Quiz #2 Flashcards
What are the 2 main divisions of the nervous system?
central nervous system
- integrating centre
- spinal cord and brain
peripheral nervous system
- all neural tissue outside CNS
- afferent and efferent neurons
What are neurons?
excitable cells that send and receive electrical signals rapidly over long distances
What is the role of the brain and spinal cord in the CNS?
integrating centre for homeostasis, movement, etc.
controls the entire nervous system
What is the structure of a neuron?
cell body
- contains nucleus and other organelles
dendrites
- thin, branched processes that receive incoming signals
- allow communication with multiple other neurons
- increase surface area
dendritic spines
- very fine, branched processes
- further increase surface area
axon
- carries electrical signal from cell body to target
- has axon hillock (where axons and action potentials initiate), axon terminal (where NT vesicles are released), and collaterals (spare branching off axon)
What is a synapse?
site of communication between the axon of one neuron and the dendrite of another OR between the axon of one neuron and an effector organ
pre-synaptic neuron to post-synaptic neuron
if the action potential is strong enough it will propagate across multiple neurons to get to its intended destination
What is anterograde transport?
transport from cell body to axon terminal
What is retrograde transport?
transport from axon terminal to cell body
- slow: through cytosol
- fast: using network of microtubules and neurofilaments, kinesin proteins carry NT vesicles
Describe the stages of fast axonal transport.
FAT walks vesicles and mitochondria along microtubule network
vesicles released into synapse by exocytosis
synaptic vesicle recycling (some come back into pre-synaptic neuron via reuptake)
retrograde FAT
old membrane components digested by lysosomes
What are the types of neurons?
multipolar
bipolar
pseudounipolar
anaaxonic
What are multipolar neurons?
most common
many processes, highly branched
lack long extensions
ex. motor neuron
What are bipolar neurons?
2 approximately equal fibers off the cell body
single axon, single dendrite
common with special senses
What are pseudounipolar neurons?
single axon
dendrites fused to axon, cell body attached to axon
most afferent/sensory neurons
What are anaxonic neurons?
no axon
numerous dendrites
interneurons in CNS
What is the difference between afferent, efferent, and interneurons?
afferent - carry info from sensory receptors to CNS
efferent - carry response from CNS to effector organs
interneurons
- interconnecting neurons with complex branching
What are the types of sensory/afferent receptors?
interoceptors
- monitor internal systems and senses
exteroceptors
- monitor external and distance senses
proprioceptors
- monitor position and movement
What are the 2 divisions of the efferent system?
somatic
- skeletal muscle
autonomic
- smooth muscle, cardiac muscle
What are neuroglial cells?
“glue”
make up half the volume of the nervous system
essential to survival and function
What are the types of neuroglia?
ependymal microglia astrocytes oligodendrocytes Schwann cells/satellite cells
Describe the main role of ependymal cells.
line central canal of spinal cord and brain
- secrete and circulate CSF
Describe the main role of microglia.
clean up cellular debris, waste, and pathogens
smallest and least numerous
Describe the main role of astrocytes.
make up 1/2 the cells of the brain
communicate via gap junctions
maintain blood-brain barrier
guide neuron development
Describe the main roles of oligodendrocytes.
wrap around axons to form myelin sheaths
- white matter
- only in CNS
Describe the neuroglia of the PNS.
schwann cells
- form myelin sheaths around axons
- takes many cells to sheath entire axon
- leave tiny gaps called nodes of ranvier
satellite cells
- non-myelinated schwann cells
- form supportive capsules around nerve cells
- regulate environment around neuron
What is myelination?
increases speed of action potentials by insulating axons
makes nerves appear white (white matter)
What are nodes of Ranvier?
gaps between internodes where axons may branch
What are internodes?
myelinated segments of axon
What is an action potential?
large, rapid change in membrane potential produced by depolarization of an excitable cell to threshold (-55 mV)
What is equilibrium potential?
transmembrane potential at which there is no net movement of a particular ion across the cell membrane
What are the 3 requirements for membrane potential?
ICF and ECF differ markedly in ionic concentration
selective permeability
cell transport do not ensure equal distribution across membrane
What is the resting membrane potential?
-70 mV
inside relative to outside
How are ions distributed when the cell is at rest?
outside - more Na+ and Cl-
inside - more K+ and organic anions
How do voltage gated channels work?
respond to change in transmembrane potential
activation gate (voltage dependent) opens, period of latency before inactivation gate (voltage and time dependent) closes, during latency molecules flow inward
What is a graded potential?
changes in transmembrane potential
signal travels short distance, losing strength as it goes
IPSPs or EPSPs
if enough strength at integrating region, forms action potential
may go above threshold (-55 mV) locally, but if below this at the axon hillock then no action potential will occur
What is repolarization?
when stimulus is removed and transmembrane potential returns to normal
What is hyperpolarization?
increased negativity of resting potential as a result of opening K+ cells
What is the all-or-none principle?
if a stimulus exceeds the threshold amount, the AP will be the same no matter how large the stimulus from the graded potential
strength of graded potential has no influence on amplitude, action potential is either triggered or it is not
What happens to the cell at +30 mV?
Na+ inactivation channels close, K+ channels open
repolarization begins
What is the absolute refractory period?
membrane can’t produce another AP because Na+ channels are inactivated
AP can’t overlap
ensures 1 way travel of AP
What is relative refractory period?
follows the absolute refractory period
when K+ channels are still open so it is possible, but more difficult for an AP to occur
What are the 2 methods of action potential propagation?
continuous propagation - unmyelinated axons
saltatory propagation - myelinated axons
Describe continuous propagation.
after AP fires, Na+ influx depolarizes adjacent region and generates new AP, repeats all along the axon
amplitude always the same
conduction is slow
What things determine the speed of an action potential?
diameter
- larger = faster
myelination
- myelinated = faster
Describe saltatory conduction.
APs leap from node of Ranvier to node of Ranvier where there are high concentrations of Na+ channels, and they are regenerated
myelin sheath prevents Na+ and K+ from leaving the cell
conduction is faster
What are electrical synapses?
pass electrical signals through direct physical contact (gap junctions)
can be excitatory or inhibitory
What are chemical synapses?
used by most neurons
cells not in direct contact, signal is transmitted across a gap by NT binding to receptor on postsynaptic cell that affects AP
Describe the events at a chemical synapse.
AP arrives at end of axon terminal
Ca2+ channels open allowing it to enter down concentration gradient
influx of Ca2+ causes synaptic vesicles to move to the presynaptic membrane and fuse
once fused, contents released (exocytosis) to diffuse across cleft and bind to postsynaptic neuron receptors
generates a response
NT either diffuse out of the cell, are degraded by enzymes, or actively transported back into presynaptic cell
What are ionotropic receptors?
NT binds to a receptor on a channel that causes conformational change
What are metabotropic receptors?
NT binds to a receptor which activates a G-protein that activates a response
can either:
- open/close ion channel (direct coupling)
- activate/inhibit enzyme that produces a second messenger to carry out cellular tasks (second messenger system - slow but more broad effects)
What are cholinergic synapses?
any synapse that releases acetylcholine (ACh)
can be excitatory or inhibitory depending on receptor subtype (nicotinic or muscarinic)
What is acetylcholinesterase?
AChE
enzyme that breaks down acetylcholine into acetate and choline
rapidly breaks down ACh where choline can be transported back into presynaptic axon terminal (co-transport with Na+) and recycled to make more ACh
What are nicotinic receptors?
ligand-operated/ionotropic
generate EPSP bringing closer to AP threshold (excitatory post-synaptic potential)
What are muscarinic receptors?
G-protein operated/metabotropic
generate IPSP bringing further from AP threshold (inhibitory post-synaptic potential)
What are biogenic amines?
derived from amino acids
ex. serotonin, dopamine, histamine
What are catecholamines?
derived from tyrosine
dopamine, norepinephrine, epinephrine
What amino acid neurotransmitters act a excitatory and inhibitory synapses?
excitatory: aspartate, glutamate
inhibitory: glycine, GABA
What is summation?
additive effects of graded potentials (IPSPs and EPSPs)
temporal summation
- repeated stimulation of 1 synapse
spatial
- stimulate of several synapses at the same time
What is frequency coding?
the degree of depolarization at the axon hillock is signalled by the frequency of APs
more APs = greater NT released = greater IPSP or EPSP at next neuron
What are the 3 meninges?
dura mater - tough outside pia mater - tender inside arachnoid mater - spidery inside
What is cerebrospinal fluid?
clear, watery fluid bathing the CNS
produced by ependymal cells of choroid plexus
recycled 3 times a day
circulates through ventricles to subarachnoid space
cushions brain and maintains stable interstitial fluid environment
What is the blood brain barrier?
specialized network of capillaries that limit exchange of specific substances into the brain
tight junctions between epithelial cells
What are the 3 types of white matter fibers in the brain?
projection fibers
- connect cerebral cortex with lower brain/spinal cord
association fibers
- connect 2 areas of the cerebral cortex on the same side of the brain
comissural fibers
- connect 2 of the same cortical regions on either side of the brain
- corpus callosum
What is the spinal cord?
cylinder of nerve tissue surrounded by vertebral column
continuous with brain
origin of 31 pairs of spinal nerves
What is a dermatome?
sensory region of the skin
each served by specific spinal nerve
Describe the composition of the spinal cord/nerves.
grey matter
- dorsal horn = sensory/afferent axons
- ventral horn = motor/efferent axons
white matter
- forms tracts that are either ascending or descending
What are reflexes?
automatic patterned responses to stimuli
What are the components of the reflex arc?
stimulus sensory receptor afferent neuron integrating centre efferent neuron effector organ response
What are different ways to classify reflexes?
level of neural processing
- spinal vs cranial
efferent division control
- somatic vs autonomic
developmental pattern
- innate vs conditioned
number of synapses
- monosynaptic (only muscle spindle stretch) vs polysnaptic
What is the muscle spindle stretch reflex?
tap on the tendon causes change in muscle fiber length in quads
spindles detect change and send afferent info to spinal cord, direct excitatory connection with efferent neurons that innervate quad to extend (kick leg)
afferent info also inhibits the hamstrings to allow the movement to occur
What is the withdrawal reflex?
opposite leg sends afferent signal to extend leg so it can withdraw
gives a leg to stand on so you don’t tip over
What is perception?
conscious interpretation of the world
What is the law of specific nerve energies?
a given receptor is specific for each modality
detect specific forms of energy in the external environment
What are the different types of sensory receptors?
photoreceptors
chemoreceptors
mechanoreceptors
thermoreceptors
What do photoreceptors detect?
vision - photons of light
What do chemoreceptors detect?
taste - chemicals in saliva
smell - chemicals in mucus
pain - chemicals in ECF
What do thermoreceptors detect?
changes in temperature
specific ones for warm and cold
What do mechanoreceptors detect? (2 components)
pacinian corpuscle
- vibration and pressure
hair cells
- sound - sound waves
- balance and equilibrium - acceleration
What is sensory transduction?
conversion of stimulus energy into electrical energy
What is receptor adaptation?
decrease in amplitude of receptor potential over time in the presence of a constant stimulus
corresponding decrease in the frequency of AP and in perception of stimulus
What is a sensory unit?
single afferent neuron plus all receptors associated with it
What is a receptive field?
area in which sensory unit can be activated
Describe the generalized pathway for sensory systems.
first order neurons
- transmit from periphery to CNS
second order neurons
- interneurons
- may receive info from several first order neurons
third order neurons
- transmit to cerebral cortex for sensory perception
What factors affect sensory coding?
stimulus type stimulus intensity (frequency of AP, # of receptors activated) stimulus location (size and degree of overlap of receptive field)
What does recruitment mean?
stronger stimuli activate more receptors
What does acuity mean?
precision with which a stimulus is perceived
What is lateral inhibition?
adjacent neurons can form inhibition synapses with branches off axon of activated neuron to allow more accurate sense of precision of where a sensation is coming from
What are nociceptors?
receptors sensitive to pain
Aside from nociceptors, what else is activated in the pain response?
autonomic responses
- increased BP, sweating
emotional responses
- fear, anxiety
reflexive withdrawl
Describe the 2 pathways of pain.
A-delta afferent
- myelinated
- initial pain response
- ex. immediate pain when you first stub your toe
C afferent
- polymodal
- delayed response
- ex. dull ache in toe that comes later on
both terminate in dorsal horn of spinal cord
What additional factor determines how you perceive pain?
past experiences
What is the difference between visceral and referred pain?
visceral = pain originating from internal organs
referred = sensation “referred to body surface”
- ex. heart attack victim complains of pain on left side, not heart itself
What is the gate control theory?
why you rub a painful area to relieve the pain
stimulates pressure-sensitive fibers, collateral axon can stimulate an inhibitory interneuron to reduce pain you initially felt
What is endogenous analgesia?
brain can block pain
ex. soldiers in battle
