Anatomy and Physiology I: Central and Peripheral Nervous System Study Guide

The Central Nervous System (CNS): Structure and Function

Introduction to the CNS

The Central Nervous System (CNS) consists of the brain and spinal cord, serving as the primary control center for the body. Cephalization refers to the evolutionary development of a prominent head region, with increased neuron concentration, reaching its peak in humans.

• Basic Pattern: The spinal cord has a central cavity surrounded by gray matter, with external white matter composed of myelinated fiber tracts. The brain shares this pattern but includes additional gray matter regions.

• Major Regions: Cerebral hemispheres, cerebellum, and brain stem.

Ventricles of the Brain

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

• Lateral Ventricles: Paired, C-shaped, located in each hemisphere.

• Third Ventricle: Found in the diencephalon.

• Fourth Ventricle: Located dorsal to the pons in the hindbrain.

Cerebral Hemispheres

The cerebral hemispheres form the superior part of the brain, comprising 83% of its mass. They are characterized by gyri (ridges), sulci (shallow grooves), and fissures (deep grooves).

• Lobes: Frontal, parietal, temporal, occipital, and insula.

• Key Sulci: Central, parieto-occipital, and lateral sulci.

• Regions: Cortex (gray matter), white matter, and basal nuclei.

Cerebral Cortex

The cortex is the superficial gray matter, accounting for 40% of the brain's mass. It enables sensation, communication, memory, understanding, and voluntary movements.

• Functional Areas: Motor, sensory, and association areas.

• Motor Areas: Primary motor cortex (precentral gyrus), premotor cortex, Broca's area (speech), frontal eye field.

• Sensory Areas: Primary somatosensory cortex (postcentral gyrus), somatosensory association cortex, visual and auditory cortices, olfactory, gustatory, and vestibular cortices.

• Association Areas: Prefrontal cortex (intellect, personality), language areas (Wernicke's, Broca's), general interpretation area, visceral association area.

Lateralization and Cerebral White Matter

Lateralization refers to the specialization of each hemisphere. The left hemisphere is dominant for language, math, and logic, while the right controls visual-spatial skills, emotion, and artistic abilities.

• White Matter: Deep myelinated fibers responsible for communication.

• Types: Commissures (connect hemispheres), association fibers (within hemisphere), projection fibers (to/from lower centers).

Basal Nuclei

Basal nuclei are masses of gray matter deep within the white matter, including the caudate nucleus, putamen, and globus pallidus. They influence muscular activity, regulate attention and cognition, and inhibit unnecessary movements.

Diencephalon

The diencephalon is the central core of the forebrain, consisting of the thalamus, hypothalamus, and epithalamus.

• Thalamus: Relay station for sensory impulses; mediates sensation, motor activities, arousal, learning, and memory.

• Hypothalamus: Main visceral control center; regulates autonomic functions, emotions, temperature, hunger, and sleep.

• Epithalamus: Contains the pineal gland (secretes melatonin) and choroid plexus (produces CSF).

Brain Stem

The brain stem includes the midbrain, pons, and medulla oblongata, controlling automatic behaviors and serving as a pathway for tracts between higher and lower centers.

• Midbrain: Contains cerebral peduncles, corpora quadrigemina (superior/inferior colliculi), substantia nigra (dopamine release).

• Pons: Connects higher centers and spinal cord; relays impulses between motor cortex and cerebellum.

• Medulla Oblongata: Contains pyramids (corticospinal tracts), decussation points, nuclei for equilibrium, cardiovascular, and respiratory control.

Cerebellum

The cerebellum is located dorsal to the pons and medulla, responsible for precise timing and patterns of skeletal muscle contraction. It also plays a role in language and problem-solving.

• Anatomy: Two hemispheres connected by the vermis; folia (gyri); three lobes; arbor vitae (white matter pattern).

• Peduncles: Superior (to midbrain), middle (to pons), inferior (to medulla).

• Processing: Receives intent signals, proprioceptive and visual input, calculates movement, sends blueprint to motor cortex.

Functional Brain Systems

Limbic System

The limbic system is involved in emotions and memory, including structures such as the amygdala, cingulate gyrus, hippocampus, and hypothalamus.

• Functions: Emotional responses, memory formation, emotional reactions to odors.

Reticular Formation

The reticular formation spans the brain stem, with the Reticular Activating System (RAS) maintaining consciousness and alertness, filtering stimuli, and regulating visceral motor functions.

Brain Waves and EEG

Types of Brain Waves

EEGs record electrical activity of the brain, with wave types indicating different states:

• Alpha: Idling brain, regular and rhythmic.

• Beta: Awake, mentally alert.

• Theta: Common in children, abnormal in adults.

• Delta: Deep sleep, high amplitude.

EEGs are used to diagnose brain disorders; a flat EEG indicates clinical death.

Epilepsy

• Absence (petit mal) seizures: Mild, blank expression.

• Grand mal seizures: Severe convulsions, loss of consciousness.

• Treatment: Anticonvulsants, vagus nerve stimulators.

Consciousness and Sleep

Consciousness

Consciousness encompasses perception, voluntary movement, and higher mental processing, graded from alertness to coma.

Sleep

• NREM: Four stages, from light to deep sleep.

• REM: Dreaming, increased vital signs, muscle inhibition.

• Sleep Disorders: Narcolepsy, insomnia, sleep apnea.

Memory

Types and Mechanisms

• Short-term Memory (STM): Lasts seconds to hours, limited capacity.

• Long-term Memory (LTM): Limitless capacity.

• Fact Memory: Explicit information, context-dependent.

• Skill Memory: Motor activity, acquired through practice.

• Mechanisms: Changes in neuronal RNA, dendritic spines, synaptic proteins, neurotransmitter release, long-term potentiation (LTP).

Protection of the Brain

Meninges

• Dura Mater: Strong, two layers, forms dural sinuses and septa.

• Arachnoid Mater: Loose covering, subarachnoid space with CSF, arachnoid villi for CSF absorption.

• Pia Mater: Delicate, clings to brain surface.

Cerebrospinal Fluid (CSF)

• Functions: Buoyancy, protection, nourishment, chemical signaling.

• Choroid Plexuses: Produce and filter CSF.

Blood-Brain Barrier

• Structure: Capillary endothelium, basal lamina, astrocyte feet.

• Function: Selective barrier, allows nutrients, blocks harmful substances.

• Exceptions: Absent in vomiting center and hypothalamus.

The Spinal Cord and Disorders

Anatomy of the Spinal Cord

• Location: From foramen magnum to L1.

• Protection: Bone, meninges, CSF.

• Key Structures: Epidural space, conus medullaris, filum terminale, denticulate ligaments, spinal nerves (31 pairs), cauda equina.

• Gray Matter: Soma, unmyelinated processes, neuroglia; dorsal (sensory), ventral (motor), lateral horns (sympathetic fibers).

• White Matter: Ascending, descending, and transverse fibers; divided into funiculi (columns).

Spinal Tracts

• Ascending Pathways: Nonspecific (pain, temperature), specific (touch, proprioception), spinocerebellar (to cerebellum).

• Descending Pathways: Direct (pyramidal/corticospinal), indirect (extrapyramidal: rubrospinal, vestibulospinal, reticulospinal, tectospinal).

Spinal Cord Disorders

• Trauma: Paralysis (flaccid, spastic), transection (paraplegia, quadriplegia).

• Poliomyelitis: Destruction of anterior horn motor neurons by poliovirus.

• Amyotrophic Lateral Sclerosis (ALS): Degeneration of motor neurons and pyramidal tract fibers.

The Peripheral Nervous System (PNS)

Sensory Receptors

Sensory receptors respond to environmental changes (stimuli) and generate graded potentials.

• By Stimulus: Mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, nociceptors.

• By Location: Exteroceptors (external), interoceptors (internal), proprioceptors (muscle/tendon stretch).

• By Structure: Simple (free or encapsulated dendritic endings), complex (sense organs).

Nerves

• Structure: Bundles of axons, myelinated/unmyelinated, connective tissue wrappings, blood/lymph vessels.

• Cranial Nerves: 12 pairs, attach to brain, innervate head/neck (except vagus nerve).

• Spinal Nerves: 31 pairs, mixed nerves, connect via dorsal (sensory) and ventral (motor) roots, diverge into rami.

Plexuses

Plexuses are networks where nerve fibers from ventral rami crisscross and redistribute.

• Cervical Plexus: C1-C4, neck and diaphragm (phrenic nerve).

• Brachial Plexus: C5-T1, shoulder and upper arm.

• Lumbar Plexus: L1-L4, abdominal wall, anterior/medial thigh.

• Sacral Plexus: L4-S4, pelvic region, leg (sciatic nerve).

• Thoracic Nerves: T2-T12, do not form plexuses; give rise to intercostal nerves.

Reflexes and Pain

Reflexes

Reflexes are rapid, predictable, involuntary motor responses to stimuli, built into neural anatomy.

• Reflex Arc Components: Receptor, sensory neuron, integration center, motor neuron, effector.

• Classification: Innate/acquired, somatic/visceral, monosynaptic/polysynaptic, spinal/cranial.

• Examples: Stretch (patellar), flexor (withdrawal), crossed extensor, superficial (plantar reflex).

• Modification: By conscious effort, other reflexes, EPSPs/IPSPs, presynaptic facilitation/inhibition.

Pain

Pain warns of tissue damage and is clinically difficult to measure.

• Reception: Nociceptors activated by inflammatory chemicals (prostaglandins, bradykinins, histamine, potassium).

• Transmission: Glutamate (neurotransmitter), substance P (neuromodulator).

• Pain Threshold: Same for all; pain tolerance varies.

• Chronic Pain: Hyperalgesia, NMDA receptor activation, phantom limb pain.

• Modulation: Epinephrine/norepinephrine, endorphins/enkephalins (natural opiates), presynaptic and postsynaptic inhibition.

Table: Major Brain Regions and Their Functions

Region	Main Function
Cerebral Cortex	Sensation, communication, memory, voluntary movement
Basal Nuclei	Motor control, attention, inhibition of unnecessary movement
Thalamus	Relay station for sensory impulses
Hypothalamus	Autonomic control, emotions, temperature, hunger, sleep
Epithalamus	Melatonin secretion, CSF production
Brain Stem	Automatic behaviors, pathway for tracts, cranial nerve origin
Cerebellum	Coordination, timing, balance, cognitive functions

Table: Types of Sensory Receptors

Type	Stimulus Detected	Location
Mechanoreceptors	Pressure, vibration, stretch	Skin, muscles
Thermoreceptors	Temperature	Skin, internal organs
Photoreceptors	Light	Eyes
Chemoreceptors	Chemicals	Taste buds, olfactory epithelium, blood vessels
Nociceptors	Painful stimuli	Most tissues

Key Equations and Concepts

• EEG Frequency: $\text{Frequency (Hz)} = \frac{\text{Number of cycles}}{\text{Time (seconds)}}$

• Long-Term Potentiation (LTP): $\text{LTP} \propto \text{NMDA receptor activation} \times \text{BDNF influence}$

Additional info: These notes expand on brief points from the original study guide, providing definitions, examples, and context for each major topic. Tables are recreated for comparison and classification purposes. Equations are provided in LaTeX format as required.