notes - NPB12 Lecture 6 Cervical These are the first 8...

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Unformatted text preview: NPB12 Lecture 6 Cervical These are the first 8 segments in the neck. (C1 - C8) T horacic These are the next 12 segments in the upper and middle back. (T1 - T12) Lumbar These are the next 5 segments in the lower back. (L1 L5) Sacral These are the last 5 segments in the very lower back. (S1 - S5) T he spinal cord is actually much shorter than the backbone. The spinal cord itself, where the gray matter is, ends at about the L1-L2 region of the backbone. From there, just the spinal nerves continue down the hollow portions of the vertebrae before they exit into the body. This bundle of nerves in the lumbar and sacral regions of the backbone are called the Caudia equine (Latin for “horse tail”). Lower motor neuron: these are the motor neurons in the ventral horn of the spinal cord Upper motor neuron: these are the neurons in the brain or spinal cord send signals to ventral horn Paraplegia: Paralysis of both lower limbs (legs). Quadriplegia: Paralysis of all four limbs. "plegia" and "paresis" mean paralysis. The way that they happen are usually car accidents (45%) or other types of accidents (34%). The rest are from sporting accidents (no diving!) falls, assault, attempted suicide There are two types of motor neurons, and injury to each gives rise to very different symptoms. Lower motor neuron: These are the motor neurons in the ventral horn of the spinal cord LOWER MOTOR NEURON: Flaccid. This means what most people think it does, the muscles are in a state of no contraction (flaccid). There are no reflexes, and no resistance to passive movements. atrophy of the muscles, meaning that the muscles waste away and the limbs get very skinny Upper motor neuron: These are the neurons in the brain or spinal cord that are somehow involved in sending the signal to the ventral horn UPPER MOTOR NEURON: Spastic/Rigid. This is marked by an exaggeration of the reflexes . Passive movements are also difficult to initiate, no muscle tone Lower motor neuron injury leads to: Flaccid paralysis: Limbs are weak, no muscle tone Atrophy No reflexes No resistance to passive movements We ve seen this already with tetrodotoxin Polio Botulism Upper motor neuron injury leads to: Spastic / Rigid paralysis: Reflexes are there and are exaggerated There is muscle tone. Commonly there is a flexion of muscles that appears that it would be quite painful. Passive movements are difficult to start, but then it is easy to move the limb. •  Initially after the injury there is what is called spinal shock • This consists of flaccid paralysis for all dermatomes below (caudal) to the lesion •  No reflexes • If it is an upper-motor neuron injury, then these symptoms subside after days to weeks and spastic/rigid paralysis results. • This is the period where steroids are helpful to help prevent extensive injury. Initially there is paralysis and loss of sensation below the level of the cut there is flaccid paralysis, with minimal spinal reflexes. This period of time is called spinal shock both spasticity and rigidity occur in the muscles innervated by nerves below the lesion, no reflexes, steriods are helpful to help prevent extensive injury Complete Transection No voluntary movement Brown-Sequard Syndrome No voluntary movement No touch sensation No pain sensation No touch sensation No pain sensation lost of touch, pressure, and position, sense on ipsilateral side, loss of pain Anterior Spinal Artery Syndrome No voluntary movement Normal touch sensation No pain sensation ventral secion damaged Left Brown-Sequard Syndrome No voluntary movement No touch sensation No pain sensation Contralateral Pain Sensation Right Ipsilateral voluntary movement Ipsilateral touch sensation Left Anterior Spinal Artery Syndrome No voluntary movement Normal touch sensation No pain sensation Right Voluntary movement on both sides Pain sensation on both sides Touch sensation is okay T ouch, pressure, and position: Cell bodies in the dorsal root ganglion project their axons up the ipsilateral dorsal white matter to neurons in the brain. Motor movement: Cell bodies in the brain project down the lateral white matter. Cell bodies in the ventral horn project out the spinal nerve to the muscles. Pain, temperature: Cell bodies in the dorsal root ganglion project to cells in the dorsal horn of the spinal cord. Cells in the dorsal horn of the spinal cord project their axons up the contralateral ventro-lateral white matter to the brain. Dorsal Columns: Touch sensations from the ipsilateral side of the body To left side of brain Left to skin on left To right side of brain Right to skin on right Dorsal column pathway: Ipsilateral touch From left side of cerebral cortex From right side of cerebral cortex axons cross the midline in the brainstem (in the head) Corticospinal Tract Axons in the spinal cord control the ipsilateral ventral horn, and therefore the ipsilateral voluntary movement Axons come out and make synapses on the ventral horn motor neurons and interneurons The spinothalamic tract is axons of neurons that go from the spinal cord to the thalamus. They carry pain information from the contralateral side of the body To pain receptors on left side The post-synaptic neuron s axon crosses the midline in the spinal cord and then travels up to the brain (the thalamus) Synapse in the dorsal horn of the spinal cord Left Right Dorsal columns: Axons that carry information about touch on the ipsilateral side of the body left touch left move right pain right touch right move Corticospinal tract: axons that carry information to allow voluntary movement on the ipsilateral side of the body left pain Spinalthalamic tract: Axons that carry information about pain on the contralateral side of the body. Herniated Disk: The disk gets out of the normal location and will put pressure on the spinal nerve. This is similar to hitting your funny-bone , which is generally considered to be unpleasant. Slipped / Herniated Disk There are disks of cartilage between the vertebrae that act as cushions for the bone. If one of these swells up (herniated) or moves up against the cord (slipped), it will put pressure on the cord and either block transmission of the action potentials, and/or cause the axons to fire action potentials Whiplash: A sudden hyper-extension followed by hyper-flexion of the neck Whiplash: This is caused by a sudden hyperextension/hyper-flexion of the neck muscles. Basically it jolts and stretches the spinal cord, which causes spinal shock to varying degrees. If it is bad enough, the shock to the cord will sever it, and if this is at a high enough level (i.e. C2) it will cause death The autonomic system is also affected. The sympathetic is the fight or flight response, and serves in a manner similar to the adrenalin rush . The parasympathetic is the opposite. The sympathetic uses the more caudal segments of the spinal cord, so it is often affected by spinal cord injuries. T he parasympathetic nervous system's job can be summarized as relaxing these internal organs, whereas the sympathetic nervous system's job is to jack up the system for the "fight or flight" response. Once the cord is transected, it is the sympathetic nervous system that is hit hardest. The result is a basic slowing down of the gut, leading to constipation and poor appetite. if the patient is lifted up into a sitting position they will faint. The para sympathetic uses the rostral segments (brainstem) so is not affected. How come quadraplegics don t die of respiratory arrest? The C5 – T1 do the arms, then T2 – T9 does the chest, so how can you have your arms paralyzed but not your breathing muscles? T he easy answer is that the diaphragm is controlled by spinal cord segments C3-C5, even though the other chest muscles are controlled by the thoracic segments. Transections of the cord below this level will still allow the diaphragm to function normally The answer is that the diaphram is the main muscle that controls breathing, and it is innervated by segments C3 – C5. So you can have an injury at C5 or C6 and still control your diaphram (and breathe). If your injury is higher than C5, you will need a respirator to survive, such as Christopher Reeves What can be done to help people with spinal cord injuries? Dead is dead (Dr. Fredrick Frankenstein) But broken axons do not always kill the neuron, and in the peripheral nervous system axons do regrow. If you cut your nerve, it may grow back over time. How does it know which way to go? Sometimes it doesn t! Imagine what would happen in the spinal cord. Maybe that is why the central nervous system seems to go out of its way to prevent regrowth. ...
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