Sept 16 - pages 391-397 neurons Flashcards
what is the main receptive/input region
dendrite
dendrites
receiving signals foremother neurons
dendritic spines
thorny appendages having bulbous or spiky ends
finer dendrites are
highly specialized for collecting information
dendritic spines represent
points of close contact (synapse) with other neurons
dendrites convey incoming messages toward
the cell body
graded potentials
short-distance signals
how many axon’s does each neuron have
one
axon hillock
the cone shape area that thins out to the axon (area ‘above’)
length of the axon can be
small, non-existent or make up the majority of the neuron length
what is a nerve fibre?
any long axon
axon collaterals
the branches on the axon length
what happens to the collaterals?
split into smaller extensions called terminal branches
what can the collaterals and terminal branches be compared to?
collaterals are the big branches on a tree and terminal branches are little twigs coming off of the big branches
what is a normal number of terminal branches a neuron can have?
10,000
axolemma
cell membrane of an axon, the branch of a neuron through which signals (action potentials) are transmitted
in motor neurons, where are the nerve impulses generated and conducted?
at the junction of the axon hillock and axon and conducted along the axon to the axon terminals
where is the trigger zone located?
in the junction of the axon hillock and axon
where is the secretory region of the neuron?
axon terminal
neurotransmitters
signalling chemicals usually stored in the vesicles
what happens when impulses reach the axon terminal?
causes neurotransmitters to be released within the extracellular space
what do neurotransmitters do to nearby neurons when released? what about effector cells?
excite or inhibit neurons, inhibit effector cells
axon contains the same organelles found in the dendrites and cell body with two important exceptions, them being?
it lacks rough endoplasmic reticulum and Golgi apparatus
what are the consequences that the axon receives due to lack of 2 organelles?
depends on it cell’s body to 1) renew the necessary proteins and membrane components and 2)inefficient transport mechanism to distribute them
anterograde movement
movement away from the cell body
retrograde movement
movement towards the cell body
what cooperative efforts are needed for easy transport in neurons?
motor proteins and cytoskeletal elements including microtubules and actin filaments
what substances are move in the anterograde direction
mitochondria, cytoskeletal elements and membrane components that are used to renew axon plasma membrane and enzymes needed to synthesize certain neurotransmitters
what substances are moved in the retrograde direction
mostly organelles returning back to the cell body to be degraded or recycled
retrograde direction transport is also used for intracellular communication which includes
to advise the cell body of conditions at the axon terminals and deliver to the cell body vesicles containing signal molecules like nerve growth factor
there is one ——— transport mechanism that’s responsible for axonal transport. what ATP- dependent motor proteins does it use?
bidirectional, kinesin & dynein thats dependent on the direction of transport
myelin sheath description
white, protein-lipoid coat
myelin sheath funciton
protects and electrically insulates fibres and increases transmission speed of nerve impulses
myelinated fibers
nerve fibers that are insulated by a myelin sheat
myelin sheaths are associated only with
axons
dendrites are always
non myelinated
myelin sheath is formed by what cells in the PNS
Schwann cells
how does Schwann cells make myelin sheath?
wrapping itself several times so that the cytoplasm of the cell is forced from between the membranes
the plasma membrane of myelinating cells contains much less what than other plasma membranes in other body cells?
protein
what characteristic makes myelin sheath a good electrical insulators
lack of channel and carrier proteins
what’s a unique thing about myelin sheaths
a presence of a specific protein molecule that interlocks to form a sort of molecular velcro between adjacent myelin membranes
nodes of ranvier (myeline sheathe gaps)
adjacent Schwann cells have gaps between them and don’t touch, occurs at regular intervals of myelinated axon
nonmyelinated fibers in the PNS means
Schwann cells haven’t coiled around the nerve and a single Schwann cell stretches and coats 15 pt motor axons and the fibres are typically thin
what cells create myeline sheath in the CNS
oligodendrocytes
how do oligodendrocytes create myeline that’s different than Schwann cells?
has multiple flat processes that can coil around as many as 60 axons at the same time
in both the PNS and CNS the myeline sheath gaps
separate adjacent sections of an axons myeline sheath
why does the CNS myeline sheath lack an outer collar of perinuclear cytoplasm?
cell extensions do the coiling and the squeezed out cytoplasm is forced towards the centrally located nucleus instead of peripherally
what are non-myelinated cells cover by in long extensions in the CNS?
glial cells
what is white matter made up of?
dense collections of myelinated fibers and primarily fibre tracts
what is gray matter made up of?
mostly nerve cell bodies and nonmyelinated fibers
how are neurons classified?
by structure and function
Neurons are grouped structurally according to
the number of processes extending from their cell body
three major neurons based off structure
multipolar, bipolar and unipolar
polar ending in neuron classification meaning
end, pole (of the neuron)
multipolar neurons
many processes extend from the cell body - all are dendrites except the single axon
bipolar neurons
two processes extend from the cell body - one is a fused dendrite and other is an axon
unipolar cells
one process extends from the cell body and forms central and peripheral processes which together comprises an axon
relative abundance and location of: multipolar neurons
most abundant in the body, major neuron type in CNS
relative abundance and location of: bipolar neuron
rare, found in some special sensory organs
relative abundance and location of: unipolar neurons
found mainly in the PNS, common only in dorsal root ganglia of spinal cord and sensory ganglia of cranial nerves
what is the peripheral process in the unipolar neuron for
often associated with a sensory receptor
what is the central process in the unipolar neuron
enters the CNS
where do unipolar neurons generate from?
bipolar cells
the two processes of the bipolar cell, peripheral and central, do what during embryonic development to get a unipolar neuron
fuse
if the peripheral and central processes fuse together in a unipolar cell, is it a dendrite or axon?
axon
what three facts favour the process of the unipolar cell as an axon?
1) generates and conducts an impulse
2) when large, it is heavily myelinated
3) it has a uniform diameter and is indistinguishable microscopically Fromm an axon
how are neurons classified functionally?
based on the direction in which the nerve impulse travels relative to the CNS
what are the three neurons based on function
sensory neurons, motor neurons and interneurons
sensory neurons are also called
afferent neurons
sensory neurons definition
transmit impulses from sensory receptors towards the CNS
virtually all sensory neurons are
unipolar and their cell bodies are located in the sensory ganglia outside the CNS - their peripheral processes are very long
only the most distal parts of sensory neurons act as
impulse receptor sites
the receptor endings of some sensory neutrons are —– and therefore they function as sensory receptors
naked
motor neurons are also called
efferent neurons
motor neurons carry
impulses away from the CNS to the effector organ of the body periphery (usually muscle or glands)
most motor neurons are —– except
multipolar, except some neurons in the autonomic nervous system
interneurons are also called
association neurons
interneurons function and location
lie between sensory and motor neurons in neutral pathways and shuttle signals;s through CNS pathway where integration occurs
interneurons make up what
99% of neurons in the body including most in the CNS
almost all interneurons are
multipolar but differ in size and fibre branch pattern
action potential/nerve impulse is when
a neuron is adequately stimulated, an electrical impulse is generated and conducted along the length of its axon
what is the underlying cause of all functional activities in the nervous system?
action potential
what is always the same regardless of the source or type of stimulus?
action potential
chemically gated ion channels
open in response to binding of the appropriate neurotransmitter
voltage gated ion channels
open in response to changes in the membrane potentials
voltage is the
measure of potential energy generated by separated charge
voltage is always measured between two points and is called the
potential difference or potential
the greater the difference in charge between two points, the higher the
voltage
current definition and what can It be used for?
the flow of electrical charge from one point to another, can be used for work
resistance
is the hindrance to charge flow provided by substances through which the current must pass
insulators
have high electrical resistance
conductors
have low electrical resistance
ohm’s law gives the relationship between voltage, resistance and current with the equation
current (i) = voltage (V)/Resistance (R)
three portions of ohms law
1) current is directly proportional to the voltage
2) no net current flow between points that have the same potential
3) current is inversely related to resistance: the greater the resistance, the smaller the current
mechanically gates channels
open in response to physical deformation of the receptor (as in sensory receptors for touch and pressure)
resting potential only occurs
across the membrane
negatively charges (anion) proteins help with what
to balance out the positive charges of intracellular cations (usually potassium)
at resting membrane potential, the membrane is impermeable to
large anionic cytoplasmic proteins, very slightly permeable to sodium and 25x more permeable to potassium
the negative interior of the cell is due to
potassiums greater ability to diffuse out the cell compared to sodium
