sensory input
receptors gather info(internal and external)
integration
nervous system processes and interprets
motor output
effectors(muscles and glands) instructed to respond
CNS
central; brain and spinal cavity; i greg ration and control center
PNS
peripheral- outside CNS; nerves (bundles of axon) that extend from the brain and spinal cord, as well as ganglia (clusters of neuron cell bodies along nerve pathways)
sensory (afferent) division
nerve fibers carry info from receptors to CNS
somatic
skin, skeletal muscles and joints
visceral
organs
motor (efferent) division
impulses transmitted from CNS to effectors, two main parts
somatic
conscious control of skeletal muscles
autonomic
ANS-regulates activity of smooth and cardiac muscles, as well as glands; two functional subdivisions
Sympathetic
mobilized during activity
parasympathetic
regulates restful functions (ex. digestion)
neurons
nerve cells; generate and transmit APs; can function for a lifetime; most do not divide after maturing; high metabolic rate (requires continuous glucose and oxygen supplies)
neuroglia
support cells; more abundant than neurons to ensure proper functions
astrocyte
most abundant and most versatile-anchors neurons to capillaries for nutrients; determine capillary permeability; assist in synapse formation; remove excess ions, neurotransmitters from synapses
microglia
phagocize microorganisms and neural debris
ependymal cells
we cilia to move CSF (cerebrospinal) through/around brain and spinal
oligodendrocytes
insulate thick nerve fibers, forming myelin sheaths
satellite cells
surround neuron cells bodies in the PNS; similar function to astrocyte
schwann cells
surround all cell fibers in the PNS and form myelin sheaths around thick nerve fibers; vital to regeneration of damaged peripheral nerves
cell body
contains nucleus, cytoplasm, numerous mitochondria and other
nuclei
clusters in CNS
dendrite
short, highly branched to create large surface area to receiving signals from other neurons; send graded potential to cell body
graded potential
short, loud impulses
axon
conducting region-produces and conducts impulses away from cell body; long axons called nerve fibers
axon collaterals
only one axon arrives from cell body, but may branch
axon terminal
secretory region; end of axon branches and expand slightly at ends
nerve impulses transmitted
down plasma membrane (axolemma) to axon terminals, where neurotransmitters are secreated into extra cellular space
myelin
covers large/long axon in segments; increasing speed of impulses
nonmyelinated axon
single layer of myelin to conduct impulses more slowly
myelinated
thick layer of myelin to conduct impulses quickly
myelin sheaths gaps
schwann cells do not touch, so myelin sheaths have gaps that occur at 1mm intervals
multipolar
many process extend from the cell body. all are dendrites except for a single axon; 99% of neurons
bipolar
two processes extend from the cell body. one is fused to the dendrite, the other is an axon. only found in retina and olfactory mucosa
unipolar
one process extend from the cell body and form central and peripheral process, which together compromise an axon
sensory
afferent-transmit impulses from sensory receptors to CNS; almost all are unipolar; cell bodies located in ganglia
motor
efferent-transmit impulses from CNS to effectors; multipolar; cell bodies located in CNS
interneurons
association neurons-lie between sensory and motor neurons where intregration occurs typically in the CNS; almost all multipolar
resting membrane potential
are polarized(negative inside membrane, positive outside)
depolarization
an AP briefly reversed the RMP due to energy to entry of Na+
repolarization
once 30mV is reached, Na+ channels close, K+ channels open, K+ exit cells, restoring negativity
hyperpolarization
some K+ channels remain open, causing voltage to dip lower than original RMP
threshold
guarantees the AP; a sub threshold stimulus will not be a full AP, may increase voltage a little
all or none phenomenon
AP either happens or it doesn’t
AP
generate in axons and propagate down axolemma toward axon terminal
refractory periods
ensure AP reaches certain point before responding to stimulus from the new AP
absolute refractory period
neuron cannot respond to a new stimulus on the same spot on the membrane, regardless of its strength; lasts from the time Na+ channels open to the time they close; ensure that each AP is a separate and complete event
relative refractory period
K+ channels still open; exceptionally strong stimulus will reopen Na+ channels to generate a new AP at the same spot on the membrane before hyperpolarization is complete (and RMP is reestablished)
Absolute refractory period
ensures that a new AP will fire on the an adjacent location, as opposed to the same spot again
refractory periods
allow cells to replenish ingredients such as neurotransmitters, oxygen, glucose, calcium(muscle cells requirement for contraction) and also returns ions to original location
speed of conduction
diameter of axon(larger= faster) and degree of myleination(presence of myelin =faster)
continuous conduction
action potential propagates at the adjacent spots on the membrane of the nonmylinated slow because new APs must fire repeatedly to move down the membrane
saltatory conduction
APs only conducted in myelin sheath gaps and appear to “jump” from myelin to gap, which is 30x faster than continuous conduction