Chapter 3

• Functions of the Nervous System

  1. INPUT: Receive information from our senses

  2. PROCESSING: Integrate that information with past experiences

  3. OUTPUT: Guide our actions
• Neuron


  A nervous system cell (nerve cell) that sends and receives electrochemical signals
• Glial cell


  A nervous system cell that supports, nourishes, and insulates neurons
• Neuron


  • Sends and receives electrochemical signals
• Glial cell


  • Supports, nourishes, and insulates neurons
• The Structure of the Neuron

  1. Dendrites: Fibers that receive signals from other neurons

  2. Soma / cell body: Receives incoming signals from dendrites and passes signals on

  3. Axon: A fiber that extends from the soma and carries signals away from the soma

  4. Myelin Sheath: Covers the axon and increases the speed of the signals (120 meters / second!)

  5. Terminal Buttons: Form junctions with other neurons and release chemical signals
• Glial cells


  • Oligodendrocyte (CNS): Created the myelin sheath around the axon; speeds up the propagation of the action potential
  • Schwann cell (PNS)
  • Astrocytes: Help form the immune system of the brain – fight infections and clean up debris. Have been implicated in neurodegenerative diseases
  • Microglia
• Synapse


  The point of connection between: Two neurons, A neuron and a muscle or gland
• Elements of a synapse


  • Presynaptic membrane /neuron
  • Postsynaptic membrane / neuron
  • Synaptic cleft
• Electrochemical signal


  • Action potential: The electrical signal that moves from the cell body down the axon to the terminal buttons
  • Neurotransmitters: The chemical signal that crosses the synapse
• Action Potential


  1. Resting Potential

  2. Depolarization

  3. Repolarization

  4. Back to Resting Potential
• Resting Potential


  The neuron at resting potential has a negative charge (-70 mV)
• Depolarization


  If the charge reaches the threshold of excitation, the neuron will become positively charged
• Repolarization


  At the peak of the spike, other ion channels open and positively charged ions leave the neuron
• The action potential signal is a fixed size and a fixed duration
• All-or-nothing law


  The action potential signal is a fixed size
• Information is encoded in the frequency of action potentials and the number of neurons firing
• Summary of Action Potential

  1. The neuron at resting potential has a negative charge (-70 mV)

  2. A chemical signal arrives causing the ion channels on the dendrite's neuronal membrane to open

  3. 3a. Positively charged ions enter the neuron

  4. 3b. If that charge reaches the threshold of excitation, the neuron will become positively charged (Depolarization)

  5. 3c. At the peak of the spike, other ion channels open and positively charged ions leave the neuron (Repolarization)

  6. The initial imbalance of ions (Step 3) causes the action potential to spread down the cell body and axon
• Neurotransmitters and receptors


  Similar to a key fitting into a lock
• Excitatory


  Causes Action Potential
• Inhibitory


  Does NOT cause Action Potential
• Receiving neuron fires if excitatory > inhibitory
• Summary of Chemical Message

  1. An action potential travels down the axon

  2. The action potential triggers the release of neurotransmitters

  3. Neurotransmitters are released from the terminal button into the synapse

  4. Neurotransmitters bind to their respective receptor. Part of the process causes channels to open, producing an influx of either positively charged ions (influencing an action potential) or negatively charged ions (influencing no action potential)

  5. Neurotransmitters release from receptors after binding

  6. Neurotransmitters go through a reuptake process, where they are recycled
• Nervous System


  • Brain
  • Spinal Cord
  • Somatic Nervous System (SNS) (Voluntary)
  • Autonomic Nervous System (ANS) (Involuntary)
  • Parasympathetic Nervous System
  • Sympathetic Nervous System ("fight-or-flight")
  • Peripheral Nervous System (PNS)
  • Central Nervous System (CNS)
• Somatic Nervous System (SNS)

  • Consists of sensory neurons and motor neurons
  • Carries nerve impulses back and forth between the CNS and the skeletal muscles, skin, and sensory organs
  • Responsible for voluntary muscle movements and receiving and processing sensory information
• Autonomic Nervous System (ANS)


  • Responsible for involuntary tasks (e.g., heart rate, digestion, and breathing)
  • Operates on its own without conscious effort
  • Two subsystems: Sympathetic ("fight-or-flight"), Parasympathetic ("rest-and-digest")
• Functions of the Autonomic Nervous System

  • Sympathetic: Increases heart beat, Increase respiration, Stimulates release of glucose, Inhibits activity of intestines
  • Parasympathetic: Slows heart beat, Decreases respiration, Inhibits release of glucose, Stimulates activity of intestines
• Lobes of the Cerebral Cortex

  • Frontal Lobe
  • Parietal Lobe
  • Occipital Lobe
  • Temporal Lobe
• Frontal Lobe


  • Executive functions: Thinking, motivation, planning, impulse control, & emotional responses
  • Regulate behaviour and thought
• Damage to the frontal lobe can cause changes in motivation, creativity, self-awareness, reasoning and suitable emotional behaviour (Case study: Phineas Gage)
• Motor cortex


  • Initiates all voluntary movement
  • Motor cortex in each hemisphere controls movements on the opposite side of the body
• Broca's area


  • Located in lower left frontal lobe
  • Speech formation
  • Damage causes difficulty producing language, not understanding it (Broca's aphasia)
• Parietal Lobe


  • Interpret bodily sensations: Pressure, pain, touch, temperature, location of body parts
  • Space, time and numbers
• Somatosensory cortex


  • Thin band of cortex on front of parietal lobe
  • Receives information about touch and other skin and visceral (internal organs) senses
• Parts of our body are represented in certain parts of the motor cortex and somatosensory cortex
• The density of motor receptors in the body part indicates the degree of movement precision
• Temporal Lobe


  • Responsible for hearing and language comprehension
  • Auditory cortex processes sound
  • Processes incoming sensory information and sends it to the parietal and frontal lobes
• Wernicke's area


  • Located on the left
  • Language comprehension and producing coherent language
• Occipital Lobe


  • Responsible primarily for vision and visual perception
  • Damage can produce blindness
• The eyes and neural connection to the brain may be perfectly functional even with occipital lobe damage