Central and Peripheral Nervous System: Structure, Function, and Disorders

Central Nervous System (CNS)

Major Regions and Organization of the Brain

The brain is organized into several major regions, each with specialized functions essential for bodily control and cognition.

• Cerebrum: Largest part, responsible for higher brain functions such as thought, memory, and voluntary movement.

• Diencephalon: Includes the thalamus and hypothalamus, involved in sensory relay and homeostasis.

• Brainstem: Composed of the midbrain, pons, and medulla oblongata; controls vital functions like breathing and heart rate.

• Cerebellum: Coordinates movement and balance.

Functions of the Lobes of the Brain

• Frontal Lobe: Voluntary movement, planning, reasoning, problem-solving, and speech production (Broca's area).

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

• Temporal Lobe: Auditory processing, memory, and language comprehension (Wernicke's area).

• Occipital Lobe: Visual processing.

Main Functions of Different Parts of the Brain

• Thalamus: Relay station for sensory information.

• Hypothalamus: Regulates autonomic functions, hormone release, and homeostasis.

• Medulla Oblongata: Controls heart rate, blood pressure, and respiration.

• Pons: Connects cerebellum to cerebrum, assists in breathing regulation.

• Midbrain: Visual and auditory reflexes.

• Cerebellum: Fine-tunes motor activity, balance, and posture.

Brain Waves

Brain waves are patterns of electrical activity in the brain, measured by EEG.

• Alpha Waves: Relaxed, awake state.

• Beta Waves: Alert, active thinking.

• Theta Waves: Light sleep, drowsiness.

• Delta Waves: Deep sleep.

Disorders of the CNS

• Stroke: Disruption of blood flow to the brain, causing tissue damage.

• Epilepsy: Recurrent seizures due to abnormal electrical activity.

• Parkinson's Disease: Degeneration of dopamine-producing neurons, leading to tremors and rigidity.

• Alzheimer's Disease: Progressive memory loss and cognitive decline.

• Bell’s Palsy: Sudden weakness or paralysis of facial muscles, usually temporary.

Peripheral Nervous System (PNS)

Key Terms and Concepts

• Sensation: Awareness of changes in the internal or external environment.

• Perception: Interpretation of sensory input by the brain.

• Processing: Integration and analysis of sensory information.

• Adaptation: Decreased sensitivity to a constant stimulus.

• Diplopia: Double vision.

• Nystagmus: Involuntary, rapid eye movements.

• Ptosis Lag: Drooping of the upper eyelid.

• Reflex: Rapid, automatic response to a stimulus.

Organization of Sensation and Perception

• Sensation: Occurs at sensory receptors and is transmitted via afferent pathways to the CNS.

• Perception: Occurs in the cerebral cortex, where sensory information is interpreted.

Types of Sensory Receptors and Their Stimuli

• Chemoreceptors: Respond to chemical stimuli (e.g., taste, smell).

• Mechanoreceptors: Respond to mechanical forces (e.g., touch, pressure).

• Thermoreceptors: Respond to temperature changes.

• Photoreceptors: Respond to light (e.g., in the retina).

• Nociceptors: Respond to pain-causing stimuli.

Classification of Receptors by Location

• Exteroceptors: Located near the body surface; detect external stimuli (e.g., touch, temperature).

• Interoceptors (Visceroceptors): Detect internal stimuli from organs.

• Proprioceptors: Detect body position and movement (e.g., in muscles, tendons).

Adaptation of Receptors

• Phasic Receptors: Adapt quickly (e.g., pressure, touch receptors).

• Tonic Receptors: Adapt slowly or not at all (e.g., pain receptors, proprioceptors).

Aspects of Sensory Perception

• Pattern Recognition: Ability to identify familiar patterns in sensory input.

• Feature Abstraction: Identification of specific features of a stimulus.

• Quality Discrimination: Ability to differentiate submodalities of a sensation (e.g., sweet vs. bitter).

Classification of Nerves

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

• Motor (Efferent) Nerves: Carry impulses away from the CNS.

• Mixed Nerves: Contain both sensory and motor fibers.

Regeneration of Nerve Fibers

• Steps in Regeneration (PNS):

  1. Axon becomes fragmented at injury site.

  2. Macrophages clean out the dead axon distal to injury.

  3. Schwann cells form a regeneration tube and secrete growth factors.

  4. Axon regenerates and new myelin sheath forms.

• Why CNS Neurons Cannot Regenerate: Oligodendrocytes do not form regeneration tubes and release inhibitory factors; also, the CNS environment is less supportive of regrowth.

Cranial Nerves: Number, Name, Type, and Testing

The cranial nerves are twelve pairs, each with specific functions. They can be sensory, motor, or mixed.

Number	Name	Type	Main Function	Testing Method
I	Olfactory	Sensory	Smell	Identify odors
II	Optic	Sensory	Vision	Visual acuity test
III	Oculomotor	Motor	Eye movement, pupil constriction	Pupil response, eye movement
IV	Trochlear	Motor	Eye movement (superior oblique)	Eye movement
V	Trigeminal	Mixed	Facial sensation, chewing	Facial touch, jaw movement
VI	Abducens	Motor	Eye movement (lateral rectus)	Eye movement
VII	Facial	Mixed	Facial expression, taste	Smile, frown, taste test
VIII	Vestibulocochlear	Sensory	Hearing, balance	Hearing test, balance
IX	Glossopharyngeal	Mixed	Taste, swallowing	Gag reflex, taste
X	Vagus	Mixed	Autonomic control of heart, lungs, digestion	Gag reflex, voice quality
XI	Accessory	Motor	Shoulder and neck movement	Shoulder shrug
XII	Hypoglossal	Motor	Tongue movement	Stick out tongue

Meninges: Function and Organization

• Dura Mater: Tough, outermost layer; protects the brain and spinal cord.

• Arachnoid Mater: Middle, web-like layer; contains cerebrospinal fluid (CSF) in the subarachnoid space.

• Pia Mater: Delicate, innermost layer; adheres to the surface of the brain and spinal cord.

Ventricles: Function

• Produce and circulate cerebrospinal fluid (CSF), which cushions the brain and removes waste.

• Consist of two lateral ventricles, third ventricle, and fourth ventricle.

Reflexes and Reflex Arcs

• Reflex: An automatic, rapid response to a stimulus.

• Reflex Arc Steps:

  1. Receptor detects stimulus.

  2. Sensory neuron transmits impulse to CNS.

  3. Integration center processes information (may involve interneurons).

  4. Motor neuron transmits impulse to effector.

  5. Effector (muscle or gland) produces response.

• Patellar Reflex (Knee-Jerk): Example of a monosynaptic reflex; tapping the patellar tendon causes contraction of the quadriceps muscle.

Additional info: Some disorders and terms (e.g., Bell's palsy, diplopia, nystagmus) are included for clinical context, as they relate to cranial nerve function and neurological assessment.