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Saturday, September 4, 2010

Cranial nerves

          There are 12 pairs of cranial nerves. The names of these nerves are following.



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

          These are classified into sensory, motor and mixed nerves according to their functions.
Sensory cranial nerves: These nerves contain only afferent (sensory) fibers.
They are given below.
Ⅰ Olfactory nerve
Ⅱ Optic nerve
Ⅷ Vestibulocochlear nerve

Motor cranial nerves: These nerves contain only efferent (motor) fibers.  
They are given below.
Ⅲ Oculomotor nerve
Ⅳ Trochlear nerve
Ⅵ Abducent nerve
Ⅺ Accessory nerve
Ⅻ Hypoglossal nerve

Mixed nerves: These nerves contain both sensory and motor fibers. 
They are given below.
Ⅴ Trigeminal nerve,
Ⅶ Facial nerve,
Ⅸ Glossopharyngeal nerve
Ⅹ Vagus nerve

  • Olfactory nerve (first cranial)
          It is purely sensory nerve. The sensory receptors of the olfactory nerve are located in the superior nasal conchae (ethmoid bone) of the nose. The olfactory filament arises from the sensory receptors which pass through the foramina in the cribriform plate of the ethmoid bone. The olfactory filament ends at the olfactory bulb which lies just above the cribriform plate. Olfactory bulb continues posteriorly as the olfactory tract. Olfactory tract ends at the floor of cerebrum just anterior to the optic chiasm. Olfactory tract then divides into two branches which proceed towards the temporal lobe of cerebrum. Temporal lobe of cerebrum contains the olfactory area which is responsible for the sense of olfaction.

  • Optic nerve (second cranial)
          It is purely sensory nerve. The sensory receptors of the optic nerve are located in the retina of the eye. The retina has two types of receptors: Rods are responsible for black and white vision and cons are responsible for color vision. Rods and cons then form synapses with bipolar cells which synapse with ganglion cells. Ganglion cells then converge to form optic nerve which leaves the eye and enters the superior orbital fissure. From the superior orbital fissure it comes just below the anterior clinoid process. Here above the pituitary fossa the nerves form crossover called optic chiasm. Fibers of the optic nerve on the medial side cross over to the opposite side at the optic chiasm and continue on the medial side of the other side. Fibers of the lateral side continue on the same side. Optic chiasm diverges posteriorly to form the optic tracts. From the optic tract proceeds posteriorly and ends at the medial and lateral geniculate nuclei located on both sides of the cerebral peduncles. Fibers from these nuclei proceeds further backwards and ends at the primary visual area located in the posterior part of the occipital lobe.

  • Oculomotor nerve (third cranial)
           It arises from the anterior surface of the med brain in between two cerebral peduncles. From the posterior cranial fossa it enters the lateral aspect of the petrous part of the temporal bone. Here it lies in a cave called cavernus sinus. From the middle cranial fossa it passes into the orbit through the superior orbital fissure. After emerging from the superior orbital fissure it divides into upper and lower branches.
          Upper branch innervates the superior rectus muscle and levator palpebrii superioris muscle while the lower branch innervates inferior rectus, medial rectus and inferior oblique muscles. Along the lower fibers the parasympathetic nerve fibers also enter which innervates the ciliary muscle (causing accommodation of lens) and sphincter papillae muscles (causing constriction of pupils).

  • Trochlear nerve (fourth cranial)
          It is the only cranial nerve arising from the posterior surface of the mid brain. From the posterior cranial fossa it enters the lateral aspect of the petrous part of the temporal bone. Here it lies in a cave called cavernus sinus. From the middle cranial fossa it passes into the orbit through the superior orbital fissure. With in the orbit the Trochlear nerve innervates the only superior oblique muscle.

  • Trigeminal nerve (fifth cranial)
          It arises from the anterior side of the Pons. It proceeds from the posterior cranial fossa into the middle cranial fossa along the lateral side of the petrous part of the temporal bone. Here in the cavernus cave the trigeminal nerve forms the trigeminal ganglion. The trigeminal ganglion gives off three branches of trigeminal nerve:
i. Ophthalmic nerve
ii. Maxillary nerve
iii. Mandibular nerve

Ophthalmic nerve (V1)
          It passes from the middle cranial fossa through superior orbital fissure. Below the roof of the orbit it gives off branches shown in the following figure.
Maxillary nerve (V2)
          It arises from the trigeminal ganglion passes from the middle cranial fossa into infra temporal fossa through the foramen rotundum. In the infra temporal fossa it divides into two branches; upper and lower branches.

          Infra orbital nerve from the upper branch passes through a tunnel called infra orbital groove in the floor of the orbit. It appears below the lower margin of the orbit and divides into three cutaneous branches:

Palpebral supplying the lower eyelid

Nasal supplying lateral part of nose

Labial supplying upper lips

          Anterior superior alveolar nerve of the lower branch also passes through the infra orbital groove along the infra orbital nerve and makes a turn posteriorly after emerging from the infra orbital foramen. Posteriorly it joins the posterior superior alveolar nerve which appears here after passing through bony tunnels in the maxilla. They form a loop like structure from which gives the superior dental and gingival nerves innervating the upper teeth and upper gums. Other branches of lower part of the maxillary nerve include palatine nerves (greater and lesser palatine nerves) which innervate mucosa of the hard, soft palate and nasal mucosa. Nasopalatine nerve innervates the nasal septum. Zygomatic nerve is also a branch of lower part of maxillary nerve which divides into frontal and temporal nerves innervating the skin over the cheek bones.

Mandibular nerve (V3)
          It arises from the trigeminal ganglion in the cavernus sinus of the middle cranial fossa. From here it passes downwards and enters the infra temporal fossa through the foramen ovale. Here it gives sensory and motor branches. Motor branches innervate the muscles of mastication, these are masseter, temporalis, medial and lateral pterygoid muscles.

          Small motor branches innervate the tensor tympani and tensor veli palatine. Sensory branches are buccal nerve which innervates the cheeks (lateral part). Auricotemporal nerve passes upwards behind the neck of the mandible and innervates the skin on the lateral side of the forehead. Two main terminal branches of the mandibular nerve are the inferior alveolar nerve and lingual nerve.

          Inferior alveolar is the posterior branch which passes through the mandibular foramen in the mandible then continues in the mandible through the mandibular canal. While passing through the mandibular canal it gives off inferior dental and gingival nerves which innervate the lower teeth and lower gums. The terminal part of the inferior alveolar nerve emerges from the mandible through the mental foramen. As it emerges from the mental foramen it is called mental nerve which innervates the skin of the chin on the corresponding ipsilateral area. Before entering the mandibular foramen a small nerve called myohoid nerve separate from it and innervates the myolohoid muscle and anterior belly of digastrics muscle.

          Lingual nerve passes in front of inferior alveolar nerve and passes downward between the lateral surface of medial pterygoid muscle and medial surface of the mandible. At its origin it receives branches from seventh cranial nerve (facial nerve) called chorda tympani. Chorda tympani and lingual nerve passes downward jointly and innervates the anterior two third of the tongue responsible for taste (chorda tympani) and general sensation from anterior two third of the tongue (lingual nerve).

  • Abducent nerve (sixth cranial)
          This nerve arises in between the Pons and Medulla oblongata. From the posterior cranial fossa it enters the lateral aspect of the petrous part of the temporal bone. Here it lies in a cave called cavernus sinus. From the middle cranial fossa it passes into the orbit through the superior orbital fissure. Within the orbit the Abducent nerve innervates the only lateral rectus muscle.

Thursday, September 2, 2010

Joints of the Upper Limb

Shoulder Joint
                         The synovial  ball and socket variety of joint is formed by the glenoid cavity of the scapula and head of the humerus. It is the most mobile joint of the body.This joint is also known as glenohumeral joint. The joint has the following characteristics.
  • Articular Capsule 
                        The joint surface is covered with the sleeve of hyaline cartilage called as articular capsule. The articular capsule starts from the superior border of glenoid cavity and ends at the anatomical neck of the humerus. The inferior portion of the capsule is very weak.
  • Glenohumeral Ligament
                         This ligament starts from the glenoid cavity and ends at the anatomical neck of the humerus. It is made up of three bands of fibrous tissue.
  • Coracohumeral ligament  
                         It starts from the coracoid process of humerus and ends at the greater tuberosity of the humerus. It strengthens the shoulder joint.
  • Transverse Humeral Ligament
                         It starts from the greater tuberosity and ends at the lesser tuberosity. This ligament provide stability to the shoulder joint.
  • Glenoid Lambrum
                         The glenoid rim is the fibro-cartilage which deepens the shoulder joint and also provide extra stability to the shoulder joint.
  • Bursa
                         There are four bursa present around the shoulder joint.
  1.    Sub-acromial bursa
  2.    Sub-coracoid bursa
  3.    Sub-scapular bursa
  4.    Sub-deltoid bursa
  • Movements
              Flexion:
                            Anterior fibres of deltoid
                            Pectoralis major
                            Biceps
                            Coracobrachialis
              Extension:
                                Posterior fibres of deltoid
                                 Latissimus dorsi
                                Teres major
              Abduction:                             
                                Middle fibres of deltoid
                                Supraspinatus
              Adduction:
                                Pectoralis major
                                 Latissimus dorsi
                                Teres major
                                Teres minor
              Lateral rotation:
                                 Infraspinatus
                                 Teres minor
              Medial rotation:
                                 Subscapularis
                                 Latissimus dorsi
                                 Teres major


Elbow Joint
                         The synovial hinge joint formed by the articulation of trochlear notch of ulna and head of radius with trochlea and capitulum of the humerus. It is extremely stable joint of the body having the following characteristics.
  • Articular Capsule
                         The joint surface is covered by the articular capsule which starts anterioly from the radial and coronoid fossa and ends at the annular ligament and coronoid process. The articular capsule protects the inner parts of the elbow joint.
  • Annular Ligament
                          The annular ligament is round in shape which surrounds the radial head.
  • Ulnar Collateral Ligament
                          It starts from the medial epicondyle and ends at the coronoid and olecranon processes of ulna.
  • Radial Collateral Ligament
                          It starts from the lateral epicondyle and ends at the annular ligament and radial notch of ulna.
  • Movements
             Flexion:
                           Brachialis
                           Biceps brachii
                           Brachioradialis
                           Pronator teres    
             Extension:
                           Triceps
                            Anconeus

Proximal Radioulnar Joint
                       The  pivot type of synovial joint formed by the articulation of radial head with radial notch of ulna.
Distal Radioulnar Joint
                       The pivot type of  synovial joint which is formed by the articulation of ulnar head with ulnar notch of radius.
  • Movements
             Pronation:
                               Pronator teres
                                Pronator quadratus
             Supination:
                                Biceps brachii
                                 Supinator  


   
Wrist Joint
                      The condyloid type of synovial joint formed by the distal end of the radius and the articular disc of the distal radioulnar joint with the proximal row of carpal bones except the pisiform i.e scaphoid, lunate and triquetrium.
  • Movements
              Flexion/extension  
              Radial (abduction) deviation
              Ulnar (adduction) deviation
              Circumduction 
    
Carpometacarpal and Intermetacarpal Joints
                      These all are plane synovial joints except that of thumb which is saddle joint.
  • Movements
               Only Gliding

Metacarpophalangeal Joints
                       These are condyloid type of synovial joints which allow movement in two directions.
  • Movements 
               Flexion
               Extension
               Abduction
               Adduction
               Circumduction

Interphalangeal Joints
                           These are uniaxial hinge joints which allow movement in only on direction.
  • Movements
              Flexion
             Extension


Pectoral Girdle
                            The pectoral girdle(clavicle and scapula) connects the upper limb to the trunk, therefore, its articulations are includeed with those of upper limb.
Sternoclavicular Joint
                             This is a saddle type of synovial joint and is the only bony articulation between the upper limb and the axial skeleton.The medial end of the clavicle articulates with the manubrium of the sternum.
  • Movements
             Allows movements of the pectoral girdle and upper limb. In flexion of the upper limb, the SC joint (i.e., clavicle on sternum) moves anteriorly, posteriorly and inferiorly.

Acromioclavicular Joint
                                This is a plane type of synovial joint. Acromial end of the clavicle articulates with the acromion of the scapula.
  • Movements
              The acromion of the scapula rotates on the acromial end of the clavicle.

Skull and Facial Muscles

  • Frontalis muscle
Origin:
          Epicranial aponeurosis

Insertion:
          Supra orbital margin

Function:
          Raises the upper eyelids, and wrinkles the skin of the forehead

  • Occipitalis muscle
Origin:
          Posterior margin of the occipital bone and mastoid process of temporal bone

Insertion:
          Epicranial aponeurosis

Function:
          Draws skin of the scalp backward

Facial Muscles

  • Orbicularis oris muscle
Origin:
          Upper and lower margins of lips

Insertion:
          Angle of the mouth

Function:
          Closes the mouth

  • Orbicularis oculi muscle
Origin:
          Upper and lower margins of the orbit

Insertion:
          Angle of the orbits

Function:
          Closes the eye

  • Zygomatic major muscle
Origin:
          Zygomatic bone

Insertion:
          Angle of the mouth

Function:
          Raises the upper lip

  • Zygomatic minor muscle
Origin:
          Zygomatic bone

Insertion:
          Lower lip

Function:
          Depression of lower lip

  • Levator labii superioris muscle
Origin:
          Upper lip

Insertion:
          Angle of the mouth

Function:
          Raises the upper lip

  • Depressor labii inferioris muscle
Origin:
          Lower lip

Insertion:
          Angle of the mouth

Function:
          Depression of lower lip

  • Levator palpebrii superioris muscle
Origin:
          Roof of the orbit and lesser wing of the sphenoid bone

Insertion:
          Skin of the superior eyelid

Function:
          Elevates the upper eyelid

  • Buccinator muscle
Origin:
          Alveolar processes of maxillae and mandible

Insertion:
          Upper and lower lips

Function:
          Approximation of upper and lower lips as in ‘whistling’

  • Risorius muscle
Origin:
          Fascia over the parotid gland

Insertion:
          Lower lip

Function:
            Draw the mouth backward

  • Mentalis muscle
Origin:
          Angle of mandible

Insertion:
          Mental foramen

Function:
          Movement of mandible

  • Corrigurator supercilli muscle
Origin:
          Medial side of supra orbital margin

Insertion:
          Eyebrow

Function:
          Movement of eyebrow

Wednesday, September 1, 2010

Bones of the Skull

The most complex bony structure of the body is Skull and is formed by the cranium and facial bones.
Cranium –It protects the brain and is the site of attachment for head and neck muscles.
Facial bones−It supply the framework of the face, the sense organs, and the teeth

Cranium

          Formed from eight large bones
               Unpaired bones include
               • Occipital bone
               • Frontal bone
               • Sphenoid bone
               • Ethmoid bone

               Paired bones include
               • Temporal bones
               • Parietal bones

  • Occipital bone
          It is the most posterior of the cranial bones forming the posterior wall and base of the skull. It is consist of two parts; squamous part and basilar part. In between these part is the foramen magnum of the occipital bone through which passes the spinal cord. The squamous part lies posterior to the foramen magnum and the basilar part lies anterior to the foramen magnum. On the inferior surface of the basilar part just anterior to the foramen magnum lie two projections called as occipital condyles which project inferiorly and posteriorly. The occipital condyle make joint with the superior articular facets of the 1st cervical vertebrae called as atlanto−occipital joint. This joint transmits the weight of skull bones to the vertebral column and helps in making movements like when we say Yes (flexion anteriorly and posteriorly). On the posterior external part of the squamous part is the external occipital protuberance and beneath it lies two curve lines called as superior nuchal line and inferior nuchal line. Just anterior and lateral to the foramen magnum on both sides are the hypoglossal canal for the passage of hypoglossal nerve. On both sides of the hypoglossal canal lies a depression which is the passage way for sigmoid sinus. The basilar part of the occipital bone attaches to the sphenoid bone and petrous part of the temporal bone. Laterally between the petrous part of the temporal bone and occipital bone lie the jugular foramen through which passes the 9th, 10th and 11th cranial nerves plus internal jugular vein.


  • Temporal bones
          They form the lateral walls of the skull. Anteriorly articulate with the zygomatic bones, medially with the sphenoid bone and posteriorly with the occipital bone. Like the occipital bone it has two parts; squamous part which is superior part and petrous part which lies inferiorly. From the inferior surface of the petrous part projects two protuberances the mastoid process which lies posterior to the external auditory meatus and the styloid process anterior and medial to the external auditory meatus. Just posterior to the external auditory meatus is an opening called stylomastoid foramen through which passes the 7th cranial nerve (facial). Petrous part has a cavity which lodges middle and internal parts of ear. On the front, temporal bone form zygomatic process which articulates with the temporal process of zygomatic bone forming zygomatic arch.


  • Frontal bone
          It forms the anterior portion of the cranium (floor of anterior cranial fossa) and makes the roof and lateral wall of the orbit. It also gives shape to the forehead. Anteriorly it articulates with the nasal bones while posterior with the sphenoid bone (posteroinferiorly) and parietal bone (posterosuperiorly). Above the nasal bones is the body of frontal bone having cavities called as frontal sinuses. Laterally frontal bone articulates with the zygomatic bone and helps in the formation of zygomatic arch.


  • Sphenoid bone
          It is only bone which articulates with all the other bones of the cranium. It forms the floor of the middle cranial fossa. Anteriorly it articulates with the frontal and ethmoidal bones, laterally with the temporal bones and posteriorly with the occipital bone. Sphenoid bone has two pair of wings: greater wings and lesser wings. These wings give sphenoid bone bat shaped appearance. The greater wings form the floor and wall of middle cranial fossa. The lesser wings form the anterior wall of the middle cranial fossa. The most anterior part of the lesser wings is called sphenoid ridges (concha) which separates the anterior cranial fossa from the middle cranial fossa. Between the two greater wings lies the body of sphenoid bone. The body has two anterior projections called as anterior clinoid processes and two posterior projections called as posterior clinoid processes. In-between these two projections lie a pituitary fossa which accommodates the pituitary gland. Both anterior and posterior clinoid process along with pituitary fossa form a saddle like structure called as sella turcica. From the inferior surface of the body of sphenoid bone arise two projections called as lateral and medial pterygoid processes. In between these processes lies the pterygoid fossa.

           Through the lesser wing of the sphenoid bone passes a canal called as optic canal through which passes the optic nerve. Between the lesser and greater wings anteriorly lies a fissure called superior orbital fissure through which passes the ophthalmic division of trigeminal nerve. Most anterior of the greater wing has a foramen rotundum through which passes the maxillary division of trigeminal nerve. Posterior to the foramen rotundum is foramen ovale through which passes the mandibular division of trigeminal nerve. Posterior and lateral to the foramen ovale is the foramen spinosum through which passes the middle meningeal artery.

  • Ethmoid bone
          It is one of the smallest among the cranial bones. It helps in the formation of some part of anterior cranial fossa. Anteriorly it articulates with the nasal bones, posteriorly with the sphenoid bone and laterally with the frontal bone. Ethmoid bone has four parts.

          • Cribriform plate is the most superior part of the ethmoid bone. It has central upward projection called as crista galli (site of attachment of falx cerebri or durra matter). The two horizontal plate of cribriform plate contain foramina for the passage of olfactory nerve.

          • Perpendicular plate projects downward and helps in the formation of the nasal septum. It has two borders. Anterior border articulates in front with the frontal bone while the upper part of the posterior border articulates with the sphenoid bone and lower part of the posterior border with the vomer bone.

          • 2 Labyrinths (Medial and Lateral labyrinths): The lateral labyrinth forms the medial wall of the orbit which is called lamina papyraceae. The medial labyrinth forms two projections, which protrudes inside the nasal cavity forming two projections called as the superior nasal conchae and middle nasal conchae. These nasal conchae contain air cells which make the ethmoid sinuses. Superiorly these sinuses communicate with the frontal sinus while laterally with the maxillary sinuses.


  • Parietal bones
          They form the roof and lateral walls of the cranium. Parietal bones articulate with the frontal bone anteriorly by coronal suture, posteriorly with occipital bone by lambdoid suture and laterally with the temporal and sphenoid bones through the squamous sutures. Parietal bones contain no foramina but contain numerous grooves on its inferior surface for the passage of the blood vessels.

Facial Bones
          Facial skeleton is composed of fourteen bones of which only the mandible and vomer are unpaired. The paired bones are the maxillae, zygomatics, nasals, lacrimals, palatines, and inferior conchae.

  • Mandible bone
          It is unpaired, strongest and the only moveable bone of the skull. Mandible has two parts i.e. two rami and one body. The rami join the body at the angle called as angle of the mandible. The superior part of the mandible has two projections called as coronoid process (anteriorly) and condyloid process (posteriorly). The condyloid process makes joint with the mandibular fossa of the temporal bone making the only moveable joint of the skull called as temporal mandibular joint. There are two foramen in the mandible; mental foramen which lies just below the 2nd premolar teeth and mandibular foramen which lies on the medial aspect of the ramus of the mandible. The upper margin of the body of mandible has inferior alveolar processes which fit the lower teeth.

  • Vomer bone
          It is the unpaired bone which forms the central part of the floor of the nasal cavity. Superiorly it articulates with the ethmoid bone, inferiorly with the palatine bone and palatine processes of the maxillae.

  • Nasal bones
          They form the roof and anterior wall of the nose. Superiorly they articulate with the frontal bone, posteriorly with the lacrimal bones and inferiorly with the maxillae.

  • Maxillary bones
          They articulate with all the bones of the facial skeleton except the mandible. Superiorly they articulate with the nasal and lacrimal bones, laterally with the zygomatic bones, medially with the vomer and inferior nasal conhae and posteriorly with the palatine bones. Both maxillary bones contain air filled cavities called as maxillary sinuses which open into the nasal cavity.

  • Zygomatic bones
          They form the lateral wall of the facial skeleton. They are also called cheek bones as they form the prominence of the cheeks. Anteriorly they articulate with the maxillary bone, posteriorly with the temporal bone and superiorly with the ethmoidal bone.

  • Lacrimal bones
          They lie posterior to the nasal bones. Through the lacrimal bones passes the lacrimal canal which is a passage for tears into the nasal cavity.

  • Palatine bones
          They lie posterior to the maxillary bones (palatine processes). They form the posterior one third of the hard palate separating the nasal cavity from the oral cavity.

  • Inferior nasal conchae
          These are the two small bones which form the inferior lateral wall of the nasal cavity. Superiorly articulate with the middle nasal conchae of the ethmoid bone while laterally with the maxillary bones.

 
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