Sacral Plexus and Sciatic Nerve Overview

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Questions and Answers

What is the main function of the sciatic nerve?

Exclusively sensory with no motor functions

Only for proprioception in the thigh

Primarily sensory with some motor innervation (correct)

Only motor innervation of the leg

Which muscles does the sciatic nerve innervate?

Adductor longus muscle only (correct)

Piriformis and quadratus femoris

All muscles in the gluteal region

Both gluteus maximus and medius

Where does the sciatic nerve typically bifurcate?

Above the knee joint

In the upper thigh at the superior corner of the popliteal fossa (correct)

At the level of the sacroiliac joint

Right as it exits the greater sciatic foramen

What is a common cause of sciatica?

Compression of the sciatic nerve due to herniated disc Signup and view all the answers

What anatomical structure does the sciatic nerve emerge from?

Greater sciatic foramen Signup and view all the answers

What is the average width of the sciatic nerve?

2 cm Signup and view all the answers

Which of the following nerves is NOT a branch of the sacral plexus?

Brachial nerve Signup and view all the answers

What role do olfactory ensheathing cells play in the nervous system?

They support the re-growth of axons in the olfactory nerve. Signup and view all the answers

Which of the following conditions is characterized by the detection of non-existent smells?

Phantosmia Signup and view all the answers

What is the relationship between the optic chiasm and visual defects related to hypophyseal tumors?

Compression of the optic chiasm can lead to visual defects. Signup and view all the answers

Why is it challenging to regenerate axons in the optic nerve after injury?

Oligodendrocytes do not support regeneration. Signup and view all the answers

What important function is associated with the uncinate fasciculus in the human brain?

It connects parts of the limbic system with frontal lobe regions. Signup and view all the answers

What is the result of a cut sciatic nerve?

Complete insensitivity below the knee except for the medial malleolus to the big toe Signup and view all the answers

What clinical sign is used for diagnosing sciatica?

Lasegue sign Signup and view all the answers

Which nerve is primarily affected in cases of 'foot drop'?

Common peroneal nerve Signup and view all the answers

What might occur if the sciatic nerve is tied to an artery during amputation?

Severe sciatic stump pain Signup and view all the answers

What is a potential outcome of a lesion in the upper gluteal nerve?

Positive Trendelenburg sign Signup and view all the answers

Which area does the common peroneal nerve provide sensory information to?

Lateral compartment of the leg and dorsum of foot Signup and view all the answers

What causes paresthesia around the third and fourth toes?

Pressure on the digital nerves from tight shoes Signup and view all the answers

What happens when the tibial nerve is lesioned?

Inability to flex the toes and plantar flex the foot Signup and view all the answers

Where does the tibial nerve branch off from?

Unified sciatic nerve Signup and view all the answers

What is the primary function of the pudendal nerve?

Supplies motor function to perineal muscles and sensation to external genitalia Signup and view all the answers

Which nerve is primarily responsible for sensation in the inferior surface of the buttock?

Posterior femoral cutaneous nerve Signup and view all the answers

What anatomical structure is primarily innervated by the coccygeal plexus?

Muscles of the perineum Signup and view all the answers

Which cranial nerve is responsible for the sensation of taste from the posterior third of the tongue?

Glossopharyngeal nerve (CN IX) Signup and view all the answers

What is the consequence of a lesion in the superior gluteal nerve?

Weakness during hip abduction and extension Signup and view all the answers

The hypoglossal nerve primarily affects which of the following functions?

Movement of the tongue Signup and view all the answers

Which statement best describes the function of cranial nerve III (oculomotor nerve)?

Controls eye muscle movements and parasympathetic functions Signup and view all the answers

Damage to the trigeminal nerve affects which primary functions?

Sensory and motor functions of the jaw and face Signup and view all the answers

Which nerve does not emerge from the brainstem?

Olfactory nerve (CN I) Signup and view all the answers

What is the functional significance of the anal reflex during pudendal nerve anesthesia?

Confirms successful anesthesia and relaxation of pelvic muscles Signup and view all the answers

What is the role of the nervus terminalis in relation to luteinizing hormone-releasing hormone (LHRH) cells?

It facilitates the migration of LHRH cells to the hypothalamus. Signup and view all the answers

Which hormone is primarily released by the neurons associated with the nervus terminalis?

Luteinizing hormone-releasing hormone (LHRH) Signup and view all the answers

What is the significance of the axons of olfactory receptor cells converging in the olfactory bulb?

They create glomeruli that connect to olfactory bulb neurons. Signup and view all the answers

How do the peripheral unmyelinated fibers of Nerve 0 reach the olfactory mucosa?

They cross the lamina cribrosa medially. Signup and view all the answers

What distinguishes the structure of olfactory receptors found in the nasal epithelium?

They are bi-polar neurons with specialized cilia. Signup and view all the answers

Which area is primarily affected by the fibers of Nerve 0 as they project into the brain?

Medial olfactory stria and hippocampus Signup and view all the answers

What might be a result of an alteration in the function of the nervus terminalis?

Development of Kallmann's syndrome. Signup and view all the answers

Compare to other animals, how is human olfaction characterized?

Less efficient than in less evolved species. Signup and view all the answers

What happens to the vomeronasal organ in humans during development?

It regresses and becomes a developmental relic. Signup and view all the answers

Which structure is involved in the central pathway of olfactory processing?

Hippocampus Signup and view all the answers

Study Notes

Sacral Plexus

Formed from spinal nerves L4-S4, it gives rise to several nerves: sciatic, upper gluteal, lower gluteal, posterior cutaneous of the femur, and pudendal.
Sciatic nerve branches into the tibial nerve and common peroneal nerve; it is the largest nerve in the body, measuring about 2 cm wide.

Sciatic Nerve

Arises from L4-S3, primarily sensory but also has motor functions.
Emerges from the greater sciatic foramen and enters the gluteal region between the greater trochanter and ischial tuberosity.
Composed of common peroneal and tibial nerves; these typically separate at the popliteal fossa but can vary greatly in individual anatomy.
Does not innervate gluteal structures; primarily affects the adductor longus muscle.

Lesions of the Sciatic Nerve

"Sciatica" results from nerve compression, leading to pain and weakness in the thigh and leg.
Most commonly caused by herniated discs; other causes include tumors, trauma, or improper needle injections.
Diagnosed using Lasegue sign and leg raise test; a positive sign indicates nerve distress.
Severe injuries may result in paralysis and insensitivity below the knee, except for some areas innervated by the saphenous nerve.

Common Peroneal Nerve

Branches from the sciatic nerve at the popliteal fossa, innervating the lateral compartment of the leg and providing sensation to the dorsum of the foot.
Very superficial near the fibula, making it susceptible to trauma.
Lesions can lead to "foot drop," causing the foot to remain in plantar flexion.

Tibial Nerve

Also branches from the sciatic nerve; it runs posteriorly and innervates the posterior leg compartment and sole of the foot.
It is covered by muscles in the popliteal fossa and is the most superficial structure in this area.
Lesions may cause difficulties in plantar flexion, leading to a pes calcaneus gait.

Other Nerves from the Sacral Plexus

Upper gluteal nerve (L4-S1): Innervates gluteus minimus, medius, and tensor fascia lata. Lesions may lead to Trendelenburg sign and duck gait.
Lower gluteal nerve (L5-S2): Innervates gluteus maximus; lesions result in weakness during thigh extension.
Posterior femoral cutaneous nerve: Provides sensory innervation to the posterior thigh and buttocks.
Pudendal nerve (S2-S4): Innervates perineal muscles and provides sensation to external genitalia; local anesthesia is often applied during delivery.

Clinical Relevance

Injury to the pudendal nerve may affect pelvic floor functionality and cause pain during delivery.
The coccygeal plexus, also part of the sacral plexus, innervates pelvic floor muscles, and injuries can lead to perianal sensation loss.

Cranial Nerves Overview

Cranial nerves are essential for sensory functions such as smell, taste, vision, and motor functions related to facial movement, swallowing, and visceral regulation.
Key cranial nerves include the olfactory (CN I), optic (CN II), and others from III-XII, relating to eye movement, facial sensations, and functions of the heart and digestive system.

Nerve Zero

Also known as nerve N, located near the olfactory nerve; it plays a role in hormonal modulation and the olfactory system.
Involved in Kallmann's Syndrome, characterized by anosmia and altered gonadal functions.

Olfactory Nerve (CN I)

Critical for the sense of smell, with receptors embedded in the nasal epithelium.
Functions in detecting environmental chemicals and interpersonal communication via pheromones.### Olfactory System
Olfactory receptors form bundles of fibers grouped into 20 fascicles to enter the lamina cribrosa.
Thin axons (100-400 nm) are ensheathed by olfactory ensheathing cells, which possess properties of both Schwann and astroglial cells.
These ensheathing cells support axon regeneration, making them intriguing for experimental research, particularly in spinal cord injuries.
Despite the potential, studies involving spinal cord engraftment of these cells showed unsatisfactory results.
Fibroblasts associated with the dura mater are also present along the olfactory nerve.
Conditions affecting olfactory function include anosmia, phantosmia, and cacosmia, as well as uncinate crises — olfactory hallucinations tied to stimulation of the uncinate fasciculus.

Olfactory Pathway and Neurodegenerative Diseases

The olfactory pathway might serve as a route for neurodegenerative diseases, like Parkinson’s and Alzheimer’s, in line with Braak's hypothesis.
Anosmia is a common symptom of COVID-19, potentially due to viral infection of olfactory ensheathing cells leading to inflammation of olfactory nerves.

Optic Nerve

The optic nerve consists of axons from retinal ganglion cells, considered an extension of the central nervous system.
Axons are myelinated by oligodendrocytes rather than Schwann cells, making regeneration after injury unlikely.
The optic nerve originates from the optic disk, devoid of photoreceptors, known as the blind spot.
Exits the orbit from the Ring of Zinn, traversing the optic canal to reach the optic chiasm near the hypophysis.
At the optic chiasm, nasal retinal ganglion cell axons cross over, leading to contralateral representation of visual fields.
The optic tracts relay sensory information from opposite visual fields; right optic tract processes information from the left field.
A portion of the optic nerve is structurally sensitive to increased intraocular pressure, which can lead to damage and potential glaucoma-related degeneration of retinal ganglion cells.

Anatomical and Pathophysiological Considerations

The optic nerve is approximately 5 cm long and connects the eye to the brain, playing a critical role in vision.
Hypophyseal tumors can compress the optic chiasm, often revealing visual defects as an early symptom.
The lamina cribrosa, through which optic nerve fibers pass, supports these fibers as they exit the eye, but is more susceptible to pressure changes, contributing to damage if intraocular pressure rises.

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Description

This quiz covers the anatomy and function of the sacral plexus, including its origin from L4-S4 spinal nerves and the various nerves it forms, such as the sciatic nerve. It also delves into the sensory and motor roles of the sciatic nerve, making it essential for understanding lower limb innervation.