BIO 201: Chapter 4.1 Neurohistology and Neurophysiology

nerve cell/neuron

basic functional unit of the nervous system

neurosoma

cell body and control center of a neuron which contains the nucleus and organelles

axon

slender and long projection that rapidly conducts signals away from the neurosoma

dendrite

primary site for receiving signals from other neurons that is named for resembling tree branches

dendritic branches

smaller branches arising from big and thicker dendrites

epineurium

dense irregular connective tissue that covers the whole nerve branch

fascicles

bundles or group of neurons

perineurium

connective tissue that covers fascicles

endoneurium

delicate thin layer of connective tissue that covers each separate neuron

myelin sheath

spiral layer of insulation around the nerve fiber that is production through myelination

functions of myelin sheath

insulates the nerve axon from surround tissue and increases the speed and efficiency of conduction

axon terminal

distal end of an axon that is a synapse

synapse

location where a neurotransmitter, like acetylcholine, epinephrine, and serotonin, are released

multipolar neurons

most common type of neuron that has multiple dendrites and one axon

bipolar neurons

found in the nerves of the retina, have one long dendrite and one axon

pseudounipolar neurons

appears to have two branches and shaped like a T but actually only had a single axon with dendrites at one end and a synapse at the other

axon hillock

mound where the axon originates

initial segment of axon

very first part of the axon coming out of the axon hillock

neurofibrils

part of the cytoskeleton made up of bundles of actin filaments

telodendria

extensive complex fine branches that give rise to axon terminals

axon terminal

bulbous end that forms the synapse to the next nerve

nissl bodies

dark staining regions made up of rough ER and free ribosomes that help to identify them

neuroglia

5 types of glial cells that make up majority of the cells in the nervous system

astrocytes

star-shaped with long projections that wrap around blood vessels of the brain

• form a blood-brain barrier to control what enter nerve tissue

true

true or false: astrocytes are the most abundant glial cell in the central nervous system

ependymal cells

resemble cuboidal epithelium

• produce cerebrospinal fluid

• cover the choroid plexus that lines the brain ventricles

microglia

small macrophages that act as phagocytes to remove damaged neurons and infections

• macrophages: immune system cells that wander

• phagocytes: cell eaters

oligodendrocytes

produce myelin sheath in the CNS only

• resemble an octopus due to its bulbous body and arm-like processes

nodes of ranvier

gaps between myelin sheaths

schwann cells

produce myelin sheath in the PNS only and assist in the regeneration of damaged fibers

excitability

ability of a nerve cell to respond to a stimulus that may be mechanical, chemical, or electrical

conductivity

ability of the cell to carry the excitation response along the length of the nerve cell axon

resting membrane potential

nerve cell at rest with (-70 mV)

action potential

electrochemical change that disturbs the resting membrane potential of a cell

depolarization

wave that a action potential travels down an axon

post-synaptic neuron

target cell that a neurotransmitter will bine to in order to activate a cell

asymmetric distribution

the voltage difference across the cell membrane arises from _____ of ions in extracellular and intracellular compartments

neurophysiology step 1

resting membrane potential maintained by the sodium-potassium pump

• extracellular compartment has high concentration of Na+ and low concentration of K+

• intracellular compartment has high concentration of K+ and low concentration of Na+

neurophysiology step 2

• depolarization: Na+ gates open and Na+ rushes from area of high concentration to area of low concentration, making nerve cell more positive and less polarized

• threshold: depolarization reaches irreversible point or threshold (-55 mV) that initiates the action potential or nerve impulse which travels down the length of the axon

• repolarization: membrane shifts permeability and K+ ions move out of the cell to shift the voltage back into negative numbers

neurophysiology step 3

action potential reaches the end of the presynaptic cell’s axon and enters the terminal region

• triggers the opening of voltage-gated calcium channels which then triggers the exocytosis of acetylcholine from synaptic vesicles traveling through the synaptic cleft

• acetylcholine binds to neurotransmitter receptors on post-synaptic cell