Chapter 12 Part 1- Spinal Cord Flashcards
Where does the spinal cord reside
Extends from foreman magnum to about L2
Spinal cord anatomy
Cervical, thoracic, lumbar, sacral
-31 pairs of spinal nerves
- two enlargements (cervical supplies upper limbs and lumbar supplies lower limbs)
-conus medullaris - tapered inferior end
-cauda equina- spinal nerves extending beyond medullaris
Meninges of spinal cord
Connective tissue membranes surrounding spinal cord and brain
Dura mater - tough outer layer
Arachnoid Mater - thin and wispy
Pia mater - thin, bound tightly to surface of brain and spinal cord
Filum terminale
Formed by pia mater, this anchors the spinal cord to the coccyx and the denticulate ligaments that attach the spinal cord to the dura matter
Spaces in meninges
Epidural - contains blood vessels, areolar connective tissue and fat
Subdural- beneath dura
Subarachnoid - CSF fluid and blood vessels within
Layer of meninges
Epidural space
Dura mater
Subdural space
Arachnoid mater
Subarachnoid space
Pia mater
Denticulate ligaments
Points in the arachnoid mater where nerves exit the spinal cord
Arrangement of matter in spinal cord
Gray matter (neuron, cell, cell bodies, dendrites, axons) is inside in a butterfly arranged in horns (anterior, posterior, and lateral)
The white matter is myelinated axons on the outside in ascending and descending columns -dorsal, ventral, and lateral (with nerve tracts)
Commissures
Connect left and right halves of spinal cord. Grey has central canal.
Roots
Spinal nerves arise from rootless to form roots.
Dorsal root has dorsal root ganglion (a collecting of unipolar sensory neuron cell bodies)
Motor neurons travel through ventral root
Where do sensory neurons travel once out of the dorsal root
To the gray matter where they synapse with other neurons or interneurons
Where do motor neurons travel once cell bodies live in the spinal cord
Reside in the anterior horn and lateral horn, then travels via the ventral root into spinal nerves
Reflexes
Basic functional unit of nervous system and simplest portion capable of receiving a stimulus and producing a response. An automatic response to a stimulus that occurs without conscious thought.
Can be somatic (skeletal) or autonomic (homeostasis)
Components of a reflex
Sensory receptor to detect
Sensory neurons to transmit
Interneuron - can be excitatory or inhibitory
Motor neuron
Effector organ- responds with reflex
Major reflexes to know
Stretch
Golgi tendon
Withdrawal
Withdrawal with reciprocal innervation
Cross extensor
Simplest type of somatic reflex
Stretch - no Interneuron
Stretch reflex
Muscles contract in opposition to a stretching force (by means other than yourself (ex- physician tap))
Gamma motor neurons
Regulate sensitivity of the muscle spindle so that reflex can still occur
Receptor of stretch reflex
Muscle spindle; bundle of 3-10 small skeletal muscle cells contractile only at their ends, that respond to stretch
Stretching the muscle causes:
Stretch of spindle
Stimulation of sensory neurons travel through
Stimulation of alpha neurons at spinal cord
Alpha neurons stimulate muscle, causing contraction of the stretched muscle
Example of stretch reflex
Patellar reflex - doctor tapping below knee
Golgi tendon reflex
Prevents contracting muscles from applying excessive force on tendons. Produces a sudden relaxation of the muscles
Receptor of Golgi tendon reflex
Golgi tendon organ. Encapsulated nerve ending in tendon near muscle that detect excessive stretch and tension placed on the tendon.
Example of Golgi tendon reflex
Weight lifter suddenly drops heavy weight.
Process of Golgi tendon reflex
- Muscle contracts and tendon is stretched, increasing tension
- If a great amount of tension is applied, sensory neurons of Golgi are stimulated
- Sensory neurons stimulate inhibits neurons to releases inhibitory NTs
- Alpha motor neurons inhibited and relax
Alpha motor neurons
Neurons in the spinal cord that are imbedded into skeletal muscle
Withdrawal reflex
Function is to remove a body limb or other part away from a painful stimukus
Withdrawal reflex subdivisions
Reciprocal - causes relaxation of antagonistic muscles
Crossed extensor - causes extension of opposite limb
Process of withdraw reflex
- Step on tack and sensory neurons send input to spinal cord of CNS
- Excitatory interneurons excite alpha neurons which tell muscle to remove limb
- Collateral neurons tell brain but synapse on inhibitory interneurons in cord (reciprocal innervation)
Receptor of withdrawal reflex
Pain receptors
Crossed extensor reflex
Same scenario as withdrawal but sensory neurons create collateral branches that also synapses with excitatory interneurons in spinal cord that cross over white commissure fibers to gray matter and alpha neurons of the other side. Result is alpha motor neuron on side facing injury causes limb to be withdrawn and on other said, the neuron causes extension of other limb to maintain balance
How many pairs of spinal nerves
31
Where do spinal nerves exit
Through intervertebral foramina, except first pair and last four
What regions form plexuses
Cervical, brachial, and lumbar
Cervical plexus
C1-c4
-services head and neck structures
Major nerve in cervical plexus
Phrenic nerve - from c3-c5
Innervates diaphragm and controls breathing
Brachial plexus
C5-T1
Creates several branches (peripheral nerves)
-axillary, radial, musculotaneous, ulnar, median
Lumbosacral plexus
L1-S4
Serve lower limbs
Major nerve— sciatic nerve
What does thoracic vertebrae do in terms of spinal nerves
No plexuses.. supports the trunk of the body
Peripheral nerves
Named nerves stemming from plexuses
Consists of bundles of axons
Organization of connective tissue in a peripheral nerve
Endoneurium - between bundles of axons
Perineurium - surrounds bundles of axons to form fascicles
Epineuarium - groups of fascicles are covered with this making up the entire nerve
Numbers of spinal nerve organization
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
Dermatomal map
Skin area map of sensory nerve distribution by letter and number
