Glial cells, nerves, action potentials, synapses, and reflexes quiz

What are the three main functions of the nervous system?

1. Sensory input from receptors (afferent nerves)

• Congenital insensitivity to pain (CIPA) → someone is born without pain receptors (doesn’t feel pain)

2. Integration

3. Motor output to effector cells (efferent neurons)

What are neurons?

Nerve cells, conduct nerve impulses, have cell bodies, dendrites, axons

• Sensory, interneurons, motor

What are all neurons?

• Excitable

• Conductivity

• Highly specialized

• DON’T DIVIDE INTO AN ADULT

What are glial cells?

Connective tissue in CNS

• NOT excitable

Astrocytes

• Form tight junctions between cell lining brain capillaries (blood-brain barrier)

Oligodendrocytes

• Make myelin sheaths in CNS

Satellite cells

What are the three types of structural neurons?

Unipolar, bipolar, multipolar

What is a unipolar neuron?

Found in ganglia outside of brain and spinal cord

• Ganglia: mass of neuron cell bodies, usually outside the CNS

• Dendrites and axons are continuous

What is a bipolar neuron?

Rare, specialized parts of eye, nose, and ears

What is a multipolar neuron?

• Common in brain and spinal cord

• 2 or more dendrites and a single axon

What is the difference between a dendrite and axon?

• Dendrites

  • Receive info

  • Highly branched

  • Provide receptor surfaces

  • 80%-90% of total surface area

  • Transmits towards cell body

• Axons

  • Arises from cell body

    • Axonal hillock

  • Conducts impulses away from cell body

  • Has mitochondria, microtubules, neurofibrils

  • It is a long cytoplasmic process

What do sensory neurons do?

• Carry impulses from periphery to the brain and spinal cord

• Afferent neurons: conduct inward or towards something

• Most are unipolar

What do interneurons do?

• Lie within the brain and spinal cord

• Transmit impulses to one part of brain/spinal cord to another

• Also called association

What do motor neurons do?

• Carry impulses out of brain and spinal cord to effectors (muscles and glands)

• Efferent neurons: conducting outward or away from something

• Most are multipolar

What is the resting membrane potential?

• A difference in charge across the cell membrane

• Resting potential → -70 mv

  • Inside is negative compared to the outside

• Three Na⁺ enters cell, two K⁺ leaks out of the cell

• The Na⁺/K⁺ pump restores the resting membrane potential

  • Dumps three Na⁺ out and two K⁺ in

What is an action potential (nerve impulse)?

• All neural activities begin with a change in resting potential

• All-or-Nothing Principle: a neuron either fires or does not fire

What are the steps to an action potential?

1. Resting state

• Neuron is at −70 mV (resting potential)

2. Stimulation

• Neuron receives a stimulus

• Na⁺ channels open at the axon hillock

• Na⁺ moves into the cell

• Membrane becomes less negative (depolarization)

3. Threshold

• If membrane reaches −55 mV, the neuron fires

• This is the threshold: minimum needed to trigger an action potential

• Na⁺ floods into the neuron

4. Action potential

• Membrane rapidly depolarizes to about +30 mV

• Inside of the cell becomes positive

• This is the big spike on the graph

5. Repolarization

• Na⁺ channels close

• K⁺ channels open

• K⁺ moves out of the cell

• Membrane potential drops back down

6. Hyperpolarization

• Membrane briefly goes below −70 mV

• This is the dip under the resting line

7. Refractory period

• Neuron cannot fire normally while resetting

What is the difference between the absolute and relative refractory period?

Absolute refractory period:

• From −55 mV to +30 mV

• No new action potential possible

• Na⁺ channels are open/inactive

Relative refractory period:

• From +30 mV back to −70 mV

• Neuron can fire again, but needs a stronger stimulus

• K⁺ channels still open

What is saltatory conduction?

• Myelin increases resistance to flow of ions

• Ions can only cross membrane at the nodes of ranvier

• AP “jumps” from node to node

Axons have multiple branches, allowing what?

Allowing it to make synapses on various postsynaptic cells

• Also, a single neuron can receive thousands of synaptic inputs from many different presynaptic (sending neurons)

How are neurotransmitters (NTs) transmitted?

1. AP reaches the axon terminal and depolarizes the membrane

2. Voltage-gated Ca2+ channels open and Ca2+ flows in

3. Ca2+ influx triggers synaptic vesicles to releases NTs

4. The NT binds to receptors on target cell

5. Removal of NT

• Reuptake

• Breakdown by enzymes

• Diffuse off of synapse

What is the reflex arc?

• Reflexes: automatic, subconscious responses to stimuli within or outside the body

• Ganglion: a collection of nerve cell bodies

What are the parts of a reflex?

Receptor

Sensory neuron

Interneuron

Motor neuron

Effector

What is the receptor and sensory neuron?

Receptor

• The receptor end of a dendrite or a specialized receptor cell in a sensory ogran

• Sensitive to a specific type of internal or external change

Sensory neuron

• Dendrite, cell body, and axon of a sensory neuron

• AFFERENT

• Transmits nerve impulse from the receptor into the brain or spinal cord

• Enter the spinal cord dorsally

What is the interneuron, motor, and effector?

Interneuron

• Dendrite, cell body, and axon of a neuron within the brain or spinal cord

• Serves as processing center; conducts nerve impulses from the sensory neuron to a motor neuron

Motor neuron

• Dendrite, cell body, and axon of a motor neuron

• EFFERENT

• Transmits nerve impulse from the brain or spinal cord out to an effector

• Exit the spinal cord ventrally

Effector

• A muscle or gland

• Responds to stimulation by the motor neuron and produces the reflex or behavioral action