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o Cerebrum, Cerebellum, Brain Stem


• Cerebrum=

o 2 hemispheres: R & L
o 4 lobes: frontal, parietal, temporal, occipital


• Frontal Lobe=

o principal speech area: Broca’s, motor component of speech
o primary motor area (precentral gyrus): motor homunculus (inverted human: HAL)


• Parietal Lobe=

o primary sensory area (postcentral gyrus): sensory homunculus
o Major association areas located where lobes meet


• Temporal and occipital lobes:

o T: auditory area, hearing, superior temporal gyrus; Language: Wernicke’s area: sensory component of speech
o O: vision: primary visual cortex


• other subdivisions of cerebrum:

o gyri (bulges)
o fissures (large indentations)
o sulci (small indentations)


• Cerebellum:

o 2 hemispheres, cortex of gray matter on surface, central masses of motor related nuclei, bands of white matter
o attached to brain stem by 3 cerebellar peduncles
o fxn: equilibrium and position sense (unconscious proprioception); fine movement; control of muscle tone; overall coordination of muscular activity for proprioception, descending traffic from higher centers
o Spinocerebellar tract: receives afferent info from periphery; Tracts come from same side and do not cross


• Cerebellar Disorders:

o Ataxia: awkwardness of posture and gait
o ↓ tendon reflexes on affected side
o Asthenia: muscles tire easily
o Tremor: usu intention tremor (w purposeful movt)
o Nystagmus


• Brain stem:

o 3 parts: Midbrain, Pons, Medulla
o Most CNs (except I, II) derived from brain stem (12 pair); 3 sensory, 5 motor, 4 mixed; (CNs actually considered part of PNS)


• CNs:

o Olfactory (I); sensory; smells
o Optic (II); sensory; sees
o Oculomotor (III); motor; constricts pupil, accommodates
o Trochlear (IV); motor; moves eyes
o Trigeminal (V); mixed; chews and feels front of head
o Abducens (VI); motor; moves eyes
o Facial (VII); mixed; moves the face, tastes, salivates, cries
o Vestibulocochlear (VIII); sensory; hears, regulates balance
o Glossopharyngeal (IX); mixed; tastes, salivates, swallows, monitors carotid body and sinus
o Vagus (X); mixed; tastes, swallows, lifts palate, talks, communication to and from thoraco-abdominal viscera
o Spinal Accessory (XI); motor; turns head, lifts shoulder
o Hypoglossal (XII) motor; moves tongue


• Spinal cord:

o enters skull thru foramen magnum to become brain stem
o Central gray matter (neuronal cell bodies and synapses)
o Peripheral white matter (ascending and descending pathways)
o Ascending pathways: sensory info to brain
o Descending pathways: motor instructions down from brain
o Sites of contralateral crossing over of pathways within the white matter is important clinically


• Tracts of spinal cord:

o Ascending (sensory): Pain-temperature, Proprioception: stereognosis, Light Touch
o Descending (motor)


• Ascending tracts:

o Spinothalamic, posterior columns, spinocerebellar


• Spinothalamic Tract

o Pain-temperature, some light touch
o Crosses over to other side of spinal cord almost immediately → ascends to thalamus and cerebral cortex on that opposite side
o → a lesion in spinothalamic tract → loss of pain-temperature sensation contralaterally, below level of lesion


• Posterior Columns:

o conscious Proprioception/stereognosis, vibration, and some light touch
o 2 columns: fasciculus gracilis, fasciculus cuneatus.
o Initially remains on same side of spinal cord. Crosses over at junction of spinal cord and brain stem


• Spinocerebellar

o unconscious proprioception
o Does not cross spinal cord
o Ipsilateral sxs


• Descending Tracts (Motor)

o =Corticospinal Pathway
o Extends from motor area of cerebral cortex down thru brain stem, crossing over at medial lemniscus (junction bw brain and spinal cord)
o Synapses in anterior horn (motor grey matter) of spinal cord just prior to leaving cord
o Upper Motor Neuron (UMN): pathway from brain to spinal cord before synapse
o Lower Motor Neuron (LMN): postsynaptic pathway from spinal cord to periphery (peripheral nerve)


• Diencephalon

o = all the structures w “thalamus” = thalamus, hypothalamus, epithalamus, subthalamus
o Thalamus: Sensory relay and integrative center connects many areas of brain: cerebral cortex, basal ganglia, hypothalamus, brain stem; All sensory pathways synapse in thalamus, then relayed
o Hypothalamus: Contains a few nuclei w variety of functions; Produces hormones that control: body temp, hunger, moods, release of hormones from many glands: pituitary, sex drive, sleep, thirst
o Epithalamus: Main part is pineal gland
o Subthalamus


• Basal ganglia

o Part of base of brain, 3 clusters of neurons (caudate nucleus, putamen, globus pallidus), responsible for involuntary movements: tremors, athetosis, chorea


• Disorders of Basal Ganglia

o Parkinsonism: rigidity; slowness; resting tremor; mask-like facies; shuffling gait, assoc w degeneration in basal ganglia, substantia nigra
o Chorea: sudden, jerky, purposeless movements
o Athetosis: slow writhing, snake-like movements, esp. fingers and wrists
o Hemiballismus: sudden wild flail-like movt of one arm


• Basic Functional Unit of CNS:

o neuron: Info travels down dendrite into neuronal cell body and axon; Information shared bw neurons thru synapses
o pathway= chain of communicating neurons. In CNS a bundle of pathway axons= a tract, fasciculus, peduncle, or lemniscus; Outside CNS (peripheral nerves, which connect CNS with skin, muscles, other organ systems) a bundle of pathway axons = nerves


• Blood Supply to brain

o 2 main pairs of arteries supply brain
o 2 internal carotid: supply anterior cerebrum: become anterior cerebral a and middle cerebral a
o 2 vertebral arteries: supply posterior cerebrum (vertebral artery changes its name to → Basilar at level of Pons → Posterior Cerebral Artery at Cerebrum)


• Meninges

o PAD surrounds entire CNS including spinal cord and optic nerve
o Pia mater: thin and vascular, closest to tbrain
o Arachnoid: avascular
o Dura: thick, double layer of CT contiguous w bone with thick venous channels. Dips down bw cerebral hemispheres as false cerebri, bw cerebrum and cerebellum as tentorium cerebelli


• Sinuses

o Superior Sagittal Sinus: Spinal fluid drains here
o Cavernous Sinus: Drains eye; potential source into brain of infx from eye or face
o Transverse Sinus: Runs by ear: may become involved in inner ear infx



o Clear colorless fluid secreted by choroid plexus into ventricles


• General Organization of PNS

o Spinal Nerves (31 pair)
o Somatic Nervous System: Voluntary control of body via skeletal muscles
o Autonomic or Visceral Nervous System: parasympathetic and sympathetic


• Parasympathetic Division

o Synapse very close to or within their end organs
o Anabolic system, conserving energy: Slows heart rate, promotes absorption and digestion of food
o CN 3,7, 9, 10 have parasympathetic components
o CN3: ciliary body of iris→ constriction
o CN7: lacrimal, submandibular, sublingual glands → tearing, salivation
o CN9: parotid → salivation
o CN10: many organs (lungs, heart, stomach, intestines)


• Sympathetic Division:

o Motor fibers synapse relatively near spinal cord
o catabolic system, expending energy: fight or flight response to danger
o ↑ HR and contractility of heart, shunting blood to muscles and heart


• Neurologic Approach to the Patient

o Stepwise Approach:
o Where is the lesion?
o What is the lesion?
o Identify pathophysiology
o Generate DDx
o Select specific tests


• Where is the lesion?

o Location of the lesion(s) causing sxs
o One lesion or multifocal? Multifocal implies metastatic dz, MS, presence of 2 different dzs, malingering, hysteria
o Confined to nervous system or part of systemic do?
o What part of nervous system is affected? Peripheral nerves, spinal cord, brainstem, higher