Exam 4 Flashcards
functions of the nervous system
sensory (impulse)
integrative (sorts info)
motor (response)
central nervous system
brain & spinal cord
peripheral nervous system
nerve cells & fibers outside the brain & spinal cord
afferent
brings information from the periphery to the central nervous system (part of PNS)
efferent
sends information from the central nervous system out to the periphery (part of PNS)
somatic
voluntary (efferent)
autonomic
involuntary (efferent)
sympathetic
fight or flight (autonomic)
parasympathetic
vegetative functions (autonomic)
enteric nervous system
the brain of the gut (previously considered part of the autonomic nervous system)
nerve
collection of nerve fibers in the PNS
tract
collection of nerve fibers in the CNS
gray matter
mostly neuron cell bodies
white matter
all fibers, mostly myelinated
nucleus
collection of nerve cell bodies in the CNS
ganglion
collection of nerve cell bodies in the PNS
stimulus
excites neuron
neurons
- the only cells that can carry the impulse
- large excitable cells that conduct the impulse
- little mitosis after birth
glial cells
(supportive)
PNS= Schwann cell & satellite cells in ganglia
CNS= oligodendrocytes, astrocytes, microglia, ependymal
schwann cell
makes myelin
oligodendrocytes
part of myelin
astrocytes
blood/brain barrier
microglia
phagocytic cells
ependymal
line vessel cavities & cerebral spine
nerve cell body
- contains lots of rough ER
- also contains nucleus, neurofibrils (intermediate filaments), microtubules & other organelles
- lipofuscin granules (yellow-brown pigment related to aging)
dendrite
- the nerve fiber(s) which carries the impulse to the cell body
- some cytoplasm
- often highly branched
- the afferent fiber
axon
- the nerve fiber(s) which carries the impulse away from the cell body to an effector
- only one per neuron
- the efferent fiber
types of neurons
structure -multipolar -bipolar -psuedounipolar/unipolar function -sensory= afferent -association/interneurons= integrative motor= efferent
myelinated nerve fibers
- myelin insulates axon; increases speed of AP conduction
- composed of plasma membranes of schwann cells (PNS) or oligodendrocytes (CNS)
- gaps= nodes of ranvier
- saltatory conduction= impulses jumps from gap to gap
unmyelinated nerve fibers
- processes aren’t as important
- slower conduction
- still have a schwann cell sheet
plasma membrane
- composed primarily of lipid (non-polar)
- non-polarized substances can get through the lipid bilayer
- special ion channels in the plasma membrane allow polarized substances (Na, K, Ca) to get across lipid bilayer
types of ion channels
leakage= random open/close ligand-gated= opens/closes i.r.t NTs, hormones, calcium, etc. (ex. neuromuscular junction) mechanical-gated= opens/closes i.r.t. pressure, vibration, etc. voltage-gated= opens/closes i.r.t. change in membrane potential
electrical gradient
different charge on either side of the membrane
chemical gradient
different concentrations of Na and K on either side of the membrane
electrochemical gradient
- outside= more positive (Na)
- inside= less positive (K)
- channels do not effect charge
sodium potassium pump
- effects electrochemical gradient
- for every 3 Na that get pumped out, only 2 K get pumped in
potential
difference between inside & outside the membrane
resting membrane potential
charge= -70mV
graded potential
- a small deviation from the membrane potential caused by a stimulus
- if it makes membrane depolarize a little, then membrane is more excitable
- if it makes the membrane more polarized, the membrane is less excitable (inhibited)
- are local and graded (not all-or-none)
- summation= added together
- often occur in sensory receptors
- can occur in dendrites/cell bodies (post-synaptic potential)
action potential
- nerve impulse
- a series of changes in the potential (voltage) of the membrane
- depolarization= membrane gets more +
- repolarization= membrane goes back to -
- refractory period= another AP cannot fire for awhile
- all-or-none
- can only go in one direction bc refractory period
depolarization
- Na rushes in (flood gates have been opened)
- K rushes out
- the membrane potential rises towards 0 and even gets positive
- eventually gets so positive inside that further influx of positive ions is repelled
repolarization
- the sodium potassium pump kicks in again
- Na is pumped out of the axon
- K is pumped into the axon
- not at equal rates bc pump
- a hyper-polarization phase may occur in which the membrane overshoots the membrane potential
refractory period
- absolute= no stimulus can provoke another AP (Na channels inactivated; resting)
- relative= an AP can be initiated only by a greater than normal stimulus
- larger the diameter of the axon, the shorter the absolute refractory period
- cardiac muscle has the shortest refractory period
self-propagating (AP)
- at the leading edge of an AP, sodium gates open, allowing sodium ions to flow into cell
- this flow of ions triggers more sodium gates to open, causing the AP to move
- at the trailing edge of an AP, potassium gates open, allowing positive ions to flow out, and restoring the resting potential of the neuron
- like the domino effect
axon hillock
very beginning of the axon (trigger zone)
continuous conduction
- relatively slow
- step-by-step depolarization and repolarization
- found in unmyelinated fibers
- takes more energy
saltatory conduction
- impulse jumps from node to node
- faster
- takes less energy bc fewer regions of the membrane undergo depolarization/repolarization and Na pump doesn’t have to work so hard
- in myelinated nerves
affects on speed of propagation
- presence of myelin (myelin=fast)
- diameter of axon (large=fast)
- temperature (cold=slows pain impulses)
A nerve fiber
- largest
- shortest refractory period
- myelinated
- large sensory & motor fibers
B nerve fiber
- middle diameter
- longer refractory period
- myelinated
- sensory from skin and viscera to CNS
- motor to some autonomics
C nerve fiber
- smallest
- longest refractory period
- unmyelinated
- heat, cold, pain, and some motor
signal transmission at the synapse
- usually axon of first neuron to dendrite of second neuron= axodendritic
- some axon-axon and some axon/cell body synapse
- two types: electrical (ex. cardiac muscle) & chemical (have to have NT)
electrical synapse
- impulse conducted directly between cells via gap junctions (no NT involved)
- faster than chemical synapse
- better synchronization (ex. cardiac muscle)
- doesn’t have a latent period bc no synapse
chemical synapse
presynaptic neuron releases NT which diffuses across the synaptic cleft and binds to the receptor on the postsynaptic neuron, which produces some postsynaptic potential
transmission of impulse
- nerve impulse arrives at presynaptic terminal
- the depolarization of the presynaptic axon opens voltage-gated Ca channels
- Ca ions flow into the cell
- at resting conditions, [Ca] greater outside of cell
- intracellular [Ca] triggers exocytosis of synaptic vesicles, which release NTs, which diffuse across synaptic cleft and bind to receptors on post-synaptic membrane
- NT/receptor complex opens ion channels and ions flow in
- if Na channels are opened, Na rushes in= depolarization
- if Cl channels are opened, Cl rushes in= hyperpolarization
if sum of postsynaptic potentials doesn’t reach threshold…
- membrane may be excited/more likely to fire (slightly depolarized)= EPSP
- membrane may be inhibited/less likely to fire (hyperpolarized)= IPSP
how synapse turns off…
- NT diffuses away from the synaptic cleft
- NT is degraded by enzymes
- NT is taken up by presynaptic site
- -SSRIs= seratonin specific reuptake inhibitors
ACh
- excitatory or inhibitory
- NMJ, some other PNS and CNS synapses
- inactivated by acetylcholinesterase
cholinergic
has ACh at synapse
adrenergic/noradrenergic
has epinephrine/norepinephrine at synapse
dopaminergic
has dopamine at synapse
amino acid NTs
glutamate
aspartate
glycine
GABA
biogenic amines
tyrosine L-Dopa dopamine norepinephrine epinephrine -all are based on tyrosine -nor=nitrogen w/o radical group
nitric oxide
- synthesized as needed
- lipid soluble
- immediate action
- highly reactive but short acting
- relaxes vascular smooth muscle
neuropeptides
(chains of amino acids)
endorphins
enkephalins
substance P (P=pain)
diverging neural circuit
from one neuron to many neurons (one impulse causes many things)
converging neural circuit
from many neurons to one neuron (multiple synapses to one cell body)
reverberating neural circuit
a series of coordinated impulses (ex. respiratory rhythm)
nerve tissue repair in PNS
if cell body remains intact, the peripheral nerves may repair (cell bodies in spinal cord)
nerve tissue repair in CNS
- some new neurons in the hippocampus
- problems with scar tissue after injury interfere with repair
repair of fibers in PNS
- 24-48 hrs post injury: Nissl bodies (RER) break up= chromatolysis
- 3-5 days post injury: distal to the injury axon swells, breaks into fragments, myelin deteriorates= Wallerian degeneration
- leftovers are phagocytized by macrophages, etc.
- if schwann cell tube is present, the regenerating axon will sprout
multiple sclerosis
- autoimmune
- demyelinating disease
- causes loss of coordination/senesation
epilepsy
abnormal electrical events
Guillain-Barre
ascending paralysis
neuropathy
- something wrong with the nerves
- tingling or small odd senesations