Nervous System and Central Nervous System: Study Guide (CH 11 & 12a)

Study Guide - Smart Notes

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The action potential is a rapid electrical signal that travels along the membrane of a neuron, allowing communication within the nervous system.

Generation: Action potentials are initiated when the membrane potential reaches a threshold, typically due to the opening of voltage-gated sodium channels. This causes a rapid influx of Na+ ions, depolarizing the membrane.
Propagation: The depolarization spreads to adjacent regions, opening more sodium channels and moving the action potential along the axon. Repolarization follows as potassium channels open, allowing K+ to exit the cell.
Key Steps:
1. Resting state:
2. Depolarization: influx
3. Repolarization: efflux
4. Hyperpolarization: temporary overshoot
Example: Transmission of a pain signal from a finger to the spinal cord.

The nervous system is divided into structural and functional components for organization and specialization.

Structural Divisions:
- Central Nervous System (CNS): Brain and spinal cord
- Peripheral Nervous System (PNS): Nerves and ganglia outside the CNS
Functional Divisions:
- Sensory (Afferent) Division: Transmits sensory information to the CNS
- Motor (Efferent) Division: Sends commands from CNS to effectors (muscles/glands)
- Somatic Nervous System: Voluntary control of skeletal muscles
- Autonomic Nervous System: Involuntary control (sympathetic and parasympathetic)

The adult brain is organized into distinct regions, each with specialized functions.

Cerebrum: Largest part, responsible for higher functions
Diencephalon: Includes thalamus, hypothalamus, epithalamus
Brain Stem: Midbrain, pons, medulla oblongata
Cerebellum: Coordinates movement and balance
Example: The cerebrum is involved in reasoning, while the cerebellum manages coordination.

The cerebral cortex is divided into lobes and functional areas, separated by fissures.

Lobes: Frontal, parietal, temporal, occipital, insula
Fissures: Longitudinal (separates hemispheres), lateral (separates temporal lobe), central (separates frontal and parietal lobes)
Functional Areas:
- Motor Areas: Control voluntary movement
- Sensory Areas: Receive sensory input
- Association Areas: Integrate information

Lateralization refers to the specialization of functions in each hemisphere of the brain.

Left Hemisphere: Language, logic, analytical tasks
Right Hemisphere: Spatial abilities, creativity, emotion
Example: Speech production is typically localized in the left hemisphere (Broca's area).

The primary motor cortex and somatosensory cortex are mapped to specific body regions, forming a "homunculus" or body map.

Primary Motor Cortex: Located in the precentral gyrus; controls voluntary movements
Somatosensory Cortex: Located in the postcentral gyrus; receives sensory input
Homunculus: Visual representation of the body, showing areas with greater motor or sensory control (e.g., hands, face)
Example: Fine motor control in fingers is represented by a large area in the motor homunculus.

The brain stem is essential for basic life functions and connects the brain to the spinal cord.

Midbrain: Visual and auditory reflexes, motor control
Pons: Relay between cerebrum and cerebellum, regulates breathing
Medulla Oblongata: Controls heart rate, respiration, and other autonomic functions
Example: The medulla oblongata regulates breathing and heart rate.

The cerebellum is located at the back of the brain and is involved in coordination and balance.

Structure: Two hemispheres, surface cortex of gray matter, internal white matter (arbor vitae)
Function: Coordinates voluntary movements, maintains posture and balance, motor learning
Example: The cerebellum helps you ride a bicycle by coordinating muscle activity.

The diencephalon is located deep within the brain, between the brain stem and cerebrum.

Subdivisions:
- Thalamus: Relay station for sensory information
- Hypothalamus: Controls autonomic functions, endocrine system, homeostasis
- Epithalamus: Includes pineal gland, regulates sleep-wake cycles
Example: The hypothalamus regulates body temperature and hunger.

The brain contains four ventricles, which are interconnected cavities filled with cerebrospinal fluid (CSF).

Lateral Ventricles: Located in each cerebral hemisphere
Third Ventricle: Located in the diencephalon
Fourth Ventricle: Located between the brain stem and cerebellum
Example: CSF flows from the lateral ventricles to the third and then fourth ventricle.

Cerebrospinal fluid is produced by the choroid plexus and circulates through the ventricles and subarachnoid space.

Formation: Choroid plexus filters blood plasma to produce CSF
Circulatory Pathway: Lateral ventricles → third ventricle → fourth ventricle → subarachnoid space → absorbed by arachnoid villi into venous blood
Example: CSF cushions the brain and removes waste products.

The CNS is protected by three main structures: meninges, cerebrospinal fluid, and the blood brain barrier.

Meninges: Three connective tissue layers (dura mater, arachnoid mater, pia mater) surround the brain and spinal cord
Cerebrospinal Fluid: Provides cushioning, buoyancy, and chemical stability
Blood Brain Barrier: Selectively restricts passage of substances from blood to brain tissue, protecting neurons from toxins and pathogens
Example: The blood brain barrier prevents most drugs from entering the brain.