2.1.1 circuits

Flashcards testing concepts of neural circuit structures, divergence and convergence, excitation and inhibition, withdrawal reflex pathways and timing, and information encoding via motor neuron action potential discharge patterns.

In neural circuit diagrams, how are cell bodies, axons, axon terminals, and synapses represented?

Cell bodies are represented by circles, axons by lines exiting the circles, axon terminals by triangles or two short V-shaped lines, and synapses by spaces between the axon terminals and the next cell body.

What defines divergent processing in a neural circuit, and what is a specific example given in the lecture?

Divergent processing occurs when a given neuron or neuronal pool communicates with many neurons or neuronal pools; an example is the transfer of sensory information from the eye to various parts of the brain.

What is convergent processing, and from which brain regions does the diaphragm muscle receive involuntary versus voluntary commands?

Convergent processing occurs when information from multiple neurons or neuronal pools converges into one destination. The diaphragm receives involuntary commands from respiratory centres in the medulla oblongata and voluntary commands from the cerebral cortex.

How do serial processing and parallel processing differ in neural circuits?

In serial processing, information is passed sequentially from one neuron or neuronal pool to another. In parallel processing, neurons or neuronal pools process the same information simultaneously.

How do excitation and inhibition alter the membrane potential of the target neuron?

Excitation tries to depolarise the next neuron, moving its membrane potential closer to the threshold for discharging an action potential. Inhibition tries to hyperpolarise the next neuron, pushing its membrane potential further away from the threshold.

What structural symbols and car analogies are used to identify excitatory and inhibitory neurons?

Excitatory neurons are identified by a plus symbol ($+$, like an accelerator), while inhibitory neurons are identified by a negative symbol ($-$, like a brake).

What is the complete anatomical pathway of the withdrawal reflex from stimulus detection to motor response?

Sensory receptors on dendrites in the skin detect the stimulus $\rightarrow$ sensory axons enter the spinal cord via the dorsal root $\rightarrow$ sensory neurons synapse onto excitatory interneurons $\rightarrow$ interneurons synapse onto motor neurons $\rightarrow$ motor axons exit via the ventral root $\rightarrow$ skeletal muscle contracts.

Why does the immediate withdrawal reflex not involve the brain, and how much time would brain involvement add?

Excluding the brain provides the fastest response. Involving the brain would add $30\text{ to }40\text{ milliseconds}$ ($10\text{ to }15\text{ ms}$ up the spinal cord, several ms for processing, and $10\text{ to }15\text{ ms}$ back down).

How does the brain receive information about a tissue-damaging stimulus during a withdrawal reflex without delaying the reflex response?

Information is transmitted up to the brain via a second axon branch (collateral) coming off the spinal cord interneurons.

Approximately how many motor neurons innervate skeletal muscle fibres in the human biceps muscle in real life?

There are several hundred motor neurons that innervate skeletal muscle fibres in the biceps muscle.

What are three different patterns of action potential discharge that can produce a $50MAX_FORCE$ ($50SI_PERCENT$) contraction force in the biceps muscle?

1) Discharge $50SI_PERCENT$ of motor neurons at a moderate rate (about $15\text{ action potentials per second}$); 2) Discharge $30SI_PERCENT$ of motor neurons at a higher rate ($25\text{ action potentials per second}$); or 3) Discharge $100SI_PERCENT$ of motor neurons at a slow rate ($8\text{ to }10\text{ action potentials per second}$).