The Nervous System

1. The Nervous System

2. Introduction • In all animals, except the sponges, responses to stimuli depend on the activities of networks of nerve cell, or neurons. • Neurons are specialized cells for transmitting neural signals, which are electrical signals and chemical messages.

3. Parts of the Neuron • Dendrites: projections used to conduct electrical messages received from other neural cells to the cell body. • Cell Body: Contains lots of ribosomes and RERs to make proteins needed for the neuron; also passes received messages out through the axon.

4. Parts of the Neuron • Axon: long projection that conducts electrical messages away from the cell body; connect with other neurons/cells at synapses. • Schwann Cells: a form of glial cells that make up the myelin sheath; support and protect the axon.

5. Parts of the Neuron • Myelin Sheath: an electrical insulating cover of the axon that speeds up the transmission of electrical signals. Majority of neurons are myelinated. • Node of Ranvier: gaps in the myelin sheath that allow for saltatory conduction of an action potential (i.e. the signal jumps from gap to gap)

6. Nervous System • In most animals, neurons and the supporting tissue are organized into a nervous system. • The nervous system works in conjunction with many of the body’s other systems in order to maintain homeostasis.

7. Nervous System • The nervous system contains 2 distinct parts: • Central Nervous System(CNS) • Contains the nerves in your brain and spinal cord. • Has control over the majority of body processes as it controls the peripheral nerves.

8. Nervous System 2) Peripheral Nervous System (PNS): • Contains all the nerve cells that are not associated with the CNS. • Autonomic division controls all involuntary processes in our bodies. • Somatic division controls all voluntary processes in our bodies.

9. Neural Signalling • An animal is constantly being bombarded with stimuli. • Appropriate response to stimuli depends on neural signalling, which is communication between neurons.

10. Neural Signalling • Neural signalling involves four processes: • Reception • Transmission • Integration • Action

11. Neural Signalling • Reception is the process of detecting stimuli. • It is the job of special neurons called sensory neurons (unipolar neurons) or organs like the eyes and ears.

12. Neural Signalling • Transmission is the process of sending messages along the nervous system usually to or from the brain. • Sensory neurons carry messages to the central nervous system. • Afferent neurons are any neurons that carry messages to the CNS. Therefore sensory neurons are afferent neurons.

13. Neural Signalling • Integration involves sorting and interpreting messages and determining the appropriate response. • Interneurons (bipolar neurons) do this job. Their cell body and axon are located within the CNS.

14. Neural Signalling • Action involves the actual response to stimuli by the body’s effectors. • Motor neurons (multipolar neurons) do this job. They carry messages away from the CNS to effectors like muscles. • Efferent Neurons are any neurons that take messages away from the CNS, therefore motor neurons are efferent neurons.