Peripheral Nervous System Nerves outside the brain

Peripheral Nervous System Structures Sensory receptors Mechanoreceptors (touch, pressure, vibration, and stretch) Thermoreceptors (temperature changes) Photoreceptors (light energy) Chemoreceptors (chemicals in solution) Nerves (cranial and spinal) Cordlike organ that is part of the PNS Consists of parallel bundles of peripheral axons enclosed by connective tissue wrappings Ganglia Collections of neuron cell bodies associated with nerves in the PNS Efferent motor endings

Peripheral Nervous System 12 cranial nerves Associated with the brain We need to learn their: Names Locations Functions 31 spinal nerves Associated with the spinal cord Plexus

Cranial Nerves 10 of 12 cranial nerves attach to the brain stem Their name reflects their function or the major structures they control Numbered (Roman numerals) in order from anterior to posterior Described by name, Roman numeral, and function Function can be purely sensory, motor, or both

Cranial Nerves I Olfactory nerve (sensory) smell II Optic nerve (sensory) vision III Oculomotor nerve (motor) eye muscles IV Trochlear (motor) V Trigeminal nerve (sensory/motor) sensory for face motor for chewing VI Abducens nerve (motor)

Cranial Nerves VII Facial nerve (sensory/motor) sensory for taste Motor for facial expression VIII Vestibulococchlear nerve (sensory) balance and hearing IX Glossopharyngeal nerve (sensory/motor) motor for pharynx X Vagus nerves (sensory/motor) pharynx, larynx, and viscera XI Accessory nerve (motor) neck and upper back XII Hypoglossal nerve (motor) tongue

Cranial Nerves Here are mnemonic devices for the 12 cranial nerves: On occasion our trusty truck acts funny – very good vehicle anyhow On old Olympus' towering tops, a fin and German viewed some hops. Olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulococchlear, glossopharyngeal, vagus, hypoglossal

Cranial Nerves Cranial nerves can have sensory only, motor only, or mixed functions Sensory only Olfactory and optic are sensory only Motor only Oculomotor Trochlear Abducens Accessory Hypoglossal Mixed (sensory and motor) Trigeminal Facial Vestibulococchlear Glossopharyngeal Vagus Mnemonic device to help: Some say marry money but my brother says big butts matter more. Some Scientists Make Money But My Brother Says Beautiful Blonds Make More

Olfactory (I) Sensory Smell Imbalance: fracture of ethmoid bone or lesions may result in partial or total loss of smell Optic (II) Sensory Vision Imbalance: damage to optic nerve results in blindness in eye served by nerve; damage beyond optic chiasm results in partial vision loss

Eye and peripheral vision Oculomotor (III) Motor Eye and pupil movement Imbalance: eye cannot move up, down or inward; at rest eye rotates laterally and trouble focusing on close objects Trochlear (IV) Motor Eye and peripheral vision Imbalance: Trauma or paralysis results in double vision and reduced ability to rotate eye inferolaterally

Trigeminal (V) Both (sensory and motor) Ophthalmic division (s) Maxillary division (s) Mandibular division (s & m) Largest of the cranial nerves Imbalance: trigeminal neuralgia – caused by inflammation of the nerve, stabbing pain that lasts for a few seconds to a minute, provoked by a sensory stimulus Abducens (VI) Motor Abduction of eye Imbalance: eye cannot be moved laterally; at rest, affected eyeball rotates medially

Facial Nerves (VII) Both (sensory and motor) Muscles of facial expression: temporal, zygomatic, buccal, mandibular, cervical (m) Taste buds (anterior) (s) Imbalance: Bell’s Palsy – paralysis of facial muscles on affected side and partial loss of taste sensation; Lower eyelid droops, corner of mouth sags, tears drip continuously from eye and eye cannot be completely closed

Vestibulocochlear (VIII) Sensory Hearing (cochlear) Equilibrium (vestibular) Imbalance: lesions of cochlear nerve result in nerve deafness; damage to vestibular produces dizziness, rapid involuntary eye movement, loss of balance, nausea and vomiting Glossopharyngeal (IX) Both (sensory and motor) Pharynx (throat)(m) Taste buds and throat (posterior) (s) Imbalance: injury impairs swallowing and taste

Vagus (X) Only cranial nerve to extend beyond head and neck Both (sensory and motor) Pharynx, larynx, heart, lungs, and abdominal organs (m) Thoracic and abdominal organs (s) Imbalance: Injury can lead to hoarseness or loss of voice, difficulty swallowing and impaired digestive system motility Total destruction of nerves is incompatible with life because they are needed to maintain normal activity

Hypoglossal (XII) Motor Accessory (XI) Motor Trapezius and sternocleidomastoid Hypoglossal (XII) Motor Glossal = tongue Muscles of the tongue Imbalance: difficulty in speech and swallowing

Spinal Nerves Spinal nerves are named for the region from which they arise A pair of spinal nerves at each vertebrae for a total of 31 pairs 8 pairs of cervical (1 extra) 12 pairs of thoracic 5 pairs of lumbar 5 pairs of sacral 1 pair of coccyx

Spinal Nerves All are mixed nerves (sensory and motor) Each nerve connects to the spinal cord by a dorsal and ventral root Ventral root – motor Dorsal root – sensory

Spinal Nerves The spinal nerve is actually short (1-2 cm) Immediately it divides into its ramus (branch) Dorsal rami – serve the skin and muscles of the posterior trunk Ventral rami – forms a complex of networks for the anterior and limbs called plexuses

Plexuses All ventral rami (except thoracic) branch and join one another lateral to the vertebral column that form a complex network called a plexus Nerve plexuses occur in cervical, brachial, lumbar and sacral regions to serve the motor and sensory needs of the limbs The fibers diverge again from the plexuses to form the peripheral nerves

Examples of Nerve Distribution Figure 7.23

Spinal Nerve Plexuses PLEXUS SPINAL ROOTS (ORIGIN) BODY AREA SERVED IMBALANCE Cervical C1-C5 Skin of neck, shoulder and clavicle region Diaphragm (phrenic nerve) and muscles of shoulder and neck Irritation of the phrenic nerve causes spasms of the diaphragm - hiccups Brachial C5– C8 and T1 All nerves that innervate upper limb Arm muscles – deltoid, triceps, biceps, flexor, extensor, wrist and hands Cutaneous sensation of the upper limb Weakness or paralysis of entire upper limb Carpal tunnel syndrome the median nerve is compressed “The funny bone” results from an injury to the ulnar nerve

Spinal Nerve Plexuses PLEXUS SPINAL ROOTS (ORIGIN) BODY AREA SERVED IMBALANCE Lumbar L1– L4 Innervation of lower limb and abdomen Muscles of the thigh, leg and foot Cutaneous sensation of thigh, leg, foot, external genitalia and lower abdomen Compression of the spinal roots of the lumbar plexus results in walking problems Sacral L4 – S4 Innervation of the buttock, pelvic structures and lower limb Sciatic nerve is the thickest and longest nerve in the body –entire lower limb Muscles of the posterior surface of buttock, thigh, leg and foot, Cutaneous sensation of posterior surface of buttock, thigh, leg and foot, Sciatica – stabbing pain over the course of the nerve from injury to sciatic nerve such as disc herniation or improper injection in the buttock

Reflexes

The Reflex Anyone who has had a routine physical examination is familiar with the reflex tests done to assess neural function. A tap with a reflex hammer stretches your quadriceps tendon and your anterior thigh muscles contract, which results in the knee-jerk response This response shows that the spinal cord and upper brain centers are functioning normally Abnormal reflex test responses may indicate such serious disorders as intracranial hemorrhage, multiple sclerosis, or hydrocephalus

Reflex Arc Reflex Reflex arc Rapid, predictable, involuntary motor response to stimuli Inborn or acquired reflexes Occur over neural pathways called reflex arcs Reflex arc Receptor  sensory neuron  integration center (monosynaptic or polysynaptic)  motor neuron  effector

Reflexes Receptor Sensory neuron Integration center Motor neuron Site of the stimulus Sensory neuron Transmits afferent impulses to the CNS Integration center Single synapse (monosynaptic) Multiple synapses (polysynaptic) btw the afferent Motor neuron Conducts efferent impulses from the integration center to an effector organ Effector Muscle fiber or gland cell that responds to the impulses

Reflex Arcs Monosynaptic reflex arc – knee-jerk reflex Polysynaptic reflex arc – most reflexes

Types of Reflexes Somatic reflexes Any reflex in which the skeletal muscles are the effectors Stretch reflexes Maintain posture, balance and locomotion Produced by tapping a tendon, which stretches the attached muscle Knee-jerk (patellar) reflex Superficial reflexes Gentle cutaneous stimulation Plantar reflex tests the integrity of lower spinal cord Corneal reflex Gag reflex http://www.getbodysmart.com/ap/nervoussystem/neurophysiology/restingpotentials/na_kpump/tutorial.html

Types of Reflexes Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Digestive system regulation (saliva) Elimination (excretion) Change size of eye pupil Sweating

Types of Reflexes