The Nervous System

last authored: Sept 2009, Dave LaPierre
last reviewed:

 

Introduction

The nervous system is the control and processing system of the body, likely representing the most complicated structures in the universe. The central nervous system (CNS) is composed of the brain and spinal cord, while the peripheral nervous system contains nerves carrying signals to and from the CNS.

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Components

The brain and spinal cord are the site of processing, integration, and output of the nervious system. From them come nerves (general info), including cranial nerves and spinal nerves.

 

 

 

 

 

The CNS and nerves are composed of cells called neurons which are arranged into neural circuits. Signals are propogated via action potentials and between neurons via neurotransmitters. The support cells of the nervous system are called glial cells.

 

 

 

Meninges

The meninges are the matrix coverings of the brain and spinal cord.

 

Dura

The dura is the tough outer layer of the CNS.

The falx separates the two hemispheres, while the tentorium does something else.

 

Arachnoid Membrane

The arachnoid membrane is composed of webs of cells joined by tight junctions. It prevents cerebrospinal fluid from encountering the dura. The arachnoid

 

Pia

Pia is a thin, shiny layer of mesnchymal cells lying directly on the brain and spinal cord. Blood vessels lie outside the pia and carry a sleeve of pia with them as they enter the brain.

Pia extends into sulci, such that the entire surface area of the brain is covered with it.

Pia does not prevent exchange between the brain extracellular fluid, which bathes neurons, and the cerebrospinal fluid, which exists in the subarachnoid space.

 

 

 

Glial Cells

Meaning 'glue', in Greek, glia are involved in nearly every function of the brain. They fill all the spaces around neurons, with an approximate width of only 0.02 µm between cells.

Glial cells outnumber neurons 100:1 and are responsible for myelinating neurons.

 

Oligodendrocytes

While Schwann cells myelinate single axons, oligodendrocytes can myelinate up to 100 axons each.

 

Schwann Cells

Schwann cells envelop the NMJ

 

 

Microglial Cells

 

 

 

 

 

 

 

 

 

 

 

Function of the Nervous System

The brain holds the mind and being, though opinions on their specific relationship vary widely.

 

The autonomic nervous system is also called the visceral system due to its close association with the organs of the thorax, abdomen, and pelvis. The autonomic nervous system controls involuntary, homeostatic functions such as heart rate and digestion. The fight-or-flight sympathetic nervous system and the rest-and-digest parasympathetic nervous system are the two opposing forces of the ANS. It also contains the enteric nervous system, regulating the gut.

 

The somatic nervous system includes the motor system and the sensory systems.

 

 

Sensory Systems

 

Our senses allow us about to learn about our environment and our interactions with it, generating an internal representation of the world around us.

 

Sensation begins with receptors that generate signals passing to the CNS, where perception takes place.

All sensory systems convey four basic types of information: modality, location, intensity, and timing. Modality is determined by stimulus energy, both frequency and amplitude.

 

Biological perception of each of the senses is discussed under their respective headings, while a more conceptual approach is taken here.

 

The bodily senses include touch, pain, and temperature. Deep sensation includes muscle and joint position sense (proprioreception), deep muscle pain, and vibration.

 

Dermatomes are segmental areas of the skin which are innervated by the sensory components of specific spinal nerves.

 

Special senses, - vision, smell, taste, hearing, and balance - are communicated via cranial nerves.

 

Visceral sensation, relayed by the autonomic nervous system, describe hunger, nausea, and visceral pain.

 

 

 

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