Organization of the Nervous System and the Brain

Organization of the Nervous System

• Central Nervous System (CNS) and Peripheral Nervous System (PNS)
• Instructor: Sarah (Robin to Dr. Stone's Batman)
• Office hours available - reach out to Sarah, Caitlin, or Lisa Cay

Objectives

• Describe the general organization of the nervous system.
• Understand gray matter and white matter.

Nervous System

Central Nervous System (CNS)

• Brain
• Spinal Cord
• Information integration occurs here -- signals coming from and going to the CNS
• Coordinated activity happens here

Peripheral Nervous System (PNS)

• Everything else besides the brain and spinal cord.
• 31 pairs of spinal nerves
• Brachial plexus, lumbar plexus, sacral plexus
• 12 pairs of cranial nerves (even though they originate from the brain, they are part of the PNS)
• Ganglia (bubbles of cell bodies outside the CNS)

Somatic Nervous System

• Conscious decisions to move your body
• Sensory perception

Autonomic Nervous System

• Involuntary functions (breathing, heart rate)

Cells in the Central Nervous System

• Neurons:
  • Primary signaling cells
  • Have axons and dendrites
  • Dendrites receive signals
• Neuroglial cells:
  • Support cells
  • Astrocytes
    • Maintain blood-brain barrier
    • Interface between blood and brain
    • Star-shaped
  • Ependymal Cells
    • Have cilia
    • Line inner parts of hollow spaces
    • Allow for cerebrospinal fluid circulation
  • Microglia
    • Tiny
    • Support functions
    • Keep brain healthy
    • Help develop new nerves
  • Oligodendrocytes (CNS) / Schwann Cells (PNS)
    • Wrap around axons
    • Create myelin: a fatty protective layer insulating cells
    • Allow signals to move faster

Basic Structure of a Neuron

• Soma (cell body):
  • Contains organelles
• Dendrites:
  • Receive signals
• Multipolar neuron:
  • Multiple dendrites
• Every neuron has at least one dendrite and one axon.
• Axon:
  • Sends out signals
• Myelin Sheath:
  • Formed by Schwann cells
  • Insulates axon

Basic Terms to Orient Ourselves

• Terms vary in different parts of the nervous system.

Spinal Cord Cross-Section

• Central Nervous System (CNS): Spinal cord itself
• Peripheral Nervous System (PNS): Nerves coming off the spinal cord

Collections of Neuronal Cell Bodies (Somas)

• CNS: Nucleus (found in brain itself)
• PNS: Ganglion
  • Dorsal Root Ganglion: Important ganglion containing sensory neurons

Orientation

• Dorsal: Posterior (back)
• Ventral: Anterior (front)
• Dorsal Root Ganglion: Indicates posterior side of spinal cord

Spinal Nerve Composition

• Made of axons

• Dorsal root ganglion contains sensory neurons

• Sensory information enters the spinal cord and synapses with neurons in the dorsal horn

• Motor information exits the spinal cord via the ventral root

• Spinal nerve:

  • Formed where dorsal and ventral roots come together
  • Contains sensory and motor information

PNS Collections

• Collection of cell bodies: Ganglion
• Collection of axons: Nerve

CNS Collections

• Collection of cell bodies: Nucleus
• Collection of axons: Tract or Fasciculus
  • Highway to the brain
  • Contributes to gray and white matter

Gray and White Matter

White Matter

• Primarily myelinated axons
• White due to myelin

Gray Matter

• Neuronal cell bodies, dendrites, and synapses

Distribution

• Brain:
  • White matter inside
  • Gray matter mostly outside
• Spinal Cord:
  • White matter outside
  • Gray matter inside (dorsal and ventral horns)

Brain Organization

• Cerebrum
• Central Brain
• Brain Stem
• Spinal Cord

Brain Views

• Cerebrum: Majority of the brain
• Cerebellum: Tiny brain (sits inferior to cerebrum)
• Brain Stem: Anterior to cerebellum

Hemispheres

• Brain divided into two hemispheres
• Grooves contain blood vessels

Lobes

• Four lobes: Frontal, Parietal, Temporal, Occipital
• Lobes named after the bones they are near

Gyri and Sulci

• Gyri: Elevated ridges
• Sulci: Grooves
• Fissures: Deep sulci
  • Increase surface area for more neurons and brain activity

Important Fissures

• Longitudinal fissure: Divides hemispheres
• Transverse fissure: Separates cerebrum from cerebellum
• Lateral fissure (Sylvian fissure): Divides parietal and frontal lobes

Important Sulci

• Central sulcus: Separates frontal and parietal lobes
  • Precentral gyrus: Anterior to central sulcus (motor cortex)
  • Postcentral gyrus: Posterior to central sulcus (sensory cortex)
• Parieto-occipital sulcus: Separates parietal and occipital lobes

Cranial Fossae

• Anterior cranial fossa: Frontal lobe sits here
• Middle cranial fossa: Temporal lobe sits here
• Posterior cranial fossa: Cerebellum sits here

Cerebral Hemisphere Regions

• Cerebral Cortex: Outermost layer of gray matter
• Inner White Matter: Signals traveling
• Basal Nuclei: Innermost nuclei

Cerebral Cortex Functions

• Conscious thought speech, memory, motor function

Cortical Areas

• Motor Areas Initiate movement (precentral gyrus)
• Sensory Areas Receive sensory information (postcentral gyrus)
• Association Areas Complex integrative functions

Hemispheric Control

• Each hemisphere controls contralateral (opposite) side of the body.

Cortices Within Cerebral Cortex

• Motor cortex
• Sensory cortex
• Prefrontal cortex
• Visual cortex
• Auditory cortex
• Speech areas

Cerebral Cortex Details

• Great matter

Functions

• Sensory
• Motor
• Complex integration

Prefrontal Cortex

• Anterior to central sulcus in the frontal lobe
• Personal traits, personality, decision making
• Last part of the brain to develop
• Area 9-12 and 44-47

Motor Cortex

• Area directly anterior to the central sulcus
• Area 4

Broca's Area

• In the frontal lobe on the left hemisphere
• Motor movements for speech

Wernicke's Area

• Speech interpretation
• Understanding what is being said

Patient Frustration

Broca's Aphasia

• Person trying to communicate is frustrated because they can't say what they want to say

Wernicke's Aphasia

• Person listening is frustrated because the speaker thinks they are making sense, but they are not

Parietal Lobe

• Houses the sensory cortex (postcentral gyrus)

Occipital Lobe

• Visual cortex

Homunculus

• Neurological map of the motor and sensory cortices
• Size of body part representation correlates with how much of the cerebral cortex is dedicated to that part
• Lateral side of head: face and mouth
• Medial parts of cortex: lower limb areas

White Matter Fibers

Commissural Fibers

• Connect cortex of different hemispheres
• Corpus callosum

Association Fibers

• Stay in the same hemisphere
• Connect different cortexes in the same hemisphere

Projection Fibers

• Leave the cerebral hemisphere
• Go to the brain stem or spinal cord
• Spinal tracts

White Matter Summary

Association fibers

• Within hemisphere

Commissural Fibers

• Between hemispheres
• Corpus callosum

Projection Fibers

• Cerebral cortex to lower CNS

Basal Nuclei

• Collection of nerve cell bodies deep in the cerebral hemisphere
• Caudate nucleus, putamen, globus pallidus
• Influence motor function
• Regulate initiation and termination of movements
• Damage can lead to Parkinson's or Huntington's disease

Basal Nuclei Location

• Coronal section: poppy areas in middle
• Lateral view: tadpole shape
• Caudate: tail of the tadpole

Central Brain

Thalamus

• Major relay center for all sensations except olfaction (smell)
• Directs sensory information to the appropriate area of the sensory cortex

Hypothalamus

• Maintains body's internal environment and homeostasis
• Connected to the pituitary gland (hormone production)
• Controls autonomic, limbic, and endocrine functions

Epithalamus

• Contains pineal gland
• Produces melatonin

Brain Stem

• Midbrain, pons, medulla oblongata
• Contains cranial nerve nuclei
• Has ascending and descending axons
• Controls autonomic functions

Midbrain

• Anteriorly (ventrally): cerebral peduncles
• Posteriorly (dorsally): four lumps called colliculi (two superior and two inferior)
• Superior colliculi: associated with vision
• Inferior colliculi: associated with hearing
• Substantia nigra: pigmented material, degeneration causes Parkinson's disease
• Cranial Nerves: 3 and 4

Pons

• Conduction tracts between higher brain centers and spinal cord
• Connects to cerebellum
• Cranial Nerves: 5, 6, 7, and 8
  • Visual:Pom poms, 5,6,7 and 8
• Signals move laterally through the Pons

Medulla Oblongata

• Reflex center
• Visceral motor functions (cardiovascular, respiratory centers)
• Pyramids: axons on the anterior side
• Decussation of the pyramids: signals cross to opposite side of body
• Cranial Nerves: 8, 9, 10, 11, and 12

Cerebellum

• Provides timing and patterns for smooth and coordinated movements
• Error-correcting feedback from movements
• Damage to this area can prevent learning from mistakes

Structure

• Two cerebellar hemispheres
• White matter and gray matter
• Gray matter on the outside, white matter on the inside
• Arbor vitae: white matter with tree-like appearance
• Folia: gray matter on the outside (looks like leaves)