Nervous Tissue Flashcards
Central Nervous System (CNS)
consists of the brain and spinal cord, which are enclosed and protected by the cranium and vertebral column
Peripheral Nervous System (PNS)
consists of nervous tissue outside of the CNS;
composed of nerves and ganglia
Autonomic Nervous System (ANS)
considered to be part of the PNS
Neuron (Nerve Cell)
conduct nerve impulses or action potentials; composed of
dendrites
cell body/ soma
axon
dendrites
pick up message & send to Cell Body
cell body/ soma
contain nucleus & translate message
axon
sends translated message to target; longest part of neuron
Supporting cells (glial cells/ neuroglia)
are NOT neurons; 4 found in
Central Nervous System; Astrocytes, Oligodendrocytes, Microglia, Ependymal Cells,
2 found in Peripheral Nervous System:
Schwann Cells, Amphicytes
astrocytes
maintain blood/ brain barrier
cerebral spinal fluid and blood stay away from each other
oligodendrocytes
produce myelin
microglia
phagocytic
ependymal cells
produce CSF (cerebral spinal fluid)
Schwann cells
produce myelin
amphicytes
may support or protect damaged neurons
Classes of neurons
afferent (sensory)
efferent (motor)
interneurons( association neurons)
afferent (sensory) neurons
transmit information toward CNS
efferent (motor) neurons
transmit information from CNS
interneurons (association neurons)
transmit information within CNS
multipolar neuron
many branches off cell body;
located in CNS
MOST COMMON
bipolar neuron
two branches off cell body;
found in retina; olfactory cells
unipolar neuron
one branch off cell body; neurons that carry sensory signals to the spinal cord
located in PNS
anaxonic neuron
multiple dendrites, but no axon; do not produce action potentials;
found in retina (process visual contrast)
depolarization
Sodium enters neuron (+30 mv)
repolarization
Potassium exits neuron (-70 mv)
hyperpolarization
more Potassium exits neuron (about -80 mv)
activation of sodium/potassium pump
3 sodium exit / 2 potassium enter
mover toward threshold
minimum voltage needed to start the nerve impulse
usually – 55 mv
types of conduction
saltatory
continuous
saltatory conduction
myelinated axons; faster conduction (impulse jumps from node of
Ranvier to node of Ranvier); type A axons (largest diameter; 300 mph impulse;
ex: danger & reflex) (skeletal muscle)
type B axons (smaller diameter; 40 mph impulse; quick pain;
ex: needle)
theres pain and then it goes away
continuous conduction
unmyelinated axons; slower conduction (impulse travels entire length of axon); type C axons (smallest diameter; 2 mph impulse;
ex: throbbing pain i.e. angina)
angina: heart isn’t getting enough oxygen
pain doesn’t go away
components of a chemical synapse
Terminal end of pre-synaptic axon
Synaptic Vesicles (within pre-synaptic axon; contain NT’s)
Synaptic Cleft (space)
Postsynaptic Cell (target of NT’s)
neurotransmitter storage and release
Action Potential (nerve impulse) reaches terminal end of the pre-synaptic axon
Voltage-gated Calcium channels open
Calcium enters the terminal end of the pre-synaptic axon
Neurotransmitter release and diffusion into the Synaptic Cleft
Neurotransmitter binds to receptors on the Postsynaptic Cell
Neurotransmitter is removed from the Synaptic Cleft
SNARE Proteins
are proteins in the nerve terminal; are involved in moving synaptic vesicles to terminal for release of NT into synaptic cleft)
Synaptotagmin
a protein present in the wall of the synaptic vesicle; helps bind calcium; and helps stimulate the process of exocytosis)
Acetylcholine (Ach)
at neuron-muscular junction
stimulates contraction of skeletal muscles
released by cholinergic neurons
binds to Nicotinic Receptors (respond to the drug Nicotine)
degraded by the enzyme Acetylcholinesterase; ( Sarin nerve gas, inhibits this enzyme, and Ach builds up; results in uncontrolled muscle contractions and then paralysis ).
Catecholamines
dopamine
norepinephrine
epinephrine
dopamine
muscle coordination; decreased dopamine leads to Parkinson’s disease; muscle tremors; treated by drug L-DOPA
L-DOPA is a mood elevation
Parkinson’s disease is when one doesn’t produce enough dopamine
Norepinephrine
also hormone in adrenal medulla
Epinephrine
also hormone in adrenal medulla; increases heart and respiratory rates; opens air passages
Seratonin
( formed from the amino acid tryptophan )
at least 16 types of receptors
may help regulate food intake; mood; and anxiety ( possible anti-depressant and decrease appetite )
Paxil – is a serotonin re-uptake blocker; increases concentration of Serotonin; aids in the treatment of depression
Histamine
aids in the allergic response
attracts macrophages to remove the allergen (invader)
Glutamate
many receptors
plays role in brain cell death after injury; releases toxic levels of intra-cellular calcium which kills neurons
use receptor antagonists to help minimize spread of cell death following injury to the brain
GABA (Gamma Aminobutyric Acid)
binds to ionotropic receptor; increases chloride flux into cell
these receptors also bind Xanax and Valium; help reduce anxiety; guard against seizures; and induce sleep; GABA may induce sleep
what are the types of Amino Acids
GABBA
Glutamate
Glycine
Glycine
regulate skeletal muscle contractions
neurotoxin Strychnine is an antagonist of the Glycine receptor; leads to convulsions; spastic skeletal muscle contractions; and death due to paralysis of respiratory muscles
Neuropeptides
( 85 types; contain 2 or more amino acids )
One type is: Substance P – involved in pain sensation; transmission of pain impulses from peripheral receptors to the central nervous system; Naked Mole Rats lack substance P and do not feel pain.
types of Neural circuit
diverging circuit
converging circuit
reverberating circuit
parallel after discharge circuit
diverging circuit
One nerve fiber branches and synapses with several post-synaptic cells
Each of those may synapse with many more, so input from one neuron may produce output through hundreds of neurons
Example – one motor neuron of the brain can stimulate thousands of muscle fibers
Converging Circuit
Input from many nerve fibers is funneled to one neuron or neural pool
Examples:
Such arrangement allows input from your eyes, inner ears, and stretch receptors in your neck to be directed to an area of the brain concerned with the sense of balance
A respiratory center in your brainstem receives input from other parts of your brain, from receptors for blood chemistry in your arteries, and from stretch receptors in your lungs; the respiratory center can then produce an output that takes all of these factors into account and sets an appropriate pattern of breathing
Reverberating Circuit
Neurons stimulate each other in a linear sequence such as A > B > C > D;
but neuron C sends an axon collateral back to A
As a result, every time C fires it not only stimulates output neuron D, but also re-stimulates A and starts the process over
Such a circuit produces a prolonged or repetitive effect that lasts until one or more neurons in the circuit fail to fire, or an inhibitory signal from another source stops one of them from firing
Examples:
A reverberating circuit sends repetitious signals to your diaphragm and intercostal muscles to make you inhale; when the circuit stops firing, you exhale; the next time it fires, you inhale again
May also be involved in short-term memory
May play a role in uncontrolled “storms” of neural activity that occur in epilepsy
Parallel after discharge circuit
An input neuron diverges to stimulate several chains of neurons
Each chain has a different number of synapses, but eventually they all re-converge on a single output neuron; their signals arrive at the output neuron at different times
The output neuron may go on firing for some time after input has ceased
No feedback loop; once all of the neurons in the circuit have fired, the output ceases
Continued firing after the discharge has stopped is called after-discharge
Examples:
When you stare at a lamp, then close your eyes, and continue to see the image of it for a while
Important in withdrawal reflexes; in which a brief pain produces a longer lasting output to the limb muscles and causes you to draw back your hand or foot from danger
