9 Peripheral Nervous System Flashcards
Q: What does the PNS consist of? (5) What percentage of all neurons are in the PNS?
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%
Q: What are the 2 parts of the PNS?
Further division? (2) What do they control? (3)
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
Q: How is the PNS functionally split? How do they relate?
End point? (5)
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
Q: What are the 3 types of sensory receptors?
A: -somatic sensory receptors (position, touch, pain, pressure, temperature)
- special sensory receptors (smell, taste, vision, balance)
- visceral sensory receptors (monitor internal organs)
Q: How many nerves does the PNS consist of? 2 types? Name them. What does naming relate to?
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
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: 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)
Q: What is the basic route for nerve signals of the autonomic nervous system? What does it specifically involve?
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
Q: What does the ANS control? eg? 2 main divisions?
A: visceral functions largely outside of our awareness
heart rate
sympathetic and para
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: 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
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: 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
Q: Compare the SNS and ANS.
effectors? neurons? stimulating or inhibiting? NT? when does it fire?
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
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: 1- doesn’t have ganglion
2- where pre and post ganglionic neurons synapse
1-where cell body of sensory neuron is
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: 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
Q: What is a ramus? carry? In relation to spinal nerves?
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
Q: What’s the structure of a PNS nerve? (6)
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
Q: How can PNS nerves vary? How are neurons grouped? (3) 3 groups?
A: myelinated or unmyelinated
Neurons grouped based on the diameter, signal conduction velocity and myelination state
A, B, C
Q: What are the 3 groups of PNS neurons? diameter? conduction velocity? myelin? conduct? types?
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)
Q: What do spinal nerves exit? form? Describe. Examples (6) What forms from them?
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
Q: What is a dermatome? variation? Layout? Clinical significance?
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
Q: Distribution relationship of nerves?
A: spinal nerve distribution is different to peripheral nerve distribution
Q: What are myotomes? compared to dermatome? Distribution? (4) Clinical significance?
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)
Q: What is a peripheral neuropathy? What may it do? (4)
A: a result of damage/disease to your peripheral nerves
impair sensation, movement, gland or organ function
Q: What are the 3 types of peripheral neuropathies? Describe what they cause.
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
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: 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
Q: What are the 3 classifications of PNS nerve injury? Include connective tissue affected.
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
Q: Describe the 4 stages of peripheral nerve regeneration from injury. Where does this specifically occur? they can undergo? (2)
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)
Q: What is an EMG? Technique for? What does it produce? What does it involve? (2)
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
Q: What does an EMG allow?
A: Electromyography
Distinguish between muscle conditions that begin in the
muscle (myopathy) and nerve disorders (peripheral neuropathies) that cause muscle weakness
Q: What is a NCS? Technique for? How is it conducted? (3)
A: Nerve Conduction Study (NCS) = Technique for evaluating the speed of nerve impulses - nerve conduction velocity (NCV)
- Nerves are stimulated with small electrical impulses by one electrode
- while other electrodes detect the electrical impulse “down-stream” from the first electrode
- Distance between electrodes and time taken for electrical impulses to travel between electrodes are used to calculate the speed of nerve signals
Q: How can an NCS be interpreted? result of? (5)
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
Q: What is NCV related to? (2) Newborns? Adult values?
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
Q: Name 3 diagnostic techniques for evaluating and recording PNS function.
A: electromyography
nerve conduction study
somatosensory evoked potential
Q: What is SEP? Reason for measuring? How?
A: Somatosensory Evoked Potential (SEP)
assess whether sensations (pain, temperature and touch) in the periphery are being transmitted to the brain/CNS
- Stimulating electrodes are placed on the arm and/or leg
- Recording electrodes are placed on the head and/or spine
Q: What can a SEP indicate? Usually combined with? to? eg?
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)
