ch. 48 part 1 Flashcards
two divisions of nervous system
- CNS
- PNS
central nervous system
brain and nerve cord
- spinal cord in vertebrates
peripheral nervous system
all neurons and projections of their plasma membranes that are outside of the CNS
neurons
cells that send and receive electrical and chemical signals to and from other neurons or other cells throughout the body
which animal does not have neurons
sponges
structure of the neuron
- soma/cell body
- dendrites
- axons
cell body or soma
- contains nucleus and organelles
dendrites
- extensions of plasma membrane
- single or branching
- incoming singals
axons
- extension of plasma membrane (neurolemma)
- typically single
- sending signals
- axon hillock near cell body
- axon terminals
axon terminals
convey electrical or chemical message to other cells
neurolemma
outer portion of myelin sheath created by Schwann cells
glia cells
- perform various functions
- many times more numerous than neurons
- can function as stem cells to produce more glial cells and neurons
types of glia cells in CNS
- astrocytes
- microglia
- ependymal cells
- oligodendrocytes
astrocytes (star cell)
- metabolic support
- maintain blood-brain barrier
provide structural support - regulate ion, nutrient, and dissolved gas concentrations
- absorb and recycle neurotransmitters
- form scar tissue after injury
microglia (little glue)
- remove cellular debris, wastes, and pathogens by phagocytosis
what is the myelin sheath interrupted by
nodes of Ranvier
what produces the nodes of Ranvier
oligodendrocytes (CNS) and Schwann cells (PNS)
dendro
tree
oligo
few or little
cyte
cells
types of glia cells in the PNS
- Schwann cells
- satellite cells
ependymal cells
- line ventricles (brain) and central canal (spinal cord)
- assist in producing, circulating, and monitoring of cerebrospinal fluid
oligodendrocytes
- myeline CNS axons
- provide structural framework
Schwann cells
- surround axons in PNS
- are responsible for myelination of peripheral axons
- participate in repair process after injury
satellite cells
- surround neuron cell bodies in ganglia
- regulate O2, CO2, nutrient, and neurotransmitter levels around neurons in ganglia
synapse
junction between an axon and another cell
chemical messengers released from synaptic terminal at synapses
neurotransmitters
process of releasing neurotransmitters
- action potential travels down axon to terminal
- Ca2+ channel increases Ca2+ channel in presynaptic neuron
- binds to vesicle filled with Ca2+
- exocytosis of vesicle, neurotransmitters travel across synaptic cleft
- neurotransmitters bind to receptors on postsynaptic membrane
presynaptic cell at synapse
neuron
postsynaptic cell at synapse
neuron, muscle, or gland cell
3 main types of neurons
- sensory neurons (afferent)
- motor neurons (efferent)
- interneurons
sensory/afferent neurons
- detect information form outside world/internal body conditions
- transmit to CNS
afferent
bring to or lead toward
motor/efferent neurons
- send signals away from CNS to elicit response
efferent
conduct away or carry off
interneurons (association neurons)
form interconnections between other neurons in the CNS
inter
between
telodendria
synaptic knobs
reflex arc
stimulus from sensory neurons sent to CNS (dorsal root ganglion), little/no interpretation (few/no interneurons), signal transmitted to motor neurons to elicit response
- quick/automatic response
potential =
voltage
membrane potential
difference in charge inside and outside the cell
- polarized
what separates charges in and out of the cell?
plasma membrane barrier
resting membrane potential
when neurons not sending signals
what axons are used to read voltage measurements
squid giant axons
voltmeter function
records voltage difference between the microelectrodes inside and outside the neuron
- measure of membrane potential
- measurement made as a function of time
what are plasma membranes not very permeable to
cations and anions
- separates charge by keeping different ions largely inside or outside cell
resting potential value inside cell
-70 mv
is the interior or exterior of the cell more negative at rest
interior
what are negative ions within the cell drawn to
positive ions arrayed on the outer surface
3 factors contributing to resting potential
- Na+/K+ -ATPase (sodium-potassium pump)
- ion specific channels allow passive movement of ions
- negatively charged molecules such as proteins more abundant inside cell
Na/K pump
transports 3 Na+ out for every 2 K+ moved in
are there more ungated K+ or Na+ channels
K+
is the membrane more permeable to K+ or Na+ at rest
K+
where are negatively charged molecules more abundant at rest
inside the cell
equilibrium potential
opposing forces of chemical and electrical gradients can create an equilibrium where there is no net movement
what do all cells have?
a membrane potential
what cells are excitable
neurons and muscle cells
excitable
capacity to generate electrical signals
3 types of gated ion channels
- voltage-gated
- ligand-gated
- mechanically-gated
voltage-gated
open and close in response to voltage changes
ligand-gated
open and close in response to ligands or chemicals
mechanically-gated
open due to distortions in the cell membrane (touch)
polarization
changes in membrane potential
depolarization
cell membrane is less polarized, less negative relative to surrounding solution
- gated channels open allowing Na+ to flow in and membrane potential becomes more positive (less negative)
hyperpolarization
cell membrane more polarized, more negative
- K+ moves out of the cell making the cell membrane less positive (more negative)
graded potentials
- depolarization or hyperpolarization
- varies depending on strength of stimulus
- occur locally and dendrites or cell body
- spreads short distance and dies out
- act as triggers for action potential
