15CHAPTER 13: SPINAL CORD, SPINAL NERVES, REFLEXES Flashcards
What are the function of the spinal cord?
Conduction – sensory info in, motor info out.
Locomotion – Contain central pattern generators = Control extensors and involved in walking
Reflexes – Involuntary stereotyped responses to stimuli
What are the regions of the spinal cord?
Cervical, Thoracic, Lumbar, and Sacral
Where is there lots of nerves to supple upper and lower limbs?
Cervical and lumbar enlargements
What is the medullary cone?
Tapered tip of cord
What is the cauda equine?
Collection of lumbar and sacral spinal nerves (L2 to S5)
What are menings?
Fibrous layers enclosing spinal cord
What are the 3 layers of meninges?
Dura mater, Arachnoid mater, pia mater
What is dura mater?
Tough collagenous sleeve around SC (dural sheath)
Where are epidural spaces found and what are they filled with?
Between dural sheath and vertebral bones – filled with fat and blood vessels
What is considered the ‘site of epidural anesthesia utilized during childbirth’?
Epidural space
What is arachnoid mater?
Adheres to dura mater
Subarachnoid space = loose mesh of fibers filled with CSF
located between dura mater and pia mater
What is pia mater?
Thin membrane covering spinal cord
Extends beyond medullary cone à terminal filum (coccygeal ligament) and anchors cord to Co1
What ligament anchor the cord laterally to the dura mater?
Denticulate ligaments
Sensory info always goes _____, while motor info always goes.
Up, down
What does decussation mean?
when a tract crosses to the other side
What does contralateral mean?
Origin and destination are on opposite sides
What does ipsilateral mean?
Origin and destination are on same side
In general, sensory input to the brain passes through what 3 neurons?
- 1st order neuron from receptor to spinal cord or medulla
- 2nd order neuron from spinal cord and medulla to thalamus
- 3rd order neuron from thalamus to cerebral cortex
State the origin, destination and the information provided by the cuneate fasciculus tract.
O= Chest and upper limb (T6 and up) D= medulla, Info= touch and proprioception
State the origin, destination and the information provided by the gracile fasciculus tract.
O= below chest (below T6), D= medulla, Info= touch and proprioception.
State the origin, destination and the information provided by the spinothalamic tract.
O= spinal cord, D= thalamus, Info= pain and temp, tickle, itch
State the origin, destination and the information provided by the spinocerebellar tract.
O=Spinal cord, D= Cerebellum, Info= proprioception from limbs and trunk
Motor pathways involve what 2 neurons?
- Upper motor neuron from brain à spinal cord
- Lower motor neuron from spinal cord à muscle or target organ
State the origin, destination and the information provided by the corticospinal tract?
O= motor cortex, D= ventral grey matter of spinal cord, Info= fine motor control of limbs
State the origin, destination and the information provided by the tectospinal tract?
O= midbrain (tectum), D= ventral grey matter of spinal cord, Info= reflexive movement of head and neck to sound and sight “hey you”
State the origin, destination and the information provided by the reticulospinal tract?
O= brainstem (reticular formation), D= ventral grey matter of spinal cord, Info= Balance and posture,
Analgesic (reduce transmission of pain signals back to brain)
State the origin, destination and the information provided by the vestibulospinal tract?
O= Pons (vestibular nuclei), D= spinal cord, Info= balance and posture
What is a nerve?
Numerous axons (nerve fibers) bound by CT.
What are fascicles?
Bundles of unmyelinated and myelinated nerve fibers (axons)
What does endoneurium surround?
Axons and schwann cells (covers the neurilemma)
What does perineurium surround?
fascicles (made of epithelial cells)
What does epineurium surround?
many fascicles (made of dense CT)
What are the different functions on nerve fibers (axons) and what are there target/source?
somatic or visceral
Target/source:
-somatic – innervate skin, skeletal muscles, bones, joints
-or visceral – innervate blood vessels, glands, viscera
What is a ganglion?
swelling in a nerve- collection of bell bodies (sensory neurons) outside CNS.
How many pairs of spinal nerves emerge through intervertebral foramen?
31 pairs
Proximal Branches branch into what 2 roots? What do they do?
Dorsal and ventral roots close to the spinal cord
Distal Branches branch into 3 after leaving the vertebrae, what are these branches?
Meningeal Branch
Dorsal ramus
Ventral Ramus
What does the ventral ramus supply?
Supplies ventral and lateral skin, trunk muscles, limbs
What does the dorsal ramus supply?
Supplies muscles and joints of the spine and skin of the back
Ventral rami branch and merge repeatedly to form what?
5 nerve plexuses:
Cervical, brachial, lumbar, sacral and coccygeal
Where is the Cervical nerve plexus located, what is the important nerve and what does it supply?
deep in the neck, C1 to C5,
important nerve = phrenic nerve
supplies neck and phrenic nerve to the diaphragm
Where is the Brachial nerve plexus located, what is the important nerve and what does it supply?
near the shoulder, C5 to T1,
important nerve = radial nerve
supplies upper limb and some of shoulder and neck
Where is the Lumbar nerve plexus located, what is the important nerve and what does it supply?
in the low back, L1 to L4,
important nerve = femoral nerve
supplies abdominal wall, anterior thigh and genitalia
Where is the Sacral nerve plexus located, what is the important nerve and what does it supply?
What are the functions of stretch reflexes?
Maintains muscle tone (esp. important for postural muscles)
Stabilizes joints by balancing tension in antagonistic muscles (extensors and flexors)
in the pelvis, L4, L5 and S1 to S4,
important nerve = sciatic nerve
supplies remainder of lower trunk and lower limb
Where is the Coccygeal nerve plexus located, what does it supply and what nerve innervates the head?
S4, S5 and Co1
skin over coccyx (tailbone) and anus
What is the dermatome?
Area of skin that provides sensory input to, or is innervated by, one spinal nerve
What are the somatic reflexes?
Quick, involuntary, stereotyped reactions of glands or muscle to sensory stimulation = involuntary contraction of a muscle
What are the 4 ‘Natures of Reflexes’?
- Require stimulation- Respond to sensory input
- Quick- Few if any interneurons involved
- Involuntary- difficult to supress, automatic
- Stereotyped- occurs in essentially the same way each times.
What innervates the head?
Cranial Nerves
What kind of reflex is salivation in response to food commercial?
Conditioned reflex
What kind of reflex is stomach responding to action in mouth?
Visceral reflex
What kind of reflex involves somatic nervous system?
Somatic reflex
What kind of reflex is related to pain withdrawal?
Somatic reflex
What are muscle spindles?
proprioceptors embedded in skeletal muscle fibers that respond to stretch of muscle.
What happens when you tap on a tendon?
Stretches and stimulates the muscle spindle.
Sensory input is sent via the primary afferent neuron. What does this cause?
It synapses directly on the alpha motor neuron in the alpha motor neuron of the spinal cord which will cause a reflexive contraction of the extensor muscle (quad) = monosynaptic reflex
What is Polysynaptic reflex?
Signals travel over many synapses to muscle
What does the golgi tendon organ respond to?
Respond to excessive contraction in the muscle
What happens when excessive tension on tendon inhibits motor neuron to muscle?
Muscle contraction decreased
Golgi Tendon Reflex monitor?
Monitors degree of contraction to spread workload across whole muscle e.g., maintain a grip
