Peripheral Nervous System Flashcards
What are the divisions of the autonomic branch of the peripheral nervous system?
Visceral divides into motor and sensory. Motor divides into sympathetic and parasympathetic
What are the three characteristics of the somatic nervous system?
Supplies somatic (body wall) structures: skin, muscle, bone, parietal membranes (contact with body wall, innervated same)
Motor: skeletal muscle for voluntary control with the exception of the reflex arc (bypass conscious control)
Sensory: pain (direct from site of injury, sharp, focussed, well localized), temperature, touch, proprioception
What are the three characteristics of the autonomic nervous system?
Supplies viscera (internal organs): glands, smooth muscle, cardiac muscle, visceral membranes (contact body organs), involuntary or autonomous control
Motor: sympathetic and parasympathetic
Sensory: visceral afferents (pain) which is stretch and ischemia (lack of O2 at organs), vague, ill defined and ache like, perceived as indirect or referred pain, usually referred to the dermatomes
What is the difference between spinal nerves and cranial nerves?
Spinal nerves emerge from the spinal cord, and cranial nerves emerge from the area of the brainstem
How many pairs of spinal nerves are there? How do they correlate to the vertebra?
31 pairs
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
There is one more cervical vertebra than cervical spinal nerve because all cervical spinal nerves emerge above their corresponding vertebra until C7, where the C8 spinal nerve emerges below the C7 vertebra and from that point down all spinal nerve emerge below their corresponding vertebra
What is the classification of spinal nerves in terms of afferents and efferents?
General afferents: somatic afferents (PTTP from body wall) and visceral afferents (pain, distention, chemical)
General efferents: somatic efferents (motor neurons in ventral horn projecting to skeletal muscles) and visceral afferents (autonomic fibres innervating smooth muscle, cardiac muscle, and glands)
What is the portion of the spinal cord that contains the sensory neurons?
Sensory information comes into the spinal cord via the dorsal and ventral primary ramus, into the spinal nerve, then to the dorsal root ganglion (contains cell bodies) and then to dorsal root, and then dorsal horn and up to the brain
What is the portion of the spinal cord that contains the motor neurons?
Motor information comes down from the brain into the ventral horn, then into the ventral root, and then into the spinal nerve which bifurcates into the dorsal and ventral primary ramus and out to skeletal muscle
What happens after the spinal nerve bifurcates into the dorsal and ventral primary ramus?
The dorsal primary ramus goes out to cutaneous region to form posterior cutaneous branch (supplies the skin) and the ventral primary ramus forms the anterior cutaneous branch and lateral cutaneous branch
Both the anterior, posterior and lateral cutaneous branches meet up and thus one spinal nerve innervates one strip of skin around the body
Where do the spinal nerves emerge from the spinal cord?
Intervertebral foramen: emerges here then bifurcates into the dorsal and ventral primary rami
What is within the structure of a spinal nerve?
Epineurium: surrounds entire nerve (all fascicles)
Perineurium: surrounds each individual fascicle
Endoneurium: surrounds each individual axon
Nerve to fascicle to axon
Blood vessels between all fascicles
What are the 5 steps in the reflex arc? What is the purpose of the reflex arc?
Step 1: Arrival of stimulus and activation of receptor in periphery
Step 2: Activation of sensory neuron (through DRG, DR, dH)
Step 3: Processing of information in the CNS (synapse on second order neuron)
Step 4: Activation of motor neuron
Step 5: Response by effector
Intense stimuli coming into spinal cord bypasses brain to get fast response and protect the body from pain
What are dermatomes?
Strips of the body that are innervated by one spinal nerve
Upper and lower extremities are continuation of the body wall innervation
Dermatomes do not change as we grow
Dorsal primary rami: innervates specific organs and ventral does not
What do the three somatic nerve plexuses innervate?
Brachial plexus: upper extremity
Lumbar plexus: lower anterior abdominal wall, medial and anterior thigh, inguinal region
Lumbosacral plexus: lower extremity, gluteal region, perineum and genitals
What are the spinal nerves involved in the brachial plexus? Do they come from ventral or dorsal primary rami? And what are the 5 main nerves they aggregate into?
Ventral primary rami of C5, C6, C7, C8 and T1
Axillary, median, musculocutaneous, radial, ulnar
What are the spinal nerves involved in the lumbar plexus? Do they come from ventral or dorsal primary rami? And what are the 6 main nerves they aggregate into?
Which of these main nerves form the reflex arc?
Ventral primary rami of L1, L2, L3 and L4
Iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral and obturator
Reflex arc: ilioinguinal and genitofemoral
What are the spinal nerves involved in the lumbosacral plexus? Do they come from ventral or dorsal primary rami? And what are the 6 main nerves they aggregate into?
Ventral primary rami of L4, L5, S1, S2, S3
Tibial, common peroneal, superior gluteal, inferior gluteal, pudendal, posterior femoral cutaneous
What are the two divisions of the motor portion of the autonomic nervous system? What are their other names and what areas of the spinal cord do they correlate to?
Sympathetic: thoracolumbar, T1-L2, fight, flight, fright
Parasympathetic: craniosacral, CN III, VII, IX, X and S2,S3,S4, rest, relax and regenerate
What is the neuronal organization of the synapse in the somatic motor system?
One axon emerges from the CNS and travels to effector site
COMMON FINAL PATHWAY
1 neuron synapse
What is the neuronal organization of the synapse in the autonomic nervous system?
2 neurons synapse
Preganglionic fibre: from CNS to autonomic ganglion
Postganglionic fibre: from ganglion to effector site
What is the difference in the 2 neuron system between the sympathetic and parasympathetic NS?
Sympathetic: ganglion is close to/ next to the spinal cord, therefore preganglionic neuron is SHORT, post is long
Parasympathetic: ganglion is close to effector tissue, therefore preganglionic neurons is LONG, post is short
What are some characteristics of the sympathetic nervous system?
Innervates all organ systems and SKIN
SKIN: contains erector pili/ sweat/ sebaceous/ adipose tissue that all need sympathetic innervation
Sympathetic chain ganglia: the string of ganglia all along the spinal cord due to innervation of skin everywhere on body
Where is the break between what part of the vertebra (in sympathetic NS) innervates supradiaphragmatic or subdiaphragmatic structures?
T5 is the break, subdiaphragmatic structures are innervated by nerves below T5 (T1-T5) and supradiaphragmatic are innervated by those above (T5-L2)
What are the 8 main sympathetic actions?
Eye: pupil dilation
Trachea/bronchioles: dilation
Salivary glands: thick viscid secretion (dry mouth)
Heart: increase rate and contractility
Ureters and bladder: relax detrusor, contract trigone/ sphincter
Genitals: male ejaculation, females uterus relaxes
GI: decrease motility and tone, contract sphincter
Blood vessels: skeletal muscle dilate, viscera constrict
What are some characteristics of the parasympathetic NS?
Supplies same organs as sympathetic EXCEPT THE SKIN
Splanchnic nerves contain preganglionic axons
Why does the parasympathetic NS not innervate the skin?
We do not need fine control of accessory skin structures, sufficient to have a mechanism to turn them on and off (sympathetic)
What are the 8 major parasympathetic actions?
Eye: pupil constrict, accommodation reflex (eyes move medial, lens changes shape, pupils constrict)
Trachea/bronchioles: constrict and increase secretion
Lacrimal glands: stimulate tears
Salivary glands: copious watery secretion
Heart: decrease rate and contractility
Ureters and bladder: contract detrusor, relax trigone/ sphincter
Genitals: stimulates erection
GI: increase motility and tone, contract sphincter
What are the two pathways that help shunt post ganglionic sympathetic neurons to the skin? Why are they named as such?
White ramus communicans: communication between spinal nerve and the sympathetic ganglion, more myelin
Gray ramus communicans: gets the postganglionic neurons from the ganglion back into the spinal cord to it can go to the skin (body wall)
What is the pathway for the sympathetic neurons going to the supradiaphragmatic organs?
Preganglionic neurons go out of the spinal cord via the ventral horn, ventral root, spinal nerve to the sympathetic ganglion where it synapses onto post ganglionic neurons and these are sent to the specific tissues
What is the pathway for sympathetic neurons going to the subdiaphragmatic organs?
Preganglionic neurons leave spinal cord via ventral horn, ventral root, spinal nerve to sympathetic ganglion where they DO NOT synapse and instead pass right through into the splanchnic nerve which go to the abdominal aortic ganglion where they synapse and branch to the fore/mid/ hind gut ganglion
What controls both autonomic motor systems?
Hypothalamus
What is the pathway of general visceral afferents in comparison to the efferents?
They follow the exact same pathway as the motor afferents back to the brain
How is sensory information received in the brain?
It is received in the brain in terms of which area of the spinal cord is innervating it, for example T1-T5 innervates many sensory structures in the head (eye, glands, heart and lungs), so when sensory info from these are in the brain the brain reads them as sensory info from T1-T5 and the sensory homunculus reads it like this
Referred pain
