Nervous Tissue Flashcards
1
Q
The nervous tissue consists of which type of cells?
A
Neurons and neuroglia.
2
Q
What are neurons commonly called?
A
Nerve cells
3
Q
Every neurons have 3 essential components, which are?
A
Cell body(Perikaryon or Soma), axon and dendrites.
4
Q
Neurons can’t undergo cell division hence is termed as?
A
They are non-mitotic or amitotic.
5
Q
What does neurons need continuously to survive?
A
Oxygen and nutrients.
6
Q
What are neurons?
A
- Neurons are information messengers. They transmit information between different areas of the brain and between the brain and the rest of the nervous system.
- They are the structural and functional unit of the nervous system.
- They conduct nerve impulses from one part of body to another.
7
Q
What other characteristics does neurons have?
A
- Excitability/Irritability.
- Conductivity.
- They have a high metabolic rate.
- They have extreme longevity.
- Typically non-mitotic.
8
Q
Which area of neurons conduct impulses?
A
Axon
9
Q
What is excitability/irritability?
A
It is the ability to initiate nerve impulses in response to a stimuli.
10
Q
What is conductivity?
A
The ability to transmit an impulse.
11
Q
What is a stimulus?
A
A stimulus is any change in the environment that is strong enough to initiate an action potential.
12
Q
What is an action potential(Nerve impulse)?
A
An action potential(nerve impulse) is an electrical signal that travels along the surface of the membrane of a neuron.
13
Q
What forms the grey matter in the nervous system?
A
Cell bodies
14
Q
Where are grey matter located in the nervous system?
A
They are found at the periphery of the brain, in the center of the spinal cord.
15
Q
What is a cell body?
A
- “soma” or “perikaryon”
- neuron’s control center
- responsible for receiving, integrating and sending nerve impulses
16
Q
A cell body of a neuron consist of what structures?
A
It consist of plasma membrane, cytoplasm, nucleus with prominent nucleolus, Nissl bodies(containing Rough Endoplasmic Reticulum) and free ribosomes.
17
Q
What are group of cell bodies called in the CNS?
A
Nuclei
18
Q
What is Ganglia?
A
Clusters of neuron cell bodies located outside the CNS.
19
Q
What is an axon (nerve fiber) ?
A
It is a general term for any neuronal process(extension) that emerges from the cell body of a neuron.
20
Q
What forms the white matter of the nervous system?
A
Axons and dendrites
21
Q
Where is white matter located in the nervous system?
A
White matter is found in the deeper tissues of the brain in the sub-cortical.
22
Q
What is the function of an axon?
A
An axon propagates nerve impulses away from the cell body towards another neuron, a muscle fiber or a gland cell
23
Q
Where do protein synthesis occur?
A
Protein synthesis occurs in cellular structures called ribosomes which are right outside the nucleus.
24
Q
What is a chromatophilic substance?
A
- It consist of free and bound ribosomes producing proteins, also called Nissl bodies.
Dendrites, cell bodies, and chromatophilic substance account for the gray color of gray matter.
25
What is part of the CNS?
Brain and the spinal cord.
26
What structures are part of the PNS?
1) Cranial nerves(Nerves that extends from the brain)
2) Spinal nerves(Nerves that extends from the spinal cord)
3) Ganglia (Clusters of neuron cell bodies(somas) located outside the CNS)
Basically all nervous tissue outside the CNS.
27
What is the cone-shaped elevation part that extends from the cell body of a neuron called?
Axon hillock.
28
What does the term Anaxonic means?
That the neuron has only one axon.
29
What does the cytoskeleton of a neuron contain?
Neurofibrils and Microtubules.
30
What are neurofibrils?
Neurofibrils are composed of bundles of intermediate filaments that provide the cell shape and support.
31
What are Microtubules?
They are small tubes formed by thirteen filamentous strands. Each filament is composed of a protein chain called tubulin.
32
What is the purpose of microtubules?
Microtubules in a neuron are used to transport substances to different parts of the cell.
33
How are dendrites differentiated with axons?
Dendrites are shorter, smaller processes(extensions). They branch off the cell body of a neuron and cluster close to it.
34
What are the functions of dendrites?
1) They act as the receiving or input portion of a neuron that is it receives signals from other neurons.
2) Dendrites convey incoming impulses towards the cell body.
35
How are bundles of axon in the CNS called?
Tracts or Commissure
36
Why can't protein synthesis occur in an axon?
Because axons doesn't have Rough Endoplasmic Reticulum.
37
How are bundles of axons in the PNS called?
Nerves
38
How is the cytoplasm of axon called?
Axoplasm
39
How is the plasma membrane of an axon called?
Axolemma
40
Along the length of an axon there may have some particular side branches that comes out at a right angle on the axon. What is it called?
Axon collaterals.
41
At their end, axons and axon collaterals further branches profusely into many fine processes. What are they called?
Axon terminals(Telodendria)
42
What are the bulb-shaped structures at the tips of some axon terminals(Telodendria) called?
Synaptic knobs or terminal boutons.
43
What are the functional divisions of the nervous system?
Sensory afferent division and Motor efferent division.
44
How does the sensory afferent division works?
Information(Input) received by the sensory receptors is passed to a sensory(afferent) neuron by an appropriate stimulus by which an action potential(impulse) is formed in its axon which is then conveyed into the CNS through cranial or spinal nerves.
45
What is the function of a receptor?
A receptor detects external or internal changes and send the information to the CNS in the form of impulses by the way of the afferent neurons.
46
How does the motor efferent division works?
Motor(efferent) neurons transmit motor impulses(output) from the CNS to effectors(Muscles and Glands) in the periphery(PNS) through cranial or spinal nerves.
47
Which neurons lies between motor and sensory neurons and consist of 99% of neurons in the body?
Interneurons
48
The sensory(Afferent) division can be further divided into 3 other sensory system. What are they?
Somatic, Special and Visceral sensory system.
49
Somatic sensory system receives sensory information from which organs or structures?
From skin, fascia, joints and skeletal muscles
50
What kind of senses are involved in the general somatic sensory system?
Touch, Pain, Pressure, Vibration, Temperature and Proprioception.
51
Special sensory system receives sensory information from what?
Taste, Vision, Hearing, Balance and Smell.
52
What is the function of visceral sensory system?
- Monitor internal organs
| - Nerve impulses are transmitted from blood vessels and viscera to the CNS.
53
The visceral senses primarily include:
Temperature and Stretch of the organ wall.
54
The motor(efferent) division can be further divided into 2 other motor system. What are they?
Somatic Nervous System(SNS) and Autonomic Nervous System(ANS).
55
What is the Somatic Nervous System(SNS)?
- Part of Motor Nervous System
- It conducts nerve impulses from the CNS to the skeletal muscles causing them to contract.
- It is called voluntary nervous system (contraction under conscious control).
56
What is the Autonomic Nervous System?
- Part of Motor Nervous System
- Innervates internal organs.
- Regulates smooth muscle, cardiac muscle, and glands without our control. (involuntary nervous system)
- Divided into sympathetic and parasympathetic.
57
What does structural classification of neurons means?
The number of processes extending from the cell body of a neuron.
58
Define Unipolar neuron?
Unipolar neuron has a single short process that extends from the cell body and branches into two or more processes that extends in opposite directions.(Mostly sensory neurons).
59
What is the peripheral process of a unipolar neuron?(Process = Extension)
- It is the process that extends peripherally and is associated with sensory reception.
- Region from the dendrite to the cell body.
60
Define Bipolar neuron?
Bipolar neurons has only two processes that extends in opposite directions of the cell body. One process called dendrite and another process is called axon.(Bipolar neurons are rare and normally found in the retina of the eye and olfactory mucosa)
61
Define multipolar neurons?
- Multipolar neurons are defined as having 3 or more processes that extend out from the cell body.
- Most common. Many dendrites and single axon extending from cell body.
- e.g motor neurons.
62
The principal region of the neuron for receiving information is the __________.
Dendrite
63
Information is carried away from the neuron cell body by the __________.
Axon
64
The normal site for initiation of a neuronal action potential is the ______ ___________.
Axon Hillock
65
Glial cells(Neuroglia) provide protection and support for __________.
Neurons
66
Which part of the neuron is involved in sending an impulse to the synapse area or to an effector?
Axon
67
Impulses that are going to the CNS are called ________ and impulses going away from the CNS are called ________.
Afferent ; Efferent
68
Which functional division of the nervous system would be responsible for the physiological changes seen during exercise(e.g increased heart rate and sweating)?
The ANS which is part of the motor(efferent) division.
69
If a thermoreceptor is sensitive to temperature sensations, what would a chemoreceptor be sensitive to?
Molecules
70
What is the central process of a unipolar neuron?
It is the process that extends from the cell body into the CNS.
71
The CNS and PNS performs what three general functions?
1) Monitor changes and collect information-Sensory
2) Processing and evaluating information-Integrative
3) Responding to Information-Motor
72
What is a sensory neuron?
- Afferent neuron, transmit nerve impulses from sensory receptors to CNS.
- Mostly Unipolar.
- Housed in posterior dorsal root ganglia.
73
What is a motor neuron?
- Efferent neuron(causing effect) transmit nerve impulses from CNS to muscles (causing contraction) or glands.
- Multipolar
74
What are Interneurons and its function?
They are relay neurons that connect two brain regions. (They are Multipolar)
Func :-They carry out the integrative process of the nervous system.
-Facilitates communication between sensory and motor neurons.
Note : It is located within the CNS.
75
What is another term for Neuroglia?
Glia cells
76
What is a Glia cell?
-They are cells that do not transmit nerve impulses, rather they physically protect and nourish neurons.
-They are organized, supporting framework for all nervous tissue.
-They are smaller than neurons.(Also more numerous than neurons)
-They have the ability to multiply and divide(undergo mitosis) in the mature nervous system.
Note: In cases of injury or disease, Neuroglia multiply to fill in the spaces formerly occupied by neurons.
77
How much volume does the glia cells account for in the nervous system?
For about half of the volume.
78
Name the Glia cells found in the CNS.
- Astrocyte
- Ependymal cell
- Microglial cell
- Oligodendrocyte
79
Name the Glia cells found in the PNS.
- Satellite cells
| - Neurolemmocytes
80
How can neuroglia be distinguished from neurons?
By their smaller size and their darker-staining nuclei.
81
What are the characteristics of an astrocyte?
- They are star-shaped cells.
| - They have many radiating processes.
82
Which type of Glia cells are the most numerous in the CNS?
Astrocytes(It constitutes over 90% of the tissue in some areas of the brain)
83
Give two functions of an Astrocyte.
- It helps form the Blood Brain Barrier(BBB).
| - Regulate tissue composition.
84
What is the BBB and its function in CNS?
It is a living barrier formed from astrocytes located between capillaries and neurons.
It strictly controls substances entering the nervous tissue in the brain from the bloodstream.
85
What are the characteristics of Microglia cells?
- They are small and ovoid cells that give off numerous spine-like projections.
- They are phagocytic cells that is they are phagocytes.(Derived from monocytes)
86
Which type of glia cells have the lowest % in the CNS?
Microglia cells
87
Give two functions of a Microglia cell.
- It removes neuronal debris.(Dead brain cells)
| - It phagocytizes microorganisms in response to infection.
88
What are the characteristics of Ependymal cells?
- They are cuboidal to columnar cells.
- They are arranged in a single layer.
- They possess microvilli and cilia.
89
Give two functions of Ependymal cells.
- It helps form the choroid plexus which produces cerebrospinal fluid(CSF) via ependymal cells that line the ventricles of the brain (choroid plexus also forms the blood-CSF Barrier).
- The beating of their cilia helps to circulate the CSF that fills the central cavities of the brain
90
What are the characteristics of Oligodendrocytes?
They resemble astrocytes but are smaller and contain fewer processes which are flat.
91
Give two functions of Oligodendrocytes?
- Myelinates and insulates CNS axons.
| - Increases the transmission rate of nerve impulses.
92
Give two functions of Satellite cells.
Protects(envelope cell bodies) and regulates nutrients for cell bodies in ganglia.
Note : Satellite cells are flattened cells.
93
Give two functions of Neurolemmocyte(Schwann cells)?
- Myelinates and insulates PNS axons.
| - Increases the transmission rate of nerve impulses.
94
What is the process of myelination?
It is a process by which part of an axon is wrapped with a myelin sheath forming a white glossy protective fatty coating also called Myelin.
95
What are the functions of the myelin sheath?
It supports, protects and insulate an axon.
96
What is meant by "integration" and does it primarily occur in the CNS or the PNS?
Integration involves processing and interpreting sensory information and making a decision about motor output. Integration occurs primarily in the CNS.
97
What do you understand when it is said that the nervous system monitor changes and collect information?
It uses its millions of sensory receptors to monitor changes occurring both inside and outside the body; these changes are called stimuli, and the gathered information is called sensory input which is then going to be sent to the CNS.
98
The nervous system responds to information after the integration process. What does it do?
If required it then effects a response by activating muscles or glands (effectors) via motor output.
99
What kind of conduction occurs in Myelinated Axons?
Saltatory conduction
100
Due to continuous conduction, Unmyelinated Axons conduct nerve impulses from which stimuli?
Pain stimuli
101
What kind of conduction occurs in Unmyelinated Axons?
Continuous conduction
102
What is Saltatory conduction?
It is a conduction where nerve impulses "jump" from neurofibril node to neurofibril node.
Note: Saltatory conduction requires less energy(ATP) than does an Unmyelinated axon.
103
Between a Myelinated and Unmyelinated axon which transmit nerve impulses faster?
A myelinated axon produces a faster nerve impulse.
104
What is continuous conduction?
It is a conduction where nerve impulses must travel the entire length of an axon.
105
What conditions are required for regeneration of PNS axon to occur?
- The cell body remains intact.
- The Schwann cells(Neurolemmocytes) that produces myelin should remain functional.
- No impendiment of scar tissue formation.
106
What are the 3 factors that is going to affect PNS regeneration of an axon when it begins to regenerate?
- Amount of damage
- Neurolemmocyte secretion of nerve growth factors.
- Distance between injured site and the effector organ.
107
What is the role of neurolemma in regeneration?
The neurolemma provides a regeneration tube that guides regrowth of a severed axon.
108
What is chromatolysis and how is it associated with regeneration of axons?
It is the dissolution of the Nissl bodies in the cell body of a neuron.
Nissl substance contain Rough Endoplasmic Reticulum and Poly Ribosomes which are necessary in order to meet the demand needed for protein synthesis for regrowth of a severed axon.
109
What is Wallerian Degeneration?
It is the degeneration of the distal portion of an axon and its myelin sheath.
110
What happens to a PNS axon after it has been cut?(Process of Regeneration)
1) Proximal end seals and swells.
2) Distal end degenerates(Wallerian Degeneration).
3) Surviving Schwann cells engulf the myelin fragments. (From axon distal to injury)
4) Macrophages gets rid of the debris.
5) Neurolemmocytes form regeneration tube(with endoneurium).
6) Axon regenerates, remyelinates. (New myelin sheath produced)
7) Axon reestablishes contact with effector.
111
What is the function of the regeneration tube in repair of neurons?
The tube provides the medium needed to guide the growth of a severed axon across the injured area into the distal area previously occupied by the original axon.
112
What may deter growth of new axons after formation of a regeneration tube?
- Too large gap at site of injury and effector organ.
| - Collagen fibers that may have filled the gap.
113
What is a nerve?
A nerve is a cable-like bundle of parallel axons.
114
Nerves are considered organs of which nervous system?
PNS
115
What are the 3 layers of protective connective tissue wrappings?
- Endoneurium(Innermost layer)
- Perineurium(Middle layer)
- Epineurium(Outermost layer)
116
Define the endoneurium layer?
It is a delicate layer of loose connective tissue that wraps around each individual nerve fiber(axon).
Note: It also wraps around the fiber's associated Schwann cells.
117
Define the perineurium layer?
It is a cellular and fibrous connective tissue layer that wraps groups of axons into fascicles.
118
Define the epineurium layer?
- It is a superficial connective tissue covering.
- This thick layer of dense irregular fibrous connective tissue encloses the the entire nerve providing shape and support.
119
What are mixed nerves?
They are nerves that contain both sensory and motor fibers and transmit impulses both to and from the CNS.
120
What is a synapse?
It is a functional junction or point of close contact where information is transferred between two neurons or between a neuron and an effector cell.
121
What is a presynaptic neuron?
It is a neuron that transmit nerve impulses towards a synapse.
122
What is a postsynaptic neuron?
It is a neuron that conduct impulses away from the synapse.
123
Name the 3 types of synapses based on contact?
Axodendritic
Axosomatic
Axoaxonic
124
Define the Axodendritic synapse?
It is a synapse between the axon endings of one neuron and the dendrites of other neurons.
125
Define the Axosomatic synapse?
It is a synapse between the axon endings of one neuron and the cell body(Soma) of another neuron.
126
Define the Axoaxonic synapse?
It is a synapse between the axon endings of one neuron and the axon endings of another neuron.
127
What is the purpose of a synapse?
They are essential for the transmission of nerve impulses from one neuron to another.
128
In the human body where do electrical synapses occur?
Visceral smooth muscle
Cardiac muscle
A developing embryo
Hippocampus
129
For an electrical synapse, what kind of junction are there?
Gap junction
130
What is a gap junction?
It is a junction that acts as a tunnel allowing ions and small molecules to flow directly from one neuron to the next.
131
Give 2 advantages of electrical synapse?
Faster communication- The action potential passes directly from the presynaptic cell to the postsynaptic cell.
Synchronization- Electrical synapses can synchronize(coordinate) the activity of a group of neurons or muscle fibers.
132
Which is faster between electrical and chemical synapse at transmitting information?
Electrical synapse is faster.
133
Describe how information is transmitted in an electrical synapse?
As ions flow from one cell to the next through the connexons, the action potential spreads from cell to cell.
134
How is a chemical synapse different from an electrical synapse?
A chemical synapse involves the use of neurotransmitters whereas for an electrical synapse it involves the use of ions.
135
What is a synaptic cleft?
It is a narrow gap filled with interstitial fluid at a chemical synapse and across which a neurotransmitter diffuses to affect the postsynaptic cell.
136
A typical chemical synapse is made up of two parts. What are they?
Presynaptic membrane - knoblike axon terminal
Postsynaptic membrane - neurotransmitter receptor region(Axon, dentrite or cell body)
137
What does presynaptic membrane(neuron) do?
It releases a signalling molecule called a neurotransmitter, such as acetycholine(ACh).
Note : Other neurotransmitters that neurons use are noradrenaline and gamma aminobutyric acid(GABA).
138
What is the purpose of postsynaptic membrane?
It is responsible for receiving chemical signal hence it contains receptors.
139
What does synaptic vescicles store?
It stores neurotransmitters.
140
How is the flow of information and communication for chemical synapses?
It is a Unidirectional flow.
141
Which factors influences the rate of conduction of impulses in chemical synapses?
Axon's diameter.
Presence(or absence) of Myelin sheath.
142
By which process are neurotransmitters released?
By the exocytosis process.(A type of active transport)
143
How are groups of interneurons(Billions of them) within the CNS called?
Neuronal pools (Neuronal Circuit/pathways).
144
List the 4 types of circuits of Neuronal pools(based upon function)?
- Converging
- Diverging
- Riverberating
- Parallel-after-discharge
Note : A pool may be localized or its neurons may be distributed in several different regions of the CNS.
