Nervous System 1 Flashcards
How many nerve pairs in PNS
43
12 pairs of cranial nerves (bypass spinal cord)
31 pairs of spinal nerves
Two subdivisions of the nervous system
CNS (brain and spinal cord)
Peripheral NS (PNS) - nerves leading to and from CNS
3 functions of NS
Sensory
Integrative
Responsive
Sensory
Detection of internal/external changes
Integrative
To decide on a course of action
Responsive
Motor neurons –> adjustments
Plastic
Changeable/mold-able
-the brain is plastic
What controls entire body?
nervous (fast) and endocrine systems (hormones- more slowly)
3 properties of nerve cells
Excitability, conductivity, and secretion of neurotransmitters and other chemical messengers
How and how fast does the nervous system transmit messages?
Using both electrical impulses and neurotransmitters at great speed (1-10 msec.)
Go/stop very quickly
Are NS effects local? When does the response stop?
It’s effects are relatively local and the response stops when the stimulus ceases
In the NS, what does prolonged stimulation result in?
Adaptation
How does the endocrine system send messages?
Send chemical messages (hormones) into the bloodstream that are generally much slower to act
Diff between where NS messages go and endocrine messages go
NS- effects are relatively local
Endocrine- send chemical messages (hormones) into bloodstream
What can responses in endocrine system be?
Systemic (affects entire body)- are slow to adapt and last long after the stimulation ceases
Exception to endocrine responded being systemic- slow to adapt and last long after stim ceases
Adrenaline (epinephrine)
Neuroglia
Cell of nervous system that’s NOT neurons
Helper cells of nervous tissue; bind neurons together and provide a supportive framework among other functions.
How many neuroglia are there compared to neurons and what do they NOT do?
They outnumber neurons 50 to 1
They do NOT conduct an impulse
6 types of neuroglia
Schwann cells (PNS), satellite cells (PNS), oligodendrocytes (CNS), astrocytes (CNS), ependymal cells (CNS), and Microglia (CNS).
Schwann cells
(Neuroglia in PNS)
Form neurilemma (membrane) around all cells they cover and often a myelin sheath around neuron fibers they cover in successive wrappings. Necessary for the regeneration of cut neurons.
Myelin sheath
Not every nerve has this; light in color fat
Cover neurons so impulse can move very fast
How do schwann cells make myelin
Make concentric circles around nerve
Gaps of Schwann cells are called ..
Nodes of ranvier
Covered sections of schwann cells are called…
Internodes
Satellite cells in PNS
Little is known of their function
Saltatory conduction
Electrical impulse on myelinated cell
Where on a neuron does myelin cover
Axon NEVER dendrites
Both neurilemma and myelin around one axon
What do you need to repair nerves
Need schwann cells
Oligodendrocytes
(Neuroglia- CNS)
Name=a few branches
Form myelin sheaths in CNS and wrap several cells
**Saltatory conduction is possible here also
Can one oligodendrocyte myelinate many axons?
YES
Astrocytes
(Neuroglia- CNS)
- Abundant, star-shaped cells in CNS
- In contact with endothelial cells (doesn’t conduct electrical impulse)
- produce some factors that encourage some stem cells to become transformed into neurons; under specific lab conditions, some stem cells can be coaxed into becoming astrocytes
What USED to be the believed function of astrocytes
We’re believed to be a major component of the blood brain barrier.
What is the blood brain barrier now recognized for
It’s recognized to be more attributable to tight junctions and the basal lamina of the endothelium in the brain
Ventricles
Spaces in the brain (4) lines with epithelium inside; there are ependymal cells that make cerebral spinal fluid
Ependymal cells
(CNS- nueroglia)
Helper cells- Produce and circulate cerebral spinal fluid (CSF); lines cavities in brain and spinal cord; MAY BE CILIATED
Microglia
(Neuroglia-CNS)
Helper cells- Small mobile macrophages develop from monocytes (wbc) and wander freely through CNS
get rid of waste
Soma/perikaryon
Control center of neuron (cell body) contains the nucleus and nucleolus, Nissl bodies (rough ER), supportive neurofibrils, and pigment (lipofuscin or “aging bodies”)
Nissl bodies (rough ER)
Contain ribosomes that make protein- makes something
Lipofuscin
“Aging bodies”
In soma of neuron; a harmless by-product of lysosomal breakdown (so by this we can tell how old a neuron is)
How can we tell how old a neuron is
By looking at the soma where there is lipofuscin (aging bodies)
What do mature neurons lack?
Centrioles and do not undergo mitosis past adolescence (neurons generally don’t divide)
Major cytoplasmic inclusions
(Not membrane bound)
Glycogen granules
Lipid droplets
Melanin (pigment)
Lipofuscin
Dendrites
Cellular extensions from the cell body that have receptors for neurotransmitters and recover signals from other neurons
Axon hillock
Gives rise to axon; axons vary greatly in length and end in a synaptic end bulb through which neurotransmitters are passed to the next neuron
Large neural fibers
In neuron, conduct impulses more rapidly than small ones
Myelinated fibers
Whitish color, FASTER than those that are non-myelinated bc ability to do Saltatory conduction
Collateral
Even if neuron is cut, it can use “side roads” to get where it needs to go.
can axons split?
Yes
Bipolar neuron
Neurons with one axon and one dendrite
Unipolar
(Ganglia outside CNS)
Neurons with one extension from the soma, branches shortly thereafter: peripheral process and central process.
Multipolar neuron
Neurons with one axon and several
dendrites (most common type)
Sensory neuron
Conducts nerve impulses from receptors in peripheral body parts into the brain or spinal cord
Interneuron
Transmits nerve impulses between neurons within the brain and spinal cord
Motor neuron
Conducts nerve impulses from the brain or spinal cord out to effectors-muscles or glands
What kind of neurons are mostly unipolar
Somatic sensory neurons (eye, ear, nose)
Peripheral process
Unipolar branch to these dendrites near peripheral body part
Central process
Unipolar neurons branch to this where it enters the brain or spinal cord
How are neurons classified
According to the number of extensions arising from the soma (all one way conduction- cant go back)
Axon all transport in neurons
Refers to the ways in which material within a neuron is moved (way things move in the cytoplasm)
Anterograde
(Axonal transport)
Movement away from the soma (cell body, perikaryon) toward axon
Retrograde
(Retro=back)
Movement towards the soma (perikaryon, cell body)
Can peripheral nerve fibers regenerate
Sometimes if the soma is not damages and some of the neurilemma remains intact (must be in close proximity). Need nucleus !
Neurilemma’s role in regeneration
It forms a regeneration tube through which the growing axon re-establishes its connection (allows axon to reconnect where it broke off)
What happens when a damaged nerve fiber originally led to a skeletal muscle
The muscle atrophies (shrivels/shrinks) in the absence of innervation but may under some circumstances grow when the connection is re-established
Resting membrane potential
At resting potential neurons are polarized with a resting membrane potential (RMP) of -70mV
*every cell in body
What contributes some RMP
Sodium-potassium pump; accounts for 70% of energy requirements of nervous system
Why is an electrical charge called a potential
Because it has the POTENTIAL to make charged particles move
Local potential
- Small deviation in the RMP caused by a stimulation
- something that can make charge a little more excitatory but it doesn’t continue (not permanent)
What are 4 attributes of local potentials
Graded, decremental, ineffective beyond a short distance, irreversible
Are local potentials excitatory or inhibitory?
Can be either or
Na+ to K+ ratio
3:2
Cell is more negative on inside, positive on outside
First known neurotransmitter
Acetylcholine
How do neurons, muscle cells, and Neuroglia communicate
Through gap junctions
How is much communication in nervous system accomplished?
neurotransmitters
presynaptic neuron
before synapse (axon) houses the vesicles filled with neurotransmitter in its synaptic knob
postsynaptic neuron
(proteins embedded in membrane)
contains no specializations other than proteins that function as receptors and ion gates
end plate in muscle
Motor end plate
End plate in neuron
Dendrites
Innocuous
Harmless
Can cells have receptors anywhere else other than dendrites?
Some cells have receptors in cell body; can skip over dendrites, usually happens with multiple nerve impulses
How many neurotransmitters are there?
Over 100 diff chemicals (about 120)
4 major neurotransmitters
- Acetylcholine
- Epinephrine (adrenaline)
- Norepinephrine (noradrenaline)
4 serotonin
Neuropeptides
NOT neurotransmitter !!!
Doesn’t originate in axon, short chain of amino acids that may modify neurotransmitter activity (can effect synapse)
Cholinergic synapse
Mediated by acetylcholine
Presynaptic neuron
Transmits an impulse to its synaptic knob—> synaptic vesicles—> ACh—> cleft
Post synaptic neuron
ACh binds to gated channa causing them to open; sodium and potassium cross the membrane —> a local postsynaptic potential (PSP) is
What will the postsynaptic potential (PSP) do if it’s strong enough
Opens voltage-gated ion channels, causing the neuron to fire
How do synaptic vesicles move to the end of the neuron to release neurotransmitters
By calcium ions
Acetylcholine
CNS, PNS, both?
Neurotransmitter
CNS- involved in control of skeletal muscle actions
PNS- stimulates skeletal muscle contraction at neuromuscular junctions. Excite or inhibit in autonomic nervous system actions depending on receptors
Dopamine
CNS, PNS, both?
Neurotransmitter
CNS- creates a sense of feeling good; deficiency in some brain areas associated with Parkinson’s disease
PNS- don’t need to know
Serotonin
CNS, PNS, both?
Neurotransmitter
CNS- primarily inhibitory; leads to sleepiness; enhanced by Prozac (SSRI)
Substance P
CNS, PNS, both?
Neurotransmitter
PNS- excitatory; results in perception of pain (increase pain perception)
Endorphins enkephalins
CNS, PNS, both?
Neurotransmitter
CNS- generally inhibitory; reduce pain by inhibiting substance P release
Alzheimer’s disease
—>Symptoms/Neurotransmitter imbalance/excess?
- Deficient acetylcholine
- memory loss, depression, disorientation, dementia, hallucinations, death
Clinical depression
—>Symptoms/Neurotransmitter imbalance/excess?
- Deficient norepinephrine and/or serotonin
- debilitating, inexplicable sadness
Hypersomnia
—>Symptoms/Neurotransmitter imbalance/excess?
- excess serotonin
- excessive sleeping
Insomnia
—>Symptoms/Neurotransmitter imbalance/excess?
- deficient serotonin
- inability to sleep
Mania
—>Symptoms/Neurotransmitter imbalance/excess?
- excess norepinephrine
- elation, irritability, over talkativeness, increased movements
Parkinson’s disease
—>Symptoms/Neurotransmitter imbalance/excess?
- deficient dopamine
- tremors of hands, slowed movements, muscle rigidity
Tryptophan
—> neurotransmitter affected, mechanism of action, effect
- affects serotonin
- stimulates neurotransmitter synthesis
- sleepiness
Curare
—> neurotransmitter affected, mechanism of action, effect
- acetylcholine
- decreases neurotransmitter in synaptic cleft
- muscle paralysis
Nicotine
—> neurotransmitter affected, mechanism of action, effect
- acetylcholine
- stimulates synthesis of enzyme that degrades neurotransmitter (acetylcholinesterace)
- increases alertness
Cocaine
—> neurotransmitter affected, mechanism of action, effect
- norepinephrine
- blocks re uptake
- euphoria (false sense of well being)
Monoamine oxidase inhibitors
—> neurotransmitter affected, mechanism of action, effect
- Norepinephrine
- blocks enzymatic degradation of neurotransmitter in presynaptic cell
- mood elevation (**cant take with SSRI- over excitation)
Selective serotonin reuptake inhibitors (SSRI)
—> neurotransmitter affected, mechanism of action, effect
- serotonin
- blocks reuptake
- mood elevation, anti-anxiety agent
Cessation of the signal (via neurotransmitter)
-ACh binds to receptors for very short time then dissociates from it
-removal of addition neurotransmitter in synapse by:
Diffusion
Reuptake by synaptic knob
Chemical degradation by enzymatic activity
2 examples of chemical degradation by enzymatic activity and what they do
- Acetylcholinesterace
- Monoamine oxidase (MAO)
They cease the neurotransmitter signal
What are 4 things required to qualify something as a neurotransmitter?
A substance must be synthesized by a presynaptic neuron (made in axon), released in response to stimulation, bind to specific receptors on postsynaptic cells, and alter the physiology of the same.
Neuropeptides
But-brain peptides
Neuromodulators
Hormones/neuropeptides
Inorganic gases
Nitric oxide (NO) -this influences erections
Summation
The process of adding up incoming information (nerve impulses) and responding to the net effect of it. This occurs in the AXON HILLOCK of the neuron
Why is it said that presynaptic cells converging on a single neuron facilitate each other?
Because each synapse makes it easier for the others to cause firing
Can axons form synapse with soma of another neuron
Yes
Neural coding
The way in which the nervous system converts information to a meaningful pattern of action potentials (making a message an electrical signal)
Recruitment
Aka multiple motor unit summation
-nervous system is able to judge stimulus strength by which neurons, and how many of them, are firing
Synaptic potential (presynaptic facilitation)
Occurs at synapses when thought or actions occur repeatedly, producing a well-worn pathway (repetitiveness influences pathways)
Prolonged use of a pathway causes..?
More calcium to accumulate in the synaptic knob, making impulse transmission easier in the future. *this is the process involved in learning
What is the process involved in learning?
Prolonged use of the pathway causes more calcium to accumulate in the synaptic knob, making impulse transmission easier in the future
Presynaptic inhibition
One neuron suppresses the release of neurotransmitter by another
Neuronal pools
Neurons actually function in these much larger groups, filled with thousands to millions of interneurons (association neurons in CNS*)
What happens as input fiber enters neuronal pool?
It branches and synapses with numerous neurons
What is the nature of stimulus in a neuronal pool?
Excitatory, inhibitory, or both
Neuronal circuit
The connection pathway among a series of neurons: diverging circuits, converging circuits
Neuron convergence
2 neurons come together helping 1 so it can continue
Neuron divergence
Neuron comes apart; one neuron helps 2 other neurons
