2-2. Spinal Cord & Structures
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66 terms
Terms | Definitions |
|---|---|
 vertebral column structure | -32 vertebral levels -7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, 3-5 fused coccygeal vertebrae |
| vertebral level | -each has muscles, skin, bones -trunk=stack of coins -each=segment -neurons supply instruction to/from segments via spinal nerves |
| spinal nerves numbering | -based on where it exits from vertebral canal and vertebral level |
| spinal segment | each region on spinal cord that supplies a pair of spinal nerves |
| spinal cord length | -shorter than vertebral canal -most spinal segments are located more superiorly than associated pair of spinal neres exit |
| T10 vertebral level | -L1 spinal segment located and exits |
| L1-L5 spinal segment is directly dorsal to | T10-T12 (half) |
| S1-S5 spinal segment is directly dorsal to | T12 (half)-L1 (half) |
| misalignment between spinal segment and vertebral level due to | -result of differential growth -fetal development-vertebral column elongates faster than spinal cord; column pulls and elongates lower spinal nerves -lower spinal nerves forms bundle=cauda equina |
| cauda equina | bundle of spinal nerves at L2-L5-S1 |
| meninges | -covers & protects the brain & spinal cord |
| dura mater | -outermost & toughest layer -in vertebral canal, surrounded by fatty cushion |
| epidural space | -fatty cushion that surrounds spinal cord below dura mater -site for anesthetic injection during labor |
| epineurium | -extension of dura mater and surround spinal nerves |
| arachnoid mater | -deep of the dura mater -spongy looking meninges with subarachnoid space |
| pia mater | -deepest meninges & directly meets with spinal cord |
| pia mater specialization | -1-there are at least 20 pairs of lateral projections=denticulate ligaments -2-filum terminale |
| denticulate ligaments | -lateral projections -anchor spinal cord to dura mater -limit movement of spinal cord |
| filum terminale | -at end of conus medularis -pia mater continues as thin thread that anchors end of spinal cord to the sacrum |
| spinal cord parts | -3 -white matter (outer region), grey matter, central canal |
| spinal cord white matter | -myelinated axons -oriented vertically to/from CNS -grouped in 3 columns on each sagittal plane |
| spinal cord grey matter | -3 columns: dorsal horn, ventral horn, lateral horn |
| lateral horn of spinal cord grey matter | -only present at thoracic spinal levels -contains sympathetic nervous system neurons |
| central canal of spinal cord | center, cavity in continuity with ventricles in the brain |
| spinal cord is devoted to | -either sending information up to the brain or sending motor commands down to the appropriate level of the spinal cord |
| ascending pathways | -systems of neurons that bring information to the brain -signals travel along 3 neurons, considered 1st, 2nd, and 3rd order neurons |
| spinothalamic tract | example of an ascending pathway |
| path of ascending pathway | -neuron (1st order): it enters the dorsal horn where sensory neurons synapse with interneurons -the interneuron (2nd order): it decussates (crosses) to the contralateral (opposite) side and its axon enters the white matter. From here, the axon runs up to the thalamus where it synapses -another interneron (3rd order): the axon is wired to the appropriate part of the somatosensory cortex |
| descending pathways | -systems of neurons that bring motor information from the brain down to the appropriate spinal level |
| corticospinal tract | -example of a descending pathway |
| primary motor cortex | where voluntary motor commands originate from |
| descending path | -upper motor neuron- -this interneuron travels down the white matter corticospinal tract -decussation occurs in the medulla, and the tract continues down the spinal cordmuscles -at the appropriate spinal level, the axon leaves the tract and enters the ventral horn where it synapses with |
| upper motor neuron | -pyramidal neuron |
| lower motor neuron | -this is the motor neuron of the Peripheral Nervous System (PNS) -it leaves the spinal cord to innervate skeletal musclesSynapse in ventral horn |
| spinal nerve forms from | joining of dorsal & ventral roots |
| dorsal & ventral roots | 2 major tributaries that form the spinal nerve |
| dorsal root | -carries sensory infromation to the dorsal horn of the spinal cord -has a large collection of cell bodies that form the dorsal root ganglion - |
| pseudounipolar | -sensory neurons are unique in having the cell body in the middle of the course of the axon - such neurons are called unipolar |
| ventral root | -neurons of the ventral root have their cell bodies in the ventral and lateral horns of the spinal cord -the axons of the ventral root are entirely motor |
| somatic | -outer body -bones, skeletal mucles, skin |
| visceral | -interior cavities of the body -digestive, respiratory, cardiovascular systems |
| visceral and sensory | Besides a simple division between sensory and motor, the nervous system is also distinguished on the basis of |
| 4 functional components of gray matter of spinal cord | ■ Somatic sensory: from skin, skeletal muscles, joints ■ Visceral sensory: from the viscera ■ Somatic motor: to skeletal muscles ■ Visceral motor: to smooth muscle and glands |
| rami= | branches of spinal nerve from its roots |
| rami main branches | dorsal ramus, ventral ramus, communicating rami |
| dorsal ramus | carries somatic motor and somatic sensory to the dorsal body wall |
| ventral ramus | carries somatic motor and somatic sensory to the lateral and anterior body wall |
| communicating rami | -carry visceral motor (sympathetic) and visceral sensory neurons to and from the viscera (heart, lungs, abdominal organs) -distribute neurons via sympathetic chain |
| sympathetic chain | -runs parallel to the spinal cord and sends branches towards the thoracic and abdominal cavities |
| ascending tracts | -inform your brain of sensations and descending tracts give voluntary commands -many sensory inputs elicit automatic motor responses (brain not involved in response to stimulus) |
| spinal reflexes | -elicit automatic motor responses when the brain is not involved in the response to the stimulus -these are involuntary circuits |
| simplest reflexes | sensory neuron synapsing with a motor neuron |
| monosynaptic reflexes | simplest of reflexes involving a snesory neuron synapsing with a motor neuron |
| monsynaptic reflex path | -stimulus-sensory neuron in spinal cord-sends axon terminal to ventral horn-motor neurons stimulated |
| monosynaptic reflex example | stretch reflex |
| stretch reflex | -stretch of the muscle reflexively causes contraction of the same muscle leading to greater stability of joints -the patellar (or knee-jerk) reflex is one example of a stretch reflex |
| stretch reflex example | -the patellar (or knee-jerk) reflex |
| awareness of reflex | -the sensory neuron also sends a projection upward along an ascending tract in order to inform the brain of the sensation. Although the brain is not participating in the reflex, it is nonetheless aware of the stimulus |
| stimulus path of stretch reflex | 1. Stimulation of stretch receptor 2. Signal occurs along sensory neuron 3. Synapse with motor neuron 4. Signal occurs along motor neuron |
| polysynaptic reflexes | -many reflexes involve one or several interneurons |
| withdrawal reflex | -example of polysynaptic reflex -protective in nature. |
| stepping on nail | -withdrawal reflex -immediate response of your foot is to withdraw -the stimulus travels along a sensory neuron, and in the spinal cord synapses with one or several interneurons |
| synapsing allows | -signal to diverge to multiple locations |
| divergence of signal | -ex: motor neurons are stimulated in hip, thigh, & lower lege -inhibitor signals may be sent to muscles that oppose withdrawal -In some reflexes, signals are sent to the contralateral side of the body, ensuring that you withdraw one foot from the source of pain and stabilize the other leg to remain standing -there are hundreds of such reflexes wired into your spinal cord, all functioning without direction from the brain |
| pathway of nail stimuli | 1. Stimulation of pain receptor 2. Signal occurs along sensory neuron 3. Synapse with interneuron(s) 4. Signal occurs along motor neuron 5. Muscle is stimulated to contract, withdrawing limb from pain |
| draw: A motor neuron to a back muscle A motor neuron to your six pack abs A motor neuron to your stomach A sensory neuron from the skin of your back A sensory neuron that tells you that you're full A sensory neuron from your belly button | ... |
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