Chapter 13- Neural Tissue Flashcards
nervous system
coordinate all body systems
- accomplished by the transmission of signals
- body parts to CNS
- CNS to body parts
- Electrochemical signaling
endocrine system
slower scale
-uses chemicals in the blood stream called hormones
general makeup of NS
- many organs, each composed of several tissue
- connective tissue
- blood vessels
- neurons
- neuroglia
2 groups of NS
CNS
-brain and spinal chord
PNS
-cranial and spinal nerves (ganglia)
CNS makeup
brain and spinal chord
- covered by meninges (house fluid)
- starts as a hollow tube
- bathed in cerebrospinal fluid
- integration center
PNS makeup
consists of cranial and spinal nerves that contain both sensory and motor fibers
-connects CNS to muscles, glands, and all receptors
-brings info to and from CNS
(only sensory OR motor neurons)
PNS: 2 types
Afferent division= sensory
Efferent division= motor
–somatic (conscious control)
–autonomic (unconscious)
Receptors
detect stimuli
sensory
afferent PNS
integrative
CNS
motor
efferent PNS
effector
muscle/gland
Nervous tissue
neurons -structural and functional units -excitable -amitotic (unrepairable) Neuroglia cells -accessory cells -act like connective tissue
3 major structures of neurons
soma
dendrites
axon
soma
cell body
-mononucleate
soma consists of
nissi bodies: ribosomes clusters, give gray color
axon hillock: connects soma to axon
perikaryon: region around the nucleus
neuronfibrils: cytoskeleton that extend into dendrites/axons; gives shape
dendrites
- respond to neurotransmitters
- short, branched, unmyelinated
- specialized for contact with other neurons
- conducts impulses towards the cell body
axon
- only one cell
- conducts nerve impulses away from soma
- can give off collaterals (branches at end)
- end in synaptic terminals
- produce neuraltransmitters
- may contact one of three things: another neuron, muscle fibers, gland
myelin sheath
glial cells that may wrap around the axon
axonal transport (axoplasmic flow)
movement of cellular materials (NOT signals) through axon
anterograde
away form soma; neurotransmitters, organelles, nutrients
retrograde
toward soma; degraded materials to be recycled and extracellular substances
axoplasma
- cytoplasm of an axon
- consists of
- few organelles
- cytoskeletal proteins
- -form cytoskeleton
- -maintain shape
- generate axonal transport
axolemma
-plasma membrane of an axon consists of: -collaterals: side branches -telodendria: terminal extensions -synaptic terminal: contains synaptic vesicles; where neuron contacts pstsynaptic cell
structural classification of neurons
anaxonic
bipolar
unipolar
multipolar
anaxonic
small neurons
axons can not be distinguished from dendrites
-CNS, especially interneurons that coordinate special senses
no axon
bipolar
- several small dendrites converge onto one (one really long dendrite, looks like axon)
- dendrite and axon separated by soma
- unmyelinated
- sensory neurons of special sensory organs
unipolar
- pseuod-unipolar
- several small dendrites converge onto one large one
- dendrite and axon continuous
- usually myelinated
- majority of sensory neurons in PNS
multipolar
- many dendrites extend from soma
- long axon
- myelinated
- majority of motor neurons in PNS
- spinal interneurons in CNS
Afferent Neuons
Have sensory function
- cell body usually are outside CNS
- have receptor ends on dendrites or are associated with receptor cells in sense organs
- carry impulses from peripheral body parts to brain or spinal cord
afferent neruon receptors
exteroceptors: touch, temperature, pressure, light, chemicals
proprioceptors: monitor muscle and skeleton position
interoceptors: monitor internal systems (digestion, respiration, urinary)
Interneurons
- only in CNS
- classified based on effects
- -excitatory
- -inhibitory
- most abundant
- -link 2 or more neurons
efferent neurons
have motor function
- cell body usually are inside CNS
- carry impulses from the brain or spinal cord to peripheral body parts
somatic efferent neurons
controls skeletal muscle
autonomic/visceral efferent neurons
smooth muscle/glands
neuroglial cells in PNS
satellite
schwan cell
neuroglial cells in CNS
astrocytes
oligodendrocytes
ependymal cells
microglia
Astrocytes
largest and most common star shaped functions: -structure and repair -metabolism -regulate ions and nutrition -guide neurons to targets -form blood-brain barrier
oligodendrocytes
like astrocytes but smaller
functions
-form myelin in CNS
-sequester debris
Microglia
-smallest and least common
-derived from myeloid cells
functions:
-help support neurons
-phagocytosis
-increase in number during injury or disease
ependymal
-columnar/cuboidal
-microvilli on luminal surface
-joined by gap junctions
functions:
-help produce cerebrospinal fluid
-form porous layer
-monitor CSF composition
satellite
associated with soma
assist with exchange of nutrients
isolates neuron from extraneous stimuli
schwann cells
produce myelin in PNS
encloses axons of longer peripheral nerves
functions:
-support neurons
-prevent contact
-myelinate large PNS axons (myelin sheath)
unmyelinated axons
- appear gray
- many axons associate with a single schwann cell
- CNS: no glial cells
myelinated
- appear white
- CNS: oligodendrocytes myelinate part of several axons
- PNS: schwann cell myelinates part of one axon
myelin structure
- myelin
- neurilemma
- nodes of ranvier
myelin
plasma membrane of schwann cell wrapped around axon
neurilemma
part of schwann cell that contains cytoplasm
nodes of ranvier
gaps in myelin sheath
myelination process
starts at week 14 and completed by age 2-3 years
myelin functions
isolate axons
increase rate of action potential
regeneration of nerve fibers: PNS
can regenerate a fraction of axons
- schwann cells participate in process
- called wallerian degeneration
wallerian degeneration
regeneration of PNS axons
steps of nerve regeneration
- injury separates axon from cell body
- distal portion of axon will deteriorate along with myelin sheath - macrophages clean up
- some schwann cells remain
- get thin basement membrane and layer of CT around schwann cells - forms hollow tube leading to original connection of axon
- proximal end sprouts
- sprout may grow into tube - remaining schwann cells produce new myelin around growing axon
- new axon grows 3-4mm/day
repair in CNS
more limited
- degeneration occurs after injury
- oligodendrocytes do not proliferate
- proximal end sprouts but has no tube to follow
- astrocytes produce scar tissue and chemicals blocking regrowth
- generally results in paralysis
irritability
ability to respond to stimuli
excitability
ability to transport and impulse
action potential
an electrical impulse changing the permeability of a membrane
nerve impulse
AP moving down an axon
- impulse travels faster when:
- -axon is myelinated
- -has a larger diameter
synapse characteristics
functions as control/transmission point site of communication between -sensory structure and neuron -neuron and effector -2 neurons -any two cells with gap junctions
electrical synapse
- gap junctions cause the exchange of charged ions between two cells
- communicating charge through ions
chemical synapse: definition
chemicals are released by one cell and travel to another
chemical synapses: about
- synaptic vesicles house neurotransmitter
- only exist in the presynaptic cell
- release neurotransmitter into the synaptic cleft
- receptors on post-synaptic membrane register the neurotransmitter
- proliferates AP from one cell to the next
- communication in one direction only
- only axons have synaptic vesicles
steps at chemical synapse
- AP reaches synaptic knob of presynaptic neuron
- neurotransmitter released
- neurotransmitter crosses cleft and binds to receptors in post-synaptic membrane
- change in permeability results, can be excitatory or inhibitory - neurotransmitter is then removed from synaptic cleft
- permeability returns to original state
neuronal pools
- receive impulses from afferent fibers (input)
- impulses carried away on efferent fibers (output)
- afferent fibers can branch manny times as they enter a pool
types of neuronal pools
convergence divergence serial processing parallel processing reverberation
serial processing
one neuron to another in series
divergence
when impulse leaves a pool, it may spread into several output fibers
-allows impulse to be amplified
convergence
single nerve in pool may receive impulses from 2 or more incoming fibers
- if lead to same nerve they are said to converge
- allows summation of impulses from different sources
parallel processing
processing information from several neurons at once
reverbration
positive feedback continues activity of circuit
- enhances signal so happens repeatedly
- promote a behavior, keep responding same way
facilitation: threshold
- one neuron may receive either excitatory and inhibitory stimuli from multiple neurons
- the net effect of all this input results in a net charge. if this charge is positive enough it will result in AP
- this point where AP can be produced is known as threshold
facilitaiton: facilitated
if a neuron is excited, but still below threshold:
-no impulse, but nerve is more excitable to next impulse
-nerve is said to be facilitated
whole system allows for multiple sources to manage nervous system
CNS structures
nuclei
center
tracts
nuclei
collection of neuron cell bodies
center
collection of neuron cell bodies working together
tracts
bundles of axons
PNS structures
ganglia
nerves
ganglia
collection of neuron cell bodies
nerves
bundles of axons
