THE NERVOUS SYSTEM

Learning Outcomes

• C11 – analyse the transmission of nerve impulses– Describe the structure of a neuron– Identify the function of dendrite, axon,

cell body, axoplasm, axomembrane– Differentiate between sensory, motor

and interneurons

• Consists of the brain, spinal cord and nerves throughout the body

Central Nervous System

• CNS consists of the brain and spinal cord

Peripheral Nervous System

• PNS consists of nerves throughout the body

• Carries messages to and from the CNS

Neurons

• Neurons are nerve cells

• Neurons have 3 main parts

• Cell body contains the nucleus and organelles

• Axon transmits an impulse away from the cell body to the next cell

• Dendrite receives an impulse and transmits it to the cell body

• Axoplasm refers to the cytoplasm within the axon

• Axomembrane refers to the plasma membrane of the axon

• Long axons are covered in a myelin sheath

• Nodes of Ranvier are intermittent gaps in the sheath

• Schwann cells wrapped around the axon contain myelin (a specialized phospholipid) in their plasma membranes

Types of Neurons

• Sensory neurons carry impulses from sensory receptors to the CNS

• Have long dendrites• Motor neurons carry impulses from the

CNS to an effector (muscle or gland)• Have long axons• Interneurons connect other neurons to

the CNS

Fig. 17.2

Transmission of Nerve Impulses

• Nerve impulses travel along neurons by means of electrochemical changes in the neuron membranes

• The space between neurons is called the synapse

• Neurotransmitters carry impulses across the synapse