Detailed Notes on Nervous System Anatomy and Function

The Sympathetic Nervous System vs. The Parasympathetic Nervous System

  • The sympathetic nervous system is described as "fight or flight".
  • The parasympathetic nervous system is described as "rest and digest".

Neurotransmitters and Activation

  • The sympathetic nervous system is referred to as adrenergic because it is activated by adrenaline.
  • The parasympathetic nervous system is referred to as cholinergic because its neurons release the neurotransmitter acetylcholine (ACh).
  • Neurons in the sympathetic nervous system release the neurotransmitter norepinephrine.
  • Muscarinic receptors are affected by parasympathetic neurotransmitters.
  • Common neurotransmitters include norepinephrine, serotonin, dopamine, and acetylcholine.

Brain Structures and Their Functions

  • Cerebrum: The largest and most superior portion of the brain.
  • Diencephalon: Located between the cerebrum and the brain stem; houses the hypothalamus and pituitary gland.
  • Brain Stem: Spans the region between the diencephalon and the spinal cord.
    • Pons: Connects the cerebellum with other portions of the brain and helps regulate respiration.
    • Medulla Oblongata: Sits between the pons and the spinal cord, linking the brain with the spinal cord. It contains centers for controlling vital functions such as respiration and heartbeat.
  • Cerebellum: Sits below the posterior portion of the cerebrum and coordinates voluntary muscles, maintains balance, and muscle tone.
  • Midbrain: Connects the cerebrum and diencephalon with the spinal cord. It contains reflex centers concerned with vision and hearing and connects the cerebrum with lower portions of the brain.

Meninges

  • The meninges consist of three layers of connective tissue that surround both the brain and the spinal cord to form a complete enclosure.
    • Pia Mater: The inner most layer, attached to the nervous tissue of the brain and spinal cord, following all contours. It is a delicate connective tissue layer.
    • Arachnoid: The middle layer of the three connective tissue layers.

Central Nervous System (CNS) vs. Peripheral Nervous System (PNS)

  • The brain and spinal cord make up the central nervous system (CNS).
  • The cranial nerves and spinal nerves make up the peripheral nervous system (PNS).
  • Fiber bundles within the PNS are called nerves.
  • Fiber bundles within the CNS are called tracts.

Divisions of the PNS

  • Somatic Nervous System: The voluntary division of the PNS.
  • Autonomic Nervous System: The involuntary division of the PNS.

Neurons and Nerve Impulses

  • Neurons are the functional cells of the nervous system.
    • Dendrites: Carry impulses to the cell body.
    • Axons: Carry impulses away from the cell body.
    • Sensory (Afferent) Neurons: Conduct impulses to the spinal cord and brain.
    • Motor (Efferent) Neurons: Conduct impulses from the CNS to muscles and glands.
    • Interneurons: Relay information from place to place within the CNS.

Myelin Sheath Formation

  • In the PNS, the myelin sheath is formed by Schwann cells.
  • In the CNS, the myelin sheath is formed by oligodendrocytes.

Synapses and Neural Pathways

  • Synapse: The junction point for transmitting nerve impulses from one neuron to another cell.
  • Ascending Tracts: Sensory impulses entering the spinal cord are referred to as ascending tracts.
  • Descending Tracts: Motor impulses traveling from the brain are carried in descending tracts towards the PNS.

Autonomic Nervous System Function

  • The autonomic nervous system carries out automatic and unconscious visceral responses.