The Nervous SystemThe Nervous System

IntroductionIntroduction• 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.

Parts of the NeuronParts 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.

Parts of the NeuronParts 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.

Parts of the NeuronParts 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)

Nervous SystemNervous 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.

Nervous SystemNervous System

• The nervous system contains 2 distinct parts:

1) 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.

Nervous SystemNervous System2) 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.

Neural SignallingNeural Signalling

• An animal is constantly being bombarded with stimuli.

• Appropriate response to stimuli depends on neural signalling, which is communication between neurons.

Neural SignallingNeural Signalling

• Neural signalling involves four processes:

1) Reception

2) Transmission

3) Integration

4) Action

Neural SignallingNeural 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.

Neural SignallingNeural 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.

Neural SignallingNeural 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.

Neural SignallingNeural 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.