Lesson 12 Flashcards
endocrine system
communicates by means of chemical messengers (hormones) secreted into the blood
nervous system
utilizes neurons (nerve cells) to send messages from cell to cell by electrical and chemical means
three steps of nervous system communication
- receives stimuli from external environment and transmit it to the CNS
- CNS processes the info and determines response
- CNS issues commands to muscle and gland cells to carry out response
central nervous system (CNS)
brain and spinal cord
peripheral nervous system (PNS)
nerves and ganglia
nerve
a bundle of nerve fibers (axons) wrapped in fibrous connective tissue (PNS)
ganglion
a knot-like swelling in a nerve where neuron cell bodies of PNS are concentrated
what are the two major divisions of the PNS?
sensory and motor
sensory (afferent) division of the PNS
carries signals from receptors (sense organs) to the CNS
somatic sensory division of the PNS
carries signals from receptors in the skin, muscles, bones, and joints
visceral sensory division of the PNS
carries signals from the viscera (heart, lungs, stomach, bladder)
motor (efferent) division of the PNS
carries signals from the CNS to effectors (glands and muscles that carry out the response)
somatic motor division of the PNS
carries signals from SKELETAL muscles; causes voluntary muscle contraction and autonomic reflexes
visceral motor division of the PNS
aka autonomic nervous system (ANS)
carries signals to glands, cardiac, and smooth muscle; no voluntary control
the visceral motor division is also known as?
the autonomic nervous system (ANS)
sympathetic division of the ANS
stimulates and prepares the body for action
parasympathetic division of the ANS
has a calming effect on the body
enteric plexus
within the digestive tract, enables coordination within the digestive tract
tract
a bundle of axons in the CNS
nucleus
a cluster of neuronal cell bodies in the CNS
excitability
ability to respond to stimuli
conductivity
produce electrical signals that are conducted to other cells
secretion
when a signal reaches the end of an axon, the neuron secretes a neurotransmitter that stimulates the next cell
sensory (afferent) neurons
detect stimuli and transmit information about them toward the CNS
interneurons
receive signals from other neurons, processes this info, and makes resulting ‘decisions’
motor (efferent) neurons
send signals out to muscles and gland cells
cell body
also called neurosoma, soma, or perikaryon; contains nucleus and many organelles
neurites
extensions of the neuron reaching out to other cells
dendrites
most numerous neurites, resemble branching of a tree; primary sites for receiving signals from other neurons
axon (nerve fiber)
long, cylindrical extension; relatively unbranched but may give off axon collaterals; specialized for rapid conduction of nerve signals
axon hillock
the beginning of an axon; mound on one side of the cell body
axoplasm
cytoplasm in neurons
axolemma
neuronal cell membrane
terminal arborization
very branches end of an axon
axon terminal (terminal bouton)
a bulbous end to each branch of arborization
a neuron never has more then _____ axon
one
multipolar neuron
one axon, many dendrites; most common type in the body, most are in the CNS
bipolar neuron
one axon and one dendrite ; olfactory cells, neurons of the retina, sensory neurons in the ear
unipolar neuron
single process leading away from the cell body, splits into peripheral process and central process
anaxonic neuron
many dendrites but no axon; found in brain, retina, and adrenal gland
axonal transport
two-way passage of materials along an axon
anterograde transport
movement away from the cell body, down the axon; driven by motor protein kinesin
retrograde transport
movement up the axon toward the cell body; driven by motor protein dynein
rabies virus
bypasses CNS defenses by infecting the CNS through retrograde transport; the virus is transported back to the CNS from the infected nerve
neuroglia/glial cells
non-neuronal supportive cells
functions of glial cells (4)
- form supportive tissue framework
- binds neurons together
- in fetus, guide migrating neurons to their destination
- cover mature neurons (except synapses)
glial cells: oligodendrocytes
form the myelin sheaths in the CNS
glial cells: ependymal cells
line internal cavities of the brain; secrete and circulate cerebrospinal fluid (CSF)
glial cells: microglia
macrophages; engulf debris, provide defense against pathogens
glial cells: astrocytes
most abundant type; wide variety of functions
the many functions of astrocytes (know some)
Provide framework for nervous tissue; extensions (perivascular
feet) contact capillaries and stimulate formation of blood-brain
barrier; adjust blood flow; supply neurons with lactate for energy;
secrete nerve growth factors; influence synaptic signaling;
regulate composition of tissue fluid; form scar tissue when
neurons are damaged, a process called astrocytosis or sclerosis
peripheral glial cells: schwann cells (neurolemmocyte)
envelop axons of the PNS, form myelin sheath, and assist in regeneration of damaged fibers
peripheral glial cells: satellite cells
surround nerve cell bodies in ganglia of PNS; provide insulation around cell body and regulate chemical environment
where do brain tumors arise from?
- meninges (protective membranes of CNS)
- metastasis from non neuronal tumors
- glial cells that are mitotically active throughout life
gliomas
tumors of glial cells; grow rapidly and are highly malignant
myelin sheath
spiral layers of insulation around an axon, formed by Schwann cells (PNS) and oligodendrocytes (CNS)
myelination
the process of creating the myelin sheath, completed by late adolescence
neurilemma
the thich, outermost layer of a Schwann cell of the myelin sheath; contains nucleus and most of its cytoplasm
myelination in the CNS
- Each oligodendrocyte extends several processes that wrap around small portions of many axons in its immediate
vicinity - nucleus can not migrate around the axon like Schwann cells
in both the PNS and CNS, the myelin sheath is _____
segmented
node of Ranvier
gaps between segments of the myelin sheath
internodal segments
myelin-covered segments
initial segment
bare section of axon between the axon hillock and the first glial cell
trigger zone
axon hillock and initial segment of axon; important role in initiating nerve signal
Multiple Sclerosis
- oligodendrocytes and myelin sheath in the CNS deteriorate
- myelin is replaced with hardened scar tissue
- nerve conduction disrupted
- onset between 20-40
- autoimmune triggered by virus?
Tay-Sachs disease
- hereditary disorder seen mainly in infants
- abnormal accumulation of glycolipid called GM2 in the myelin sheath
unmyelinated axons
- membrane folds once around each axon; does not spiral repeatedly around it
- wrap serves as the nuerolemma
- basal lamina surrounds Schwann cells
steps of regeneration
- axon distal to the injury degenerates, macrophages clean up tissue debris
- bell body swells, ER breaks up, nucleus moves off center
- axon stump sprouts multiple growth processes
- Schwann cells neurolemma, endoeurium, and basal lamina form a regeneration tube
- etc.
