Learning Outcomes

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Learning Outcomes

• To describe the major components of the Central,
  Peripheral and Autonomic Nervous systems.
• To understand the functions of these components.
• To explain how a nervous impulse is transmitted.
• To explain the underlying physiology behind the
  lesions/damage that occurs in the nervous system.

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Spinal cord structure
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Spinal cord has two main functions 1). SC
connects a large part of the peripheral nervous
system to the brain. 2) SC acts as a minor
coordinating centre responsible for some simple
reflexes (e.g withdrawal reflex). 31 pairs of
spinal nerves arise along the spinal cord
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• Extension of brain stem
• Long slender cylinder of nerve tissue (45 cm
  long, 2cm diameter).
• Enclosed by a protective vertebral column
  (vertebrae).
• Paired spinal nerves emerge from spinal cord.
• Spinal nerves named according to region of
  vertebral column from which they emerge.

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Peripheral Nervous System

• 31 pairs of Spinal nerves
• 12 pairs of Cranial nerves
• Autonomic Nervous System

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• 8 pairs Cranial Nerves
• 12 pairs Thoracic Nerves
• 5 pairs Lumbar Nerves
• 5 pairs Sacral Nerves
• 1 Pair Coccygeal Nerves

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• During development, vertebral column grows 25cm
  longer than SC.
• Nerves pass down SC and exit at particular points
  from the vertebral column.
• At the lower end of vertebral column is a thick
  bundle of elongated nerve roots called Cauda
  Equina (horses tail).
• At this region Spinal Taps
• can be taken (collection of CSF).
• No SC, so no damage caused.

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• A cross section of the SC shows it is composed of
  grey matter in the centre surrounded by white
  matter.

Dorsal horn
Grey matter
White matter
Ventral horn
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• Grey Matter.
• resembles the letter H (butterfly)
• consists of mixture of multipolar neurone cell
  bodies (colour)
• consists of 2 prominent projections
• Posterior Dorsal Horn
• Anterior Ventral Horn

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• Dorsal Horn
• Groups of afferent fibres carrying impulses from
  peripheral sensory receptors enter through the
  dorsal root into here.
• Ventral Horn
• Nerve fibres exit from here through ventral roots
  to skeletal muscles.
• Dorsal and ventral roots are very short and
• fuse to form the spinal nerves.

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• Poliomyelitis
• polio grey matter
• myelitis inflammation of SC
• Polio virus enters through faeces contaminated
  water.
• Polio virus causes destruction of anterior
  ventral horn motor neurones.
• Muscles atrophy due to wasting (astronauts)
• Death by paralysis of respiratory or cardiac
  muscle
• Salk and Sabin polio vaccines eliminated disease.

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White Matter - Composed of myelinated and
unmyelinated nerve fibres. - Divided into
Posterior funiculi
Lateral funiculi
Anterior funiculi
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Spinal Cord Segments
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• Spinal tracts are bundles of axons grouped
  together into columns that extend length of the
  spinal cord
• A spinal tract consist of neuronal axons that
  have a similar destination and function
• Part of a multineurone pathway that connect the
  brain to the rest of the body
• Each tract either
• - begins with a particular part of the brain
• (Motor / descending tract)
• - ends with a particular part of the brain
• (Sensory /ascending tract)
• Tracts are named according to their origin and
  point of termination.

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The Brain
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• The brain is organised into several different
  regions dependent upon function, anatomy and
  development.
• 1). Brain stem
• - Midbrain
• - Pons
• - Medulla
• 2). Cerebellum
• 3). Forebrain
• Although specific activity is attributed to
  particular regions, complex interplay between
  regions exists.

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• A majority of the brain which we recognise is the
  Cerebrum (outer wrinkly part).
• Deep folds divide each half of the Cerebrum into
  4 major lobes.
• - Occipital lobes process visual input
• - Temporal lobes process sound
• - Parietal lobes receive and process
  somesthetic sensations (touch, pressure,
  heat, cold, pain) and proprioception
  (awareness of body position)
• - Frontal lobes 3 functions
• voluntary motor activity,
  speaking ability, thought

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• Cerebral Hemispheres (Cerebrum).
• Largest part of the brain
• Account for about 80 of brain weight.
• Divided into 2 halves
• - Right cerebral hemisphere
• - Left cerebral hemispheres.
• They are connected together by the Corpus
  Callosum.
• This is a thick band of neuronal axons
  transversing between the 2 hemispheres.

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• The entire surface of the cerebral hemispheres
  are marked by elevated ridges of tissue called
  Gyri.
• These are separated by shallow grooves called
  sulci.
• The deepest of these grooves are called fissures.
• The median longitudinal fissure separates the
  cerebral hemispheres from one another.
• The transverse fissure separates the cerebral
  hemispheres from the cerebellum below it.

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Parts of the Brain

• Cerebrum
• Thalamus
• Hypothalamus
• Cerebellum
• Midbrain
• Pons
• Medulla Oblongata

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• Cerebral lobes and their function
• Frontal - voluntary motor activity
• - speech
• - thought
• Temporal - process sound
• Occipital - process visual input
• Parietal - process somesthetic sensations
  (touch, pressure, heat, cold
• - proprioception awareness of body
  position

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www.smc.edu
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The Brain

• Cerebral cortex cognition, senses, movement
• Cerebellum coordination of muscle contraction
• Thalamus relay center
• Hypothalamus homeostasis
• Limbic System instincts, emotions
• Brain Stem medulla controls breathing, blood
  pressure, heart rate

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Parts of the Brain
Cerebrum
Thalamus
Hypothalamus
Midbrain
Pons
Cerebellum
Medulla Oblongata
Tortora, G. J. and Grabowski, S. (2000)
Principles of Anatomy and Physiology
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The Cerebrum
www.smc.edu
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www.smc.edu
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The Spinal Cord

• Spinal cord has two main functions
• 1). SC connects a large part of the peripheral
  nervous system to the brain.
• 2) SC acts as a minor coordinating centre
  responsible for some simple reflexes (e.g
  withdrawal reflex).
• 31 pairs of spinal nerves arise along the spinal
  cord

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Peripheral Nervous System

• 31 pairs of Spinal nerves
• Join together to form Plexuses
• 12 pairs of Cranial nerves
• Autonomic Nervous System

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Lesions/Damage to the Nervous System
  Any localised damage to spinal cord or spinal
roots will attribute to some form of functional
loss. - Paralysis (loss of motor
function) - Parasthesias (loss of
senses)   The effects of disease or injury upon
the CNS and periphery depend on the -
severity of the damage - type of neurones
involved - position of neurones involved
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• Normal muscle function requires intact
  connections along motor pathway.
• Chain of nerve cells that runs from the brain
  through the spinal cord out to the muscle is
  called the motor pathway.
• Damage at any point reduces brain's ability to
  control muscle's movements.
• Reduced efficiency causes weakness (paresis).

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• Complete loss of communication prevents any
  willed movement.
• Lack of control is called paralysis.
• Paralysis may affect an individual muscle, but
  usually affects an entire body region.
• Distribution of weakness an important clue to
  location of the nerve damage that is causing the
  paralysis.
• Words describing the distribution of paralysis
  use the suffix "-plegia," from the Greek word for
  "stroke.

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• The types of paralysis are classified by region
• Monoplegia affecting only one limb
• Diplegia affecting the same body region on
  both sides of the body (both arms, for
  example, or both sides of the face)
• Hemiplegia affecting one side of the body
• Paraplegia affecting both legs and the trunk
• Quadriplegia affecting all four limbs and the
  trunk.

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• The nerve damage that causes paralysis may be in
  the
• - brain or spinal cord (CNS)
• - nerves outside the spinal cord (PNS).
• The most common causes of damage to the brain
  are
• - Stroke
• - Tumour
• - Trauma (caused by a fall or a blow)
• - Multiple sclerosis (destruction of Myelin
  sheath))
• - Cerebral palsy (defect or injury to the brain
  that occurs at or shortly after birth)
• - Metabolic disorder (interferes with body's
  ability to maintain itself).

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• Damage to spinal cord is most often caused by
  trauma, (fall/car crash). Other conditions that
  may damage nerves within or immediately adjacent
  to spine include
• - Tumour
• - Herniated disk (also called a ruptured or
  slipped disk)
• - Spondylosis (a disease that causes stiffness
  in the joints of the spine)
• - Rheumatoid arthritis of the spine
• - Neurodegenerative disease (a disease that
  damages nerve cells)
• - Multiple sclerosis.

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• Paralysis originating in the brain may sometimes
  be flaccid, that is, the affected muscles may be
  loose, weak, flabby, and without normal reflexes.
• More frequently it is spastic, that is, the
  affected muscles are rigid and the reflexes
  accentuated.
• Paralysis originating in a motor nerve (UMN) of
  the spinal cord is always spastic
• Paralysis originating in peripheral nerves (LMN)
  is always flaccid.

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• Cerebrovascular Accident (Stroke)
• CVAs are bleeds into the brain
• obstruction of blood supply to brain
• CVAs often affect Motor cortex and its major
  pathways.
• These tracts cross in medulla therefore
• - left hemiplegia (stroke on right side of
  brain)
• - right hemiplegia (stroke on left side of
  brain)
• Small bleeds close to brain surface may result in
  weakness on one side (hemiparesis)
• - good chance of recovery
• Larger/deeper bleeds may cause profound paralysis
• - may result in permanent damage

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• Pupillary Reflex
• Clinical test for brain stem function
• Shine bright light into patients eye
• Normal response pupils constrict in response to
  light stimulus
• Reflex via autonomic nervous system
• Sensory input of bright light- to brain via optic
  nerve (II) parasympathetic impulses out via
  oculomotor nerve (III) circular muscles of eye
  constrict
• Pupil observation important when considering head
  injury care

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• Plantar (sole) reflex
• Tests integrity of spinal cord from L4-S2
• Determines functionality of corticospinal tracts
• Normal response is a downward flexion (curling)
  of toes
• If corticospinal tract damaged, normal plantars
  reflex replaced by Babinskis sign
• Toes fan backwards

Normal
Abnormal