Term
| what is the difference between the the epidural space in the skull and spine? |
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Definition
| in the skull, the epidural space is a potential space which may be occupied by blood/pus/tumor. in the spine/vertebral canal, the epidural space is a real space w/fat and venous plexi. |
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Term
| why is the level of the foramen magnum a location where the neuroaxis can get into trouble? |
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Definition
| this area includes the transition between the spinal cord and medulla, the 2 vertebral arteries and the spinal accessory/vagus nerve - all of which are at a higher risk of compression at this location. |
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Term
| what is tonsillar herniation? |
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Definition
| when the tonsils of the cerebellum (bumps on lower part of the cerebellum) are displaced down through the foramen magnum due to increased intracranial pressure - which can crush the ventricular system (foramina of lushka and magendie = increased intracranial pressure) and spinal cord. this may compress the RAS. |
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Term
| what level does the spinal cord end at? |
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Definition
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Term
| when questions on an exam refer to segmental levels such as C8-T1, what needs to be clarified? |
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Definition
| if the question is referring to the vertebral level, spinal cord level or spinal nerve. since the spinal cord ends around L1-2, the segments may not correlate with the vertebral level, for ex: w/a fracture of 11th thoracic vertebra, you may see findings in that pt related to distribution of L2-L4 b/c the cord has been displaced from corresponding vertebral level. |
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Term
| what is the cauda equina made up of? how can a lesion here produce a pure sensory or pure motor finding? |
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Definition
| roots of the spinal nerves. roots are specific (motor/sensory) in function - they are not mixed until they get the sacrum in many circumstances, therefore if a lesion affects a root before it gets to the sacrum and becomes mixed - it may produce a pure sensory or pure motor finding. |
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Term
| what are the 4 parts of the brain stem? |
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Definition
| the roof system layer (cerebellum, colliculi, epithalamus/pineal gland), the ventricular system layer (4th+3rd ventricle and the cerebral aqueduct), the tegmentum (*reticular formation, specific cranial nerve nuclei, ascending/descending tracts, and thalamic/hypothalamic nuclei), and the cerebral efferent layer (corticospinal/corticobulbar tracts and internal capsule) |
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Term
| what are the critical pathways? |
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Definition
| spinal reflex (brain stem reflex), corticospinal pathway (corticobulbar), posterior column-medial lemniscus pathway, anterolateral system pathway (spinothalamic), spinocerebellar pathway, and the ascending reticular activating system. |
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Term
| what is the ascending reticular activating system (RAS)? |
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Definition
| this longitudinal system is the core of the CNS (if shut down = death), is very important in monitoring circadian rhythms/automatic processes, and affects consciousness/unconsciousness. |
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Term
| what 2 neurotransmitters are associated w/the RAS? |
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Definition
| norepinephrine (NT - can provide buzz and "makes things happen") and serotonin (seems to be a "balancer" of neuronal activity in the RAS - both excitatory and inhibitory). |
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Term
| what is the locus coeruleus? |
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Definition
| a group of neurons in the brain stem which is associated w/the RAS and sends norepinephrinergic projections out into the rest of the brain - receptors for NE exist throughout the cerebrum. it is tinted blue-black (coeruleus) due to the high number of catecholaminergic neurons (make NE). |
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Term
| what is unique about neurons in the brain in terms of membrane potential? |
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Definition
| neurons in the brain operate at threshold and are held there by NE for a period of time (which is released volumetrically by the RAS). when the NE runs out or the neurons have to go back to resting membrane potential = "tiredness". |
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Term
| why is the tentorial incisure an area where the neuroaxis can get into trouble? how does this affect the RAS? |
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Definition
| the tentorial incisure is a hole in the tentorium cerebelli through which the brainstem passes. the tentorium cerebelli is composed of dura which is rigid and fibrous - therefore the brainstem may be damaged if it is pushed against the sides of the incisure as occurs in a *midline shift. if this occurs and the RAS is compressed, NE input to the cerebral hemispheres ceases and resting membrane potential, severe hyperpolarization or cell death may occur and the pt may go into a coma. |
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Term
| what may cause a fixed/dilated pupil? |
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Definition
| the oculomotor nerve is responsible for parasympathetic innervation to the eye = pupil constriction. it runs between the brainstem and edge of the tentorium and if compressed via midline shift, sympathetic innervation is unopposed = fixed/dilated pupil. |
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Term
| when does compression of the RAS occur? |
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Definition
| tonsillar herniation and uncal herniation |
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Term
| what is uncal herniation? |
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Definition
| the uncus is a large nucleus in the temporal lobe containing the amygdala which may compress the brainstem in the case of displaced temporal lobes. uncal herniation refers to compression of the brainstem (and RAS) rather than the uncus itself. |
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Term
| what characterizes the gray and white matter seen in the spinal cord? |
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Definition
| in the spinal cord, the center is composed of neurons which have a grayish-red tint due to increased blood supply and the outer area is composed of axons surrounded by white and fatty myelin. |
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Term
| do spinal nerves have more than one of each dorsal/ventral root? what is the clinical implication of this? |
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Definition
| yes, one spinal nerve may have many dorsal and ventral rootlets. this may result in just partial sensory loss which may become progressive as more rootlets become involved (as w/a schwannoma). |
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Term
| what is the layout of the white matter in the spinal cord? |
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Definition
| the white matter is broken up into 3 main bundles: anterior funiculus, lateral funiculus, and posterior funiculus (aka posterior column, further divided into midline fasiculus gracilis and lateral fasiculus cuneatus). |
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Term
| what is the layout of the gray matter in the spinal cord? |
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Definition
| the gray matter is divided into 10 neuronal/laminar groups (divided by cell body size). the most posterior lamina 1+2 have clinical significance as they are associated w/the response to pain (they are in close proximity to the DRG, which contains cell bodies of sensory neurons). lamina 1+2 are often damaged in DM and are basically the beginning of the anterolateral system (pathway for pain and temperature perception in the periphery). the lamina 8 neurons are found along the entire length of the the spinal cord and give rise to axons which go out through the ventral roots and innervate the musculature of the axial skeleton (trunk muscles: erector spinae, multifidi, abdominal, intercostal, etc). the lamina 9 muscles are the biggest motor neurons in the spinal cord and innervate the appendicular musculature (shoulder girdle, forearm, *hands, thigh, leg, feet) - they are only found in C5-T1 (upper limbs) and L2-S4 (lower limbs). the lamina 9 neurons are also called the *alpha motor/anterior/ventral horn/lower motor neurons and will produce paralysis if damaged (lamina 8 can sustain some damage due to overlap of innervation). |
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Term
| what determines if a CNS neuron is a "lower motor neuron"? |
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Definition
| if it has contact w/skeletal muscle (as CN 3,4,6 do) not where in the neuraxis it is located. |
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Term
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Definition
| a *single* lower motor neuron and all of the skeletal muscles it innervates (no overlap). |
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Term
| effectors are only as good as the ______? |
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Definition
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Term
| what are the 3 components to the spinal reflex? |
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Definition
| 1) sensory neuron: cell body in DRG, 2) motor neuron: lamina 9/lower motor neuron (LMN), and 3) interneuron: inside gray matter, modulates activity between sensory and motor neurons. |
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Term
| how does the deep tendon reflex work? |
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Definition
| tapping the tendon puts a slight stretch on the muscle, altering its steady state and causing a response by the lower motor neuron. |
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Term
| what does the patellar tendon reflex test? how is this documented? |
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Definition
| 1) integrity of the muscle (quads). 2) nerves innervating the group of muscles attached to the tendon (femoral). 3) spinal cord segment (L2-L4). this is documented as "normal" if bilaterally symmetric, "hyporeflexive" if one side is sluggish, or "hyperreflexive" if exaggerated on one side. |
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Term
| what characterizes lower motor neuron (LMN) disease? |
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Definition
| signs: hyporeflexia/areflexia, flaccid paralysis *to passive/resistive movement*, muscle atrophy (becomes just connective tissue due to lack of ACh), fasciculations/fibrillations (tested on EMG machine - as motor neurons die, they release ACh into the neuromuscular junction w/o any control by an AP = quivering muscle), weakness (loss of motor units), and absent hoffman/babinski reflex (aberrant reflexes are lost). LMN disease is often due to metabolic problems, ALS (amyotrophic lateral sclerosis), genetic spinal muscle atrophies, infection (polio), and trauma (compression). |
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Term
| what sensory-motor loops can be tested within the skull? |
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Definition
| the 6 cardinal eye movements exam tests and isolates the extraocular *skeletal muscles (example of alpha/lower motor neurons in the head) of the oculomotor, trochlear, and abducens nerves. the corneal/blink reflex tests the sensory component of the trigeminal nerve and the motor (skeletal) component of the facial nerve. the gag reflex tests the sensory innervation of the glossopharyngeal to the posterior tongue and the motor innervation of the vagus. the vestibular/semicircular canal sensory can be tested by spinning the pt or changing the temp of the external ear canal. the jaw jerk test assesses the muscles of mastication which are innervated by the mandibular branch of the trigeminal nerve and should contract symmetrically when the jaw is tapped. |
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Term
| how are reflexes modulated to produce voluntary movement? |
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Definition
| the same sets of neurons and motor units which form reflex loops tested in deep tendon reflexes are used in voluntary motor activity - but they are governed by 3 levels of CNS centers. 1) segmental spinal controllers/interneuronal sets, 2) suprasegmental controllers (descending corticospinal: axial/appendicular musculature and descending corticobulbar: head musculature), 3) extreme suprasegmental controllers: prefrontal cortex (planning+prediction) and limbic cortex (discretion). |
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Term
| where is the corticospinal pathway located? why is it named such |
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Definition
| in the lateral funiculus of the white matter in the spine. the corticospinal pathway is named such as it starts in the cortex (primary motor cortex - brodman's area 4) and ends in the spinal cord - about 1.5 ft long. |
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Term
| what is the internal capsule? |
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Definition
| the bundle of axons which meet ventrally as they go down from the primary motor cortex to the spinal cord. |
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Term
| what are the cerebral peduncles? |
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Definition
| what the axons coming ventrally from the internal capsule are called before they get to the pons. after they drop out from under the pons they are called the pyramids. (remember it is the same axon, same function, but the terminology changes as you move to different areas of the brain) |
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Term
| what occurs at the junction of the medulla and spinal cord (C1-2)? what is the lateral corticospinal pathway? |
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Definition
| 70-90% of corticospinal axons coming from the cerebral cortex will cross to the opposite side at that location from the L brain cross over to control the R side of the body and vice versa = area of decussation. *when something crosses the midline it becomes at risk - b/c then both sides of the body are at risk even w/a relatively small lesion* that 70-90% of neurons is called the *lateral corticospinal pathway, which can be tested (go to lamina 9 cervical and lumbosacral enlargements), while the other 10-30% remain ipsilateral as the *anterior corticospinal pathway and not much is known about their function (mostly go to lamina 8 axial skeleton positional muscle innervation). |
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Term
| what is the function of the corticospinal pathway? |
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Definition
| sending signals for conscious/voluntary motor movement from the prefrontal or limbic cortex, synapsing in lamina 9 and influencing activity of the lower motor neurons in movement of the extremities. |
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Term
| where is the corticospinal pathway most influential? |
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Definition
| in the distal parts of the extremities, for actions such as rapid independent finger movement (which depends on pure corticospinal innervation). |
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Term
| is the corticospinal pathway involved in control of the musculature found in the pelvic and urogenital diaphragm? |
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Definition
| yes - the corticospinal pathway controls the levator ani to maintain viscera, bladder and rectal control |
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Term
| what is hemiplegia? quadriplegia? paraplegia? |
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Definition
| hemiplegia = paralysis of upper limb/lower limb on same side. quadriplegia = total paralysis from neck down. paraplegia = both lower limbs are paralyzed (damage in lower back). |
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Term
| what is the blood supply to the internal capsule? what happens w/a vascular accident on one side of this? |
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Definition
| the *lenticulostriate branches of the MCA. w/a vascular accident on one side, paralysis is produced on the contralateral side (most often a complete side: hemiplegia). |
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Term
| what part of the internal capsule does the corticospinal pathway pass through? |
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Definition
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Term
| what part of the internal capsule does the corticobulbar pathway pass through? |
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Definition
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Term
| how is the corticospinal pathway tested? |
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Definition
| via rapid independent finger movements, deep tendon reflexes (if lower motor neuron is damaged = hyporeflexia, if upper motor neuron is damaged = hyperreflexia) |
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Term
| what is the upper motor neuron? |
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Definition
| the neuron which arises in primary motor cortex, axons through internal capsule, cerebral peduncle, pons, pyramid, crosses, lateral corticospinal pathway, synapses on lamina IX neuron - has nothing to do w/level of the body. |
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Term
| why does a damaged upper motor neuron result in hyperreflexia? |
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Definition
| b/c the upper motor neuron acts as a governor on the lower motor neuron |
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Term
| what needs to be done to dx spasticity? |
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Definition
| attempt passive movement and find resistance |
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Term
| what are the signs of upper motor neuron damage? |
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Definition
| hyperreflexia, spastic paralysis, no muscle atrophy, no fasciculations/fibrillations (muscle is not dying), weakness (b/c can't control reflexes), and present babinski/hoffman reflex (aberrant reflexes present - flailing away [dorsiflexion] from stimulus vs normal attempt at gripping stimulus). |
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Term
| what is different about the corticobulbar pathway as compared to the corticospinal pathway? |
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Definition
| the corticobulbar pathway goes through the internal capsule, comes out the genu and then innervates the face *bilaterally (as opposed to the corticospinal pathway) w/the exception of the facial nucleus which is ipsilaterally innervated in the lower part of the face. |
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Term
| what cranial nerve is responsible for facial expression? |
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Definition
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Term
| what cranial nerves are responsible for initiation of eating? |
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Definition
| the trigeminal, the glossopharyngeal, the vagus, and the hypoglossal (initiates swallowing). |
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Term
| what nerves are responsible for breathing? |
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Definition
| cervical nerves 3,4,5 - which form the phrenic nerve and keep the diaphragm "alive" as well as CN 10 which innervates the larynx (specifically the posterior cricoarytenoid muscles which abduct to allow air passage). the thoracic nerves also innervate the intercostals which facilitate breathing. |
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Term
| what nerves are responsible for speech? |
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Definition
| CN 12 - articulation and CN 10 - phonation |
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Term
| what is the rubrospinal pathway? |
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Definition
| a pathway which arises from the red nucleus (b/c has prominent blood supply) in the brain stem which gives rise to the decussating pathway and works closely w/the corticospinal pathway (they sit close together in the lateral funiculus). the cerebellum is the main driver of the red nucleus and the rubrospinal pathway is mainly involved in innervation of the girdle musculature and hip (positioning, getting extremity ready). |
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Term
| what characterizes the spinocerebellar pathway? |
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Definition
| it is an unconscious pathway, but if lesioned = clumsy ataxia in the pt. this cannot be specifically tested. |
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Term
| what is the dorsal column-medial lemniscus system? |
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Definition
| an ascending pathway which starts in the periphery and moves up the cerebral cortex, taking afferent stimuli up to the level of consciousness. |
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Term
| what is the first neuron in the dorsal column-medial lemniscus system? |
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Definition
| the dorsal root ganglion cell, which extends one axon out to the periphery and one axon up the spinal cord to the tip of the brainstem (thus they run about 5-6 ft). |
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Term
| what parts of the white matter in the spinal cord are composed of what parts of the dorsal column-medial lemniscus system? |
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Definition
| information from T5-6 and below is carried in the fasiculus gracilis. information from T5-6 and above is carried in the fasiculus cuneatus. |
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Term
| what is the second neuron in the dorsal column-medial lemniscus system? |
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Definition
| the nucleus cuneatus and nucleus gracilis, both of which synapse w/the axons of the dorsal root neurons then form the medial lemniscus at the level of the medulla/pons/midbrain - which is a band on the middle aspect of the brainstem that decusates on each side as it extends toward the cerebral cortex (therefore below this level, a spinal cord lesion will affect the ipsilateral side - but above this level of decussation, a lesion on one side will be apparent on the contralateral side). |
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Term
| what is the third neuron in the dorsal column-medial lemniscus system? |
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Definition
| the medial lemniscus synapses in the thalamus - which is the intermediator of what makes it to the level of consciousness. neurons in the thalamus then send axons up through the internal capsule to the cerebral cortex (post-central gyrus: the primary sensory cortex) in a homuncular fashion. the rest of the parietal-occipital lobe is what actually interprets this information. |
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Term
| what is the specific function of the dorsal column-medial lemniscus system? how is this tested? |
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Definition
| epicritic or discriminatory sensation. this can be tested via the 2-point touch function (blind object identification), vibration (tuning fork - tests efficacy of myelinated pathway), conscious proprioception (efficient gait/move toe and ask pt which way you moved it), and touch direction/texture (palm writing). |
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Term
| what is one of the first pathways to go in demyelinating disease? |
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Definition
| the dorsal column-medial lemniscus system |
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Term
| what is a brown-sequard lesion? |
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Definition
| an experimentally produced lesion to study the phenomenon of decussation (via a hemisected spinal cord) |
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