Anatomy Exam 3 (Peripheral Nervous System)

Spinal Cord

Begins at foramen magnum

Functions:

• sensory and motor innervation of body

• 2-way conduction of signals between body and brain

• major center for reflexes

Terminates at L1/l2 as Conus Medullaris

Filium terminate extends from conus

Spinal Cord

Each spinal cord segment has a mixed spinal nerve with dorsal and ventral roots

Cauda equina is the collection of spinal nerves traveling inferiorly to exit at associated intervertebral foramen

Spinal cord meninges

Epidural Space: filled with fat and veins

Dura mater

Arachnoid mater

pia mater

Biggest difference between this and cranial cavity is that there is one extra space before DURA.

Spinal Cord segment

The spinal cord transmits nerve signals from motor cortex to the body, and from afferent fibers of sensory neruons to sensory cortex of the brain

The spinal cord is divided into SEGEMENTS. each segment pair of spinals nerves is formed

There are 31 spinal cordsegments

Gray Matter and white matter

Spinal cord Gray matter

Organized into two (or three) “horns”

Anteriror/ ventral horn: houses somatic motor cell bodies

Posterior/Dorsal Horn: recives sensory neuronal input

Sometimes- Lateral Horn: houses visceral motor cell bodies

Spinal Cordroots

Roots emerge from dorsal and ventral horns

One-way pathway for neuron signals

Anterior root(down by ventral horn):

• motor (efferent) axons found here

• motor signals travel from cell body through axon

Posterior/ Dorsal root:

• sensory (afferent) axons and Cell bodies

Sensory cell bodies found in dorsal root ganglion

• SA = Sensory Afferent

• ME = Motor Efferent

• DA = Dorsal Afferent

• VE = Ventral Efferent

Mixed spinal Nerve

like a highway, as we aproach the spinal cord we start to have one way highways

Nerve Plexuses

A nerve plexus is a network of nerves formed by VENTRAL rami only

All spinal Nerves except T2-T12 branch rejoin

Each muscle in a limb receives its nerve supply from more than one spinal nerve… damage to one spinal nerve cannot completely paralyze any limb muscle

Cervical Plexuses

• The cervical plexuses innervate the muscles of the neck and the diaphragm

  • Phrenic Nerve: innervates the diagrpham

Brachial Plexus

Partly in neck, partly in axilla

Gives rise to most nerves of the upper limb

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Terminal Branches of Brachial Plexus

Axillary Nerve: innervates deltoid muscle

Musculocutaneous nerveL innervates anterior compartment of arm

Radial Nerve: innervates posterious compartment of arm and forearm

Ulnar nerve: innervates ulnar side of anterior forearm

Median Nerve: innervates radial side of anterior forearm

• Axillary: Shoulder (Deltoid) - Think “Axe swings”.

• Musculocutaneous: Anterior Arm (Biceps) - Think “Flexing”.

• Radial: Posterior Arm & Forearm - Think “Radical skateboard tricks”.

• Median: Thumb Side of Forearm - Think “Middle, precision grip”.

• Ulnar: Pinky Side of Forearm - Think “Under, funny bone”.

Axillary Nerve

Sensory innervation: shoulder joint and skin on part of deltiod

Motor innervation: treres minor and deltioid

Musculocutaneous nerve

Sensory innervation: skin sensation for lateral forearm

Motor innervation: anterior compartment of arm

Radial Nerve

Sensory innervation: skin over dorso-lateral arm and forearm and hand

Motor innervation: posterior compartment of arm and forearm (extensor compartment)

Median Nerve

Sensory innevration: skin of lateral palm and digits 1-3 and lateral side of digit 4

motor innervation: anterior compartment of forearm. intrisic muscle of the thumb

Ulnar nerve

Sensory information: skin of medial hand medial side

Motor innervation: hand muscles on ulnar side of anterior forearm

Lumbar Plexus

Femoral nerve:

Sensory innervation: skin of anteror medial thigh, skin of medial leg and foot

Motor innervation: muscles of anterior thigh, thigh flecors and leg extensors

Obturator Nerve:

Sensroy innervation: skin of medial thigh

Motor innervation: muscles of medial thigh (adductors)

Sacral Plexus

Gluteal nerves:

Superior gluteal nerve

motor innervation: gluteus medius and minimus tensor fascia lata

Inferior gluteal nerve:

motor innervation

Gluteus maximus

Sciatic Nerve

Innervation to most posterior side of leg. Splits in two different nerves

Tibial nerve: postero and lateral leg. musclesof posterior thigh

Common fibular nerve: anterior lateral leg. Muscles of anterior leg

Pudendal Nerve

Innervates gential region

Muscles of perineum