Nervous System

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Nervous System

• Anatomy and Physiology

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What are the major functions of the nervous
system?

• The master controlling and communicating system
  of the body
• Functions
• Sensory input monitoring stimuli occurring
  inside and outside the body
• Integration interpretation of sensory input
• Motor output response to stimuli by activating
  effector organs

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How is the nervous system organized?

• Central nervous system (CNS)
• Brain and spinal cord
• Integration and command center
• Peripheral nervous system (PNS)
• Paired spinal and cranial nerves
• Carries messages to and from the spinal cord and
  brain

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What are the divisions of the peripheral nervous
system?

• Sensory (afferent) division
• Sensory afferent fibers carry impulses from
  skin, skeletal muscles, and joints to the brain
• Visceral afferent fibers transmit impulses from
  visceral organs to the brain
• Motor (efferent) division
• Transmits impulses from the CNS to effector organs

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What are the parts of the motor division?

• Somatic nervous system
• Conscious control of skeletal muscles
• Autonomic nervous system (ANS)
• Regulate smooth muscle, cardiac muscle, and
  glands
• Divisions sympathetic and parasympathetic

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What are the functions of the sympathetic and
parasympathetic divisions?

• Parasympathetic- resting and digesting system
• Most active in nonstressful situations
• Keeps energy use low and maintains vital
  housekeeping activities running.
• Sympathetic division- fight or flight division
• Exercise, excitement, emergency, and
  embarrassment division
• Prepares the body for action

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What types of supporting cellsmake up central
nervous tissue?

• Known as neuroglia or glial cells
• Astrocytes-star shaped cells that connect neurons
  together and to their blood supply.
• Microglia- function as phagocytes by engulfing
  foreign invaders.
• Ependymal- (epithelial-like) provide a barrier
  between brain and spinal fluid.
• Oligodendrocytes- connect thick neuronal fibers
  and produce an important insulating material
  called the myelin sheath.

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What are neurons?

• Conduct messages in the form of nerve impulses
• They number in the billions (much higher in
  anatomy teachers)
• Have extreme longevity
• Most cannot divide (hippocampus is a rare
  exception it is involved in memory).
• Have a high metabolic rate require mucho oxygen
  and glucose
• 3 basic regions dendrites, cell body, and axons
• Impulses travel from dendrites to cell body to
  axons

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How is a nerve impulse transmitted across a
neuron?

• The sodium-potassium pump creates a resting
  potential across the membrane of a neuron.
• When a threshold stimulus is applied to the
  neuron, an action potential travels down the
  neuron. (action potentialnerve impulse)
• The nerve impulse will jump from the axon to the
  dendrite of another neuron across a synapse by
  the use of neurotransmitters

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What is the all-or-none phenomenon?

• An action potential either happens completely or
  not at all.
• Many sub-threshold stimuli can cause an action
  potential. Neurons can have different thresholds
  (pain)
• It is similar to the flash point of a burning
  twig. As a match is placed under a twig, the twig
  must get hot enough to produce a flame on the
  twig.

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What is saltatory conduction?

• Myelin sheath found on the axon insulates and
  doesnt allow the depolarization of the membrane.
  
• The action potential must jump from one node of
  Ranvier to the next. This makes the action
  potential move faster down the axon.
• Some can reach speeds of 100 m/s.
• Unmyelinated neurons propagate slow action
  potentials that must move from one site to the
  next. This is called continuous conduction.

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Saltatory conduction
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What is a synapse?

• Synapses are gaps between neurons
• Exists between the axon of one neuron and the
  dendrite of another.
• Neurons can have a large number connecting to
  numerous other neurons. (This accounts for the
  complexity of the nervous system)
• When an action potential reaches the end of an
  axon, neurotransmitters are stimulated to flood
  the gap and bond to ion channels on the post
  synaptic neuron.
• This causes an action potential to be produced.

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Vesicles with neurotransmitters
Synapse
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Page 409
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What are neurotransmitters?

• Molecules that bridge the synapse
• Over 50 different types have been discovered
• Some can be excitatory or inhibitory
• See page 416-417 for types

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What are reflexes?

• Rapid, automatic responses to stimuli, in which a
  particular stimulus always causes the same motor
  response.
• Produces the simplest behaviors. Ex. Removing
  hand from a hot object.
• Occur over neural pathways called reflex arcs.
• 5 basic components receptor, sensory neuron,
  integration center, motor neuron, and effector.

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What are the major parts of the brain?

• Cerebral hemispheres, diencephalon, Brain stem,
  and cerebellum
• Cerebrum and cerebellum have a gray matter nuclei
  surrounded by white matter and a gray matter
  cortex.
• Gray matter- unmyelinated neurons
• White matter- myelinated neurons

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What are the functions of the cerebral cortex?

• Interprets sensory impulses (including
  auditory,visual, and olfactory), controls
  voluntary and skilled skeletal muscle, functions
  in intellectual and emotional processing.
• Shows lateralization of function
• Most people the left hemisphere is dominant and
  is specialized for language and mathematical
  skills
• The right hemisphere is more concerned with
  visual-spatial skills and creative endeavors.
• Right hemisphere controls the left side of the
  body (motor control) and vice versa.

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See page 436
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What are the functions of the diencephalon?

• Consists of the thalamus, hypothalamus and
  epithalamus and encloses the third ventricle.
• Thalamus-Relay station for sensory and motor
  impulses to and from the cerebrum. Functions in
  memory.
• Hypothalamus-Regulates hormonal output of the
  pituitary gland, regulates body temp., food
  intake, water balance, thirst, and biological
  rhythms and drives. (limbic system)
• Limbic System- functional system involving
  cerebral structures and the diencephalon that
  mediates emotional responses and is also involved
  in memory.

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What are the parts and functions of the brain
stem?

• Medulla oblongata- respiratory rhythm, heart
  rate, and blood pressure
• Pons- regulation of respiration
• Midbrain- visual and auditory reflex centers and
  fear response

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What is the function of the cerebellum?

• Cerebellum processes and interprets impulses from
  the motor cortex making movements smooth and well
  timed. (coordination)

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What protects the brain?

• The brain is protected by bone, meninges,
  cerebrospinal fluid, and the blood-brain barrier.
• Meninges have 3 layers
• Dura mater- tough layer of fibrous connective
  tissue
• Arachnoid mater- filled with large blood vessels
  and CSF
• Pia mater- delicate connective tissue with
  capillaries
• Blood-brain barrier- keep blood products separate
  from neurons. Formed from tight capillary walls
  and ependymal cells that form a tight membrane
  around capillaries.
• CSF- liquid cushion produced by the choroid
  plexus and fills the cranial cavity.

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Blood-brain barrier
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What is the spinal cord?

• Two-way impulse conduction pathway and a reflex
  center.
• Lies within the vertebral column
• Protected by meninges and CSF
• 31 pairs of spinal nerve roots extend from the
  cord.

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