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CHAPTER 15
THE BRAIN
Six Major Divisions of the Adult Brain
1. Cerebrum
2. Diencephalon
3. Mesencephalon
4. Pons
5. Cerebellum
6. Medulla Oblongata
Cerebrum
Divided into large paired cerebral hemispheres separated by the longitudinal fissure
Conscious thought process, intellectual functions, memory storage and retrieval
Conscious and subconscious regulation of skeletal muscle contractions
Diencephalon – the deep portion of the brain attached to the cerebrum
3 regions
1. epithalamus- roof of diencephalons- contains hormone secreting pineal gland
2. thalamus (rt & lft) from the walls of diencephalons- sensory information relay processing center
3. Hypothalmus- the floor of the diencephalons- visceral control center (pituitary gland)
contains centers involved with emotions, autonomic function and hormone production. Link between nervous
and endocrine system.
Brain stem
Consists of the
Midbrain- mesencephalon – processes visual and auditory information
Pons & Cerebellum –metencephalon – motor centers
Medulla oblongata- myelencephalon- autonomic centers for cardiovascular, respiratory and digestive activities
Gray and White matter organization
Inner region of gray matter matter surrounded by tracts of white matter.
Gray- surrounds ventricles and passageways form clusters of neuron cell bodies called nuclei.
White- in cerebrum and cerebellum , covered by neural cortex- a superficial layer of gray matter.
Ventricles- Fluid filled cavities within the brain
4 ventricles- 1 in each cerebral hemisphere
3rd in diencephalon
4th between pons and cerebellum extending into the medulla oblongata and
continuous with spinal cord
septum pellucidum separates the lateral ventricles of the cerebral hemisphere
interventricular foramen- allowa communication with the ventricle of the diencephalons
mesencephalon aqueduct- canal that connects the third ventricle with the fourth
Cranial Meninges – surround the brain and act as shock absorbers
Same 3 layers as SC meninges
1. dura mater
a. falx cerebri- projects between the cerebral hemispheres
b. tentorium cerebelli-between cerebellum and cerebrum
c. falx cerebelli- divides 2 cerebellar hemispheres
2. Arachnoid- acts as roof over cranial blood vessels
3. Pia mater- anchored to the brain with astrocytes
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CHAPTER 15 (contd.)
Blood–brain barrier – special mechanism that prevents the passage of substances from the blood to the CSF
and brain
Cerebrospinal fluid (CSF)
 Cushions neural structures
 Supports the brain
 Transports nutrients, chemical messengers and waste products
 Formed in the choroids plexus- combination of ependymal cells and permeable capillaries
 Originates in the roof of the 3rd ventricle
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CEREBRUM
Largest region of the brain
Conscious thought processes and all intellectual functions originate in the cerebral hemispheres
Gyri- elevated ridges
sulci- shallow depressions
Fissures- deep grooves
Lobes named after overlying bones
Central sulcus separates the motor and sensory portions of the cortex
Neurons of primary motor cortex are pyramidal cells
Association areas- associated with sensory or motor regions of the cortex, interpret incoming data or
coordinate a motor response.
a.) Somatic motor association (premotor cortex) responsible for the coordination of learned motor activities
b.) Somatic sensory association- integrates and interprets sensations concerning size and shapes of object
Integration centers- receive and process information from many different association areas (split brain concept)
Left- written lang. scientific skills, numerical Rt.-left hand, musical, artistic, space/pattrn
 Central white matter, covered by gray matter
 Contains fibers that form bundles from 1 region to another
1. association fibers- interconnections within the hemisphere
2. commissure fibers- connect the 2 hemispheres
3. projection fibers- link cerebrum with other regions of brain and spinal cord
Basal nuclei- paired masses of gray matter within the cerebral hemisphere
1. basal nuclei
2. caudate nucleus
3. claustrium
4. amygdaloid body
5. globus pallidus
Limbic system- A combination of the cerebrum, diencephalons and mesencephalon. Responsible for
establishing emotional states and related behavior, and facilitating memory storage and retrieval.
Fornix- tract of white matter that connects the hippocampus to the hypothalamus
Mammillary bodies- prominent nuclei in the floor of the hypothalamus
DIENCEPHALON – connects the cerebral hemispheres to the brain stem
1.Epithalamus- roof of 3rd ventricle, houses pineal gland
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2.Thalamus- lt. & rt. Separated by 3 ventricle
Consists of paired of oval masses of mostly gray matter organized into nuclei.
Acts as relay station for sensory and motor impulses
a. intermediate mass- bridge of gray matter that crosses the 3rd ventricle to join the masses
b. nuclei- all sensory impulses except smell; motor nuclei- voluntary motor actions and arousal
3. Hypothalamus- Contains centers involved with emotions and visceral processes; Connection between the
nervous and endocrine system (mind over body phenomenon, associated with rage and aggression,
feeding/satiety center)
 Infindibulum connects hypothalamus to pituitary gland
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MESENCEPHALON (midbrain)
Contains cerebral aquaduct
Cerebral peduncles- pair of fiber bundles (both motor and sensory) connects upper and lower brain
Tectum- dorsal portion of midbrain- contains corpora quadrigemina (4 rounded elevations)
1. superior colliculi- 2 elevations- reflex centers for movement of eyeballs and head &
neck in response to visual stimuli
2. inferior colliculi- 2 elevations- reflex centers for movement of head and trunk in
response to auditory stimuli
PONS
Nuclei and white fibers in scattered tracts bridge connecting the SC with the brain and parts of brain with each
other. Fibers run in two directions
1. middle cerebral peduncles- transverse fibers connect rt and lft sides
2. longitudinal fibers- belong to motor sensory tracts that connect SC with medulla or upper parts of
brain stem.
CEREBELLUM
Second largest
Tentorium cerebelli- extension of cranial dura mater to separate cerebrum from cerebellum
Vermis- central constricted area
Hemispheres- anterior, posterior and floccundular
Falx cerebelli- extension of cranial dura mater between hemispheres
Cortex- gray matter (surface)
Cerebellar peduncles- attaches cerebellum to brain stem. Mostly efferent fibers
1. inferior cerebellar- connect cerebellum with medulla at base of brain stem and SC
2. middle cerebellar – cerebellum with pons
3. superior cerebellar- cerebellum with midbrain
4. Function: coordinates subconscious contraction of skeletal muscles. Maintain equilibrium and posture,
predict future position of body while moving.
MEDULLA OBLONGATA
Contains all ascending and descending tracts between the SC and the brain
Pyramids- ventral sides of medulla -2
Nucleus gracilis- rt and left, found on dorsal side of medulla
Nucleus cuneatus- rt and left found on dorsal side of medulla- receive sensory fibers form ascending tracts
of SC and relay info to opposite side of the medulla
 3 cortex centers
1. cardiac center- regulates rate of heartbeat and force of the contraction
2. medullary rhythmicity area of respiratory center- adjusts basic rhythym of breathing
3.vasomotor (vasoconstrictor)- regulates the diameter of blood vessels.
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CRANIAL NERVES
 Numbered according to their position along the longitudinal axis of the brain. LEARN THEM!