structure and function of cells of the nervous system Flashcards
neuron
type of cell that makes up the nervous system and supports cognitive function
how does a neuron support cognitive function?
information processing and information transmitting element
structures that most neurons have
soma
dendrites
axons
terminal buttons
functional division of neurons
sensory
motor
interneurons
sensory neurons
detect changes in the internal and external environment (CNS and PNS)
motor neurons
controls muscle contraction and also gland secretion (CNS and PNS)
interneurons
involved in cognition
lie entirely within the CNS
structural division of neurons
multipolar
bipolar
unipolar
multipolar neuron
neuron with one axon and many dendrites attached to its soma
bipolar neuron
neuron with one axon and one dendrite attached to its soma
unipolar neuron
neuron with one axon attached to its soma, the axon divides with one branch receiving sensory information and the other sending the information to the central nervous system
three types of multipolar neuron
motor neuron of the spinal cord
pyramidal cell of the hippocampus
purkinje cell of cerebellum
glial cells
oligodendrocytes
astrocytes
microglia
epyndymal cells
what are microglia
modified immune cells
another name for astrocytes
star cells
what do astrocytes provide?
physical support to neurons
nourishment
what do astrocytes control?
chemical composition of fluids surrounding neurons
what happens when neurons die?
astrocytes clean up debris and form scar tissue
function of oligodendrocytes
support axons and produce myelin sheath (lipid insulation)
nodes of Ranvier
bare portion of axon (no myelin sheath)
oligodendrocytes in CNS
wrapped around several adjacent axons
oligodendrocytes in PNS
single schwann cell wrapped around the PNS axon
the blood brain barrier
a semipermeable barrier between the CNS and circulatory system
function of the blood brain barrier `
to help regulate the flow of nutrient rich fluid into the brain
area postrema
a region of the medulla where the blood brain barrier is wear
purpose of the area postrema
Allows toxins in the blood to stimulate this area, which initiates vomiting - poison expelled from the body
4 steps of withdrawal reflex
1) dendrites of sensory neuron detect painful stimulus
2) Action potential along axon of sensory neuron
3) excites interneuron in the spinal cord, which excites the necessary motor neuron
4) motor neuron causes contraction of muscle, causing it to move away from the site of pain
membrane potential
electrical charge across a cell membrane
the difference in electrical charge inside and outside the cell
stored up source of electrical energy
resting potential
membrane potential of a neuron when it is not being altered by inhibitory or excitatory post synaptic membrane potentials
normal resting potential value
-70mV
depolarization
reduction of negative charge (towards 0) of the membrane potential when we stimulate a neuron
action potential
the brief electrical impulse that provides the basis for conduction of information along the axon
threshold of excitation
the value of the membrane potential that must be reached to produce an action potential
hyperpolarisation
increase in the membrane potential of a cell
becoming more negative
what is the membrane potential a balance of?
diffusion and electrostatic pressure
diffusion
movement of molecules from areas of high concentration to areas of low concentration
electrostatic pressure
when substances dissolve in water, they split into two parts with opposing electrical charge: ions
what is exerted by electrostatic pressure?
attraction of oppositely charged ions and repulsion of similarly charged ions
intracellular fluid
fluid contained within cells
extracellular fluid
body fluid that is located outside cells
how can sodium be found outside a cell when both diffusion and electrostatic pressure tend to push it inside?
sodium potassium pump
sodium potassium pump
protein in the membrane that pushes sodium out the cells
active mechanism in the membrane that extrudes Na out (3) and transports K in (2)
what does action potential result from (general)
movements of ions through membranes
ion channels allow
flow of specific ions when open
4 stages of a sodium channel during action potential
1) closed
2) open
3) refractory
4) reset
all or none law
one an action potential begins, it proceeds without decrement to the terminal buttons
how can the speed of conduction be calculated?
from the delay between stimulus and AP
rate law
variations in the intensity of a stimulus are represented by variations in the rate at which the axons fires
what does a stronger rate of firing cause (muscle)
stronger muscle contractions
what law is the all or none law supplemented by?
the rate law
saltatory conduction
conduction of action potentials by myelinated axons
APs appear to jump from one nod of Ranvier to the next
advantages of saltatory conduction
economy- less energy used by the Na-K pump (located at the nodes of Ranvier)
speed: conduction much faster than in an unmyelinated axon
what conduction do unmyelinated axons show?
continuous
what is a synapse?
the junction between two neurons
the primary means of communication between two neurons
what is the synaptic cleft? what size is it?
a very narrow gap of about 20 nm between neurons
why do we need neurotransmitters?
action potentials (electrical impulses) cannot cross the synaptic cleft
presynaptic neuron
neuron sending impulse
postsynaptic neuron
neuron receiving impulse
what is neurotransmitters made by? where are they stored?
made by presynaptic neuron
stored in synaptic vesicles
what are neuroreceptors?
chemical gated ion channels on the postsynaptic membrane that have specific binding sites for neurotransmitters
direct opening of an ion channel
ionotropic receptor
indirect opening of an ion channel
metabotropic receptor
EPSP
excitatory post-synaptic membrane potential
excitatory depolarisation of the post-synaptic membrane
IPSP
inhibitory post-synaptic potential
inhibitory hyperpolarisation of the post-synaptic membrane
what is the nature of post-synaptic potential dependant on?
post synaptic receptors: which ion channels they open
what is the nature of post-synaptic potential dependant on?
post synaptic receptors: which ion channels they open
what is the nature of post-synaptic potential dependant on?
post synaptic receptors: which ion channels they open
what is the nature of post-synaptic potential dependant on?
post synaptic receptors: which ion channels they open
three major types of ion channel
Na+, K+, Cl-
influx of sodium causes? (EPSP/IPSP)
EPSP
influx of potassium causes? (EPSP/IPSP)
IPSP
influx of chloride causes? (EPSP/IPSP)
IPSP
neuronal integration
process by which inhibitory and excitatory post synaptic potentials summate and control the rate of firing of a neuron
