CH 34 BIO

Can a single neuron have thousands of synapses and added effects of all of them determine if an AP is initiated at the axon hillock?

A single neuron can have thousands of synapses. The added effects of all of them determine if the AP is initiated if it crosses the threshold.

Label the parts of a neuron including dendrites, cell body, axon, and axon terminals. Explain the direction of conduction throughout a neuron.

Dendrites: numerous, short, highly branched extensions of cell body. Cell body: houses nucleus and organelles Axon: long extension from neuron that carries impulses away from cell body Axon terminals: bulb at the end of the axon that has neurotransmitters and takes part in synapses. Direction: the dendrites receive a lot of signals, the signals are integrated, and the action potential is fired at the axon hillock. Then it travels down the axon to the axon terminal where it comes into contact with a muscle cell or postsynaptic neuron.

What regulates the flow of ions through plasma membranes?

Ion channels

Draw (list in order) the flow of information through the nervous system during the following conditions: knee-jerk reflex, increase in heart rate when seeing an angry bear, and stimulation of digestion after a large meal.

Knee-jerk reflex: CNS responsible. Receptor detects stimulus, sends AP down the sensory neuron to the integration center of the spinal cord, then IC sends AP to the motor neuron. Seeing angry bear: SYMPNS responsible. PNS tells motor division, which tells ANS then SYMPNS releases norepinephrine. Digestion after meal: PARANS responsible. PNS tells motor division, which tells ANS then PARANS releases acetylcholine

Why do all animal cells have a negative membrane potential at rest? (HINT: pump, leaky channels)

Na-K pump. Also, this is maintained because of leaky K+ channels - K+ slowly leaks out at all times.

What is the difference between a nerve net and centralized nervous system? What are the benefits of each?

Nerve net: no central processing unit, all neurons connect to one another, but movements are very simple, no complex processing or coordination. This works for simple organisms like starfish. Can survive without all body parts. Centralized nervous system: much more complex nervous system with brain (cephalization) and spinal cord (centralization). Allows for more complex movement and prcoessing.

What is the difference between a nerve and a neuron?

Nerve: axons of many neurons, like wires in a telephone cable Neuron: single cell with dendrites, axon, etc.

Explain the functions of the parasympathetic and sympathetic nervous systems and their general effects on airways, heart rate, digestion, sex organs.

Parasympathetic: inhibiting system. Rest and digest response (slow heart rate, slow breathing, increased digestion). After eating a big meal. Sympathetic: activating system. Fight or flight response (increased heart rate, increased breathing, slow digestion). Seeing a bear.

Define peripheral and central nervous systems.

Peripheral nervous system: sensory and motor neurons. Perceive information from the environment and allow us to respond, connecting the central nervous system to the tissues. Central nervous system: brain and spinal cord, integrates sensory information in ganglia. Example: reflexes.

What causes action potential spikes that last only for a few moments (ms)?

Rapid changes in ion movement across the axon plasma membrane caused by changes in voltage gated ion channel openings.

Which ion channels are open and which direction are ions flowing during different phases of an AP spike?

Resting membrane potential = -60mV. When the potential increases up to about -50mV, the voltage-gated Na+ channel opens and Na+ flows into cell (depolarization). Then once the potential is about 40mV, the Na+ channels close and K+ channels open. K+ is pushed out of the cell (repolarization). Then the resting membrane potential is reached and the K+ channels close slowly, so the cell hyperpolarizes and returns to resting potential.

What is the distribution of Na+ and K+ in a cell? Where is the concentration higher of each? Why?

SALTY BANANA - more K+ inside, more Na+ outside due to Na-K pump in plasma membrane.

Define somatic and autonomic pathways.

Somatic: voluntary movements, used with skeletal muscle and contracts. ACh. Autonomic: involuntary movements, subconscious responses to the environment. Routine functions like heartbeat, breathing, etc.

Which neurotransmitters are released to target organs by the parasympathetic system? The sympathetic system?

Sympathetic = norepinephrine. Parasympathetic = Acetylcholine

Explain how a signal in the form of an AP in one neuron is transmitted to a second neuron via chemical synapse.

The AP from the neuron reaches the axon terminal, causes the synaptic membrane to depolarize and Ca2+ voltage-gated channels open. -> Ca2+ influx causes synaptic vesicles with neurotransmitters to fuse with the membrane, and the neurotransmitters leave, attach to ligand-gated ion channels in postsynaptic membrane. -> Na+ flows in and depolarizes the neuron, causing graded potentials which can be AP's if the threshold is crossed.

Explain how a spike at one end of an axon causes a spike in the neighboring part of an axon. How does the Myelin sheath function to increase the speed of propagation?

The AP is self-regenerating and moves down the axon through depolarizing the adjacent cell. The voltage-gated channels continue to open/close properly down the different axons. -> The Myelin sheath (glial cells) insulates the axons and maintains the AP as it moves