Transcript Neuroanatomy

Introduction to Neuroanatomy:
Major Structures of the Central
Nervous System (CNS) and Sites
for Dysfunction
Anatomy & Physiology
Spring 2016
Stan Misler
<[email protected]>
Why study neuroanatomy?
The brain is the basis for the mind and the soul. “The engine of reason
and the seat of the soul“. Reality is not absolute but rather how regions
of brain acquire and interpret features of the environment
Physicians use history and symptoms of illness to track down types of
brain disorders (epilepsy, stroke, blood collection, movement or sensory
disorder including demyelination) and then use computerized
tomography (CT or MRI) with functional imaging to carefully localize
lesions prior to angiography for aneurysm, surgery or radiation
treatments for tumor or epileptic focus, spinal tap in comatose patient.
Computerized tomography: horizontal, coronal and sagittal section
Computerized Tomography vs. Plain x-ray film
Imaging skull but
no brain tissue
CT: Rotating x-ray tube and detector give
cross-sectional slices with minimized
problem of superposition, improved image
contrast and way to record small differences
in tissue contrast
Magnetic resonance imaging of brain is more detailed
than dissection of preserved brain after death
Functional imaging (changes in regional bloodflow) localizes
specific regions of activity and confirms cerebral hemispheric
specialization
CNS composed of nuclei, (collections of synapses or
cell bodies = gray matter) + myelinated tracts
connecting the nuclei = white matter
Ascending tracts from spinal cord
Through brainstem to cerebral cortex
Descending tracts from cerebral cortex
through brainstem to spinal cord
Major landmarks of the central nervous system
(CNS): spinal cord + brain (midsaggital section)
Structure / Function correlates in CNS
Spinal cord: stretch + withdrawal reflexes; stereotyped limb movements
Brainstem: Neural ensembles in brainstem reticular formation
coordinate reflexes and simple behaviors (crying & suckling) to keep baby alive
(i) medulla oblongata: control of chewing, swallowing, digestion,
breathing, heart rate; reflexes for sneezing, coughing & vomiting
(ii) pons: connects cerebellum to cerebral hemispheres
(iii) midbrain: eye movements, visual and auditory reflexes
(superior and inferior colliculi) = info not sent to cerebral cortex
(iv) reticular formation (diffuse internal network of brainstem)
generates motor patterns
Brainstem is origin of cranial nerves to head, face, ears and eye muscles
Cerebellum: specialized motor movement processor : timing, coordination,
precision (by moderating force and range of motion); learning of motor skills)
(Brainstem + cerebellum = ancient hind brain as in frog)
Diencephalon: (i) thalamus: sensorimotor waystation (all sensory input except
olfaction + all motor outputs); conscious awareness may originate from
bidirectional loops (cortex <-> thalamus)
(ii) hypothalamus: regulates autonomic, endocrine, reproductive
and visceral functions and aggression some via pituitary gland
Telencephalon = cerebral cortex (wrinkled outer layer)
deep structures = basal ganglia for precision of motor activity and
limbic system = hippocampus for memory storage of facts and events (up to
2 years) + amygdala for autonomic and endocrine responses to emotional
states + comparison of emotional experiences with past ones
Motor cortex: initiation of skilled voluntary movements
Sensory cortex: Incoming stimuli from thalamus e.g., lateral
geniculate nucleus from retina to occipital cortex;
Prefrontal cortex = executive function = social interaction and moral
sense
Association cortex: mixed modality
Cortex is site of cognition: ability of brain to attend to, identify and act on
complex stimuli
(diencephalon + telencephalon = more modern forebrain beginning with reptiles)
Limbic system
Basal ganglia
Structure /Dysfunction Correlates in CNS
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Lower motor neuron injury -> flaccid paralysis
Upper motor neuron (pyramidal system) injury -> spastic paralysis
Basal ganglia injury -> movement disorders
Cerebellum -> ataxia
Ocular motor system injury -> loss of conjugate gaze
Somatosensory system injury -> anesthesia and analgesia
Visual system injury -> anopsia
Auditory system injury -> deafness
Gustatory and olfactory system injury -> ageusia and anosmia
Cerebral cortex injury -> aphasia, agnosia and apraxia
Limbic system injury -> antegrade amnesia and inappropriate behavior
Hypothalamic injury -> vegetative and endocrine imbalance
Autonomic nervous system injury -> visceral abnormalities
Disorder of blood supply to CNS -> stroke
Disorder of cerebrospinal fluid system -> hydrocephalus
Cerebrum including cortex in detail
Posterior gyrus =
primary motor cortex
for voluntary
movement
Secondary motor
cortex for planning of
sequence of motor
commands
Prefrontal cortex:
Executive function
Prospective short-term
memory (motor act to be
performed)
In hippocampus consolidation
of short to long term memory =
comparison with older
memories may take min to hrs
Association areas of
cortex for
multitasking:
simultaneous tasks
reduce encoding
(memorizing) and
retrieving (recalling)
Motor function
Especially amygdala
Somatosensory and motor homunculi
Limbic system
Basal ganglia
Corticospinal (Pyramidal) and extrapyramidal
efferent motor tracts
Indirect control of spinal activity modulating
posture, muscle tone and movement speed;
activated by supplemental motor cortex
Somatosensory afferent
tract from spinal cord to
cerebral cortex