Nervous System Flashcards
Cell Body
location of nucleus, ER, ribosomes
Dendrites
appendages from soma that received incoming signals from other cells
Axon Hillock
- integrates incoming signals from dendrites
- plays key role in initiation of APs by summing inhibitory and excitatory signals from dendrites
Myelin
- insulate axons to prevent signal loss/crossing of signals
- maintains electric signal in neuron
- increases speed of conduction
- nonpolar
- made of lipids (poor conductor of electricity)
Oligodendrocytes
- produce myelin in the CNS
- can myelinate multiple neurons at once
Schwann Cells
- produce myelin in the PNS
- can only myelinate one neuron at once
Synapse
space between neurons containing the synpatic cleft, nerve terminal, and postsynaptic membrane
Nerve
multiple neurons bundled together in the PNS
Ganglia
- structures containing cell bodies of neurons and glial cells
- function like relay stations - one nerve enters and the other exits
Tracts
- bundles of axons in the CNS
- only carry one type of information
Nuclei
group of cell bodies in the same tract
Glial Cells
- non-neuronal cells in both the CNS and PNS
- function in myelin formation, supporting neurons, and providing nutrients to neurons
Astrocytes
- nourish neurons
- form blood-brain barrier – controls the transmission of solutes from bloodstream into nervous tissue
Ependymal Cells
- line ventricles of the brain
- produce cerebrospinal fluid which physically supports the brain and acts as shock absorber
Microglia
phagocytic cells that ingest and break down waste products and pathogens in CNS
Resting Potential
- net electric potential difference that exists across cell membrane
- -70 mV
- more negative inside the cell than the outside
What is the concentration of K+ inside the cell?
140mM
What is the concentration of K+ outside the cell?
4mM
What is the equilibrium potential of K+?
-90mV
Potassium Leak Channels
allow slow leak of K+ outside the cell
Is the cell more permeable to K+ or Na+?
K+
What is the concentration of Na+ inside the cell?
12mM
What is the concentration of Na+ outside the cell?
145mM
Sodium Leak Channels
slow leak of Na+ into the cell
What is the equilibrium potential of Na+?
60mV
Na+/K+ ATPase
pumps 3 Na+ out of cell and 2 K+ into cell
Threshold Potential
- ranges from -55mV to -40mV
- reached when the axon hillock receives enough excitatory input and an AP is triggered
Temporal Summation
- multiple signals integrated during short period of time
- number of small excitatory signals firing at nearly the same moment
Spatial Summation
- additive effects are based on the number and location of the incoming signals
- large number of inhibitory signals firing directly on soma cause more hyperpolarization of axon hillock than depolarization caused by few excitatory signals on dendrites
Steps of Action Potential (6)
(1) cell brought to threshold (-50mV)
(2) opening of voltage-gated Na+ channels (triggered by depolarization)
(3) Na+ channels inactivated at +35mV (inactive until resting potential is reached)
(4) K+ voltage-gated channels open to repolarize the cell
(5) efflux of K+ causes overshoot of resting potential (hyperpolarization)
(6) Na+/K+ ATPase restores resting potential
3 States of Na+ Channel
- closed: before cell reaches threshold and after inactivation has been reversed
- open: from threshold to about 35mV
- inactive: from about 35mV to resting potential
Absolute Refractory Period
no amount of stimulation can cause AP to occur
Relative Refractory Period
must be greater than normal stimulation to cause AP because membrane is more negative than it is at resting potential
List the steps involved in impulse propagation (4)
(1) Na+ rushes into one segment of axon and causes depolarization in surrounding regions of axon
(2) depolarization brings subsequent segments of axon to threshold which opens Na+ channels in those segments
(3) each segment continues through rest of AP on wavelike fashion until AP reaches nerve terminal
(4) after each AP goes through a segment, the segment becomes refractory which prevents information from flowing in opposite direction
What are the effects on resistance and conduction when axon length increases?
- increased resistance
- slower conduction
How does increasing cross-sectional area of an axon effect AP propagation?
leads to faster propagation due to decreased resistance
Saltatory Conductance
“hopping” of AP signal from one node of ranvier to the next along the axon
Effector Cell
postsynaptic cell that is a gland or muscle that receives a signal from a neuron
How are neurotransmitters released from the nerve terminal?
-AP opens Ca2+ channels in nerve terminal which allows Ca2+ to flow into cell and triggers fusion of membrane-bound vesicles with cell membrane at synapse leading to exocytosis of neurotransmitter
What happens if NT binds to a ligand-gated ion channel on the post synaptic cell?
cell will be depolarized or hyperpolarized
What happens if NT binds to a G-protein coupled receptor on the post synaptic cell?
there will be changes in levels of cAMP or an influx of Ca2+
List 3 mechanisms to regulate NTs
- NTs broken down by enzymatic reactions –ex. breakdown of ACh by AChE
- NTs brought back into presynaptic neuron via reuptake carries –ex. reuptake of serotonin, dopamine, NE
- NTs may diffuse out of synaptic cleft –ex. NO is a gaseous signaling molecule that does thus
List functions of the nervous system
- sensation and perception
- cognition and problem solving
- memory
- emotion and emotional expression
- regulation of endocrine organs
- motor function
- executive function and planning
- language comprehension and creation
- balance and coordination
- regulation of heart rate and breathing etc
Sensory Neurons
- known as afferent neurons
- transmit sensory information from receptors to spinal cord and brain
- cell bodies located in dorsal root ganglion toward back of spinal cord
Motor Neurons
- efferent neurons
- transmit motor information from the brain and spinal cord to muscles and glands
- run from brain along opposite side if spinal cord and in the ventral root to control movement of skeletal muscle and glandular secretion
Interneurons
- found between other neurons
- predominantly located in the brain and spinal cord
- often linked to reflexive behavior
Which type of neurons are the most numerous in the human body?
interneurons
White Matter
- found in brain
- consists of axons encased in myelin sheaths
Grey Matter
- found in brain
- consists of unmyelinated cell bodies and dendrites
What are the four divisions of the spinal cord from top to bottom?
(1) cervical
(2) thoracic
(3) lumbar
(4) sacral
Vertebral Column
- transmits nerves at the space between adjacent vertebrae
- protects spinal cord
Dorsal Root Ganglion
where the cell bodies of sensory neurons are found in the spinal cord
Peripheral Nervous System
- composed of nerve tissue and fibers outside of the brain/spinal cord
- includes all 31 pairs of spinal nerves and 10/12 pairs of cranial nerves
- connects CNS to rest of body
- consists of somatic NS and autonomic NS
What two nerves are outgrowths of the CNS?
optic nerve and olfactory nerve
Somatic Nervous System
- consists of sensory and motor neurons distributed throughout skin/joints/muscles
- motor neuron goes directly from spinal cord to muscle without synapsing
Autonomic Nervous System
- controls involuntary muscles association with many internal organs and glands
- independent of conscious control
- manages heartbeat, respiration, digestion, temperature control and glandular secretions
- use of two neurons in series (preganglionic neuron and postganglionic neuron) to transmit signals from spinal cord
- contains 2 subdivisions: sympathetic NS and parasympathetic NS
Where is the soma of a preganglionic neuron located?
CNS
Where does the preganglionic neuron synapse on the soma of a postganglionic neuron?
PNS
Parasympathetic Nervous System
- main role is to conserve energy
- associated with rest and sleep states
- acts to reduce heart rate, constrict bronchi, constrict pupils, stimulates saliva, stimulates bile release, contracts bladder
- manages digestion by increasing peristalsis and exocrine secretions
What is the main NT responsible for parasympathetic responses?
ACh
Vagus Nerve
- cranial nerve X
- responsible for much of parasympathetic intervention of thoracic and abdominal cavity
Sympathetic Nervous System
- activated by stress
- functions: increase heart rate, redistributes blood to muscles of locomotion, increase blood glucose concentration, relaxes bronchi, dilates eyes
Sympathetic preganglion neurons release: ____
Sympathetic postganglion neurons release: ____
- ACh
2. NE
Monosynaptic Reflex Arch
- single synapse between sensory neuron that receives the stimulus and the motor neuron that responds to it
- ex. knee-jerk reflex
Polysynaptic Reflex Arch
- there is at least one interneuron between the sensory and motor neruons
- ex. stepping on a nail
Describe the processes that occur when you step on a nail (involves withdrawal reflex)
(1) extremity that steps on nail flexes and pulls foot away from nail (monosynaptic reflex)
(2) interneurons that connect to incoming signals in spinal cord provide signals to motor neurons in opposite leg
(3) quads in opposite leg are stimulated and person can maintain balance
Enteric Division of the NS is part of the ___ NS.
autonomic
The ___ NS is typically active in digestive tract, pancreas and gallbladder.
Enteric
The Enteric NS regulates ____ and ____
- secretion
- peristalsis
What 3 ions are neurons selectively permeable to?
- K+
- Na+
- Cl-
What is the concentration of Cl- inside the cell?
10mM
What is the concentration of Cl- outside the cell?
120mM
K+ flows from high to low concentration, which means it naturally wants to flow ___ the cell
out of
Na+ flows from high to low concentration, which means it naturally wants to flow ___ the cell
into
Cl- flows from high to low concentration, which means it naturally wants to flow ___ the cell
into
During the resting potential of a neuron (___mV), all ___ channels are closed and all ___ channels are open
- (-70mV)
- gated
- ungated
If the potential is above ___mV an AP must occur. If it is below this voltage then an AP will not occur.
-50mV
What occurs during the first step of an AP, when the neuron receives a signal?
(1) NT bings to a receptor
(2) receptor bings to the Na+ ligand-gated channels which then open and allow Na+ to flow into the cell
What occurs during the second step of an AP?
(1) cell gets more positive as Na+ flows in; voltage-gated Na+ channels continue to open as depolarization occurs
(2) cell fires an AP once it reaches -50mV, and depolarization continues
What occurs during the third step of an AP, the peak point of an AP (+35mV)?
(1) voltage-gated Na+ channels close
(2) some voltage-gated K+ channels open which allow K+ to rush out of the cell and thus makes the cell less positive
What occurs during the fourth step of an AP, repolarization?
(1) voltage-gated K+ channels stay open until the membrane potential is about -90mV
What occurs during the fifth step of an AP, hyperpolarization?
(1) the membrane potential dips below resting potential (-70mV)
(2) voltage-gated K+ channels begin to close at -90mV
What occurs during the sixth and final step of an AP, refractory period?
(1) cells works to restore resting potential via Na+/K+ ATPase which pumps 3 Na+ out and 2 K+ in per 1 ATP
Nodes of Ranvier are enriched in ___ gated channels. This is also where charge crosses the membrane.
Na+
opening of these channels allows for Na+ to rush into the sell and trigger an AP that sends the signal down the cell
How do Ionotropic receptors work?
an ion binds to the receptor which opens a channel
How do Na+ ligand gated channels work?
- a ligand (typically a NT) binds and opens the channel for Na+ to flow in
- the cell gets more positive inside
How do Cl- ligand gated channels work?
- a ligand binds and opens the channel for Cl- to flow into the cell
- the cell gets more negative on the inside which inhibits the post synaptic potential and hyperpolarizes the cell
At what membrane potential do K+ channels close?
-90mV
What is the primary function of the myelin sheath?
it increases the rate of conduction of APs
What ion regulates synaptic vesicle discharge?
Ca2+
What are 3 ways that can stop an AP?
- enzyme degrades NT after being signaled to the post-synaptic neuron
- re-uptake of NT back into the pre-synaptic neuron
- NT diffuses into the blood
How do SSRI’s work?
- prevent the re-uptake of serotonin into the pre-synaptic neuron, which means that serotonin is left in the synaptic cleft longer which could signal to the next neuron more and fire more APs
- depression occurs when serotonin doesn’t trigger enough APs
What two functional groups are found in ACh?
- ester
- amine
Can ACh cross the membrane?
No - it must bind to an extracellular receptor
How does ACh work at the neuromuscular junction (NMJ)?
(1) ACh binds to a Na+ ligand gated channel at the post-syn motor neuron
(2) Na+ rushes into cell and triggers an AP (excitatory!!)
(3) muscle contracts
Metabolic ACh receptors are located in the ___ and ___
- CNS
- heart
ACh binding at a metabolic ACh receptor on the heart, signals a __-___ cascade which leads to a ___ heart rate
- g-protein
- reduced
What 3 NTs are biological amines?
- NE
- Dopamine
- Serotonin
__ and __ are derived from the amino acid Tyrosine
- NE
- Dopamine
__ is derived from the amino acid Tryptophan
Serotonin
___ and ___ effect sleep, mood, attention and learning
- Dopamine
- Serotonin
Norepinephrine
- in the ANS it is excitatory (involuntary-autonomic function)
- can also act as a hormone (remember hormones are found in the blood)
Dopamine
- generally excitatory but can be inhibitory at some sites
- found in both the CNS and PNS
Serotonin
- generally inhibitory
- found in the CNS
What are the 3 main amino acids found in the nervous system?
- GABA (gamma-aminobutyric acid)
- Glutamate
- Glycine
GABA is a(n) ____ NT that works by increasing membrane permeability to __ which makes the cell more ___ and thus ___ any other APs
- inhibitory
- Cl-
- negative
- inhibits
Glutamate is ____ and involved in ___ __ memory
- excitatory
- long-term
Glycine is ____ and found in the ___ NS
- inhibitory
- central
Substance P is a ____ that is involved in the perception of ____.
- neuropeptide
- pain
Met-Enkephalin (an endorphin) is _____ and ____ pain perception
- inhibitory
- decreases
