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Physiology III
Spinal Cord And Peripheral Nerves
Class Notes

The spinal cord is encased in the bony vertebral column and is attached to the brainstem. That sc is the major conduit of info from skin, joints, and muscles of body to brain and visa versa. A transection in the sc results in anesthesia in the skin and paralysis of the muscles in parts of the body caudal to the cut. Paralysis in this case does not mean that the muscles cannot function,, rather that they cannot be controlled by the brain. The sc communicates with the body via the spinal nerves which are part of the peripheral nervous system. Spinal nerves exit the spinal cord through notches between each vertebrae of the vertebral column. Each spinal nerve attaches to the sc by means of two branches, the dorsal root and the ventral root. The dorsal root brings axons into the sc (sensory) , and the ventral root axons carry information away from the sc (motor)

  1. posterior (dorsal) horn – grey matter (gray matter is a generic term for a collection of neuronal cell bodies in the CNS)
  2. lateral horn-grey matter
  3. anterior (ventral) horn-grey matter
  4. cervical and lumbar enlargements-thickening in the spinal cord where the neurons for the limbs go thru.
  5. posterior columns-white matter - axons
  6. lateral columns-white matter
  7. anterior columns-white matter
  8. dorsal columns-white matter
  9. dorsal column nuclei – in the medulla not spinal cord.
  10. Anterolateral system- a group of white matter in which sensory information ascends contralaterally up the spinal cord to meet in the VPL in the thalamus. This pathway transmits information about fine touch.
  11. Information enters through the dorsal horns at the 3rd and 4th lamanae –I think. ( my definition). – text definition is that the anterolateral (spinothalamic) pathways reach the thalamus, transmits information about pain, thermal sensation, crude touch. This info is transmitted slower than discriminative information. The anterolateral fibers originate in the dorsal horns where the dorsal root neurons enter the spinal cord, they cross in the anterior commissure, with in the few segments of origin, to the opposite anterolateral white column where they ascend upward toward the brain. The anterolateral pathway also projects into the intermediate nuclei of the thalamus, which have close connections to the limbic cortical systems. This circuitry that gives touch its affective or emotional aspects eg: particular unpleasantness of heavy pressure and the pecular pleasantness of tickling and gentle rubbing of the skin). The anterolateral pathway is multisynaptic and, therefore slow and crudely graded.

  12. Cortico spinal tract- the motor cortex is located in the posterior part of the frontal lobe. It consists of the primary, premotor, and supplementary motorcortex. The primary motor cortex is thick and contains many layers of pyramid shaped output neurons. some of the large pyrimidal cells project to the brain stem and spinal cord. These UMNs send their axons through the subcortical white matter and the internal capsule to the deep surface of the brain stem, through the ventral bulge of the pons, to the ventral surface of the medulla where they form a ridge or pyramid. At the junction between the medulla and the cervical spinal cord most of the UMN axons cross the midline and decussate to form the LATERAL CORTICOSPINAL TRACT or pyrimidal tract in the lateral white matter of the spinal cord.
  13. Anterior (ventral) root- white, motor
  14. posterior (dorsal) root – white, sensory
  15. cauda equina- the area (lumbar) where the dorsal and ventral roots angle downward from the spinal cord.
  16. dermatomes- represent somesthetic innervation of the body, including the head. Thirty three spinal (segmental) nerves provide sensory and motor innervation of the body wall, the limbs, and the viscera. Sensory input is to each spinal cord segment is provided by afferent sensory neurons with cell bodies in the dorsal root ganglia. Each segment of the body, with a few exceptions, contains a pair of dorsal root ganglia. The region fo the body wall that is supplied by a single pair of dorsal root ganglia is called a DERMATOME. Segmental organization of the body and the nervous system is represented by the dermatomes, though according to our professor overlapping does occur.

Here are some other significant terms – COLLECTIONS OF NEURONS

  1. gray matter – a generic term for a collection of neuronal cell bodies in the CNS. When a freshly dissected brain is cut open, neurons appear grey
  2. cortex – a collection of neurons that forms a thin sheet, usually at the brain’s surface. Cortex is Latin for bark. Eg the cerebral cortex is the sheet of neurons found just under the surface of the cerebrum.
  3. Nucleus – a clearly distinguishable mass of neurons, usually deep in the brain ( not to be confused with the nucleus of a cell). Nucleus is from the Latin word nut eg. The lateral geniculate nucleus , a cell group in the brainstem that relays information from the eye to the cerebral cortex.
  4. Substantia – a group of related neurons deep with in the brain, but usually with less distinct borders than those of nuclei. Eg. The substantia nigra (from Latin for black substance), a brain stem cell group involved in the control of voluntary mvt.
  5. Locus (plural: loci)- a small, well defined group of cells. Eg: the locus ceruleus (Latin for blue spot), a brainstem cell group involved in the control of wakefullness and behavioral arousal.
  6. Ganglion (plural: ganglia) – a collection of neurons in the PNS. Ganglion is from the Greek word ‘knot". Eg: the dorsal root ganglia, which contain cell bodies of sensory axons entering the spinal cord via the dorsal roots. Only one cell group in the CNS goes by this name, the basal ganglia, which are structures lying deep with in the cerebrum that control movement.

Here are some other significant terms – COLLECTIONS OF AXONS

  1. nerve – a bundle of axons in the PNS. Only one collection of CNS axons is called a nerve: the optic nerve
  2. white matter – a generic term for a collection for CNS axons. When a freshly dissected brain is cut open, axons appear white.
  3. Tract – a collection of CNS axons having a common site of origin and a common destination. EG: the corticospinal tract which originates in the cerebral cortex and ends in the spinal canal.
  4. Bundle – a collection of axons that run together but do not necessarily habe the same origin and destination. Eg. The medial forebrain bundle, which connects cells scattered with in the cerebrum and brainstem.
  5. Capsule – a collection of axons that connect the cerebrum with the brainstem. Eg: the internal capsule, which connects the brain stem with the cerebral cortex.
  6. Commissure – any collection of axons that connect one side of the brain with the other side.
  7. Lemniscus – a tract that meanders through the brain like a ribbon. Eg; the medial lemniscus, which brings touch information form the spinal cord through the brainstem.

Embryologic develpopment –

  1. endoderm – gives rise to the lining of many internal organs – viscera
  2. mesoderm – gives rise to bones and muscles
  3. ectoderm – gives rise to the nervous system and skin
  4. neural tube- is where the entire nervous system develops from
  5. neural crest – is a small piece of neural ectoderm that comes from the neural folds of the neural tube, and this small piece is where the peripheral nervous system is derived from.
  6. the neural crest is in close association with the underlying mesoderm which is involved in formation of vertebrae.
  7. The entire brain derives from three primary vesicles of the neural tube
  8. the rostral most vesicle is the proencephalon, pro is Greek for before. Encephalon is Greek for brain, the proencephalon is also called the forebrain
  9. behind the proencephalon is the mesencephalon, or mid brain
  10. caudal to # 10, is the third primary vesicle – hind brain
  11. forbrain = optic vesicles and telencephalic vesicles and diencephalon
  12. the retina at the back of the eye and the optic nerve connecting the eye to the diencephalon, are part of the brain, not the PNS
  13. the telencephalon forms and consists of the two cerebral hemispheres, and the olfactory bulbs sprout from vesicle off the telencephalon.

Thalamus is a gateway to the cerebral cortex for sensory pathways of the eye, ear, and skin.

The cerebral aquaduct is a good landmark for identifying the midbrain

The third ventridcle is next to the diencephalon

The midbrain serves as a conduit for information passing from the spinal cord to the forbrain and visaversa. The midbrain contains axons descending from the cerebral cortex to the brain stem and the spinal cord. For example the corticospinal tract courses through the midbrain en route to the spinal cord. Damage to this tract courses through the midbrain on one side produces a loss of voluntary control of movement on the opposite side of the body. The tectum ( the dorsal surface of the mesencephalon) differentiates into two structures which receive sensory information – the superior colliculus and the inferior colliculus. The superior colliculus recieves direct input from the eye, so its called the optic tectum, which controls eye mvts via synaptic connections with motor neurons which innervate the eye muscles.) the inferior colliculum recives sensory info from the ear.

The tegmentum is the floor of the midbrain and this is a colorful region as it contains the substantia nigra & the red nucleus which is involved in the control of voluntary movement. Other cells groups scattered in the mid brain have axons that project widely thru out much of the CNS and function to regulate consciousness, mood, pleasure, and pain.

HINDBRAIN – cerebellum, pons, medulla, 4th ventricle . – It’s a conduit for information passing from the forebrain to the spinal cord, and visa versa. Neurons of the hind brain contribute to the processing of sensory information, control voluntary mvt, and regulation of the ANS.

The cerebellum is an important mvt control center. It recieves massive axonal inputs from the spinal cord and the pons. The spinal cord inputs provide information about where the body is in space. The inputs from the pons relay information from the cerebral cortex, specifying the goals of intended movements. The cerebellum compares these types of information and calculates the sequences of muscle contractions that are required to achieve movement goals. Damage to the cerebellum results in uncoordinated and inaccurate movements.

>90% of human axons passing thru the midbrain synapse on neurons in the pons. Pontine cells relay this information to the cerebellum on the opposite site. The pons serves as a massive switchboard connecting the cerebral cortex to the cerebellum. The word pons=bridge in Latin.

The axons that do not terminate in the pons continue caudally and enter the medullary pyrimids. Most of these axons originate in the cerebral cortex and are part of the corticospinal tract. Thus "pyrimidal tract’ is is often used as a synonym for corticospinal tract. Near the medullary pontine line each pyrymidal tract crosses over from one side of the midline to the other(decussation). The medulla contains neurons that have sensory and motor function.


The brainstem forms the stalk from which the cerebral hemispheres and the cerebellum sprout. The brain stem is a complex nexus of fibers and cells that in part serves to relay information ferom the spinal cord and cerebellum and visa versa. How,ever, the brainstem is also the site where vital functions are regulated , such as breathing, consciousness, and the control of body temp. Indeed, while the brain stem is considered the most primitive part of themamillian brain, it is also the most important to life. One can survive damage to the cerebrum, and cerebellum, but damage to the brain stem usually means rapid death. the brain stem is involved in the ability to stand erect despite the force of gravity. Input from brain stem structures automatically influence reflex mechanisms of the spinal cord and allow maintenance for body posture, pacing of steps, and recovery of posture when balance is interrupted. The motor centers of the brain stem are: red nucleus, lateral vestibular nucleus, superior colliculus, and certain parts of the reticular formation. The brain stem has externalwhite matter and internal gray nuclei.

  1. open medulla – the area in the medulla where the central canal opens to form the 4th ventricle.
  2. closed mudulla – the area in the medulla where the central canal is small
  3. forth ventricle – the area in the brainstem which houses CSF.
  4. inferior olive
  5. reticular formation – in the pons and medulla gives rise to 2 reticulospinal tracts a. the medullary fibers, which excite flexor neurons and inhibit flexors & b. pontine fibers which excite extensors and inhibit flexors. Interplay between these descending tract systems modifies the excitability of spinal reflexes to produce complex motor movement, such as coordination of walking, and running mvts, and righting reflexes which maintain or reestablish body and head positions. Many fundamental automatic mvt patterns are provided by the brain stems reticular formation circuitry, including respiratory mvts, sneezing, coughing, and chewing and swallowing.
  6. raphe nuclei -
  7. pyramids
  8. pyramidal decussation
  9. medial lemniscus
  10. cerebellar peduncles
  11. pons
  12. pontine nuclei
  13. crus cerebri
  14. substantia nigra
  15. red nucleus
  16. inferior colliculus
  17. superior colliculus
  18. periaquaductal gray matter
  19. cerebellum – lies behind the cerebrum and is located above the 4th ventricle. It interrelates visual, auditory, somasthetic and vestibular information with ongoing motor acitvity so that highly skilled movement can be smoothly performed. The word cerebellum is Latin for "little brain". The cerebellum contains as many neurons as both cerebral hemispheres combined. The cerebellum is primarily a a movement control center ha;ving extensive connections with the cerebrum and the spinal cord. In contrast to the cerebral hemispheres, the left cerebellar hemisphere is concerned with the movements of the left side of the body and the right cerebellar hemisphere is concerned with movements of the right side. The has an outer cortex of of gray matter and a core of white matter, like the cerebrum. A series of nuclei are embedded deep in the white matter. Axons from cells of the cortex and association fibers from the nuclei connect cortex to cortex communication, cortex to nuclei communication, and visa versa. Projection fibers from the nuclei relay information to many regions, particularly to the motor cortex by means of a thalamic relay. Pg 1036
  20. cerebellar hemispheres – two large lateral masses
  21. vermis – the unpaired median portain of the cerebellum
  22. cerebellar deep nuclei,
  23. cranial nerves – 5,7,8,9,10,11,12 – exit & entrance from the brainstem the cranial nerves arise from the brainstem and innervate mostly the head. Some cranial nerves are part of the the CNS, and some are part of the somatic PNS, and some are part of the visceral PNS.
  24. 5- trigenimal – is part of the somatic PNS and carries somatic sensory touch info from the skin of the face to the brainstem

    10- vagus – is part of the visceral PNS. It descends with in the neck to innervqate many internal organs of the chest and abdomen. (Vagus is from the latin word wandering). See class exercise h/o

  25. location of associated nuclei in brainstem and major functions – see h/o

Last Updated 04/10/00 12:27:15 PM
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