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

Central Nervous System (CNS)

Functions of Brain Lobes

The brain is divided into several lobes, each responsible for distinct functions related to motor control, sensory processing, language, and personality.

• Frontal Lobe: Voluntary motor functions, verbal communication, personality.

  • Primary Motor Cortex: Conscious control of precise, skilled voluntary movements (pyramidal cells in gyri).

  • Premotor Cortex: Controls learned, repetitious, or patterned motor skills; plans movements.

  • Broca's Area: Usually in the left hemisphere; active during speech preparation; directs muscles of the tongue.

  • Frontal Eye Field: Controls voluntary eye movements.

• Parietal Lobe: Comprehends language, senses heat, pain, and other sensations; spatial awareness.

  • Primary Somatosensory Cortex: Receives information from skin, joints, and tendons; spatial discrimination.

  • Somatosensory Association Cortex: Integrates temperature and pressure sensations (e.g., identifying objects by touch).

• Temporal Lobe: Understanding speech, sound and taste processing, memory.

  • Primary Auditory Cortex: Processes pitch, rhythm, and loudness.

  • Auditory Association Area: Stores memories and permits perception of sound.

  • Wernicke’s Area: Language recognition; damage results in nonsensical speech.

  • Olfactory Cortex: Awareness of odors.

• Occipital Lobe: Visual processing.

  • Primary Visual Cortex: Receives visual information from retinas.

  • Visual Association Area: Interprets visual stimuli; recognizes faces.

• Insula Lobe: Taste and visceral sensations.

  • Gustatory Cortex: Perception of taste.

  • Visceral Sensory Area: Perceptions of internal organs (e.g., full bladder).

Multimodal Association Areas

These areas integrate information from multiple sensory modalities.

• Anterior: Intellect, cognition, recall, personality.

• Posterior: Patterns, faces, written and spoken language.

• Limbic: Emotional impact, memory formation.

Organization of Major Brain Regions

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

• Brain Stem: Controls automatic behaviors; cranial nerves (except olfactory and optic) emerge here.

• Cerebral Hemispheres: Grey matter (40% of brain); left hemisphere (language, math, logic), right hemisphere (visual-spatial skills, intuition, artistic skills). Each hemisphere controls the opposite side of the body.

• Midbrain: Visual and auditory reflexes.

• Pons: Relay site from motor cortex to cerebellum.

• Medulla Oblongata: Relays information from hypothalamus; controls heart rate, breathing, vomiting, coughing, sneezing, swallowing.

• Cerebellum: Calibrates motor control, language, attention, balance.

• Diencephalon: Thalamus and hypothalamus; helps maintain homeostasis.

Cerebral White Matter

White matter consists of myelinated fibers that communicate between the cerebral cortex and lower CNS.

• Association Fibers: Connect different parts of the same hemisphere (horizontal).

• Projection Fibers: Connect hemispheres with lower brain or spinal cord (vertical).

• Commissures: Connect left and right hemispheres (e.g., corpus callosum).

Basal Nuclei (Basal Ganglia)

Basal nuclei influence muscular control, attention, and cognition.

• Thalamus: Relay station for sensory information.

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

• Pituitary Gland: Master gland; controls other glands, responds to stress.

  • Anterior Lobe: Produces thyroid stimulating hormone, follicle stimulating hormone; aids in growth.

  • Posterior Lobe: Produces oxytocin and antidiuretic hormone (ADH).

• Pineal Gland: Produces melatonin; involved in sexual development and sleepiness.

Cerebral Peduncles and Corpora Quadrigemina

• Cerebral Peduncles: Fiber tracts relaying information between brain regions.

• Corpora Quadrigemina: Four colliculi; superior (visual reflexes), inferior (auditory relay).

• Substantia Nigra: Dark due to melanin; precursor to dopamine; site of Parkinson’s disease.

Meninges

The meninges are protective coverings of the brain and spinal cord.

• Dura Mater: "Tough mother"; leathery, protective.

• Arachnoid Mater: "Spider mother"; loose covering, cerebrospinal fluid flows here.

• Pia Mater: "Soft mother"; delicate connective tissue, closely adheres to brain.

Ventricles of the Brain

Ventricles produce and move cerebrospinal fluid (CSF) for protection, buoyancy, and waste removal.

• Lined by ependymal cells.

• Connected to each other and the central canal of the spinal cord.

• Includes two lateral ventricles, third, and fourth ventricles.

Functional Brain Systems

• Limbic System: Emotional responses, memory formation.

  • Amygdaloid Body: Recognizes angry faces, elicits fear response.

  • Cingulate Gyrus: Expresses emotions, resolves mental conflict.

• Reticular Formation: Sends impulses to cerebral cortex; keeps it conscious and alert; filters out repetitive/weak stimuli.

Brain Waves

Brain waves are patterns of neuronal and electrical activity generated by synaptic activity on the cortex.

• Alpha Waves: Regular rhythm; awake but relaxed.

• Beta Waves: Mentally alert; less regular.

• Theta Waves: Common in children.

• Delta Waves: Deep sleep; may indicate brain damage.

Brain Disorders

• Epileptic Seizures: Abnormal electrical activity.

  • Absence Seizure (Petit Mal): Mild, common in children; brief loss of awareness.

  • Tonic-Clonic (Grand Mal): Severe; loss of consciousness, convulsions.

• Alzheimer's Disease: Dementia; beta amyloid plaques, neurofibrillary tangles, brain cell death.

• Parkinson's Disease: Degeneration of dopamine-releasing neurons; tremors, motor dysfunction.

• Huntington's Disease: Hereditary; accumulation of huntingtin protein; degeneration of basal nuclei and cortex; wild movements, mental deterioration.

• Stroke: Disruption of blood flow to the brain.

Memory

• Short-Term Memory (STM): Limited capacity (7-8 items); temporary.

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

• Factors Affecting Transfer: Emotional state, rehearsal, association, automatic memory.

Peripheral Nervous System (PNS)

Key Terms and Concepts

• Sensation: Awareness of changes in internal/external environment.

• Perception: Conscious interpretation of stimuli.

• Processing: Receptor specificity and receptive field.

• Adaptation: Reduced responsiveness to unchanging stimuli.

• Diplopia: Double vision.

• Nystagmus: Jittery eye movements.

• Ptosis Lag: Droopy eyelids.

• Bell’s Palsy: Sudden facial muscle weakness/paralysis.

• Dysphagia: Difficulty swallowing.

• Reflex: Rapid, predictable motor response to a stimulus.

Organization of Sensation and Perception

Sensation occurs at the level of sensory receptors; perception occurs in the cerebral cortex.

Types of Sensory Receptors

• Mechanoreceptors: Touch, pressure, vibration, stretch, itch.

• Thermoreceptors: Temperature changes.

• Photoreceptors: Light energy.

• Chemoreceptors: Chemicals (smell, taste, blood chemistry).

• Nociceptors: Pain-causing stimuli.

Receptor Classification by Location

• Exteroceptors: Respond to stimuli outside the body; near body surface; include special sense organs.

• Interoceptors: Respond to stimuli within the body; in viscera and blood vessels.

• Proprioceptors: Respond to degree of stretch; located in skeletal muscles, tendons, joints, ligaments; advise brain on movement.

Receptor Adaptation

• Phasic Receptors: Adapt quickly (pressure, touch, smell).

• Tonic Receptors: Adapt slowly (chemicals in blood).

• Non-Adapting: Pain and proprioceptors.

Aspects of Sensory Perception

• Perceptual Detection: Detecting that a stimulus has occurred.

• Pattern Recognition: Determining how much of a stimulus is acting.

• Spatial Discrimination: Locating the stimulus.

• Feature Abstraction: Identifying specific texture and shape.

• Quality Discrimination: Identifying submodalities of sensation.

Classification of Nerves

• Sensory (Afferent): Carry impulses to CNS.

• Motor (Efferent): Carry impulses from CNS.

• Mixed: Carry both sensory and motor fibers; most common.

• Somatic/Viceral: Somatic afferent/efferent; visceral afferent/efferent.

Nerve Structure

• Endoneurium: Surrounds individual axons and myelin sheath.

• Perineurium: Covers fascicles (bundles of axons).

• Epineurium: Covers multiple fascicles (entire nerve).

Regeneration of Nerve Fibers

• Axons can be repaired in PNS.

• Steps:

  1. Distal part of axon dies.

  2. Macrophages clean up injury site.

  3. Schwann cells align to form regeneration tube.

  4. Axon grows through regeneration tube.

• CNS neurons cannot regenerate due to oligodendrocytes (growth-inhibiting proteins) and astrocyte scar tissue.

Referred Pain

Pain stimuli from internal organs (viscera) are perceived as originating from somatic regions.

Cranial Nerves

Identification, Function, and Testing

The twelve cranial nerves are identified by number, name, type, main function, and testing method.

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

Mnemonic: "On occasion our trusty truck always fails. Very good vehicle any how."

Testing Methods: Each nerve has specific clinical tests, such as smell identification, visual acuity, eye movement tracking, facial muscle actions, hearing tests, gag reflex, and tongue movement.

Spinal Nerves

• 31 pairs of mixed nerves.

• Supply all parts of the body except the head.

Reflexes

Definition and Steps in Reflex Arc

A reflex is a rapid, predictable motor response to a stimulus, which can be inborn or learned.

• Involves peripheral nerves and spinal cord; can be modified by the brain.

• Steps in Reflex Arc:

  1. Receptor: Detects stimulus.

  2. Sensory Neuron: Transmits 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 (Stretch Reflex)

Monosynaptic reflex; tapping on patellar tendon causes contraction of quadriceps muscle.

Additional info:

• Parkinson's disease is treated with L-dopa, deep brain stimulation, and gene therapy.

• Huntington's disease is fatal within 15 years of onset; research includes stem cell implants.

• Memory transfer is best when alert, motivated, or surprised; repetition and association aid transfer.

• Oligodendrocytes in CNS inhibit axon regrowth; astrocytes form scar tissue quickly.