Peripheral Nervous System & Special Senses Notes | BP101T
Subject: Human Anatomy and Physiology
Subject: Human Anatomy and Physiology
a2g Tricks
The Peripheral Nervous System (PNS) is the essential component of the nervous system that lies outside the brain and spinal cord. It serves as the critical communication bridge, ensuring information flow between the CNS and the entire body.
Bundles of nerve fibers (axons) carrying electrical impulses.
Collections of neuron cell bodies situated outside the CNS. They function primarily as vital relay and processing stations.
The Somatic Nervous System (SNS) is responsible for all voluntary activities. It establishes the link between the CNS and the physical environment.
CNS → Efferent Neuron → Skeletal Muscle
Neurotransmitter: Acetylcholine. Note: The SNS pathway involves no intervening ganglia.
The Autonomic Nervous System (ANS) controls all involuntary activities necessary for survival, primarily focused on maintaining homeostasis.
It regulates internal organs including the heart, blood vessels, glands, and the smooth muscles of the digestive and respiratory systems.
| ANS Division | Primary Function | Mnemonic |
|---|---|---|
| Sympathetic | Emergency system (Mobilization) | Fight or Flight |
| Parasympathetic | Normal resting system (Conservation) | Rest and Digest |
| Organ | Effect |
|---|---|
| Heart | Increases heart rate |
| Eye | Pupil dilates (Mydriasis) |
| Lungs | Bronchi dilate |
| Blood Vessels | Vasoconstriction (to non-essential areas) |
| GIT | Decreases digestion |
| BP | Increases |
| Organ | Effect |
|---|---|
| Heart | Decreases heart rate |
| Eye | Pupil constricts (Miosis) |
| Lungs | Bronchi constrict |
| GIT | Increases digestion & motility |
| Glands | Increases secretion |
This table is a Guaranteed AKTU question. Memorize the contrast points thoroughly.
| Feature | Sympathetic (FIGHT) | Parasympathetic (REST) |
|---|---|---|
| Origin | Thoraco-lumbar | Cranio-sacral |
| Neurotransmitter | Noradrenaline (mainly) | Acetylcholine |
| Function | Energy Mobilization | Energy Conservation |
| Heart Rate | ↑ Rate | ↓ Rate |
| Pupil | Dilates | Constricts |
Spinal nerves are key components of the PNS arising directly from the spinal cord. They are defined as mixed nerves because they contain both sensory (afferent) and motor (efferent) fibers.
Total Spinal Nerves = 31 pairs
Mnemonic: “8–12–5–5–1”
| Region | Number (Pairs) |
|---|---|
| Cervical | 8 (C1–C8) |
| Thoracic | 12 (T1–T12) |
| Lumbar | 5 (L1–L5) |
| Sacral | 5 (S1–S5) |
| Coccygeal | 1 |
Each spinal nerve is formed by the mandatory union of two specialized roots within the vertebral column:
Dorsal Root (Sensory) → Ventral Root (→ Spinal Nerve (Mixed)
Cranial nerves are specialized nerves that arise directly from the brain (primarily the brainstem). They are critical for controlling the functions of the head, neck, and certain internal organs.
Total = 12 pairs (numbered I to XII).
Meaningful Mnemonic Sentence (O O O T T A F V G V A H):
Oh Old Owl Tried To Act, Found Very Good Village And Home.
| No. | Name | Main Function | Type |
|---|---|---|---|
| I | Olfactory | Smell (Sensory) | Sensory |
| II | Optic | Vision (Sensory) | Sensory |
| III | Oculomotor | Eye movement, pupil constriction | Motor |
| IV | Trochlear | Eye movement | Motor |
| V | Trigeminal | Face sensation, Chewing (Motor) | Mixed |
| VI | Abducens | Lateral eye movement | Motor |
| VII | Facial | Facial expression, Taste | Mixed |
| VIII | Vestibulocochlear | Hearing & Balance | Sensory |
| IX | Glossopharyngeal | Taste, Swallowing | Mixed |
| X | Vagus | Control of Heart, Lungs, Digestion | Mixed |
| XI | Accessory | Neck and shoulder movement | Motor |
| XII | Hypoglossal | Tongue movement | Motor |
Mnemonic for Functional Type (S=Sensory, M=Motor, B=Both):
Some Say Money Matters, But My Brother Says Big Brains Matter More
| CN | Word | Type |
|---|---|---|
| I | Some | Sensory |
| II | Say | Sensory |
| III | Money | Motor |
| IV | Matters | Motor |
| V | But | Both |
| VI | My | Motor |
| VII | Brother | Both |
| VIII | Says | Sensory |
| IX | Big | Both |
| X | Brains | Both |
| XI | Matter | Motor |
| XII | More | Motor |
The eye is the highly specialized sensory organ responsible for vision. It operates analogously to a camera, converting focused light into electrical nerve impulses.
This layer is rich in blood vessels and controls light entry:
The neural layer containing photoreceptors:
| Photoreceptor | Function |
|---|---|
| Rods | Vision in dim light (Black/White) |
| Cones | Color and bright light vision |
The Fovea centralis is the spot of sharpest color vision.
Light → Cornea → Aqueous Humor → Pupil → Lens
↓ (Focusing)
Retina (Rods/Cones) → Electrical Impulses
↓
Optic Nerve → Brain (Interpretation)
| Disorder | Description | Correction |
|---|---|---|
| Myopia (Nearsightedness) | Image forms in front of retina. Distant objects blurred. | Concave Lens |
| Hypermetropia (Farsightedness) | Image forms behind retina. Near objects blurred. | Convex Lens |
| Cataract | Lens becomes opaque (cloudy vision). | Surgical removal |
| Glaucoma | Increased intraocular pressure damaging the optic nerve. | Medication/Surgery |