Bio 205 Lecture 18 - Nervous System and Cranial Nerves

Cell Anatomy

1. Anatomy: Neuron. Body (soma), axon, dendrite
2. Excitation: Resting potential, depolarization, action potential, and nerve impulse
3. Signalling: Synapse, Pre-synaptic, post-synaptic, neurotransmitters, neuromodulators
4. Support: Neuroglia, Schwann cells, myelination

CNS vs. PNS

Organization of spinal PNS and CNS

1. Cross section of spinal coord
   1. white matter
      1. nerve tracts
   2. gray matter
      1. Nuceli, ganglia
   3. PNS:
      1. all craniates except lampreys: Dorsal root, Ventral root, spinal nerve, dorsal rami, ventral rami
      2. lampreys: separate dorsal and ventral nerves
2. Neurons: basics
1. Motor (efferent)
   1. soma in ventral horn of gray matter
   2. exit ventral root (amniotes), some exit dorsal root in anamniotes
2. Sensory (afferent)
   1. Neural crest derived
   2. soma in ganglia
   3. enter dorsal root into dorsal horn
3. interneurons
4. tracts
3. Neurons: functional groups
   1. Motor
      1. somatic
      2. visceral (see below)
         1. autonomic nervous system
         2. two-neuron system
   2. sensory
      1. somatic
      2. visceral

Oganization of cranial PNS and CNS

1. Motor components
   1. somatic: extraoccular eye, tongue muscles
   2. somatic - branchiomeric: arch muscles
   3. visceral
2. sensory components
   1. general somatic
   2. special somatic (neurogenic placodes) - hearing, lateral lines
   3. general visceral
   4. special visceral (gustatory)

Autonomic Nervous System (Visceral Motor)

differences with somatic motor

• derivation of innervated structures:
  • somatic motor innervates derivatives of paraxial mesoderm
  • visceral motor innervates
    • smooth and cardiac muscle from lateral plate mesoderm
    • glands from endoderm or ectoderm
• soma lie outside CNS and is a two-neuron system
• preganglionic and postganglionic neurons

two divsions

• sympathetic
• parasympathetic

Differences between sympathetic and parasympathetic

• Functional
  • sympathetic
    • "Energy expenditure"
    • 1. sweat glands stimulated to release heat
    • 2. skin arterioles constricted to shunt blood to heart and muscles
    • 3. bronchi dilate for increased air flow
    • 4. bowel quieted and its vessels constrict
    • 5. pupils dilate to increase visual input
  • parasympathetic
    • "energy conservation"
    • 1. hear slows
    • 2. bowel increases activity to process food
    • 3. exocrine glands stimulated - helps to process food
    • 4. bronchi and pupils constrict
  • mnemonics
    • sympathetic - "fight or flight" but not "fright"
    • parasympathetic - "rest and digest"
• Anatomical
  • sympathetic -body wall and viscera
  • parasympathetic - viscera only
  • sympathetic -dissectible ganglia outside of structure
  • parasympathetic - ganglia lie diffusely in innervated structure
  • sympathetic -T1-L2 - thoracolumbar
  • parasympathetic - brainstem and sacral - craniosacral
• Visceral motor to head follows arteries

Cranial nerves (these are not in exact order but it is easier to remember them this way)

Are these serially homologous with spinal nerves or are they fundamentally different?

Special sensory nerves unique to the head

I. olfactory nerve - really many nerves innervating the olfactory epithelium and, if present, the vomeronasal organ.

II. Optic nerve - not really a nerve but a brain tract, since the retina is an outward extension of the brain.

VIII. vestibulocochlear or statoacoustic or auditory, or acoustic and sometimes octavolateralis. This is sensory to the inner ear and intimately related to the sensory fibers to the lateral line in fishes and larval amphibians. Remember, the inner ear is for both balance and hearing.

Lateral line nerves (unnumbered)

1. anterior three enter a unique ganglion anterior to VII
2. posterior three enter a unique ganglion anterior to X

Ventral somatic motor - extraoccular eye muscle and hypobranchial

III. Occulomotor - somatic motor to the dorsal, ventral, and medial rectus and the inferior oblique mm.

IV. trochlear - somatic motor to the superior oblique m. Remember, this muscles wraps around a trochlea (pulley), hence the name of the nerve

VI. abducens - somatic motor to the lateral rectus m. which abducts the eye.

XII - hypoglossal - ventral rami of occipital nerves that may or may not exit as a "cranial" nerve, innervate hypobranchial muscles, including tongue

Four pharyngeal arch nerves which have both motor and sensory fibers - dorsal nerves

V. Trigeminal - innervates the first arch which includes the jaw muscles and, in mammals, a little muscle in the middle ear (tynsor tympani - homologous to a jaw m in non-mammals). Three branches: an opthalmic branch to the orbit and forehead region, a maxillary branch to the upper jaw and a mandibular branch to the lower jaw

VII. Facial - innervates the second arch, which includes the facial mm. and mm related to the hyoid bone and the stapes (stapedius m.).

IX. glossopharyngeal - innervates the third arch which includes pharyngeal mm. and also sensory to the back of the tongue (hence name).

X. vagus - motor to the arches 4 - 7. Sensory to most of gut and other thoracic and abdominal organs.

Nerves that are considered cranial nerves in most tetrapods but not in most fishes. It depends on if they exit the skull through a foramen.

XI. accessory nerve. This is a cervical spinal nerve that, in amniotes, enters the skull through the foramen magnum and then rexits again through the jugular foramen. It is motor to cervical mm. In anamniotes it is the accessory branch of the vagus.