Anatomy 18.1-Peripheral-nervous-system cranial-nerves
Transcript of Anatomy 18.1-Peripheral-nervous-system cranial-nerves
The Department of Human anatomy
Peripheral nervous system.The Cranial Nerves Part - 1
Plan
The peripheral nervous system- Structural Organization
spinal nerves cranial nerves ganglia
The peripheral nervous system (PNS) consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system (CNS) to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain barrier, leaving it exposed to toxins and mechanical injuries. The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system.
Nervous System: Structural Organization
Structural subdivisions of the nervous system: Central nervous system (CNS)
brain and spinal cord Peripheral nervous system (PNS)
cranial nerves (nerves that extend from the brain) spinal nerves (nerves that extend from the spinal
cord) ganglia (clusters of neuron cell bodies (somas)
located outside the CNS)
Functional Organization of the PNS
Figure 14.1
Spinal Nerves 31 pairs – contain thousands of nerve
fibers Connect to the spinal cord
8 pairs of cervical nerves (C1-C8)12 pairs of thoracic nerves (T1-T12)5 pairs of lumbar nerves (L1-L5)5 pairs of sacral nerves (S1-S5)1 pair of coccygeal nerves (Co1)
Spinal Nerves Posterior View
Figure 14.9
Spinal Nerves Posterior root– contains
sensory fibers Anterior root– contains
motor fibers Just outside the spinal
cord there is a spinal ganglion consisting of nerve cells
Anterior and posterior roots join to form mixed spinal nerve
Outside the intervertebral foramen the spinal nerve divides into :1. Ramus communicans (white and gray)2. Ramus dorsalis3. Ramus ventralis
4. Ramus meningeus
Innervation of the Skin: Dermatomes Dermatome – an area of skin
Innervated by cutaneous branches of a single spinal nerve
Upper limb – skin is supplied by nerves of the brachial plexus
Lower limb Lumbar nerves – anterior surfaceSacral nerves – posterior surface
Map of Dermatomes – Anterior View
Figure 14.17a
Map of Dermatomes – Posterior View
Figure 14.17b
The plexusesForms by ventral rami
Cervical plexus Brachial plexus Lumbar plexus Sacral plexus Coccygeal plexus
Thoracic ventral rami do not form nerve plexuses
Cervical plexus (C1-C4) innervates the muscles and skin of the neck and shoulder
most important:Its phrenic nerve* (C3-C5) is the sole motor supply of diaphragm: one reason why neck injuries are so dangerous – can be lethal (respiratory arrest = stop breathing)
Brachial plexus Serves upper limbs
and shoulder girdle Arises primarily from
C5-T1 Main nerves:
Musculocutaneous – to arm flexors
Median – anterior forearm muscles and lateral palm
Ulnar – anteromedial muscles of forearm and medial hand
Axillary – to deltoid and teres minor
Radial – to posterior part of limb
Musculo-cutaneous
Median
Ulnar
Axillary
Radial
Lumbar plexus
L1-L4 Lies within the psoas major muscle Innervates anterior and medial muscles of
thigh through femoral and obturator nerves respectively
Femoral nerve also innervates skin on anterior thigh (including quads) and medial leg
Sacral plexus L4-S4 Supplies muscles
and skin of posterior thigh and almost all of the leg
Main branch is the large sciatic nerve,
Coccygeal plexus
This plexus is formed by the fifth sacral nerve (with a contribution from S4) and the coccygeal nerve. It gives rise to the anococcygeal nerve (provides sensory innervation to the skin over the coccyx)
Names of cranial nerves
Ⅰ Olfactory nerve Ⅱ Optic nerve Ⅲ Oculomotor nerve Ⅳ Trochlear nerve Ⅴ Trigeminal nerve Ⅵ Abducent nerve Ⅶ Facial nerve Ⅷ Vestibulocochlear nerve Ⅸ Glossopharyngeal nerve Ⅹ Vagus nerve Ⅺ Accessory nerve Ⅻ Hypoglossal nerve
Classification of cranial nerves Sensory cranial nerves: contain only afferent (sensory) fibers
ⅠOlfactory nerve ⅡOptic nerve Ⅷ Vestibulocochlear nerve
Motor cranial nerves: contain only efferent (motor) fibers Ⅲ Oculomotor nerve Ⅳ Trochlear nerve ⅥAbducent nerve Ⅺ Accessory nerv Ⅻ Hypoglossal nerve
Mixed nerves: contain both sensory and motor fibers--- ⅤTrigeminal nerve, Ⅶ Facial nerve, ⅨGlossopharyngeal nerve ⅩVagus nerve
Cranial Nerve I: Olfactory Arises from the olfactory epithelium Passes through the cribriform plate of the ethmoid bone Fibers run through the olfactory bulb and terminate in the
primary olfactory cortex (uncus) Functions solely by carrying afferent impulses for the sense of
smell Lesions result in ANOSMIA
Cranial Nerve II: Optic Arises from the retina of the
eye Optic nerves pass through the
optic canals and converge at the optic chiasm
They continue to the thalamus where they synapse
From there, the optic radiation fibers run to the visual cortex
Functions solely by carrying afferent impulses for vision
Cranial Nerve III: Oculomotor Fibers extend from the ventral midbrain, pass
through the superior orbital fissure, and go to the extrinsic eye muscles
Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape
The latter 2 functions are parasympathetically controlled
Parasympathetic cell bodies are in the ciliary ganglia
Cranial Nerve III: Oculomotor
Figure III from Table 13.2
Cranial Nerve IV: Trochlear
Fibers emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures; innervate the superior oblique muscle
Primarily a motor nerve that directs the eyeball
Cranial Nerve IV: Trochlear
Figure IV from Table 13.2
Cranial Nerve V: Trigeminal Composed of three divisions
Ophthalmic (V1) Maxillary (V2) Mandibular (V3)
Fibers run from the face to the pons via the superior orbital fissure (V1), the foramen rotundum (V2), and the foramen ovale (V3)
Ophthalmic nerve Sensory from the eyes,
conjunctiva and orbital contents including the lacrimal gland
Maxillary nerve Sensory branches from
anterior and middle cranial fossa, nasopharynx, palate, nasal cavity, teeth of the upper jaw, maxillary sinus, skin of the side of the nose, lower eyelid, cheek, upper lip
Mandibular nerve Motor fibers innervate
muscles of mastication, tensor tympani, anterior belly of digastric
Sensory fibres from the skin of the lower face, cheek, lower lip, ear, external auditory meatus and temporal region, anterior two thirds of the tongue, teeth of the lower jaw, mastoid air cells, mucous membrane and dura in the middle cranial fossa
Lesion involves loss of sensation, weakness in chewing, Jaw deviation towards the affected side
(Tic douloureux) or trigeminal neuralgia
- Most excruciating pain known
- Caused by inflammation of nerve
- In severe cases, nerve is cut; relieves agony but results in loss of sensation on that side of the face
Cranial Nerve VI: Abducens Fibers leave the inferior pons and enter the orbit
via the superior orbital fissure Primarily a motor nerve innervating the lateral
rectus muscle (abducts the eye; thus the name abducens)
Cranial Nerve VII: Facial
Fibers leave the pons, travel through the internal acoustic meatus, and emerge through the stylomastoid foramen to the lateral aspect of the face
Motor functions include; Facial expression Transmittal of parasympathetic impulses to
lacrimal and salivary glands (submandibular and sublingual glands)
Sensory function is taste from taste buds of anterior two-thirds of the tongue
Cranial Nerve VII: Facial
Figure VII from Table 13.2
Facial Nerve (CN VII) Bell’s palsy: paralysis of facial
muscles on affected side and loss of taste sensation
Caused by herpes simplex I virus Lower eyelid droops Corner of mouth sags Tears drip continuously and eye
cannot be completely closed (dry eye may occur)
Condition may disappear spontaneously without treatment
Cranial Nerve VIII: Vestibulocochlear Fibers arise from the hearing and equilibrium
apparatus of the inner ear, pass through the internal acoustic meatus, and enter the brainstem at the pons-medulla border
Two divisions – cochlear (hearing) and vestibular (balance)
Functions are solely sensory – equilibrium and hearing
Cranial Nerve VIII: Vestibulocochlear
Figure VIII from Table 13.2
Cranial Nerve IX: Glossopharyngeal Fibers emerge from the medulla, leave the skull
via the jugular foramen, and run to the throat Nerve IX is a mixed nerve with motor and
sensory functions Motor – innervates posterior 1/3 of the tongue
and pharynx, and provides motor fibers to the parotid salivary gland
Sensory – fibers conduct taste and general sensory impulses from the tongue and pharynx
Cranial Nerve IX: Glossopharyngeal
Figure IX from Table 13.2
Cranial Nerve X: Vagus
The only cranial nerve that extends beyond the head and neck
Fibers emerge from the medulla via the jugular foramen
The vagus is a mixed nerve Most motor fibers are parasympathetic fibers to
the heart, lungs, and visceral organs Paralysis leads to hoarseness Total destruction incompatible with life
Cranial Nerve X: Vagus
Cranial Nerve XI: Accessory Formed from a cranial root emerging from the
medulla and a spinal root arising from the superior region of the spinal cord
The spinal root passes upward into the cranium via the foramen magnum
The accessory nerve leaves the cranium via the jugular foramen Innervates the trapezius and sternocleidomastoid,
which move the head and neck
Cranial Nerve XI: Accessory
Figure XI from Table 13.2
Cranial Nerve XII: Hypoglossal
Fibers arise from the medulla and exit the skull via the hypoglossal canal
Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech
If damaged, difficulties in speech and swallowing; inability to protrude tongue
Cranial Nerve XII: Hypoglossal
Figure XII from Table 13.2