A + P Nervous System I Flashcards
two type of neural tissue
neurons
neuroglia
neurons function
send and receive signals
neuroglia function
support and protect neurons
nervous system anatomical division
Central Nervous System
Peripheral Nervous System
CNS
- consists of
- jobs
- the brain is also…
consists of
-brain
-spinal cord
jobs
-integrates, processes, and coordinates sensory data and motor commands
the brain is also the seat of higher functions, such as intelligence, memory, learning and emotion
PNS
- consists of…
- functions
consists of -cranial and spinal nerves functions -delivers sensory info to the CNS -carries motor commands to the peripheral tissues and systems
PNS functional divisions
Sensory (afferent division)
motor (efferent division)
sensory division function
carries sensory information from receptors to CNS
motor division function
carries motor commands from CNS to PNS muscles and glands
motor division functional division
somatic nervous system
autonomic nervous system
somatic nervous system function
controls voluntary and involuntary skeletal muscle contraction
autonomic nervous system function
provides involuntary automatic regulation of smooth muscle, cardiac muscle,and glandular secretions
autonomic nervous system divisions
sympathetic division (SNS) parasympathetic Division (PSNS)
SNS function
provides a stimulating effect
PSNS
provides a relaxing effect
neuron basic structure
cell body (soma)
axon
dendrites
synapse
cell body composition
single nucleus
cytoplasm (perikaryon: contains mitochondria, ribosomes, endoplasmic reticulum)
cytoskeleton (neurofilaments and neurotubules)
axon
- capability
- axon hillock
- -what is it?
- telodendria
- -what is it?
capability
-long cytoplasmic process capable of propagating an electrical impulse known as an action potential
axon hillock
-wide base of the axon connected to the cell body
telodendria
-the distal end of the axon that is divided into finger-like branches called telodendria
dendrites
- visual characteristics
- function
visual characteristics
-slender processes that extend from the cell body, highly branched
-each branch contains dentritic spines (80-90% of total neuron surface area)
function
-dendritic spines receive information from other neurons
synapse
- function
- two cells of each synapse
function
- a specialized site where the neuron communicates with another cell
- two cells
- -presynaptic cell (sends the message; usually a neuron)
- postsynaptic cell (receives the message, can be another neuron or other type of cell)
types of synapses
- neuromuscular
- neuroglandular
neuromuscular
-synapse between a neuron and a muscle
neuroglandular
-synapse between a neuron and a gland
synaptic cleft
-what is it?
small gap between the pre-synaptic and post-synaptic cells
communication across synaptic cleft
-how?
- presynaptic terminal releases chemical neurotransmitters
- neurotransmitter release is triggered by an action potential
neurons transmit electrical signals called impulses or _____
action potentials
neuron characteristics
- lifespan
- reproductive capability
- metabolic rate
- -result of the metabolic level
- can live your whole life
- amitotic
- high metabolic rate - need more glucose and O2 than other cells
- -can only live for a few minutes without O2
structural classification of neurons
anaxonic neurons
bipolar neurons
unipolar neurons
multipolar neurons
anaxonic neurons
- location
- visual characteristics
location -found in the brain and sense organs visual -two or more processes -dendrites cannot be distinguished from axons
bipolar neurons
- location
- visual characteristics
location
-found only in sensory organs (ex. receptor cells in the retina, nasal passages)
visual
-two processes that extend from the cell body: one is a fused dendrite and the other is an axon
unipolar neurons
- location
- visual characteristics
location
-found in the PNS in the dorsal root ganglia of the spinal cord, and the sensory ganglia of cranial nerves
visual
-contain a single very long axon emerging from the cells body
-axon consists of a central (proximal) process and a peripheral (distal) process receiving impulses from a sensory receptor
multipolar neurons
- location
- visual characteristics
location
-most common (99%) and the major neuron in CNS
visual
-two or more processes extend from the cell body
-all are dendrites except for a single long axon
functional classification of neurons
sensory (afferent) neurons
motor (efferent) neurons
inerneurons (association neurons)
sensory neurons
- function
- structural classification
function
-carry impulses toward the CNS
structural
-unipolar in that the cell bodies are found in the ganglia close to the spinal cord
motor neurons
- function
- structural classification
function
-carry impulses away from the CNS
structural
-multipolar cell bodies are located primarily in the CNS (cell bodies form the grey matter of the brain and spinal cord; axons form white matter)
interneurons
- function
- structural classification
function
-transfer impulses between sensory and motor neurons in the CNS
structural
-multipolar mostly
neuroglia (glial cells) characteristics
supporting cells of the nervous system
found primarily in the CNS
four types of neuroglia in the CNS
ependymal cells
astrocytes
oligodendrites
microglia
ependymal
- location
- functions
location -line the central canal of the spinal cord and ventricles of the brain functions -help produce CSF -circulate CSF (primarily)
astrocytes
- functions
- prevalence
functions -secrete chemicals to maintain the blood-brain barrier -form the structural framework for the CNS -repair damaged nerve tissue -control interstitial environment -guide neuron development prevalence -largest and most numerous
oligodendrites
-function
form the myelin sheaths around axons in the CNS (forming nodes and internodes)
microglia
- prevalence
- function
- function in injury
prevalence
-smallest and rarest
function
-contain thorny processes that touch and monitor the health of neurons
function in injury
-migrate toward injured cells and turn into macrophages to phagocytize neuronal debris and microorganisms
PNS neuroglia types
satellite cells
schwann cells
satellite cells
- location
- function
location
-surround neuron cell bodies within ganglia
function
-relatively unknown
-may play a role in regeneration of nerve and muscle tissue
schwann cells
-location
surround and form myelin sheaths around the larger nerve fibers in the PNS
membrane ion channel types
leak channels
gated channels
leak channels
- composition
- characteristic
composition -made of integral membrane proteins characteristic -always open -involved in passive transport (diffusion and facilitated diffusion which requires no energy)
gated channels
- composition
- changing protein shape requires…
composition -made of integral membrane proteins -have a molecular "gate" which is usually one or more protein molecules that can change shape to open or close the channel in response to various signals changing protein shape requires... -energy unlike leak channels
types of gated cells
chemically-gated
voltage-gated
mechanically-gated
chemically-gated
-open…
open in response when bound to a specific molecule (ligand), such as neurotransmitters
voltage-gated
-open or close…
open or close in response to changes in the membrane potential, such as Na+, K+, and Ca2+ channels
mechanically-gated
open or close…
open or close in response to physical distortion of the membrane surface, such as sensory receptors for touch, pressure, and vibration
resting membrane potential
there is an electrical or potential difference between the two side of a neuron membrane
this difference is called the resting membrane potential (RMP)
factors responsible for the membrane potential involve the types of ions that are naturally found inside and outside of our cells
where are Na+ and K+ concentrated
Na+ are concentrated outside of the cell membrane
K+ are concentrated inside the cells along with negatively charged proteins in the cytosol
_____ tends to diffuse outward through _____ channels driven by the _____ _____ of _____ ions
K+
leak
concentration gradient
-K+
_____ tends to diffuse into the membrane from the outside
Na+
the membrane is more permeable to _____ than _____ so _____ diffuses out faster than _____
K+
Na+
K+
Na+
the result of the previous
the cell experiences a net loss of + charges from the inside to the outside of the membrane resulting in an excess of - charges on the inside
typical RMP
-70 mV
why does the RMP remain stable
Na+-K+-ATPase pump
when will changes in the RMP occur
when a stimulus either alters a membrane’s permeability to Na+ or K+
when a stimulus alters the Na+-K+-ATPase pump
function of stimuli on the membrane
open gated ion channels
opening of gated ion channels result
accelerates Na+ transport
-this causes a change in membrane potential
result of Na+ transport increasing
-final membrane potential
depolarization of the cell
final membrane
-+30 mV
result of K+ rushing out in response to Na+ rushing in
repolarization
hyperpolarization
too much K+ rushes out and the membrane potential is more negative than the RMP
graded potentials
- location
- characteristics
location
-occur in all nerve cells but only affect a limited portion of the cell membrane
characteristics
-can stimulate or inhibit glandular secretions, but the impulse is not great enough to affect a skeletal muscle or neuron as it diminishes rapidly with distance
how does a GP happen?
-how is the RMP restored
some Na+ channels open and no K+ channels
leak channels and the Na+-K+-ATPase pump restore
action potential
- location
- where does it begin and travel to in neurons
location
-can occur in skeletal muscle fibers and axons
where it begins
-begins in the axon hillock and travels the length of an axon toward a synapse
how does an AP happen
-how is the RMP restored
APs involve the opening and closing of LOTS of Na+ and K+ channels
restored by leak channels and the Na+-K+-ATPase pump
membrane threshold required to begin an AP
-60 mV
phases of the AP
- Na+ channels open at threshold and depolarization occurs
- NA+ rushes into the cytoplasm and causes a rapid depolarization of the membrane
- in less than (1 ms) the inner surface of the cell contains more + ions than - (+30 mV) and the Na+ channels close
- this triggers K+ channels to open, driving K+ out of the cell and repolarizing the cell
- as the RMP returns, both gates of the Na+ channels have closed and the K+ channels begin to close
- -some K+ channels remain open and the membrane potential hyperpolarized
- Na+-K+-ATPase pump repolarizes the cell quickly (1 ms)
refractory period
-significance
the duration of time from threshold to the end of hyperpolarization
-during this time the membrane cannot respond normally to further stimulation
how do neurotoxins like tetrodotoxin (TTX) from the puffer fish and other neurotoxins from poisonous snakes work?
block neuronal Na+ channels resulting in paralysis of respiratory muscles
conduction of the AP
at the peak of the AP (+30mV) the inside of a given site of the membrane has an excess of + ions
the + ions spread along inner surface of the membrane towards the adjacent negative charges and produces a local current that depolarized adjacent portions of the membrane
the Na+ channels open adjacent portions of the membrane and new cycles of Na+ and K+ movement produce additional APs. This continues down the entire length of the axon
axon types
-conduction speed
unmyelinated
-conduct impulses at a rate of 1 m/s
myelinated
-conduct impulses about 50x faster
node of Ranvier
area where APs occur on myelinated axons (saltatory conduction) thereby allowing the impulse to skip the internodes and travel much faster
multiple sclerosis physiology
progressive destruction of myelin sheaths accompanied by axon damage and scarring of neural tissue
conduction of the AP
at the peak of the AP (+30mV) the inside of a given site of the membrane has an excess of + ions
the + ions spread along inner surface of the membrane towards the adjacent negative charges and produces a local current that depolarized adjacent portions of the membrane
the Na+ channels open adjacent portions of the membrane and new cycles of Na+ and K+ movement produce additional APs. This continues down the entire length of the axon
axon types
-conduction speed
unmyelinated
-conduct impulses at a rate of 1 m/s
myelinated
-conduct impulses about 7x faster
how are the neurotransmitter and AP terminated
degradation of the neurotransmitter by enzymes (AChE)
removal of the neurotransmitter by astrocytes or postsynaptic terminal where it is then destroyed by enzymes
natural diffusion of neurotransmitter away from the synapse
multiple sclerosis physiology
progressive destruction of myelin sheaths accompanied by axon damage and scarring of neural tissue
information transfer across a chemical synapse
nerve impulse reaches axon terminal containing synaptic vesicles with neurotransmitter (ex. Ach) inside each vesicle
Ca2+ gates open in the presynaptic axon terminal (depolarization has opened Na+ channels too) and Ca2+ floods into the terminal from the extracellular fluid
Ca2+ acts as a messenger instructing the synaptic vesicles to fuse with the axon membrane and empty in the synaptic cleft
the neurotransmitter binds with postsynaptic protein receptors, which change shape, causing a Na+ channel to open, Na+ influx, and an AP
termination of the neurotransmitter and AP
how does Ca2+ leave the cell?
via a Ca2+ pump or is taken up by the mitochondria
what happens to a severed nerve axon
the proximal segment swells and experiences some retrograde degeneration
Wallerian degeneration occurs in the distal segment
macrophages and Schwann cells then phagocytize debris from the axon and myelin sheaths to create a “channel” within the endoneurium for a new axon
growth factors secreted by Schwann cells and other molecules can form new axon “sprouts” on the proximal segment that will grow into new axons within the endoneurium “channel”
Schwann cells will remyelinate the new axons in the final phases of regeneration
Wallerian degeneration
the myelin sheath and axon degenerate due to the absence of nutrients from the cell body
how do neurons in the PNS die?
if a neuron dies then other neurons stimulated by its axon also die
death of a neuron occurs if damage occurs to (or close to) the cell body
cut or compressed axons can regenerate if the cell body remains intact
labeling of a severed nerve axon
the end still attached to the cell body is labeled the proximal segment
the other end is the distal segment
what happens to a severed nerve axon
the proximal segment swells and experiences some retrograde degeneration
Wallerian _______ occurs in the distal segment
macrophages and Schwann cells then phagocytize debris from the axon and myelin sheaths to create a “channel” within the endoneurium for a new axon
growth factors secreted by Schwann cells and other molecules can form new axon “sprouts” on the proximal segment that will grow into new axons within the endoneurium “channel”
Schwann cells will remyelinate the new axons in the final phases of regeneration
Wallerian _________
the myelin sheath and axon degenerate due to the absence of nutrients from the cell body
what happens if a nerve axon is completely severed and the surrounding connective tissue is severely damaged
Schwann cells may not be able to reach the proximal segment
the only way a new axon will grow is with surgical intervention
