Phgy 222

• Nervous system


  Coordinates the activities of many other organ systems, activates muscles for movement, controls the secretion of hormones from glands, regulates the rate and depth of breathing, and is involved in modulating and regulating a multitude of other physiological processes
• Divisions of the nervous system

  • Central nervous system
  • Peripheral nervous system
• Central nervous system (CNS)


  • Includes the brain and spinal cord
  • Formed by neurons and supporting cells called neuroglia
  • Contains more than 100 billion neurons
  • Structures are arranged in two layers: gray matter and white matter
• Gray matter

  Formed by nerve cell bodies and the proximal parts of nerve fibers
• White matter


  Formed by remaining parts of nerve fibers
• Brain and spinal cord

  • Surrounded by three layers of meninges: dura mater, arachnoid mater, and pia mater
  • Suspended in cerebrospinal fluid
• Major divisions of the brain

  • Prosencephalon (forebrain)
  • Mesencephalon (midbrain)
  • Rhomboencephalon (hindbrain)
• Prosencephalon


  • Further divided into Telencephalon (cerebral hemispheres, basal ganglia, hippocampus, amygdaloid nucleus) and Diencephalon (thalamus, hypothalamus, metathalamus, subthalamus)
• Rhomboencephalon


  • Further divided into Metencephalon (pons and cerebellum) and Myelencephalon (medulla oblongata)
• Divisions of the peripheral nervous system

  • Somatic nervous system
  • Autonomic nervous system
• Somatic nervous system


  Concerned with somatic functions, includes nerves supplying skeletal muscles, responsible for muscular activities and movements of the body
• Autonomic nervous system


  Concerned with regulation of visceral or vegetative functions, also called vegetative or involuntary nervous system, further divided into Sympathetic and Parasympathetic nervous systems
• Divisions of the nervous system

  • Afferent system (sensory part)
  • Efferent system (motor part)
• Afferent system


  • Most activities of the nervous system are initiated by sensory experience exciting sensory receptors, transmits sensory information from the receptors of the entire body surface and from some deep structures to the central nervous system
• Efferent system


  • Controls contraction of skeletal muscles, contraction of smooth muscle in internal organs, and secretion of active chemical substances by exocrine and endocrine glands
• Neuron


  Structural and functional unit of the nervous system, contains nucleus and organelles, has branches or processes called axon and dendrites, and does not have a centrosome so cannot undergo division
• Classification of neurons


  • Depending on number of poles
  • Depending on function
  • Depending on length of axon
• Structure of a neuron

  • Nerve cell body (soma or perikaryon), dendrites, and axon
  • Dendrites are short processes, axons are long processes
  • Dendrites and axons are called nerve fibers
• Nerve cell body


  • Contains cytoplasm (neuroplasm), large nucleus with one or two prominent nucleoli, Nissl bodies, neurofibrils, mitochondria, and Golgi apparatus
  • Nissl bodies are concerned with protein synthesis
  • Neurofibrils consist of microfilaments and microtubules
• Dendrite


  • Branched process of neuron, transmits impulses towards the nerve cell body, contains Nissl granules and neurofibrils
• Axon


  • Longer process of neuron, arises from axon hillock, extends for a long distance away from the nerve cell body, transmits impulses away from the nerve cell body, forms nerve fibers and fasciculi
• Structure of the axon

  • Axoplasm (long central core of cytoplasm) covered by axolemma (tubular sheath-like membrane), referred to as the axis cylinder
  • Axoplasm contains mitochondria, neurofibrils, and axoplasmic vesicles
  • Lacks Nissl bodies, so proteins needed by axons are synthesized by soma and transported by axonal flow
• Myelinated nerve fibers


  Nerve fibers wrapped in a thick lipoprotein myelin sheath, which insulates the fiber and allows for faster conduction of impulses
• Non-myelinated nerve fibers


  Nerve fibers without a myelin sheath
• Myelin sheath


  • Not a continuous sheath, absent at regular intervals called nodes of Ranvier
  • Segment between two nodes is called an internode
  • Formed by Schwann cells in the neurilemma
• Synapse


  Junction between two neurons, physiological continuity but not anatomical continuation
• Anatomical classification of synapses

  • Axoaxonic
  • Axodendritic
  • Axosomatic
• Functional classification of synapses

  • Electrical synapse
  • Chemical synapse
• Electrical synapse


  Synapse in which the physiological continuity between the presynaptic and postsynaptic neurons is provided by gap junctions, allowing for direct exchange of ions and minimal synaptic delay, with impulses transmitted in either direction
• Chemical synapse


  Junction between a nerve fiber and a muscle fiber or between two nerve fibers, where signals are transmitted by the release of chemical transmitters, with no continuity between the two neurons due to the presence of a synaptic cleft
• Chemical synapse


  • The terminal of the presynaptic axon contains the presynaptic membrane, mitochondria, and synaptic vesicles
  • Has both excitatory and inhibitory functions
• Renal system or urinary system


  Has maximum excretory capacity and plays a major role in homeostasis
• Kidneys


  • Bean-shaped, about the size of a closed fist, lie against the back of the abdominal wall, outside the peritoneal cavity, just above the waistline in the lumbar area, right kidney sits slightly higher than the left one because of the position of the liver, about 4 1/2 inches long and 2 1/2 inches wide
• Kidneys


  • Highly vascular (contain a lot of blood vessels), divided into three main regions: renal cortex (outer region which contains about 1.25 million renal tubules), renal medulla (middle region which acts as a collecting chamber), and renal pelvis (inner region which receives urine through the major calyces)
• Nephron


  The microscopic structural and functional unit of the kidney, composed of a renal corpuscle and renal tubule
• Renal corpuscle


  • Consists of a tuft of capillaries called a glomerulus and an encompassing Bowman's capsule
• Renal tubule


  • Extends from the capsule, composed of epithelial cells with a lumen
• Functions of the kidney


  • Urine formation
  • Osmoregulation
  • Secretion of hormones
• Urine formation


  1. Glomerular filtration

  2. Tubular reabsorption

  3. Tubular secretion
• Glomerular filtration


  The first step in renal processing, involves the filtration of plasma in the glomerulus, a process of bulk flow: water and low molecular weight substances move from the lumen of the capillary, across the filtration membrane, and into Bowman's space