Spinal Cord and Spinal Nerves: Anna made Flashcards
Spinal Cord
Spinal cord housed within the vertebral foramen
Meninges of Spinal Cord
- Dura mater
- Epidural space
- Subdural space - Arachnoid mater
- Subarachnoid space w/CSF
- Pia mater
where does the spinal cord start and end
medulla oblongata to L1 vertebra
cervical enlargment
neural innervation to upper extremities
Lumbar enlargement
neural enlargement to lower extremities
conus medullaris
inferior aspect of spinal cord
how many pairs of spinal nerves are there
31 pairs
Cauda equina
- “Horse’s tail”
- Axons of lumbar and sacral spinal nerves coursing inferiorly from conus medullaris to nerve origin
Filum terminale
- Extension of pia mater
- Attaches to sacrum
Denticulate ligaments
- Lateral extensions of pia mater
- Attach to dura mater
cervical region
C1-8
thoracic region
T1-12
Lumbar region
L1-5
Sacral region
S1-5
coccygeal region
Co1 or C0
Rootlets and roots of spinal nerves
Axons extend from spinal cord to innervate tissues
Anterior median fissure
Groove in front of spinal cord
Posterior median fissure
Groove in back of spinal cord
Gray Matter
Unmyelinated tissue (synapses)
Anterior horns of gray matter
Cell bodies of somatic motor neurons
Lateral horns of gray matter
Cell bodies of autonomic motor neurons (only segments T1-L2)
posterior horns of gray matter
Synaptic knobs of sensory neurons and cell bodies of interneurons
Gray commissure
- Band of gray matter surrounding central canal
- Connect left and right gray matter
Gray Matter: Nuclei
Groups of cell bodies in the CNS
Gray Matter: Nuclei: Posterior horn
Sensory nuclei receive afferent somatic and autonomic signals
Gray Matter: Nuclei: Lateral horn
Motor nuclei send out efferent autonomic signals
Gray Matter: Nuclei: Anterior horn
Motor nuclei send out efferent somatic signals
White Matter of Spinal Cord
Myelinated axons ascending to and descending from the brain
also has the posterior, lateral, and anterior funiculus
Posterior funiculus
Ascending sensory tracts
- white matter
Lateral funiculus
- Sensory and motor tracts
- white matter
Anterior funiculus
- Sensory and motor tracts
- white matter
how many neurons are in Sensory and Motor Pathways
Chain of two or more neurons
paired pathways
left and right tract
decussate pathways
- Cross the midline
decussate pathways: Contralateral
- Control opposite side of body
- most common
decussate pathways: Ipsilateral
- Control same side of body
sensory pathway
Tracts for proprioception, touch, temperature, pressure, pain, BP, stretch of organs, chemistry of blood and gut
Somatosensory pathways
Sensory information from muscles, joints, skin
Viscerosensory pathways
Sensory information from organs and vessels
how many neurons do sensory pathways use
2-3 neurons
Sensory Pathway Neurons: primary (1st order) neuron
- unipolar neuron with peripheral process with dendrites in tissue
- cell body in posterior root ganglion
- central process with synaptic knobs in posterior gray horn
- synapses with secondary neuron in posterior gray horn
Sensory Pathway Neurons: secondary (2nd order) neuron
- interneuron (multipolar)
- axon decussates in spinal cord or brain
- synapses with tertiary neuron in thalamus
Sensory Pathway Neurons: tertiary (3rd order) neuron
- interneuron (multipolar)
- cell body in thalamus
- sends information to somatosensory cortex
Somatic Motor Pathways
- Control skeletal muscle
- Involve 2-3 neurons
Upper motor neurons
- “Descending” tracts
- Begin in motor cortex, cerebral nuclei, brainstem nuclei
Substantia nigra, striatum
- Excite or inhibit lower
motor neurons
Lower motor neurons
- “Efferent” pathways
- Begin in cranial nerve nucleus or anterior horn of spinal cord
- Synapse with effectors
Direct pathway
- Conscious voluntary control
- Involves 2 neurons
Upper motor neuron
Originates at precentral gyrus of cerebral cortex
Axon part of one of two corticospinal tracts
* Lateral corticospinal tract
* Anterior corticospinal tract
Lower motor neuron
Originates in anterior gray horn of spinal cord
Synapses with skeletal muscle
direct pathway: Lateral corticospinal tract
- Decussates in medulla
- Targets appendicular skeletal muscle
- 85% of direct pathway neurons
direct pathway: Anterior corticospinal tract
- Does not decussate
- Targets axial skeletal muscle
- 15% of direct pathway neurons
Indirect Pathway
Unconscious, reflexiven control
- lateral pathway
- medial pathway
indirect: lateral pathway
- Precise, discrete movement of limbs
- Lateral corticospinal tract and rubrospinal tract (tegmentum to spinal cord)
indirect: medial pathway
- Muscle tone and movement of axial muscles
- Face, head, neck, trunk
Anterior nerve root
Axons of motor neurons
Cell bodies located in
anterior and lateral horns
Posterior nerve root
Axons of sensory neurons
Cell bodies located in
posterior root ganglion
where does spinal nerve exit spinal column
intervertebral foramen
Spinal nerve branches: Posterior ramus
Innervates muscles and skin of back
Spinal nerve branches: Anterior ramus
Innervates trunk, upper and lower limbs
Spinal nerve branches: Rami communicantes
Small branches of autonomic fibers
Nerve Plexus
- Network of branching spinal nerves
- Provide a backup system for sensory and motor function
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus - Give rise to peripheral (named) peripheral nerves
cervical plexus
- C1-C5
- innervates neck, head, shoulders
- phrenic nerve: innervates diaphragm
phrenic nerve
innervates diaphragm
brachial plexus
- C6-T1
- innervates upper extremities
- axillary nerve (deltoid)
- median nerve (ant. forearm)
- radial nerve (post./lat. forearm)
- ulnar nerve (medial forearm)
Lumbar plexus
- L1-L5
- femoral nerve (hip, ant. thigh)
- obturator nerve (medial thigh)
Sacral plexus
- S1-S5
- sciatic nerve (glutes, post. thigh)
- longest and largest nerve in the body
- tibial nerve (hams, adductors)
- common fibular nerve (knee and leg movers)
Dermatomes
An area of skin supplied
by sensory neurons of a
single spinal nerve
- Borders overlap
- Some overlap of function
- Referred pain
reflexes
- Shortest neural pathway from stimulus to response
- Survival mechanism
- Involuntary
- Stimulus
- Sensory neuron
- Interneuron (maybe)
- Motor neuron
- Effector
Spinal Reflex Classifications
- Spinal or cranial
- Somatic or visceral
- Monosynaptic or polysynaptic
- Ipsilateral or
contralateral - Innate or acquired
- Salivation, vomiting
Golgi-Tendon Reflex
- Monitors tension in tendon
- Inhibits tonic contractions
- IPSPs to agonist muscle
-Involuntary relaxation - Spinal
- Polysynaptic
- Somatic
- Ipsilateral
- Innate
- Reciprocal activation
- EPSPs to antagonist muscle
- IPSPs to agonist muscle
Stretch reflex
- “Muscle spindle fiber”
- Senses speed and force of contraction
- Recruits more motor units
- EPSPs to agonist
- Involuntary contraction
- Spinal
- Monosynaptic
- Somatic/autonomic
- Ipsilateral
- Innate
- Reciprocal inhibition
- IPSPs to antagonist muscle
- EPSPs to agonist
Withdrawal reflex
- Initiated by pain receptors
- EPSPs to agonist muscle
- Contracts body part away from painful stimulus
Crossed-extensor reflex
- Occurs with withdrawal reflex
- EPSPs to contralateral extensors
- Stabilizes body
Reflex Testing
Reflexes tested for diagnosis r/t muscles, nerves, spinal cord segments
Hypoactive reflex
Damage to spinal cord or muscle disease
Hyperactive reflex
- Damage to brain or spinal cord
- Clonus: Rhythmic, oscillating movements with reflex testing
