Peripheral Nervous System: Definition, Parts, Functions, Disorders

Definition Of The Peripheral Nervous System (PNS)

The peripheral Nervous System is the nervous system that exists outside the brain and spinal cord. It acts as the middle man between the Central Nervous System and the limbs and organs, transmitting impulses necessary for action, voluntary and involuntary, therefore, sustaining the overall functioning of the body.

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This Story also Contains

1. Definition Of The Peripheral Nervous System (PNS)
2. Components Of The Peripheral Nervous System
3. Divisions Of The Peripheral Nervous System
4. Functional Of The Peripheral Nervous System
5. Disorders Of The Peripheral Nervous System
6. Diagnostic Methods For PNS Disorders
7. Recommended Video On ‘Peripheral Nervous System’

Components Of The Peripheral Nervous System

It comprises nerves, ganglia, and their protective and supporting connective tissue coverings respectively.

Nerves

Groups of axons are wrapped by connective tissue that transmit signals between the CNS and the periphery.

Types Of Nerves

• Sensory Nerves: Carry sensory information from receptors to the CNS.

• Motor Nerves: Transmit motor commands from the CNS to muscles and glands.

• Mixed Nerves: Contain both sensory and motor fibres, thus capable of transmitting signals in both directions.

Ganglia

• Sensory (Dorsal Root Ganglia): Contains cell bodies of sensory neurons.

• Autonomic Ganglia: Contains cell bodies of neurons in the autonomic nervous system.

Connective Tissue Coverings

• Endoneurium: Surrounds individual nerve fibres (axons).

• Perineurium: Encloses bundles of nerve fibres (fascicles).

• Epineurium: Encases the entire nerve, providing protection and support.

Diagram: Human Nervous System

Divisions Of The Peripheral Nervous System

The PNS is divided into the somatic and autonomic nervous systems, each with distinct functions.

Somatic Nervous System:

• Spinal Nerves: 31 pairs that emerge from the spinal cord.

• Cranial Nerves: 12 pairs that emerge directly from the brain.

• Role in Voluntary Movements: Controls skeletal muscle contractions and mediates conscious movements.

Autonomic Nervous System:

• Sympathetic Nervous System: Prepares the body for 'fight or flight' responses.

• Parasympathetic Nervous System: Promotes 'rest and digest' activities.

• Regulates involuntary functions such as heart rate, digestion, and respiratory rate.

Functional Of The Peripheral Nervous System

The PNS is essential for reflex actions and the transmission of nerve impulses.

Reflex Arc

• Examples of Reflex actions are knee-jerk reflex and withdrawal reflex.

Transmission Of Nerve Impulses

• Involves the movement of sodium and potassium ions across the neuron membrane, generating an electrical impulse.

• Neurotransmitters are released from the axon terminal of one neuron and bind to receptors on the dendrite of another neuron, facilitating signal transmission.

Disorders Of The Peripheral Nervous System

Several conditions can affect the PNS, leading to various symptoms and requiring different treatments.

Peripheral Neuropathy

• Caused by diabetes, infections, and injuries; symptoms include numbness, tingling, and pain in the affected area.

• Treatment Includes medications, physical therapy, and addressing underlying causes.

Guillain-Barré Syndrome

• An autoimmune disorder is often triggered by an infection, leading to muscle weakness and paralysis.

• Treatment includes Plasmapheresis, immunoglobulin therapy, and supportive care.

Carpal Tunnel Syndrome

• Compression of the median nerve, causing pain and numbness in the hand.

Bell’s Palsy

Sudden weakness or paralysis of facial muscles, usually temporary.

Diagnostic Methods For PNS Disorders

Accurate diagnosis is crucial for effective treatment of PNS disorders.

• Electromyography (EMG)

• Nerve Conduction Studies (NCS)

• MRI and CT Scans

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