MCAT Nervous System

Question 1

Job of neurons

Answer 1

Responsible for receiving, integrating, and transmitting information.

Interneurons transmit information between 2 neurons. The most abundant type of neuron in the body.

Question 2

Describe the following parts of the neuron?
- Soma
- Dendrites
- Axons
-Axon hillock
-Axon terminal

Answer 2

• Soma- where the nucleus and organelles are held.
• Dendrites- branching extensions from the soma that receives the signals from other neurons.
• Axons- allows the travel of electrical signal down to the axon terminal.
• Axon hillock- the part between the axon and the soma.
• Axon terminal - where NTs are released in the synaptic cleft.

Question 3

Types of neurons:

Bipolar neuron

Multipolar neuron

Unipolar neuron

Answer 3

Bipolar neuron - Neuron has one axon and one dendrite.

Multipolar neuron - Neuron has multiple dendrites and one axon.

Unipolar neuron- cell body that’s off to the side of an axon and dendrite that has been fused.

Question 4

Sensory (afferent) neurons v. Motor ( efferent) neurons

Answer 4

• Sensory ( afferent) - carries sensory information to CNS.
• Motor ( efferent) - sends information from CNS to the periphery to cause some desired effect.

Question 5

Role of myelin. What creates myelin?

Answer 5

Myelin is a phospholipid layer around the axon that insulates allowing speeding up the the electrical signal. Provides nutrients to myelinated regions through gap junctions and transporters.

They have gap junctions called nodes of ranvier interspersed throughout the myelin. Allows the electrical signal to jump from node to node this “ jumping” is called saltatory conduction.

Question 6

Oligodendrocytes v. Schwann cells

Answer 6

• Oligodendrocytes- make myelin in CNS
• Schwann cells- make myelin in PNS.

Question 7

Effects of demyelination

Answer 7

slowing down of the movement of the electrical signal.

Question 8

Role of glial cells ( neuroglia, glia). Describe each of them.
- Ependymal cells
-Oligodendrocytes
- Microglia
- Astrocytes

Answer 8

Neuroglia supports neurons.

• Ependymal cells - creates ependymal cells that serves to help protect the brain from trauma.
• Oligodendrocytes- creates myelin in CNS
• Microglia- immune cells that phagocytize invaders, waste, dead neurons
• Astrocytes- contains gap junctions to create blood brain barrier. Takes up K+ ions near neurons, exchange metabolic substrates between the neurons.

Question 9

What are the glial cells of the PNS?

Answer 9

Schwann cells make myelin for neurons in the PNS.

Satellite cells are similar to astrocytes in the CNS and provides structural and nutrient support to neurons.

Question 10

Membrane potential.

What happens at resting membrane potential?

Answer 10

The charge difference across the membrane that drives the movement of ions.

Inside the membrane is more negative then outside.

Question 11

Equilibrium potential

Answer 11

When the electrical gradient and chemical gradients cancel each other out.

Question 12

Electrochemical gradient

Answer 12

The combined effect that the electric gradient and the chemical gradient has on the movement of ions.

Question 13

Resting membrane potential.
Discuss how the RMP is created and maintained?

Answer 13

The membrane potential when the neuron is at rest. It’s around -70mv.

RMP is created and maintained by NA+/K+ ATPase which pumps 3 sodium ions out and 2 potassium in against their concentration gradients using ATP. Potassium and sodium leaks channels stay open allowing the ions to travel down their concentration gradients allowing the ATPase to pump them again.

K+ is more permeable than Na+ ions to the plasma membrane.

Question 14

What is an action potential?

Answer 14

A moving excitation that causes a change in the membrane potential. It’s initiated by the trigger zone which is located within the axon hillock.

Question 15

What are the phases of an action potential?

Answer 15

• Rising phase - Na+ rushes into cells has activation gates open causing the inside membrane charge to get more positive ( depolarization). Once it reaches -55mv an action potential is fired.
  When it reaches +40mv it’s called the overshoot and after this follows the falling phase.

-Falling phase - Na+ inactivation gates close and K+ voltage gated channels open and inside membrane becomes more negative ( repolarization). The channels take too long to close and so the membrane potential goes below the RMP, this is called hyperpolarization.

• Restoring phase - membrane potential comes back to the RMP of -70mv as voltage gated channels close and the NA+/K+ ATpase and leak channels open back up.

Question 16

Synapse

Answer 16

The site of communication between neurons (NTs can travel across or being direct contact).

Consist of axon terminal, synaptic cleft, and dendrites of postsynaptic cleft.

Question 17

What are the two types of synapses?

Answer 17

Electrical- signal directly crosses to postsynaptic neuron.

Chemical- signal crosses across synaptic cleft

Question 18

How are NTs in the synapse cleaned up?

Answer 18

Either by being degraded by enzymes, diffusing out of synapse, or reuptake by presynaptic neuron.

Question 19

How are neurotransmitters released?

Answer 19

By Ca2+ entering the axon terminal via voltage gated calcium channels . Ca2+ results in NT’s being fused with membrane, diffuses across synaptic cleft.

• Excitatory NTs - cause postsynaptic neuron to depolarize.
• Inhibitory NTs- cause postsynaptic hyperpolarization.

Question 20

Graded potentials

Answer 20

Used by the soma and is creating a potential that is proportional to the strength of the signal coming from the dendrites.

The signals than are brought down to the axon hillock where at the trigger zone an action potential is fired if it reaches threshold. THIS is an all or nothing signal.

Question 21

Summation. What are the two types?

Answer 21

The integration of the multiple signals incoming from presynaptic neurons.

• Spatial summation - summation of all the signals coming from multiple presynaptic neurons.
• Temporal summation- summing up the repeated signals from one presynaptic neuron.

Question 22

Difference between the CNS and PNS?

Answer 22

CNS receives, integrates, and responds to internal or external information.

PNS receives information from CNS about an apropiate response. It also takes in sensory info and bring it to the CNS.

Question 23

What are bundle of cell bodies called on PNS and CNS? What about bundle of axons?

Answer 23

CNS- bundles of cell bodies = nuclei, axon bundles = tracts.

PNS= bundles of cell bodies = ganglion, axon bundles= nerves.

Question 24

Preganglionic neurons v. postganglionic neurons

Answer 24

Preganglionic- extends from CNS to ganglion from periphery.

Postganglionic- extends from ganglion to target tissue.

Question 25

White matter v. Grey matter

Answer 25

Grey matter is somas, dendrites, and unmyelinated axons.

White matter is myelinated axons.

Question 26

Where is white matter and grey matter located in the brain and spinal cord?

Answer 26

In the brain grey matter is on the periphery while white matter is on the inside.

In the spinal cord white matter is on the periphery and grey matter is on the inside.

Question 27

What does the peripheral nervous system divide into?

Answer 27

The somatic nervous system which is responsible for voluntary control and autonomic nervous system which is under involuntary control.

Question 28

What does the autonomic nervous system divide into?

Answer 28

The parasympathetic NS ( rest and repose) and the sympathetic NS ( fight or flight).

Question 29

What’s released by the pre and postganglionic neurons of the sympathetic and parasympathetic NS.

Answer 29

For both pre and post Ach is released but norepinephrine is released from the postganglionic in sympathetic NS and Ach from the parasympathetic NS.

Question 30

Describe the different lengths of pre and postganglionic neurons in the sympathetic and parasympathetic NS?

Answer 30

For sympathetic NS preganglionic neurons are shorter than postganglionic.

For parasympathetic NS preganglionic neurons are longer than postganglionic.

Question 31

How is information sent to the spinal cord.

Answer 31

Afferent neurons being sensory information to the dorsal side of the spinal cord while efferent neurons leave from the ventral side.

As nerves enter or leave the spinal cord they split, these are called roots.
- Dorsal root- brings sensory information to dorsal side of s. cord.
- Ventral root- motor information transmits info from ventral side of S. cord.

Question 32

Reflexes and the reflex arc?

Answer 32

Reflexes are responses that bypass the interpretation from the brain about the response.

The reflex arc is the neuronal pathway responsible for a specific reflex.

• Monosynaptic reflex arc- sensory ( afferent) neuron synapses directly onto motor ( efferent) neuron.
• Polysynaptic reflex arc - An interneuron is inbetween the afferent and efferent neurons.

Question 33

Supraspinal reflexes v. Spinal reflexes

Answer 33

Supraspinal reflexes are reflexes that involves input from the brain.

Spinal reflexes are reflexes that doesn’t involve input from the brain, just the spinal cord.