Ch. 13
The Central Nervous
System
Objectives
• Be able to identify the various features of the
spinal cord
• Be able to identify the major parts of the brain
and their functions
• Understand how tracts and nuclei are
arranged along the brain stem
The Spinal Cord
• Extends form the foramen magnum to L1 or L2
– About 42 cm long and 1.8 cm thick
• Three main functions
– Conduction
• Conducts information up and down the cord, to and away
from the brain and other regions of the trunk
– Locomotion
• Central pattern generators
– Reflexes
• Spinal reflexes involuntary response to a stimuli
Spinal Cord
• Two longitudinal grooves
– Anterior median fissure
– Posterior median sulcus
• 31 pairs of spinal nerves
– Segments
• Divided into 4 regions
– Cervical, thoracic, lumber,
and sacral
– Terminates at medullary
cone
• Cauda equina
anatomyatlases.org
Spinal Meninges
• Fibrous connective
tissue sheets
• Three layers
– Dura mater
– Arachnoid mater
• Subarachnoid space
– Below medullary cone,
lumbar cistern
• CSF
– Pia mater
• Denticulate ligaments
daviddarling.info
Cross Sectional Anatomy
d.umn.edu
Spinal Tracts
• Ascending tracts
– Carry sensory
information up
• Descending tracts
– Carry motor output
down
• Decussation
– Contralateral
– Ipsilateral
• Sensory info typically
carried by three neurons
• Motor info carried by two
neurons
withealth.net
Overview of the Brain
• Control center of the body
– Composed of an abundance of neurons
• Divided into three major regions
– Cerebrum
• Divided into left and right hemispheres by longitudinal fissure
– Gyri, sulci,
– Communicate via the corpus callosum
– Cerebellum
• Posterior and inferior to the cerebrum
• Second largest part of the brain
– Brain stem
• What remain of the brain if the cerebrum and cerebellum are
removed
– Diencephalon, midbrain, pons , and medulla
Grey and White Matter
• Arranged opposite of the spinal cord
arrangement
– Cortex composed of grey matter
– Deep nuclei as well
– Rest of brain is white matter running in tracts
Embryonic Development
niaaa.nih.gov
Embryonic Development
Meninges
• Dura mater
– Composed of two layers
• Periosteal layer
• Meningeal layer
– Dural sinuses
» Superior sagittal
» Transverse
• Arachnoid mater
• Pia mater
health.allrefer.com
Ventricles
• Ventricles – four internal chambers of brain
– Lateral (2), third, cerebral aqueduct, fourth,
central canal
– Choroid plexus – mass of blood capillaries that
line ventricles
• Produce cerebral spinal fluid
faculty.irsc.edu
Cerebral Spinal Fluid
• Clear, colorless liquid that fills the ventricles and
canals of the CNS
– Contains more Na+ and Cl- than plasma
• Reabsorbed by the subarachnoid villi
• Three functions
– Buoyancy
– Protection
– Chemical stability
Blood Brain Barrier
• Brain require significant supply of blood
– Oxygen and glucose
• Exposure to blood would make it susceptible to harmful
agents
• Blood-Brain barrier
– Tight junctions between endothelial cells of brain capillaries
– Permeable to water, glucose, O2, alcohol, anesthetics
• Blood-CSF barrier
– Tight junctions between ependymal cells of choroid plexus
Cerebrum
• Divided into cerebral hemispheres
– Gyri, sulcus , and fissures
– Lobes
• Frontal, parietal, temporal, occipital
• Insula, fifth lobe, deep
– Three regions (superficial to deep)
• Grey matter cortex
• Inner white matter
• Deep basal nuclei
emc.maricopa.edu
Cerebral Cortex
• The “boss”
– Allows us to feel, move (voluntary), communicate,
remember and understand
• Grey matter
– Cell bodies, dendrites, and unmyelinated axons
– No nerve tracts
• Three kinds of functional regions
– Motor areas – voluntary movement
– Sensory areas – conscious awareness of sensations
– Association areas – integrate different info for purposeful
action
Motor Areas
• Primary motor cortex
– Precentral gyrus
– Pyramidal cells
• Conscious control of precise or skilled
voluntary movement
• Axons become corticospinal tract in spinal
cord
– Motor homunculus
• Premotor cortex
– Controls and coordinates skilled motor
activity
• Brocas area
– Motor speech area
– Planed motor activity
thebrain.mcgill.ca
Sensory Areas
• Primary somatosensory
cortex
– Postcentral gyrus
• Sensory information relayed via
three-neuron synaptic chain
– Sensory homunculus
• Somatosensory association
area
– Integrates different sensory
information from PSC and
produces an understanding of
what is being felt
Sensory Areas
Association Areas
• Prefrontal cortex
– Involved with intellect, cognition, recall, judgment,
consciousness, reasoning, and personality
• Language area
– Wernicke’s area
• Sounding unfamiliar words
• Visceral association area
– Cortex of insula
– Conscious perception of visceral sensations
Cerebral White Matter
• Responsible for communication within cerebral areas and between
cortex and and lower CNS
– Myelinated axons that form tracts
• Classified based on direction they run in
– Commissural tracts
• Enable communication between hemispheres
– Corpus callosum
– Association tracts
• Connect different parts of the same hemisphere
– Long, different lobes
– Short, different gyri
– Projection tracts
• Connect cerebrum to lower brain and cord centers
• Internal capsule – dense band of tracts between thalamus and basal nuclei
• Corona radiata – fanning out of band
Basal Nuclei
• Deep subcortical nuclei lateral to
thalamus
• Three nuclei recognized
– Caudate, putamen, globus pallidus
– Lentiform nucleus
• Putamen and globus pallidus
– Corpus striatum
• Putamen and caudate
• Involved with motor control
scienceblogs.com
The Diencephalon
• Consists of three paired structures
– Thalamus
• Relay to the cerebral cortex
• Key role in motor control
– Hypothalamus
thebrainwiki.com
• Major control center of autonomic and endocrine systems
• Hormone secretion, autonomic effects, thermoregulation,
food and water intake, memory
– Epithalamus
• Pineal gland
The Brain Stem
• Three regions: midbrain, pons, and medulla
• Midbrain
– Cerebral peduncles
• Descending corticospinal tract
– Cerebral aqueduct
– Tectum – posterior to aqueduct
• Corpora quadrigemina nuclei
orble.com
– Superior colliculi – coordinate head and eye movements
– Inferior colliculi – auditory relay, reflexive response to sounds
– Sustancia nigra – inhibitory motor center
• Rich in melanin, precursor to dopamine
– Red nucleus – fine motor control
• Connects with cerebellum
– includes nuclei of oculomotor and trochlear nerves
Pons
• Bulging brain stem region between midbrain
and medulla
• Consists of tracts
• Nuclei of trigeminal, abducens, and facial
nerves
• Respiratory centers
Medulla
• Most inferior part of brain stem
• Descending tract
– Anterior corticospinal tracts (pyramidal)
– Tectospinal tracts – motor control of neck
• Ascending tracts
– Inferior olivary nuclei
• Send proprioceptive info to cerebellum
– Gracile and cuneate nuclei
• Second order neurons decussate, form medial lemniscus
• Cardiac and respiratory centers
• Reticular formation – grey matter
Cerebellum
• Located dorsal to medulla and pons
– Connected via cerebellar peduncles
• Cerebellar features
–
–
–
–
hemispheres connected via vermis
Gyri called folia
Three lobes: anterior, posterior, flocculonodular
Arbor vitae – white matter
• Functions
– Coordinated body movements and maintaining
equilibrium