Nerve Notes

NEURON Nerve tissue are made of neuron (nerve cell) and neuroglia Neuron are made of: Cell body – contains nucleus and other organelles Dendrites – receiving portions, short, tapered and highly branched

Axon – conducts nerve impulses to another neuron or to an effector organ (muscle or gland) Axon arises from the axon hillock Axons start as a single fiber, but may give off branches called axon collaterals

Axon and collaterals end in axon terminals which end in synaptic end bulbs end bulbs contain synaptic vesicles that contain neurotransmitters (chemical messengers)

MYELIN increases the speed at which the impulse travels Most axons are surrounded by a myelin sheath Myelin acts as an insulator increases the speed at which the impulse travels Gaps between myelin sheath are called the nodes of Ranvier

CLASSIFICATION OF NEURON Multipolar – several dendrites and one axon – neurons of CNS are mostly this type Bipolar – one main dendrite and one axon – usually found in special sense organs

Unipolar - just one process, and are always sensory neurons Unipolar - just one process, and are always sensory neurons. Axon terminals are in CNS and cell bodies in ganglia outside CNS

FUNCTIONAL CLASSIFICATION Sensory or afferent neurons – transmit sensory impulses (toward CNS), have specialized receptor ends at tips of dendrites or the dendrites are in contact with specialized receptor cells in skin or sense organs Most are unipolar, some are bipolar

Motor or efferent neurons – transmit motor nerve impulses from CNS to effectors Interneurons – multipolar neurons in CNS.that form links between other neurons