Organization of the Nervous System Flashcards
The Central Nervous System is comprised of:
The brain and spinal cord
How many neurons are in the body?
100 Billion
How many dendritic synapses are on each neuron?
100 to 200,000
How many synapses are in the nervous system?
1 Trillion
What are axon branches called?
Collaterals
What is myelin sheath made of?
Schwann cells
Gaps between myelinated segments are called?
Nodes of Ranvier
Afferent nuron:
Sensory, Dorsal
Efferent Neuron:
Motor, Ventral
Interneurons are generally:
Inhibitory
Bipolar neurons
Found in eyes, nose and ears
Have a single axon and a single dendrite extending from opposite sides of the cell
Unipolar neurons
Found in ganglia outside CNS
Arising from a single short fiber extending from the cell body
Multipolar neurons
Found in the brain and spinal cord
Have many nerve fibers arising from their cell bodies
Sensory neurons (afferent neurons)
Usually unipolar, although some are bipolar neurons
Interneurons
Are multipolar neurons lying within the CNS that form links between other neurons
Motor neurons
Are multipolar neurons that conduct impulses from the CNS to effectors
The peripheral nervous system breaks down into:
Somatic and Autonomic
The Autonomic nervous system breaks down into:
The Sympathetic and Parasympathetic
What does the Somatic NS do?
Carries sensory information form sensory organs to the CNS and relays motor (movement) commands to muscles; controls voluntary movements
What does the Autonomic NS do?
Regulates involuntary bodily processes, including heart rate, respiration, digestion, and pupil contraction operates automatically without conscious direction
Lower regions of the brain control:
Automatic, instantaneous muscle responses
High regions of the brain control:
Deliberate complex muscle movements, thought processes
What is the “Reflex Arc”
Interneuron is used for a quick reflex
How much sensory information is discarded by the brain?
99% (clothing contact, background noise, etc.)
What are Glia?
Structural neurons in the brain
The side of the body (or spinal cord) opposite:
Contralateral
The same side of the body (or spinal cord):
Ipsilateral
What is it called when a nerve crosses to the other side?
It Decussates
Axo-somatic Synapse
The synapse between an axon and the soma (cell body)
Axo-dendritic Synapse
A synapse between an axon and a dendrite
Axo-axonic Synapse
A synapse between an axon and another axon
Neuropeptides are what size?
Big
Neurotransmitters are what size?
Small
Things that can happen to synapses
Facilitation, inhibition, disfacilitation, disinhibition
Where are neurotransmitters synthesiszed?
Within the presynaptic neuron
A biochemical mechanism for inactivation of a neurotransmitter
is always present
A ligand-gated ion channel is considered:
Ionotropic (e.g. nicotinic)
A G-protein-coupled receptor is considered:
metabotropic (e.g. muscarinic)
Open a Cation channel (Like Na+)
Excitatory transmitter
Open an anion channel (Like Cl-)
Inhibitory transmitters
Where are Neuropeptides synthesized?
Ribosomes
Neuropeptides usually:
Slow actions, are larger molecules
Synthesis of DOPA
Tyrosine hydroxylase catalyzes the conversion of Tyrosine into DOPA
The rate-limiting enzyme in catecholamine biosynthesis is?
Tyrosine hydroxylase
Synthesis of Dopamine
DOPA decarboxylase decarboxylizes DOPA into Dopamine
Synthesis of Norepinephrine
Dopamine is converted by Dopamine beta-hydroxylase (DBH) into Norepinephrine
Synthesis of Epinephrine
Norepinephrine is converted by phenylethanolamine-N-methyltransferase (PNMT) into Epinephrine
5-hydroxytryptamin (5-HT, serotonin) Synthesis
tryptophan
tryptophan hydroxylase
5-hydroxytryptophan
decarboxylase
5-hydroxytryptamin (5-HT, serotonin)
Synthesis of GABA
glutamate is decarboxylated by glutamate decarboxylate into GABA
GABA (gamma aminobutyric acid) Metabolism
GABA
GABA-glutamate transaminase
succinate semialdehyde
succinate-semialdehyde-dehydrogenase
into succinate
GABA is:
The major inhibitory transmitter in the brain
glutamate is:
the major excitatory transmitter in the brain
Norepinephrine metabolism
If metabolized by monoamine oxidase (MAO) initially it is changed into dihydroxymandelic acid and then is converted to Vanillylmandelic acid (VMA) by catechol-O-methyltransferase (COMT)
if metabolized by COMT initially it is changed into Normethanephrine and then metabolized into VMA by MAO
Epinephrine metabolism
Monoamine oxidase (MAO)
dihydroxymandelic acid
Vanillylmandelic acid (VMA)
catechol-O-methyltransferase (COMT)
Or
COMT
Metanephrine
MAO
VMA
How many kinds of neurotransmitters are produced by the nervous system
At least 50
Acetylcholine action (e.g.):
Voluntary movement of the muscles
Epinephrine action (e.g.)
“fight or flight”
Norepinephrine action (e.g.)
Wakefulness or arousal
Dopamine action (e.g.)
Voluntary movement and emotional arousal
Serotonin action (e.g.)
Memory, emotions, wakefulness, sleep and temperature regulation
GABA (gamma aminobutyric acid) action (e.g.)
Motor behavior
Glutamate action (e.g.)
Excitatory relative of GABA
Glycine action (e.g.)
Spinal reflexes and motor behavior
Neuromodulators action (e.g.)
sensory transmission - especially pain
Nerve Organization
Nerve - Fascicle - bundle of nerve fibers - single nerve fiber
Nerves can be:
sensory, motor, or mixed carrying both sensory and motor fibers
Actual somatic receptors (big multi-celled structures which collect External data and send it via the nerves to the CNS) are represented by:
Big “R” Receptors
Receptors (the tiny intracellular structures that respond to some signal)
Small “r” receptors
Neuronal reflexes in the cord can assist with:
Walking, Withdrawal reflex, Balancing reflex, Autonomic reflex
The cold is not just a telephone wire it clearly has its own primitive __________ ___________?
Memory circuits
Arterial pressure, Respirations, Equilibrium, Salivation, Emotions, are all considered?
Subconscious activities
Considered lower brain/Sub cortical level where “Subconscious Activities” happen:
Medulla, Pons, Mesencephalon, Hypothalamus, Thalamus, Cerebellum, & Basal Ganglia.
Higher brain/ Cortical level:
“Memory Storehouse” Functions with the lower Bain, cannot function alone, Precise, Thought process.
Aa:
Motor, Myelinated, Large (Muscle control)
Aa/B:
Sensory, Myelinated, Large (Touch, Vibration, Position perception)
A gamma:
Sensory, Thinly myelinated, Small (Cold perception, Pain
C:
Sensory, Un-myelinated, Small (Warm perception, Pain)
A gamma:
Autonomic, Thinly myelinated, Small (HR, B/P, Sweating, GIT, GUT, Function)
C:
Autonomic, Un-myelinated, Small (HR, B/P, Sweating, GIT, GUT, Function)
What is the “labeled line” principle?
One nerve fiber only has one type of receptor and only carries one type of sensation (Pain, Temperature, Touch, etc.). If activated, it will only carry this sensation regardless of the manner in which it is stimulated. Thus, each axon could be “labeled” as a specific sensation going to a specific location in the brain.
What is the Law of projection?
Each nerve fiber if stimulated, (anywhere along its entire length) the stimulus is perceived as if it is coming from its point of origin.
What is “Population Coding”
In populating coding, one cell can encode more than one sensory modality, and it is the combination of many cells that make up the perception. An example of this is color vision. Each color photoreceptor is most sensitive to a specific color (blue, green, or red), but a range of wavelengths can elicit changes in firing rates in the neuron. Therefore, the responses from a population of color photoreceptors must be combined to perceive the full spectrum of color.
Higher level processing of taste and olfaction also uses population coding – sometimes the sense of smell is needed in addition to the sense of taste to fully perceive a flavor. Have you ever been congested from a cold and food just doesn’t taste the same? That’s due to this combining of the senses for a full perception.
FabFive “R” Receptors - what Receptor responds to touch or pressure?
Mechanoreceptors
FabFive “R” Receptors - what Receptor responds to heat or cold?
Thermoreceptors
FabFive “R” Receptors - what Receptor detects tissue damage?
Nociceptors
FabFive “R” Receptors - what Receptor detects change in body chemistry?
Chemoreceptors
FabFive “R” Receptors - what Receptor detect emitted electromagnetic radiation (i.e. light)
Electromagnetic Receptors
How many and what types of thermoreceptors are there?
Cold receptors and Warm receptors
Are there more “cold spots” or warm spots”?
There are 3 to 10 more “cold spots” than “warm spots”
What does a Nociceptor sense?
Responds to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. this process, called nociceptoin usually causes the perception of pain.
Water are Nociceptor free nerve endings found?
Viscera, material walls, periosteum, skin, organ capsules, and joint surfaces.
Characteristics of FAST nerve fibers:
Bigger, Myelinated, Type A
Characteristics of SLOW nerve fibers:
Small, Unmyelinated, Type C
What receptors “never adapt”
Chemoreceptors and fee nerve endings
Spatial summation
a lot of stimuli from a lot of DIFFERENT places
Temporal summation
A lot of stimuli form ONE place that occur closely spaced in time
What is it called when - A single neuron within a pool receives impulses from two or more fibers which makes it possible for the neuron to summate impulses from different sources?
Convergence
What is it called when - Impulses leaving a neuron in a pool are passed into several output fibers, a pattern that serves to amplify an impulse?
Divergence
What is it called when a neuron provides both excitatory and inhibitory input simultaneously, stimulating excitatory synapses on one neuron and inhibitory on another?
Reciprocal inhibition (e.g. patellar tendon (knee jerk) reflex)
Oscillatory circuits are important for:
Neuronal pools that must fire repeatedly (cardiac, respiratory, and vascular controls)
Oscillatory circuits - Interneurons:
Serve to modulate responses (add shades of gray-modulation)
Oscillatory circuits - Nerves can:
re-excite themselves, and also inhibit themselves
