Neural Basis of Movement

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1 Summary Motor nerve impulses travel down the axon jumping from one Node of Ranvier to the next. This action caused by a change in the polarity from negative to positive inside that Node. At rest each node is maintained as negative inside (-70mvl) by the Sodium pump.

2 Summary If the inside level at the Node gets above minus 55 mvl, the pump is over powered and the Node goes quickly from negative to positive (action potential) to positive again, and the next Node gets affected. This jumping action is both fast and efficient (uses less energy) and is known as Saltatory conductance

3 Neural Basis of Movement Skeletal muscles are under the control of the nervous system (brain & spinal cord) which determines which muscles shall contract, when, how fast and to what extent, and with what change in force and velocity. Motor system nerves are somewhat like electrical wires in that they are insulated, but have a gap between each.

4 Central Nervous System CNS Control center Peripheral Nervous System PNS Connects CNS with the rest of the body

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7 The Basic Unit of the Nervous System The neuron is the functional unit of the nervous system. Humans have about 100 billion neurons in their brain alone!

8 Types of Neurons

9 The Motor Neuron and Its Function

10 Motor Neuron Motor neurons have a long axon and short dendrites and transmit messages from the central nervous system to the muscles (or to glands).

11 Components While variable in size and shape, all neurons have three parts. Dendrites receive information from another cell and transmit the message to the cell body. Cell body contains the nucleus, mitochondria and other organelles. Axon conducts messages away from the cell body.

12 Motor end plate Receptive Segment Cell Body Dendrites: receive message Conductive Segment Myelin sheath Nodes of Ranvier Axon: transmits message to terminal ending Transmissive Segment Terminal ending on muscle: sends message to adjacent neuron

13 The Neuron s Function Receptive Receptive segment (dendrites) Receives continuous synaptic input (chemical) from other neurons Conductive segment (axon) Conduction of neural information in the form of nerve impulses (electrical) Conductive Transmissive segment (axon terminals) Converts electrical nerve impulse to chemical form (neurotransmitter) and sends it off to synapse Transmissive

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16 Major Components involved in Nerve Impulse Sodium (N+) Potassium (K+) Chloride (Cl-) Anion (A-)

17 Some General Principles Likes are repelled, opposites attract Things move from areas of higher concentration, to areas of lower concentration Functions of the body are always concerned with efficiency

18 Sodium gates and potassium gates open in the membrane to allow their respective ions to cross. Sodium and potassium ions reverse positions by passing through membrane protein channel gates that can be opened or closed to control ion passage. Sodium crosses first.

19 Neuron Sheath Motor neuron axons are wrapped in a myelin sheath formed from the plasma membranes of specialized cells known as Schwann cells.

20 Myelin Sheath The gap between Schwann cells is known as the node of Ranvier, and serves as points along the neuron for generating a signal. Signals jumping from node to node travel hundreds of times faster than signals traveling along the surface of the axon. This jumping process is known as Saltatory conductance

21 Myelin sheath: fatty covering or insulator Skipping of the impulse allows faster conduction

22 Inactive Motor Neuron The voltage potential is -70 mv (millivolts) of a cell at rest (resting potential). Resting potential results from differences between sodium and potassium positively charged ions, and negatively charged. Positive Sodium ions (N+) are more concentrated outside the membrane, while negative ions (Cl- & A-) and potassium ions are more concentrated inside the membrane.

23 Sodium Pump This imbalance is maintained by the active transport of ions to reset the membrane known as the sodium potassium pump. The sodium-potassium pump maintains this unequal concentration by actively transporting ions against their concentration gradients.

24 Steps in an Action Potential At rest the outside of the membrane is more positive than the inside. (-70mvl) Sodium moves inside the cell causing an action potential (-55mvl), the influx of positive sodium ions makes the inside of the membrane more positive than the outside. Potassium ions flow out of the cell, restoring the resting potential net charges. Sodium ions are pumped out of the cell and potassium ions are pumped into the cell, restoring the original distribution of ions.

25 Action potential - one Node of Ranvier at a time Changed polarity of the membrane, Passage of ions across the cell membrane at the Node of Ranvier causes the action potential.

26 Neural Impulses Transport the information necessary for all activities we carry out The language of the nervous system Relay of impulse within neuron: Rest: polarization Membrane potential = -70 mv Stimulus: depolarization (mv) Rest: polarization Action Potential +40 mv Resting Potential Stimulus

27 Saltatory Conductance The action potential happens at one area (Node of Ranvier) at a time but spreads to the next area of the membrane as the previous Node returns to its resting state. In this way the impulse (message) travels along the length of the cell membrane, jumping from Node to Node.

28 Nodes of Ranvier: Skipping of the impulse allows faster conduction Saltatory Conductance

29 Refractory Period After passage of the action potential, there is a brief period, the refractory period, during which the membrane cannot be stimulated. This prevents the message from being transmitted backward along the membrane.

30 Synapses The junction between a nerve cell and another cell is called a synapse. Messages travel within the neuron as an electrical action potential. The space between two cells is known as the synaptic cleft. To cross the synaptic cleft requires the actions of neuro transmitters. Neurotransmitters are stored in small synaptic vessicles clustered at the tip of the axon.

31 Vessicles Arrival of the action potential causes some of the vesicles to move to the end of the axon and discharge their contents into the synaptic cleft. Released neurotransmitters diffuse across the cleft, and bind to receptors on the other cell's membrane, causing ion channels on that cell to open. Some neurotransmitters cause an action potential, others are inhibitory.

32 Synapse,Vesicles, Neurotransmitters

33 Neurotransmitters Neurotransmitters tend to be small molecules, some are even hormones. The time for neurotransmitter action is between 0,5 and 1 millisecond. Neurotransmitters are either destroyed by specific enzymes in the synaptic cleft, diffuse out of the cleft, or are reabsorbed by the cell.

34 The neurotransmitters cross the cleft, binding to receptor molecules on the next cell, prompting transmission of the message along that cell's membrane.

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36 Diseases that affect the function of signal transmission can have serious consequences. Parkinson's disease has a deficiency of the neurotransmitter dopamine. Progressive death of brain cells increases this deficit, causing tremors, rigidity and unstable posture. L-dopa is a chemical related to dopamine that eases some of the symptoms (by acting as a substitute neurotransmitter) but cannot reverse the progression of the disease.

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