Central Nervous System (CNS): Brain & Spinal Cord; integrating and common command center of all the nervous systems; interprets incoming sensory info and dictates motor responses

Peripheral Nervous System (PNS): Cranial & Spinal Nerves (extend from brain/spinal cord); Spinal nerves carry info to & from spinal cord; Cranial nerves carry info to & from brain; motor/efferent division separated into Somatic and Autonomic Nervous Systems;

Somatic: Voluntary; conducts impulses from CNS to skeletal muscles

Autonomic: Involuntary; conducts impulses from CNS to organs/glands/cardiac & smooth muscle;

Sympathetic Division: most active during excitive/emergency situations

Parasympathetic Division: active during restful situations like digestion; conserves energy

Nervous tissue made up of 2 types of cells:

1. Neurons: excitable cells that transmit electrical signals (APs); Don't usually replicate; highly metabolic- require continuous supply of oxygen & glucose; made up of:

Cell body (soma): contains nucleus and nucleolus; no mitotic spindles (nerves do not divide).

Processes: numerous dendrites- main receptive input to cell; single axon- corresponds to output of cell; arrises from axon hillock and branches at ends to form terminal boutons; myelin sheath covers or insulates axon to speed up transmission of impulses.

2. Supporting Cells:Nonconducting CT cells; support/surround neurons 10:1; Neuroglia (CNS) & Schwann and Satellite (PNS).

Multipolar: many processes; most common (99%)

Bipolar: 2 processes- one from each side of cell body; rare- in some sense organs like hearing/vision.

Unipolar (pseudo): appears to have 1 process but it actually has an incoming and outgoing process; found in sensory ganglia (dorsal root ganglia).

Sensory (afferent): transmit impulses from sensory receptors in skin/internal organs toward CNS; most unipolar & located outside of CNS in ganglia.

Motor (efferent): carry impulses away from CNS to effector organs; multipolar- for the most part, cell bodies located in CNS.

Association: ?

Neuroglia: 4 types

1. Astrocytes: numerous processes which produce a star shape; most abundant type of glial cell; make exchanges between capillaries & neurons, control chemical environment (correct ion concentrations).

2. Microglia: small cells with large processes; monitor health of neurons they contact (act as phagocytic cells).

3. Oligodendrocytes: fewer branches than astrocytes; line up on processes of neurons in CNS & wrap tightly around fibers producing insulating or MYELINATING effect; form myelin sheaths in CNS.

4. Ependymal Cells: squamous, columnar, or cuboidal; line cavities of brain & spinal cord (ventricals); ciliated- help form & circulate cerebospinal fluid

Scwann: forms myelin sheath in PNS

Satellite: surround cell bodies of neurons in ganglia; supportive to neurons; takes care of health & environment

Axon Diameter: the large the diameter of an axon, the faster it will conduct a current; varies from axon to axon considerably; larger axons offer less resistance to flow of current.

Myelin Sheath: myelinated axons conduct impulses faster than unmyelinated axons.

Continuous Conduction: slow AP conducted at sites adjacent to another in unmyelinated axons.

Saltatory Conduction: fast AP conducted at Nodes of Ranvier in myelinated axons.

Classified by diameter & degree of myelination;

Group A: Somatic sensory & motor fibers- largest diameter & degree of myelination; fastest conducting

Group B: Innervate viscera & pain fibers from skin- lightly myelinated; intermediate speed of conducting

Group C: Visceral & some pain/touch- smallest diameter; unmyelinated (continuous conduction); slowest conductivity

1. Epineurium: outermost layer; covers whole nerve.

2. Perineurium: middle layer; covers fascicles.

3. Endoneurium: inner layer; covers fibers or individual processes of neurons (axon + myelin sheath).