Study Guide: Nervous System and Senses

Study Guide - Smart Notes

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The nerve is a fundamental component of the nervous system, responsible for transmitting electrical impulses throughout the body.

Nerve: A bundle of axons (nerve fibers) enclosed within connective tissue.
Structure: Consists of axons, myelin sheath, endoneurium (surrounds individual axons), perineurium (bundles axons into fascicles), and epineurium (outermost layer).
Function: Conducts sensory and motor information between the body and the central nervous system (CNS).
Example: The sciatic nerve is the largest nerve in the human body, running from the lower back down the leg.

The human body contains 12 pairs of cranial nerves and 31 pairs of spinal nerves, each with specific functions and regions they innervate.

Cranial Nerves: Emerge directly from the brain and brainstem; each has a Roman numeral, name, function, and type (sensory, motor, or both).
Spinal Nerves: Emerge from the spinal cord and are distributed to various body regions; associated with specific spinal cord segments.
Dermatome: An area of skin supplied by a single spinal nerve. Shingles is a viral infection that affects a dermatome, causing pain and rash.
Referred Pain: Pain perceived at a location other than the site of the painful stimulus, often due to shared nerve pathways.
Plexuses: Networks of intersecting nerves (e.g., brachial plexus) that serve specific body regions.
Example Table: 12 Cranial Nerves

Number	Name	Function	Type
I	Olfactory	Smell	Sensory
II	Optic	Vision	Sensory
III	Oculomotor	Eye movement	Motor
IV	Trochlear	Eye movement	Motor
V	Trigeminal	Facial sensation, chewing	Both
VI	Abducens	Eye movement	Motor
VII	Facial	Facial expression, taste	Both
VIII	Vestibulocochlear	Hearing, balance	Sensory
IX	Glossopharyngeal	Taste, swallowing	Both
X	Vagus	Autonomic control of viscera	Both
XI	Accessory	Neck muscles	Motor
XII	Hypoglossal	Tongue movement	Motor

Additional info: Table entries inferred from standard anatomy knowledge.

A reflex arc is the neural pathway that mediates a reflex action, allowing for rapid, involuntary responses to stimuli.

Reflex: An automatic, rapid response to a stimulus.
Components: Sensory receptor, sensory neuron, integration center (spinal cord or brain), motor neuron, effector.
Steps: Stimulus → receptor → sensory neuron → integration center → motor neuron → effector → response.
Action Potentials (APs): Electrical signals transmitted along neurons.
Synapse: Junction between two neurons where neurotransmitters are released.
Example: The patellar (knee-jerk) reflex is a classic example of a monosynaptic reflex arc.

The nervous system transmits information via two major pathways: sensory (afferent) and motor (efferent).

Sensory Pathway: Carries information from sensory receptors to the CNS.
Motor Pathway: Transmits commands from the CNS to effectors (muscles or glands).
Example: Touching a hot object activates sensory neurons, which relay the signal to the CNS, triggering a motor response to withdraw the hand.

The autonomic nervous system (ANS) regulates involuntary body functions and is divided into sympathetic and parasympathetic branches.

Sympathetic Division: Prepares the body for 'fight or flight' responses (increases heart rate, dilates pupils).
Parasympathetic Division: Promotes 'rest and digest' activities (slows heart rate, stimulates digestion).
Associated Nerves: Sympathetic nerves arise from thoracic and lumbar spinal segments; parasympathetic nerves include cranial nerves III, VII, IX, and X (vagus nerve is most significant).
Neurotransmitters: Sympathetic uses norepinephrine; parasympathetic uses acetylcholine.
Receptors: Different responses are mediated by specific receptors (adrenergic for sympathetic, cholinergic for parasympathetic).
Example Table: Effects on Organ Systems

Additional info: Table entries inferred from standard physiology knowledge.

Sensory receptors detect changes in the environment and convert them into neural signals. Their organization affects sensitivity and perception.

Sensory Receptor: Specialized cell or structure that responds to specific stimuli.
Free Nerve Endings: Unencapsulated dendrites that detect pain, temperature, and crude touch.
Sensation: Awareness of a stimulus.
Perception: Interpretation of sensory information by the brain.
Adaptation: Decreased sensitivity to a constant stimulus over time.
General Senses: Include touch, pain, temperature, pressure, and proprioception.
Special Senses: Include vision, hearing, equilibrium, taste, and smell.

Different types of receptors are specialized for detecting specific types of stimuli.

Meissner's Corpuscles: Detect light touch; located in dermal papillae.
Pacinian Corpuscles: Detect deep pressure and vibration; found in deeper dermis and subcutaneous tissue.
Pain Receptors (Nociceptors): Detect tissue damage and pain.
Association: Each receptor type is linked to a specific sensation (e.g., thermoreceptors for temperature).

Each special sense has dedicated organs, processes, and associated cranial nerves.

Vision: Detected by the eye; optic nerve (II) transmits signals.
Hearing and Equilibrium: Detected by the ear; vestibulocochlear nerve (VIII) involved.
Taste: Detected by taste buds; facial (VII), glossopharyngeal (IX), and vagus (X) nerves involved.
Smell: Detected by olfactory epithelium; olfactory nerve (I) involved.

The eye contains internal and accessory structures essential for vision. Disorders can affect visual acuity and perception.

Internal Structures: Retina, lens, optic nerve.
Accessory Structures: Eyelids, lacrimal glands, conjunctiva.
Blind Spot: Area on the retina without photoreceptors where the optic nerve exits; causes a gap in the visual field.
Rods and Cones: Photoreceptors; rods detect light intensity, cones detect color.
Vision Disorders: Myopia (nearsightedness), hyperopia (farsightedness), astigmatism, presbyopia.

The ear is divided into external, middle, and internal parts, each with specific roles in hearing and balance.

External Ear: Auricle and auditory canal; collects sound waves.
Middle Ear: Tympanic membrane and ossicles; transmits vibrations.
Internal Ear: Cochlea (hearing), vestibule, and semicircular canals (balance).
Pathway of Hearing: Sound waves → tympanic membrane → ossicles → cochlea → auditory nerve.
Cochlea: Converts mechanical vibrations into nerve impulses.
Equilibrium: Detected by vestibular apparatus; body uses head position to maintain balance.

Aging can affect the function of all sensory systems, leading to decreased sensitivity and perception.

Smell and Taste: Reduced sensitivity due to loss of receptors.
Vision: Increased risk of cataracts, presbyopia, and macular degeneration.
Equilibrium and Hearing: Loss of hair cells in the inner ear can lead to balance issues and hearing loss.