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.

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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.

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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

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