Processes

1. Processes Armlike projections from the cell body. Bundles of processes in the CNS are called �Tracts.� Bundles of processes in the PNS are called �Nerves.� There are 2 types of processes: 1. Dendrites- are short, tapered, and branch. Responsible for sensory input and impulse transmissions. 2. Axons- can be extremely long (3-4 ft) Generate and transmit impulses.

2. Myelin Sheath This is a protein-lipoid that covers, protects, and insulates nerve fibers from one another. It also increases the speed of nerve impulses. Dense collections of myelinated fibers are called �white matter� and are mostly fiber tracts. Dense collections of nerve bodies (unmyelinated) are called �gray matter.�

3. Neurons are Classified Structurally and Functionally: Structurally: Multipolar- Have three or more processes. Most common type (>99 %). Bipolar- Have two processes (one axon and one dendrite). Found in special sense organs. Unipolar- Have one process that branches into an axon and a dendrite. Found in the ganglia of PNS.

4. Neurons are Classified Structurally and Functionally (cont.): Functionally: This is based on the direction impulses travel in relationship to the CNS. Sensory- transmits from receptors to CNS. Nearly all of these are unipolar. Motor- Transmits from CNS to effector organs. Most are multipolar. Interneurons- are found between motor and sensory neurons and transmit signals through the CNS. Most are multipolar.

5. Nerve Impulse Transmission: The operation of the nervous system depends on the flow of information through chains of neurons. This occurs at synapses (junctions between neurons or neurons and effector cells). Most synapses occur between axonal endings of one neuron and the dendrites of another. Impulses conducted toward the synapse are called the Presynaptic Neurons and away from the synapse is the Postsynaptic Neuron.

6. There are Two Type of Synapses: 1. Electrical- Is the least common type. Is very fast (100m/s) Have protein channels that interconnect the cytoplasm of neighboring neurons. Current-carrying ions flow directly from one neuron to the next. Responsible for stereotyped movement (ex. Jerky movement of eyes). Most of these synapses are replaced by chemical synapses by adulthood.

7. There are Two Type of Synapses(cont.): 2. Chemical- Is the most common. Have slower impulses (.3-5m/s) Designed to release and receive neurotransmitters. Neurotransmitters cause the opening and closing of ion channels in cell membranes. Consist of two main parts: 1. Axonal Terminal- knob-like end of axon with synaptic vesicles. 2. Receptor Region- possesses neurotransmitter receptors. The space between the two is the synaptic cleft.

8. Steps to Impulse Transmission Across a Chemical Synapse: A depolarization wave (nerve impulse) causes Ca ions gates to open in the axonal terminal. Ca ions promote fusion of synaptic vesicles to the terminal membrane causing a release of neurotransmitter by exocytosis. The neurotransmitter diffuses across the synaptic cleft and bind to the receptors of the postsynaptic membrane.

9. Steps to Impulse Transmission Across a Chemical Synapse: 4.The binding of the neurotransmitter causes the postsynaptic membrane to open ion channels (depolarization). 5. The neurotransmitter is broken down quickly by enzymes allowing for repolarization.

10. The Central Nervous System: Made up of the brain and spinal cord. Parts of the brain: Ventricles: These are hollow chambers filled with cerebralspinal fluid. There are 4 interconnected and they are found deep within the brain. Cerebral Hemisphere: Make up about 83% of the brain�s mass. Form the superior part of the brain. Surface is covered with ridges (gyri) and grooves (sulci). Deep grooves are called Fissures. Longitudinal fissure- separates the right and left hemispheres. Transverse fissure-separates the cerebral hemispheres from cerebellum.