Nervous System Divisions

Here are the study notes for the text:

The nervous system is divided into the Central Nervous System (CNS) and Peripheral Nervous System (PNS)
CNS consists of the brain and spinal cord, enclosed within protective cranial vault (skull) and vertebral column
PNS consists of cranial nerves and spinal nerves, functioning as an input-output system for relaying impulses to the CNS and transmitting output messages to control effectors (muscles and glands)

Somatic Nervous System: consists of motor and sensory pathways that regulate voluntary control of skeletal muscle
Autonomic Nervous System: consists of motor and sensory components that regulate body's internal viscera through involuntary control of organ systems (sympathetic and parasympathetic systems)

Neurons: primary cells of the nervous system, respond to stimuli and conduct impulses
Supporting cells (neuroglial cells): provide structure, support, and nutrition for neurons

Three components: soma (cell body), dendrites (multiple branch extensions that receive nerve impulses), and axon (long, conductive projection that carries impulses away from the cell body)
Classified into bipolar, multipolar, and unipolar neurons based on structure and function
Functionally, neurons can be sensory (afferent), motor (efferent), or interneurons

Four types: astrocytes (fill spaces between neurons and surround blood vessels, contribute to blood-brain barrier), oligodendrocytes (deposit myelin in the CNS), microglia (remove debris in CNS), and ependymal cells (line CSF-filled cavities in CNS)

An important component of the axon, acts as an insulating substance, and helps increase nerve conduction velocity
Formed by Schwann cells in the PNS and oligodendrocytes in the CNS
Disorders of the myelin sheath, such as multiple sclerosis and Guillian-Barre syndrome, can lead to demyelination and axon death

Brain: consists of the cerebrum, cerebellum, brain stem, and limbic system
Cerebrum: divided into two hemispheres, with gray matter (cerebral cortex and basal ganglia) and white matter (myelinated nerve fibers)
Spinal cord: divided into gray matter (cell bodies of neurons) and white matter (myelinated nerve fibers)

Divided into the telencephalon (cerebrum) and diencephalon (thalamus and hypothalamus)
Cerebrum: divided into two hemispheres, with a cerebral cortex and basal ganglia
Thalamus: major integrating center for afferent impulses to the cerebral cortex
Hypothalamus: regulates body temperature, endocrine function, and emotional expression

Consists of the cerebellum, pons, and medulla
Cerebellum: responsible for maintaining balance and posture
Pons: an important center for control of respiration
Medulla: regulates vital reflexes, including heart rate, blood pressure, and respiration

Parkinson's disease: characterized by the degeneration of dopamine-producing neurons in the substantia nigra
Alzheimer's disease: characterized by the presence of senile plaques and neurofibrillary tangles, leading to brain atrophy and cognitive decline

Meninges: three layers of protective tissue that cover the CNS (pia mater, arachnoid, and dura)
Blood-Brain Barrier: a selective barrier that permits the passage of essential substances while restricting the entry of toxins
Autoregulation: the ability of the CNS to maintain constant blood flow despite changes in systemic arterial pressure### Neural Cells and Cerebral Blood Flow
Neural cells function only with aerobic metabolism
Increases in carbon dioxide or hydrogen ion (acidosis) increase cerebral blood flow
Decreased oxygen levels increase cerebral blood flow
Acidosis depresses neural activity, and increased blood flow helps to wash away acidic materials from brain tissue

A stroke is an acute focal deficit from a vascular disorder that injures brain tissue
Risk factors for stroke include:
- Age (risk increases with age, 1%/yr in persons 65-75 yrs old)
- Gender (men have a 19% greater incidence than women)
- Ethnicity (African-Americans have a 60% greater risk of death & disability from stroke)
- Heart disease (especially atrial fibrillation & other conditions that predispose to clot formation)
- Polycythemia and sickle cell anemia predispose to clot formation
- Alcohol consumption contributes to stroke through induction of cardiac arrhythmias, hypertension, and reduced cerebral blood flow
- Cocaine use can cause both ischemic and hemorrhagic strokes

Caused by thrombus or emboli in cerebrovascular vessels
Can cause a central core of dead or dying cells, surrounded by a penumbra (area of minimally perfused cells)
Thrombotic stroke is the most common cause of ischemic strokes, often occurring in atherosclerotic blood vessels
Transient ischemic attack (TIA) is a temporary disturbance in cerebral blood flow, often providing a warning of impending stroke
Embolic stroke is caused by a moving blood clot that travels from its origin to the brain

Classification based on shape and size:
- Saccular (berry)
- Fusiform (giant)
- Mycotic
- Traumatic

Bleeding into the subarachnoid space, often due to ruptured cerebral aneurysm
Manifestations include:
- Atypical headache (often with a history of headache preceding onset)
- Meningeal irritation (nuchal rigidity, photophobia)
- Cranial nerve deficits (diplopia, blurred vision)
Complications can include:
- Rebleeding
- Vasospasm
- Hydrocephalus