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THE NERVOUS SYSTEM . Divisions of the nervous system. Anatomical Organization of the Nervous System. Major Regions of the Brain. Figure 15.1 Major Divisions of the Brain. Neuronal Organization: CNS. Two kinds of neural tissue found in both brain and spinal cord:

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neuronal organization cns
Neuronal Organization: CNS
  • Two kinds of neural tissue found in both brain and spinal cord:
  • Gray matter = neuroglia & unmyelinated axons, and dendrites of neurons
  • -forms the outer layer of the cerebrum = cerebral cortex
  • Gray matter also contains nuclei deep in the brain = clusters of neuronal cell bodies in CNS
  • Collections of nuclei can form a center (higher brain function)
neuronal organization cns6
Neuronal Organization: CNS
  • 2. White matter = myelinated axons
  • White matter tracts = bundles of axons
    • For the conduction of nerve impulses
    • Brain – three types of tracts (commisural, association, projection)
    • Spinal cord - Two types: sensory and motor tracts (ascending and descending)


  • Cerebrum= largest portion
  • -left and right cerebralhemispheres divided by the longitudinal fissure
  • -connected by the corpus callosum
  • -folded into ridges and grooves: grooves = sulci
  • -sulci divide the cerebrum into lobes
  • -ridges = gyri(gyrus)
  • many gyri and sulci have specific names
  • e.g. Central sulcus
    • Frontal and parietal lobes


  • -cerebrum is comprised of white and
  • gray matter:
  • 1. white matter - neurons with
  • long, myelinated axons
  • -organized into tracts
  • -three categories of tracts
  • commisural – join areas between hemispheres
  • e.g. corpus callosum
  • b. association – joins areas within
  • a hemisphere
  • c. projection – joins cerebrum to brain stem

2. gray matter: cerebral cortex

-outermost layer of the cerebrum

-contains gyri for specific processing of sensation, -area of voluntary movement, speech, all thought processes

-called motor and sensory areas


Motor and Sensory gyri of the Cerebral cortex

e.g. primary somatosensory area (postcentral gyrus): touch, proprioception, pain, itching, thermal - forms a “map” of the entire body

e.g. primary visual, auditory & gustatory areas

e.g. primary motor area(precentral gyrus): controls voluntary contractions

-also contains gyri that are called association areas for integration and analysis of incoming info & help in making of “decisions”

e.g. somatosensory, visual, auditory association areas


-2. gray matter: basal ganglia:

- multiple nuclei found deep within the cerebrum

-first described by Thomas Wells - 1664

- links to the midbrain

-1. receives input from the cortex & provides output to the motor areas of the cortex via the thalamus

-2. integrates motor commands

-3. regulates the initiation & termination of muscle mve.

-4. also functions to anticipate body movements & controls subconscious contraction of skeletal muscle

basal ganglia
Basal Ganglia
  • comprised of the:
  • 1. striatum
    • caudate nucleus: activity occurs prior to eye movements
    • putamen: precedes or anticipates body movements
    • nucleus accumbens
  • 2. globus pallidus: regulates muscle tone for movements
  • 3. claustrum
  • 4. substantia nigra: high concentration of dopanergic neurons
  • 5. subthalmic nucleus


  • Diencephalon
    • includes the hypothalamus, thalamus, epithalamus and subthalamus
    • thalamus: 80% of the diencephalon
      • paired oval masses of gray matter organized into nuclei, interspersed with white matter
      • major relay station for most sensory impulses from the SC, brain stem
      • crude perception of pain, heat and pressure (refined in cerebrum)
      • transmits motor information from cerebellum to the cerebrum
      • relays nerve impulses to and from different areas of the cerebrum plus cerebrum into the brain stem/cerebellum
thalmic nuclei
Thalmic nuclei
  • reticular
  • pulvinar
  • geniculate – medial and lateral
  • anterior
  • medial
  • ventral – lateral, posterior and anterior
  • lateral – posterior and dorsal


  • hypothalamus
    • -emotions, autonomic functions, hormone production
    • -made of numerous nuclei and tracts
  • 1. control of the ANS – integrates signals from the ANS (regulated smooth and cardiac muscle contraction)
  • major regulator of visceral activities (heart rate, food movements, contraction of bladder)
  • 2. produces hormones & connects with pituitary to regulate its activity

3. regulates emotional and behavioral patterns – rage,

aggression, pain and pleasure + sexual arousal

4. regulates eating & drinking – hypothalamus contains

a thirst center which responds to a rise in osmotic

pressure in the ECF (dehydration)

5. controls body temperature – monitors temp of blood

flowing through the hypothalamus

hypothalmic nuclei
Hypothalmic nuclei
  • mamillary bodies
  • supraoptic
  • preoptic
  • dorsomedial
  • ventromedial
  • anterior hypothalmic
  • posterior hypothalmic
  • paraventricular
  • suprachiasmatic
  • arcuate


  • epithalamus – consists of the pineal gland and habenular nuclei
  • -pineal gland – part of the endocrine system
  • -secretes the hormone melatonin
  • -increased secretion in dark
  • -promote sleepiness and helps set the circadian
  • rhythms of the body (awake/sleep period)
  • subthalamus – works with the cerebrum and cerebellum to control body
  • movements


  • comprised of three structures: midbrain, pons & medulla


  • Medulla oblongata
    • Continues to become the spinal cord
    • forms the inferior part of the brain stem
    • relays sensory information and controls automatic motor functions
    • white matter contains sensory/ascending and motor/descending tracts
    • contains several nuclei also
    • these nuclei regulate autonomic functions - reflex centers for regulating heartbeat and BP (cardiovascular center), respiration (respiratory center), plus vomiting, coughing, sneezing, hiccuping and swallowing
    • nuclei in the posterior part are associated with sensations of touch, proprioception, pressure and vibration

-associated with 5 pairs of

cranial nerves








  • Pons

= “bridge”

    • connection from cerebrum to cerebellum
    • consists of multiple nuclei and tracts
    • nuclei control both somatic (voluntary) and visceral (involuntary) motor responses
      • Pontine nuclei – relays information from cerebrum into the cerebellum
      • Pneumotaxic area – controls breathing (with medulla)
      • Apneustic area– controls breathing (with medulla)


  • Midbrain (Mesencephalon)
    • relay station between the cerebrum and the spinal cord, and between cerebrum and cerebellum
    • extends from the pons to the diencephalon – as cerebral peduncles
      • White matter tracts
      • motor tracts to the SC & sensory tracts into the thalamus
    • also connects cerebrum to cerebellum via cerebellar peduncles – white matter tracts (motor & sensory)

Midbrain (Mesencephalon)

    • Anterior portion:
    • cerebral peduncles (white matter tracts to/from cerebrum)
    • release of dopamine from substantianigra (nuclei) - loss of these neurons = Parkinsons
    • red nuclei forms synapses with cerebellum to coordinate muscle movements
    • Posterior portion = tectum
      • -White matter tracts = cerebellar peduncles (white matter tracts to cerebellum)
      • -Corpora quadrigemina - colliculi
        • -Reflex centers for eye movement, head and neck movement (protection), pupil size and eye tracking
    • divided into hemisphere with lobes - like the cerebrum
      • anterior and posterior lobes
    • has a superficial layer of gray matter called the cerebellar cortex - like the brain
    • deep to this gray matter are tracts of white matter and gray matter nuclei
    • controls voluntary and involuntary motor activities
      • evaluates and coordinates motor activities initiated by the cerebrum and corrects problems by sending info back to the cerebrum
      • regulate posture & balance
    • uses sensory data and stored memories
the limbic system
The Limbic System



cingulate gyrus

anterior thalmic nuclei

hypothalmic nuclei


  • called the emotional brain
  • group of structures that surround the brain stem
  • involved in olfaction and memory
  • emotion – anger, fear, happiness…
    • associated with specific responses – behavioral patterns
  • basic behavioral patterns
    • preparing for attack, laughing, crying, blushing
    • also includes sexual behaviors for the continuation of the species
    • connects with the hypothalamus to regulate these behaviors

olfactory tract

mamillary body


parahippocampal gyrus


the limbic system26
The Limbic System
  • called the emotional brain
  • involved in olfaction and memory
  • main components:
    • 1. limbic lobe: includes the hippocampus (within the parahippocampal gyrus), the cingulate gyrus, the insula and the dentate gyrus
    • 2. amygdala: integration center between the limbic system, cerebrum and various sensory systems
    • 3. olfactory bulbs
    • 4. septal nuclei
    • 5. mammillary bodies of the hypothalamus
    • 6. fornix - tract of white matter that connects the hippocampus to the hypothalamus
      • fibers end at the mammillary bodies
    • 7. hypothalmic nuclei
    • other areas include the anterior nuclear group of the thalamus and the reticular system within the brain stem
protection the cranial meninges
Protection: The Cranial Meninges
  • Cranium is covered with protective membranes = meninges
    • Cranial meninges are continuous with spinal meninges
    • 3 layers: 1. outer, fibrous dura mater – forms sheets (falx) that separate the cerebrum and the cerebellum into the hemispheres and the cerebellum from the cerebrum
    • comprised of an outer endosteal layer and and inner meningeal layer
    • large spaces for the circulation of blood can be found between the two dural layers = sinuses
  • e.g. superior sagittal sinus
    • 2. middle arachnoid mater
    • 3. inner, thin pia mater
cranial meninges
Cranial Meninges
    • -there are spaces between these membranes
        • A. subarachnoid space: between the arachnoid and pia maters
        • large veins run through the subarachnoid space
  • e.g. cerebral veins
        • B. subdural space: between the arachnoid and the dura mater
        • C. epidural space – between the dura mater and the vertebral canal in the spinal column
protection csf
Protection: CSF
  • brain contains fluid-filled chambers = Ventricles
    • 2 lateral ventricles, 1 third ventricle, 1 fourth ventricle
    • connects to the central canal which runs into the spinal canal
    • These chambers contain cerebrospinal fluid
    • made by specialized cells in the ventricles – choroid plexus (ependymal cells)
    • continually circulates - ventricles and central canal to subarachnoid space

CSF is gradually reabsorbed into the

  • blood through fingerlike projections
  • into the dural venous sinuses = arachnoid
  • granulations
the blood supply to the brain
The blood supply to the brain
  • Arterial blood reaches brain via internal carotid and the vertebral arteries
    • give rise to the Circle of Willis
      • loops around the optic chiasma
      • the loop is formed from anterior and posterior communicating arteries
      • from this loop branches the anterior, middle and posterior cerebral arteries
    • the posterior communicating and cerebral unite to form the basilar artery
    • from the basilar artery branches numerous smaller arteries – e.g. cerebellar and pontine
    • the basilar the formed from the union of the vertebral arteries
  • Venous blood leaves via internal jugular veins
spinal cord
Spinal Cord
  • length in adults = 16 to 18 inches
  • Cervical and lumbar enlargements
    • cervical = C4 to T1, nerves to and from upper limbs
    • lumbar = T9 to T12, nerves to and from lower limbs
  • Tapers to conus medullaris
  • filium terminale arises from the CM - extension of the pia mater that anchors the SC to the coccyx
  • 31 segments each with
    • Dorsal root ganglia
      • Sensory neuron cell bodies
    • Pair of dorsal roots
    • Pair of ventral roots

Inferior End of Spinal Cord

  • Conus medullaris
    • cone-shaped end of spinal cord
  • Filum terminale
    • thread-like extension of pia mater
    • stabilizes spinal cord in canal
  • Caudae equinae (horse’s tail)
    • dorsal & ventral roots of lowest spinal nerves
  • Spinal segment
    • area of cord from which each pair of spinal nerves arises


  • and lumbar
  • enlargements
histology of the spinal cord
Histology of the Spinal Cord
  • Central gray matter
    • Contains cell bodies of neurons and glial cells + unmyelinated axons
    • Gray matter projections are horns
  • Peripheral white matter
    • Myelinated and unmyelinated axons
    • Organized as tracts or columns
  • Organization of Gray Matter
  • 1. Posterior gray horns
    • Somatic and visceral sensory nuclei
  • 2. Anterior gray horns
    • Somatic motor control
  • 3. Lateral gray horns
    • Visceral motor neurons
  • Gray commissures
    • Axons of interneurons crossing cordated and unmyelinated axons
organization of white matter
Organization of White Matter
  • Six columns (funiculi)
    • Anterior, lateral and posterior white columns
    • Contain tracts of myelinated neurons
      • Ascending tracts relay sensory information up the spinal cord to brain – in through the dorsal root of the spinal nerve
      • Descending tracts carry motor information down the spinal cord - out to the muscles via the ventral root of the spinal nerve
white matter tracts
White matter tracts
  • Motor tracts:
  • lateral corticospinal: cortex to spinal cord
  • anterior corticospinal: cortex to spinal cord
  • recticulospinal tracts (lateral & medial): brain stem)to spinal cord
  • rubrospinal tract: midbrain to spinal cord
  • vestibulospinal tract: inner ear to spinal cord
  • tectospinal tract: tectum to spinal cord
  • Sensory tracts:
  • spinocerebellar (posterior & anterior): spinal cord to cerebellum
  • posterior column
  • spinothalmic (Anterior & lateral): spinal cord to thalamus