Nervous Tissue - Chapter 13

Question 1

What is the difference in the endocrine and nervous systems? How are they similar?

Answer 1

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

Question 2

What three jobs of the nervous system fall into these categories?

1. Sensory
2. Integrative
3. Motor

Answer 2

1. Sensory - collect info (about changes in body and external environment, sends those messages to brain and spinal cord)
2. Integrative - process and evaluate (CNS processes info and relates it to past experiences and determines response)
3. Motor - initiate response (CNS issues commands to muscles and glands to carry out response)

Question 3

What are the two subdivisions of the nervous system?

Answer 3

1. Central Nervous System (CNS) - brain and spinal cord

2. Peripheral Nervous System (PNS) - everything else

Question 4

What is the difference in a nerve and a ganglion?

Answer 4

1. Nerve - bundle of nerve fibers (axons) wrapped in fibrous CT
2. Ganglion - knot-like sweeping in a nerve where neuron cell bodies are concentrated

Question 5

What are the 2 divisions of the PNS?

Answer 5

1. Sensory (afferent) Division - carries signals from receptors to CNS
2. Motor (efferent) Division - carries signals from CNS to effectors (glands and muscles)

Question 6

What are the subdivisions of the Sensory Division of the PNS and what do they do?

Answer 6

1. Somatic sensory division - carry signals from receptors in skin, muscles, bones, and joints
2. Visceral sensory division - carry signals to guts, organs, etc.

Question 7

What are the two subdivisions fo the Motor Division

Answer 7

1. Somatic motor division - sends signals to skeletal muscles for contraction and reflexes (voluntary responses)
2. Visceral motor division - signals to glands, cardiac and smooth muscles (involuntary responses)

Question 8

The visceral motor division of the PNS is further divided into 2 more subparts. What are those and what do they do?

Answer 8

1. Sympathetic division - action (accelerates heart rate and respirations, inhibits digestive and urinary systems)
2. Parasympathetic division - calming (slows heart rate and breathing, stimulates digestive and urinary systems)

Question 9

What are 3 universal properties of neurons?

Answer 9

1. Excitability/irritability - response to environmental changes/stimuli
2. Conductivity - response to stimuli by producing, quickly conducted to other cells at distant locations
3. Secretion - electives signal reaches the end of nerve fiber, the cell secretes a chemical neurotransmitter which influences the next cell

Question 10

How long to nerve cells live? How often do they reproduce?

Answer 10

Live a very long time
Don’t make new nerve cells after maturity
Non-mitotic (mostly)

Question 11

What are the three functional classes of neurons?

Answer 11

1. Sensory (afferent) neurons - detect stimuli and transmit information TOWARD the CNS (light, heat, pressure, chemicals, etc)
2. Interneurons - entirely within the CNS, connect motor and sensory pathways, receive signals from many neurons and carry out integrative functions, ~90% of all neurons
3. Motor (efferent) neurons - send signals AWAY from CNS (to muscle and gland cells, aka the effectors)

Question 12

What is the job of the neurosoma in the structure of a neuron? What’s another name for it?

Answer 12

Aka cell body or soma
Control center
Single, centrally located nucleus, typical organelles (lots of mitochondria, no centrioles cause no mitosis)

Question 13

What are the axoplasm and axolemma?

Answer 13

Axoplasm - cytoplasm of axon

Axolemma - plasma membrane of axon

Question 14

What are dendrites?

Answer 14

Branches from neurosoma, receive signals

Question 15

What is the effect of a neuron having more dendrites?

Answer 15

It can receive more information, more precise pathways for reception and processing

Question 16

What is an axon? What does it do? What are some key features of an axon?

Answer 16

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)

Question 17

What are the four different classes of neurons?

Answer 17

1. Multipolar (one axon, multiple dendrites)
2. Bipolar (one axon, one dendrite)
3. Unipolar (single process)
4. Anaxonic (no axon, many dendrites)

Question 18

What is a multipolar neuron and what does it do?

Answer 18

One axon, multiple dendrites
Most common (most neurons in CNS)
Motor neurons (muscles/glands)

Question 19

What is a bipolar neuron and what does it do?

Answer 19

One axon, one dendrite

Sensory (olfactory cells, retina, inner ear [rare])

Question 20

What is a unipolar neuron and what does it do?

Answer 20

Single process leading away from neurosoma (branches like a T)
Sensory cells from skin and organs to spinal cord

Question 21

What is an anaxonic neuron and what does it do?

Answer 21

Many dendrites but no axon

Retina, brain, and adrenal gland

Question 22

Do you have more neurons or glial cells? Why/how?

Answer 22

Glial cells (by at least 10 to 1)
They're capable of mitosis

Question 23

What are the (4) functions of glial cells?

Answer 23

1. Protect neurons and help them function
2. Bind neurons together and form framework for nervous tissue
3. Guide migrating neurons to their destinations (in vitro)
4. Insulation - prevents neurons from touching each other, gives precision to conduction pathways

Question 24

What types of neuroglia can be found in the CNS?

Answer 24

1. Oligodendrocytes
2. Ependymal cells
3. Microglia (least abundant)
4. Astrocytes (most abundant)

Question 25

What are oligodendrocytes and where are they found?

Answer 25

Neuroglia cells of CNS Large, bulbous cells Form myelin sheath - speeds up signal conduction Arm-like processes wrap around nerve fibers

Question 26

What are ependymal cells and where are they found?

Answer 26

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)

Question 27

What are microglia cells and where are they found?

Answer 27

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)

Question 28

What are astrocytes and where are they found?

Answer 28

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

Question 29

What types of neuroglia can be found in the PNS?

Answer 29

1. Schwann cells | 2. Satellite cells

Question 30

What are Schwann cells and where are they found?

Answer 30

Neuroglia cells of PNS Wrap around nerve fibers to form myelin sheath (provides insulation, increases speed of impulse) Assist in regeneration of damaged fibers

Question 31

What are Satellite cells and where are they found?

Answer 31

Neuroglia cells of PNS Surround the neurosomas in ganglia Provide electrical insulation Regular the chemical environment

Question 32

What is the job of the myelin sheath?

Answer 32

Insulates the nerve fiber

Question 33

What is the myelin sheath made of?

Answer 33

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

Question 34

What is myelination? When does it happen?

Answer 34

Production of myelin sheath Begins during fetal development Proceeds rapidly during infancy

Question 35

What is the neurilemma?

Answer 35

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

Question 36

Describe the myelin sheath of the PNS

Answer 36

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

Question 37

Describe the myelin sheath of the CNS

Answer 37

Oligodendrocytes myelinated several nerve fibers Cannot migrate around any one of them like Schwann cells Myelination spirals inward No neurilemma or endoneurium

Question 38

The axon hillock has two important "zones" or "segments." What are they and what do they do?

Answer 38

1. Trigger Zone - important in initiating a nerve signal | 2. Initial segment - short section of nerve fiber between axon hillock and first glial cell

Question 39

Why is the myelin sheath segmented? What are the segments called?

Answer 39

To allow for signal transduction - signal "jumps" from node to node 1. Myelin sheath caps (aka nodes of Ranvier) - gap between segments 2. Internodes - myelin-covered segments from one gap to the next

Question 40

Describe the use of ion channels in a nerve signal

Answer 40

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

Question 41

What is the job of myelin in reference to voltage gated ion channels?

Answer 41

It speeds up conduction Minimized leakage of Na+ out of cell Lower attraction between ions inside/outside cell

Question 42

Do unmyelinateud axons exist? If yes, where?

Answer 42

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

Question 43

What determines the speed at which a nerve signal travels along the surface of a nerve fiber?

Answer 43

1. Diameter of fiber (larger fibers conduct more rapidly) | 2. Presence or absence of myelin (speeds signal conduction)

Question 44

Where do you find slow conduction speeds? Fast?

Answer 44

Slow - gastrointestinal tract Fast - Skeletal muscles (improves balance and coordinated body movement)