Nervous

• Nervous system


  Bears a major responsibility for maintaining body homeostasis
• Nervous system


  • Chief functions: monitor, integrate, & respond to information in the environment
• Anatomical divisions of the nervous system

  • Central nervous system (brain & spinal cord)
  • Peripheral nervous system (cranial & spinal nerves)

  
• Functional divisions of the nervous system

  • Sensory (afferent) division
  • Motor (efferent) division

  
• Motor division


  Includes the somatic (voluntary) system and the autonomic (involuntary) system
• Components of the central nervous system

  • Brain
  • Spinal cord

  
• Brain


  • Provides for: voluntary movements, interpretation, integration of sensation, consciousness, cognitive function

  
• Regions & organization of the brain

  • Cerebral hemispheres (left & right)
  • Diencephalon
  • Brain stem
  • Cerebellum

  
• Ventricles


  Brain contains 4 ventricles filled with cerebrospinal fluid
• Cerebral hemispheres


  • Exhibit gyri, sulci, & fissures
  • Longitudinal fissure partially separates the hemispheres
  • Other fissures or sulci subdivide each hemisphere into (cerebral) lobes

  
• Lateralization of cortical function

  • Left hemisphere is dominant (specialized for language & mathematical skills)
  • Right hemisphere is more concerned with visual-spatial skills & creative endeavors
• Diencephalon


  Encloses the third ventricle and includes the thalamus, hypothalamus, & epithalamus
• Thalamus


  • Major relay station for sensory impulses, inputs from subcortical motor nuclei & the cerebellum, and impulses travelling to association cortice from lower centers

  
• Hypothalamus


  • Important autonomic nervous system control center, pivotal part of the limbic system, maintains water balance & regulates thirst, eating behavior, gastro-intestinal activity, body temperature, & the activity of the anterior pituitary gland
• Epithalamus


  Includes the pineal gland which secretes the hormone melatonin
• Components of the brainstem

  • Midbrain
  • Pons
  • Medulla oblongata
• Midbrain


  • Contains the corpora quadrigemina (visual & auditory reflex centers), the red nucleus (subcortical motor centers), and the substantia nigra
• Pons


  • Mainly a conduction area, its nuclei contribute to regulation of respiration & cranial nerves V–VII
• Medulla oblongata


  • The pyramids form the ventral face, important nuclei regulate respiratory rhythm, heart rate, & blood pressure & serve cranial nerves VIII–XII, the olivary nuclei & cough, sneezing, swallowing, & vomiting centers are also in the medulla
• Cerebellum


  • Coordinates motor activity so that smooth, well-timed movements occur
• Structures that protect the brain

  • Bone
  • Meninges
  • Cerebrospinal fluid
  • Blood-brain barrier
• Meninges


  The dura mater, arachnoid mater, and pia mater enclose the brain, spinal cord & their blood vessels
• Cerebrospinal fluid (CSF)


  Formed by the choroid plexuses from blood plasma, circulates through the ventricles & into the subarachnoid space, returns to the dural venous sinuses via the arachnoid villi, supports & cushions the brain & cord & helps to nourish them
• Blood-brain barrier (BBB)


  Reflects the relative impermeability of the epithelium of capillaries of the brain, allows water, respiratory gases, essential nutrients, & fat-soluble molecules to enter the neural tissue but prevents entry of other, water-soluble, potentially harmful substances
• Spinal cord


  • A 2-way impulse conduction pathway, a reflex center, resides within the vertebral column & protected by meninges & cerebrospinal fluid, extends from the foramen magnum to the end of the first lumbar (L₁) vertebra
• 31 pairs of spinal nerve roots issue from the spinal cord
• Cross-sectional anatomy of the spinal cord

  • The central gray matter is H-shaped, ventral horns mainly contain somatic motor neurons, lateral horns contain visceral (autonomic) motor neurons, dorsal horns contain interneurons
• Components of the peripheral nervous system

  • Sensory receptors
  • Nerves conducting impulses to & from the CNS
  • Their associated ganglia & motor endings

  
• Cranial nerves


  • 12 pairs of cranial nerves originate from the brain, emerge through the skull to innervate the head & neck, but only the vagus nerves extend into the thoracic & abdominal cavities
• Olfactory nerves (I)


  Concerned with the sense of smell
• Optic nerves (II)


  Transmit visual impulses from the retina to the thalamus
• Oculomotor nerves (III)


  Emerge from the midbrain & serve 4 extrinsic eyeball muscles, the levator palpebrae superioris of the eyelid, & the intrinsic ciliary muscle of the eye & constrictor fibers of the iris
• Trochlear nerves (IV)


  Emerge from the dorsal midbrain & carry motor & proprioceptor impulses to & from superior oblique muscles of the eyeballs
• Trigeminal nerves (V)


  Emerge from the lateral pons as the major general sensory nerves of the face, has three sensory divisions: ophthalmic, maxillary, & mandibular; the mandibular branch also contains motor fibers that innervate the chewing muscles
• Abducens nerves (VI)


  Emerge from the pons & serve the motor & proprioceptive functions of the lateral rectus muscles of the eyeballs
• Facial nerves (VII)


  Emerge from the pons as the major motor nerves of the face, carry sensory impulses from the taste buds of anterior 2/3 of the tongue
• Vestibulocochlear nerves (VIII)


  Transmit impulses from the hearing & equilibrium receptors of the inner ears

  
• Glossopharyngeal nerves (IX)


  Transmit sensory impulses from the taste buds of the posterior 1/3 of the tongue, innervate some pharyngeal muscles & parotid glands
• Vagus nerves (X)


  Almost all motor fibers are autonomic parasympathetic fibers, motor efferents to, & sensory fibers from, the pharynx, larynx, & visceral organs of the thoracic & abdominal cavities
• Spinal accessory nerves (XI)

  Consist of a cranial root arising from the medulla