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Anatomy #2- Thorax > Peripheral Nervous System > Flashcards

Peripheral Nervous System Flashcards

1
Q

Can neurons divide?

A

No, neurons cannot divide. As you age, neurons are lost. They have plasticity so that others can take over the job if needed.

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2
Q

Neuron body structure

A
  • Neurons can be very long and extend throughout the body
  • Longest living cell
  • Largest volume of a cell
  • Most similar to skeletal muscle cells due to ability to be very long.
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3
Q

Main regions of the neuron

A
  1. Dendritic zone- receives input
  2. Axon- conducts excitation
  3. Telodendritic zone- transmits output
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4
Q

Where is the decision to send the signal on made?

A

Cell body at the axon hillock

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5
Q

Cell body or perikaryon

A

Located within dendritic zone; associated with axon

Come in variety of different shapes and sizes
- Larger processes result in larger cell bodies
- Faster transmission requires larger axon and larger cell body

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6
Q

Dendrites

A

Highly branched processes

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7
Q

Telodendrites

A
  • Highly branched region at the end of axon
  • Have terminal expansions (bulbs) that store and release neurotransmitters
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8
Q

Why does a neuron have a very developed nucleolus?

A

Needs a lot of proteins/neurotransmitters for passing signal onward

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9
Q

Neuronal communication

A

Neurons are very interconnected. Will be connected telodrites to cell body, telodrites directly onto the telodrites of another neuron. (axodendritic synapse, axosomatic synapse, axoaxonic synapse)

Can be rerouted to another neuron if one dies/is lost

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10
Q

Types of neurons

A
  1. Multipolar
  2. Bipolar- found in sensory
  3. Unipolar- found in sensory
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11
Q

Supporting cells of the PNS

A

Neurolemmocytes
- Schwann cells
- Satellite cells

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12
Q

Schwann cells

A
  • Ensheath or myelinate axons
  • Less than 1mm in length so need many schwann cells to enclose entire length of axon
  • In both non-myelinated and myelinated nerve fibers
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13
Q

Non-myelinated nerve fiber and schwann cells

A

Each schwann cell cell ensheaths a number of axons but there is no myelin sheath formed around each axon

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14
Q

Myelinated nerve fiber and schwann cells

A
  • Each schwann cell ensheathes only one axon (through a overlapping of inner layers) in a myelin sheath
  • Very small in diameter
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15
Q

Satellite cells

A

Encapsulate neuron bodies in ganglia

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16
Q

Satellite cells and non-myelinated ganglia

A

Encapsulate the neuron bodies in the ganglia

17
Q

Satellite cells and sensory (cranio-spinal) ganglia

A

Form tight capsule around the ganglia

18
Q

Satellite cells and autonomic ganglia

A

Form loose capsule around ganglia

19
Q

Myelin formation in PNS

A
  • Myelin sheath is interrupted at nodes. The nodes are covered by cytoplasmic processes of adjacent Schwann cells which have a continuous basal lamina
  • Have internodes and paranodes
20
Q

Myelin formation in CNS

A
  • Nodes are not covered.
  • There are thicker nodes and thinner internodes in CNS than PNS
  • One oligodendrocyte can provide myelin sheath to as many as 50 axons
21
Q

Components of Peripheral Nervous System

A

Includes both cranial and spinal nerves
- Have both roots (proximal part of nerve) and distal branches
- And ganglia

22
Q

Nerve fiber

A

Made up of 1 axon, its associated myelin sheath, and neurolemmocytes

23
Q

Afferent vs. efferent nerve fibers

A

Afferent
- Axons of unipolar neurons located in sensory (cranio-spinal) ganglia

Efferent
- Axons of multipolar neurons located in CNS or in autonomic ganglia

24
Q

Somatic vs. visceral nerve fibers innervation

A

Somatic
- Innervate skin, skeletal muscle and joints

Visceral
- Innervate cardiac & smooth muscles, and glands

25
Q

Neuron types in visceral efferent pathways

A
  1. Preganglionic neurons: cell bodies in CNS
  2. Postganglionic neurons: cell bodies in ganglia, non-myelinated axons having varicosities; NT release and diffuse from multiple sites, and postsynaptic specializations are not evident
26
Q

Components of a nerve

A

A nerve is made up of thousands of axons either non-myelinated (ensheathed) or myelinated by neurolemmocytes

Parts:
1. Endoneurium- fibrocyte and collagen fibers surrounding neurolemmocytes
2. Perineurium- surrounds nerve fascicles. Has two layers: a inner cell layer & a fibrous layer
3. Epineurium- connective tissue surrounding multiple fascicles.

27
Q

Layers of perineurium

A
  1. Inner cellular layer (epitheloid tube)
  • Perineural epitheloid cells (squamous) arrange in concentric layers that are joined by tight junctions providing a cell barrier. Each layer is covered by basal lamina on both sides. The cells proliferate arounf some receptors
  1. Outer fibrous layer- collagenous connective tissue merges with epineurium
28
Q

Ganglia

A

Localized enlargement of a nerve containing neuron cell bodies

29
Q

Sensory ganglia

A
  • Contain primary afferent neurons (unipolar neurons)
  • Cell bodies are superficial and nerve fibers towards center
  • Centrally placed nucleus with dispersed Nissl’s substances
  • Satellite cells form tight capsule around neuron cell bodies

Ex. dorsal root ganglia (of spinal cord) and ganglia in cranial nerves

30
Q

Autonomic ganglia

A
  • Multipolar neurons in autonomic nerves
  • Eccentric nucleus and marginally distributed Nissl’s substance
  • Loose encapsulation by satellite cells
  • Cholinergic presynaptic neurons synapse on postganglionic neurons
  • Postsynaptic neurons can be cholinergic and adrenergic
  • Synaptic vesicles have electron-dense core
31
Q

CNS components

A

Includes the tube (brain and spinal cord)

Central processing unit that makes decisions on what to do

32
Q

PNS components

A
  • Brings sensory input to the CNS so the CNS can make the decision and then makes the decision happen
  • Involves both the cranial and spinal nerves
33
Q

Parts of the brain and spinal cord

A

Spinal cord
1. Cervical
2. Thoracic
3. Lumbar
4. Sacral

Brain
1. Forebrain
2. Midbrain
3. Hindbrain

34
Q

Breakdown of the Peripheral Nervous System

A
  1. Somatic (skeletal muscles and skin)- conscious decisions
    - Afferent (sensory)
    - Efferent (motor)
  2. Visceral (cardiac muscles, smooth muscles, glands)
    - Afferent (sensory)
    • General system- pain
      receptors in visceral
      organs
    • Special system- senses
      • Efferent (motor)- autonomic, unconscious control
35
Q

What makes up a spinal nerve?

A
  1. Dorsal root (sensory): somatic and visceral afferents
  2. Ventral root (motor): somatic and visceral efferents
36
Q

Autonomic nervous system

A

separated into Parasympathetic (craniosacral) feed and breed & Sympathetic (thoracolumbar) fight or flight divisions

37
Q

Sympathetic nervous system

A
  • Fight or flight
  • More generalized response
  • Thoracic-lumbar T1-L5
  • Post-synaptic neurons release norepinephrine
  • Adrenergic: epinephrine, dopamine, isoproterenol
38
Q

Parasympathetic nervous system

A
  • Rest and digest or feed and breed
  • More specific and discrete response
  • Post-synaptic neurons release acetylcholine
  • Cholinergic agents: nicotine, muscarine, caffeine, pilocarpine
  • Anticholinergic: atropine
39
Q

Organs that only have sympathetic innervation

A
  • Sweat glands
  • Pilo-erector muscles
  • Uterus
  • Kidney

Anatomy #2- Thorax (11 decks)

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