Nervous System controls the body and is the communicating system of the body

General Schematic of Nervous System

Major functions of the nervous system Sensory input – receives stimuli occurring inside and outside the body Integration – interprets sensory input Motor output – responds to stimuli by activating effector organs

What are the three major anatomical parts of the nervous system? Organization What are the three major anatomical parts of the nervous system? brain spinal cord nerves

A) Central nervous system (CNS) brain and spinal cord serves as integration and command center B) Peripheral nervous system (PNS) cranial and spinal nerves carries messages to and from the body to the spinal cord & brain

Divisions of the PNS I. Sensory (afferent) division A) Somatic sensory afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain B) Visceral afferent fibers – transmit impulses from visceral organs to the brain

II. Motor (efferent) division transmits impulses from the CNS to effector organs A) Somatic nervous system Conscious control of skeletal muscles B) Autonomic nervous system (ANS) e.g. Regulate smooth muscle, cardiac muscle, and glands

(1) Parasympathetic division- “resting and digesting system” e.g. nonstressful situations Keeps energy use low and maintains vital activities running

(2) Sympathetic division- “fight or flight” division e.g. exercise excitement emergency embarrassment Prepares the body for action

I. Cells of the Nervous System A) Neuroglia (glial cells) are helper cells that support neurons e.g. aids in the formation of the blood-brain barrier

1. Neuroglia of the CNS a) astrocytes - star shaped cells that connect neurons together and to their blood supply. provide both mechanical and metabolic support for neurons, regulating the environment where they function; they contribute to the blood-brain barrier and control transport of substances from the blood to neural tissue; they also help coordinate nerve pathway development

b) microglia- function as phagocytes by engulfing foreign invaders.

c) ependymal- (epithelial-like) provide a barrier between brain and cerebrospinal fluid. form the linings of the ventricles of the brain and the central canal of the spinal cord; make a contribution to the production of cerebrospinal fluid (CSF) 

d) oligodendrocytes- branched; connect thick nerve fibers; produce a myelin sheath around neurons.

2. Neuroglia of the PNS a) Schwann cells = produce myelin sheath

B) Neurons = are the functional cells of nervous system that actually transmit messages Conduct messages in the form of nerve impulses They number in the billions

Have extreme longevity Most cannot divide (except in hippocampus which is involved in memory) Have a high metabolic rate; high O2 and glucose requirement

Flashback! What are the 3 regions of a neuron?

3 regions: dendrites, cell body, and axon Impulses travel from dendrites to cell body to axons

What’s the difference between these 3 types of neurons?

II. Classification of neurons A) Structural classification Multipolar (most common) Bipolar (rare) Unipolar (PNS)

HG: Some neurons are very short > 1 mm in length HG: Some neurons are very short > 1 mm in length. Some neurons are very long...a meter or more! The axon of a motor neuron in the spinal cord that innervates a muscle in the foot can be about 1 meter (3 feet) in length. the axon of a motor neuron is 10,000 times as long as the cell body is wide. If you use a ping-pong ball (diameter = ~3.8 cm or 1.5 inch) to model the cell body, your axon would have to be 38,000 cm (380 meters) or 1,247 feet in length. If you use a basketball (diameter = ~24 cm or 9.5 inch) as the cell body, then your axon would have to be 240,000 cm (2.4 kilometers) or 7874 ft (1.49 miles) in length!

B) Functional Classification

B) Functional Classification Sensory neurons PNS mostly unipolar; some bipolar Interneurons CNS multipolar Motor neurons