Nervous Tissue - Chapter 13 Flashcards
What is the difference in the endocrine and nervous systems? How are they similar?
Differences:
- Endocrine sends chemical messages int he form of hormones secreted into the bloodstream
- Nervous sends electrical and chemical messages from cell to cells, more focused signaling
Similarities:
- Both maintain internal coordination
- Both send messages to other parts of the body
What three jobs of the nervous system fall into these categories?
- Sensory
- Integrative
- Motor
- Sensory - collect info (about changes in body and external environment, sends those messages to brain and spinal cord)
- Integrative - process and evaluate (CNS processes info and relates it to past experiences and determines response)
- Motor - initiate response (CNS issues commands to muscles and glands to carry out response)
What are the two subdivisions of the nervous system?
- Central Nervous System (CNS) - brain and spinal cord
2. Peripheral Nervous System (PNS) - everything else
What is the difference in a nerve and a ganglion?
- Nerve - bundle of nerve fibers (axons) wrapped in fibrous CT
- Ganglion - knot-like sweeping in a nerve where neuron cell bodies are concentrated
What are the 2 divisions of the PNS?
- Sensory (afferent) Division - carries signals from receptors to CNS
- Motor (efferent) Division - carries signals from CNS to effectors (glands and muscles)
What are the subdivisions of the Sensory Division of the PNS and what do they do?
- Somatic sensory division - carry signals from receptors in skin, muscles, bones, and joints
- Visceral sensory division - carry signals to guts, organs, etc.
What are the two subdivisions fo the Motor Division
- Somatic motor division - sends signals to skeletal muscles for contraction and reflexes (voluntary responses)
- Visceral motor division - signals to glands, cardiac and smooth muscles (involuntary responses)
The visceral motor division of the PNS is further divided into 2 more subparts. What are those and what do they do?
- Sympathetic division - action (accelerates heart rate and respirations, inhibits digestive and urinary systems)
- Parasympathetic division - calming (slows heart rate and breathing, stimulates digestive and urinary systems)
What are 3 universal properties of neurons?
- Excitability/irritability - response to environmental changes/stimuli
- Conductivity - response to stimuli by producing, quickly conducted to other cells at distant locations
- Secretion - electives signal reaches the end of nerve fiber, the cell secretes a chemical neurotransmitter which influences the next cell
How long to nerve cells live? How often do they reproduce?
Live a very long time
Don’t make new nerve cells after maturity
Non-mitotic (mostly)
What are the three functional classes of neurons?
- Sensory (afferent) neurons - detect stimuli and transmit information TOWARD the CNS (light, heat, pressure, chemicals, etc)
- Interneurons - entirely within the CNS, connect motor and sensory pathways, receive signals from many neurons and carry out integrative functions, ~90% of all neurons
- Motor (efferent) neurons - send signals AWAY from CNS (to muscle and gland cells, aka the effectors)
What is the job of the neurosoma in the structure of a neuron? What’s another name for it?
Aka cell body or soma
Control center
Single, centrally located nucleus, typical organelles (lots of mitochondria, no centrioles cause no mitosis)
What are the axoplasm and axolemma?
Axoplasm - cytoplasm of axon
Axolemma - plasma membrane of axon
What are dendrites?
Branches from neurosoma, receive signals
What is the effect of a neuron having more dendrites?
It can receive more information, more precise pathways for reception and processing
What is an axon? What does it do? What are some key features of an axon?
Nerve fiber
Transmits nerve impulses AWAY from the cell body
Key features: axon hillock (mound on neurosoma), Axon collaterals (major beaches of axon), branch (telodendria), synaptic terminal (tip of branch), Myelin sheath (may enclose axon)
What are the four different classes of neurons?
- Multipolar (one axon, multiple dendrites)
- Bipolar (one axon, one dendrite)
- Unipolar (single process)
- Anaxonic (no axon, many dendrites)
What is a multipolar neuron and what does it do?
One axon, multiple dendrites Most common (most neurons in CNS) Motor neurons (muscles/glands)
What is a bipolar neuron and what does it do?
One axon, one dendrite
Sensory (olfactory cells, retina, inner ear [rare])
What is a unipolar neuron and what does it do?
Single process leading away from neurosoma (branches like a T)
Sensory cells from skin and organs to spinal cord
What is an anaxonic neuron and what does it do?
Many dendrites but no axon
Retina, brain, and adrenal gland
Do you have more neurons or glial cells? Why/how?
Glial cells (by at least 10 to 1) They're capable of mitosis
What are the (4) functions of glial cells?
- Protect neurons and help them function
- Bind neurons together and form framework for nervous tissue
- Guide migrating neurons to their destinations (in vitro)
- Insulation - prevents neurons from touching each other, gives precision to conduction pathways
What types of neuroglia can be found in the CNS?
- Oligodendrocytes
- Ependymal cells
- Microglia (least abundant)
- Astrocytes (most abundant)
What are oligodendrocytes and where are they found?
Neuroglia cells of CNS
Large, bulbous cells
Form myelin sheath - speeds up signal conduction
Arm-like processes wrap around nerve fibers
What are ependymal cells and where are they found?
Neuroglia cells of CNS
Line internal cavities of the brain (and central canal of SC)
Secrete and circulate CSF (choroid plexus, resemble cuboidal epithelium with cilia on apical surface)
What are microglia cells and where are they found?
Neuroglia cells of CNS - least abundant
Phagocytic cells (develop from WBC)
Wander the CNS looking for debris and damage (replicate in response to infection, become concentrated in areas of damage, influential during development)
What are astrocytes and where are they found?
Neuroglia cells of CNS - most abundant
Covers brain surface and most non-synaptic regions of neurons in the gray matter
Functions: supportive framework, blood brain barrier, monitor neuron activity, regulate blood flow, secrete nerve growth factors, stabilize chemical environment, add/eliminate synapses, form scar tissue and fill space of nerve damage
What types of neuroglia can be found in the PNS?
- Schwann cells
2. Satellite cells
What are Schwann cells and where are they found?
Neuroglia cells of PNS
Wrap around nerve fibers to form myelin sheath (provides insulation, increases speed of impulse)
Assist in regeneration of damaged fibers
What are Satellite cells and where are they found?
Neuroglia cells of PNS
Surround the neurosomas in ganglia
Provide electrical insulation
Regular the chemical environment
What is the job of the myelin sheath?
Insulates the nerve fiber
What is the myelin sheath made of?
Oligodendrocytes in CNS, Schwann cells in PNS
Essentially an extension fo the plasma membrane of glial cells
Primarily made of lipids
White coloration fo myelinated parts of NS
What is myelination? When does it happen?
Production of myelin sheath
Begins during fetal development
Proceeds rapidly during infancy
What is the neurilemma?
Thick, outermost coil of myelin sheath
Contains nucleus and most of its cytoplasm
Basal lamina and a thin layer of fibrous CT (endoneurium) lie external to the neurilemma
Describe the myelin sheath of the PNS
Schwann cells spirals repeatedly around a single nerve fiber
Up to 100 layers of membrane
No cytoplasm between layers
Neurilemma is outermost layer w/ nucleus
Describe the myelin sheath of the CNS
Oligodendrocytes myelinated several nerve fibers
Cannot migrate around any one of them like Schwann cells
Myelination spirals inward
No neurilemma or endoneurium
The axon hillock has two important “zones” or “segments.” What are they and what do they do?
- Trigger Zone - important in initiating a nerve signal
2. Initial segment - short section of nerve fiber between axon hillock and first glial cell
Why is the myelin sheath segmented? What are the segments called?
To allow for signal transduction - signal “jumps” from node to node
- Myelin sheath caps (aka nodes of Ranvier) - gap between segments
- Internodes - myelin-covered segments from one gap to the next
Describe the use of ion channels in a nerve signal
Nodes of Ranvier are violated-gated ion channels. As Na+ enters the cell at a node, the electrical field repels positive ions inside, transferring energy down the axon rapidly (the signal)
Then, the next node is reached with a signal strong enough to open the voltage gated ion channels, and it starts all over
What is the job of myelin in reference to voltage gated ion channels?
It speeds up conduction
Minimized leakage of Na+ out of cell
Lower attraction between ions inside/outside cell
Do unmyelinateud axons exist? If yes, where?
Yes:
PNS - unmyelinateud axons propagate impulses by continuous conduction (implies travels entire length of axon), partially enveloped by Schwann cells, but does not wrap around each axon
CNS - unmyelinateud axons are anchored together by astrocytes
What determines the speed at which a nerve signal travels along the surface of a nerve fiber?
- Diameter of fiber (larger fibers conduct more rapidly)
2. Presence or absence of myelin (speeds signal conduction)
Where do you find slow conduction speeds? Fast?
Slow - gastrointestinal tract
Fast - Skeletal muscles (improves balance and coordinated body movement)
