Nervous System Overview

Functions: Sensory input (gathering information), Integration (processing and interpreting sensory input), Motor output (activation of muscles or glands).
Structural Classification: Central nervous system (CNS) - brain and spinal cord; Peripheral nervous system (PNS) - nerves extending from the brain and spinal cord.
Support Cells (Neuroglia): Astrocytes (most abundant), Microglia (phagocytes), Ependymal cells (line cavities), Oligodendrocytes (wrap around nerve fibers in CNS), Satellite cells (protect neuron cell bodies in PNS), Schwann cells (form myelin sheath in PNS).
Neurons: Specialized cells that transmit messages.
- Cell body: Nucleus and metabolic center.
- Processes: Dendrites (toward cell body), Axons (away from cell body).

General functions: Support, insulate, and protect neurons.
Astrocytes: Abundant, star-shaped cells that brace neurons, form barrier between capillaries and neurons & control chemical environment.
Microglia: Spiderlike phagocytes that dispose of debris.
Ependymal cells: Line cavities of the brain and spinal cord; help circulate cerebrospinal fluid (CSF).
Oligodendrocytes: Have processes that form myelin sheaths around CNS nerve fibers
Satellite cells: Protect neuron cell bodies; surround neurons in PNS.
Schwann cells: Form myelin sheath in peripheral nervous system.

Sensory (afferent) division: Carries information to the CNS.
Motor (efferent) division: Carries impulses away from the CNS.
- Somatic nervous system (voluntary): Consciously controls skeletal muscles.
- Autonomic nervous system (involuntary): Automatically controls smooth and cardiac muscles and glands (sympathetic and parasympathetic subdivisions).

Resting neuron: Membrane is polarized (fewer positive ions inside the cell).
Depolarization: Stimulus changes membrane permeability and sodium (Na+) ions rush inward, changing membrane potential.
Action potential: If stimulus is strong enough, depolarization causes a complete reversal of membrane polarity.
Propagation of action potential: The action potential travels along the entire axon.
Repolarization: After the action potential, potassium (K+) ions rush out of the neuron, restoring the negative charge inside and positive charge outside.
Transmission at synapses: Neurotransmitters are released to transmit the signal across the gap (synapse).

A direct route from a sensory neuron, to an interneuron, to an effector.
A rapid, predictable, and involuntary response to a stimulus.
- Examples, patellar (knee-jerk) reflex & flexor (withdrawal) reflex.

Cerebral hemispheres: Paired superior parts of the brain, include more than half of the brain mass; ridges (gyri) and grooves (sulci).
Lobes of the cerebrum: Divided into Frontal, Parietal, Occipital, and Temporal lobes by fissures (deep grooves).
Specialized areas in cerebrum: Primary somatic sensory area (receives impulses), Primary motor area (sends impulses to skeletal muscles), Broca's area (speech).
Other areas: Gustatory areas (taste), Auditory areas (sound), Visual areas (vision), Olfactory areas (smell).
Interpretation areas: Speech/language region, Language comprehension region, general interpretation area.
Basal nuclei: Islands of gray matter buried deep within white matter.

Thalamus: Relay station for sensory impulses.
Hypothalamus: Important autonomic nervous system center (regulates body-temp, water balance, metabolism, emotions; associated with pituitary gland); produces hormones.
Epithalamus: Contains the pineal body (endocrine gland).

Midbrain: Contains reflex centers for vision and hearing.
Pons: Mostly composed of fiber tracts.
Medulla oblongata: Lowest part of brain stem, includes important control centers (heart rate, blood pressure, breathing).

Nerves and ganglia (outside the central nervous system).
Nerves: Bundles of neuron fibers (endoneurium, perineurium, epineurium).
Classification of nerves: Mixed nerves (both sensory and motor fibres); sensory (afferent) nerves; motor (efferent) nerves.
Cranial nerves: 12 pairs; primarily serve the head and neck.
Spinal nerves: 31 pairs; named for the region from which they arise.
Spinal nerve plexuses: Networks of nerves serving motor and sensory needs of the limbs (cervical, brachial, lumbar, sacral).