerves Neurons (dendrite,body, axon, myelin sheath) Neuroglia Synapse Action potential

Central Nervous System (CNS)  Brain and spinal cord  Directs activity of entire nervous system Peripheral Nervous System (PNS)  Spinal nerves  cranial nerves  Sensory receptors  (everything outside the nervous system)

Somatic nervous system (voluntary)  Stimulates and controls skeletal muscles Autonomic nervous system (involuntary)  Controls cardiac and smooth muscles, and glands  Includes sympathetic and parasympathetic branches  Parasympathetic nervous system – controls all automatic day-in-and- day-out functions of circulatory, respiratory, and digestive systems  Sympathetic nervous system – activate fight or flight

 Respond to internal and external stimuli  Transmit nerve impulses to and away from CNS  Interpret nerve impulses at the cerebral cortex  Assimilate experiences in memory and learning  Initiate glandular secretion and muscle contraction  Program instinctual behavior

Two categories exist: neurons and neuroglia

neurons  Cells that transmit information in the form of nerve impulses  Three types depending on function: sensory (afferent), motor(efferent), interneurons neuroglia  Provide support and protection  CNS (4 types): - astrocytes, microglia, ependymal cells, oligodendrocytes  PNS (2 types): - Schwann cells, satellite cells Look up and record the description and function of each type of cell

neuronsneuroglia

Action Potential Synapse

In an inactive neuron (at rest), there are K+ ions inside the cell and Na+ ions outside the cell The inside of the membrane is more negatively charged than outside = polarized When stimuli activates a neurons, hundreds of Na channels open, allowing Na ions to rapidly diffuse into the cell/neuron As a result, electrical charge inside the cell becomes more + = depolarized Depolarization opens more ion channels, generating a wave of depolarization This electrical charge is known as nerve impulse, or action potential Following the discharge of the action potential, the membrane becomes permeable to K+ ions, which rapidly diffuse out of the cell and begin the process of restoring the membrane to its resting state = repolarization The time between the completion of the action potential and repolarization is = refractory period and the cell cannot respond to another stimulus Note: cell membrane is essentially impermeable to large negatively charged ions that are present inside the neuron, therefore fewer negatively charged ions move out than positively charged particles;

 Speed at which nerve transmission travels is determined by 3 things: 1. axon diameter- the larger the axon, the greater the number of ions to conduct current 2. presence of myelin sheath – conduction in nonmyelinated axons is much faster because fatty myelin is an electrical insulator and action potentials jump over the myelinated regions (from node (of Ranvier) to node) where the axon is exposed= salutatory conduction ; this results in significantly faster impulse transmission than is possible in nonmyelinated axons 3. body temperature – warmer temperatures increase ion diffusion rates Limb position – 119m/s Information/impulses from objects we touch – 76m/s Thought signals – m/s Pain – less than 1m/s

 Communication between neurons occurs at the synapse  The synapse is the site where the neurotransmitter is released from the nerve axon terminal  Transmission of nerve impulses is an ELECTROCHEMICAL event (action potential=electrical and synapse=chemical)

1. Action potential reaches axon terminal and Ca++ gates and Ca ions enter the terminal 2. Influx of Ca causes vesicles to join cell membrane adjacent to synaptic cleft forming pores 3. Release and diffusion of neurotransmitter across synaptic cleft to receptor sites on the next nerve or to a muscle fiber (postsynaptic)