Nervous System

• Central Nervous System (CNS)

  Brain and spinal cord
• Peripheral Nervous System (PNS)


  Nerves and ganglia outside the central nervous system
• Function of Nervous System

  • The brain sends messages to the opposite side of the body
  • The brain receives messages from the opposite side of the body
• Divisions of Peripheral Nervous System

  • Sensory - receive
  • Motor - actor
• Types of actions in Peripheral Nervous System

  • Voluntary actions
  • Involuntary actions
• Sympathetic nervous system

  Fight or flight
• Parasympathetic nervous system

  Rest and digest
• Roles of the Nervous System

  • Sensory input - gathering information
  • Integration - to process and interpret sensory input and decide if action is needed
  • Motor output - A response to integrated stimuli
• Central Nervous System (CNS)

  Brain and spinal cord, develops from the embryonic neural tube
• Regions of the Brain

  • Cerebral hemispheres - Paired (left and right) superior parts of the brain, include more than half of the brain mass, surface is made of ridges (gyri) and grooves (sulci)
  • Diencephalon - Sits on top of the brain stem, enclosed by the cerebral hemispheres, made of thalamus, hypothalamus, and epithalamus
  • Brain stem - Attaches to the spinal cord, includes midbrain, pons, and medulla oblongata
  • Cerebellum - Two hemispheres with convoluted surfaces, provides involuntary coordination of body movements, functions in balance and coordination
• Lobes of the Cerebrum

  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe
• Sensory and Motor Areas of the Cerebral Cortex

  Specialized areas for interpretation, speech/language, language comprehension, and general interpretation
• Layers of the Cerebrum

  • Gray matter - Outer layer, composed mostly of neuron cell bodies
  • White matter - Fiber tracts inside the gray matter
• Protection of the Central Nervous System

  • Scalp and skin
  • Skull and vertebral column
  • Meninges - Dura mater, arachnoid layer, pia mater
  • Cerebrospinal fluid
  • Blood brain barrier
• Spinal Cord


  • Extends from the medulla oblongata to the region of T12, enlargements occur in the cervical and lumbar regions, 31 pairs of nerves, function is to conduct nerve impulses and serve for spinal reflex centers
• Peripheral Nervous System (PNS)


  Nerves and ganglia outside the brain and spinal cord
• Cells of the Nervous System

  • Supporting cells
  • Neurons
• Neuroglia vs. Neurons

  Neuroglia divide, neurons do not, most brain tumors are "gliomas" and involve the neuroglial cells, not the neurons
• Examples of Neuroglia


  • Astrocytes
  • Microglia (CNS)
  • Ependymal cells (CNS)
  • Oligodendrocytes (CNS) - Produce myelin sheath around nerve fibers in the central nervous system
  • Schwann cells - Form myelin sheath in the peripheral nervous system
• Neurons


  Nerve cells specialized to transmit messages, with a cell body, dendrites, and axons
• Axons and Nerve Impulses


  • Axons end in axonal terminals containing vesicles with neurotransmitters, separated from the next neuron by a synaptic cleft
• Nerve Fiber Coverings


  Schwann cells produce myelin sheaths, nodes of Ranvier are gaps in the myelin sheath along the axon
• Neuron Cell Body Location


  Most are found in the central nervous system, in the gray matter and nuclei, ganglia are collections of cell bodies outside the central nervous system
• How Neurons Function

  • Irritability - ability to respond to stimuli, conductivity - ability to transmit an impulse, plasma membrane at rest is polarized with fewer positive ions inside the cell than outside
• Starting a Nerve Impulse

  Depolarization - a stimulus depolarizes the neuron's membrane, allowing sodium to flow inside the membrane, initiating an action potential
• The Action Potential

  • Potassium ions rush out of the neuron after sodium ions rush in, depolarizing the membrane, the sodium-potassium pump restores the original configuration using ATP
• Nerve Impulse Propagation


  The impulse continues to move toward the cell body, impulses travel faster when fibers have a myelin sheath
• Continuation of the Nerve Impulse between Neurons


  Neurotransmitter is released from a nerve's axon terminal, the dendrite of the next neuron has receptors that are stimulated by the neurotransmitter, initiating an action potential in the dendrite
• The Reflex Arc


  Rapid, predictable, and involuntary responses to stimuli, a direct route from a sensory neuron, to an interneuron, to an effector
• Functional Classification of the Peripheral Nervous System


  • Sensory (afferent) division - Nerve fibers that carry information to the central nervous system, with somatic sensory fibers for voluntary and visceral sensory fibers for involuntary
  • Motor (efferent) division - Nerve fibers that carry impulses away from the central nervous system, with somatic nervous system for voluntary and autonomic nervous system for involuntary
• Autonomic Nervous System


  The involuntary branch of the nervous system, consists of only motor nerves, divided into sympathetic and parasympathetic divisions
• ANS Organization

  • Hypothalamus, brain stem, spinal cord, and visceral reflexes
• Sympathetic Nervous System


  Mobilizes the body's resources for emergencies and creates the fight-flight response, arouses
• Parasympathetic Nervous System


  Activates processes that conserve bodily resources, showing heart rate, reducing blood pressure, calms - rest and digest
• Neurotransmitters


  • Acetylcholine - Secreted by cholinergic fibers, all preganglionic neurons, all parasympathetic postganglionic neurons
  • Norepinephrine - Secreted by adrenergic fibers, all postganglionic neurons except preganglionic fibers which are cholinergic, also in sweat glands, piloerector muscle, and some blood vessels
• Receptors


  • Acetylcholine receptors - Muscarinic receptors, nicotinic receptors
  • Adrenergic receptors - Alpha receptors (alpha 1, alpha 2), Beta receptors (beta 1, beta 2)
• Development Aspects of the Nervous System


  • Formed during the first month of embryonic development, maternal infection can have harmful effects, the hypothalamus is one of the last areas of the brain to develop, no more neurons are formed after birth but growth and maturation continues for several years, the brain reaches maximum weight as a young adult
• Nervous System Disorders


  • Meningitis - inflammation of meninges
  • Encephalitis - inflammation of the brain
  • Hydrocephalus - water on the brain
  • Cerebral palsy - neuromuscular disability where voluntary muscles are poorly controlled
  • Spina bifida - results when vertebrae from incompletely formed
  • Parkinson's disease - disorder in the ganglia characterized by shaking
  • Orthostatic hypertension - type of low blood pressure
  • Brain shrinkage - common but sped up in boxers and alcoholics
  • Epilepsy - seizures
• Traumatic Brain Injuries


  • Concussion - slight brain injury with no permanent damage
  • Contusion - nervous tissue destruction occurs, does not regenerate
  • Cerebral edema - swelling from inflammatory response, may compress and kill brain tissue
• Cerebrovascular Accident (CVA)


  Commonly called a stroke, the result of a ruptured blood vessel supplying a region of the brain, brain tissue supplied with oxygen from that blood source dies, loss of some functions or death may result