The Peripheral Nervous System Chapter 13

Divisions of the Nervous System

Classification of Sensory Receptors By Stimulus Type – Mechanoreceptors – Thermoreceptors – Photoreceptors – Chemoreceptors – Baroreceptors – Nociceptors By Location – Exteroceptors – Interoceptors – Proprioceptors

Unencapsulated Nerves

Encapsulated Nerves

Connective Tissues of a Nerve

Types of Nerves Sensory (afferent) Nerves Motor (efferent) Nerves Mixed Nerve (both)

Regeneration of an Injured Nerve

Cranial Nerves - 12 pairs - Classified as sensory, motor or mixed - First two pairs attach to the forebrain - Remaining ten pairs attach to the brainstem

Cranial Nerves

Olfactory Nerve (I)

- Sensory only - Sense of smell - Olfactory bulbs that terminate into filaments piercing the cribriform plate of the ethmoid bone. - Anosmia: loss of smell

Optic Nerve (II)

- Sensory only - Vision - Begins at the retina, converges at the optic chiasma, partial crossing over of the fibers to enter the thalamus. Optic radiations take impulse to the visual cortex in the occipital lobe. - Anopsias= loss of vision

Oculomotor Nerve (III)

- Motor only - Controls 4 of the six eye muscles for eyeball movement and pupil constriction: - Superior rectus - Medial rectus - Inferior rectus - Inferior oblique External Strabismus=eye rotates laterally

Oculomotor Nerve (III)

Trochlear Nerve (IV)

- Motor only - Movement of one eye muscle: superior oblique muscle - Downward and lateral movement of the eyeball. - Damage to this nerve can cause double vision and the inability to rotate the eye inferolaterally

Trigeminal Nerve (V)

- Mixed nerve - Largest cranial nerve - Sensory=somatic sensations of the face - Motor=controls muscles of mastication - Three divisions: V 1 - Ophthalmic division V 2 - Maxillary division V 3 - Mandibular division - Tic douloureux=inflammation of the trigeminal nerve

Abducens Nerve (VI)

- Motor only - Innervates the lateral rectus muscle of the eye - Moves eyeball laterally - Internal Strabismus=eye rotates medially

Abducens Nerve (VI)

Facial Nerve (VII)

- Mixed nerve - Motor=Controls muscles of facial expression - Motor=Controls lacrimal and two of the three types of salivary glands (sublingual and submandibular glands) - Sensory=Taste of anterior 2/3 of tongue - Bell’s palsy=unilateral facial paralysis

Vestibulocochlear Nerve (VIII)

- Sensory only - Vestibulo branch: equilibrium - Cochlear branch: hearing - Travels through the internal acoustic meatus - Nerve deafness caused by damage to the cochlear branch while dizziness and vertigo are caused by damage to the vestibular branch

Glossopharyngeal Nerve (IX)

- Mixed nerve - Motor=muscle innervations to part of the tongue and pharynx - Sensory=Taste for bitter on the posterior 1/3 of the tongue - Swallowing and gag reflex

Vagus Nerve (X)

- Mixed nerve - Motor=heart rate, breathing, and digestive function, muscles of the voicebox. - Sensory=taste from the posterior portions of the tongue and pharynx (taste), abdominal and thoracic viscera - Destruction of the vagus nerve is incompatible with life

Accessory Nerve (XI)

- Motor (primarily) - Innervates trapezius and sternocleidomastoid muscle Damage would result in the inability to shrug the shoulders and turn the head

Hypoglossal Nerve (XII)

- Motor (primarily) - Tongue movements: swallowing and speech

Spinal Nerves - Mixed nerves - 31 pairs of spinal nerves total - (8) Cervical - cervical and brachial plexus - (12) Thoracic - intercostal nerves and cervical and lumbosacral enlargement - (5) Lumbar - lumbar plexus - (5) Sacral - sacral plexus - (1) Coccygeal

Distribution of Spinal Nerves

Formation of Spinal Nerves

Cervical Plexus

Most branches are cutaneous nerves that supply sensory impulses from the skin of the neck, ear, back of the head and shoulders Other branches innervate the muscles of the anterior neck Phrenic nerve = sole motor nerve supply to the diaphragm for breathing

Brachial Plexus

Median nerve: Flexor muscles of the anterior forearm and intrinsic muscles in palm; pronates the forearm, flex the wrist and fingers, and oppose the thumb Radial nerve: largest branch; posterior muscles of the arm and forearm; innervates all the extensor muscles for elbow, wrist, and finger extension, forearm supination, and thumb abduction

Brachial Plexus Ulnar nerve: produces wrist and finger flexion and adduction as well as abduction of the medial fingers Suprascapular nerve: innervates the supraspinatus and infraspinatus muscles for movement of the shoulder

Brachial Plexus

Thoracic Nerves

Lumbar Plexus

Femoral nerve: the largest terminal nerve of this plexus and innervates the anterior muscles of the thigh (thigh flexors and knee extensors). Branches to form the saphenous nerve on the medial thigh and knee. Obturator nerve: innervates the adductor muscles of the leg.

Lumbar Plexus

Sacral Plexus

Sciatic nerve: which supplies the entire lower limb (leg) except the anteromedial thigh. The sciatic nerve is also the thickest and longest nerve in the body and branches to form the 1- tibial nerve (which further branches to form the sural nerve and plantar nerves) and the 2- common fibular nerve

Reflexes

Reflex Activity

Types of Reflexes Somatic Reflexes – Stretch reflexes – Golgi tendon reflexes – Flexor reflexes (withdrawal) – Crossed extensor reflexes – Superficial reflexes Autonomic Reflexes

Stretch Reflex

Golgi Tendon Organ

Flexor reflex and Crossed Extensor Reflex

Superficial Reflex