Central and Peripheral Nervous System

Overview – Central and Peripheral Nervous System

• Neuronal classification 
  • based upon the type of neurotransmitter they release and which inhibitor acts on them
  • cholinergic: acetylcholine (ACh)
    • inhibitors
      • muscarine (M)
      • nicotinic (N)
  • adrenergic: epinephrine (Epi)
  • noradrenergic: norepinephrine (NE)
  • dopaminergic: dopamine (D₁ and D₂)
• Central Nervous System (CNS)  = brain and spinal cord
• Autonomic: controls activities NOT under direct conscious control
  • parasympathetic (ACh M)
    • cardiac muscle
    • smooth muscle
    • nerve terminals  
    • gland cells
  • sympathetic
    • cardiac muscle (NE)
    • smooth muscle (NE)
    • sweat glands (ACh M)
    • gland cells (NE)
    • renal vascular smooth muscle (D₁)
    • nerve terminals (NE)
• Somatic (ACh N): controls activities under direct conscious control (movement and respiration)
• skeletal muscle

ACh receptors

• Nicotinic ACh receptors
  • ligand-gated Na⁺/K⁺ channels
  • 2 subtypes
    • N_N
      • found in the preganglionic efferent fibers synapsing in the autonomic ganglia 
    • N_M
      • found in the somatic motor fibers synapsing on neuromuscular junction
• Muscarinic ACh receptors
  • G-protein coupled receptors
  • 5 subtypes 
    • M₁
    • M₂
    • M₃
    • M₄
    • M₅

What Is the Central and Peripheral Nervous System?

The central nervous system (CNS) and peripheral nervous system (PNS) are two main components of the overall nervous system in the human body.

1. Central Nervous System (CNS): The CNS consists of the brain and spinal cord. It serves as the control center for the entire nervous system and is responsible for processing and coordinating sensory information, initiating motor responses, and carrying out higher cognitive functions. The brain is involved in activities such as thinking, memory, emotions, and perception, while the spinal cord serves as a pathway for transmitting signals between the brain and the rest of the body.
2. Peripheral Nervous System (PNS): The PNS includes all the nervous tissue located outside of the CNS. It connects the CNS to various organs, muscles, glands, and sensory receptors throughout the body. The PNS is further divided into two main components: the somatic nervous system (SNS) and the autonomic nervous system (ANS).

• Somatic Nervous System (SNS): The SNS controls voluntary movements and transmits sensory information from the body’s external environment to the CNS. It consists of sensory neurons that carry information from sensory receptors (e.g., touch, temperature, pain) to the CNS, and motor neurons that transmit signals from the CNS to skeletal muscles, enabling voluntary movements.
• Autonomic Nervous System (ANS): The ANS regulates involuntary bodily functions and maintains internal homeostasis. It controls activities of organs, glands, and smooth muscles, which are not under conscious control. The ANS can be further divided into the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS), which often have opposing effects on various physiological processes.
  • Sympathetic Nervous System (SNS): The SNS is responsible for the body’s response to stress or emergency situations. It activates the “fight-or-flight” response, increasing heart rate, dilating pupils, inhibiting digestion, and releasing stress hormones like adrenaline.
  • Parasympathetic Nervous System (PNS): The PNS promotes the body’s “rest-and-digest” response, conserving energy and maintaining normal bodily functions. It slows heart rate, stimulates digestion, constricts pupils, and promotes relaxation.

Structures of the Central and Peripheral Nervous System

Structures of the Central Nervous System (CNS):

1. Brain: The brain is the most complex organ in the CNS. It consists of several interconnected regions, including the cerebrum (responsible for higher cognitive functions), cerebellum (involved in coordination and balance), and brainstem (regulating vital functions such as breathing and heart rate).
2. Spinal Cord: The spinal cord is a long, cylindrical bundle of nerves that extends from the base of the brain down the vertebral column. It serves as a pathway for transmitting signals between the brain and the rest of the body. The spinal cord also contains neural circuits that can generate reflex actions independently of the brain.

Structures of the Peripheral Nervous System (PNS):

1. Nerves: The PNS consists of numerous nerves that extend from the CNS to various parts of the body. Nerves are bundles of specialized nerve fibers called axons, which transmit electrical signals. There are two types of nerves in the PNS:
   • Cranial Nerves: These nerves emerge directly from the brain and primarily innervate the head, neck, and face.
   • Spinal Nerves: These nerves arise from the spinal cord and innervate the rest of the body.
2. Ganglia: Ganglia are clusters of nerve cell bodies located outside the CNS. They are present in the PNS and can be classified into two types:
   • Sensory Ganglia: These ganglia contain cell bodies of sensory neurons and are responsible for relaying sensory information from peripheral receptors to the CNS.
   • Autonomic Ganglia: Autonomic ganglia are involved in the transmission of signals within the autonomic nervous system. They connect the CNS with the target organs and contain cell bodies of autonomic motor neurons.
3. Receptors: The PNS includes various sensory receptors that detect and transmit information about the external and internal environment to the CNS. These receptors include those for touch, pain, temperature, pressure, proprioception (body position sense), and special senses (e.g., vision, hearing, taste, smell).

Overall, the CNS comprises the brain and spinal cord, while the PNS consists of nerves, ganglia, and sensory receptors that extend throughout the body, connecting it to the CNS and enabling communication and control over bodily functions.

Treatment for Central and Peripheral Nervous System Conditions

The treatment for central nervous system (CNS) and peripheral nervous system (PNS) conditions varies depending on the specific condition and its underlying cause. Here are some general treatment approaches for common CNS and PNS conditions:

1. Central Nervous System (CNS) Conditions:
   • Neurological Disorders: Neurological disorders such as epilepsy, multiple sclerosis, Parkinson’s disease, Alzheimer’s disease, and stroke may be managed with a combination of medications, physical therapy, occupational therapy, speech therapy, and lifestyle modifications. In some cases, surgical interventions may be considered.
   • Traumatic Brain Injury (TBI): Treatment for TBI typically involves immediate medical attention, stabilization, and management of complications. Rehabilitation therapies, including physical therapy, occupational therapy, speech therapy, and cognitive rehabilitation, are crucial for recovery.
   • Brain Tumors: Treatment for brain tumors may include surgery, radiation therapy, chemotherapy, targeted therapy, and supportive care. The specific treatment plan depends on factors such as the type, size, and location of the tumor.
2. Peripheral Nervous System (PNS) Conditions:
   • Peripheral Neuropathy: Treatment for peripheral neuropathy focuses on managing the underlying cause, relieving symptoms, and preventing further nerve damage. Medications, physical therapy, pain management techniques, and lifestyle modifications are commonly used.
   • Guillain-Barré Syndrome (GBS): GBS requires immediate medical attention and hospitalization. Treatment often involves intravenous immunoglobulin (IVIG) or plasmapheresis to reduce the immune system’s attack on the peripheral nerves. Rehabilitation therapy may be necessary for recovery.
   • Peripheral Nerve Injuries: Treatment for peripheral nerve injuries depends on the severity and location of the injury. It may include surgical repair, physical therapy, occupational therapy, and pain management techniques.

It’s important to note that these treatment approaches are general guidelines, and the specific treatment plan for a particular condition should be determined by healthcare professionals based on a thorough evaluation and diagnosis. Treatment may also involve a multidisciplinary approach, with specialists from various fields working together to provide comprehensive care.

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