Different areas of cortex – occluding blood vessels supplying these will compromise their function:
primary sensory
cortex – in parietal lobe; first part to receive information from the senses
primary motor
cortex – in parietal lobe, rostral to primary sensory cortex; tells muscles what to do
primary visual
cortex – in occipital lobe; first part to receive information from sight
(b) diencephalon
– includes thalamus, hypothalamus, optic vesicle, neural retina
(2) Midbrain
(Mesencephalon) – middle portion; gives rise to mesencephalon (Peduncles, etc)
(3) Hindbrain
(Rhombencephalon)–posterior; becomes metencephalon (cerebellum, pons) and myelencephalon (medulla)
Spinal Cord
– different spinal levels control different parts of body; location of injury along spine determines effects
Peripheral Nerves
– Peripheral Nervous System – connects CNS to other organs of the body
Autonomic Nervous System
– has sympathetic and parasympathetic division
Functions
Two Primary Systems
(1) Sensory system
– receives input (internal mileiu or environment) and brings it to the brain
(2) Motor system
– takes info from CNS and brings it out to effector systems (muscles, organs, etc)
Association areas of brain
– between sensory and motor – expresses our behavior in response to input
highly interconnected – function independently and interdependently – diseases manifest this point
Damage to the Nervous System can have extremely diverse effects
– two extremes:
(1)
Destruction of Peripheral Function only: Amyotrophic Lateral Sclerosis (Lou Gehrig’s Disease)
afflicts Steven Hawkins, a theoretical physicist who cannot control his body and can only communicate via computer
Hawkins’ cognitive function is completely untouched
(2)
Destruction of Central Function only: Hydroencephaly
complete lack of cerebrum, leaving only cerebellum and brain stem (head is empty so flashlight shines through it)
motor control is intact (opposite of Hawkins) – baby was still able to cry, orient to sound, and feed
These two examples demonstrate cellular diversity (destruction or absense of different neurons cause vastly different effects) and regional specialization (different parts of nervous system have different functions)
Neurology in Clinical Medicine
25%
of all patients visiting a general practitioner’s office have complaints relating to the nervous system.
many neurological disorders are treatable: headache, seizure, epilepsy, dizziness, back/neck pain, neuropathy, parkinsonism
advances in neuro-imaging (MRI, CT scans) have provided clinical neuroscientists with the ability to perform high-resolution examination of the anatomical and functional basis of neurological disease without using invasive procedures (like spinal taps)
Four Steps a Neurologist must Take in Examining a Patient
:
(1) Phenomenology
– signs and symptoms (onset, progression, etc)
(2) Physiologic Disturbance
– physiology behind symptom
example:
dizziness could be caused by problems in vestibular system (Cranial Nerve VIII), postural hypertension, etc
(3) Anatomical or topographic diagnosis
– think about where the problem could be located
example:
vertigo could be a problem of inner ear (if tinnitus also involved) or brain stem (if difficulty swallowing)
(4) Pathological Diagnosis
– pathology behind the problem
There is no substitute for a good history and physical exam, so never take a diagnosis at face value – always try to evaluate the patient for yourself.
Cortical Function
Two Hemispheres: Left and Right
the dominant hemisphere is responsible for language, speech, and calculation
the non-dominant hemisphere is responsible for 3D or spatial perception and nonverbal ideation (music, poetry, etc.)
of those who are right-handed (85-90% of population), 99% localize language in the left hemisphere
NOTE:
aphasia is defined as loss of capacity for communication by speech, writing, or signs. It is distinguished from dysarthia, disturbance of articulation caused by paralysis.
Broca’s speech area
– posterior part of the inferior precentral gyrus in the dominant hemisphere.
responsible for motor aspect of speech; connected to Wernicke’s speech area through the arcuate fasciculus
Broca’s aphasia – from lesions in Brocca’s speech area; causes patients to speak slowly (non-fluent) and with effort; however, they have good comprehension of spoken and written language
Wernicke’s speech area
– located in the posterior part of the superior temporal gyrus in the dominant hemisphere
responsible for sensory part of speech; connected to Brocca’s area also through the arcuate fasciculus
Wernicke’s aphasia – from lesions in dominant hemisphere; patients have poor comprehension of speech, speak faster than normal, and have difficulty finding the right words to express themselves; patients usually unaware of the deficit
Parietal lobe
– many complex sensory and somatosensory areas; interrelates somatosensory, auditory, and visual stimuli
lesions can lead to neglect syndrome on the contralateral side; patient may not even be aware of other side
Temporal lobe
– primarily concerned with recognition
lesions can lead to agnosia, the lack of sensory-perceptional ability to recognize objects
agnosia can be visual, auditory, or tactile
prosopagnosia
– not recognizing faces.
Frontal lobe
– integrates information from other lobes of the brain.
lesions can cause inappropriate behaviors, lack of hygiene, and docility
most lesions are caused by head injury, and both hemispheres are usually involved