The PNS Flashcards
The Somatic Nervous System
- supplies somatic (body wall) structures - skin, muscle, bone, parietal membranes
- motor (skeletal muscle - voluntary control) (exception = reflex arc)
- sensory - pain (direct, sharp, focussed and well-localized), temperature, touch, proprioception
The Autonomic Nervous System
- supplies viscera (internal organs) - glands, smooth muscle, cardiac muscle, visceral membranes (involuntary control)
- motor (sympathetic and parasympathetic)
- sensory - visceral afferents = pain (stretch or ischemia, indirect or referred, usually referred to the dermatomes
Spinal Nerves
emerge from the spinal cord (superior to respective vertebrae in cervical region, inferior to vertebrae in thoracic - coccygeal regions) 31 pairs: - 8 cervical - 12 thoracic - 5 lumbar - 5 sacral - 1 coccygeal
Cranial Nerves
emerge from the area of the brain stem
General Afferents
Somatic Afferents (GSA) & Visceral Afferents (GVA)
Somatic Afferents (GSA)
pain, temperature, touch, proprioception (PTTP) from body wall
Visceral Afferents (GVA)
pain, distension, chemical from visceral structures
- sensory info input = dorsal root –> dorsal horn
- info returns to same region that it was initiated (ie. T1-T5)
General Efferents
Somatic Efferents (GSE) & Visceral Efferents (GVE)
Somatic Efferents (GSE)
motor neurons in ventral horn projecting to skeletal muscles
Visceral Efferents (GVE)
autonomic fibres innervating smooth muscle, cardiac muscle, and glands
Intermediate Zone (Autonomic)
AKA Lateral Horn - pertuberance of spinal cord
Ventral Primary Ramus
anterior branch of spinal nerve (PNS), travels along rib
Dorsal Primary Ramus
posterior branch of spinal nerve (PNS), passes through & innervates musculature
Dorsal Horn
sensory input
Ventral Horn
motor output
Anterior Cutaneous Branch
spinal nerve branch (skin innervation)
Lateral Cutaneous Branch
spinal nerve branch (skin innervation)
Posterior Cutaneous Branch
spinal nerve branch (skin innervation)
Intervertebral Foramen
window between vertebrae that spinal nerve innervates - follows rib around the body
Epineurium
coating around the entire spinal nerve
Perineurium
coating around the individual fascicles of a spinal nerve - each fascicle responsible for particular type of info
Endoneurium
coating around the individual axons of a spinal nerve
Reflex Arc
a strong enough pain signal coming from receptor is able to bypass brain by collateral of secondary motor neuron - still processed by brain but not required for movement
Step 1 - arrival of stimulus and activation of receptor
Step 2 - activation of a sensory neuron
Step 3 - information processing in CNS
Step 4 - activation of a motor neuron
Step 5 - response by effector
Dermatomes
each strip of skin corresponds to a specific spinal nerve
- nerves grow longer to maintain the original point of contact despite growth of the body
Somatic Nerve Plexuses
Plexus = network of nerve
- Brachial Plexus
- Lumbar Plexus
- Lumbosacral Plexus
Brachial Plexus
innervates upper extremity C5, C6, C7, C8, and T1 Creates 5 main nerves: 1. Axillary 2. Median 3. Musculocutaneous 4. Radial 5. Ulnar
Lumbar Plexus
innervates lower anterior abdominal wall, medial and anterior thigh, inguinal region L1, L2, L3, L4 Creates 6 main nerves: 1. Iliohpogastric 2. Ilioinguinal 3. Genitofemoral 4. Lateral Femoral Cutaneous 5. Femoral 6. Obturator
Lumbosacral Plexus
innervates gluteal region, lower extremity, perineal region and genitals L4, L5, S1, S2, S3 Creates 6 main nerves: 1. Tibial 2. Common Peroneal 3. Superior Gluteal 4. Inferior Gluteal 5. Pudendal 6. Posterior Femoral Cutaneous
Autonomic Motor Nerves
Sympathetic - Thoracolumbar - T1-L2
Parasympathetic - Craniosacral - CN III, VII, IX, S2, S3, S4
Somatic Motor System
one axon emerges from CNS –> effector site
“common final pathway”
Autonomic Motor System
“2 neuron system”
- Preganglionic Fibre (from CNS –> autonomic ganglion)
- Postganglionic Fibre (from ganglion to the effector site)
Sympathetic Nervous System
short preganglionic, long postganglionic
- form sympathetic chain ganglia to pass info to regions not normally mediated by T1 - L2
- ganglion relatively close to spinal cord
- splanchnic nerves
Parasympathetic Nervous System
long preganglionic, short postganglionic
- no skin supply
Sympathetic Actions
- pupil dilation
- trachea and bronchiole dilation
- salivary glands secrete thick, viscid fluid
- increased heart rate and contractility
- contraction of anal sphincter
- decreased gastrointestinal motility and tone, contract sphincter
- stimulation of ejaculation, uterus relaxes
- skeletal muscles dilate, viscera constrict
Parasympathetic Actions
- pupils constrict, accommodation reflex
- trachea and bronchioles constrict, increased secretion
- tears stimulation (lacrimal glands)
- salivary glands secrete water (copious)
- relaxation of anal sphincter
- decreased heart rate and contractility
- increased gastrointestinal motility and tone
- erection (both sexes)
Sympathetic Chain
motor info output
ventral horn –> spinal nerve –> white ramus communicans –>
a. supradiaphragmic organs = ganglion (T1-T5)
b. infradiaphragmic organs = splanchnic nerve
c. sympathetic trunk (moves info to all spinal nerves)
d. Gray ramus communicans (–>peripheral)
Splanchnic Nerve
innervates organs below the diaphragm, synapses along a major artery/blood vessel
- postganglionic nerve then follows along blood vessel to destination (organ)
White Ramus Communicans
white communicating branch where sympathetic spinal nerve branches off to the sympathetic chain
white because myelinated
Gray Ramus Communicans
where sympathetic postganglionic nerve from sympathetic chain rejoins spinal nerve
gray because not as myelinated as white ramus communicans
Autonomic Motor Command Centre
Hypothalamus
- not under conscious control
Greater Splanchnic Nerve
T5-T9
Lesser Splanchnic Nerve
T10-T11
Sensory Homunculus
interpretation according to which spinal nerve input is coming from
- correspons to general (autonomic) pain
