Nervous System

• Neurons are cells of the nervous system
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  • Sensory neurons carry impulses from senses to spinal cord and brain
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  • Cell body contains the nucleus and most of cytoplasm
• Nerve impulse depends on movement of cations across the cell membrane
• Resting Potential is the difference in electrical charge across the cell membrane of a resting neuron, created by the concentration of sodium and potassium ions
• Action potential is the reversal of charges across the cell membrane as sodium and potassium ions travel across it
• Threshold is the minimum stimulus required to activate a nerve impulse
• Synapse is the gap between axon terminals and the next cell
• Neurotransmitters are chemicals used to transport the impulse across the synaptic gap
• Central Nervous System relays messages, processes info, and analyzes info
• Parts of the CNS:

  • Brain
  • Spinal cord
• Meninges are three layers of connective tissue that surround the CNS and provide protection
• Cerebrospinal Fluid bathes the brain and spinal cord, protecting them
• Cerebrum is responsible for voluntary movements and divided into 2 hemispheres by the corpus callosum

  • Right hemisphere is creative/artistic; left hemisphere is analytical/logical/mathematical
  • Hemispheres are divided into 4 lobes: frontal, parietal, temporal, occipital
• Cerebellum coordinates and balances muscle action
• Brain Stem connects brain and spinal cord, contains the pons and medulla oblongata, and controls blood pressure, heart rate, breathing, and swallowing
• Thalamus is found between brainstem and cerebrum, receiving messages from sense organs and sending them to the appropriate part of the cerebrum
• Hypothalamus is found just below the thalamus, controlling hunger, thirst, fatigue, anger, and body temp
• 31 pairs of spinal nerves originate in the spinal cord

  • Reflexes are processed here
• Peripheral Nervous System receives info from the environment and relays commands from the CNS to organs and glands
• Parts of the PNS: cranial nerves, spinal nerves, and ganglia (bundles of cell bodies)
• • Hypoglossal Nerve: motor nerve to tongue
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  • Olfactory Nerve: sensory nerve for smell
• Two divisions of PNS: sensory and motor
• Sensory Division transmits impulses from sense organs to the CNS
• Motor Division has somatic and autonomic divisions

  • Somatic Nervous System regulates voluntary activities and some reflexes
  • Autonomic Nervous System regulates involuntary activities such as heartbeat
  • Two Divisions: sympathetic and parasympathetic with opposite effects on the same organ system
• Sensory receptors are neurons reacting to stimuli and concentrated in sense organs
• Five categories of sensory receptors:

  • Pain receptors located throughout the body except the brain
  • Thermoreceptors located in skin, hypothalamus, and body core, detecting variations in body temp
  • Mechanoreceptors located in skin, skeletal muscles, and inner ears, sensitive to touch, pressure, stretching of muscles, sound, and motion
  • Chemoreceptors located in nose and taste buds, sensitive to chemicals in the environment
  • Photoreceptors located in eyes, sensitive to light
• Vision:

  • Retina is the innermost layer of the eye
  • Rods detect low levels of light
  • Cones detect colors
  • Optic nerve carries impulses from the eye to the brain for interpretation
• Hearing and Balance:

  • Vibrations cause tiny hair cells in the cochlea of the inner ear to move, creating nerve impulses transferred to the cochlear nerve and then the brain
  • Semicircular canals monitor the position of your head in relation to gravity and help maintain equilibrium
• Smell and Taste:

  • Sense of smell detects chemicals
  • Taste buds on the tongue detect salty, sweet, sour, and bitter tastes
• Touch:

  • Skin is the largest sense organ
  • Greatest density of touch receptors are in the fingers, toes, and face
• What kind of neurotransmitter sends a message?

  Excitatory
• What kind of neurotransmitter does not send a message?

  Inhibitory
• What is a type of inhibitory neurotransmitter?

  GABA
• What is a type of excitatory neurotransmitter?

  Acetylcholine
• What is the resting potential?


  -70mV
• What is the threshold?

  -55mV
• Pain receptors are located where?

  Throughout the body except in brain
• Where are thermoreceptors located?

  Skin, hypothalamus, and body core