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HBS Unit 2 Review Sheet


Covered in this Review Sheet:

            1. Brain Lobes & Structures
            2. Neurons
            3. Resting Membrane Potential
            4. Action Potential
            5. Synaptic Transmission
            6. Petallar Reflex
            7. Blood Sugar Feedback
            8. Anatomy of the Eye
            9. Common Eye Disorders


Forebrain Structures - (Activity 2.1.2 - Build a Brain)

Frontal Lobe


      1. Personality
      2. Planning
      3. Critical Thinking
      4. Emotion
      5. Inhibition
      6. Motor
      7. Speech Production

Key Structures:

      1. Primary Motor Cortex (pre-central gyrus)
      2. Prefrontal Cortex
      3. Broca’s Area

Parietal Lobe


      1. Sensations from the body
      2. Integration of sensory information

Key Structures:

  1. Primary Somatosensory Cortex (post-central gyrus)

Temporal Lobe


      1. Memory
      2. Emotional Associations
      3. Speech Comprehension

Key Structures:

  1. Hippocampus
  2. Amygdala
  3. Wernicke’s Area

Occipital Lobe


      1. Visual Processing
        1. Color
        2. Depth Perception
        3. Motion
        4. Object Recognition

Key Structures:

      1. Visual Cortex
Rotating brain with brain lobes color coded.
 Author: Database Center for Life Science(DBCLS) | Source: WikiCommons | License: (CC BY-SA 2.1 JP

Hindbrain Structures - (Activity 2.1.2 - Build a Brain)




      1. Muscle memory
      2. Coordination
      3. Balance
      4. Gait
      5. Precision


Key Structures:

      1. Arbor Vitae

Medulla Oblongata


      1. Autonomous Life Functions
        1. Heart Rate
        2. Blood Pressure
        3. Respiration Rate
        4. Vomiting



      1. ‘Bridge’ brain/spinal cord
 Author: OpenStax | License: CC BY 4.0



Neurons - (Activity 2.2.1 - The Neuron)

Structures & Functions

Dendrite –
Receives neurotransmitter from the axon terminal of another neuron.

Soma – The cell body of the cell. Contains cell organelles including the nucleus.

Axon hillock – Structure that join the soma and axon. Site of origination for the action potential.

Axon – Long extension of the cell body that sends the electrical signal to the axon terminal.

Nodes of Ranvier – Contains voltage-gated ion channels. Facilitates the transmission of the action potential.

Myelin Sheath – Produced by the myelin sheath, the myelin sheath is the fatty tissue that insulates part of the axon. Facilitates saltatory conduction

Axon Terminal – End of the axon that contains neurotransmitters than can be released into the synapse.

Synapse – The space between the axon terminal of a pre-synaptic neuron and the dendrite of a post-synaptic neuron.


 Author: OpenStax | License: CC BY 4.0



Types of Neurons - (Activity 2.2.1 - The Neuron)

Motor Neurons


    1. Dendrities and soma in the ventral horn.
    2. Axons leave through the ventral horn.
    3. Synapse onto a muscle fiber.


Function: Send motor information to the muscle (efferent). 

Sensory Neurons


      1. Dendrities in the skin/muscle.
      2. Axons extend into the spinal cord via the dorsal root
      3. Soma in the dorsal root ganglion.
      4. Synapse onto motor and inter- neurons.

Send peripheral sensory information to the spinal cord (afferent). 


Interneurons exist entirely in the gray matter of the spinal cord. 

Sends mostly inhibitory signals. 



Resting Membrane Potential - (Activity 2.2.2 - The Secret to Signals)

The resting membrane potential ‘sets the stage’ for a neuron to send an action potential.

Importance: A voltage potential is an essential prerequisite for neuronal communication. 

Maintenance: The Na+/K+ ATPase helps to pump Na+ ions out of the cell and K+ ion into the cell. This establishes the concentration gradient. Since there is more K+ inside the cell, they will leave the cells through K+ leak channels that slowly allow K+ to flow out from the cell.


The resting membrane potential is the voltage created at the membrane via the separation of ions inside and outside the cell. In most neurons the resting membrane potential is around -70mV. This means that the inside of the cell is more negative relative to outside of the cell.



Action Potential - (Activity 2.2.2 - The Secret to Signals)


  1. Neurotransmitters bind ligand-gated Na+ channels on the dendrites of a post synaptic neuron. This causes the channels to open and positively charged Na+ ions begin to enter the cell. As a result, the voltage inside the cell begins to increase.

  2. Once enough Na+ has entered the cell to raise the membrane voltage to the threshold voltage (-55mV), voltage-gated Na+ channels at the axon hillock open. The opening of these Na+ channels cause a massive influx of positively charged Na+ ions which depolarize the neuron to a positive voltage.

  3.  At this point, the cell is in an absolute refractory period where voltage-gated Na+ channels are temporarily inactivated. The voltage-gated K+ channels are open and begin to let positively charged K+ ions out of the neuron; thus dropping the voltage down.

  4. However, the voltage-gated K+ channels are open long enough to let out so much K+ that the potential drops below -70mV and the neuron is in a state of hyperpolarization.

  5.  Voltage-gated Kchannels close, allowing the membrane potential to be restored via inward-rectifying Kchannels.


Waveform of an action potential.
 Author: OpenStax | License: CC BY 4.0


      1. Depolarization impulses enter the synaptic terminal/button via the axon of the presynatic neuron.

      2. As a result, voltage-gated Ca2+ channels open and allow Ca2+ to enter the cell.

      3. Calcium in the presynaptic terminal causes neurotransmitters to bind to the membrane and release neurotransmitter into the synaptic cleft; a process called exocytosis

      4. Neurotransmitter in the synaptic cleft binds ligand-gated ion channels on the postsynaptic cell.

      5. Ligand-gated ion channels on the postsynatic cell open to allow ions into the cell. This can cause depolarization of the postsynaptic cell.

Diagram of the chemical synapse and synaptic transmission.
 Author: OpenStax | License: CC BY 4.0



Patella Reflex Arc - (Activity 2.2.3 - It's All in the Reflexes)



    1. The patellar tendon is hit with the reflex hammer.
    2. Sensory stretch receptors in the muscle fiber sends sensory information to the spinal cord.
    3. That sensory information enters the spinal cord via the dorsal root and synapses on an interneuron and a motor neuron in the ventral horn.


        • The motor neuron then sends motor information away from the spinal cord via the ventral root.
        • The motor neuron send a signal to the quadriceps muscle fiber to contract.
        • The interneuron prevents a separate motor neuron from allowing the hamstring to contract.


    4. Taken together, the quadriceps muscles contracts and the hamstring stays relaxed. As a result, the lower leg is becomes extended.



Title: Patellar Reflex Arc | Author: Backyard Brains | License: CC BY-SA 3.0



Hormones & Blood Sugar Regulation - (Activity 2.3.1 - Hormones Connection)

Diagram of the pancreas with the anatomical structure labelled.
 Author: OpenStax | License: CC BY 4.0

Pancreas Functions

Digestive System → secretes enzymes into the small intestine
Endocrine System → secrete hormones to regulate blood sugar

The alpha cells produces the hormone glucagon attempting to raise blood sugar levels when they fall too low.

The beta cells produces the hormone insulin. Insulin promotes the uptake of glucose by cells and the storage of glucose by the liver.

Hyperglycemia Feedback 

      1. After eating a carbohydrate-dense meal, blood sugar  becomes elevated.
      2. Elevated blood sugar stimulates beta-cells in the pancreas to secrete insulin into the blood stream.
      3. Insulin helps the body lower blood sugar through a couple of ways:

→ Insulin interacts with insulin receptors on cells. This causes glucose transporters to become expressed on the cell membrane and glucose can now enter the cell via the transporters.
→ Insulin causes the liver to remove glucose from the blood and store it as glycogen

Hypoglycemia Feedback


      1. If you haven’t eaten in a while, your blood sugar will begin to drop.
      2. The drop in blood sugar stimulates alpha cells of the pancreas to secrete glucagon into the blood.
      3.  Glucagon helps the body raise blood sugar in a couple of ways:

→ Inhibiting cells from absorbing glucose from the blood.
→ Stimulating the liver to breakdown glycogen into glucose.




Anatomy of the Eye - (Activity 2.4.1 - Exploring the Anatomy of the Eye)

Labelled eye diagram.

Title: Diagram of the Human Eye | Author: Rhcastilhos & Jmarchn. | License: CC BY-SA 3.0

Structure & Function

Cornea –
Tough and transparent tissue that covers the anterior eye. It protects the anterior eye and refracts light as it enters.

Aqueous Humor – Provides nutrition to the cells of the anterior eye and regulated intraocular pressure that maintains the shape of the eye.

Iris – Circular muscles that contracts or dilates to change the size of the pupil.

Pupil – Hole in the anterior eye that allows for light to enter.

Lens – Posterior to the pupil/iris the lens refracts light and focuses it onto the retina.

Vitreous – Transparent, gelatinous substance in the posterior eye that helps maintain eye shape.

Retina – Light procressing structure that contains photoreceptors and neurons that send light information to the brain.

Choroid – Epithelial tissue layers that provides nutrients to the retina and filters excess light.

Optic Disk – Location where the optic nerve exits the eye. Also our blind spot, since there are no photoreceptors/retina.

Optic Nerve –  Axons from the neurons of the retina that send light information to the brain.

Tapetum – Not present in humans. This shiny blue structure is located in the back of eye and shines light back onto the retina. Aids vision at times of limited light.



Common Eye Disorders - (Activity 2.4.2 - Visual Perception)


Nearsightedness. Can clearly see objects near; distant objects are blurry.

Causes: (i) Eye too long (ii) Lens too strong

 Focus: Before the retina.

Correction: Divergent lens.


Farsightedness. Can clearly see distant objects; near objects are blurry.

Causes: (i) Eye too short (ii) Lens too weak

Focus: After the retina.

Correction: Convergent lens.

Light diagram for an eye that has myopia.
 Author: OpenStax | License: CC BY 4.0
Light diagram for an eye that has hyperopia.
 Author: OpenStax | License: CC BY 4.0
  1. Clark MA, Douglas M, Choi J. “35.2 How Neurons Communicate.” Biology 2eOpenStax, License: CC BY 4.0 License Terms: Edited & Adapted | Access for free at
  2. Clark, MA, Douglas M, Choi J. “Neurons and Glial Cells.” OpenStax, 28 Mar. 2018, CC BY 4.0 License Terms: Edited & Adapted | Access for free at
  3. Young, KA., Wise, JA., DeSaix, P., Kruse, DH., Poe, B., Johnson, E., Johnson, JE., Korol, O., Betts, JG., & Womble, M. “File:1225 Chemical Synapse.jpg” Wikimedia Commons, License: CC BY 4.0
  4. Backyard Brains. “Patellar Reflex_web.jpg” Backyard Brains, License: CC BY-SA 3.0 License Terms: No edits were made.
  5. Betts, JG, Young KA, Wise JA, Johnson E, Poe B, Kruse DH, Korol O, Johnson JE, Womble M, DeSaix P. “The Endocrine Pancreas.” Anatomy & Physiology. OpenStax, 2013. License: CC BY 4.0 License Terms: Edited & Adapted | Access for free at
  6. Rhcastilhos, Jmarchn. “File:Schematic diagram of the human eye en.svg” Wikimedia Commons, License: CC BY-SA 3.0
  7. Urone PP, Hinrichs R. ‘26.2 Vision Correction.’ College Physics. OpenStax. 21 June 2012. CC BY 4.0 License Terms: Edited & Adapted |