BIO 348 Lecture 6: Neuroanatomy

Dorsoventral (in basic neuroanatomy)

vertical axis that runs from dorsum (back) to entrum (belly)

Rostrocaudal/Anteroposterior (in basic neuroanatomy)

longitudinal axis that extends from rostrum (beak) to cauda (tail)

Mediolateral (in basic neuroanatomy)

horizontal axis that runs from the midline (medial) to the lateral margin of the animal

Dorsoventral (in human brain)

axis extends along the top (head)/bottom (chin)

Rostrocaudal/Anteroposterior (in human brain)

axis extends from front (eyes) to back

Mediolateral (in human brain)

horizontal axis that runs from the midline (medial) to the lateral margin of the animal

Two divisions of the vertebrate nervous system

• CNS

  • brain and spinal cord

• PNS

  • Sensory division

    • somatic sensory division and visceral sensory division

  • Motor division

    • somatic motor division

    • visceral motor division

      • sympathetic and parasympathetic

Central Nervous System

• comprised of brain and spinal cord

• 7 main regions of the CNS

• further anatomical and functional specialization within each region

• simple behaviors are functionally localized in discrete brain regions

Spinal Cord

• cervical

• thoracic

• lumbar

• sacral

Brain Stem

• necessary passage for all ascending and descending tracts between forebrain and spinal cord

• modulates sensory, motor, and reflex behaviors (feeding, drinking, respiration)

• modulation of arousal; CNS activity

Medulla

• in brain stem

• relates autonomic functions such as respiration, heart rate, and blood pressure

• PreBotzinger complex - generates respiratory rhythm

Pons

• in brain stem

• cranial nerve nuclei

• mediates sensory and motor control of head and neck

Midbrain

• in brain stem

• voluntary motor control (substantia nigra)

• processing of auditory and visual information (superior and inferior colliculi)

Cerebellum

• motor control - modifies motor commands to adapt to desired output, accuracy of movement 

• maintaining posture

• receives sensory information from the spinal cord, balance from vestibular organs in the inner ear, motor & sensory information from the cortex

• certain forms of learning

Diencephalon

• thalamus

  • sensory relay center; information from visual, auditory, and somatosensory pathways relay here on their way to the sensory cortices

• hypothalamus

  • integrates physiology and behavior; regulates homeostatic behaviors, including feeding, thirst, regulation of sleep-wake cycle, reproduction

Cerebrum

• cerebral cortex

  • higher order sensory and cognitive processing

  • sulci and geri increase the surface area of the cortex

    • anatomically defined

    • consistent across individuals

    • serve as anatomical landmarks demarcating specific brain regions

• hippocampus

  • learning and memory

• amygdala

  • formation and storage of memories associated with emotion

Cerebral Cortex

• frontal lobe

  • short term memory, planning, control of movements

• sensory processing

  • parietal lobe

• temporal lobe

  • auditory information learning and memory emotion

• occipital lobe

  • visual processing

Ventricles contain…

• cerebrospinal fluid

  • provides protection by buffering the brain

  • “floats” the CNS, reduces weight of the brain and pressure at the base of the brain - brain weighs 1300g, but in CSF 25g

  • removes waste from CNS to blood stream

  • produced by choroid plexus - epithelial cells found inside the lateral ventricles

Meninges protect…

• the CNS

• 3 layers

• meningeal cells are fibroblasts

• bacterial meningitis result from bacterial infection and inflammation of meninges

Functional organization of the CNS

• brain and spinal cord are bilaterally symmetrical

• contralateral control of functional systems

  • sensory and motor functions on one side of the body are processed/controlled by the opposite side of the brain

  • many projections cross to the contralateral hemisphere in the brain system known as “decussation”

  • damage to one side of the brain will impair function of the contralateral side of the body

• CNS is topographically organized

  • circuit tracing

    • retrograde tracers travel from axon to cell body

    • anterograde tracers travel from cell body to axon terminal

  • neurons projecting to specific muscle groups are organized and localized to specific regions

  • neurons are organized in an orderly fashion such that information arriving to CNS forms representative neural maps

  • motor neurons and the muscles they innervate are topographically organized

    • motor neurons innervating a single muscle distributed in columns

    • all the motor neurons that innervate a given muscle 
      (motor neuron pool) are organized in a column that traverses several segments of spinal cord

    • motor neuron pools are differentially distributed between spinal cord segments

• Neurons are organized in an orderly fashion such that information arriving to CNS forms representative neural maps

• Spatial arrangement and density of sensory receptors is mapped onto the primary sensory cortex, reflect degree of sensory sensitivity

Medial Motor Column

innervates axial musculature; mediates posture

Spinal Accessory Column

innervates neck muscles

Phrenic Motor Column

innervates diaphragm, mediates respiration; rhythmic activity

Preganglionic Motor Column

spinal visceral motor neurons; innervate smooth muscle

Hypaxial Motor Column

innervates musculature of the body wall (intercostal and abdominal muscles)

Lateral Motor Column

innervates limb muscles

Primary motor cortex

motor maps reflect the density of neuronal innervation, correlated with the degree of fine motor control

Primary somatosensory cortex

abundance of neurons receiving input from a specific region is associated with degree of sensory sensitivity