chapter 13

 Overview of the Nervous System

Location & Origin

• The nervous system is dorsal in position (toward the back of the body).

• It is hollow inside — containing ventricles (in the brain) and a central canal (in the spinal cord).

• It is ectodermal in origin, meaning it develops from the ectoderm, the outermost embryonic layer.

Main Divisions

System	Abbreviation	Major Components	Function
Central Nervous System (CNS)	CNS	Brain and spinal cord	Processes and integrates information
Peripheral Nervous System (PNS)	PNS	Cranial nerves and spinal nerves	Sends information to and from the CNS

 

Afferent (Sensory) Pathway

Carries input toward the CNS.

1. Somatic Sensory – sensations from the body wall and limbs (e.g., touch, pain, temperature, pressure).

2. Visceral Sensory – sensations from internal organs (e.g., GI tract, blood vessels).

 

Efferent (Motor) Pathway

Carries output from the CNS to effectors.

1. Somatic Motor – voluntary control of skeletal muscles.

2. Visceral Motor (Autonomic) – involuntary control of smooth muscles, cardiac muscles, and glands.

 

Autonomic Nervous System (ANS)

Division	Function	State of Activity
Sympathetic Nervous System	“Fight or Flight” – increases heart rate, blood flow, respiration	Active in stress
Parasympathetic Nervous System	“Rest and Digest” – slows heart rate, increases digestion	Active in rest

2. Embryonic Development of the Nervous System

Formation Process

1. Neural Plate appears from ectoderm on the dorsal surface of the embryo (about week 3).

1. The plate folds to form Neural Folds and a Neural Groove.

2. The folds fuse in the midline forming the Neural Tube, which later becomes the CNS.

3. The hollow inside becomes the central canal (spinal cord) and ventricles (brain).

Notochord (below the neural tube) will guide the development of vertebral bones and spinal alignment.

 Brain Development: Vesicles and Flexures

Primary Brain Vesicles (3 weeks)

1. Prosencephalon → forebrain

2. Mesencephalon → midbrain

3. Rhombencephalon → hindbrain

Secondary Brain Vesicles (5 weeks)

Primary Vesicle	Secondary Vesicles	Adult Brain Structure
Prosencephalon	Telencephalon and Diencephalon	Cerebral hemispheres, thalamus, hypothalamus
Mesencephalon	(unchanged)	Midbrain
Rhombencephalon	Metencephalon and Myelencephalon	Pons, cerebellum, medulla oblongata

Major Brain Flexures

• Cephalic flexure – dorsal bend between forebrain & midbrain.

• Cervical flexure – dorsal bend between hindbrain & spinal cord.

• Pontine flexure – ventral bend between midbrain & hindbrain.

[Embryo at 3 weeks showing brain flexures]

4. Ventricles and Cerebrospinal Fluid (CSF)

[Insert Diagram: Lateral, third, and fourth ventricles with CSF flow arrows]

• Ventricles are cavities within the brain derived from the neural canal.

• Lined by ependymal cells (glial cells that help circulate CSF).

CSF Production

• Produced by choroid plexus (network of blood capillaries within ventricles).

• Volume: ~150 mL in adults.

• Functions:

  • Cushions and protects the brain and spinal cord.

  • Maintains stable chemical environment.

  • Provides buoyancy (reduces brain weight).

  • Removes waste.

Septum pellucidum & corpus callosum

• Septum pellucidum – thin membrane that separates the right and left lateral ventricles.

• Corpus callosum – large commissural fiber tract connecting right and left cerebral hemispheres.

Pathway of CSF Flow

1. Lateral ventricles →

1. Interventricular foramina (of Monro) →

2. Third ventricle →

3. Cerebral aqueduct (of Sylvius) →

4. Fourth ventricle →

5. Median aperture (foramen of Magendie) + 2 lateral apertures (foramina of Luschka) →

6. Subarachnoid space →

1. Reabsorbed into venous blood via arachnoid villi in the superior sagittal sinus.

[Insert Diagram: CSF circulation and absorption through arachnoid villi]

5. Meninges - layers

Layers

1. Dura mater – tough, fibrous outer layer.

   • Periosteal layer (attached to skull).

   • Meningeal layer (around brain & spinal cord).

2. Arachnoid mater – middle layer; web-like network connecting to blood vessels.

3. Pia mater – delicate inner layer adhering tightly to brain surface; rich in capillaries.

5. Meninges - spaces

• Epidural space – outside dura; used for anesthesia.

• Subdural space – between dura and arachnoid (potential space).

• Subarachnoid space – between arachnoid and pia; contains CSF.

5. Meninges - clinical notes

• Epidural hematoma – arterial bleeding between skull and dura.

• Subdural hematoma – venous bleeding between dura and arachnoid.

• Lumbar tap (spinal tap): 10–15 mL of CSF withdrawn from lumbar region to test for meningitis, infection, or pressure.

6. Brain Lobes and Fissures

• Frontal lobe – planning, reasoning, movement, speech.

• Parietal lobe – sensory perception (touch, pressure, pain, temp).

• Temporal lobe – hearing, smell, language.

• Occipital lobe – vision.

• Insula – deep within lateral sulcus; taste, emotional context.

• Cerebellum – coordination and balance.

Major Fissures

• Longitudinal fissure: separates right & left cerebral hemispheres.

• Transverse fissure: separates cerebrum and cerebellum.

• Central sulcus: separates frontal and parietal lobes.

• Lateral sulcus (Sylvian): separates temporal lobe.

• Parieto-occipital sulcus: separates parietal and occipital lobes.

[Insert Diagram: Falx cerebri and tentorium cerebelli positions]

7. Functional Areas of the Brain

[Insert Diagram: Functional cortical areas, color-coded motor/sensory]

Brain Mapping (Korbinian Brodmann, 1909)

• Identified 52 functional areas of the cerebral cortex (Brodmann areas).

• Primary areas: handle direct sensory/motor input.

• Association areas: integrate information from multiple regions.

Major Functional Areas

#	Area	Location	Function
1	Primary Motor Cortex	Precentral gyrus	Voluntary control of skeletal muscles
2	Premotor Cortex	Anterior to precentral gyrus	Controls learned, skilled movements
3	Frontal Eye Field	Frontal lobe	Controls voluntary eye movement
4	Prefrontal Cortex	Anterior frontal lobe	Cognition, personality, decision making
5	Primary Visual Cortex	Occipital lobe	Image processing (“see the object”)
6	Primary Auditory Cortex	Temporal lobe	Sound perception and recognition
7	Primary Gustatory Area	Insula	Taste perception
8	Primary Somatosensory Cortex	Postcentral gyrus	Touch, pressure, temperature, pain
9	Broca’s Area	Left frontal lobe	Motor speech – articulation of words
10	Wernicke’s Area	Left temporal/parietal junction	Comprehension of spoken/written language

White matter fiber types & Reticular Activating System

Cerebral white matter tracts

• Commissural fibers – connect right & left halves (e.g., corpus callosum, anterior commissure).

• Association fibers – connect different areas within the same hemisphere.

• Projection fibers – vertical fibers connecting cortex with lower centers (thalamus, brainstem, spinal cord).

Reticular Activating System (RAS)

• Network in brainstem (midbrain, pons, medulla).

• Active → awake, alert, conscious.

• Inactivated → sleep, depression of CNS.

• Severely damaged → coma, loss of consciousness.

Association Areas

• General Interpretative (Gnostic) Area: integrates input from visual, auditory, and tactile senses into a common thought.

• Visual Association Area: interprets what is seen.

• Auditory Association Area: interprets sounds.

[Insert Diagram: Homunculus – motor & sensory representation on cortex]

Convolutions, sulci, gyri, and neuron numbers

• Convolutions: folds on the brain surface that increase surface area.

• Sulci – shallow grooves.

• Fissures – deep grooves (include all 3 meninges).

• Gyri – elevated ridges between sulci.

• Approximate neuron numbers:

  • Total brain: ~86 billion neurons.

  • Cerebrum: ~16 billion.

  • Cerebellum: ~70 billion.

Lateralization of Cortical Function

• Left hemisphere: language, math, logic, reasoning.

• Right hemisphere: creativity, spatial awareness, facial recognition, music.

8. Diencephalon and Brainstem p1

Diencephalon

• Thalamus: relay center for sensory information (80% of diencephalon).

• Hypothalamus: controls autonomic functions (hunger, thirst, temperature, hormones).

• Epithalamus (Pineal gland): secretes melatonin, regulates sleep and circadian rhythm.

 

Midbrain (Mesencephalon)

• Corpora quadrigemina:

  • Superior colliculi – visual reflexes, eye-head coordination.

  • Inferior colliculi – auditory reflexes, startle response.

• Red nucleus: controls limb movement; high blood supply.

• Substantia nigra: produces dopamine; regulates movement via basal ganglia.

  • Loss of dopamine → Parkinson’s disease.

8. Diencephalon and Brainstem p2

Basal Ganglia

• Clusters of neurons for planning and execution of voluntary actions.

• Includes caudate nucleus, putamen, and globus pallidus.

Part	Deficiency	Disorder
Caudate	Overactive → OCD	Underactive → ADHD
Putamen	Deficiency → Tourette’s syndrome
Globus pallidus	Deficiency → Parkinson’s disease

 

Pons and Cerebellum (Metencephalon)

• Pons: “bridge” between cerebellum and medulla; regulates breathing, bladder, facial expressions.

• Cerebellum: coordinates skilled muscle movement, balance, and posture.

  • Arbor vitae: white matter pattern (tree-like).

  • Gray matter: contains neuron cell bodies.

 

Medulla Oblongata (Myelencephalon)

• Contains cardiovascular and respiratory control centers.

• Regulates heart rate, blood pressure, and breathing rhythm.

• Reflex centers for swallowing, coughing, vomiting.

9. Limbic System and Brain Disorders

Limbic System

• The “emotional brain.”

• Includes: hippocampus, amygdala, hypothalamus, fornix, and cingulate gyrus.

• Amygdala: emotions such as fear, anger, anxiety.

• Hippocampus: memory formation.

9. Limbic System and Brain Disorders

Condition	Description
Concussion	Sudden blow or jolt; brain moves violently but no tissue damage or bleeding. Causes dizziness or memory loss.
Contusion	Tissue damage with hemorrhage (bleeding). More serious than concussion.
Hemiplegia	Paralysis of one side of the body.
Paraplegia	Paralysis from waist down.
Quadriplegia	Paralysis from neck down.
Cerebral Palsy	Permanent movement disorder due to oxygen deprivation at birth.
Anencephaly	Absence of brain except brainstem.
Microcephaly	Underdeveloped, small brain (can be caused by Zika virus).

10. Brain Waves and Sleep

[Insert Diagram: EEG wave patterns – alpha, beta, theta, delta]

Electroencephalogram (EEG)

Measures electrical activity in the brain.

Wave Type	Frequency	State
Alpha	8–13 Hz	Relaxed, eyes closed
Beta	14–30 Hz	Alert, eyes open
Theta	4–7 Hz	Light sleep or daydreaming
Delta	3–5 Hz	Deep sleep (restorative)
Gamma	~100 Hz	Highly active brain

Sleep Stages

1. NREM Sleep (Non-Rapid Eye Movement) – 75% of total sleep

   • Stage 1: 5–10 min – light sleep, drifting.

   • Stage 2: 10–20 min – slower HR, body temp drops, sleep spindles.

   • Stages 3/4: Deep, restorative sleep; slow delta waves; muscles relax.

2. REM Sleep (Rapid Eye Movement) – 25% of total sleep

   • Brain highly active; vivid dreams; body largely paralyzed.

   • Occurs about 90 min after sleep onset.

   • Episodes lengthen toward morning.

[Insert Diagram: Sleep cycle timeline (10 pm – 6 am with REM stages labeled)]

• Melatonin from pineal gland promotes sleep onset.

• Insomnia: difficulty falling or staying asleep.

EEG

• Theta waves in awake adults – can be seen in extreme emotional stress.

• Delta waves in an awake adult – usually indicate brain damage.

Extra CSF details & hydrocephalus

• CSF composition: similar to blood plasma but:

  • Very few WBCs.

  • No RBCs (unless hemorrhage).

  • Lower protein than plasma.

• Rate: continuously produced, total ~500 mL/day, but only ~150 mL present at any moment (constant reabsorption).

• Normal CSF pressure: about 7–10 mm (hydrostatic pressure).

• Hydrocephalus:

  • Blocked CSF flow or absorption → ventricles enlarge → increased pressure.

  • In infants: head enlargement; in adults: brain compression.

  • Treated with ventriculoperitoneal (VP) shunt (tube from ventricle to abdominal cavity).

Cranial fossae & brain herniation

• Cranial fossae:

  • Anterior cranial fossa – holds frontal lobes.

  • Middle cranial fossa – holds temporal lobes.

  • Posterior cranial fossa – holds cerebellum and brainstem.

• Brain herniation:

  • Mass/hematoma (epidural or subdural) can force brain tissue downward through tentorial notch.

  • Can compress the brainstem, which is life-threatening.