9 Peripheral Nervous System Flashcards Preview

LCRS Neuroscience and Mental Health > 9 Peripheral Nervous System > Flashcards

Flashcards in 9 Peripheral Nervous System Deck (34)
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1
Q

Q: What does the PNS consist of? (5) What percentage of all neurons are in the PNS?

A

A: peripheral nerves, primary sensory cell bodies, dorsal root ganglia, sensory receptors, neuromuscular junction

everything that is not the CNS (brain and spinal cord)

~10%

2
Q

Q: What are the 2 parts of the PNS?

Further division? (2) What do they control? (3)

A

A: somatic: mainly involve voluntary action of body

autonomic:
- (sympathetic) SNS controls skeletal muscle contractions
- (autonomic) ANS provides automatic regulation of smooth muscle, cardiac muscle, glands, adipose tissue

3
Q

Q: How is the PNS functionally split? How do they relate?

End point? (5)

A

A: motor (efferent) and sensory (afferent)

start with receptors in periphery that detect changes in external and internal environment -> record sensory info -> transmitted to CNS via PNS

exit CNS and enter motor division of the PNS where information is carried to peripheral tissues/systems either via ANS or SNS

reach effectors= target organs whose activities are changed in response to neural commands

for SNS= skeletal muscle

for ANS= smooth, cardiac muscle, glands, adipose tissue

4
Q

Q: What are the 3 types of sensory receptors?

A

A: -somatic sensory receptors (position, touch, pain, pressure, temperature)

  • special sensory receptors (smell, taste, vision, balance)
  • visceral sensory receptors (monitor internal organs)
5
Q

Q: How many nerves does the PNS consist of? 2 types? Name them. What does naming relate to?

A

A: 43 pairs

12 cranial nerves
31 spinal nerves

cranial:
1-olfactory nerve
2-optic nerve
3-oculomotor nerve
4-trochlear nerve
5-trigeminal nerve
6-abducens nerve
7-facial nerve
8-vestibulocochlear nerve
9-glossopharyngeal nerve 
10-vagus nerve 
11- accessory nerve 
12-hypoglossal nerve

=> naming relates to location where they exit brain stem nuclei

spinal:
8 cervical nerves (nerve is above corresponding vertebral bone)
12 thoracic (nerve is below corresponding vertebral bone)
5 lumbar (below)
5 saccral (below)
1 coccygeal

=> numbered and named according to level they exit the vertebral column

6
Q

Q: What is the basic route for nerve signals of the somatic nervous system? (4) What type of control can it provide and of what?

A

A: Basic route of nerve signals
begins in the primary motor
cortex = upper motor neuron in primary motor cortex ->

synapses with somatic motor nuclei of spinal cord OR brainstem (lower motor neuron) ->

NMJ (nerves terminate here) ->

allows muscle contraction (produce the motor response)

of skeletal muscle

  • conscious (voluntary) MAINLY
  • sub conscious (automatic/reflexive)
7
Q

Q: What is the basic route for nerve signals of the autonomic nervous system? What does it specifically involve?

A

A: Basic route of nerve signals
begins in the visceral motor nuclei in the
hypothalamus

  • > synapse with autonomic nuclei in brain stem OR spinal cord (preganglionic neuron)
  • > synapse with post ganglionic nuclei in autonomic ganglia
  • > stimulate smooth, cardiac muscle, glands, adipocytes (adipose tissue)

2 ganglionic neurons

8
Q

Q: What does the ANS control? eg? 2 main divisions?

A

A: visceral functions largely outside of our awareness

heart rate

sympathetic and para

9
Q

Q: Which nerves form the sympathetic division of the autonomic NS? What do they form? What state does it keep body in? Which NT is released at the synapse?

A

A: Formed by
neurons from
spinal nerves
T1 to L2

Form ganglia chain on each side (lateral) of the vertebral column

active (“fight or flight”)

Acetlycholine
(ACh) and
noradrenaline
release at the synapse

10
Q

Q: Which nerves form the parasympathetic division of the autonomic NS? What do they form? What state does it keep body in? Which NT is released at the synapse?

A
A: Formed by
neurons from
cranial (III,XII,IX,X)
and sacral (S2-S4)
nerves

Do not involve
ganglia chain- usually have ganglia near organs they
innervate

homeostatic resting state and responsible for digestion (“Resting and digesting”)

ACh release at the
synapse

11
Q

Q: Compare the SNS and ANS.

effectors?
neurons?
stimulating or inhibiting?
NT?
when does it fire?
A

A: SNS

  • Voluntary effectors (e.g., striated muscle)
  • Single motor neuron from spinal cord to target organ
  • Always stimulatory
  • ACh released at the synapse
  • Do not fire at rest

ANS
- Involuntary effectors (e.g., cardiac muscle, glands)
- Usually two neurons from spinal cord to target organ
(ganglionic synapse) (pre and post ganglionic N)
- Stimulatory or inhibitory
- ACh and/or NE released at the synapse
- Have a baseline firing

12
Q

Q: Where’s the ganglion of and how many neurons are between effector/periphery and CNS:

somatic motor neurons?
autonomic motor neurons?
sensory neuron?

A

A: 1- doesn’t have ganglion
2- where pre and post ganglionic neurons synapse
1-where cell body of sensory neuron is

13
Q

Q: What are ganglia? include? (2)
How is each spinal nerve attached to the spinal cord? (2) describe. Join to form?

Include in a diagram.

What does a typical spinal nerve innervate?

A

A: Ganglia - cell bodies, dendrites and synapses in the PNS

  • Each spinal nerve is attached to the spinal cord by two roots
  • Dorsal (posterior) root - brings afferent (sensory) signals from the periphery to the CNS
  • Ventral (anterior) root - takes efferent (motor) signals from the CNS to the periphery
    (motor neurons)
  • The two roots join to form a mixed, spinal nerve

band of skin (dermatome) / muscle

14
Q

Q: What is a ramus? carry? In relation to spinal nerves?

A

A: what each spinal nerve splits into (lateral branches of spinal cord)

both motor and sensory fibres

spinal splits into dorsal and ventral ramus

  • dorsal= innervates muscle and skin of back
  • ventral= innervates muscle and skin of every other part of body including limbs
15
Q

Q: What’s the structure of a PNS nerve? (6)

A

A: single axon is covered in myelin sheath (Myelin in the PNS is derived from Schwann cells) ->

covered by connective tissue layer called endoneurium

lots of axons / bundle makes fascicle

fascicle is wrapped up in perineurium

lots of fascicles make the spinal nerve

Epineurium surrounds the entire nerve

16
Q

Q: How can PNS nerves vary? How are neurons grouped? (3) 3 groups?

A

A: myelinated or unmyelinated

Neurons grouped based on the diameter, signal conduction velocity and myelination state

A, B, C

17
Q

Q: What are the 3 groups of PNS neurons? diameter? conduction velocity? myelin? conduct? types?

A

A: A group: large diameter, high conduction velocity, and are myelinated - alpha, beta, delta, gamma types

B group: myelinated, small diameter, low conduction velocity - conduct autonomic information

C group: unmyelinated, small diameter, low conduction velocity - dull, aching, burning pain and temperature sensation (conduction of sensory input from periphery to CNS)

18
Q

Q: What do spinal nerves exit? form? Describe. Examples (6) What forms from them?

A

A: intervertebral foramina to
form nerve plexuses

networks of intersecting spinal nerves

cervical, brachial (C5-8 and T1), lumbar, sacral, celiac, and coccygeal plexuses

from each plexus you get trunks -> further divide into peripheral nerves

19
Q

Q: What is a dermatome? variation? Layout? Clinical significance?

A

A: Areas of skin supplied by a single sensory spinal nerve
-in each different dermatome you will find different peripheral nerves responsible for sensation/contraction

Stacked along the thorax and abdomen; longitudinally along the limbs

Clinical significance: can determine the site of spinal damage by simple pin prick exam

20
Q

Q: Distribution relationship of nerves?

A

A: spinal nerve distribution is different to peripheral nerve distribution

21
Q

Q: What are myotomes? compared to dermatome? Distribution? (4) Clinical significance?

A

A: Groups of muscles supplied by a single spinal nerve root - motor equivalent

Distributions are in the upper and lower extremities are - C1/C2: neck flexion/
extension; 
T1: finger abduction; 
L3: knee extension; 
S2: knee flexion

Clinical significance:
important part of neurological examination (e.g., testing for muscle weakness)

22
Q

Q: What is a peripheral neuropathy? What may it do? (4)

A

A: a result of damage/disease to your peripheral nerves

impair sensation, movement, gland or organ function

23
Q

Q: What are the 3 types of peripheral neuropathies? Describe what they cause.

A

A: - Sensory nerves (sensation): cause tingling, pain,
numbness
- Motor nerves (movement): cause weakness to
hands and feet
- Autonomic nerves (involuntary functions): cause
changes in heart rate or blood pressure

24
Q

Q: What is the cause of a peripheral neuropathy? (6) 2 names in terms of number of nerves affected? What percentage of neuropathies have an unknown origin? name?

A

A: Causes can be metabolic, toxic, inflammatory,
traumatic, genetic, infective
=>many causes

  • Mononeuropathy: refers to a single nerve being
    affected
  • Polyneuropathy: refers to several nerves being
    affected
  • ~30% of neuropathies are “idiopathic” - i.e. of
    unknown origin
25
Q

Q: What are the 3 classifications of PNS nerve injury? Include connective tissue affected.

A

A: - Neuropraxia: involves a reversible conduction block characterised by selective demyelination of the axon sheath (lesion at level of myelinated axon)- endoneurium and axon still intact
- e.g., nerve compression

  • Axonotmesis: demylination and axon loss - epineurium and perineurium remain intact - still some continuity within the nerve - degeneration occurs below and slightly proximal to the site of injury
  • Neurotmesis: most severe form of nerve injury - associated with complete nerve division and disruption - e.g., commonly seen after lacerations or ischemic injuries
  • > Damage to the epineurium (around the entire nerve) - no nerve growth
26
Q

Q: Describe the 4 stages of peripheral nerve regeneration from injury. Where does this specifically occur? they can undergo? (2)

A

A: lesion at node of ranvier

break down occurs below and slightly proximal to lesion- myelinated part is broken up and macrophages digest debris

schwann cells are responsible for restoring myelin and axonal function (growth factors help)

complete regen of neuron and NMJ

=> adult PNS nerves (can undergo long distance axon regeneration and substantial functional recovery)

27
Q

Q: What is an EMG? Technique for? What does it produce? What does it involve? (2)

A

A: Electromyography (EMG) = technique for evaluating and recording electrical activity produced by muscles

Produces an electromyogram

Intramuscular EMG and surface EMG electrodes
- Intramuscular EMG - involves inserting a needle electrode through the skin into the muscle
- Surface EMG - placing electrodes on the skin over the
muscle

28
Q

Q: What does an EMG allow?

A

A: Electromyography

Distinguish between muscle conditions that begin in the
muscle (myopathy) and nerve disorders (peripheral neuropathies) that cause muscle weakness

29
Q

Q: What is a NCS? Technique for? How is it conducted? (3)

A

A: Nerve Conduction Study (NCS) = Technique for evaluating the speed of nerve impulses - nerve conduction velocity (NCV)

  1. Nerves are stimulated with small electrical impulses by one electrode
  2. while other electrodes detect the electrical impulse “down-stream” from the first electrode
  3. Distance between electrodes and time taken for electrical impulses to travel between electrodes are used to calculate the speed of nerve signals
30
Q

Q: How can an NCS be interpreted? result of? (5)

A

A: Slower than normal speed could indicate nerve damage from direct trauma, diabetic or peripheral neuropathy, viral nerve infection or nerve entrapment diseases like the Carpal Tunnel Syndrome among other conditions

31
Q

Q: What is NCV related to? (2) Newborns? Adult values?

A

A: nerve conduction velocity

diameter of the nerve and the degree of myelination (the presence of a myelinsheath on the axon) of the nerve

Newborn infants have values that are approximately half
that of adults

Adult values are normally reached by age 3 or 4 years of
age

32
Q

Q: Name 3 diagnostic techniques for evaluating and recording PNS function.

A

A: electromyography

nerve conduction study

somatosensory evoked potential

33
Q

Q: What is SEP? Reason for measuring? How?

A

A: Somatosensory Evoked Potential (SEP)

assess whether sensations (pain, temperature and touch) in the periphery are being transmitted to the brain/CNS

  1. Stimulating electrodes are placed on the arm and/or leg
  2. Recording electrodes are placed on the head and/or spine
34
Q

Q: What can a SEP indicate? Usually combined with? to? eg?

A

A: Somatosensory Evoked Potential (SEP)

Evoked potentials in the recording electrodes can indicate the integrity of transmission at peripheral mechanoreceptors to the cerebral cortex

Usually combined with EMG and NCV tests to assess the patient for generalised disorders of the nervous system like multiple sclerosis (MS)