nervous tissue Flashcards
3 fxns of nervous system
- collect info in pns, send to cns
- process and evaluate info
- cns responds, pns carries commands to effectors
somatic sensory
sensory inout that is consciously perceived from receptors
ex: eyes ears skin
visceral sensory
sensory input that is not consciously perceived from receptors of blood vessels and internal organs
ex: heart
somatic motor
motor output that is consciously or voluntarily controlled
effector is skeletal muscle
autonomic motor
motor output that is not consciously or is involuntarily controlled; effectors are cardiac muscle, smooth muscle, and glands
neurons
excitable cells that initiate and transmit nerve impulses
glial cells
nonexcitable cells that support and protect neurons
fxns of glial cells
protect and nourish neurons, provide an organized supporting framework for all nervous tissue
astrocytes
most abundant glial cells
versatile
regulate tissue fluid composition, structural framework, replacing damaged neurons, neuronal development, anchor neurons, exchange bw neurons and vasculature
astrocytosis
replacing damaged neurons
synaptic transmission
important in synapse maintenance, number of synapses, and may play a role in signaling
loss observed in neurological disorders/neurogenerative diseases
ependymal cells
epithelial, line cavities of brain and spinal cord, slender processes that branch out for communication, choroid plexus in association with nearby capillaries for CSF production
microglia
small cells with thorny processes that monitor health of nearby cells, transform into macrophage to protect CNS from invading microbes and dead neural tissue
oligodendrocytes
large cells with bulbous body and slender cytoplasmic processes that ensheathe axons (myelin sheath)
satellite cells
flattened cells arranged around neuron cell bodies in ganglia, separate cell bodies from interstitial fluid, control chemical environment, regulate exchange of nutrients and wastes between neuron and environment
ganglion
group if nerve cell bodies in the PNS
schwann cell
neurolemmocyte
form myelin sheath around axon in PNS, act as phagocyte to remove debris, peripheral nerve fiber regeneration
neuron special characteristics
high metabolic rates, extreme longevity, amitotic, PM site of electrical signaling
neuron cell body
soma
activity occurs here
has nissl bodies, golgi, neurotubules, neurofibrils, pigment inclusions
neurotubules
movement of substances
neurofibrils
intermediate filaments, help form myofibrils
dendrites
short branches that receive signals
axon
arises from axon hillock, send signals to other cells
anterograde movement
from soma to synaptic knobs (away)
retrograde movement
from synaptic knobs to soma (toward)
structural classifications of neurons
number of neuron processes
unipolar, bipolar, multipolar
most common neuron type
multipolar
functional classifications of neurons
direction of nerve impulse
sensory, motor, interneuron
sensory neuron impulses move
toward CNS
motor neuron impulses
from CNS to PNS
interneuron
intermediate, typically multipolar, in CNS
afferent transmission
info goes from PNS to CNS
efferent transmission
info goes from CNS TO PNS
unipolar neurons are generally involved in
sensation
bipolar neurons are generally involved in
sensation in special senses
myelination fxn
produces faster nerve impulse conduction
myelin
lipid-protein composite, support protect and insulate axon
formed by schwann cells and oligodendrocytes
saltatory conduction
node jumping
why is myelination only on axon and not on dendrites or soma?
dendrites and soma need the surface area for better communication
unmyelinated axons observe
continuous conduction, but are slower
synapse
specialized jxn where nerve impulse is transmitted
no synapses are found where … is present
myelination
electrical synapses
gap jxns formed by connexons, no delay
chemical synapses
most numerous, use neurotransmitter, synaptic delay
functional syncytium
group of cells working as a single unit
rate of nerve impulse conduction can only be influenced by 2 factors
- axon’s diameter
- presence/absence of myelin sheath
nervous system coordinates and integrates nervous activity because neurons are organized into complex patterns called…
neuronal circuits
4 types of circuits
converging, diverging, reverberating, parallel-after discharge
pns regeneration of axons
- amount of damage
- secretion of nerve growth factors
- distance between site of damage and effector organ
cns regeneration of axons
very limited due to
1. no release of nerve growth factors
2. high cellular density tends to complicate regrowth
3. both astrocytes and CT coverings may form scar tissue, obstructs axon regrowth
nerve
cablelike bundle of parallel axons in the pns
tract
term for nerve in the cns
nerves are surrounded by 3 consecutive ct wrappings
endoneurium, perineurium, and epineurium
classification of nerves
direction of transmission
sensory, motor, and mixed
