Nervous System Transmits information from 1 part of the body to another, rapid communication

2 major divisions  Central Nervous system (CNS)– brain and spinal cord  Peripheral (PNS)– nerves of the body Autonomic nervous system (ANS)– regulates involuntary functions

Cells of nervous system  Neurons – made of dendrites, cell body, axons Dendrites – take information to cell body Axons – take information away from cell body  3 types of neurons Sensory – to brain or spinal cord (afferent) Motor – away from brain/spinal cord (efferent) Interneuron – conduct impulses from sensory to motor neurons.

Structure of neuron  See handout Myelin – white fatty substance that covers some axons outside of CNS Schwann cell – forms myelin Nodes of Ranvier – indentions between schwann cells Neurilemma – outer cell membrane of a schwann cell

Neuroglia cells (glia)  Support cells for neurons, do not transmit impulses.  3 types of glia Astrocytes – star like extensions that hold neurons and blood vessels together. Microglia – small, used as microphages (microbe eating scavengers) Oligodendrocytes – hold nerve fibers together and produce fatty myelin sheath that envelops nerve fibers in the brain and spinal cord (instead of schwann cells)

Disorders of nervous tissue  Neuromas – tumors of nervous system, seen mostly in glia cells (glioma)  Multiple neurofibromatosis – inherited Numerous fibrous neuromas  Multiple sclerosis – (CNS) disorder of oligodendroglia Myelin lost and destroyed becomes plaque like lesions Nerve conduction impaired

Nerves – see figure 9-6  Group of peripheral nerve fibers (axons) in PNS  Look white, covered in myelin  CNS – called “ tracts ”,  White matter – part of CNS covered in myelin, axons  Grey matter – dendrites and cell bodies not covered in myelin sheath

Nerve structure  Endoneurium – thin fibrous connective tissue covering of each axon  Fascicles – group of wrapped axons  Perineurium – thin, fibrous covering of fascicles  Epineurium – tough fibrous covering of entire nerve

Reflex arc  Specialized type of neuron pathway that nerve impulses travel  2 neuron arc, simplest, ex – knee jerk  3 neuron arc, ex. Withdrawal reflex  impulse ->receptor (end of dendrite) -> sensory neuron ->cell body (ganglion)-> axon-> synapse ->chemicals sent across gap ->dendrite -> cell body (ganglion) -> axon of motor neuron -> creates reflex.

Nerve impulses  Self propagating wave of electrical disturbance that travels along the surface of a neuron ’ s plasma membrane.  Must be initiated by a stimulus (pressure…  At rest, the membrane has slightly + charge (Na+) outside and – inside  When stimulated, inside membrane becomes + and – outside temporarily.  Impulses travel in 1 direction across neurons surface.  Saltatory conduction – faster impulses when nerve has myelin covering.