CNS

• Central nervous system (CNS)


  Includes brain and spinal cord

  
• Brain


  Made up of billions of nerve cells or neurons; protected by bones of skull

  
• Spinal cord


  Begins at foramen magnum and continues through vertebral foramina of first cervical to first or second lumbar vertebra; made up of millions of neurons; much fewer than brain; enables brain to communicate with most of body below head and neck

  
• Peripheral nervous system (PNS)


  Consists of all nerves in body outside protection of skull and vertebral column; nerves consist of axons of neurons bundled together with blood vessels and connective tissue; carry signals to and from CNS; classified based on origin or destination

  
• Nerves

  • 12 pairs of cranial nerves traveling back to or from brain
  • 31 pairs of spinal nerves traveling back to or from spinal cord

  
• Neuron


  Has three main functional regions: receptive region (includes dendrites and cell body), conducting region (includes axon), secretory region (includes axon terminal)

  
• Neuron classification


  • Multipolar neurons (single axon and multiple dendrites, make up over 99% of all neurons)
  • Bipolar neurons (one axon and one dendrite with cell body between them, found in eye and olfactory epithelium)
  • Pseudounipolar neurons (one fused axon that extends from cell body and divides into two processes, carry sensory information related to pain, touch, and pressure)

  
• Brain


  Soft, whitish-gray organ, anatomically continuous with spinal cord; resides in cranial cavity and directly or indirectly controls most of body's functions; weighs between 1250 and 1450 grams; made of mostly nervous tissue; contains epithelial and connective tissues as well; internal cavities called ventricles filled with cerebrospinal fluid; receives about 20% of total blood flow during periods of rest
• Divisions of the brain

  • Cerebrum
  • Diencephalon
  • Cerebellum
  • Brainstem

  
• Cerebrum


  Four lobes in each hemisphere: frontal lobe, parietal lobe, temporal lobe, occipital lobe

  
• Diencephalon


  At physical center of brain; composed of four components: thalamus, hypothalamus, epithalamus, subthalamus

  
• Cerebellum


  Structure of the cerebellum
• Brainstem


  Midsagittal section and external anatomy of the brainstem

  
• Cranial meninges and dural sinuses

  Structure of the brain protection

  
• Spinal cord


  Long tubular organ enclosed within protective vertebral cavity; blends with inferior portion of brainstem; ends between first and second lumbar vertebrae; 43–46 cm (17–18 inches) in length and only ranges from 0.65–1.25 cm (0.25–0.5 inches) in diameter; central canal is an internal cavity continuous with brain's ventricles and filled with cerebrospinal fluid
• Major nerves


  • Cervical plexus (innervates muscles of neck and diaphragm)
  • Brachial plexus (innervates pectoral girdles and upper limbs)
  • Lumbosacral plexus (innervates pelvic girdle and lower limbs)
  • Lumbar plexus (major nerves are femoral, obturator, and saphenous)
  • Sacral plexus (major nerves are gluteal and sciatic)
• Polarization

  Any state, positive or negative, other than 0 mV
• Depolarization


  Change that makes the membrane potential less negative than the resting potential
• Repolarization


  The membrane returns to resting potential after depolarization
• Hyperpolarization


  Makes the membrane more polarized, more negative inside
• Threshold potential


  Minimum potential required to trigger an action potential
• Resting potential


  Membrane potential when the cell is not actively transmitting a signal
• Parts of a neuron

  • Nucleus
  • Input Zone (Dendrites and Cell body)
  • Trigger Zone (Axon hillock)
  • Conducting Zone (Axon)
  • Output Zone (Axon terminals)

  
• Divisions of the nervous system

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

  
• Divisions of the PNS

  • Afferent division
  • Efferent division
• Divisions of the efferent division

  • Somatic nervous system
  • Autonomic nervous system
• Divisions of the autonomic nervous system

  • Sympathetic nervous system
  • Parasympathetic nervous system
• Effector organs


  • Skeletal muscle
  • Smooth muscle
  • Cardiac muscle
  • Glands
• Afferent neuron


  Sends signals toward the CNS, generates action potentials from sensory receptors at its peripheral end, has a long axon, found mainly in the PNS

  
• Efferent neuron


  Sends signals away from the CNS to an effector organ, has a long peripheral axon in the PNS

  
• Interneuron


  Found entirely within the CNS, lies between afferent and efferent neurons

  
• Types of glial cells

  • Astrocytes
  • Oligodendrocytes
  • Microglia
  • Ependymal cells
• Astrocytes


  • Hold neurons together
  • Guide neurons during development
  • Establish a blood-brain barrier
  • Repair brain injuries
  • Play a role in neurotransmitter activity
  • Take up excess K+ from the brain ECF
• Oligodendrocytes


  • Form myelin sheaths around axons in the CNS
  • Secrete nerve-growth-inhibiting proteins in fetal life
• Microglia


  • Are the immune defense of the CNS
  • Activated microglia releases destructive chemicals against targets
• Ependymal cells


  • Line the internal cavities of the CNS
  • Help form cerebrospinal fluid
  • Serve as neural stem cells with the potential of forming glial cells and neurons

  
• Protections of the CNS

  • Cranium encloses the brain
  • Vertebral column encloses the spinal cord
  • Wrapped by meninges (dura mater, arachnoid mater, pia mater)
  • Surrounded by cerebrospinal fluid (CSF)
  • Blood-brain barrier limits access of blood-borne substances to the brain
• CSF formation and circulation

  1. Produced by choroid plexuses inside ventricles

  2. Circulates through ventricles

  3. Enters subarachnoid space between arachnoid mater and pia mater

  4. Drained into blood by arachnoid villi
• Blood-brain barrier


  • Highly selective series of capillaries that regulate exchange between blood and brain
  • Allows limited number of substances to pass from blood to brain cells
  • Brain needs constant input of oxygen and glucose from blood
• Outline of brain anatomy

  • Brain stem
  • Cerebellum
  • Forebrain (Diencephalon, Cerebrum)