Anatomy: Nervous System- Neurons + Glia

What does the nervous system do?

It is the body’s master control and communication system/

What are the primary functions of the nervous system?

• Sensory Input — detect changes (internal & external)

• Integration and Coordination — process and decide

• Motor Output — respond via muscles or glands

What are the key properties of the nervous system?

• Excitability – ability to respond to stimuli

• Conductivity – ability to transmit electrical signals

• Secretion – release neurotransmitters at synapses

What are the major divisions of the nervous system?

CNS

• Brain

• Spinal Cord

• Integration & Decision-Making Center

PNS

• Everything outside the CNS

• More prone to injury (less protection)

What are the functional divisions of the PNS?

• Sensory (afferent)

• Motor (efferent)

What do afferent (sensory) signals do?

They carry info to the CNS

What do efferent (motor) signals do?

They carry out the commands from the CNS

What are the motor subdivisions?

• Somatic Nervous System (SNS)

• Autonomic (visceral) Nervous System (ANS)

What does the SNS involve?

They use skeletal muscles to carry out voluntary movements/actions.

What does the ANS involve?

They use smooth muscles, cardiac muscles, and glands to carry out involuntary movements/actions.

What divisions is the ANS further broken down into?

• Sympathetic Nervous System: fight-or-flight

  • ex. increase HR, BP, and alertness while slowing digestion

• Parasympathetic Nervous System: rest-and-digest

  • calms the body down

  • lowering HR and helping with digestion

• Enteric Nervous System

  • network within the GI tract that controls digestion

  • works somewhat independently

What are the two neural tissue cell types?

• Neurons: conduct electrical signals

• Neuroglia: support, protect, insulate neurons

50% neurons / 50% glia by volume

What are the characteristics of neurons?

• Specialized for communication

• Do not divide

• Poor at repair

• Require glial support

What is the structural anatomy of a neuron?

• Dendrites: Receive signals

• Soma (cell body): Integrates signals

• Axon: Transmits signal

• Axon Terminals (boutons): Release neurotransmitters

What are the functional classes of neurons?

Type	Direction	Location
Afferent (sensory)	To CNS	PNS → CNS
Interneurons	Within CNS	CNS only
Efferent (motor)	From CNS	CNS → PNS

What are the structural classes of neurons?

Type	Description
Multipolar	Many dendrites, one axon (most common)
Bipolar	One dendrite, one axon (special senses)
Unipolar	One process splits → CNS & PNS (sensory neurons)

What neuroglia (glial cells) are located in the CNS?

• Astrocytes

• Microglia

• Ependymal Cells

• Oligodendrocytes

What neuroglia (glial cells) are located in the PNS?

• Schwann Cells

• Satellite Cells

What are the functions of astrocytes?

Structural support, blood-brain barrier, scar formation

What are the functions of microglia?

Immune defense, phagocytosis

What are the functions of ependymal cells?

Produce & circulate CSF

What are the functions of oligodendrocytes?

Form myelin in CNS

What are the functions of schwann cells?

Myelin in PNS (1 axon segment each)

What are the functions of satellite cells?

Support neuron cell bodies in ganglia

What is myelin, and what does it do?

• Lipid-rich insulating sheath

• Increases conduction speed

• Creates white matter

CNS	PNS
Oligodendrocyte	Schwann cell
One cell → many axons	One cell → one axon

What are the Nodes of Ranvier?

• Gaps in myelin

• Enables saltatory conduction (jumping signal)

Impulse speed of conduction depends on:

• Axon diameter

• Presence of myelin (not stimulus strength)

What is a synapse (chemical)?

Junction between neurons or neuron → muscle/gland

What are the steps of a synapse?

1. Action potential reaches axon terminal

2. Vesicles release neurotransmitter

3. Neurotransmitter crosses synaptic cleft

4. Binds postsynaptic receptors

5. Signal is excitatory or inhibitory

What are the neural circuits (neural pools) and their purpose?

Circuit Type	Purpose
Divergence	One neuron → many targets (motor control)
Convergence	Many inputs → one neuron (sensory integration)
Reverberating	Feedback loop (breathing)