Chapter 33_1 flashcards
(18 cards)
Two Main Divisions of the Nervous System
Central Nervous System (CNS): Brain and spinal cord. Peripheral Nervous System (PNS): Cranial and spinal nerves.
Motor vs. Sensory Tracts in the CNS
Corticospinal Tract: Major pathway for motor neurons descending from the brain to the spinal cord. Spinothalamic Tract: Major pathway for sensory neurons traveling from the periphery up to the brain.
Contralateral Control of the Body
Most motor and sensory nerve fibers (about 80%) cross over to the opposite (contralateral) side of the body at the medulla (an area called the decussation). This means an injury to one side of the brain affects the opposite side of the body.
Four Major Lobes of the Cerebrum
Frontal Lobe: Voluntary movement, decision making, social judgment. Parietal Lobe: Sensation, proprioception. Temporal Lobe: Hearing, smell, memory. Occipital Lobe: Vision.
Hemispheric Specialization: Categorical vs. Representational
Categorical Hemisphere (usually left): Responsible for language, speech, and sequential-analytical processes. Representational Hemisphere (usually right): Focuses on facial recognition, music, and visual-spatial relationships.
Speech and Language Centers: Broca’s & Wernicke’s Areas
Broca’s Area: Controls the ability to speak (expressive function). Wernicke’s Area: Controls the ability to comprehend language (receptive function). Both are usually in the left hemisphere.
Aphasia: Expressive vs. Receptive
Expressive Aphasia (Broca’s area damage): The person cannot form words but can understand what is being said. Receptive Aphasia (Wernicke’s area damage): The person can speak but uses illogical language and cannot understand what is being said.
Brainstem: Components & Function
Components: Midbrain, pons, and medulla oblongata. Function: The “vital sign center” that controls consciousness and regulates heart rate, respiratory rate, and blood pressure.
Cerebellum: Function & Blood Supply
Responsible for smooth, coordinated movements, balance, posture, and equilibrium. Damage affects the same (ipsilateral) side of the body. Perfused by the posterior cerebral arteries. Vertebral-basilar insufficiency (VBI) can cause cerebellar ischemia.
Brain’s Blood Supply: Major Arteries
The brain is supplied by the internal carotid arteries (which branch into the anterior and middle cerebral arteries) and the vertebral arteries (which form the basilar artery and posterior cerebral arteries).
Circle of Willis: Function & Clinical Significance
A ring of arteries at the base of the brain that connects the anterior and posterior circulation. It provides collateral blood flow in case a major cerebral artery is blocked. It is also a common site for aneurysm formation.
Middle Cerebral Artery (MCA): Clinical Significance
Supplies about 80% of the brain’s tissue. Occlusion of the MCA or its branches is the cause of most strokes.
Cerebral Metabolism: Oxygen & Glucose Needs
The brain is the most energy-consuming organ, using 20% of the body’s oxygen. It relies solely on a continuous supply of oxygen and glucose to function. Brain cells cannot perform anaerobic metabolism and die within 5-6 minutes of oxygen deprivation.
Stroke: The Two Main Types
- Ischemic Stroke (85% of cases): Caused by a thrombus or embolus blocking a cerebral artery. 2. Hemorrhagic Stroke (15% of cases): Caused by the rupture and hemorrhage of a cerebral artery.
Transient Ischemic Attack (TIA): Definition
A “mini-stroke” where neurological deficits are temporary (usually resolve within an hour) and reversible because the body’s fibrinolytic system dissolves the clot. TIAs are a major warning sign of an impending stroke.
Cerebral Infarction vs. Ischemic Penumbra
Cerebral Infarction: The death of brain cells in the core area of ischemia, which is irreversible. Ischemic Penumbra: The area of hypoperfused brain tissue surrounding the core infarction. These cells are salvageable if blood flow is restored quickly (“Time is brain”).
Glutamate Toxicity in Ischemic Stroke
Ischemia causes brain cells to release excess glutamate, an excitatory neurotransmitter. This leads to an over-influx of calcium into neighboring neurons, activating degradative enzymes and causing cell death, thereby extending the stroke area.
Cushing’s Triad: Significance
A sign of increased intracranial pressure (ICP) and pressure on the brainstem. The triad includes: 1. Hypertension (high blood pressure). 2. Bradycardia (slow heart rate). 3. Irregular respirations.
