Nervous Tissue

Central Nervous System

• Brain

• Spinal cord

Peripheral Nervous System

• Cranial Nerves

• Autonomic nervous system ganglia

• Spinal nerves

Axon

• Initial segment: part of axon closest to axon hillock. Most impulses arise at junction between axon hillock and initial segment (trigger zone)

• Propagates impulse away from cell

Multipolar Neurons

• Multiple processes: several dendrites and one axon

• Most neurons in brain and spinal cord are ___

Bipolar Neurons

Two processes: one dendrite and one axon

Unipolar Neurons

One process: dendrites and axon fuse together

Sensory/Afferent Neurons

Convey (deliver) into CNS

Motor/Efferent Neurons

Convey action potentials away from the CNS

Interneurons/Association Neurons

• Process incoming sensory information from sensory neurons and elicit (trigger) motor response by activating appropriate motor neurons

• 99% of neurons are ___

Nerves

Bundle of parallel axons found in peripheral nervous system

Epineurium (Surround, Tissue Type)

• Surrounds entire nerve

• Dense irregular CT

Perineurium (Surround, Tissue Type)

• Surrounds fascicles (bundles of axon)

• Dense irregular CT

Endoneurium (Surround, Tissue Type)

• Separates and insulates each axon

• Areolar CT

Neuroglia/Glial Cells (Characteristics)

• Found in CNS and PNS

• Support, nurture and protect neurons and maintain interstitial fluid that bathes them

• Smaller than neurons, but 5-50 times more numerous

• Do not generate or propagate action potential

• Can multiply & divide in mature nervous system

Astrocytes

Largest and most numerous of the neuroglia in the central nervous system that compose the blood brain barrier

Oligodendrocytes

Found in CNS that form and maintain myelin

Microglia

Function as phagocytes, remove cellular debris & phagocytize microbes and damaged nervous tissue

Ependymal Cells

Produce, monitor & assist in circulation of cerebrospinal fluid

Myelin Sheath

• Multilayered lipid and protein covering

• Insulates (enclose) axon and increases speed of nerve impulse

Pump

• Moves substances against concentration gradient (low → high)

• Requires energy

Channel

• Moves substances down its concentration (high → low)

• Passive process

Receptive Segment

• Dendrites and cell body

• Chemically gated channels found at K⁺ and Cl^-

• Excitatory neurotransmitter is released and inside of cell becomes more positive

• Inhibitory neurotransmitter is released and inside of cell becomes more negative

Initial Segment

• Axon hillock

• Voltage gated

• Determine if threshold membrane potential -55mV is reached

Conductive Segment

• axon hillock to synaptic knob

• voltage gate

• Action potential propagates along the length of an axon to nerve signal/impulse

Transmissive Segment

• Synaptic knob

• Voltage-gated

• Calcium channels open enabling calcium to move down its gradient into the synaptic knob

• Calcium ions bind to synaptic vesicles and triggers release of neurotransmitters

Resting Membrane Potential

• Relative difference in charge across the plasma membrane of resting, excitable cell

• Value is -70 millivolts

Depolarization

Occurs when the inside of a cell becomes more positive than the resting membrane potential +30mV

Repolarization

Occurs when the inside of the cell returns to a negative value -70mV

Graded Potential

• Occurs in the receptive segment of neuron (dendrites, cell body)

• Decreases in intensity

Action Potential

• Generates in the initial segment of the axon and propagates along the axon

• Happens when voltage gated channels open from reaching minimum voltage, this triggers successive channels to open all while the intensity is maintained.

Schwann Cells/Neuroclemmocytes

Found in PNS that form myelin sheath around axons of neurons