Peripheral Nervous System Chapter 14

Spinal Nerves 31 pairs of spinal nerves are connected to the spinal cord – Numbered according to the portion of the vertebral column at which they exit 8 cervical nerve pairs 12 thoracic nerve pairs 5 lumbar nerve pairs 5 sacral nerve pairs 1 coccygeal nerve pair – All spinal nerves carry both motor and sensory fibers so they are designated as mixed nerves

Structure of Spinal Nerves Ventral and dorsal roots join to form spinal nerves Each spinal nerve branches into a dorsal ramus and ventral ramus. (plural = rami)

Dermatomes & Myotomes

Dermatomes Dermatome: a skin surface area supplied by sensory fibers of a given spinal nerve

Myotome Myotome: a skeletal muscle or group of muscles that receives motor axons from a given spinal nerve

Cranial Nerves

Olfactory Nerve (I) – Sensory – Sense of smell Optic Nerve (II) – Sensory – vision Oculomotor Nerve (III) – Motor – Eye movements, regulation of pupil size Trochlear Nerve (IV) – Motor – Eye movements

Cranial Nerves Trigeminal Nerve (V) – Mixed – Sensations of head and face, proprioception – Chewing movements Abducens Nerve (VI) – Motor – Abduction of eye Facial Nerve (VII) – Mixed – Taste – Facial expressions, secretion of saliva & tears Vestibulocochlear Nerve (VIII) – Sensory – Balance, equilibrium, hearing

Cranial Nerves Glossopharyngeal Nerve (IX) – Mixed – Sensations of tongue, reflex control of blood pressure & respiration – Swallowing movements, secretion of saliva Vagus Nerve (X) – Mixed – Sensations and movements of organs supplied (ex: slows heart, increases peristalsis, contracts muscles for voice production) Accessory Nerve (XI) – Motor – Shoulder movements, turning head movements, movement of viscera, voice production Hypoglossal Nerve (XII) – Motor – Tongue movements

Cranial Nerves Acronyms Names: On Old Olympus’ Tiny Tops, A Friendly Viking Grew Vines And Hops Functional Classification: Some Say ‘Marry Money’; But My Brother Says ‘Bad Business, Marry Money’

Reflexes A reflex is the action that results from a nerve impulse passing over a reflex arc – A predictable response to a stimulus – Conscious or unconscious – Somatic Reflexes Skeletal muscle contraction – Autonomic Reflexes Contraction of smooth or cardiac muscle; glandular secretion

Somatic Reflexes of Clinical Importance In certain diseases or after trauma to the nervous system certain reflexes may be abnormal Testing of reflexes is a valuable diagnostic tool

Stretch Reflexes Knee jerk or patellar reflex – Extension of lower leg in response to tapping patellar tendon – L2-L4 segments of the spinal cord Ankle jerk or Achilles reflex – Plantar flexion of the foot in response to tapping the Achilles tendon – S1-S2 segments of the spinal cord

Stretch Reflexes Biceps Reflex – Flexion at the elbow in response to tapping the brachii tendon – C5-C6 segments of the spinal cord Triceps Reflex – Extension at the elbow in response to tapping proximal to the elbow – C6-C7 segments of the spinal cord

Cutaneous Reflexes Cutaneous reflexes result from stimulation of the skin receptors Babinski Reflex – Reflex in response to stimulation of the outer portion of the sole of the foot (make a ‘J’ from the heel along the lateral edge through the ball of the foot) – Infant (to 1 ½ yrs): extension and fanning of toes – Children & adults: plantar flexion – Change in response due to corticospinal tract becoming fully myelinated – A + babinski’s in an adult means destruction to the corticospinal tract

Cutaneous Reflexes Abdominal Reflex – Drawing in of the abdominal wall in response to stroking the side of the abdomen – T9-T12 spinal nerves and segments of the spinal cord