Peripheral Nervous System 1 and 2

Peripheral Nervous System 1

Review of Nerves

Nerve: bundle of axons that serve same function

Sensory: afferent

Motor: efferent

Mixed: both afferent and efferent, most common

Spinal Nerves

  • 31 pairs(on both sides) of spinal nerves connected to cord
  • Comes from the ventral and dorsal nerve root
  • Numbered by level of vertebral colum where they emerge from, mirrors # of vertebrae
    • Cervical Nerves: C1-C8 → one that comes out between skull and C1 vertebrae and one below C7 which makes 8
    • Thoracic nerves: T1-T12
    • Lumbar nerves: L1-L5
    • Sacral nerves: S1-S5
    • 1 coccygeal nerve pair

Cauda Equina

  • Nerve roots extending from conus medullaris (end of spinal cord) form ‘horse’s tail’ of spinal nerve roots
  • Filum terminale is within cauda equina

Structure of Spinal Nerves

  • Sensory neurons with cell bodies in dorsal root ganglion, axons in dorsal root
  • Enters spinal cord and synapes occurs in grey matter, synapses with processing centre
  • Synapse occurs with motor neuron in ventral part of grey matter, cell bodies in ventral horn
  • Exits spinal cord with axons in ventral root
  • Dorsal and ventral root come together to form spinal nerve, then splits off into dorsal and ventral rami (arm)

Rami of spinal nerves

  • Large branches that spinal nerve divides into dorsal and ventral rami

Dorsal:

  • Innervates (nerve supplies) muscles and skin or dorsal surface of head, neck, and trunk
  • Contains both sensory and somatic motor neurons (toskeletal muscles)

Ventral:

  • Contains sensory and somatic as well as autonomic motor neurons
  • Innervates muscles, glands, and skin in extremities, and lateral and ventral neck and trunk, can form plexuses
  • Autonomic fibers stimulate things we don’t have control over, eg. digestive system
  • They also connect with sympathetic rami and chain ganglion (fight or flight nervous system)

Nerve Plexus

  • Group of nerve travelling same direction, formed from ventral rami of most spinal nerves
  • Not found in T2-T12
  • Spinal nerves are rearranged for their final destination, reducing amount of nerves to supply each body part
  • Each nerve that emerges contains all fibers to innervate particular part of body

Major Plexuses

Cervical Plexus

  • Ventral rami C1-C5, deep in neck, innerate muscles and skin of neck, upper shoulders, part of head, and diaphragm

Brachial Plexus

  • Deep in shoulder, ventral rami C5-T1, innervate lower shoulder and arm

Lumbar Plexus

  • Lumbar area of back, ventral rami of L1-L4, innervates abdomen, back, anterior thigh and leg (using femoral nerves)

Sacral plexus

  • Pelvic region, ventral rami of L4-S4, innervate skin of leg, muscles posterior thigh, leg and foot using tibia, fibular, and sciatic nerves
  • Sends branches of more posteriorly

Coccygeal plexus

  • Pelvic region, ventral rami of S4-S5, connects with coccygeal nerve, innervates skin over coccyx

Phrenic Nerves (TEST QUESTION)

  • From cervical plexus: specifically C3, C4, and C5
    • C3, C4, C5 keeps diaphragm alive
  • Controls the diaphragm a main muscle for respiration
  • Spinal cord injury between C1-C5, means paralysis of phrenic nerves, means paralysis of diaphragm, cannot breath independently

Dermatomes and Myotomes

Dermatome

  • Area of skin that is supplied by sensory fibers of given spinal nerve, regions overlay considerably

Myotomes

  • Region of skeletal muscles innervated by motor fibers of given spinal nerve

Two functional divisions of PNS

Somatic nervous system

  • Involved with skeletal muscles, voluntary, except for certain reflexes
  • Relies on sensory input from special senses
  • Motor output goes to skeletal muscles
  • It regulates skeletal movements needed for survival, breathing, and heat production
  • Doesn’t include smooth and cardiac muscles and glands

Autonomic Nervous System

  • Automatic functions in body

Reflexes

  • We don’t have control over the action of our skeletal muscles
  • Involves reflex arc, nerve impuls passes over reflex arc and produces a predictable response
  • Skeletal muscles than contract, subconscious

Reflex Arc

  • A signal conduction route to and from CNS
  • If center of reflex arc is in spinal cord; spinal reflex

Two neuron (monosynaptic) arc

  • Simplest form, afferent and efferent neurons

Three- neuron (polysynaptic) arc

  • Most common, afferent, inter, and efferent neuron

Classification of Reflex Arcs

Contralateral: sensory receptors that pick up information and effectors are on opposit side of body

Ipsilateral: sensory receptors that pick up information and effectors are on smae side of body

  • Patellar reflex

Segmental: contained in one segment of spinal cord

  • Patellar reflex

Intersegmental: multiple segments of spinal cord, more complex

More classifications

Cranial reflex: processing center of arc is in brain

SPinal reflex: processing center of arc is in spinal cor

Effector tissues:

  • Somatic reflex: arc edns with contraction of skeletal muscles
    • Patellar reflex
  • Autonomic reflex: arc ends with smooth or cardiac muscle contraction, gland secretion

Stretch reflex: arc started with stretching muscle

  • Patellar reflex

Extenosr reflex: arc ends with extension of muscle

  • Patellar reflex

Superficial reflex: arc started by superficial sensors activating

Deep reflex: arc started by sensory sensors activating deep in muscle

  • Patellar reflex

Peripheral Nervous System 2 (online)- Cranial Nerves

Cranial Nerves and Mnemonics

  • First letter of each word in sentence correlates with first letter of name of each cranial nerves from 1-12
  • On Old Olympus Tiny Tops, A Friendly Viking Grew Vines And Hops
  • Functional Classification: Some Say Marry Money But My Brothers Say Bad Business Marry Money

Cranial Nerves

  • 12 pairs (oneach side)
  • Most come off of brainstem, identified by name or number
  • Made of bundles of axons

Functions

  • Mixed Nerve (B): axons of sensory and motor neurons
  • Sensory Nerves: axons of sensory neurons
  • Motor Nerve (M): mainly motor neurons, some sensory fibers (proprioceptors), motor neurons can be voluntary or involuntary

Olfactory Nerve (1)

  • On, Some
  • Sensory function only: responsible for smell
  • Nerve Ending: nasal mucosa (olfactory bulbs), on roof of nasal vacity

Optic Nerve (2)

  • Old, Say→ Sensory nerve only: responsible for sight,
  • Nerve Ending: retina of eye, some fiber cross over at the optic chiasm (behind in middle of two eyes) to continue in the contralateral optic tract
  • Some proprioception: perception of movement and body position

Oculomotor Nerve (3)

  • Olympus, Marry→ Motor function, contains some sensory/proprioceptors, autonomic function
  • Nerve endings: most external eye muscles, to move eyeball, autonomic fibers will regulate amount of light entering eye (smooth muscle in iris to contract and relax), cililary muscles helps focus on near objects

Trochlear Nerve (4)

  • Tiny, Money→ motor: controls superior oblique muscles in eye, some proprioceptors
  • Nerve Ending: innervates superior oblique muscles of eye

Trigeminal Nerve (5)

  • Tops, But → mixed nerve: splits into 3 branches (nerve endings), ophthalmic, maxillary, and mandibular nerve
  • Sensory: receives inputs from skin and mucosa of head and teeth, head and face proprioception and sensation
  • Motor Function: controls muscles of mastication (chewing)

Abducens Nerve (6)

  • A, My→ motor function only, some proprioception
  • Nerve Endings: innervates lateral rectus muscles in eye
  • If injured, then lose ability to pull eye

Facial Nerve (7)

  • Friendly, Brothers→ Mixed nerve
  • Motor: superficial muscles of face and scalp, autonomic fibers to salivary glands
  • Sensory: taste buds of anterior two thirds of tongue (taste)
  • Controls facial expression, salivary and tear secretion
  • In injured, mouth droops, pokerfaced expression

Vestibulocochlear Nerve (8)

  • Viking, Say→ sensory function with 2 sensory nerves
  • Vestibular nerve fibers: input from semicircular canals (in inner ears), helps with balance
  • Cochlear Nerve fibers: input from spiral ganglion of cochlea (in inner ears for hearing)
  • If injured, can lead to deafness

Glossopharyngeal Nerve (9)

  • Grew, Bad→ Mixed nerve: senosory, motor, autonomic
    • Tougus and throat
  • Sensory: allows sensation to part of tongue and throat (pharynx)
  • Motor: allow for movements of tongue and motor control of swallowing
  • Autonomic: reflex control of bloop pressure via carotid sinus, saliva and swallowing

Vagus Nerve (10)

  • Vines, Business→ Mixed nerve, mainly autonomic, main nerve of parasympathetic division of autonomic nervous system, contorls many visceral (organ) activities
  • Sensory: inputs from pharynx, larynx, trachea, hear, cartid body, lungs, bronchi, esophagus, stomach, small intestine, gallbladder
  • Motor: Controls pharynx, larynx, trachea, hear, carotid body, lungs, bronchi, esophagus, stomach, small intestine, gallbladder (regulates heart, respiration, digestion, etc)

Accessory Nerve (11)

  • And, Marry→ Motor only, proprioception with muscles it innervates, originated in C1- C5 spinal nerves
  • Innervates trapezius and sternocleidomastoid muscles (head and shoulder movement)

Hypoglossal Nerve (12)

  • Hops, Money→ motor only, under tongue, proprioceptive input from muscles it innervates
  • Controls tongue muscles