17/18. Spinal Cord & Nerves Flashcards
Overview of spinal cord
Part of CNS, communicates with body by spinal (peripheral) nerves
Link between brain and body through white matter tracks
Major center for reflexes in gray matter
Divided into segments based on associated vertebrae
Ends at the level of L1
Spinal cord protected by
Vertebral column (occupies vertebral canal)
Meninges (dura mater, arachnoid mater, pia mater)
Cerebrospinal fluid that flows in subarachnoid space
General features of spinal cord
Spinal nerves leave spinal cord through intervertebral foramina to travel to targets
Spinal cord does not extend the full length of vertebral canal
Cauda equina present
Filum terminale also present
Conus medullaris
Cone-shaped end of spinal cord
Cauda equina
Continuation of nerve roots in vertebral canal
Fillum terminale
Continuation of pia mater beyond conus medullaris
Anchors to coccyx and tethers spinal cord
Development of spinal cord
After 3 months of development, spinal cord grows more slowly than vertebral column
At birth, ends at L3
Adulthood, ends a L1
Lumbar puncture
Clinical correlate performed below L1 where spinal cord does not extend
Regions of spinal cord
Spinal cord segments are sections of spinal cord with a pair of spinal nerves attached
Segments: cervical (8), thoracic (12), lumbar (5), sacral (5)
Cervical and lumbar regions are enlarged for innervation for upper and lower extremities, respectively
Naming for spinal cord segments
Named for spinal nerve that emerges
Cervical - nerve # corresponds with vertebra below
Thoracic and lower - nerve # corresponds with vertebra above
Features of cross-section of spinal cord
Gray matter, white matter, and central canal
Characteristics of gray matter of spinal cord
Mostly cell bodies
Interior, looks like butterfly
Posterior wings = dorsal horn
Anterior wings = ventral horn
Characteristics of white matter of spinal cord
Mostly myelinated axons
Located on outside
Communication between different parts of cord and brain
Characteristics of central canal in spinal cord
Contains CSF
Neurons of spinal cord
In the back, out the front (dorsal root for sensory input and ventral root for motor output)
Neurons include sensory neurons, interneurons, and motor neurons
Spinal nerves join ventral and dorsal roots and contain both sensory and motor neurons
Characteristics of sensory neurons of spinal cord
Unipolar
Dorsal root ganglion (DRG) is a cluster of cell bodies
Attaches at dorsal root
Characteristics of interneurons of spinal cord
Multipolar
Cell bodies in dorsal horn
Characteristics of motor neurons of spinal cord
Multipolar
Cell bodies in ventral horn
Characteristics of spinal nerves (extremity vs axial)
Spinal nerves connect spinal cord to targets of the body
Named and numbered for the vertebral region they emerge (8 cervical spinal nerves but 7 cervical vertebrae)
Nerves to the extremities form nerve plexuses
Nerves to thorax and abdomen follow simple segmented pattern
Spinal nerve components
Carries both motor and sensory neurons
Sensory neurons enter spinal cord through dorsal root to dorsal horn (cell bodies in DRG)
Motor neurons leave spinal cord through ventral root to join spinal nerve (cell bodies in ventral horn)
Dorsal rami supply deep back and neck
Ventral rami supply rest of body wall and extremities
Motor and sensory functions of dorsal rami
Motor - muscles of deep back and neck
Sensory - skin over vertebral column
Motor and sensory functions of ventral rami
Motor- all other skeletal muscles in body wall and extremities
Sensory- rest of skin covering neck, thorax, abdomen, and extremities
MS and location of intercostal nerves
Travel between ribs
Motor to intercostal muscles
Sensation from segmented regions of thoracic wall
Location and MS of nerves of abdominal muscles
Travel between layers of abdominal muscles
Somatic motor to abdominal muscles
Sensation from segmented regions of abdominal wall
Characteristics of nerve plexuses
Network of ventral rami from multiple segments
Muscles of extremities perform complex functions- need sophisticated innervation from multiple SC segments
Types of nerve plexuses
Brachial plexus= motor and sensory to upper extremity
Lumbosacral plexus= motor & sensory to lower extremity
Nerves of upper extremity
Axillary nerve
Musculocutaneous nerve
Radial nerve
Median nerve
Ulnar nerve
All coming from brachial plexus
Characteristics of brachial plexus
Anterior rami of C5-T1
Sensory- skin of upper extremity
Motor- skeletal muscles of upper extremity
5 terminal branches
Pathway of extremity nerves
Roots from spinal cord
Trunks
Divisions
Cords
Branches
Roots and MWS of axillary nerve
Roots- C5 and C6
Motor- Teres minor (rotator cuff) and deltoid
Weakness with damage- shoulder abduction and shoulder lateral rotation
Sensory- skin over shoulder
Roots and MWS of musculocutaneous nerve
Roots- C5, C6, C7
Motor- Coracobrachialis, biceps brachii, brachialis
Weakness with damage- flexion at elbow, supination
Sensory- skin over lateral forearm
Roots and MWS of radial nerve
Roots- C5, C6, C7, C8,T1
Motor- triceps brachii, posterior forearm compartment
Weakness with damage- extension at elbow, wrist, & fingers, supination
Sensory- skin over posterior arm, forearm, hand
Roots and MWS of median nerve
Roots- C6, C7, C8, T1
Motor- anterior forearm compartment
Weakness with damage- flexion at wrist & fingers, pronation
Sensory- skin over lateral palm, fingertips of digits 1-3
Roots and MWS of ulnar nerve
Roots- C8 and T1
Motor- anterior forearm compartment
Weakness with damage- finger abduction and adduction
Sensory- skin over medial hand
Nerves of lower extremity
Femoral nerve, obturator nerve, gluteal nerves, sciatic nerve consisting of tibial nerve & common fibular nerve, superficial fibular nerve, and deep fibular nerve
Components of lumbosacral plexus
Lumbar plexus and sacral plexus
MWS of femoral nerve
Motor- iliopsoas, quadriceps femoris, sartorius
Weakness with damage- flexion at hip, extension of knee
Sensory- skin over anterior thigh, medial leg
MWS of obturator nerve
Motor- adductor longus, brevis, & magnus, gracilis
Weakness with damage- adduction of thigh at hip
Sensory- skin over medial thigh
MW of gluteal nerves
Motor- gluteus Maximus, medius, minimus, and tensor fascia lata
Weakness with damage: extension at the hip
Characteristics of sciatic nerve
Consists of tibial nerve and common fibular nerve
Joined by connective tissue
“Sciatica” = compression of sciatic nerve resulting in pain down back of lower extremity
MWS of tibial nerve
Motor- hamstring muscles, posterior compartment soft leg (superficial & deep)
Weakness with damage- extension of hip, flexion at knee, plantarflexion at ankle, toe flexion
Sensory- skin over sole of foot
MW of common fibular nerve
Motor- short head of biceps femoris
Weakness in flexion of knee may not be apparent
MWS of superficial fibular nerve
Motor- lateral compartment of leg
Weakness with damage- eversion of foot
Sensory- skin over dorsum of foot (not between first 2 toes)
MWS of deep fibular nerve
Motor- anterior compartment of leg
Weakness with damage- dorsiflexion of foot, extension of toes, inversion of foot
Sensory- skin between first 2 toes
