1a Peripheral Nervous System + Disorders Flashcards
What is the PNS composed of?
The nerves and ganglia outside the brain and spinal cord
What are the two divisions of the PNS?
The sensory (afferent) and motor (efferent) division
What are the two divisions of the motor peripheral nervous system?
Somatic and Visceral (Autonomic)
What are the two divisions of the autonomic nervous system?
Sympathetic and parasympathetic
How many pairs of cranial nerves are there?
12
How many pairs of spinal nerves are there?
31
What do somatic sensory neurones do?
They receive sensory input from the periphery - eg Skin, Skeletal Muscle and tendons
What are the some external receptors which detect somatic sensory stimuli and what do they detect?
Exteroreceptors detect pain, temperature and pressire
Noiceoreceptors
Mechanoreceptors
Thermoreceptors
What are the internal sensory receptors?
Proprioreceptors and enteroreceptors
What do muscle spindle receptors do?
Detect changes in the length of muscle
What do golgi tendon receptors do?
detect changes in the tension of tendons
From what do visceral sensory neurones pick up stimuli from? And what stimuli
Pain, fullness and blood pressure from thoracic, pelvic and abdominal organs
What do somatic motor neurones do?
Innervate skeletal muscle for movement
From where do somatic afferent nerves convey information?
Skin, skeletal muscle and joints
What is a dermatome?
Area of skin that is supplied by a single spinal nerve
What is a myotome?
Group of muscles innervated by a single spinal nerve
From where do visceral afferent nerve carry information?
Thoracic, Abdominal and Pelvic Organs
What does the sympathetic system innervate?
The visceral organs and vasculature
What does the parasympathetic system innervate?
Only visceral organs
What is a ganglion?
A collection of cell bodies outside the CNS
What is a nucleus?
A collection of cell bodies inside the CNS
What is a plexus?
A network of interconnecting nerves
Where do afferent fibers have their cell bodies?
In spinal ganglia
Where do visceral efferent nerves synpase?
An autonomic ganglion
What is the perineurium?
A layer of connective tissue which covers the individual fascicles
What is the epineurium?
The external vascular layer which covers the entire NERVE
What is the endoneurium?
Layer of connective tissue which covers individual axons
What are the two classification systems for nerves?
- Based on conduction velocity, with A being the fastest
- Based on axonal diameter - using roman numerals and one has largest diameter
What do photoreceptors do?
Detect light in retina
what is the specialsed synpase betwen a motor neurone and a muscle called?
Neuromuscular juction
What is a motor unit?
A single motor neurone together with all the muscle fibres it innervates
What happens when one motor unit is stimulated?
all the muscle fibers in that unit will contract
What is reflex action?
Involuntarily coordinated pattern of muscle contraction and relaxation
Outline the process of the tendon reflex action
- Stretching stimulates sensory receptor (tendon golgi)
- Sensory neurone activated
- Sensory neurone activates motor neurone within the spinal cord (integrating centre)
- Motor neurone is activated
- Effector (quadricep muscle of thigh) contracts, causing a knee jerk
What is meant by a monosynaptic reflex?
Simple reflex involving only one synapse between the sensory and motor neurone
What is the antagonist muscle of the quadriceps?
Hamstring muscles
What happens if there is a lesion in the dorsal root?
Loss of sensation in the dermatome supplied by the corresponding spinal nerve
What happens if there is a lesion in a somatic sensory nerve?
loss of sensation in the area of disribution of that peripheral nerve
Why is loss of sensation at dermatomes sometimes not detected?
There may some overlap in dermatome innervation
What happens if there is a lesion in the ventral root?
Muscle weakness, as the spinal nerve that innervates the muscle has been shut off
Why is paralysis of muscles not always seen?
More limb muscles are innervated by more than one nerve so paralysis is unlikely
What happens if there is damage directly to the motor neurone?
Paralysis of the muscle as the impulse cannot reach the muscle
Why are there 30 dermatomes but 31 spinal nerves?
C1 does not have a sensory root so dermatomes begin with C2
What is lumbar spinal radiculopathy commonly known as?
Sciatica, caused by compression of the sciatic nerve
what is a radiculopathy?
When the nerve root in the spine become compressed leading to pain, weakness and tingling sensations
What can cause radiculopathy?
A slipped / herniated disc
What is a slipped disc?
When the soft cushion of tissue between bones pushes out and presses on nerve
What happens to the intervertebral foramine when there is a slipped disc?
It narrows
What can be used to confirm diagnosis of sciatica?
The straight leg raise - stretches sciatic nerve and recreates the pain felt by the patient
What are some treatment options for sciatica?
Painkillers, Exercise, Epidural infection delivered into the causal part of sine (sacral hiatus), decompression surgery
What are some non disc causes of sciatica?
Other non-disc causes include malignancy (e.g. metastatic bone disease), arthritis, bone growths, piriformis syndrome (where the nerves are compressed by the contraction of the piriformis muscle in the buttocks).
Which spinal segments are involved in the autonomic nervous system (visceral motor)
Thoracolumbar (T1-L2) and craniosacral outflow (cranial nerves III, VII, IX, X)
