The Central Nervous System Made up of the brain and spinal cord Is responsible for integrating, coordinating, and processing sensory and motor commands.

Peripheral Nervous System Includes all the nerual tissue outside of the CNS Two divisions: A. Afferent Division of the PNS- delivers the information to the CNS B. Efferent Division of the PNS- carries motor commands from the CNS to peripheral tissues

Efferent Division Two Divisions: 1. Somatic Nervous System: provides voluntary control 2. Autonomic Nervous System: provides automatic involuntary control of smooth muscles, cardiac muscles, glandular tissues.

Autonomic Nervous System A. Sympathetic Division: accelerates body functions B. Parasympathetic Division: slows body functions

Neural Tissue Composed of Two Main Types of Cells: Glial Cells (or neuroglial cells) Neurons 1. Glial: Make up the support system for the nervous system Non-conducting, non-excitable Separate and insulate the neurons Most abundant type of nerve cell

1. Glial Cells A. 4 in the CNS B. 2 in the PNS A. The glial cells in the CNS include: 1. Oligodendroglia: form Myelin Sheaths around the neuron in the CNS which insulate the axon. 2. Microglia: special type of microphage or phagocytic white blood cell -Protect the CNS by engulfing invading microorganisms and dead neural tissue that might cause disease

3. Astrocytes: - Brace neurons and anchor them to the capillaries - Actively transport substances from the blood to the heart - Form the BLOOD BRAIN BARRIER protecting CNS neurons form harmful substances in the bloodstream - Control the chemical environment around the neurons in the CNS

4. Ependymal Cells - ciliated cells - Line the central canal of the spinal cord and the chambers of the brain. -Provide protective cushioning for the vital organs and chambers of the brain - produce cerebrospinal fluid - cilia circulate the cerebrospinal fluid around the organs of the nervous system.

B. Glial Cells in the PNS 1. Schwann Cells: - form myelin sheathes around every axon outside the CNS - serve to increase the rate of impulse conduction in the PNS 2. Satellite Cells: - control the chemical environment of the PNS much as astrocytes control the chemical environment around the neurons in the CNS.

Neurons True nerve cells Structural and functional unit of the nervous system Receive stimuli by the PNS Relay stimuli- through PNS and CNS Analyze the stimuli- CNS Initiate an appropriate response- CNS

Structure of a Nerve Cell A. Cell Body B. Two types of Cytoplasmic Extensions A. Cell Body: Soma Contains Perikaryon- the cytoplasm (neuroplasm) that surrounds a Nucleus with a single prominent Nucleolus Contain rough ER and free ribosomes called NISSL BODIES that are the site of protein synthesis. Axon Hillock: area where the axon meets the cell body

Nerve Cell Processes Two Types: 1. Dendrites- “afferent processes” typically short with many branches Receive and conduct impulses toward the cell body 2. Axons- “efferent processes” Long fiber that varies in length depending on the location f the neuron A Single axon may have one or more branches called collaterals from the main axis Axons and their collaterals end in fine branches called terminal filaments

On the end of the terminal filament are Synaptic Knobs: vesicles which contain the chemicals called… Neurotransmitters When the nerve impulse arrives at the end of an axon…neurotransmitters are released into the… Synaptic Cleft- or space between two adjacent neurons The synaptic cleft is responsible for transferring the effect of a stimulus to the next cell (nerve cell or other effector) e.g. Acetylcholine (neuromuscular junction)

Myelin Sheath: in many cases surrounds the axon cylinder, is produced by oligodendrocytes or a Schwann Cell Along the Myelin Sheath are indentations called Nodes of Ranvier Myelin Sheath has a thin covering called a Neurilemma- which repairs damages to the nerve processes.

White Matter vs. Grey Matter Most of the neurons INSIDE of the brain and on the OUTSIDE of the spinal cord are covered with myelin sheath and along with the entire PNS make up the WHITE MATTER of the nervous system. Neurons that are not covered by a myelin sheath form the GREY MATTER of the CNS Found covering the brain and the central part of the spinal cord.

Clusters of cell bodies in the CNS are called “nuclei” Cluster s of cell bodies in the PNS are called “ganglion”

Types of Neurons 1. Anaxonic Neurons: 1. Small 2. No anatomical clues to distinguish axons from dendrites 3. Processes are never myelinated 4. Found in the CNS and special sense organs 5. Function is poorly understood

2. Unipolar Neuron 1. Has a single process extending form the cell body, axon and dendrite are continuous, soma lies off to the side 2. The initial segment is considered the dendrites and the rest is considered the axon 3. May or may not be myelinated 4. Includes sensory neurons of the PNS

3. Bipolar Neurons 1. Have one dendrite and one axon with the cell body between them 2. Axons are not myelinated 3. Found in the sense organs 1. Retina of the eye 2. Inner ear 3. Receptors for smell 4. Relay information concerning sight, smell and hearing.

4. Multipolar Neurons 1. Have many branched dendrites and one single axon 2. Most common neuron in the CNS 3. Motor neurons that control skeletal muscles are MYELINATED multipolar neurons.