Innervation Flashcards
Extrinsic and Intrinsic Inervation
Extrinsic innervation:
- motor impulses & sensory info to CNS
- structures including abdominal part of GI tract, spleen, pancreas, gallbladder, liver
- visceral efferent fibers: part of sympathetic and parasympathetic parts of autonomic division
Components:
- posterior and anterior roots of spinal cord
- spinal nerves
- anterior rami
- white and grey rami comminicantes
- sumpathetic trunks
- splanchnic nerves,
- parasympathetic fibers
- prevertebral plexus
- related ganglia
- vagus nerve
Intrinsic innervation:
- self-sufficient network of sensory and motor neurons ENTERIC NERVOUS SYSTEM
- consists of motor and sensory neurons
Sympathetic trunk
Sympathetic trunks
two parallel nerve cords extending on either side of vertebral column
- Upper thorax: anterior to necks of ribs
- Lower thorax: lateral aspect of vertebral bodies
- Abdomen: anterolateral to lumbar vertebral bodies
2 trunks come together anterior to coccyx to form ganglion impar
- Small raised areas (collection of neuronal cell bodies aka ganglia:
- 3 cervical
- 11-12 thoracic
- 4 lumbar
- 4-5 sacral
- GANGLION IMPAR anterior to the coccyx
Ganglia and trunks are connected to adjacent spinal nerves by
- gray rami communicantes throughout length of sympathetic trunk
- white rami communicantes in the thoracic and upper lumbar parts (t1 to L2)
Neuronal fibers found in sympathetic trunks:
- preganglionic & post-ganglionic sympathetic fibers
- visceral afferent fibers
Splanchnic Nerves
- They are an important component in the innervation of abdominal viscera
- hey pass from sympathetic trunk or sympathetic ganglia to the prevertebral plexus and ganglia, anterior to the abdominal aorta
- 2 different types dependant on the type of visceral efferent fiber
- thoracic, lumbar and sacral splanchnic carry preganglionic sympathetic fibers to the ganglia in the preventable plexus and visceral afferent fibers
- pelvic splanchnic nerves carry preganglionic parasympathetic fibers from anterior rami of S2 S3 and S4 spinal nerves to an extension of the prevertebrae pleaxus in the pelvis ( aka inferior hypogastric plexus or pelvic plexus)
Thoracic Splachnic Nerves
Pass from sympathetic ganglia along the sympathetic trunk in the thorax to the prevertebal plexus and ganglia associated with the abdominal aorta in the abdomen
- greater splanchnic nerve: from T5-T9 to celiac ganglion in the abdomen
- lesse splanchnic nerve: from T9-T10 to aorticorenal ganglion
- least splanchnic nerve: from T12-renal plexus ( can sometimesnot be present)
Lumbar and sacral splanchic nerves
There are two to four lumbar splanchic nerves;
- pass from the lumbar part of sympathetic trunk and enter the prevertebral plexus
The sacral splanchnic nerves pass from sacral trunk and enter the inferior hypogastric plexus ( which is an exention of the prevertebrae plexus)
Parasypathetic trunks
Pelvic splanchnic nerves
- They are the only splanchnic nerves with parasympathetic root
- they do not orignate from the sympathetic trunk but they originate directly from anterior rami s2-s4
- The ones that originate in sacral spinal cord, pass from the S2 to S4 spinal nerves to the inferior hypogastric plexus
- once in the plexus some of the fibers pass upwards –> enter the abdominal prevertebrae plexus ang distribute with the arteries supplying the hindgut
- This provides innervation of distal one third of the transverse colon, descending colon , sigmoid colon by the preganglionic parasympathetic fibers
Vagus Nerve
- It enters the abdomen associated with esophagus as it enters the diaphragm
- provide parasympathetic innervation to foregut and mindgut
- entering the abdomen as the anterior and posterior vagal trunks –> they send branches to abdominal prevertebral plexus
- which are distributed with the other components of the prevertebral plexus
Abdominal preverterbral plexus and ganglia
- It is a collection of nerve fibers that surrounds the abdominal aorta and is continuous into its major structures
- Scattered throughout the lenght of the abdominal prevertabral plexus are cell bodies of postganglionic sympathetic fibers
- Plexuses and ganglia are named according to the associated blood vessels they are associated with (e.g. coeliac plexus and ganglia, renal plexus and ganglia).
- *Plexus = interconnecting network of nerves (or vessels)
3 major divisions:
Celiac plexus:
- large accumulation of nerve fibers associated with roots of the celiac trunks and superior mesenteric artery
- below the aortic hiatus of diaphragm
- associated ganglia: 2 celiac ganglia, a single superior mesenteric ganglion, 2 anticorenal ganglia
Aortic plexus:
- nerve fibers and associated ganglia on anterior and lateral surfaces of abdominal aorta
- extending just below the origin of the superior mesenteric artery to the bifurcation of the aorta into the two common iliac arteries
- The major ganglion in the plexus is the inferior mesenteric ganglion, at the root of the inferior mesenteric artery.
Superior Hypogastric plexus;
- contains numerous small ganglia
- It is the first part of the abdominal prevertebral plexus before it continues into the pelvic cavity
- Each of these plexuses gives origin to a number of secondary plexuses
- they are usually named after the vessels that they area ascociated
ex. the celiac plexus gives rise to;
- superior meseneric plexus
- renal plexus
Inferiorly the superior hypogastric plexus divides into the hypogastric nerves, which ascends into the pelvis and leads to the formation of the inferior hypogastric or pelvic plexus
The abdominal prevertebral plexus receices;
- pregangliotic parasympathetic and visceral afferent fibres from the vagus nerve
- pregangliotic sympathetic and visceral afferent fibres from the thoracic and lumbar splachnic
- pregangliotic parasympathetic and visceral afferent fibres from the pelvic splachnic
Enteric System
- it is a division of the visceral part of the nervous system
- it is a local neuronal circuit in the wall of the gastrointestinal tract
- consists of motor and sensory neurons
- organized into two interconnected plexuses (myenteric and submucosal)
- the enteric system regulates numerous gastrointiestinal activities ;
- basic reflex functions of secretion, absorption, mixing and gut movements without the influence of the central nervous system (CNS) or autonomic nervous system (ANS)
- However, the CNS via the sympathetic and parasympathetic nerves communicate with the intrinsic neurones of the ENS and bring about modulation GI tract functions
- ex. sympathetic innervation of the stomach
Referred pain
The cerebral cortex of the brain has no ‘sensory map’ for visceral organs and diaphragm
Therefore, the brain cannot localise pain sensation from these structures.
In these cases, pain is referred to the regions of skin supplied by nerves with the same segmental supply (dermatomes).
In the abdomen, the nerve supply to the organs is autonomic
Dermatomes
Definition: An area of skin supplied by a single spinal nerve (i.e. single segment of the spinal cord)
Adjacent dermatomes overlap so that on the trunk, at least three spinal nerves would have to be blocked to produce a region of complete anaesthesia
Epigastric pain: pain from foregut structures (as far as duodenal papilla) is referred to this region.
Structures involved: Stomach, proximal duodenum, pancreas, liver, gall bladder.
Umbilical pain: pain from midgut structures (from duodenal papilla to splenic flexure) including inflamed appendix referred to periumbilical region. It is usually colicky (intermittent with bowel contractions
When the inflammation of the appendix spreads to the surrounding peritoneum the pain becomes localized and constant at the right inguinal region.
Movement of the hip joint, coughing elicits pain.
Suprapubic (hypogastric) pain: pain from hindgut structures, descending colon to anal canal is referred here
Lumbar Plexus
- It is formed by the anterior rami of nerves L1 to L3 and most of the anterior ramus of L3
- It receives contribution from T12 (subcostal nerve)
- It forms in the substance of the psoas major muscle anterior to its attachment to the transverse processes of the lumbar vetrabrae
- anterior: genitofemoral
- medial: obturator
- lateral: iliohypogastric, ilioinguinal, femoral nerves & lateral cutaneous nerve of the thigh
Iliohypogastric and ilioinguinal nerves
- Arise as a single trunk at L1
- before or soon after psoas major they divide
- Iliohypogastric nerve
- passes across anterior surface of quadratus lumburum posterior to the kidney
- pierces transversus abdominis and continues anteriorly between that and internal oblique
- above iliac crest, lateral cutaneous branch pierces internal and external oblique
- anterior cutaneous branch: continuous anteriorly to pubic region
- Ilioinguinal;
- smaller and inferior to the iliohypogastric
- it pierces through the transverse abdominis muscle and then pierces the internal oblique and enters the inguinal canal
- provides cutaneous innervation to the anterior surface of the scrotum in men or the mons pubis in women
- it also supplies branches of the abdominal masculature
Genitofemoral
originates from anterior rami L1 and L2
Motor function;
male cremasteric muscle
Sensory function;
genital branch; skin of anterior scrotum or skin of mons pubis and labium majus
femoral branch
skin of upper anterior thigh
