Neurophysiology Part 1

Question 1

Neural Communication

Answer 1

We master our environment using highly developed senses (vision, audition etc) that provide comprehensive information to a flexible decision-making device: the brain

The brain analyses sensory information (sensations), endows them with meaning (perceptions), and stores salient information for future reference (memory)

Question 2

Microglial

Answer 2

Neural phagocytes produced by macro-phages and activated after injury, infection or disease.

Question 3

Macroglial

Answer 3

Oligodendrocytes (CNS) and Schwann (PNS) cells insulate axons, forming a myelin sheath by winding their membrane around the axon in a spiral. The more numerous astrocyte cells help maintain dynamic equilibrium and also act as reuptake vehicles.

Question 4

Neuron Feature = Soma

Answer 4

The metabolic center, includes the nucleus and the endoplasmic reticulum.

Question 5

Neuron Feature = Dendrites

Answer 5

(receivers), apical vs. basal

Question 6

Neuron Feature = Axon

Answer 6

Conveys electrical signals known as action potentials (1 ms electrical impulses traveling at 1 – 100 m / second)

Question 7

Neuron Feature = Presynaptic terminals

Answer 7

The branches of the axon, may connect with 1000 or more other neurons

Question 8

Neurons

Answer 8

> . However, for a long time it was still thought that the brain was a continuous, web-like, recticulum
. Neurons (i.e., soma) mostly aggregate in Gray Matter.
. Nervous impressions are received, stored, and transformed into efferent impulses
. Mylinated axons can clump together in nerve tracts to form White Matter, conducting neural information across long distances.
. Each neuron is a discrete cell clearly segregated from other neurons

Question 9

Types of Neurons = Unipolar

Answer 9

Found in the spine, single process (or branch). Relays touch information, and controls organs and glands. They are found in the ANS

Question 10

Types of Neurons = Bipolar

Answer 10

Sensory Neurons (all modalities except touch) with two distinct processes

Question 11

Types of Neurons = Multipolar

Answer 11

An axon with many dendrites. Varying greatly in shape, they include Interneurons (bridging motor and sensory neurons) and Motor Neurons, and are the most common neurons in the CNS

Question 12

Functional Neuron = Sensory

Answer 12

Carry information from periphery into the CNS for the purposes of both perception and motor coordination. Sometimes called afferent neurons

Question 13

Functional Neuron = Motor

Answer 13

Carry instructions from the CNS or the spinal cord to muscles, glands, and organs. Sometimes called efferent neurons

Question 14

Functional Neuron = Interneurons

Answer 14

a) Relay or projection interneurons, long axons carrying information between brain regions
b) Local interneurons, short axons in local circuits

•Begins with the stimulation of a neuron.

Question 15

The action potential (electrical)

Answer 15

The action potential is an electrical current that flows from the axon hillock and terminates at the terminal buttons

Question 16

Synaptic transmission (chemical & electrical)

Answer 16

Synaptic transmission involves molecules, known as neurotransmitters, crossing the synaptic cleft from the terminal buttons to a receptor resident in the membrane of the receiving neuron.

Question 17

Action Potential: Part 1

Answer 17

The action potential underlies all information transfer in the brain, and as an event considered homogenous

Thus, the information is determined by the pathway the signal is traveling, with the brain analysing patterns of incoming signals
At its terminus, the axon divides into fine branches that connect to other neurons. When two neurons connect we say we have a synapse

The principle of dynamic polarisation: electrical signals within a nerve flow in a single direction only

Question 18

Action Potential: Part 2

Answer 18

> . The electrical charge inside of an axon relative to the outside charge is the membrane potential
. The resting potential is -70mV (re: the outside)
. The resting potential is maintained by a concentration gradient (diffusion) and the electrical force
. Voltage-dependent ion channels control the entry of Na+ and K+ into the cell
. The Na+/K+ pump controls their exit from the cell

Question 19

Action Potential: Part 3

Answer 19

> . The action potential begins when voltage dependent ion channels open and allow Na+ to flow into the cell
. A narrow region of the axon membrane then depolarizes (becomes + with respect to the outside)
. At 1-ms it begins to repolarize (return to the resting potential)
. The next narrow region of the axon then depolarizes
And so on, like a Mexican wave along the axon’s length

Question 20

Action Potential: Part 4

Answer 20

• If an Action potential is generated at the axon hillock, it will travel all the way down to the synaptic button
• The manner in which it travels depends on whether the neuron is myelinated or unmyelinated
• Unmyelinated neurons undergo the continuous conduction of an AP whereas myelinated neurons undergo saltatory conduction of an AP.

Question 21

Action Potential: Part 5

Answer 21

Continuous conduction occurs in unmyelinated axons
In this situation, the wave of de- and repolarization simply travels from one patch of membrane to the next adjacent patch
•Saltatory conduction occurs in myelinated axons.
•Saltare is a Latin word meaning “to leap”
•Recall that the myelin sheath is not completed. There are myelin free regions along the axon, the nodes of Ranvier

Question 22

Temporal summation

Answer 22

–The same presynaptic neuron stimulates the postsynaptic
neuron multiple times in a brief period. The depolarization resulting from the combination of all the EPSPs may be able to cause an AP

Question 23

Spatial summation

Answer 23

•Multiple neurons all stimulate a postsynaptic neuron resulting in a combination of EPSPs which may yield an AP

Question 24

Refractory Periods

Answer 24

• Absolute – impossible to initiate another action potential
• Relative – harder to initiate another action potential
• Prevent the backwards movement of APs and limit the rate of firing