Nervous System Flashcards
What is the function of the nervous system
A communication system that coordinates body function using electrical and chemical signals
What is the organization of the nervous system
Central nervous system (brain and spinal cord, interneurons), peripheral nervous system (sensory neurons and motor neurons), and enteric nervous system (digestive)
What types of neurons flow into the CNS vs out
Sensory (afferent) in, motor (efferent) out
What kinds of motor neurons are there
Somatic (skeletal muscles) and autonomic (smooth muscle, cardiac muscle, endocrine and exocrine glands, and adipose tissue)
What two cells primarily make up the nervous system
Neurons and glial cells (support cells)
What is the function of the myelin sheath
To speed up communication between neurons by insulating
What is the makeup of a neuron
Dendrite (input where signals are received), cell body/soma (nucleus), trigger zone (integration and spike initiation), axon (long distance conduction), and presynaptic axon terminal (signal output)
What are the nodes of Ranvier
The space between Schwann cells in the myelin sheath where the AP must be regenerated
What two glial cells can form a myelin sheath
Oligodendrocytes (in CNS, can wrap up to 15 axons), and Schwann cells (in PNS, wrap 1 axon)
Define presynaptic and postsynaptic cells
Presynaptic delivers the signal at a synapse and postsynaptic receives that signal
What are the two kinds of electrical signals in neurons
Graded potentials (local, from input region to trigger zone), and action potentials (long distance, from trigger zone to presynaptic axon terminal)
At the trigger zone what kind of electrical signals are present
Both graded potentials and action potentials
What are the 4 characteristics of graded potentials
Originate in input region because of opening of gated channels, decrease in amplitude with distance, amplitude and duration matches that of the stimulus, can be excitatory or inhibitory
What does it mean for graded potentials to be excitatory or inhibitory
Depending on ion flow, they can depolarize the cell and make it easier to produce AP (excitatory), or hyper polarize the cell and make it harder to produce AP (inhibitory)
What are the two kinds of graded potentials
Receptor potential (starts in sensory neuron, ligand/mechanical/voltage gated) and synaptic potential (EPSP or IPSP in interneurons and motor neurons, ligand gated)
What is a subtype of synaptic graded potentials
End-plate potential in skeletal muscle (can only excite, ligand gated)
How does a graded potential trigger an action potential
The summation of different graded potentials depolarize the cell, via opening of gated channels, past a certain threshold
What happens depending on where a graded threshold adds up to in relation to the threshold
Subthreshold = no AP, suprathreshold = AP, at threshold = 50/50 chance of AP
Which electrical signal is faster
Action potentials
What are the characteristics of action potentials
Don’t decrease in amplitude as the propagate, all-or-none (don’t summate, must reset)
How does action potential relate to the stimulus
Amplitude of the stimulus relates to AP frequency, stimulus duration is proportional to the amount of time that the AP is being produced
What types of channels are used in action potential in neurons and skeletal muscle
Voltage-gated channels (H-H Na+ and H-H K+)
What are the characteristics of the H-H Na+ channel
2 gates, closed when resting or depolarized, opens to let Na+ into the cell (depolarizes cell), time dependent inactivation, positive feedback loop
What are the characteristics of the H-H K+ channel
1 gate, closed when resting or repolarized, opens to allow K+ to flow out (hyperpolarizes), delayed compared to sodium
About how much depolarization is needed to activate H-H Na+ and H-H K+
~15-20 mV
What stops the H-H Na+ positive feedback loop
Time dependent inactivation of the H-H Na+ and the delayed opening of voltage-gated K+ channels
What is afterhyperpolarization
Period of time below the resting membrane potential (caused because voltage-gated K+ channels don’t open until Vrest is reached, then take time to close)
What are the refractory periods
During and following an AP, absolute = no excitability/can’t produce AP, relative = little bit later, can produce some AP (stronger over time)
What state are channels in during each refractory period
Absolute = Na+ opens, then inactivates and K+ opens, relative = both channels are resetting
What causes AP to propagate/regenerate
Local depolarization (can’t go backwards because of refractory period)
What is another term for the speed of propagation of an AP
Conduction velocity
What 2 mechanisms increase conduction velocity
Diameter of the axon (larger = faster, bc/ small diameter creates resistance) and myelination of an axon (more myelin = more insulation = faster)
What is saltatory conduction
AP propagation through myelinated axons
What are the 2 types of synapses
Electrical and chemical
What is a characteristic of electrical synapses
Gap junctions (channels btwn. cells) that allow for synchronized activity and rapid signal conduction in both directions
What are the 4 characteristics of chemical synapses
Paracrine signaling, majority of synapses, most NTs are stored in vesicles and exocytosed in response to AP, slower but more flexible with opportunities for amplification
What do neurotransmitters diffuse across
The synaptic cleft
What is the purpose of action potential
To open voltage-gated Ca2+ channels for exocytosis of synaptic vesicle contents
What characteristics of APs does the release of neurotransmitters/neurocrines depend on
The frequency of AP (determines how much NT will be secreted) and the duration of the spike train (time releasing NT)
What are the major neurocrines of the PNS
Acetylcholine (ACh), norepinephrine (NE), and epinephrine (E)
What are the postsynaptic receptor types
ACh receptors (nicotinic and muscarinic) and adrenergic (alpha 1,2; beta 1, 2, 3)
What are the 2 basic receptor groups
Ionotropic (directly-gated, ligand-gated, channel protein) and metabotropic (indirectly-gated, GPCR/RE)
What terminates neurotransmitter activity
Inactivation (breakdown of ACh in synaptic cleft using enzymes), reuptake (NE and E transported out of the synaptic cleft), and diffusing away into the blood (not major)
What does the afferent division of the PNS do
Detects, encodes, and transmits signals about the internal and external environment to CNS
What is a phasic receptor
Rapidly adapting (only relay information about when the stimulus starts and stops)
What is a tonic receptor
Slowly adapting (continuously responds throughout stimulus duration)
What are the special sense receptors
Have specialized organs devoted to them: tase, vision, hearing, equilibrium, and smell (olfaction)
What are somatosensory receptors
Collect information from cutaneous sensations (surface): touch, pain, skin temperature, and proprioceptive sensations (muscles and joints): muscle length and force, joint position
What are interoceptors
For visceral senses, detect stimuli within internal organs (e.g. chemoreceptors, baroreceptors, osmoreceptors) –> Monitor internal environment
What is somatotopy
The spinal cord is organized based on where the information/signal is going to
What are the sensory parts of the spinal cord
Dorsal root (cell bodies stored in dorsal root ganglion apart from spinal cord) and dorsal horn (somatic and visceral)
Where are decussations (crossing over)
Medulla and dorsal column-medial lemniscus tract (fine touch, proprioception, vibration) and spinal cord in anterolateral tract (nociception, temperature, coarse touch
What are the characteristics of the thalamus
Relay station (not for olfaction) with many nuclei (one for each type of sensory information)
What are the autonomic control centers of the brain
Forebrain (diencephalon - hypothalamus) and brain stem (medulla oblongata and pons)
What types of things are under autonomic control
Temperature control, water balance (release of vasopressin), eating behavior and appetite, urinary bladder, blood pressure control, and respiratory center
Where is sensory information processed
In the cerebral cortex (in charge of perception/brain’s interpretation of sensory stimuli and planning of movements)
What does the motor cortex control and where do they travel?
Somatic motor neurons (descends through corticospinal tracts in spinal cord that cross at medulla)
What does the somatic motor division control
Skeletal muscle via somatic (alpha) motor neurons
What are 3 characteristics of alpha motor neurons
Control skeletal muscle contractions (mostly volunatry), under tonic control, neuron starts in ventral horn and leaves via ventral root
What are the characteristics of the neuromuscular junction
Somatic motor neurons (always excitatory) release ACh onto sarcolemma
What type of receptors does the sarcolemma contain
Nicotinic acetylcholine receptors (nAChR): ionotropic (ligand-gated that cause depolarization) in motor end-plate
How does a nAChR cause function
Binding of ACh opens an ion channel that lets in 2Na+ and out 1K+ (causes depolarization) that creates a graded/end-plate potential
What does the end-plate potential do
Causes voltage-gated Na+ channels to open in muscle membrane leading to sarcolemmal action potential that propagates down a T-tubule and causes muscle contraction (always supra-threshold)
How long does ACh have effects for
As long as it’s around
What does acetyltransferase do
Makes acetylcholine from acetyl CoA (comes from Krebs cycle) and choline (from diet)
What does acetylcholinesterase (AChE) do
Enzyme on postsynaptic cell membrane that breaks down ACh into acetate (waste product) and choline (transported and recycled)
What are cholinergic neurons and receptors
Neuron makes and releases ACh as a signal while the receptor (nicotinic, muscarinic) binds and responds to it
What are adrenergic neurons and receptors
Neuron makes and releases E/NE as a signal and receptor (alpha and beta) binds and responds
What are different names for types of neurocrines
Cholinergic (relates to ACh), adrenergic (NE/E), dopaminergic, serotonergic, GAB, histaminergic, glutamatergic
What sorts of things does the autonomic division of the PNS control
Cardiac and smooth muscle, exocrine and endocrine glands, lymphoid and some adipose tissue), mostly involuntary
What are the two branches of the autonomic division of the PNS
Parasympathetic and sympathetic (most effectors are connected to both, can be excitatory and inhibitory)
What is autonomic tone
Background activity that allows for a balance between the parasympathetic and sympathetic divisions)
What responses does the autonomic nervous system create and what influences them
Creates autonomic, endocrine, and behavioral responses, influenced by the cerebral cortex and limbic system
What sorts of autonomic neurons are only innervated by one branch
Sweat glands and smooth muscle of most blood vessels are only innervated by the sympathetic nervous system
How many neurons are in an autonomic pathway
At least 2 in series (meet in an autonomic ganglion)
What are the characteristics of the sympathetic pathway
Short preganglionic neurons (in thoracic and lumbar segments), ong postganglionic neurons
What are the 4 characteristics of the parasympathetic pathway
Vagus nerve contains most of the fibers, ganglia located primarily on or near target organs, long preganglionic neurons (brain stem and sacral region), and short postganglionic neurons
What are the receptors for ACh
Cholinergic (nicotinic or muscarinic)
What are the receptors for NE/E
Adrenergic (alpha or beta)
What has nicotinic receptors
Skeletal muscle, post-ganglionic neurons in parasympathetic, sympathetic, and adrenal sympathetic pathways
What has muscarinic receptors
Target tissues for parasympathetic pathways
What has adrenergic receptors
Target tissues for sympathetic and adrenal sympathetic pathways
What kinds of receptors are metabotropic
Muscarinic and adrenergic
What do autonomic postganglionic neurons synapse at
Varicosities
Which neurotransmitter lingers longer
NE (must be broken down by MAO)
Which receptor type is utilized for vasoconstriction
Alpha
What type of pathway is activated to vasoconstrict
PLC
What type of receptors cause vasodilation
Beta-2
What type of pathway is activated for vasodilation
cAMP
How does NE inactivate at a NMJ
NE diffuses away from the synapse or is removed, it can be taken back into synaptic vesicles for re-release, or it can be metabolized by MAO
What are the autonomic reflex control centers
Pons, medulla, and hypothalamus
What sensory neurons mediate spinal reflexes
Proprioceptors
What is the effector for spinal reflexes
Skeletal (extramural) muscle fibers
What are the efferent neurons in spinal reflexes
Somatic alpha motor neurons
What does the golgi tendon organ do
In line with muscle fibers, monitors muscle force and mediates the tendon reflex to regulate that muscle force
What does the muscle spindle organ do
In line with the tendon, it monitors muscle strength (usually unexpected) to mediate the stretch/patellar/knee reflex and regulate muscle length
What is the pathway in the golgi tendon reflex
Polysynaptic tonic control: Ib afferent tells the Ib inhibitory interneuron that force increased, that interneuron excites the muscle less to relax the muscle
What type of channels does the Ib afferent neuron have
Mechanically-gated channels that react to graded (receptor) potentials
What type of channels does the Ia afferent neuron have
Mechanically-gated channels that react to graded (receptor) potentials
What are the muscle spindle reflex pathways
Stretch-sensitive afferent that monitors muscle length and 2 efferent pathways (1 contracts agonist, 1 relaxes antagonist)
What happens when muscle length increases (tendon tapped)
Monosynaptic pathway contracts quadriceps, polysynaptic pathway activates Ia inhibitory interneuron and relaxes the hamstring
