Exam 2 Review: Nervous System Structure and Function

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Nervous System Overview

Central and Peripheral Nervous Systems

The nervous system is divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). Each has distinct structures and functions essential for body regulation and response.

CNS: Composed of the brain and spinal cord. Responsible for integrating, processing, and coordinating sensory data and motor commands.
PNS: Consists of all neural tissue outside the CNS. Connects the CNS to limbs and organs.
BOTH: Some structures and functions, such as certain neurotransmitters and neuroglial cells, are present in both systems.

Key Point: The CNS acts as the control center, while the PNS serves as the communication lines linking the body to the CNS.

Neuroglial Cells

Types and Functions

Neuroglial cells (or glia) support and protect neurons. They are classified based on their location in the CNS or PNS.

Astrocytes (CNS): Most abundant glial cell; maintain the blood-brain barrier, provide nutrients, and regulate ion balance.
Oligodendrocytes (CNS): Form myelin sheaths around CNS axons.
Microglia (CNS): Act as immune defense cells.
Ependymal cells (CNS): Line ventricles and produce cerebrospinal fluid.
Schwann cells (PNS): Form myelin sheaths around PNS axons.
Satellite cells (PNS): Support neuron cell bodies in ganglia.

Which neuroglial cell is most abundant? Astrocytes are the most abundant neuroglial cells in the CNS.

Synaptic Transmission

Structure and Function of the Synapse

The synapse is the junction between two neurons where communication occurs via neurotransmitters.

1. Presynaptic neuron: The neuron sending the signal.
2. Axon terminal: Contains synaptic vesicles filled with neurotransmitters.
3. Synaptic vesicles: Store neurotransmitters released into the synaptic cleft.
4. Synaptic cleft: The gap between the presynaptic and postsynaptic neurons.
5. Postsynaptic membrane: Contains receptors for neurotransmitters.
6. Neurotransmitter receptors: Bind neurotransmitters to initiate a response in the postsynaptic neuron.

Process:

An action potential arrives at the axon terminal.
Voltage-gated Ca2+ channels open, allowing Ca2+ influx.
Ca2+ triggers synaptic vesicles to fuse with the membrane and release neurotransmitters.
Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane.
This binding initiates a response in the postsynaptic neuron (e.g., depolarization or hyperpolarization).

Neurotransmitters

Major Types and Functions

Neurotransmitters are chemical messengers that transmit signals across synapses. They can be classified by their function and location.

Neurotransmitter	Main Function	Location
Acetylcholine	Excitatory at neuromuscular junctions; involved in muscle activation	BOTH (CNS & PNS)
Norepinephrine	Excitatory or inhibitory; involved in alertness and arousal	BOTH
Dopamine	Excitatory or inhibitory; involved in reward, motivation, and motor control	CNS
Serotonin	Mainly inhibitory; regulates mood, appetite, and sleep	CNS
Substance P	Involved in pain perception	BOTH
Adenosine	Generally inhibitory; promotes sleep and suppresses arousal	CNS
Cholecystokinin	Involved in satiety and digestion	CNS

Example: Acetylcholine is released at neuromuscular junctions to stimulate muscle contraction.

Additional info:

Some neurotransmitters, such as acetylcholine and norepinephrine, are found in both the CNS and PNS, while others are more specific to one system.
Neurotransmitter effects can be excitatory or inhibitory depending on the receptor type and location.