An introduction to the Nervous system

From: http://www.hiogolffitness.com/?p=262

The importance of the nervous system

• Nervous systems reponse to stimuli (external or internal) by controling the actions of the body through electrochemical messages

• Allows us to: detect light, odour, temperature or pressure… just to name a few

What is the nervous system?• Elaborate communication system (>100 billion

nerve cells in the brain alone!)

• 2 main divisions (flow chart, p412):

– central nervous system (CNS) • Brain and spinal cord• Coordinating system

– peripheral nervous system (PNS)• Nerves that carry info between organs and CNS• Subdivided into somatic (skeletal muscle, bones

and skin- relays info about environment) and autonomic (internal organs like the heart)

Anatomy of a nerve cell

• 2 types of cells– Glial: non-conducting cells important for

structural support and metabolism– Neurons: functional units of the nervous

system• Can be sensory- sense and relay info from the

environment to CNS for processing (photoreceptors for light, chemoreceptors for chemicals etc…) and are located in clusters called ganglia

• Or motor – relay information to the effectors (muscles, organs, glands)

• Or Interneurons – link neurons in the body (integrate sensory and motor neurons)

From: http://www.dmacc.edu/instructors/rbwollaston/Chapter_8_Nervous_System.htm

From: http://www.daviddarling.info/encyclopedia/N/neuron.html

Sensory neuron

Motor neuron

Parts of the neurons• Dendrites: receive info from sensory receptors by

conducting nerve impulses toward the cell body

• Axon: projects nerve impulses from the cell body

• Myelin sheath: covers many axons, insulates the neurons, preventing loss of charged ions from nerve cell. Formed by special glial cells called schwann cells.

• Nodes of Ranvier: areas between sections of myelin sheath, nerve impulses jump from one node to another (speeding up process)… so nerve impulses are quicker in mylelinated axons.

• Neurilemma: surrounds the axon and promotes re-generation of a damaged axon

Neural circuits

• Simplest nerve pathway is called a reflex arc

• Occurs without brain coordination

• 5 components: receptor, sensory neuron, interneuron, spinal cord, motor neuron and effector.

From: http://www.biologie.uni-hamburg.de/b-online/library/cat-removed/u3aos22.html