Intro to nervous system

• Nervous system is the most complex system in the body
• Composed of specialized cells called neurons and assisted by neuroglia
• Function to receive sensory stimuli and to transmit them to the effector organs
• Anaxonic neurons have no distinct axon or dendrites
• Bipolar neurons have one axon and one dendrite, found in sensory neurons of the retina, olfactory, and inner ear
• Multipolar neurons have one axon and more than two dendrites, the most common type in the central and peripheral nervous system
• Cell body: contains the nucleus, cytoplasm rich in granular and agranular endoplasmic reticulum, Nissl substance, Golgi complex, mitochondria, and microfilament
• Dendrites: short, small processes that branch profusely to receive impulses and integrate signals from other neurons
• Axon: longer than dendrites, carries impulses away from the cell body, and branches at the distal end into axon terminals
• According to the number of processes: anaxonic, bipolar, and multipolar
• According to the size of the neuron: Golgi type I with short axons and Golgi type II with long axons
• According to functional role: sensory neurons (afferent) and motor neurons (efferent)
• Non-excitable cells that support neuronal survival and activities
• 6 types of neuroglial cells, 4 in the central nervous system (CNS) and 2 in the peripheral nervous system (PNS)
• Oligodendrocytes produce myelin sheath in the CNS, while Schwann cells form myelin sheath in the PNS
• Central Nervous System (CNS) includes the brain and spinal cord, where correlation and integration of nervous information occur
• Peripheral Nervous System (PNS) consists of cranial and spinal nerves that conduct information to and from the CNS
• PNS is anatomically and functionally continuous with the CNS, conducting impulses to or away from the CNS to connect with peripheral structures
• Brain and spinal cord composed of white matter (myelinated axons) and gray matter (neuronal cell bodies)
• Brainstem includes midbrain, pons, and medulla oblongata
• Covered by meninges (dura, arachnoid, pia mater) and suspended in cerebrospinal fluid (CSF)
• Cranial nerves (12 pairs) exit the cranial cavity through the skull and are distributed in the head and neck
• Spinal nerves (31 pairs) exit from the vertebral column and are made up of bundles of nerve fibers supported by connective tissue
• Nerves consist of axons, neurolemma, and surrounding endoneurial connective tissue, supported by blood vessels
• Nerve consists of:

  • Bundle of nerve fibres outside CNS
  • Connective tissue coverings
  • Blood vessels
• Nerve is strong because it is supported by 3 connective tissues:

  1. Endoneurium: surrounds individual nerve fibre

  2. Perineurium: surrounds bundle of nerve fibres

  3. Epineurium: surrounds the nerve trunk
• Collection of cell bodies are called nuclei in the CNS

  • Collection of cell bodies are called ganglia in the PNS
  • Collection of axons are called tracts
  • Collection of axons are called nerves
• Connective tissue covering of CNS:

  • Meninges (Dura, arachnoid, pia mater)
  • Connective tissue covering of PNS:

  Endoneurium, Perineurium, Epineurium
• Spinal nerve:

  • Formed of anterior & posterior root (MIXED)
  • Anterior root carries nerve impulses away from CNS (MOTOR EFFERENT)
  • Posterior root carries nerve impulses to CNS (SENSORY AFFERENT)
• Sensation of touch, pain, temperature:

  • Afferent carry impulse to CNS through sensory fibres
  • Efferent motor fibres go to skeletal muscles and cause muscle contraction
• Ganglia:

  • Sensory ganglia for spinal & cranial nerves
  • Autonomic ganglia = Collection of cell bodies
• Somatic vs Autonomic:

  Somatic:

  • Associated with skeletal muscle voluntary control of body movements
  • Afferent: somatic sensory transmit sensation of pain, touch, temperature
  • Efferent: somatic motor innervates only skeletal muscles
• Autonomic:

  • Acts unconsciously (involuntary) and regulates bodily functions
  • Afferent: originate from visceral receptor
  • Efferent: innervates smooth muscle, cardiac muscle & glandular cells (involuntary)
• Types of fibres conveyed by peripheral nerves:

  Somatic fibres:

  • General sensory afferent (GSA)
  • General somatic efferent (GSE)

  Visceral fibres:

  • General Visceral Afferent (GVA)
  • General Visceral Efferent (GVE)
• Somatic vs Autonomic:

  Somatic:

  • Connects the skin or muscle with the central nervous system
  • Voluntary movement
  • GSA, GSE

  Autonomic:

  • Connects the internal organs with the central nervous system
  • Involuntary movement
  • GVA, GVE
• Actions of Sympathetic & Parasympathetic:

  • Have antagonist control over a viscus

  Organ Sympathetic Parasympathetic

  Eye: Pupil dilates, Ciliary muscle relaxes

  Glands: Reduce secretion, Increase secretion

  Sweat: Increase secretion

  Heart: Increase force of contraction, Decrease force of contraction

  Coronary arteries: Dilates (beta receptors), Constricts (alpha receptors)

  Lungs: Bronchial muscle relaxes, Bronchial secretion increase

  Bronchial arteries: Constricts, Dilates

  Gastrointestinal tract: Muscle in walls decrease peristalsis, Muscle in sphincter contracts
• Urinary Bladder: Bladder wall relaxes, Sphincter contracts
• Comparison of Sympathetic & Parasympathetic:

  Sympathetic:

  • Prepares body for emergency
  • Outflow: T1 - L2/3, Cranial nerves III,VII, IX, X
  • Ganglia: Paravertebral, Prevertebral, Ganglia close to viscera
  • Neurotransmitter within ganglia: Acetylcholine
  • Neurotransmitter at postganglionic endings: Norepinephrine (the most)