Ch. 13 - Spinal Cord Flashcards
What are some functions of the spinal cord?
- process reflexes
- integrate EPSPs and IPSPs
- conduct sensory impulses to brain and motor impulses to effectors
What are the meninges and spaces from superficial to deep?
epidural space dura mater subdural space arachnoid mater subarachnoid space pia mater
What is the removal of CSF called and why is this done?
spinal tap/lumbar puncture; used to diagnose pathologies, administer drugs
Why are spinal taps usually performed between L3-L4 or L4-L5 in adults?
to avoid damaging the spinal cord that ends at L1-L2
Where is the cervical enlargement in the spinal cord? Where is the lumbar enlargement?
C4-T1; T9-T12
Describe to ratio of white matter to grey matter along the spinal cord
going down the spinal cord, the ratio of white to grey DECREASES due to more sensory neurons (axon tracts) at higher levels
What are the functions of white matter?
nerve transmission to and from brain
What are the functions of grey matter?
integration of nerve impulses (EPSPs, IPSPs)
What are the posterior grey horns of the SC?
where sensory info enters
- axons of sensory neurons
- axons + cell bodies of interneurons
- somatic and autonomic
What are the anterior grey horns of the SC?
where output exits
- somatic motor nuclei to sk muscles
What are the lateral grey horns of the SC?
autonomic motor nuclei to autonomic effectors (cardiac/smooth muscle, glands)
How is white matter organized in the SC?
- divided into anterior, posterior, and lateral columns
- contain tracts (axon bundles in CNS)
What are 2 non-reflex functions of the SC?
grey - receives and integrates incoming/outgoing info
white - nerve impulse conduction to and from brain
How are the 31 pairs of spinal nerves named and numbered?
according to region and level of vertebral column from which they emerge (8C, 12T, 5L, 5S, 1C)
As spinal nerves are part of the PNS, how do they connect to the CNS?
via 2 bundles of axons (roots):
- posterior root (contains sensory axons; afferent)
- anterior root (contains motor axons; efferent)
Where are the cell bodies of sensory nerves?
posterior root ganglion
Why is there a posterior root ganglion but not an anterior root ganglion?
because motor cell bodies are within the spinal cord (in the anterior grey horns)
What is a possible of the formation of nerve plexuses instead of anterior rami directly going to part they supply?
safety feature; plexuses allow conduction of info even if one spinal nerve is cut; other nerves can carry info in/out
Why is there thoracic plexus?
anterior rami of spinal nerves T2-T12 directly innervate the intercostal spaces (intercostal nerves)
What are dermatomes?
specific segments of the skin that are innervated by all spinal nerves (except C1)
- spinal nerves carry sensory nerve impulses to spinal cord and brain
What is transection?
injury that severs spinal cord; loss of sensation and motor control below level of injury
- the higher the level of injury, the more severe the effect is
What is a reflex?
a fast, predictable, involuntary response to changes in the environment that helps maintain homeostasis
Where are spinal reflexes integrated?
grey matter of spinal cord
What are the 5 components of a reflex arc?
sensory receptor, sensory neuron, integrating center, motor neuron, effector
What are 4 important somatic spinal reflexes?
- stretch reflex
- tendon reflex
- flexor reflx
- crossed extensor reflex
What is the purpose of a stretch reflex?
controls muscle length; prevents injury from overstretching by causing muscle to contract (shorten) when it is stretched
Describe features of the stretch reflex
- monosynaptic, ipsilateral
- muscle spindle signals stretch of muscle
- motor neuron activated and muscle contracts
What is reciprocal innervation?
simultaneous contraction of one muscle and the relaxation of its antagonist (requires an interneuron; polysynaptic!)
What is the purpose of a tendon reflex?
controls muscle tension; causes muscle relaxation when muscle force is too extreme
Describe features of the tendon reflex
- polysynaptic, ipsilateral
- sensory receptors in tendons are activated
- inhibitory interneuron stimulated
- motor neuron is hyperpolarized, muscle relaxes
- reciprocal innervation causes contraction of antagonist muscle group
What is the purpose of the flexor (withdrawal) reflex?
moves a limb in response to a painful stimulus
Describe features of the flexor reflex
- polysynaptic, ipsilateral
- results in contraction of flexor muscles to move a limb to avoid injury or pain
What is the purpose of the crossed extensor reflex?
helps maintain balance during flexor reflex
Describe features of the crossed extensor reflex
- polysynaptic, contralateral
- causes synchronized extension of joints of one limb and flexion of joints in opposite limb
Describe the process of the flexor reflex
- pain sensors send signal to SC
- activation of interneurons that branch to diff SC segments
- motor fibers in several segments are activated
- multiple musc groups activated to move limb away
- reciprocal innervation
Describe the process of the crossed extensor reflex
- pain sensors in R foot send signal to SC
- activation of interneurons that synapse to motor neurons on contralateral side –> activate contralateral ext muscles
- extensor muscles contract to extend L leg and maintain balance
- reciprocal innervation
