Nerve ending synapse and sensory receptors classification (proprioceptors)

📚 Nerve Endings and Receptors Notes

🖇 Definition & Basic Concept

Nerve Endings = termination point of peripheral nerve

Two types of endings:

• Receptor (sensory nerve)
• Effector (motor nerve → muscle/gland)

Classification by tissue location:

• Epithelium
• Connective Tissue
• Muscular Tissue

📌 Nerve Endings in Epithelium

Key Feature: Generally Non-encapsulated

Types:

1. Free Nerve Endings (FNE)
2. • Location: Epidermis of skin, Cornea of eye
   • Cornea rich in FNE → sensitive to touch/pressure
2. Merkel Discs
3. • Location: Epidermis (between basal cells)
   • Found in: thick skin (palm, sole)
   • Structure: myelinated fiber loses myelin → expands as disc beneath Merkel cell
   • Function: pressure sensation
3. Peritrichial Nerve Endings
4. • Location: around hair follicle
   • Function: hair erection

🚨 Nerve Endings in Connective Tissue

Location: Dermis (beneath epidermis) + throughout body

Feature: Both encapsulated & non-encapsulated types

Non-encapsulated:

• Free Nerve Endings (FNE)

Encapsulated:

1. Meissner's Corpuscles
2. • Location: Dermal Papillae (fingerprints)
   • Structure: myelinated fiber loses myelin → spiral course in capsule
   • Function: touch sensation
2. Krause End Bulbs
3. • Location: connective tissue (especially genital area)
   • Structure: fiber loses myelin → branches in capsule
3. Ruffini End Bulbs
4. • Location: connective tissue throughout body
   • Structure: fiber loses myelin → multiple branches in capsule
4. Pacinian Corpuscles (Lamellar)
5. • Location: skin, mesentery, urinary bladder
   • Structure: concentric layers (onion-like) around nerve fiber
   • Function: pressure/proprioception
5. Golgi Tendon Organ (GTO)
6. • Location: tendon connective tissue
   • Structure: fiber loses myelin → runs between collagen fibers
   • Function: proprioception

🟠 Nerve Endings in Muscular Tissue

Muscle Spindle (proprioceptor in skeletal muscle)

Structure:

• Modified skeletal muscle
• Contains Intrafusal Muscle Fibers

Intrafusal Fiber Types:

1. Nuclear Bag fibers (nuclei collected like a bag)
2. Nuclear Chain fibers (nuclei in chain arrangement)

Innervation:

Sensory (afferent):

• Annulo-spiral → wraps around nuclear bag
• Flower-spray → associated with nuclear chain

Motor:

• A fibers → cause muscle contraction

Function: Proprioception (position & movement)

🟣 Synapses Review

Definition: Junction between:

• Two neurons
• Neuron & muscle
• Neuron & gland

Types by Signal Transmission:

1. Electrical → gap junctions
2. Chemical → neurotransmitters

Structure:

• Pre-synaptic (mitochondria + vesicles)
• Synaptic Cleft (gap)
• Post-synaptic (receptors + synaptic web)

Classifications:

By Contact:

• Axo-dendritic, Axo-somatic, Axo-axonic, Dendro-dendritic

By Morphology:

• Symmetrical vs Asymmetrical (membrane thickness)
• Terminal vs Genicular

🚨 Doctor's Questions

1. Does epithelium have glands?
2. Merkel disc location - epidermis or dermis?
3. Epithelial receptors - encapsulated or non-encapsulated?
4. Connective tissue location - above or below epidermis?
5. Meissner's corpuscles location?
6. Connective tissue endings - encapsulated or non-encapsulated?
7. Muscle spindle location?
8. Intrafusal fiber definition?
9. Nuclear bag vs chain fibers differences?
10. A vs B fibers in muscle spindle?