The Nervous System The body’s nervous system is divided into two parts: Central Nervous System Peripheral Nervous System

Peripheral Nervous System Sensory and motor neurons connected to the CNS Nerves run to and from the brain and spinal cord (cranial and spinal nerves) Made of 1) Somatic Nervous System and the 2) Autonomic Nervous System

2) Somatic Nervous System Made up of sensory nerves (bodyCNS) Motor nerves (transmit CNSbody) Under conscious control

Somatic System Carries impulses from external environment via sensory neurons that keep the CNS informed of changes, and the motor neurons adjust the position of skeletal muscles to maintain the body’s well being It does this through 12 pairs of cranial nerves and 31 pairs of spinal nerves

Cranial Nerves Transmit information about sense of smell, sight, hearing and taste, as well as general sensory receptors in the head region

Spinal Nerves Emerge from the spinal cord Named for the region they come from (i.e.Thoracic) Each one has a dorsal root (sensory fibers) that transmit info from sensory receptor to spinal cord, a spinal ganglion swelling (dorsal root ganglion) where cell bodies of sensory neurons are found, and a ventral root (motor fibers) that leaves the spinal cord to the muscles or glands.

1) Autonomic Nervous System Not consciously controlled (heart beat, peristalsis) Maintains homeostasis of internal environment Made up of the Sympathetic and Parasympathetic Nervous Systems (these control body organs)

Instead of using a single efferent (motor) neuron, as the Somatic system does, the ANS uses 2 neurons between the CNS and effector. First neuron = Preganglionic Neuron (has mylein). The cell body and dendrites are within the CNS It synapses with a Second neuron in a Ganglia outside the CNS  Postganglionic Neuron (unmyleinated)

Sympathetic Nervous System Has a shorter Preganglionic Neuron, longer Postganglionic Neurons Sets off “Flight-or-fight” reaction Releases Noradrenalin at synapses with effector Heart and breathing rates increase when SNS is stimulated Sympathetic nerves cause pupils in eyes to become large in response to low light

Parasympathetic Nervous System Has longer Preganglionic Neurons, shorter Postganglionic Neurons Opposite to the SNS When threat has passed, PNS slows heart and breathing rates Releases Acetylcholine (Ach) at synapse with effector Reverse effects of the SNS Parasympathetic nerves reduce the size of pupils when light levels are high