7- peripheral nervous system anatomy Flashcards
(19 cards)
Describe the main features of the somatic nervous system
- 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
Describe the main features of the autonomic nervous system
• Involuntary effectors (e.g., cardiac muscle, glands)
• Usually two neurons from spinal cord to target organ
• Stimulatory or inhibitory
• ACh and/or NE released at the synapse
Have a baseline firing
How are the dorsal and ventral roots different
- 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)
Describe a rami
• Rami-lateralbranchesofthe spinal nerves
Ramicarrybothmotorand sensory fibres
What 3 components make up the structure of a PNS nerve
Epineurium - connective tissue surrounding a nerve
Perineurium - connective tissue surrounding each fascicle Endoneurium - connective tissue surrounding each axon
How do the 3 types of PNS neurone differ
- Agroup:largediameter,high conduction velocity, and are myelinated - alpha, beta, delta, gamma types
- Bgroup:myelinated,small diameter, low conduction velocity - conduct autonomic information
- Cgroup:unmyelinated,small diameter, low conduction velocity - dull, aching, burning pain and temperature sensation
What is a nerve plexus
- Spinal nerves exit the intervertebral foramina to form nerve plexuses
- Nerve plexuses: networks of intersecting spinal nerves
There is a plexus which goes to EACH of the four limbs • Brachial Plexus = goes to the upper limb • There are FIVE spinal nerves contributing to the brachial plexus = C5 - T1 • As these spinal nerves leave the spinal cord, some of them merge together then later on they'll diverge • This means that you get mixing up of the individual spinal nerves so by the
What is a dermatome
Areas of skin supplied by a single sensory spinal nerve
Stacked along the thorax and abdomen; longitudinally along the limbs
What are the 12 cranial nerves and their functions
I Olfactory (Smell) II Optic (Sight) III Oculomotor (Moves eyelid and eyeball and adjusts the pupil and lens of the eye) IV Trochlear (Moves eyeballs) V Trigeminal (Facial muscles incl. chewing; Facial sensations) VI Abducens (Moves eyeballs) VII Facial (Taste, tears, saliva, facial expressions) VIII Vestibulocochlear (Auditory) IX Glossopharyngeal (Swallowing, saliva, taste) X Vagus (Control of PNS e.g. smooth muscles of GI tract) XI Accessory (Moving head & shoulders, swallowing) XII Hypoglossal (Tongue muscles - speech & swallowing)
What is neuropraxia, axonotmesis and neurotmesis
- Neuropraxia:involvesareversibleconductionblockcharacterizedby selective demyelination of the axon sheath - endoneurium and axon still intact - e.g., nerve compression
- Axonotmesis:demylinationandaxonloss-epineuriumandperineurium remain intact - still some continuity within the nerve - degeneration occurs below and slightly proximal to the site of injury
- Neurotmesis:mostsevereformofnerveinjury-associatedwithcomplete nerve division and disruption - e.g., commonly seen after lacerations or ischemic injuries
What is the difference between dorsal and ventral rami
o DORSAL RAMI innervate muscle and skin of back
o VENTRAL RAMI innervate muscles and skin of rest of body, including limbs
What happens when a peripheral nerve is damaged
A – The normal axon is contained by the endoneurium; a compression injury occurs which breaks the continuity of the AXOPLASM, therefore action potentials cannot be propagated
B - The distal part of the nerve degenerates, but the PROXIMAL STUMP remains intact (unless injury is close to soma) and macrophages phagocytose the axonal and myelin debris (WALLERIAN DEGENERATION)
C - The proximal part of the axon and cell body usually survive but undergo metabolic changes (CHROMATOLYSIS) – outgrowth of AXONAL SPROUTS from the proximal stump occurs; these are guided down by a scaffold of proliferating Schwann cells
D – When the first axonal sprout makes contact with target organ, growth and myelination occurs; the other axonal sprouts then draw back into the proximal stump
o Successful regeneration mainly depends on how badly the axons and connective tissue sheaths are damaged and the distance from the target organ
o Failure to reconnect leads to formation of a NEUROMA containing trapped axons
E – the nodes of Ranvier in the regenerated axon will be closer together than initially
What is peripheral neuropathy and what are 2 types
Progressive degeneration of peripheral nerves
AXONAL DEGERATION – leads to a complete conduction block; may be the result of prolonged and increase segmental demyelination
SEGMENTAL DEMYELINATION – Schwann cells
eventually die therefore continuous conduction
replaces saltatory which affects the conduction speed
Which nerves make up the sympathetic and parasympathetic division
Sympathetic: Formed by neurons from spinal nerves T1 to L2
Formed by neurons from cranial (III,XII,IX,X) and sacral (S2-S4) nerves
What are the 5 types of spinal nerve
Cervical, thoracic, lumbar, sacral, coccygeal
What happens when function is impaired in sensory, autonomic and motor nerves
- 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
What is a EMG
• EMG - technique for evaluating and recording electrical activity produced by muscles. Electromyogram produced
Can be surface or intramuscular emg
What is a SEP
• SEP are measured to assess whether sensations (pain, temperature and touch) in the periphery are being transmitted to the brain
Stimulating electrode on limb and recording electrode on head or neck
What is a nerve conduction study
Determines conduction velocity
One electrode stimulates nerves and another nerve defects this impulse further along nerve
• 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
