The Nervous System OR… Why you are able to poke yourself in the eye.
Functions of the Nervous System Receives sensory information from internal and external environment Processes information and transmits it around the body. Organises a coordinated response to information
Structure of the Nervous System
The Central Nervous System Brain – protected by the cranium. Spinal cord – protected by the vertebra
The Peripheral Nervous System Consists of all of the nervous system apart from the brain and spinal cord. Divided into: 1.Somatic Nervous System 2.Autonomic Nervous System
Somatic Nervous System Voluntary movement. Conveys sensory messages from the sense organs to the CNS…..AND Conveys motor messages from the CNS to the muscles and glands.
Autonomic Nervous System Involuntary movement. Regulates internal environment. Controls functioning of the heart, intestines and other organs. Divided into Sympathetic and Parasympathetic Nervous System.
Nerve Cells Basic units of the nervous system. Also known as neurons. 4 basic parts to a neuron.
Neurons 1.Dendrites = Receive messages from other neurons. 2.Soma/Cell body = Accepts impulse travelling from the dendrites. 3.Axon = Impulses travel from the soma and are carried along this thin fibre. 4.Axon terminals = Branches at the end of the axon that link with the dendrites of other neurons.
Neurons Neurons do not touch each other. Instead a chemical, called a neurotransmitter, is released from the axon terminals into a gap called a synapse. The chemical is then picked up by the dendrites of the next neuron. i.e. nerve impulses are electrochemical.
Myelin Sheath Fatty layer that protects axon, and conducts messages faster. Gaps in myelin is called nodes of Ranvier.
Match the terms with their definitions TermDefinition Neuron a. A fatty layer coating some axons. Axon b. The main cell body of a neuron. Soma c. Fibre that carries information away from the cell body of a neuron. Dendrite d. A bundle of neuron fibres. Myelin e. Branching fibre at the end of an axon. Nerve f. Carries chemical message across the synapse. Synapse g. An individual nerve cell. Axon terminal h. Microscopic space between two neurons. NT i. A neuron fibre that receives incoming messages
True or False? 1.A neuron and a nerve are structurally the same thing. 2.An axon is about 0.1mm long. 3.The transmission of a message within a neuron is electrochemical. 4.The release of NT’s occurs at the axon. 5.Axons are coated with myelin in order to protect them from damage. 6.A synapse is a gap between the axon terminal of one neuron and an adjacent neuron.
Activity: Making a Neuron 1.Use pipe cleaners to construct a model of a neuron. 2.Label the main parts of a neuron and state the function of each. 3.Indicate the direction of the nerve impulse.
Sensory (Afferent) Neuron Detect changes in the external or internal environment and transmit that information to the CNS, via the PNS.
Motor (Effector) Neuron Carry impulses away from the CNS to muscle cells or glands and cause a response.
Interneuron (Relay Neuron) Link sensory and effector neurons. Normally found in CNS in CNS (particularly PNS)
S-A-M-E Sensory = Afferent + Motor = Efferent
Reflex Arcs
Putting it all together… Create a flowchart to illustrate: 1.How sensory information is transmitted from the PNS to the CNS. 2.How motor information is transmitted from the CNS to the PNS.
The Nerve Impulse Ions are electrically charged chemical molecules, e.g. K +, Na +, Cl - etc. In and around a neuron there will be positive and negative ions. When a neuron is resting it has a negative charge. This is known as its resting potential. The neuron is said the be polarised.
The Resting Neuron
The Action Potential Along the axon membrane there are numerous ion channels. Normally these channels are blocked, but if a neuron is sufficiently stimulated the ion channels open and positive ions rush in. The neuron becomes positively charged and an action potential is been generated.
The Action Potential An action potential is a very rapid change in polarity. The neuron moves from the resting potential to some positive value in a few milliseconds.
The Action Potential If a nerve cell is stimulated past the threshold (about -30mV in humans) ion channels open and positive ions rush into the axon. This causes a region of the axon to have a more positive charge. This is called depolarisation.
The Action Potential Soon after the positively charged ions are pushed back outside. The neuron moves back to its resting potential. This is known as repolarisation.
The ion channels are only located at the nodes of Ranvier. The action potential jumps from node to node.
The Action Potential Once an action potential has occurred there is a period when the neuron is unable to conduct another nerve impulse. This is known as the refractory period. This ensures that the nerve impulse moves in one direction along the axon.
All-or-None Law Action potentials occur maximally or not at all. I.e. There is no such thing as a partial or weak action potential. Either the threshold potential is reached and an action potential occurs, or it isn't reached and no action potential occurs.
Bridging the Gap The axon ends with many small swellings called axon terminals. The small gap or space between the axon of one neuron and the dendrites or cell body of the next neuron is called the synapse or synaptic gap. The small gap or space between the axon of one neuron and the dendrites or cell body of the next neuron is called the synapse or synaptic gap. A nerve impulse cannot go backward across a synapse.
Bridging the Gap The axon terminals contain tiny vesicles filled with chemicals known as neurotransmitters. When an impulse reaches the axon terminal, NT’s are released into the synaptic gap. The NT moves through the synapse and bind to receptor molecules on the post- synaptic neuron.
Bridging the Gap
NT’s attach only to specific receptors. NT’s may excite or inhibit the next neuron. If the neuron receives enough excitatory messages an action potential is generated. Any leftover NT’s are rapidly removed or destroyed.
SYNAPTIC CLEFT OR GAP