Brain Terminology

Central Nervous System

comprises the brain & spinal cord

Peripheral Nervous System

comprises cranial nerves, spinal nerves, autonomic nervous system

Gray matter

nerve cell bodies mainly in the brain cortex or central spinal cord

White matter

myelinated axons in the brain medulla or outer spinal cord

Terms:

Nucleus

collection of nerve cell bodies inside the CNS but not in the cortex, functional group

Ganglion

collection of nerve cell bodies outside of the CNS

Nerve

bundle of afferent & efferent nerve fibers outside of the CNS

Plexus

network of nerve fibers

Tract

bundle of fibers serving a similar function

Projection area

specialized area of the brain for receiving sensory information from specific body regions & transmitting motor impulses to specific body regions

Functional classification of neurons:

• Sensory or afferent neurons - carry impulses from receptors to the CNS
  • 1st order - from receptor to spinal cord or brainstem
  • 2nd order - from spinal cord or brainstem to thalamus, cross-over occurs
  • 3rd order - from thalamus to cerebral cortex
• Motor or efferent neurons - carry impulses from the CNS to effectors (muscles or glands), always excitatory in skeletal muscle
• Interneuron or association neuron - connects afferent to efferent, excitatory or inhibitory

Somatic

involves skin, skeletal muscle, joints

Visceral

involves internal organs, blood vessels, glands, smooth & cardiac muscle

Divisions of brain:

Forebrain or prosencephalon

cerebrum, thalamus, hypothalamus, pineal body

Midbrain or mesencephalon

small area, only connection between fore & hindbrains

Hindbrain or rhombencephalon

cerebellum, pons, medulla oblongata

Brainstem = mesencephalon + pons + medulla oblongata

Hindbrain

Medulla oblongata

physically connects spinal cord to brain, extends from foramen magnum to pons, inferior portion of brain stem

1. Sensory and motor tracts pass through this area
   1. Pyramids - two rounded elongated masses on ventral surface, carry major efferent tracts from brain including the corticospinal tract
      1. Decussation - cross-over of tracts, right brain controls left musculature
2. Nuclei that receive sensory input or provide motor output, relay stations
   1. Nucleus gracilis and nucleus cuneatus - on dorsal surface
      1. Termination of ascending spinal cord tracts from lower half of body
      2. Axons leaving cross-over and enter medial lemniscus going to the thalamus
   2. Olivary nucleus - lateral surface, relay information from spinal cord, cerebral cortex and brain stem to cerebellum
   3. Nuclei of origin of 5 pairs of cranial nerves: 8-12
3. Vital reflex centers
   1. Cardiovascular - regulates heartbeat and force, vessel diameter
   2. Medullary rhythmicity - breathing rate

In general, the medulla oblongata is a relay station between spinal cord and brain, an area of termination and repositioning of spinal cord tracts, the origin of 5 pairs of cranial nerves, and contains vital reflex centers.

Pons varoli

a bridge between midbrain & medulla oblongata

1. Basilar portion
   1. Longitudinal fiber tracts are motor & sensory tracts that connect medulla oblongata with midbrain or pontine nuclei
   2. Transverse fibers connect pontine nuclei to opposite side of cerebellum via middle cerebellar peduncles, sensory
2. Dorsal portion (tegmentum)
   1. Nuclei of origin of cranial nerves 5-8 (vestibular part)
   2. Pneumotaxic and apneustic areas regulate respiration rates

Cerebellum

automatic processing center, receives and monitors proprioceptive information from the body and motor information from the cerebral cortex, integrates information and coordinates motor activities, maintains balance, fine tunes voluntary and involuntary movements

1. Hemispheres with central vermis - folded, arbor vitae, contain cerebellar nuclei that send impulses to brain centers and spinal cord
2. Cerebellar peduncles - connecting tracts
   1. Superior cerebellar peduncle - output from cerebellar nuclei to midbrain (red nucleus) and thalamus
   2. Middle cerebellar peduncle - sensory information from pons to cerebellum
   3. Inferior cerebellar peduncle - mixed fibers run between medulla oblongata and spinal cord or cerebellar nuclei
3. 4^th ventricle