Nervous System Overview

Study Notes

The nervous system is divided into two primary divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).
The CNS controls and coordinates the body by constantly monitoring and processing sensory information from inside and outside the body, combining new information with stored information to create responses.

Central Nervous System (CNS): Includes the brain and spinal cord.
Peripheral Nervous System (PNS): Includes all parts of the nervous system outside the CNS, such as nerves, sensory receptors, and clusters of neuron cell bodies.

Neurons: Handle communication and send signals.
Neuroglia (Glial Cells): Support and protect neurons. Includes astrocytes, oligodendrocytes, microglial cells, and ependymal cells in the CNS and Schwann cells (neurolemmocytes) and satellite cells in the PNS.

Neurons have a cell body, dendrites, and an axon.
The cell body is the biosynthetic center of the neuron producing important materials.
Dendrites receive signals. A neuron can have many.
The axon transmits signals, and a neuron usually only has one.

Dendrites: Receive signals from other neurons.
Axons: Transmit signals (electrical impulses) away from the cell body. Can branch to form axon collaterals.

Multipolar: Have many processes (one axon, many dendrites). Common in the brain and spinal cord.
Bipolar: Have two processes (one axon, one dendrite). Rare, typically found in sensory organs (like eyes, ears, and olfactory mucosa).
Unipolar (pseudounipolar): Have a single short process that branches like a "T", with both a peripheral process and a central process, typically associated with sensory neurons.

Nerves, in the PNS, are bundles of axons or nerve fibers surrounded by connective tissues layers.
Layers include endoneurium (around each axon), perineurium (around fascicles), and epineurium (around the whole nerve).

There are 12 pairs of cranial nerves, primarily serving the head and neck.
Some cranial nerves are purely sensory (olfactory and optic), whereas others are mixed (containing both sensory and motor components).

The spinal cord is a cylindrical structure located within the vertebral column.
It's enclosed within meninges (dura mater, arachnoid mater, and pia mater) for protection.
It's a major pathway for signals between the brain and the rest of the body.
The spinal cord houses the gray matter (with cell bodies) and white matter (with myelinated axons), analogous to a butterfly shape.

31 pairs of spinal nerves emerge from the spinal cord, exiting via intervertebral foramina.
Spinal nerves are mixed nerves that carry both sensory and motor information to and from the body.
- Dorsal rami: supply the muscles and skin of the back.
- Ventral rami: serve the anterior and lateral trunk (and form plexuses).

Networks of interlacing nerves formed by branches of ventral rami of spinal nerves.
Key plexuses include cervical, brachial, lumbar, and sacral plexuses, typically supplying the limbs and other body regions.

Reflexes are rapid, involuntary motor responses triggered by specific stimuli.
Reflex arcs are nerve pathways mediating reflexes and consist of five components: receptor, sensory neuron, integration center, motor neuron, and effector.
Reflexes can be intrinsic (inborn) or learned (acquired). Somatic and autonomic reflexes exist.
Somatic reflexes involve skeletal muscles, and autonomic reflex arcs regulate visceral activities (smooth muscle/glands/cardiac muscle). Simple vs. complex reflexes exist.

Damage to the spinal cord can result in loss of motor and sensory functions in body areas served by the affected region and areas below.

The ANS is a division of the PNS (peripheral nervous system) regulating involuntary functions such as smooth muscle, cardiac muscle, and glands.
It consists of two branches: the sympathetic and parasympathetic divisions.
These divisions have antagonistic (opposite) effects on target organs but maintain homeostasis.

The nervous system undergoes gradual changes related to aging, which can influence sympathetic functions and causes like orthostatic hypotension where blood pressure changes can cause dizziness.