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Microanatomy > Nervous Tissue > Flashcards

Nervous Tissue Flashcards

1
Q

What are the Anatomical divisions of the nervous tissue

A

CNS
- Central nervous system

PNS
- Peripheral nervous system

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2
Q

What consists of the CNS (central nervous system)
and what are they made out of

A

Brain(cerebellum, and cerebrum), and spinal cord.

All these organs are made of white matter (nerve fibers and neuroglia cells) and gray matter (neurons, nerve fibers and neuroglia cells) and are covered by three meninges.

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3
Q

What consists of the PNS (peripheral nervous system) and what are they made out of

A

Nerves outside the CNS, and ganglia.

Nerves:Bundles of nerve fibers surrounded by connective tissue sheaths

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4
Q

Nerve Fiber connective tissue sheaths

A

Epineurium, surrounds nerves; perineurium, surrounds fascicles; endoneurium, surrounds a nerve fiber.

Individual nerve fiber is enveloped by a myelin sheath produced by Schwann cells in the PNS and by oligodendrocytes in the CNS.

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5
Q

Epineurium

A

Surrounds the whole nerve

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6
Q

Perineurium

A

Surrounds fascicles of a nerve

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7
Q

Endoneurium

A

Surrounds individual nerve fiber within a fascicle

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8
Q

How does sensory transmit impulses

A

Transmit impulses to the CNS

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9
Q

How does motory transmit impulses and how is it divided

A

Transmit impulses from the CNS to the body; the motor part is divided into somatic and autonomic (sympathetic and parasympathetic) systems.

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10
Q

What are the cell types in the nervous system

A

Neurons

Neuroglia cells

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11
Q

What is a neuron

A

A cell body and processes (dendrites and an axon)

Conducts impulses

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12
Q

Cell body of a neuron (perikaryon)

A

Nucleus, RER (Nissl body), Golgi, lipofuscin granules (increase with age), neurofilaments (10 nm in diameter), and microtubules.

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13
Q

Dendrite

A

Transmits impulses toward the body, contains organelles like in the body except that Golgi is absent, has arborized terminals which permit a neuron to receive stimuli from many other neurons.

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14
Q

Axon

A

One axon per neuron, conducts impulses away from the body, originates from the axon hillock, lacks organelles except microtubules and neurofilaments, may have collateral branches, terminates in many branches (telodendrions), which form synapses with dendrites or cell bodies of other neurons or form special contacts with other cell types, such as, muscle cells.

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15
Q

What are the different types of neurons
Discuss their structure and functions

A

Multipolar
Bipolar
Pseudo-unipolar
Unipolar

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16
Q

What is the structure and function of Unipolar

A

Possess a single process, rare in vertebrates, present in the developing NT.

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17
Q

What is the structure and function of Bipolar

A

Possess a single axon and a single dendrite, present in sense organs.
examples: parts of vision, smell, taste, hearing.

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18
Q

What is the structure and function of Multipolar

A

Possess a single axon and more than one dendrite; the most common type of neuron.

Example: Sympathetic ganglion

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19
Q

What is the structure and function of Pseudo-Unipolar

A

Possess a single process that branches into an axon and a dendrite, present in spinal and cranial ganglia.

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20
Q

What is a neuroglia

A

Support, nurture and protect neurons.
Do not conduct impulses or form synapses, function to support and protect neurons.

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21
Q

Types of Neuroglia Cells in the CNS

A

Astrocytes
Oligodendrocyte
Microglia
Ependymal Cells

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22
Q

Astrocyte

A

Protoplasmic astrocytes mainly in gray matter and fibrous astrocytes mainly in white matter, feet-like processes surround blood vessels and form a part of the blood-brain barrier.

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23
Q

Oligodendrocyte

A

Necessary for the survival of neurons, located both in gray and white matter, produce myelin for axons in the CNS.

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24
Q

Microglia

A

Small, phagocytic, derived from monocytes (mesoderm); condensed, elongated nucleus, which can be confused with endothelial nuclei.

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25
Q

Ependymal Cells

A

Line the neural tube and ventricles of the brain, associated with formation of the cerebrospinal fluid (CSF), often have cilia, which aid in moving the CSF.

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26
Q

Schwann Cells

A

Are also neuroglia cells but are located around axons in the PNS. Schwann cells also synthesize myelin sheath, but each Schwann cell produces myelin for only one axon, whereas oligodendrocytes can do so for several axons.

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27
Q

Four phases of myelin formation in peripheral nerve fibers

A
  1. Schwann cell surrounding an axon
  2. Schwann cell’s cell membrane surrounds the axon, the point of attachment is called mesaxon
  3. The cell membrane rolls around the axon (like a jelly role)
  4. The myelin sheath consists of many layers of the cell membrane of Schwann cell ( that is why myelin sheath is essentially a lipid layer) and is present within the cytoplasm
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28
Q

What are the different types of nerve fibers

A

Type A
Type B
Type C

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29
Q

What is the structure and function of Type A

A

Myelinated, thick, and conduct impulse at 15-100 m/sec;

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30
Q

What is the structure and function of Type B

A

Moderately myelinated, thinner than type A, conduct impulse at 3-14 m/sec;

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31
Q

What is the structure and function of Type C

A

Thin, unmyelinated, may or may not be covered by Schwann cell or oligodendrocytes, conduct impulse at 0.2-2 m/sec.

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32
Q

What is the Ganglion and what is its structure and function

A

Aggregations of neuronal cell bodies outside the CNS. Examples: dorsal root ganglion (sensory) and autonomic (motor).

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33
Q

What is the spinal cord and what is its structure and function

A

White matter in the periphery, divided into dorsal and ventral columns; gray matter, in the form of an H in the center and is divided into dorsal, ventral (site for alpha-motor neurons) and lateral (site for sympathetic or parasympathetic neurons, depending upon the segment of the spinal cord) horns; central canal lined by ependymal cells.

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34
Q

What is the cerebellum and what is its structure and function

A

Gray matter outside and white matter inside.
Function: Maintaining balance and posture and coordination movements.

Consists of three layers:
Molecular Layer
- mainly cell processes, very few cell nuclei;

Purkinje cells layer
- multipolar neuron, each cell receives thousands of excitatory and inhibitory impulses;

Granular layer
- contains closely packed small granule cells

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35
Q

What are the meninges

A

Dura mater

Arachnoid

Pia mater

36
Q

Dura mater

A

Dense connective tissue that is fused with the periosteum in the brain but free in the spinal cord, thus no epidural space in the brain, thick dense CT lined on both sides by simple squamous epithelium

37
Q

Arachnoid

A

Thin membrane lined by simple squamous cells, connected by trabeculae to the pia mater

38
Q

Pia mater

A

Thin vascular membrane attached to the nervous tissue(the brain).

39
Q

Spaces of the meninges

A

epidural (contains fat)
- only in the spinal cord
subdural
subarachnoid (contains CSF).

40
Q

Spinal Cord meninges difference from Brain

A

Dura Mater is separate from the periosteum and its dense connective tissue is lined on both sides by simple squamous epithelium.

41
Q

What is a synapse

A

Sites where signals are transmitted from one neuron to another neuron or a muscle cell (neuromuscular).

42
Q

Types of synapses

A

Axodendritic
Axosomatic
Axoaxonic (Rare)

43
Q

Axodendritic

A

Axon transmit signals to the dendrite of another

44
Q

Axosomatic

A

Axon transmit signals to cell body of another

45
Q

Axoaxonic

A

Axon transmit signals to another axon

46
Q

Synaptic Morphology

A

Axon terminal, presynaptic membrane (contains voltage-gated Ca++ channels), postsynaptic membrane (contains receptors for neurotransmitters), and synaptic cleft.

47
Q

Types of Neurotransmitter

A

Acetylcholine
Norepinephrine
Glutamic acid
Gamma-aminobutyric acid
Dopamine
Serotonin
Glycine

48
Q

Acetylcholine

A

Released at myoneural junctions, all parasympathetic synapses, and preganglionic sympathetic processes.

49
Q

Norepinephrine

A

Released at the postganglionic sympathetic synapses

50
Q

Glutamic acid, gamma-aminobutyric acid, dopamine, serotonin, and glycine

A

Mainly released at neuronal synapses in the brain.

Is this statement referring to this flashcard or should it be moved–>Biochemical events associated with impulse transmission are the same as described for the motor end plate.

51
Q

Nodes of Ranvier

A

Regions along the length of a nerve fiber, lack myelin sheath, and represent discontinuities between adjacent Schwann cells or oligodendrocytes.

The axolemma at the nodes contains many Na+ pumps and allows jumping of the action potential from one node to the next (Saltatory conduction).

The node of Ranvier is covered only by axolemma (lacks myelin sheath or cytoplasm of SC).

52
Q

Axolemma and what is it surrounded by

A

Each axon/dendrite is surrounded by a cell membrane (axolemma), which is surrounded by Schwann cells in the case of peripheral nerve fiber and by Oligodendrocytes in the case of central nerve fibers.

53
Q

Reflex Arc

A

Consists of a minimum of two (usually more) neurons.
Parts with example:
Receptor (skin)
Afferent limb (dorsal root of the nerve
Integrating center
- First Neuron (unipolar sensory neuron of the dorsal root ganglion)
- Second Neuron (ventral motor neuron of the spinal cord)
Efferent limb (ventral root of the spinal cord)
Effector (muscle fibers)

Example:
Knee-jerk reflex (two neurons)
Withdrawal reflex (more than two neurons)
- Withdrawal of the finger from a hot surface

54
Q

Cerebral Cortex

A

Cells and fibers are arranged in layers, but their number depends on the area of the brain and the species. Large domestic species have only 3-4 layers identified.

Molecular
External Granular
External Pyramidal
Internal Granular
Internal Pyramidal
Fusiform

Note, granule cells are considered as receptor neurons, and pyramidal cells as motor neurons. Pyramidal cells are the dominant neurons.

cerebrum occupies the major part of the brain and consists of ridges (gyri) and grooves (sulci).

55
Q

Pyramidal Cells (upper motor neurons)

A

Are the most prominent and important cell type of the cerebrum and form pyramidal tracts, such as, corticobulbar and corticospinal

56
Q

Parts of the patellar reflex

A
  1. Quadriceps muscle is stretched, and a sensory impulse is generated (action potential).
  2. Sensory impulse is carried via afferent fibers of sensory neurons of dorsal root ganglion.
  3. The impulse is transmitted to the ventral motor neurons in the ventral horn of spinal cord.
  4. Motor impulse (axons of ventral motor neurons) stimulates quadriceps muscle.
57
Q

Molecular layer of the cerebral cortex

A

Fibers and neuroglia cells

58
Q

External granular of the cerebral cortex

A

Granule cells

59
Q

External pyramidal of the cerebral cortex

A

Small pyramidal cells

60
Q

Internal granular of the cerebral cortex

A

Small granule cells

61
Q

Internal pyramidal of the cerebral cortex

A

Large pyramidal

62
Q

Fusiform of the cerebral cortex

A

Irregular pyramidal

63
Q

Blood-Brain Barrier

A

Un-fenestrated endothelium with tight junctions between endothelial cells and a thick basal lamina surrounded by foot-like processes of astrocyte.

64
Q

Choroid Plexus

A

Folds of pia mater in the brain ventricles, which consist of a core of connective tissue covered by simple cuboidal ependymal cells; secrete cerebrospinal fluid.

65
Q

Cerebrospinal Fluid

A

Fills the ventricles of the brain( 2 lateral, third and fourth), central canal of the spinal cord, and subarachnoid space, produced by the choroid plexus, and reabsorbed by the arachnoid villi into venous sinuses of the brain. Contains less protein than tissue fluid.

66
Q

Degeneration and Regeneration of Nervous Tissue

A

Neurons cannot divide, thus cannot be replaced when injured. Nerve fibers regenerate.

Steps:
ia) Degeneration of the nerve fiber distal to the site of injury (Wallerian degeneration),
OR
ib) degeneration of a small part of the fiber proximal to the injury (primary degeneration),
ii) loss of Nissl bodies and lateral migration of the nucleus (chromatolysis),
iii) proliferation of Schwann cells, which form a tube-like structure, branching of the axon
iv) re-growth of fibers by sprouting,
v) growth of a nerve fiber sprout into the tube surrounded by Schwann cells, (Penetration of a branch of an axon into one of the tubes surrounded by Schwann cells (nerve regeneration is successful). )
vi) eventual re-connection of the nerve fiber (axon) with the muscle.

Note, if nerve (axons) fibers fail to connect with the muscle, then they form neuromas (usually found in horses).

67
Q

Receptors

A

Peripheral specialized nerve endings of afferent neurons, which respond to environmental changes.

Exteroceptors
Proprioceptor

68
Q

Exteroceptors

A

Peripheral specialized nerve endings of afferent neurons, which respond to environmental changes. These are associated with skin.

Non-encapsulated:
1) Free nerve endings in the epidermis, touch, and pain;
2) Merkel’s discs in the skin and buccal cavity, touch.
3) Thermoreceptors in the skin, heat, cold

Encapsulated:
1) Pacinian corpuscle: pressure, a large lamellar body found in the skin, nipples, genitalia, and tendon;
Meissner’s Corpuscle: touch and tactile, found in fingers, lips, nipples, and genitalia.

69
Q

Pacinian corpuscle

A

Concentric lamellae of flattened cells (probably modified Schwann cells) separated by thin collagen fibers and tissue fluid. The center contains non-myelinated sensory fiber that responds to deep pressure.

70
Q

Meissner corpuscle

A

Ovoid-appearing structure at the junction of the epidermis and dermis, probably specialized Schwann cells surrounded by delicate collagen fibers.

71
Q

Proprioceptor

A

Muscle spindle
Golgi Tendon

72
Q

Muscle Spindle

A

Stretch receptors within skeletal muscle that apprise the CNS about the sense of motion of muscles, joints, and tendons.

Muscle spindle showing afferent and efferent nerve fibers that make synapses with the intrafusal fibers (modified muscle fibers).

Note two types of intrafusal fibers: one with a small diameter and the other with a dilation filled with nuclei.

Muscle spindles participate in the nervous control of body posture and the coordinate action of opposing muscles.

73
Q

Parts of a Muscle Spindle

A

Extrafusal Fibers
Intrafusal Fibers

74
Q

Extrafusal Fiber

A

Normal skeletal muscle fibers;

75
Q

Intrafusal Fibers

A

Modified skeletal muscle fibers that consist of nuclear bag fibers in the center and nuclear chain fibers in the periphery.

76
Q

Innervation of Muscle Spindles

A

Type Ia
Type IIa

77
Q

Type Ia of Muscle Spindles

A

Sensory (annulospiral endings) around the center,

78
Q

Type IIa of Muscle Spindles

A

Sensory (flower spray endings) on either side of the annulospiral endings, gamma-efferent motor at both ends of the intrafusal fibers.

79
Q

Golgi Tendon

A

Function as tension receptors in the tendon, composed of encapsulated collagen fibers that are supplied by type Ib sensory fibers.

It is stimulated when the muscle contracts too strenuously and the tension on the tendon increases.

Impulses from type Ib fibers then inhibit the alpha- efferent motor neuron to the muscle, thus preventing further contraction.

80
Q

The sequence of events at the synapse

A
  1. Presynaptic membrane depolarization indues
  2. Brief opening of calcium channels
    3.Calcium influx promotes exocytosis of synaptic vesicles with
  3. Release of neurotransmitter
  4. Neurotransmitter reacts with receptors and
  5. Promotes postsynaptic membrane depolarization
  6. Membrane retrieval by coated vesicles
81
Q

The effect of thickness of a fiber

A

The thicker the fiber, the thicker the myelin sheath, and the faster the conduction of nerve impulse.

82
Q

Nuclei

A

Aggregations of nerve cell bodies within the central nervous system; examples: nuclei of cranial nerves.

83
Q

Satellite Cells

A

Neuroglia cells associated with cell bodies in the ganglia or nuclei are called satellite cells

84
Q

Locations of gray matter and white matter in the body

A

while gray matter (cell bodies of neurons, neuroglia cells and nerve fibers) is outside and white matter (neuroglia cells and nerve fibers) is inside in the brain, the reverse is the case in the spinal cord

85
Q

Central Canal

A

Central canal is lined by ependymal neuroglia cells and contains cerebrospinal fluid.

86
Q

Main functions of the Cerebrum

A

Memory, attention, perception, cognition, awareness, thought.

Microanatomy (12 decks)

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