Ch. 13 Neural Histology

Neuron

• Organ of nervous system containing a nucleus, cell body, axon, dendrites, and axon hillock

• Subdivided into Pseudounipolar, Bupolar, and Multipolar

Cell Body / Soma

• Body of a neuron, contains nucleus

• Processes information from dendrites, creates localized impulse if needed 

Dendrites

• Tail like branching protruden from end of cell body

• Transmit information to cell body

Axon Hillock

• Part of axon closest to cell body

• Makes decision to if an impulse needs to be sent or not

Axon

• Tail like protrugen from cell body

• Transmits action potential away from cell body

• Produces ATP

Glia cell

• Any supporting cell of the nervous system

• Supports the neurons

• Outnumber neurons 50 to 1

• Divides with mitosis

• Brain cancer caused by these cells

Axon collateral

• Axon type that branches off the main axon

Central axon

• Axon type that brings information into CNS from cell body

Pseudounipolar neuron

• Neuron type that appears to be on straight axon with dendrites on both sides and cell body somewhere in the middle

• Appears to only be one axon but is really two

Bipolar neuron

• Type of neuron that clearly has two axons

Multipolar neuron

• Neuron with multiple axons that attach to the cell body

Sensory / Afferant neuron

• Neuron that cell body exists in posterior root ganglion with axons reaching to spinal cord and the PNS

• Transmit senses from PNS to CNS

• Mostly unipolar, few bipolar

• Facilitates motor coordination

• Location: retina, olfactory epithelium, spiral ganglia

Interneuron

• Neuron that lives completely within the CNS, 99% of nerves 

• Acts as decision maker between motor and sensory neuron

• Receives, processes, stores information

• Mostly multipolar neurons

Motor / efferent neuron

• Neuron that’s body is in anterior horn sends an axon out to the PNC

• Sends motor impolses in response to stimuli

• Mostly motor neurons 

• Travel as cranial and spinal nerves 

Nissl Bodies

• Rough ER and Ribosome structures in cell body of neuron only

• Proteins synthesis site for neuron

Myelin sheath

• Myelin that surrounds axon of neuron

• Allows electrical impolses to move faster through axon

Endoneurium

• Connective tissue that surrounds never fibers

• Protects them from damage

Nodes of Ranvier

• Spaces between Schwann cells

• Contains high amounts of voltage-gate sodium channels

Internode

• Myelin sheath protrudens superficial to axon, surrounding it

Axodendritic synapse

• Synaps type: Axon connects to dendrite

Axosomaric synapse

• Synaps type: Axon to soma

Axoaxonic synapse

• Synapse type: Axon to axon

Synaptic knob/bulb / terminal

button

• Bulb like area of nerve at neromuscular junction

Synaptic vesicles

• Vesicle inside of axon bulb that holds neurotransmitters

• Take neurotransmitters to the muscle

Presumptic membrane

• Membrane of the axon bulb just before the synaptic cleft

Synaptic cleft

• Space between the motor end plate and synaptic bulb

Neurotransmitter

• Messenger from neuron to muscle

• Diffuses through the synaptic bulb and into the motor end plate

Post synaptic membrane

• Membrane of the motor end plate

Nicotine receptor

• Receptor of part of the motor end plate

• Binds to nicotine and acidocoline

Epineurium

• Connective tissue surrounding the entire nerve

Peripheral never

• Collection of neurons that travel bound together together

• Contains mixture of motor and sensory neurons

Perineurium

• Connective tissue surrounding nerve fascicles

Nerve facile

• Collection of axons held together by perineurium

Astrocyte cell

• Glial cell

• 90% of nervous tissue

• Makes blood-brain barrier, regulates tissue fluid, synaptic transmission

• Responsible for learning

Microgila cell

• Glial cell

• Immune cell for nervous system

Satellite cell

• Glial cell

• Surrounds neurons in posterior root ganglion

• Regulate chemical environment

Schwann cell

• Glial cell

• Makes myelin sheath in PNS

• Can myeline one axons at a time, covered some axons in CNS

• Speeds up electrical signaling by allowing saltatory conduction

Oligodendrocyte

• Glial cell

• Creates myelin sheath around axon of CNS

• Can myeline multiple axons at once, covered every single axon in CNS

• Causes white appearance of white matter 

• Speeds up electrical signaling 

Ependymal cell

• Glial cell

• Cuboidal cell with cilia

• Lines cavities of brain and spinal cord

• Produces ceribrosponal fluid from blood plasma

Terminal arborization/

Telodendria

• Branching part of an axon that protrudes from the end of the axon 

• Looks like tree branches 

• Synaptic bulbs held and end of telodendria 

Parasympathetic division

• Relaxes the body and promotes recovery

• Has control of autonomic functions such as digestion

Sympathetic division

• Prepares body for fight or flight situations 

• Controls autonomic responses like increased heart rate, dilated pupils, and energy mobilization 

Electrical synaps

• Membranes held together by gap junction 

• Two way signaling 

• Found in smooth cells, intercalated discs, some CNS neurons 

Chemical synaps

• Membranes not joint together by anything

• Most common in body

• Membranes held together by gap junction 

• One way signaling 

Choroid plexus

• Made of ependymal cells

• Where CSF is produced

Saltatory conduction

• Fast conduction in myelinated axon than non-myelinated axon and bigger diameter

• Electrical impulses bounce from one gap in myelin sheath to the other 

• Takes less ATP than continuous

• Type A: Conducts to skeletal muscles in limbs 

• Type B: Sensory axons from organs to CNS 

Continuous conduction

• Slower conduction in non-myelinated axon than myelinated axon and smaller diameter

• Electrical impulses travels down whole axon

• Takes more ATP than saltory

• Type C: Sensory axons conducting pain as well as some pressure and cold  

Cycle at chemical synapse

• Step 1: Action potential in presynaptic cell opens Ca++ channels in synaptic bulb

• Step 2: Ca++ influx causes synaptic vesicles to fuse to presynaptic membrane

• Step 3: Synaptic vesicles release neurotransmitter

• Step 4: Neurotransmitter diffusion across synaptic cleft

• Step 5: Neurotransmitter binds to receptor in postsynaptic cell

• Step 6: Stimulation or inhibition of postsynaptic cell

• Step 7: Termination of synaptic transmission