Comprehensive Study Guide: Nervous System, Special Senses (Vision & Audition) – Anatomy & Physiology I

Nervous System Overview

Basic Functions of the Nervous System

• Sensory Input: The nervous system detects changes in the internal and external environment through sensory receptors.

• Integration: Processes and interprets sensory input, deciding what action is needed.

• Motor Output: Activates effector organs (muscles and glands) to cause a response.

• Homeostasis: Maintains internal balance by regulating bodily functions.

• Mental Activity: Responsible for consciousness, memory, and thought.

Structural and Functional Classification of the Nervous System

• Structural Classification:

  • Central Nervous System (CNS): Brain and spinal cord; integration and command center.

  • Peripheral Nervous System (PNS): Cranial and spinal nerves; communication lines between CNS and body.

• Functional Classification:

  • Sensory (Afferent) Division: Transmits impulses from receptors to CNS.

  • Motor (Efferent) Division: Transmits impulses from CNS to effectors.

    • Somatic Nervous System: Voluntary control of skeletal muscles.

    • Autonomic Nervous System (ANS): Involuntary control of smooth muscle, cardiac muscle, and glands.

Types of Neurons

• Afferent (Sensory) Neurons: Carry impulses toward the CNS.

• Efferent (Motor) Neurons: Carry impulses away from the CNS to effectors.

• Interneurons (Association Neurons): Connect sensory and motor neurons within the CNS.

Neuroglia (Glial Cells)

• CNS Neuroglia:

  • Astrocytes: Support neurons, maintain blood-brain barrier, regulate environment.

  • Oligodendrocytes: Form myelin sheaths in CNS.

  • Microglia: Phagocytic cells, remove debris and pathogens.

  • Ependymal Cells: Line ventricles, produce and circulate cerebrospinal fluid (CSF).

• PNS Neuroglia:

  • Schwann Cells: Form myelin sheaths in PNS.

  • Satellite Cells: Support neuron cell bodies in ganglia.

Myelin Sheath

• Importance: Increases speed of nerve impulse conduction (saltatory conduction).

• Formation:

  • CNS: Oligodendrocytes wrap around axons.

  • PNS: Schwann cells wrap around axons, forming nodes of Ranvier.

Structure of a Typical Motor Neuron

• Cell Body (Soma): Contains nucleus and organelles.

• Dendrites: Receive signals from other neurons.

• Axon: Conducts impulses away from cell body.

• Axon Terminals: Release neurotransmitters to communicate with effectors or other neurons.

White and Gray Matter

• White Matter: Myelinated axons; transmits signals between different CNS regions.

• Gray Matter: Neuron cell bodies, dendrites, and unmyelinated axons; site of synaptic integration.

• Ganglia: Collections of neuron cell bodies in PNS.

• Tracts: Bundles of axons in CNS.

• Nerves: Bundles of axons in PNS.

Neuron Structure Classification

• Multipolar: Many dendrites, one axon (most common in CNS).

• Bipolar: One dendrite, one axon (e.g., retina, olfactory epithelium).

• Unipolar (Pseudounipolar): Single process splits into two branches (sensory neurons in PNS).

Reflexes

• Definition: Rapid, automatic response to a stimulus.

• Functional Elements: Receptor, sensory neuron, integration center, motor neuron, effector.

Action Potential Generation

• Resting Membrane Potential: Maintained by Na+/K+ ATPase pump.

• Depolarization: Na+ channels open, Na+ enters cell.

• Repolarization: K+ channels open, K+ exits cell.

• Hyperpolarization: K+ channels remain open briefly.

Equation:

$V_m = \frac{RT}{F} \ln \left( \frac{[K^+]_{out}}{[K^+]_{in}} \right)$

Additional info: This is the Nernst equation for membrane potential, showing dependence on ion concentrations.

Central Nervous System (Brain)

Embryonic Neural Tube Development

• The neural tube forms the CNS during embryogenesis.

• Primary brain vesicles: prosencephalon, mesencephalon, rhombencephalon.

• These differentiate into the cerebrum, diencephalon, brainstem, and cerebellum.

Major Brain Regions and Structures

• Cerebrum: Higher brain functions, voluntary actions, sensory perception.

• Diencephalon: Thalamus (relay center), hypothalamus (homeostasis), epithalamus.

• Brain Stem: Midbrain, pons, medulla oblongata; controls vital functions.

• Cerebellum: Coordination of movement and balance.

Cerebral Anatomy

• Lobes: Frontal, parietal, temporal, occipital.

• Gyri: Elevated ridges.

• Sulci: Shallow grooves.

• Fissures: Deep grooves (e.g., longitudinal fissure).

Meninges and Meningeal Spaces

• Dura Mater: Outermost, tough layer.

• Arachnoid Mater: Middle, web-like layer.

• Pia Mater: Innermost, delicate layer adhering to CNS surface.

• Spaces:

  • Epidural (spinal cord only): Between vertebrae and dura mater.

  • Subdural: Between dura and arachnoid.

  • Subarachnoid: Between arachnoid and pia; contains CSF.

• Difference: Epidural space is present in the spinal cord but not around the brain.

Key Brain Structures and Functions

• Thalamus: Relay station for sensory information.

• Hypothalamus: Regulates autonomic and endocrine functions.

• Midbrain: Visual and auditory reflexes.

• Pons: Relays signals, regulates breathing.

• Medulla Oblongata: Controls heart rate, breathing, blood pressure.

• Cerebellum: Coordinates voluntary movements.

Functional Areas of the Cerebral Cortex

• Motor Areas: Control voluntary movement (e.g., primary motor cortex).

• Sensory Areas: Receive sensory input (e.g., primary somatosensory cortex).

• Association Areas: Integrate information (e.g., prefrontal cortex, Wernicke's area).

Brainstem Centers and Reticular Formation

• Reticular Activating System (RAS): Maintains consciousness and alertness.

• Medullary Rhythmicity Area: Controls breathing rhythm.

• Cardiac Center: Regulates heart rate.

• Vasomotor Center: Controls blood vessel diameter.

Ventricles and CSF Circulation

• Lateral Ventricles → Third Ventricle → Cerebral Aqueduct → Fourth Ventricle → Central Canal/Subarachnoid Space.

• Choroid Plexus: Produces CSF.

• Arachnoid Villi: Absorb CSF into venous circulation.

Blood-Brain Barrier

• Structure: Endothelial cells with tight junctions, astrocyte end-feet.

• Function: Protects brain from harmful substances, maintains stable environment.

Brain Disorders

• Hydrocephalus: Excess CSF due to impaired drainage.

• Concussion: Temporary brain dysfunction from trauma.

• Contusion: Bruising of brain tissue.

• Cerebral Edema: Swelling due to fluid accumulation.

• Cerebrovascular Accident (Stroke): Blood flow disruption to brain tissue.

• Alzheimer’s Disease: Progressive neurodegeneration causing memory loss.

Spinal Cord and Peripheral Nervous System

Spinal Cord Structure

• Gross Structure: Extends from foramen magnum to L1/L2; has cervical and lumbar enlargements.

• Microscopic Structure: Central gray matter (H-shaped), surrounding white matter.

Ascending and Descending Pathways

• Ascending (Sensory) Tracts: Carry sensory information to the brain (e.g., spinothalamic tract).

• Descending (Motor) Tracts: Carry motor commands from brain to body (e.g., corticospinal tract).

Structure of a Nerve

• Endoneurium: Surrounds individual axons.

• Perineurium: Surrounds fascicles (bundles of axons).

• Epieneurium: Surrounds entire nerve.

Spinal Nerves and Plexuses

• 31 Pairs of Spinal Nerves:

  • 8 cervical

  • 12 thoracic

  • 5 lumbar

  • 5 sacral

  • 1 coccygeal

• Plexuses:

  • Cervical: Neck, diaphragm

  • Brachial: Upper limb

  • Lumbar: Lower limb, abdomen

  • Sacral: Lower limb, pelvis

Cranial Nerves

Number	Name	Main Function
I	Olfactory	Smell
II	Optic	Vision
III	Oculomotor	Eye movement, pupil constriction
IV	Trochlear	Eye movement
V	Trigeminal	Facial sensation, chewing
VI	Abducens	Eye movement
VII	Facial	Facial expression, taste
VIII	Vestibulocochlear	Hearing, balance
IX	Glossopharyngeal	Taste, swallowing
X	Vagus	Viscera control, taste
XI	Accessory	Head/shoulder movement
XII	Hypoglossal	Tongue movement

Additional info: Testing involves sensory and motor exams specific to each nerve.

Autonomic Nervous System (ANS)

Definition and Relationship to PNS

• ANS: Subdivision of PNS controlling involuntary effectors (smooth/cardiac muscle, glands).

Somatic vs. Autonomic Nervous System

Feature	Somatic	Autonomic
Effectors	Skeletal muscle	Cardiac/smooth muscle, glands
Pathways	One neuron	Two-neuron chain
Neurotransmitters	Acetylcholine	Acetylcholine, norepinephrine

Parasympathetic vs. Sympathetic Divisions

Feature	Parasympathetic	Sympathetic
Origin	Craniosacral	Thoracolumbar
Ganglia Location	Near/within target organs	Near spinal cord
General Function	"Rest and digest"	"Fight or flight"

Effects on Organs

• Sympathetic: Increases heart rate, dilates bronchioles, inhibits digestion, dilates pupils.

• Parasympathetic: Decreases heart rate, constricts bronchioles, stimulates digestion, constricts pupils.

Special Senses: Visual System

Primary and Supporting Organs of Vision

• Primary: Eyeball (globe), retina.

• Supporting: Eyelids, eyelashes, conjunctiva, lacrimal apparatus, extrinsic eye muscles.

Key Eye Structures

• Cornea: Transparent, refracts light.

• Sclera: White, protective outer layer.

• Choroid: Vascular, nourishes retina.

• Ciliary Body: Produces aqueous humor, controls lens shape.

• Iris/Pupil: Regulates light entry.

• Retina: Contains photoreceptors (rods/cones).

• Optic Disk (Papilla): Blind spot, exit for optic nerve.

• Macula Lutea/Central Fovea: High acuity vision.

• Anterior/Posterior Chambers: Contain aqueous/vitreous humor.

• Canal of Schlemm: Drains aqueous humor.

Retinal Cell Arrangement

• Light passes through ganglion cells → bipolar cells → photoreceptors (rods/cones).

Common Eye Disorders

• Myopia (Nearsightedness): Image focuses in front of retina.

• Hyperopia (Farsightedness): Image focuses behind retina.

• Glaucoma: Increased intraocular pressure damages optic nerve.

• Cataract: Clouding of lens.

Accommodation Reflex and Pupil Constriction

• Accommodation: Lens changes shape to focus on near/far objects.

• Pupil Constriction: Reduces light entry, increases depth of focus.

Rods vs. Cones

Feature	Rods	Cones
Function	Dim light, peripheral vision	Color, sharp vision
Location	Periphery of retina	Central retina (fovea)
Light Sensitivity	High	Low

Visual Pathways

• Visual fields project to opposite sides of the cerebral cortex (e.g., left visual field to right occipital lobe).

Special Senses: Auditory System

Ear Anatomy and Function

• External Ear: Auricle, external auditory meatus, tympanic membrane (collects and transmits sound).

• Middle Ear: Malleus, incus, stapes (ossicles); tympanic cavity; Eustachian tube (equalizes pressure).

• Inner Ear: Bony labyrinth (cochlea, vestibule, semicircular canals); membranous labyrinth (contains endolymph).

Key Structures and Functions

• Cochlea: Hearing; contains organ of Corti (hair cells on basilar membrane).

• Semicircular Canals: Balance (rotational movement).

• Vestibule (saccule, utricle): Balance (linear movement).

• Vestibulocochlear Nerve: Transmits hearing and balance information to brain.

Labyrinths and Fluids

• Bony Labyrinth: Filled with perilymph.

• Membranous Labyrinth: Filled with endolymph.

Receptors

• Crista (ampullaris): Rotational acceleration (semicircular canals).

• Macula: Linear acceleration (utricle, saccule).

• Organ of Corti: Hearing (cochlea).

Auditory Pathway

1. Sound waves enter external ear, vibrate tympanic membrane.

2. Ossicles transmit vibrations to oval window.

3. Vibrations travel through perilymph, move basilar membrane.

4. Hair cells in organ of Corti generate nerve impulses.

5. Signals travel via cochlear nerve to primary auditory cortex (temporal lobe).

Brain Regions for Hearing

• Primary auditory cortex (temporal lobe), auditory association areas, inferior colliculus (midbrain).