The Brain
Sections 9.11 and 9.13
* Contains approximately
100 Billion neurons
* Weighs about 3 pounds
Major Brain Structures
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Cerebrum- Divided into 4 lobes:
(frontal, parietal, occipital, temporal)
Diencephalon:
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(thalamus, hypothalamus, epithalamus)
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Brain Stem:
(midbrain, pons, medulla oblongata)
Cerebellum
**(HINT IMPORTANT –KNOW FOR YOUR
TEST)**
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Brain Blood Supply
 Oxygen – The brain requires 20% of the body’s oxygen
supply. Neurons that are without oxygen for 4 or more
minutes may be permanently damaged
 Glucose -in
the our
glucosenervous
in the blood issystem
the source of energy for
Glucose
the brain’s cells. Very little glucose is stored in the brain, so if
there isn’t enough glucose in the blood a person can
experience confusion, dizziness, convulsions and loss of
consciousness.
Cerebrum
 Two cerebral hemispheres
 Longitudinal fissure separates hemispheres.
 Surface area increased with Gyri (ridges) and Sulci
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(creases) or Fissures (deep grooves).
Connected by the Corpus Callosum
Function: Intelligence, memory, learning
Cerebral cortex – gray matter, outermost, all
conscious thinking occurs here
Olfactory bulb – sense of smell
Lobes
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Frontal
Parietal
Temporal
Occipital
Functions of the Cerebrum
Diencephalon
Main structures:
1. Thalamus – main relay station
for sensory impulses (except
smell) to the cerebral cortex.
2. Hypothalamus – regulates
visceral movement (BP, GI tract,
HR), body temperature, water
and electrolytes, hunger, thirst,
stimulate pituitary, maintains
sleep and wake patterns.
3. Epithalamus – contains the
Pineal gland which regulates
biological clock.
Cerebellum
 2nd largest part of brain
 Controls muscular
coordination
 Maintains posture
 Allows for smooth, refined
movements
 Involuntary once learned
Check point
 1. What part of the brain helps you play a musical instrument?
 2. What part of the brain has 4 lobes, what are the four lobes?
 3. This part of your brain allows you regulates body temperature,
electrolytes, and thirst, which part of the brain allow you to do
this?
The Blood Brain Barrier (BBB)
 Protects the brain from harmful substances and
pathogens by blocking passage of many
substances from the blood into brain tissue.
Does NOT protect from lipid-soluble substances such
as oxygen, carbon dioxide, alcohol, and most
anesthetic agents.
Cerebrospinal Fluid (CSF)
 A clear, colorless liquid that carries oxygen, glucose, and
other needed chemicals from the blood to the neurons. It
removes wastes and toxic substances produced by the brain
and spinal cord cells
Brain Stem
Three sections:
1. Midbrain – visual and auditory
reflex centers, main motor
pathway
2. Pons – “bridge”, relays
impulses between:
a. medulla/cerebrum
b. cerebrum/cerebellum
3. Medulla Oblongata –regulates
heart rate, blood pressure,
respiration, coughing,
sneezing, vomiting, swallowing
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Activity
 140-141 in nervous packet
 Coloring parts of the brain in nervous system packet
 LAB: Mouse party!
Central Nervous System
 Consists of Brain and Spinal Cord
The Spinal Cord
Spinal Cord
 Functions – to conduct nerve impulses and serve as
the center of spinal reflexes.
 Anatomy of the spinal cord:
1. Ascending tracts – from sensory to brain
2. Descending tracts – from brain to motor
3. Composed of gray and white matter.
4. Central canal contains the CSF.
5. Conus medullaris – end of cord at L1
6. Cauda Equina – cord fans out into nerves.
Cross-Section of Spinal Cord
Afferent impulses travel through dorsal root to cord.
Efferent impulses travel through ventral root to
effector.
Spinal Cord Protection and
Covering
 Vertebral Colum
 Ring of bone formed by vertebral foramina protect the spinal
cord
Spinal Cord Protection and
Covering
 Meninges – connective tissue
covering that protect the spinal
cord. They are found in 3 layers
Meninges: The Coverings
 Three Layers:
1. Dura mater –
outermost, tough, white
2. Arachnoid mater –
middle, web-like, CSF in
subarachnoid space
3. Pia mater – innermost,
very thin
on top of brain tissue
Meningitis: Inflammation of the meninges and
CSF; typical causes are bacteria or virus; spinal
tap needed to diagnose
Meninges
 Dura Mater – outer layer of meninges
 Composed of tough connective tissue
Meninges
 Arachnoid Mater – middle layer of meninges
 Composed of collagen and elastic fibers that resemble a spider’s
web
Meninges
 Pia Mater – inner layer of meninges
 Composed of transparent collagen and elastic fibers that adhere
to the spinal cord and brain
Cross-Section of Spinal Cord
Afferent impulses travel through dorsal root to cord.
Efferent impulses travel through ventral root to
effector.
Cross-section of Spinal Cord
Orientation of
grey and white
matter is
opposite of the
brain.
Grey matter =
cell bodies
White matter =
myelinated
axons
Subarachnoid Space
 Area between the arachnoid mater and pia mater containing
CSF
 Spinal Tap (lumbar puncture) – a long needle is inserted into
the subarachnoid space (generally between L3 & L4 or L4 & L5)
to withdraw CSF for diagnostic purposes or to introduce
medication.
Epidural
Epidural given outside of the dura mater.
External Structure
 The adult spinal cord is only about 16-18 inches long…it
ends around L2
Cauda Equina
 Nerves on the lower portion of the cord angled downward
through the vertebral canal.
Enlargements
 Cervical Enlargement – contains nerves that
supply the upper limbs
 Lumbar Enlargement – contains nerves that
supply the lower limbs
Indentations/divisions
 Anterior Median Fissure &
Posterior Median Sulcus – divide the cord into right and
left halves
Central Canal
 Space down the center of the spinal cord containing CSF
Spinal Nerves
 Paths of communication between the spinal cord and the
nerves that serve the specific regions of the body
Roots
 Connect each spinal nerve segment to the spinal cord
 Posterior (dorsal) root – contains only sensory axons
 Dorsal Root Ganglion – swollen area containing sensory cell bodies
 Anterior (ventral) root – contains both somatic motor and
autonomic motor neurons
Reflexes
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Rapid, automatic responses to specific stimuli.
Their purpose is to preserve homeostasis.
Little variability in the responses.
Only a few neurons are needed.
“Wiring” of a single reflex = “Reflex Arc”
Testing somatic reflexes can be used for diagnostic purposes.
Examples: swallowing, sneezing, vomiting, and knee jerk.
Reflex Classification
Stretch Reflex: “Patellar reflex”
Muscle spindles = sensory receptors involved
in stretch reflexes
Innate Reflex: “Withdrawal reflex”
Peripheral Nervous System
Sections 14 and 15
READ TONIGHT!!!
Peripheral Nervous System
PNS
Motor
(Efferent)
Sensory
(Afferent)
Somatic
Skin and
special senses
Somatic
(Voluntary)
Visceral
Skeletal
Muscles
Autonomic
(Involuntary)
Sympathetic
Parasympathetic
General Info
All nerves that branch off the CNS and connect to other body parts.
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Cranial nerves – 12 pairs
Spinal nerves – 31 pairs
Functions:
1. To receive stimulus input and send to CNS.
2. To relay the response from the CNS to the
appropriate effector organ.
Nerve
Anatomy
What is this?
How to remember the Cranial Nerves
 https://youtu.be/FtJtYMRVw7A
Internal Structure
 Gray Matter
 Anterior Horns – contain cell bodies of somatic motor
neurons
 Posterior Horns – contain cell bodies of somatic and
autonomic sensory neurons
 Lateral Gray Horns – present only in lower portion of the
spinal cord. Contains cell bodies of autonomic nervous system
Ventral Horn
Lateral Horn
Dorsal Horn
White Matter
 Organized into columns containing myelinated and
unmyelinated axons of sensory and motor neurons
Posterior White Column
Lateral White Column
Anterior White Column
White Matter
 Tracts – bundles of axons having a common origin or
destination carrying similar information
 Sensory (ascending) tracts – consist of axons that conduct
nerve impulses toward the brain
 Motor (descending) tracts – consists of axons that carry
nerve impulses down the spinal cord
Tracts
Spinal Nerves
 Paths of communication between the spinal cord and the
nerves that serve the specific regions of the body
Afferent or Sensory Nerves
1.
2.
3.
Picks up stimuli from:
a. internal environment – visceral
nerves
b. external environment –
somatic nerves
Sends to CNS for interpretation
Typically unipolar or bipolar
neurons
Somatic nervous system
All voluntary or conscious activities
 Nerves connect to skeletal muscles
 Pathways have one motor neuron to
muscle cells.
 Neurotransmitter: Acetylcholine
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Autonomic nervous system
- All involuntary or unconscious activities.
- Maintains internal environment
- Nerves connect to cardiac, smooth muscle or glands
- Pathways have two neurons synapsing at a ganglia before effector.
- Neurotransmitters: Acetylcholine or norepinephrine
- Two divisions counterbalance each other:
Sympathetic and Parasympathetic
Comparing Motor Neurons
Sympathetic

prepares for energy-expenditure,
excitement or stressful situations
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"fight" or take "flight“.
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Nerve fibers originate from the thoracic
and lumbar regions of spinal cord.
Short Pre and Long postganglionic fibers
Parasympathetic
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Stimulated during calm and relaxing situations
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"rest" and "digest" .
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Nerve fibers originate from the brain and
sacral region.
Long preganglionic fibers and short post
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Which pathway is
responsible here?
Sympathetic or Parasympathetic
Division of the ANS are distinguished by:
1. Unique origin sites
a. Sacrocranial vs. Thoracolumbar
2. Different lengths of their fibers
a. Preganglionic (long – Para, short – S)
b. Postganglionic (long – S, short – Para)
3. Location of their ganglia
a. P – close to effector
b. S – close to spinal cord
Brain Disorders and
Diseases
Common Brain Injuries
 Concussion – abrupt, but temporary loss of consciousness from a blow to the
head.
Symptoms: headache, confusion, memory loss, lack of concentration
 Contusion – bruising of the brain due to trauma, leaking capillaries, commonly
follows a concussion. Pia mater torn.
Signs: Immediate loss of consciousness, loss of reflexes, decreased blood pressure, cessation of
respiration.
 Laceration – tear of the brain, large vessel rupture, cerebral hematoma, increased
intercranial pressure.
Brain Tumors
Brain Aneurism
Cerebral thrombosis video
Strokes
Injury Effects
Phineas Gage
Man who survived a terrible brain injury in the
1800’s. First opportunity for scientists to study
the frontal lobe and limbic system connection.
Limbic system is the emotional region and frontal
keeps the limbic region in control.
Injury re-enactment video
CAN YOU READ THIS?
cdnuolt blveiee taht I cluod aulaclty uesdnatnrd waht I was rdanieg. The
phaonmneal pweor of the hmuan mnid, aoccdrnig to a rscheearch at
Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod
are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be in the rghit
pclae. The rset can be a taotl mses and you can sitll raed it wouthit a
porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by
istlef, but the wrod as a wlohe. Amzanig huh? yaeh and yuo Iawlyas tghuhot
slpeling was ipmorantt!