Chapter 12 - Nervous Tissue

Question 1

Nervous system is responsible for all our __, ___ and __.

Answer 1

behaviors

memories

movements

Question 2

neurology

Answer 2

branch of medical science that deals with normal functioning & disorders of the NS

Question 3

Major structures of the NS

Answer 3

12 pairs of cranial nerves

31 pairs of spinal nerves

**ganglia **outside CNS - small masses of nervous tissue, mostly neuronal cell bodies

**Enteric plexuses - **help regulate digestive system - neuron networks in walls of GI tract organs

**sensory receptors **- structure of NS that monitors change in internal/external environment

Question 4

Functions of NS (3)

Answer 4

**1) sensory **- afferent

**2) integrative - **interneurons

**3) motor - **efferent

Question 5

NS divisions (2)

Answer 5

CNS - brain & spinal cord

**PNS - **cranial & spinal nerves, connects CNS to muscles/glands/sensory receptors

Question 6

Neurons

Answer 6

functional unit of nervous system

have capacity to produce action potentials - **electrical excitability **

cell body (soma) - contains organelles

**Nissl bodies - **clusters of rough ER

**neurofibrils - **cell shape & support

**microtubules - **assist in moving materials

**dendrites & axons - **processes

**lipofuscin - **yellow/brown pigment granules in cytoplasm

Question 7

Location for most protein synthesis in Neuron

Answer 7

cell body

Question 8

Axonal transport

1) slow axonal flow
2) **fast **axonal flow

Answer 8

1) movement in one direction -away from cell body
2) either direction - use or recycling

Question 9

Structural classification of neurons

Answer 9

1) multipolar
2) bipolar
3) unipolar

Question 10

Functional classification of Neurons

Answer 10

1) sensory (afferent)
2) motor (efferent)
3) interneurons (association)

Question 11

Neuroglia

Answer 11

non-neuronal cells

1/2 the volume of CNS

Of CNS: astrocytes, oligodendrocytes, microglia, ependymal

Of PNS: Schwann, satellite

Question 12

Neuroglia of CNS

1) astrocytes

2) oligodendrocytes

3) microglia

**4) ependymal **

Answer 12

1) support, blood-brain barrier, homeostasis,
2) form **myelin sheath **around axons
3) phagocytes
4) produce cerebrospinal fluid

Question 13

Neuroglia of PNS

1) schwann cells

**2) satellite **

Answer 13

1) form **myelin sheath **around ONE axon
2) structural support & regulate exchange of materials b/w soma & interstitial fluid

Question 14

Schwann cell cytoplasm forms outer layer & inner layer is…

Answer 14

**myelin sheath **(100+ layers of schwann cell membrane)

Question 15

Subdivisions of PNS

Answer 15

**1) Somatic (voluntary) - **cutaneous &special sensory receptors → CNS

motor neurons → skeletal muscle

**2) Autonomic (involuntary) **- sensory- visceral organs → CNS

motor to smooth+cardiac muscle& glands

**A. Sympathetic - **↑ heart rate

**B. Parasympathetic **- ↓ heart rate

**3) Enteric - **involuntary sensory & motor control GI tract

function independently of ANS & CNS

Question 16

Neurons are electrically excitable due to the?

Answer 16

voltage difference across their membrane

Question 17

Neurons communicate with (2) types of electric signals

Answer 17

1) action potentials - long distance
2) graded potentials - short distance

Question 18

Resting membrane potential

What is potential energy difference at rest?

Answer 18

When neuron is at rest,

negativeions alonginsideof cell membrane &positive ions along outside

-70mV

Question 19

At rest, Neuron is said to be _____

Answer 19

polarized

Question 20

Resting potential exists because? (3)

Answer 20

1) ion concentration differs from inside to outside

**- **ECF has lots of Na+ & Cl-

cytosol has lots of K+

**2) inability of most anions to leave cell - **membrane permeability differs for Na+ & K+

3) Electrogenic nature of Na+/K+ ATPase

• inward flow of Na+ cant keep up with outward flow of K+ ( Na+ pumped out as fast as it leaks in)

this removes more positive than it brings in

Question 21

Graded potential

occur mainly in?

Answer 21

dendrites & neuronal cell bodies

**small **deviation from resting potential of -70mV

Question 22

hyperpolarizing vs depolarizing

Answer 22

**hyperpolarizing - **membrane becomes more negative

**depolarizing - **membrane become more positive

Question 23

Graded potential

The signals are graded, meaning they vary in… and are? (2)

Answer 23

1) **amplitude (size), **
depending on the strength of the stimulus

2) localized

Question 24

**Action Potential (impulse) **

Answer 24

a sequence of rapidly occurring events that decrease and eventually reverse the membrane potential (depolarization) and then restore it to resting state (repolarization)

Question 25

All-or-none principle of Action Potentials

Answer 25

if stimulus reaches **threshold, **the action potential produced is always the same

stronger stimulus does NOT produce large impulse

Question 26

(3) phases of an action potential

Answer 26

1) depolarizing phase
2) repolarizing phase
3) hyperpolarizing phase

Question 27

1) depolarizing phase

Answer 27

At rest: inactivation Na+ gate = **open, **activation gate = closed

chemical/mechanical stimulus → graded potential reaches threshold (-55mV) → Na+ channels open → inactivation gate **closes → **membrane potential = +30mV

Question 28

2) repolarizing phase

Answer 28

when threshold potential reached (-55mV) → K+ channels open (much slower than Na+ channels) → once K+ channels are **open, **Na+ channels are closed again → K+ outflow returns membrane potential to -70mV

Question 29

3) hyperpolarizing phase

Answer 29

if enough K+ leaves cell, membrane potential reaches -90mV

K+ channels close & membrane potential returns to resting potential (-70mV)

Question 30

Refractory period

Answer 30

Period of time during which neuron can not generate another action potential

Question 31

**Absolute refractory period **vs Relative refractory period

Answer 31

**absolute - (depolarzing + repolarizing phase) **

even very strong stimulus can not begin another AP

inactivated Na+ channels must return to resting state

**refractory - **(hyperpolarizing phase) **

A suprathreshold stimulus will be able to start AP

K+ channels still open but Na+ channels are closed

Question 32

**Conduction - **(2) types

1) continuous
2) saltatory

Answer 32

1) **unmyelinated + muscle fibers - **step-by-step depolarization of each portion of the length of the axolemma (axon plasma membrane)
2) **myelinated axons - **depolarization only at nodes of Ranvier (gaps in myelin sheath) where there is a high density of voltage-gated ion channels

current carried by ions flows through ECF from node to node

Question 33

Factors that affect speed of propagation (3)

Answer 33

**1) amount of myelination - **faster along myelinated axon

**2) axon diameter - **larger = faster

**3) temperature - **higher temp = faster

Question 34

The propagation speed of a nerve impulse is not related to __ __

Answer 34

stimulus strength.

Question 35

**Fiber types (3) **

**- **diameterm, absolute refractory period (ARP), myelinated/unmyelinated, sensory/motor

Answer 35

**A fibers - **largest, longest ARP

• myelinated somatic sensory & motor to skeletal muscle

**B fibers - **medium, faster ARP

• **myelinated **visceral sensory & autonomic preganglionic (CNS → ANS relay station)

**C fibers - **smallest, fastest ARP

• **unmyelinated **sensory & autonomic motor

Question 36

(2) types of **synapses **

Answer 36

1) electrical
2) chemical

Question 37

Electrical Synapse

Answer 37

ionic current spreads to next cell through gap junctions

faster, two-way transmission & capable of synchronizing groups of neurons

AP conduct directly between plasma membrane of adjacent neuron through gap junctions)

Question 38

Chemical synapse

Answer 38

one-way information transfer from presynaptic to postsynaptic neuron

plasma membranes do not touch, seperated by **synaptic cleft **

Question 39

1) axodendritic
2) axosomatic

3) axoaxonic

Answer 39

1) from axon to dendrite
2) from axon to **cell body **
3) from axon to axon

Question 40

Signal transmission at chemical synapse

Answer 40

Action potential reaches end bulb and voltage-gated Ca2+ channels open → Ca2+ inward flow triggers release of neurotransmitters → cross synaptic cleft & bind to ligand-gated receptors → channels open on postsynaptic neuron & ions flow across

Question 41

Both ____________ and ____________ neurotransmitters are present in the CNS and PNS

the same ____________ may be excitatory in some
locations and inhibitory in others.

Answer 41

inhibitory & excitatory

neurotransmitter

Question 42

Important neurotransmitters include? (8)

Answer 42

acetylcholine, glutamate, aspartate, gamma aminobutyric acid, glycine, norepinephrine, epinephrine, and

dopamine.

Question 43

Neural circuits

involved in many important activities such as? (3)

Answer 43

functional groups of neurons that process specific types of information

breathing, short-term memory. waking up

Question 44

Types of neural circuits (5)

Answer 44

1) simple series
2) diverging
3) converging
4) reverberating
5) parallel after-discharge