intro to the nervous system

2 major divisions of the nervous system

central nervous system (CNS) and peripheral nervous system (PNS)

central nervous system (CNS)

consists of the brain and spinal cord

peripheral nervous system (PNS)

consists of the nervous tissue outside of the CNS

2 cells in nervous tissue

neurons and neuroglial cells

neurons

cells capable of conducting electrical impulses

neuroglial cells

supporting cells

cell body

contains a large nucleus and cellular organelles

dendrites

slender processes that receive incoming information from other neurons

axon

a long process that is able to generate and spread the action potential

axon hillock

where the initial segment of the axon is attached to the cell body

telodendria

series of fine extensions at the end of the axon

synapse

ends of the telodendria where they form a junction with another cell or target

myelin sheath

* collective group of neuroglial cells that surround and protect the axon
* speeds up the rate of the action potential transmission

nodes

bare areas in between the neuroglial cells that make the myelin sheath

structural classification

classification based on the structure of a neuron and the number of processes that directly come off the cell body

anaxonic neuron

no axon or you cannot tell which extension is an axon and which are the dendrites

bipolar neuron

2 extensions off of the cell body

unipolar neuron

1 extension off of the cell body

multipolar neuron

3 or more extensions

functional classification

classification based on the direction that the nerve impulse travels

sensory neurons

afferent neurons that deliver impulses from receptors towards the CNS

somatic sensory neurons

monitor the outside world and is consciously perceived from receptors (eyes, ears, skin)

visceral sensory neurons

monitor our internal environment and status of our organ systems and is unconsciously perceived from receptors (heart)

motor neurons

efferent neurons that deliver impulses away from the CNS and toward effectors in the PNS

somatic motor neurons

innervate skeletal muscles and is consciously controlled

visceral motor neurons

* innervate all other targets besides skeletal muscle and is unconsciously controlled
* innervates smooth muscle, cardiac muscle, glands, and adipose tissue

interneurons

mostly located within the CNS; distribute sensory information and coordinate motor activity

ependymal cells

produce and monitor the fluid in the CNS

schwann cells (neurolemmocyte)

form the myelin sheath around axons in PNS

oligodendrocytes

form the myelin sheath around neurons in the CNS

astrocytes

* largest and most numerous neuroglia
* maintain blood-barrier
* provides structural framework for the brain and spinal cord
* repairs structural damage in neural tissue
* anchor neurons to capillaries that bring nutrients
* regulates and maintains an optimal environment for the neuron

microglia

* least numerous and smallest neuroglia in the CNS
* engulf waste products and pathogens

satellite cells

* surround the neuron cell bodies in ganglia
* regulates and maintains environment for the neuron

ganglia

clustered masses of neuron cell bodies in the PNS