Neurons

Neurons

CNS: Brain and spinal cord

PNS: Neurons that connect CNS to the rest of the body

Somatic Nervous System: Voluntary Movement, Conscious and controlled

Autonomic Nervous System: Involuntary movement

Sensory Neurons: Neurons that carry information to the CNS

Motor Neurons: Neurons that carry information from the CNS

Myelin

• Layer of fat that insulates neurons (axon) and allows them to function at a quicker speed

• White matter

CNS Myelin

• Made of oligodendrocyte

PNS Myelin

• Made of Schwann cells

• Neurilemma: the outermost layer of myelin

Role of Myelin in Conduction

• Keeps action potential from continuously spreading across cell membrane

• Insulating against the spread of current

• Speeds up conduction

Saltatory Conduction:: Myelin causes action potential to jump from sheath to sheath. Fewer actions potentials are needed for an impulse to travel any given distance. 

Dendrites: Conduct impulses to the cell body

Axon: Impulses away from the cell body

Nerves and Tracts

• Neuron fibers bundle together

• PNS – Called nerves

• CNS – Called tracts

Held together by connective tissue

• Endoneurium surrounds each individual fiber

• Perineurium surrounds each fascicle

• Epineurium surrounds the whole nerve

Mixed nerves contain both sensory and motor fibers

Neuroglia

• Support Cells

• Schwann Cells are an example

Astrocytes: Star-shaped cells that serve many functions

Oligodendrocytes: Provide Myelin Sheath for the CNS

Microglia: Remove pathogens and dead neurons

Ependymal: Provide barrier between fluid and CNS nervous tissue

Spinal Cord

• Central pathway for sensory and motor impulses to travel to and from the brain

• Ascending Tracts: Travel to the brain

• Descending Tracts: Travel from the brain