Overview
This lecture introduces fundamental neuroanatomy concepts, including the structure and function of the nervous system, sensory classifications, and the role of consciousness in sensory processing.
Central Nervous System (CNS)
- CNS consists of the brain and spinal cord
- Primary function: receive sensory information from environment and body
- Compares new sensory input with stored past information to recognize patterns
- Integrates present and past experiences to make decisions
- Processes information and generates appropriate motor responses
- Stores sensory information for future reference
Peripheral Nervous System (PNS)
- Divided into motor and sensory components
- Motor PNS: carries motor decisions from CNS to peripheral tissues
- Sensory PNS: transmits information from periphery to CNS
- Acts as communication pathway between CNS and body
Sensory System Classification
| Category | Type | Source | Examples |
|---|
| Special Senses | Vision | Eyes only | Seeing |
| Special Senses | Olfaction | Nose only | Smell |
| Special Senses | Gustation | Tongue only | Taste |
| Special Senses | Hearing | Ears only | Sound |
| Special Senses | Balance | Inner ear vestibular system | Equilibrium, position |
| General Senses | Somatic | Skin, locomotor system | Touch, pain, temperature, proprioception |
| General Senses | Visceral | Internal organs | Dull pain, distension, discomfort |
Special vs General Senses
- Special senses originate from specific, specialized body regions with dedicated receptors
- General senses can be elicited from multiple body parts
- Tongue contains both special (taste) and general (touch, temperature) sensations
- Special senses require unique anatomical structures for detection
Somatic Sensations
- Originate from superficial body parts: skin, subcutaneous tissue, integument
- Also arise from locomotor system: muscles, joints, ligaments, tendons, capsules
- Include four main types: touch, pain, temperature, proprioception
- Distinct from visceral sensations which come from deeper body structures
Visceral Sensations
- Generated from internal organs (viscera)
- Typically produce dull, poorly localized pain
- Include discomfort from organ distension
- Example: abdominal cramps and diarrhea sensations from gastrointestinal tract
- Abnormal visceral movement can trigger sensation
Proprioception
- All sensory input from locomotor system informing CNS about body position
- Enables accurate limb positioning without visual feedback
- CNS continuously computes information from joints, muscles, ligaments to track body part orientation
- Prevents simultaneous lifting of both legs during walking
- Allows accurate movement coordination (e.g., scratching ear, touching nose with closed eyes)
- Essential for coordinated movement and maintaining balance
Conscious vs Unconscious Sensations
- Some sensory information reaches conscious awareness; other information does not
- Cerebral cortex processes information at conscious level
- Blood pressure and peristalsis are typically unconscious sensations
- Sensations not reaching cerebral cortex remain unconscious
- Information can shift from unconscious to conscious when attention is directed
- Touch sensation typically reaches conscious level immediately