The Nervous System

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The Nervous System

• Chapters 10 and 11

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Nervous System

• Master controlling and communicating system

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Interesting Facts

• A 1999 study of Einsteins brain, based on
  photographs taken of it after he died in 1955,
  showed that the parietal lobes, which are linked
  to math ability, appear 15 wider than normal.
  But the size of his brain was a little smaller
  than average.
• We may be the smartest creatures on the planet,
  but others have bigger brains. Larger brains are
  needed partly to control larger muscles. A sperm
  whale's brain weighs about 17 pounds and an
  elephant's weighs a little more than 10 pounds.
• Your brain is only about 2 of your body weight,
  but brain cells use twice as much energy as other
  cells in your body. Brain cells are always
  active, even when you sleep.
• Studies suggest that your brain is aware of
  subliminal, or hidden, messages even when you
  aren't. Human faces that express emotions, such
  as smiling or frowning, seem to have the
  strongest impact.
• Researchers believe that sleep gives the brain
  time to process and store memories. People who
  dont get enough sleep have trouble concentrating
  and recalling memories.
• Brain cells are the longest living cells in the
  body. Research shows that some parts of the brain
  may be able to grow new neurons as we age. But
  most of our brain cells are present from birth to
  death. The wiring of these cells changes
  constantly through our lives.

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Basic Functions

1. Sensory input gather information
2. Integration process and interpret sensory input
3. Motor output response by muscles and glands

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Organization

• Central Nervous System (CNS)
• Brain spinal cord
• Integrative and control centers
• Peripheral Nervous System (PNS)
• Nerves (spinal nerves, cranial nerves)
• Communication lines between CNS and rest of body
• Two Divisions
• Sensory (afferent) Division Sensory receptors ?
  CNS
• Motor (efferent) Division CNS ? effectors
  (muscles glands)

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Motor Division

• Somatic nervous system (voluntary) control
  skeletal muscles
• Autonomic nervous system (ANS) (involuntary)
  regulate smooth muscles, cardiac, glands
• Subdivisions
• Sympathetic primary process is stimulating the
  body's fight-or-flight response constantly
  active at a basic level to maintain homeostasis
• Parasympathetic serves to slow the heart rate,
  increase intestinal and glandular activity, and
  relax the sphincter muscles

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Brain Anatomy
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Brain Anatomy

• Brain mass of 100-120 billion neurons and
  neuroglial cells weighing approximately 3 pounds,
  protected by cranial bones
• Cerebrum largest mass of brain (83 of brain
  mass) responsible for higher mental functions
  and distribution of impulses
• Cerebral medulla white matter, conduction
  pathways
• Cerebral cortex outer layer of gray matter
  short and long term memory

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Cerebrum

• Divided into right and left hemispheres
• left side governs right side of body
• right side governs left side of body
• Lobes
• Frontal learning, planning, organizing,
  behavior, emotion, language production/comprehensi
  on
• Motor Cortex voluntary movement
• Parietal sensory (pain/pressure), distance,
  size, shape, cognitive/intellectual processes
• Occipital vision, visual memory
• Temporal memory, auditory, olfactory, speech,
  judgment, reasoning, will power, emotion

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Brain Anatomy

• Gyrus (gyri) elevated ridges/folds
• Sulcus (sulci) shallow grooves
• Fissures deep grooves
• Longitudinal separates right and left
  hemispheres corpus callosum (large fibers that
  connect the two hemispheres)
• Transverse separates cerebrum from cerebellum
• Fissure of Rolando divides frontal and parietal
  lobes at coronal suture
• Fissure of Sylvan/lateral fissure divides
  frontal and temporal lobes

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cerebellum

• Below and posterior to cerebrum
• Outer gray, inner white forms arbor vitae
• Function is to coordinate and regulate muscular
  activity
• Damage produces ataxia (lack of coordination due
  to errors in speed, force, direction of movement

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Brain Stem

• Damage coma
• Controls heart rate and blood pressure, smell
  and taste, eye movement, appetite, vision,
  balance
• 3 Parts
• Midbrain Short section of the brain stem between
  the diencephalon and the pons
• Cerebral aqueduct CSF
• Pons The rounded bulge on the underside of the
  brain stem, where it separates the midbrain from
  the medulla oblongata.
• Medulla oblongata Portion of the brain between
  the pons and the spinal cord.

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Diencephalon

• Diencephalon area between cerebrum and midbrain
• Composed of the thalamus, hypothalamus,
  subthalamus, and epithalamus
• Thalamus gray matter, relay station for sensory
  incoming and motor outgoing impulses damage -
  increased sensitivity to pain, loss of
  consciousness
• Hypothalamus forms floor of third ventricle
• Regulates autonomic control
• Cardiovascular control, temperature control,
  appetite, water balance, GI control, emotional
  states
• Epithalamus part of the forebrain including the
  pineal gland and a region in the roof of the
  third ventricle of the brain.

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Anatomy of the Brain

• Nervous System Part 2

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White vs. Grey Matter

• The CNS is made up of two types of tissue grey
  matter and white matter.
• Grey matter is mainly composed of neuron cell
  bodies, glial cells, and unmyelinated axons
• Axons are the processes that extend from neuronal
  cell bodies, carrying signals between those
  bodies.
• In grey matter, these axons are mainly
  unmyelinated, meaning they are not covered by a
  whitish-colored, fatty protein called myelin.
• Color comes from greyish hue of the neurons and
  glial cells combining with the red of the
  capillaries to give this tissue its greyish-pink
  color
• The grey matter serves to process information in
  the brain process signals generated in the
  sensory organs or other areas of the grey matter.
  This tissue directs sensory (motor) stimuli to
  nerve cells in the central nervous system where
  synapses induce a response to the stimuli.
• White matter is mainly composed of long-range
  myelinated axons (that transmit signals to the
  grey matter) and very few neuronal cell bodies.
• Myelin forms a protective coating around these
  axons, insulating them and improving their
  transmission of neuronal signals.

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Meninges of the Brain
Brain is protected by the skull and 3 layers of
membranes called meninges

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Meninges

• DURA MATER (literally means tough mother)
• Tough outer layer
• ARACHNOID MATER (literally means spider mother)
• Beneath and stuck to the dura mater
• Stringy, web-like
• Space under the arachnoid, the subarachnoid
  space, is filled with cerebrospinal fluid and
  contains blood vessels.
• PIA MATER (means tender mother)
• Thin transparent membrane that follows the
  contour of the ridges (gyri) and valleys (sulci)
  of the brain.

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Corpus Callosum

• Broad band of nerve fibers joining the two
  hemispheres of the brain
• largest white matter structure in the brain
• This bundle of nerve tissue contains over 200
  million axons
• This neural tissue facilitates communication
  between the two sides of the brain

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Cerebellar Vermis

• The cerebellar vermis receives information from
  the spinal cord about the sense of touch
  and proprioception.
• Proprioception is the ability to sense or
  perceive the spatial position and movements of
  your body.

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CSF and Ventricles

• The ventricles of the brain are a communicating
  network of cavities filled with cerebrospinal
  fluid (CSF)
• Functions of CSF
• Protection cushion for the brain, limiting
  neural damage in cranial injuries
• Buoyancy being immersed in CSF reduces weight of
  brain and prevents excessive pressure on the base
  of the brain.
• Chemical stability  creates an environment to
  allow for proper functioning of the brain.
• The ventricular system is composed of
• Lateral ventricles (2)
• Third ventricle
• Cerebral aqueduct
• Fourth ventricle
• The choroid plexuses located in the ventricles
  produce CSF, which fills the ventricles and
  subarachnoid space, following a cycle of constant
  production and reabsorption.

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Additional Anatomical Structures

• Pineal gland Produces the hormone melatonin at
  night which helps maintain circadian rhythm and
  regulate reproductive hormones
• Mamillary bodies serve as relay stations for
  impulses important in forming and recalling
  memories
• Destruction or injury to these portions of the
  brain is often associated with amnesia
• Inferior Colliculi main auditory (sound) center
  for the body acts as the channel for almost all
  auditory signals in the human body (reflex center
  midbrain)
• Superior Colliculi movement of eyes, head and
  neck in response to visual stimuli (reflex center
  midbrain)
• Infundibulum connection between the hypothalamus
  and the posterior pituitary pituitary stalk

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The Nervous System

• Cranial Nerves and Dissection Preparation Part 3

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Cranial Nerves I and II

• Olfactory Nerve (I) responsible for smell
• Olfactory bulb Structure located in the
  forebrain that receives neural input regarding
  smell
• Optic Nerve (II) transfer of visual information
  from retina to visual centers of the brain
• Optic chiasma X-shaped structure on the
  underside of the brain formed by a partial
  crossing over of optic nerves

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Cranial Nerves 3-6

• Oculomotor nerve (III) enable movements of the
  eye and eyelid
• Trochlear nerve (IV) smallest to service the
  eye moves the superior oblique muscle of the eye
• Trigeminal nerve (V) responsible for sensation
  in the face and motor functions (biting, chewing)
• Abducens nerve (VI) controls the movement of the
  lateral rectus muscle of the eye

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Cranial Nerves 7-10

• Facial Nerve (VII) supplies the muscles of
  facial expression
• Vestibulocochlear Nerve (VIII) responsible for
  both hearing and balance and brings information
  from the inner ear to the brain
• Glossopharyngeal Nerve (IX)  receives general
  sensory from the tonsils, the pharynx, the middle
  ear and the posterior 1/3 of the tongue taste
• Vagus Nerve (X) involuntary nervous system and
  commands unconscious body procedures, such as
  keeping the heart rate constant and controlling
  food digestion

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Cranial Nerves 11 and 12

• Accessory Nerve (XI) neck muscle movements
• Hypoglossal Nerve (XII) controls movements of
  the tongue

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Arbor Vitae

• White matter of the cerebellum
• Named as much due to its branch-like appearance
• Brings sensory and motor info to and from the
  cerebellum

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Human vs. Sheep Brain (ctd.)

• The convolutions and sulci comprises of a larger
  surface area than sheep brains
• Sheep brains have less ridges and contours.
• Human behavior and motor control is typically
  controlled by the cerebellum
• Sheep brains have a much smaller cerebellum than
  the human brain, which, in comparison with humans
  and their complex learned behaviors, have less
  motor control and less learning abilities.
• The olfactory bulb is larger in the sheeps brain
  than that of the human brain
• Animals usually rely more upon their senses and
  abilities of smell than humans do.
• Humans rely more upon other senses, such as sight
  and hearing, rather than smell like sheep and
  other animals.

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Human vs. Sheep Brain

• A sheeps brain is elongated in shape, whereas a
  human brain is rounded.
• The human brain stem is towards the backbone and
  downwards, because in the human body the backbone
  is vertical
• Sheeps backbone which is horizontal, and its
  brain is directed outwards.
• The human brain is not only larger, but heavier
  than a sheeps brain,
• Sheep brain is roughly 140 grams compared to the
  human brain, and is only about one third as long.

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Human vs. Sheep Brain (ctd.)

• The pineal gland is responsible for controlling
  reproduction and circadian rhythms
• Larger in the sheeps brain when compared to the
  human brain, that has less basic instinctual
  behavior controls.
• Human hind brain positioning
• Different from the sheep because of the humans
  erect position.

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