BIOL 2304
CNS & Spinal Cord
Central Nervous System:
Brain
Spinal cord
The Brain
Performs the most complex neural functions
Intelligence
Consciousness
Memory
Sensory-motor integration
Involved in innervation of the head
Organization of CNS
Centrally located gray matter – neuron cell bodies, interneurons, unmyelinated fibers
Externally located white matter – myelinated fibers
Additional layer of gray matter external to white matter is the Cortex
Formed from neuronal cell bodies migrating externally
Located in cerebrum and cerebellum
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Basic Parts and Organization of the Brain
Divided into four regions:
Cerebral hemispheres - Account for 83% of brain mass
Diencephalon – includes thalamus and hypothalamus
Brain stem - includes midbrain, pons, and medulla
Cerebellum – “little brain”
The Cerebral Hemispheres
Frontal section through forebrain
Cerebral cortex
Cerebral white matter
Deep gray matter of the cerebrum (basal ganglia)
Corpus Callosum – commissural fibers (white matter) which connects the two hemispheres
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The Cerebral Hemispheres
Fissures – deep grooves, which separate major regions of the brain
Transverse fissure – separates cerebrum and cerebellum
Longitudinal fissure – separates cerebral hemispheres
Sulci - grooves on the surface of the cerebral hemispheres
Gyri - twisted ridges between sulci
Prominent gyri and sulci are similar in all people
Lobes, sulci, and fissures of the cerebral hemispheres
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The Cerebral Hemispheres
Central sulcus separates frontal and parietal lobes
Bordered by two gyri:
Precentral gyrus
Postcentral gyrus
Parieto-occipital sulcus - separates the occipital from the parietal lobe
Lateral sulcus - separates temporal lobe from parietal and frontal lobes
Deeper sulci divide cerebrum into lobes
The Cerebral Hemispheres
Lobes are named for the skull bones overlying them:
Frontal lobe
Parietal lobe
Temporal lobe
Occipital lobe
The Cerebral Cortex
Home of our conscious mind
Composed of gray matter - neuronal cell bodies, dendrites, and short axons
Folds in cortex – triples its size
Approximately 40% of brain’s mass
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The Cerebral Cortex - Functional Areas
Three general functional areas:
Sensory areas
Association areas
Motor areas
Each of the major senses has a specific brain region called a primary sensory cortex
There are also multimodal association areas to process information
Functional Areas Of The Cerebral Cortex
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Primary Somatosensory Cortex
Located along the postcentral gyrus
Involved with conscious awareness of general somatic senses
Primary Visual Cortex
On medial part of the occipital lobe
Largest of all sensory areas
Receives visual information that originates on the retina
First of a series of areas processing visual input
Primary Auditory Cortex
Located at superior edge of the temporal lobe
Conscious awareness of sound
Impulses transmitted to primary auditory cortex
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Olfactory Cortex
Olfactory nerves transmit impulses to the olfactory cortex
Provides conscious awareness of smells
Lies on the medial aspect of the temporal lobe
Gustatory Cortex
Involved in the conscious awareness of taste stimuli
Located on the “roof” of the lateral sulcus
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Motor Areas – Primary Motor Cortex
Controls motor functions
Located in precentral gyrus
The Diencephalon
Forms the center core of the forebrain, primarily composed of gray matter
Surrounded by the cerebral hemispheres
Composed of three paired structures: thalamus, hypothalamus, epithalamus
Border the third ventricle
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The Thalamus
Makes up 80% of the diencephalon
Contains approximately a dozen major nuclei
Acts as the relay station for incoming sensory information
Every part of brain communicating with cerebral cortex relays signals through thalamic nuclei
Is the “gateway” to the cerebral cortex
The Hypothalamus
Lies between the optic chiasm and the mammillary bodies
Pituitary gland projects inferiorly
Contains approximately a dozen nuclei
Main visceral control center of the body
The Diencephalon – The Hypothalamus
Functions include the following
Control of the ANS
Control of emotional responses
Regulation of body temperature
Regulation of hunger and thirst sensations
Control of behavior
Regulation of sleep-wake cycles
Control of the endocrine system
Formation of memory
The Diencephalon – The Epithalamus
Forms part of the “roof” (top) of the third ventricle
Consists of a tiny group of nuclei
Includes the pineal gland (pineal body)
Secretes the hormone melatonin
Under influence of the hypothalamus
Aids in control of circadian rhythm
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The Brain Stem
Several general functions
Produces automatic behaviors necessary for survival
Passageway for all fiber tracts running between the cerebrum and spinal cord
Heavily involved with the innervation of the face and head
10 of the 12 pairs of cranial nerves attach to it
The Brain Stem
Includes the midbrain, pons, and medulla oblongata
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The Brain Stem – The Midbrain
The midbrain processes visual and auditory information and generates involuntary somatic motor
responses
Has reticular activating system - arousal of the whole brain
Has nuclei for cranial nerves II and IV
Has ascending and descending tracts
Lies between the diencephalon and the pons
Cerebral peduncles located on the ventral surface of the brain, contain pyramidal (corticospinal) tracts
Superior cerebellar peduncles - connect midbrain to the cerebellum
The Brain Stem – The Midbrain
Corpora quadrigemina
The largest nuclei
Divided into the superior and inferior colliculi
Superior colliculi – nuclei that act in visual reflexes
Inferior colliculi – nuclei that act in reflexive response to sound
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The Brain Stem – The Pons
A “bridge” between the midbrain and medulla oblongata
Pons contains the nuclei of cranial nerves
V – Trigeminal nerve
VI – Abducens nerve
VII – Facial nerve
Motor tracts coming from the cerebral cortex
Pontine nuclei
Connect portions of the cerebral cortex and cerebellum
Send axons to cerebellum through the middle cerebellar peduncles
Pons
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The Brain Stem – The Medulla Oblongata
The core of the medulla contains
Much of the reticular formation
Nuclei then influence autonomic functions
Cardiac center
Vasomotor center
The medullary respiratory center
Centers for hiccupping, sneezing, swallowing, and coughing
Functional Brain Systems: The Reticular Formation
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The Brain Stem – The Medulla Oblongata
Most caudal level of the brain stem
Is continuous with the spinal cord
Choroid plexus lies in the roof of the fourth ventricle
Cranial nerves VIII–XII attach to the medulla
External landmarks of medulla
Pyramids of the medulla lie on its ventral surface
Decussation of the pyramids - crossing over of motor tracts
Inferior cerebellar peduncles - fiber tracts connecting medulla and cerebellum
The Cerebellum
Located dorsal to the pons and medulla
Smooths and coordinates body movements
Helps maintain equilibrium
Consists of two cerebellar hemispheres
Cortex – gray matter
Arbor vitae - internal white matter
Thick tracts connecting the cerebellum to the brain stem are superior, middle, inferior cerebellar
peduncles
Fibers to and from the cerebellum are ipsilateral – run to and from the same side of the body
Cerebellum receives information from the cerebral cortex
On equilibrium
On current movements of
Limbs, neck, and trunk
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The Cerebellum
Ventricles of the Brain
Expansions of the brain’s central cavity
Filled with cerebrospinal fluid (CSF)
~150 mL at any given moment
Lined with ependymal cells (glial cells)
Continuous with each other
Continuous with the central canal of the spinal cord
Ventricles of the Brain
Lateral ventricles – located in cerebral hemispheres
Horseshoe-shaped from bending of the cerebral hemispheres
Third ventricle – lies in diencephalon
Connected with lateral ventricles by interventricular foramen
Cerebral aqueduct – connects 3rd and 4th ventricles
Fourth ventricle – lies in hindbrain
Connects to the central canal of the spinal cord
Ventricles of the Brain
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Protection of the Brain
The brain is protected from injury by
The skull
Meninges
Cerebrospinal fluid
Blood-brain barrier
Cerebrospinal Fluid (CSF)
Formed in choroid plexuses in the brain ventricles
Choroid plexus is
Located in all four ventricles
Composed of ependymal cells and capillaries
Arises from blood - 500 mL/day
Reabsorbed through arachnoid villi, returned to veins
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Cerebrospinal Fluid
Fills the hollow cavities of the brain and spinal cord
Functions:
Provides a liquid cushion for the spinal cord and brain
Nourishes brain and spinal cord
Removes wastes
Carries chemical signals between parts of the CNS
Cerebrospinal Fluid (CSF)
Blood Brain Barrier
Extensive impermeable capillaries & sinuses
Perivascular feet of astrocytes cover and wrap around capillaries and promote tight junction formation
Protects brain from hormones & circulating chemicals
Prevents most blood-borne toxins from entering the brain
Not an absolute barrier
Nutrients such as oxygen pass through
Allows alcohol, nicotine, and anesthetics through
Many glucose transporters
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Blood Brain Barrier
Meninges
Functions of meninges:
Cover and protect the CNS
Enclose and protect the vessels that supply the CNS
Contain the cerebrospinal fluid between pia and arachnoid maters
Meninges
Dura Mater
Strongest of the meninges
Composed of two layers: periosteal layer & meningeal layer
Arachnoid Mater
Located beneath the dura mater
Arachnoid villi - Project through the dura mater, allow CSF to pass into the dural blood sinuses
Pia Mater
Thin, delicate connective tissue, clings tightly to the surface of the brain
Follows all convolutions of the cortex
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The Spinal Cord
Functions of the spinal cord:
Spinal nerves attach to it
Provides two-way conduction pathway
Major center for reflexes
Location of the spinal cord:
Runs through the vertebral canal
Extends from the foramen magnum to the level of the vertebra L1 or
L2
Cervical and lumbar enlargements - where nerves for upper and lower
limbs arise
Conus medullaris - the inferior end of the spinal cord
Cauda equina - collection of spinal nerve roots
Filum terminale - long filament of connective tissue, attaches to the coccyx
inferiorly
Spinal Cord Segments
Segments that indicate the region of the
spinal cord from which spinal nerves emerge
Designated by the spinal nerve that issues
from it
T1 is the region where the first thoracic nerve
emerges
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The Spinal Cord
Two deep grooves run the length of the cord
Posterior median sulcus
Anterior median fissure
White Matter of the Spinal Cord
White columns:
Dorsal (posterior) funiculus
Ventral (anterior) funiculus
Lateral funiculus
Composed of myelinated axons
Allow communication between spinal cord and brain
White Matter of the Spinal Cord
Fibers classified by type:
Ascending fibers – afferent (sensory)
Descending fibers – efferent (motor)
Commissural fibers
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Major Fiber Tracts in White Matter of the Spinal Cord
Gray Matter of the Spinal Cord
Shaped like the letter “H”
Gray commissure – contains the central canal
Dorsal horns consist of interneurons
Ventral horns and lateral horns contain cell bodies of motor neurons
Organization of the Gray Matter of the Spinal Cord
Divided according to somatic and visceral regions
SS – somatic sensory
VS – visceral sensory
VM – visceral motor
SM – somatic motor
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Review of Protection of the Spinal Cord
Protected by vertebrae, meninges, and CSF
Meninges:
Dura mater – a single layer surrounding spinal cord
Arachnoid mater – lies deep to the dura mater
Pia mater – innermost layer, delicate layer of connective tissue
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