Human Nervous System Overview

Somatic Nervous System

• Controls motor pathways to skeletal muscles
• Voluntary and conscious movements
• Message originates in the frontal lobe's pre-central gyrus
• Two neurons involved: upper and lower motor neurons
• Upper motor neuron travels to medulla oblongata
• Lower motor neuron connects to muscle fiber via medulla oblongata and spinal cord
• Acetylcholine (Ach) stimulates excitatory cholinergic receptors, causing muscle contraction
• Message originates on the opposite side of the brain relative to the affected body part (e.g., right arm movement initiated by the left brain)

Higher Brain Functions - Speech

• Primarily lateralized to the left cerebral cortex
• Wernicke area (parietal lobe): processes incoming sensory language
• Receives input from visual and auditory cortices
• Broca area (frontal lobe): responsible for motor commands for speech production
• Arcuate fasciculus: connects Wernicke and Broca areas, resembling a stringy arch

Higher Brain Functions - Memory

• Frontal cortex is crucial
• Working memory: task-oriented, short-duration (e.g., GPS directions)
• Short-term memory: lasts minutes to days (e.g., parking location)
• Long-term memory: lasts years to a lifetime (e.g., first day of high school)
• Consolidation: necessary for short-term memories to become long-term
• Emotionally intense experiences more likely to consolidate

Declarative/Explicit Memory

• Retention of facts
• Hippocampus (temporal lobe): stores factual memories
• Amygdala (temporal lobe): processes emotions, sharing pathways with the hippocampus
• Strong emotions enhance memory retention

Procedural/Implicit/Reflexive Memory

• Development of skills (e.g., riding a bicycle)
• Essentially muscle memory
• Involves the cerebellum (coordination) and premotor cortex (voluntary motors)
• Includes conditioned reflexes (e.g., Pavlov's dog)

Autonomic Nervous System

• Controls involuntary visceral functions (e.g., cardiac muscle, smooth muscle, glands, adipose tissue)
• Primarily unconscious, but sometimes conscious awareness (e.g., experiencing anxiety)
• Three neurons needed to send a signal to an internal organ:
  • Upper motor neuron from hypothalamus/medulla oblongata, entering grey matter (lateral horns)
  • Lower motor neuron (pre-ganglionic) from lateral horns to ganglia
  • Post-ganglionic LMN from ganglia to the visceral organ
• Divided into:

Parasympathetic Division

• "Rest and digest" system
• Craniosacral division (cranial and sacral nerves)
• Maintains homeostasis
• Terminal ganglia near the target organs
• Releases acetylcholine (Ach) for stimulation

Sympathetic Division

• "Fight-or-flight" response
• Thoracolumbar division (thoracic and lumbar nerves)
• Generates energy (ATP)
• Chain ganglia linked together
• Involves the adrenal glands, secreting adrenaline/epinephrine
• Uses adrenergic receptors

Sensory System Integration

• Sensation: Feeling arising from a stimulus
• Sensory receptors detect changes & undergo transduction (convert stimuli into signals)
• Classification by Stimuli: chemoreceptors, nociceptors (pain), thermoreceptors, mechanoreceptors, photoreceptors

Classification by Structure

• Free nerve endings: exposed nerve endings
• Corpuscles: nerve endings enclosed in connective tissue

Sensory Adaptation

• Receptors adjust to constant stimulation, causing them to become less responsive

General Senses

• Receptors located throughout the body (skin, muscles, joints, viscera)
• Pathway: receptor → spinal nerve → spinal cord → thalamus → cortex (parietal lobe's postcentral gyrus)
• First, second, and third-order neurons are involved in the pathway
• Decussation: crossing over of sensory pathways
• Homunculus: representation of body parts on the postcentral gyrus

Somatic Senses

• Touch and pressure: mechanoreceptors (corpuscles, free nerve endings)
• Temperature: thermoreceptors (free nerve endings)
• Pain: nociceptors (free nerve endings)
  • Acute (fast, sharp, localized)
  • Chronic (slow, general, aching)
  • Referred (pain projected to an area other than the source)
• Proprioception: sense of body position (muscle spindles, Golgi tendon organs)

Visceral Senses

• Internal organs
• Conscious and unconscious sensations
• Mechanoreceptors and chemoreceptors

Special Senses

• Receptors located only in the head
• Pathway: receptor → cranial nerve → brain

Smell (Olfaction)

• Chemoreceptors in olfactory organs (nasal cavity)
• Unique: does not pass through the thalamus
• CN I → frontal and temporal lobe to process smell

Taste (Gustation)

• Chemoreceptors in taste buds (papillae on tongue)
• CN VII (facial) and CN IX (glossopharyngeal) → thalamus → insula
• Primary taste sensations: salty, sweet, umami, sour, bitter

Hearing (Auditory)

• Mechanoreceptors in cochlea (inner ear)
• Outer ear: pinna, external auditory canal, tympanic membrane
• Middle ear: Eustachian tube, auditory ossicles (malleus, incus, stapes), oval window
• Inner ear: cochlea, perilymph, endolymph, hair cells, round window
• CN VIII (cochlear branch) → midbrain → thalamus → temporal lobe

Balance (Equilibrium)

• Mechanoreceptors in vestibular apparatus (inner ear)
• Vestibule (static balance), semicircular canals (dynamic balance)
• CN VIII (vestibular branch) → brainstem & cerebellum → thalamus → parietal lobe

Sight (Vision)

• Photoreceptors (rods and cones) in the retina (inner eye)
• Accessory organs: eyebrows, eyelids, eyelashes, extraocular muscles, lacrimal glands
• Outer tunic: cornea, sclera
• Middle tunic: choroid coat, iris, lens, ciliary bodies
• Inner tunic: retina (rods, cones, bipolar cells, ganglion cells), macula lutea, fovea centralis, optic disc
• Humors: aqueous humor (anterior cavity), vitreous humor (posterior cavity)
• CN II (optic nerve) → optic chiasm → thalamus → occipital lobe

This quiz covers the essential functions of the somatic nervous system and higher brain functions, particularly related to motor control and speech. It examines how messages travel from the brain to muscles and the areas of the brain responsible for speech production and processing. Test your understanding of these crucial neurological concepts.