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.