M5 Study Guide Final Exam

Divisions of the Nervous System

Anatomical and Functional Organization of the Central Nervous System (CNS)

The central nervous system (CNS) consists of the brain and spinal cord. It is responsible for integrating sensory information and responding accordingly.

• Anatomical Organization: The CNS is composed of the brain (cerebrum, cerebellum, brainstem) and the spinal cord.

• Functional Organization: The CNS processes incoming sensory data, coordinates voluntary and involuntary responses, and is the center for thought, emotion, and memory.

• Example: The CNS interprets signals from the eyes and coordinates muscle movement to catch a ball.

Anatomical and Functional Organization of the Peripheral Nervous System (PNS)

The peripheral nervous system (PNS) connects the CNS to limbs and organs, serving as a communication relay.

• Anatomical Organization: Includes all neural tissue outside the CNS: cranial nerves, spinal nerves, ganglia, and sensory receptors.

• Functional Organization: Divided into sensory (afferent) and motor (efferent) divisions. The motor division is further subdivided into somatic (voluntary) and autonomic (involuntary) systems.

• Example: Sensory nerves in the skin detect heat and send signals to the CNS via the PNS.

Central Nervous System: Brain and Spinal Cord

Major Structures and Regions of the Brain

The brain is divided into several major regions, each with specialized functions.

• Cerebrum: Responsible for higher brain functions such as thought, action, and sensory processing.

• Cerebellum: Coordinates voluntary movements, balance, and posture.

• Thalamus: Relay station for sensory and motor signals to the cerebral cortex.

• Hypothalamus: Regulates homeostasis, including temperature, hunger, and hormone release.

• Pons: Connects upper and lower parts of the brain; involved in breathing and communication between different brain regions.

• Medulla Oblongata: Controls autonomic functions such as heart rate and respiration.

Lobes of the Cerebral Cortex and Their Functions

• Frontal Lobe: Voluntary movement, reasoning, planning, problem-solving, and motor speech production.

• Parietal Lobe: Sensory perception and integration, spatial awareness.

• Temporal Lobe: Auditory processing, memory, and language comprehension.

• Occipital Lobe: Visual processing.

Layers of the Meninges

The meninges are three protective membranes surrounding the brain and spinal cord.

• Dura Mater: Outermost, tough layer.

• Arachnoid Mater: Middle, web-like layer.

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

Protection of the CNS

• Meninges: Provide physical protection and support.

• Cerebrospinal Fluid (CSF): Cushions the brain and spinal cord, circulates nutrients, and removes waste.

• Blood-Brain Barrier: Selectively restricts passage of substances from the blood into the CNS.

Cerebrospinal Fluid (CSF)

• Composition: Clear, colorless fluid containing water, ions, glucose, and a few cells.

• Function: Protects CNS, provides nutrients, removes waste.

• Location: Circulates in ventricles of the brain, central canal of the spinal cord, and subarachnoid space.

Spinal Cord: Cross-Sectional Anatomy

• Gray Matter: Contains neuron cell bodies; involved in processing and integration.

• White Matter: Contains myelinated axons; transmits signals up and down the spinal cord.

• Dorsal Root Ganglion: Contains sensory neuron cell bodies.

• Spinal Nerves: Mixed nerves carrying both sensory and motor fibers.

Nervous System as a Control System

• Sensory Receptors: Detect stimuli (mechanoreceptors, thermoreceptors, chemoreceptors, photoreceptors, nociceptors).

• Body Location: Exteroceptors (external), interoceptors (internal), proprioceptors (position/movement).

• Afferent Pathways: Carry sensory information to the CNS.

• Integration Center: CNS processes information.

• Efferent Pathways: Carry motor commands from CNS to effectors (muscles, glands).

• Effectors: Muscles or glands that respond to CNS commands.

Peripheral Nervous System (PNS)

Role of the Peripheral Nervous System

The PNS links the CNS to the rest of the body, transmitting sensory and motor information.

• Sensory Division: Transmits sensory input from receptors to CNS.

• Motor Division: Transmits motor output from CNS to effectors.

Efferent Divisions of the PNS

• Somatic Motor: Controls voluntary movements via skeletal muscles.

• Autonomic (Visceral Motor): Controls involuntary functions (smooth muscle, cardiac muscle, glands).

• Sympathetic Division: Prepares body for 'fight or flight' responses.

• Parasympathetic Division: Promotes 'rest and digest' activities.

Reflex Arcs

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

• Somatic Reflexes: Involve skeletal muscles.

• Autonomic Reflexes: Involve smooth muscle, cardiac muscle, or glands.

Steps of a Physiological Reflex (Control System Model)

1. Input: Stimulus detected by receptor.

2. Control Center: CNS processes information.

3. Output: Motor response sent to effector.

Autonomic Nervous System (ANS)

Definition and Relationship to PNS

The autonomic nervous system (ANS) is a division of the PNS that controls involuntary bodily functions.

• Functions: Regulates heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal.

Organization and Functions: Parasympathetic vs. Sympathetic

Division	Origin	Main Function
Sympathetic	Thoracolumbar	"Fight or flight" (increases heart rate, dilates pupils, inhibits digestion)
Parasympathetic	Craniosacral	"Rest and digest" (decreases heart rate, stimulates digestion)

Coordination of Sympathetic and Parasympathetic Divisions

• Most organs receive dual innervation from both divisions, which usually have opposite effects to maintain homeostasis.

Special Senses: Eye Anatomy and Physiology

Overview of Senses

• Sensory Receptor: Specialized cell or structure that detects stimuli.

• Transduction: Conversion of stimulus energy into electrical signals.

• Perception: Interpretation of sensory signals by the brain.

• Sensation: Awareness of a stimulus.

• Adaptation: Decreased response to a constant stimulus over time.

Types of Sensory Receptors by Stimulus

Receptor Type	Stimulus Detected
Thermoreceptor	Temperature
Photoreceptor	Light
Chemoreceptor	Chemicals
Baroreceptor	Pressure
Nociceptor	Pain
Mechanoreceptor	Mechanical forces (touch, vibration)

Key Senses and Responsible Cells

• Vision: Photoreceptors (rods and cones) in the retina.

• Auditory (Hearing): Hair cells in the cochlea.

• Tactile (Touch): Mechanoreceptors in the skin.

• Olfaction (Smell): Olfactory receptor neurons in the nasal cavity.

• Gustation (Taste): Taste receptor cells in taste buds.

• Equilibrium: Hair cells in the vestibular apparatus of the inner ear.

Gross and Microscopic Anatomy of the Eye

• Tunics of the Eye:

  • Fibrous Tunic: Sclera (white, protective outer layer) and cornea (transparent, refracts light).

  • Vascular Tunic (Uvea): Choroid (blood supply), ciliary body (lens shape), iris (controls pupil size).

  • Neural Tunic (Retina): Contains photoreceptors (rods and cones).

Anterior and Posterior Cavities of the Eye

• Anterior Cavity: Between cornea and lens; filled with aqueous humor.

• Posterior Cavity: Between lens and retina; filled with vitreous humor.

Lens and Its Role in Vision

• Lens: Transparent, biconvex structure that focuses light onto the retina by changing shape (accommodation).

Extrinsic Eye Muscles

• Six muscles control eye movement: superior, inferior, medial, and lateral rectus; superior and inferior oblique.

Path of Light Through the Eye

• Light passes through cornea → aqueous humor → pupil → lens → vitreous humor → retina.

• Structures Responsible for Refraction: Cornea and lens.

Rods and Cones: Functions and Locations

Photoreceptor	Location	Function
Rods	Peripheral retina	Low-light (scotopic) vision, no color
Cones	Central retina (fovea)	Color vision, high acuity

Signal Pathway from Retina to Brain

• Photoreceptors → bipolar cells → ganglion cells → optic nerve → optic chiasm → optic tract → thalamus (lateral geniculate nucleus) → visual cortex.

Image Formation on the Retina

• The optical system of the eye focuses an inverted image on the retina, which the brain interprets as upright.

Phototransduction and Light/Dark Adaptation

• Phototransduction: Light activates photopigments in rods and cones, leading to a change in membrane potential and generation of nerve impulses.

• Light Adaptation: Eyes adjust to bright light by decreasing sensitivity.

• Dark Adaptation: Eyes increase sensitivity in low light.

Changes in Eye Anatomy and Vision

• Nearsightedness (Myopia): Eye is too long; image focuses in front of retina.

• Farsightedness (Hyperopia): Eye is too short; image focuses behind retina.

• Color Blindness: Deficiency or absence of certain cone photopigments.

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