nervous system

• Nervous system


  Part of the human body that receives sensory input, integrates information, controls muscles and glands, and establishes and maintains mental activity
• Nervous system functions


  • Receiving sensory input
  • Integrating information
  • Controlling muscles and glands
  • Establishing and maintaining mental activity
• Divisions of the nervous system

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


  Receives stimuli, conducts action potentials, and transmits signals to other neurons or effector organs
• Structural types of neurons

  • Sensory neurons
  • Interneurons
  • Motor neurons
• Functional types of neurons

  • Sensory neurons
  • Interneurons
  • Motor neurons
• Glial cells in the CNS

  • Astrocytes
  • Ependymal
  • Microglia
  • Oligodendrocytes
• Glial cells in the PNS

  Schwann cells - form myelin sheaths

  Satellite cells - surround neuron cell bodies in sensory and autonomic ganglia and protect neurons from heavy-metal poisons
• Myelin sheath


  Protective covering that surrounds nerve fibers
• Myelinated axons


  • Conduct action potentials rapidly

  Wrapped by several layers of plasma membrane from Schwann cells (PNS) or oligodendrocytes (CNS)

  The spaces between these layers are called nodes of Ranvier
• Unmyelinated axons


  • Conduct action potentials slowly

  Rest in invaginations of Schwann cells (PNS) or Oligodendrocytes (CNS)
• Organization of nervous tissue

  • Gray matter

  White matter
• Gray matter


  Consists of groups of neuron cell bodies and their dendrites
• White matter


  Consists of bundles of parallel myelinated axons
• Resting membrane potential


  A charge difference across the plasma membrane when the cell is in an unstimulated condition, where the inside of the plasma membrane is negatively charged compared to the outside
• Establishing the resting membrane potential

  The tendency of positively charged K+ to diffuse out of the cell, which is opposed by the negative charge that develops inside the plasma membrane
• Graded potentials


  Small changes in the resting membrane potential that are confined to a small area of the plasma membrane
• Graded potentials


  • An increase in membrane permeability to Na+ can cause graded depolarization, and an increase in membrane permeability to K+ or Cl− can result in graded hyperpolarization

  Stronger stimuli produce greater potential changes than weaker stimuli

  Graded potentials can summate, or add together

  Graded potentials decrease in magnitude as the distance from the stimulation increases
• Action potential


  Rapid, all-or-none change in the membrane potential that propagates along the length of the axon
• Action potential propagation along unmyelinated axon


  Voltage-gated ion channels open and close in sequence, allowing Na+ to flow in and K+ to flow out, generating the action potential
• Spinal cord


  • The major communication link between the brain and the peripheral nervous system (PNS) inferior to the head

  Integrates incoming information and produces responses through reflex mechanisms
• Meninges of the spinal cord

  • Dura mater

  Arachnoid mater

  Pia mater
• Gray matter divisions in the spinal cord

  • Dorsal horns - contain sensory axons that synapse with interneurons

  Ventral horns - contain the neuron cell bodies of somatic motor neurons

  Lateral horns - contain the neuron cell bodies of autonomic motor neurons
• Components of the reflex arc

  • Sensory receptor

  Sensory neuron

  Interneuron

  Motor neuron

  Effector organ
• Types of reflexes


  • Somatic reflexes - remove the body from painful stimuli

  Monosynaptic reflexes - sensory neurons synapse directly with motor neurons

  Polysynaptic reflexes - involve complex pathways with interneurons between sensory and motor neurons
• Three major spinal cord reflexes

  • Stretch reflex - when a muscle is stretched quickly

  Golgi tendon reflex - helps prevent our muscles from tearing

  Withdrawal reflex - quick response to a painful stimulus
• Layers of a nerve

  • Endoneurium - heavier connective tissue layer

  Perineurium - surrounds groups of axons to form nerve

  Epineurium - binds the nerve fascicles together to form a nerve
• Organization of spinal nerves

  • 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal pair

  Spinal nerves have specific cutaneous distributions called dermatomes

  Spinal nerves branch to form rami - dorsal rami, ventral rami, communicating rami
• Dermatomes are areas of skin on the body that rely on specific nerve connections on the spine
• Dermatomes can help healthcare providers detect and diagnose conditions or problems affecting the spine, spinal cord or spinal nerves
• Diseases and disorders of the nervous system

  • Bell's palsy

  Spinal cord hemorrhage

  Epilepsy

  Poliovirus infection

  Transverse myelitis

  Alzheimer's disease

  Spinal tumor

  Herniated disk
• Central nervous system (CNS) development

  Develops from the neural plate and neural folds formed from ectoderm
• Main parts of the CNS

  • Brainstem

  Cerebellum

  Diencephalon

  Cerebrum
• Alzheimer's disease


  A progressive disease beginning with mild memory loss and possibly leading to loss of the ability to carry on a conversation and respond to the environment. It involves parts of the brain that control thought, memory, and language.
• Spinal tumor


  • Can lead to pain, neurological problems and sometimes paralysis
  • Can be life-threatening and cause permanent disability
  • Treatment may include surgery, radiation therapy, chemotherapy or other medications
• Herniated disk


  A spinal disk has a soft, jellylike center called a nucleus, encased in a tougher, rubbery exterior, known as the annulus. A herniated disk occurs when some of the nucleus pushes out through a tear in the annulus. Also called a slipped disk or a ruptured disk.
• Brain


  • Part of the central nervous system (CNS) contained within the cranial cavity
• Four main parts of the brain

  • Brainstem
  • Cerebellum
  • Diencephalon
  • Cerebrum
• Nervous system development of the CNS

  1. Neural plate forms from ectoderm

  2. Neural folds form as parallel ridges along the embryo

  3. Neural crest cells begin to form from the crest of the neural folds

  4. Neural folds meet at the midline to form the neural tube, and neural crest cells separate from the neural folds
• Brainstem


  • Connects the spinal cord to the base of the brain
  • Responsible for many essential functions
  • Consists of three parts: the medulla oblongata, pons, and midbrain