15CHAPTER 12: NERVOUS TISSUE

Question 1

Nervous system uses electrical and chemical means to send messages from cell to cell: what are the three basic steps?`

Answer 1

1. Sense organs receive information and send info to spinal cord and brain
2. Brain and spinal cord determine responses
3. Brain and spinal cord issue commands to glands and muscles

Question 2

What are the two major anatomical subdivisions of Nervous System?

Answer 2

Central nervous system (CNS)

Peripheral nervous system (PNS)

Question 3

What is the Central nervous system (CNS)?

Answer 3

brain and spinal cord enclosed in bony coverings

Question 4

What does the Peripheral nervous system (PNS) consist of?

Answer 4

Nerves and ganglion

Question 5

What is a nerve?

Answer 5

bundle of axons (nerve fibers) wrapped in connective tissue

Question 6

What is a ganglion?

Answer 6

swelling in a nerve where cell bodies of neurons are concentrated

Question 7

What are the functional divisions of PNS?

Answer 7

Sensory (afferent = toward) divisions (receptors to CNS) and
Motor (efferent = away) division (CNS to effectors)

Question 8

What are the universal properties of nerve cells (neurons)?

Answer 8

• Excitability
• Conductivity
• Secretion

Question 9

What is excitability?

Answer 9

The response to changes in the body and external environment called stimuli, like muscle

Question 10

What does conductivity produce?

Answer 10

traveling electrical signals, like muscle

Question 11

What does nerve cells secrete?

Answer 11

secrete chemical neurotransmitter (NTr), unlike muscle

Question 12

How many types of neuroglia are there and where can you find them?

Answer 12

6 kinds: 4 in the CNS and 2 in the PNS

Question 13

What are the 4 types of neuroglia of the CNS?

Answer 13

1. Oligodendrocytes
2. Ependymal Cells
3. Microglia
4. Astrocytes

Question 14

What is the function of oligodendroctyes?

Answer 14

Makes myelin sheath in CNS

Question 15

What is the function of ependymal cells and where are they found?

Answer 15

• Secrete and circulate cerebrospinal fluid

- Line internal cavities of brain and spinal cord

Question 16

What are microglia composed of?

Answer 16

Small macrophages, phagocytize pathogens, dead nervous tissue

Question 17

What are the neuroglia of the PNS?

Answer 17

1. Schwann cells

2. Satellite cells

Question 18

Where do you find satellite cells?

Answer 18

Surround somas of neurons in ganglia (collection of somas) of the PNS

Question 19

What do schwann cells do?

Answer 19

Make myelin sheath around nerve fibers (axons) in PNS

Question 20

What is the electrical insulation around axons?

Answer 20

Myelin

Question 21

What is myelin composed of?

Answer 21

80% lipid, 20% protein

Question 22

What is the function of astrocytes?

Answer 22

• Supportive framework
• Secrete nerve growth factors
• Regulate chemical composition of ECF i.e. absorb neurotransmitters and K+ ions

Question 23

What does conduction speed of nerve fibers depends on?

Answer 23

1. Diameter of the nerve fiber (axon):

2. Presence or absence of myelin: faster conduction with myelin

Question 24

What axons can regenerate?

Answer 24

Only PNS axons

Question 25

What is denervation atrophy?

Answer 25

shrinkage due to lack of nerve supply

Question 26

What is the Resting membrane potential (RMP)

Answer 26

– The charge difference across the plasma membrane
– Around -70 mV in resting neuron
– Changes in RMP allow signal conduction

Question 27

What are local potentials?

Answer 27

A short range change in the RMP; may or may not reach the trigger zone, often restricted to dendrite and soma, signal can fade, excitatory or inhibitory

Question 28

What are the 7 steps of an Action Potential?

Answer 28

1. A local potential arrives at the trigger zone from the cell soma.
2. Membrane potential depolarizes, and reaches threshold (-55 mV)
3. Voltage-regulated Na+ channels open and Na+ enters; potential rises quickly.
4. Na+ channels start to close
5. K+ channels open and K+ leaves —–This repolarizes and then
6. hyperpolarizes the membrane potential.
7. Pumps and diffusion return Na+/K+ balance.

Question 29

What is the refractory period?

Answer 29

Period of resistance to stimulation

Question 30

What are the 2 types of refractory periods?

Answer 30

Absolute refractory period

Relative refractory period

Question 31

What is a synapse?

Answer 31

A junction between two neurons or a neuron and a muscle cell

Question 32

What do presynaptic neuron (axons) release?

Answer 32

A neurotransmitter (chemical signal) which crossed the synaptic cleft and stimulates the postsynaptic neuron

Question 33

What are the steps of synaptic transmission?

Answer 33

1. AP arrives at the synaptic knob of the presynaptic neuron.
2. Calcium enters the presynaptic neuron
3. Calcium triggers exocytosis of neurotransmitter
4. Neurotransmitter diffuses across the synaptic cleft and binds to a receptor on the postsynaptic neuron and alters physiology of that cell.

Question 34

What are the 4 major categories of neurotransmitters based on chemical composition?

Answer 34

Acetylcholine (ACh), Monoamines, Amino acids and Neuropeptides.

Question 35

What are the 3 types of synapses with different modes of actions?

Answer 35

Excitatory cholinergic synapse
Inhibitory GABA-ergic (gamma aminobutyric acid) synapse
Excitatory adrenergic synapse

Question 36

What are considered neuromodulators?

Answer 36

Hormones, neuropeptides, other messengers that modify synaptic transmission

Question 37

What doe neuromodulators do?

Answer 37

• Raise or lower number of receptors in post synaptic neuron membrane
• Alter rate of neurotransmitter release, synthesis, or breakdown

Question 38

What is neural integration?

Answer 38

ability of our neurons to process info, store and recall it, and make decisions