Chapter 12 Flashcards
nervous tissue
the nervous system is composed of: (4)
brain, spinal cord, nerves, ganglia
primary tissue of nervous system
nervous tissue
ganglion
nerve cell bodies; clusters of neuron cell bodies located along nerves
pleural = ganglia
general functions of nervous system
collect, process/evaluate, and initiate response info
what component collects info?
receptors
what component processes/evaluates info?
brain and spinal cord
what component initiates response?
brain and spinal cord and effectors
(brain and spinal cord relay info to effector)
central nervous system (CNS)
brain and spinal cord
brain - protected/encased in skull
spinal cord - housed/protected within vertebral canal
peripheral nervous system
nerves and ganglia
nerves - bundles of axons and neurons
ganglia - part of axon/neuron bundle
sensory nervous system (afferent nervous system)
receives sensory information from receptors and to the CNS
(sensory input)
two types of sensory nervous system
somatic sensory and visceral sensory
somatic sensory
stimuli we are conscious of
example of somatic sensory nervous system
5 senses; taste, touch, smell, hearing, vision
visceral sensory
stimuli we don’t perceive
motor nervous system (efferent)
initiates/transmits motor info from CNS to effectors (motor output)
two types of motor nervous system
somatic motor and autonomic motor
somatic motor
voluntary signals to voluntary effectors (skeletal muscle)
autonomic motor
involuntary signals to involuntary effectors (smooth/cardiac muscles, glands)
sympathetic and parasympathetic divisions of autonomic motor nervoussystem
sympathetic = “fight or flight” ; parasympathetic = “rest and digest”
nerves
organs composed of bundles of axons, connective tissue layers, and blood vessels in PNS
fascicle
bundle of axons
3 connective tissue wrappings
epineurium, perineurium, endoneurium
epineurium
encloses whole nerve (dense irregular CT)
perineurium
encloses each fascicle (dense irregular CT)
endoneurium
encloses each individual axon (areolar CT)
vascularization of nerves
vascularized by extensive network of blood vessels thru epineurium and perineurium
cranial nerves
12 pairs; extend from the brain
spinal nerves
31 pairs; extend from the spinal cord
sensory nerves
contains sensory neurons that send signals towards CNS
motor nerves
has motor neurons that send signals away from CNS
mixed nerves
has both sensory and motor neurons; most nerves are mixed nerves, and individual axons still transmit only one type of info
5 neuron characteristics
excitability - responsive to stimuli
conductivity - propagate electrical signals
secretion - neurons release neurotransmitters
extreme longevity - cell can live throughout lifetime
amitotic - neurons no longer divide p. fetal development
cell body
soma
perikaryon
plasma membrane around cytoplasm
function of cell body (soma)
initiates graded potentials, receive information from dendrites and conducts those signals to axons
what does the cell body contain?
nucleus and Nissl bodies
nissl bodies
ribosomes and chromatophilic substance
dendrites
short branches off cell body that receives input and sends it to cell body; unmyelinated
axon
long process off cell body that contacts other neurons, muscle cells, or glands
axoplasm
cytoplasm of axon
axolemma
membrane of axon
axon terminal
end region of axon
synaptic knob
contains synaptic vesicles that contain neurotransmitters
cytoskeleton
has neurofilaments (intermediate filaments); tensile strength properties
two modes of transport
anterograde and retrograde
anterograde
movement away from cell body
retrograde
movement toward cell body
four structural classifications of neurons
multipolar, bipolar, unipolar, anaxonic
multipolar
many dendrites, one axon (most common)
bipolar
one dendrite, one axon (sensory)
unipolar
one process that splits into two processes; peripheral splits into dendrites, central splits into synaptic knobs
anaxonic
no axon, only dendrites
3 functional classification of neurons
sensory, motor, interneurons
sensory neurons
afferent neurons; input from receptors to CNS (most are unipolar)
motor neurons
output from CNS to effectors; always multipolar
interneurons
receive/process/integrate info from many other neurons and communicate between sensory and motor neurons
(within CNS; 99% of neurons)
synapses
where neurons contact other neurons/effectors
chemical
more common; presynaptic and postsynaptic neurons + synaptic cleft
presynaptic neuron vs postsynaptic
presynaptic — produces signal
postsynaptic — receives signal
synaptic cleft
small gap between presynaptic neuron and postsynaptic neuron
chemical synapse takes time and causes:
synaptic delay
neuroglia
non-excitable; found in both CNS and PNS; makes half the volume of nervous system
neuroglia characteristics
- able to divide
- protect/nourish neurons
- critical for normal neural synapse function
- provide scaffolding for nervous tissue
astrocytes
star shaped; most abundant glial cell in CNS
what do astrocytes do?
form the blood-brain barrier, controls what substances can enter the brain, regulate fluid composition around neurons, structural support for neurons
ependymal cells
line cavities in the brain/spinal cord (CNS)
what plexus are ependymal cells part of?
choroid plexus
what do ependymal cells produce?
cerebrospinal fluid
microglia
small wandering cells in CNS; phagocytotic cells of immune system; replicate in infection
oligodendrocytes
large cells w/ slender extensions that wrap around axons of neurons; myelinates/insulates CNS axons
satellite cells
arranged around neuronal cells in ganglion; PNS
neurolemmocytes
(aka Schwann cells) elongated, flat cells that ensheath PNS axons w/ myelin
myelination
process of wrapping axons in myelin
what is myelin high in?
lipid content
where can you find myelin aside from the axon?
neurolemmocytes in PNS, oligodendrocytes in CNS
pumps
helps membrane proteins move against concentration gradient; maintains concentration gradient of membrane
two types of pumps
sodium-potassium (Na and K+), calcium (Ca2+)
channels
pores that allow ions to move down concentration gradient; specific for a type of ion
leak channel
always open; passive
chemically-gated channel
normally closed; open when transmitter binds
voltage-gated channel
normally closed; open when membrane charge changes
modality-gated channel
normally closed; open when specific stimulus is present
Ohm’s law
neuron activity depends on electrical current
current
voltage/resistance; movement of charged particles across barrier
voltage
difference in electrical change between 2 places
resistance
opposition to movement
resistance
opposition to movement
in a neuron, charged particles are:
ions
current is generated when:
ions diffuse through channels
voltage exists due to:
unequal ion distribution
membrane resists:
ion flow (channels opening decrease resistance
ions while neurons are at rest
ions are unevenly distributed across plasma membrane
cytosol has more:
K+ (potassium)
interstitial fluid has more:
Ca2+ (calcium), Cl- (chloride) and Na (sodium)
membrane potential
electrical charge diff. across membrane; present within neurons at rest
graded potential
small, short-lived changes in resting membrane potential
depolarization vs hyperpolarization
depolarize - make less negative (+)
hyperpolarize - make more negative (-)
graded potentials in postsynaptic neuron (2)
excitatory postsynaptic potential (EPSP) or inhibitory postsynaptic potential (IPSP)
EPSP results in what? what ions enter?
depolarization; Na+ (sodium)
IPSP results in what? what ions enter/exit?
hyperpolarization; K+ exit (potassium leaves) and Cl- entry (chloride entry)
K+ diffusion
most important factor
K+ diffusion out the cell is due to:
concentration gradient
K+ diffusion out the cell is limited by:
electrical gradient
threshold
minimal voltage change required
