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 does the sensory division do?
Conducts signals from receptors to CNS
What does the motor division do?
Conducts signals from CNS to effectors
What are the two divisions of the motor peripheral nervous system?
Somatic and Autonomic
What does the autonomic nervous system do?
Controls involuntary response
What does the somatic nervous system do?
Controls voluntary response
What are the two divisions of the autonomic nervous system?
Sympathetic and parasympathetic
What does the sympathetic division do?
Mobilises body systems
Controls fight or flight responses
What does the parasympathetic division do?
Conserves energy
Controls rest and digest responses
What do sensory (afferent) nerves do?
Carry info towards the CNS
What do motor (efferent) nerves do?
Carry info away from the CNS
What are the 12 cranial nerves?
Olfactory
Oculomotor
Optic
Trochlear
Trigeminal
Abducens
Facial
Vestibulocochlear
Glossopharyngeal
Hypoglossal
Vagus
Accessory
What do somatic afferent nerves do?
Convey info from skin, skeletal muscle and joints
What do somatic efferent nerves do?
Convey info TO skeletal muscles
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?
From the viscera: Thoracic, Abdominal and Pelvic Organs
What can visceral efferent nerves be divided into
Sympathetic and parasympathetic
What does the sympathetic system innervate?
The visceral organs and vasculature
What does the parasympathetic system innervate?
Only visceral organs
What are the sensory receptors and what do they detect?
- Chemoreceptors - Detector molecules which bind to a receptor
- Photoreceptors - Detect light in the retina
- Thermoreceptors - Detect temperature in skin
- Mechanoreceptors - Control mechanical opening of ion channels
- Nociceptors - Detect tissue damage and interpret as pain
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
Describe the structure of peripheral nerves
- Three layers of connective tissue
- Peripheral nerves arranged in fasciculi
What is the epineurium?
The external vascular layer which covers the entire nerve
What is the perineurium?
A layer of connective tissue which covers the individual fascicles
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 (I) has largest diameter
What are the internal sensory receptors and what are their sources of stimulus?
Proprioreceptors - Movement and joint position
enteroreceptors - Movement through gut and blood pH
What are the external sensory receptors and what are their sources of stimulus?
Exteroreceptors - Pain, Temp, Touch and pressure
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
What do joint receptors do?
Detect start and end of movement
What do somatic motor neurones do?
Innervate skeletal muscle for movement
What do photoreceptors do?
Detect light in retina
What is a neuromuscular junction?
A specialised synapse between a motor neurone and a muscle fibre
What is a motor unit?
A single motor neurone together with all the muscle fibres it innervates.
It is the smallest functional unit with which to produce force.
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 reflex action
- Stretching stimulates sensory receptor (muscle spindle)
- Sensory neurone activated
- Sensory neurone activates motor neurone within the integrating centre (spinal cord)
- Motor neurone is activated
- Effector contracts and relieves the stretching
Where do visceral efferent nerves synpase?
A peripheral ganglion
What kind of sensory information do visceral sensory nerves relay and where do they relay it to and from?
Kind: Dull pain fullness and blood pressure
To: T1-L2, S2-S4 and cranial nerves 9 and 10
From: the core
What do visceral motor nerves control and where do they relay to and from?
Control: Pupils, sweat glands, salivary glands, heart muscle , airways
To: core and body wall
From: T1-L2 and cranial nerves 3,7,9,10 (craniosacral outflow)
Outline sympathetic nerve to the periphery/heart
1) Sympathetic nerve exits spinal cord via ventral root
2) Travels up or down or stays where it exits ( depending on destination of impulse) and is synapsed onto a post ganglionic neurone in a ganglion in the spine
What is a gray ramus communicans?
Vessel via which unmyelinated post ganglionic neurones travel through travel through
What is a white ramus communicans?
Vessel via which myelinated pre ganglionic neurones travel through
Outline sympathetic outflow to viscera (such as GI tract)
1) Nerves travel out of spinal cord until they reach a pre-aortic ganglia near to part of viscera it is innervating
2) It synapses there.
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)
