Nervous System 6.5.1-6.5.6

Objectives of 6.5 6.5.1:State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that can carry rapid electrical impulses. 6.5.2:Draw and label a diagram of the structure of a motor neuron. 6.5.3:State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons 6.5.4:Define resting potential and action potential (polarization, depolarization and repolarization). 6.5.5:Explain how a nerve impulse passes along a non-myelinated neuron. 6.5.6: Explain the principles of synaptic transmission.

Why do we have neural regulation Two properties of living things are; -to detect environmental changes (stimuli) -to coordinate internal activities. E.1.1 Define the terms stimulus, response and reflex in the context of animal behaviour. 1

Stimulus and response Write an example of external stimulus. State how do we detect this stimulus? What is the response? Write an example of internal stimulus.

Stimuli: A stimulus is a change in the environment (internal or external) that is detected by a receptor, and elicits a response. Response : A response is the activity of a cell or organism in terms of movement, hormone secretion or enzyme production, as a result of a stimulus.

Structure of the Nervous System Made of a network of nerves and cells that carry messages between the brain, spinal cord and parts of the body. Nervous system is divided into two parts: 1) Central Nervous System (CNS) 2) Peripheral nervous system (PNS)

Nervous System: 2 DIVISIONS 1) Central Nervous System (CNS): Brain and spinal cord. 2) Peripheral Nervous System (PNS): All other nerves that radiate from the spinal cord or brain to parts of the body.

Functions of the CNS & PNS Peripheral nerves – receive stimulus from external or internal environment. Signal is taken to brain and/or spinal cord. Spinal cord – receives a signal from peripheral nerves and sends the signal to the brain or other peripheral nerves. Brain – receives input brought from spinal cord and peripheral nerves, processes it, and then sends a signal back out. PERIPHERAL NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM

In-Class Labeling of the Neuron (6 parts) Label the neuron with the class (teachers note: this is a motor neuron. There are 3 classes of neurons discussed later)

Structure of a neuron

Parts of Neurons and their Functions Functions of Neurons: Nerve cells generate and transmit messages (as chemical & electrical signals) to different parts of the body. Structure of neurons: Cell Body – contains nucleus and organelles Dendrites – receives input Axon - conducts impulses away from the cell body Myelin Sheath – Covers the length of the axon and increases the speed of the electrical signal Axon Terminal –releases neurotransmitters into the synapse. Neurotransmitter: are chemicals (proteins) made in the cell body but released from the axon terminals that stimulate other neurons. Discuss functions of the parts of a neuron.

Dendrite Structure: Function: A single neuron may receive nerve nerve impulses from different neurons Structure: Finger-like projections from cell body Function: Receives nerve impulse from previous neuron. The Cell Body – explain that it has all the organelles of a cell. Also has plasma membrane which lets molecules in and out of the cell. This is where neurotransmitters are produced. Neurotransmitters are proteins – produced by ribosomes on rER and transported out of cell body, down length of axon terminals and released from there.

The Cell Body Structure: Function: A single neuron may receive nerve nerve impulses from different neurons Structure: Eukaryotic animal cell Has all organelles present and a plasma membrane. Function: To receive chemical signal from synapse and convert it to an electrical signal. The Cell Body – explain that it has all the organelles of a cell. Also has plasma membrane which lets molecules in and out of the cell. This is where neurotransmitters are produced. Neurotransmitters are proteins – produced by ribosomes on rER and transported out of cell body, down length of axon terminals and released from there.

Axon Axon Terminals Function: To transmit the electrical signal from the cell body to axon terminals. Myelin Sheath – increases speed of electrical signal Axon Terminals State that electrical is changed to chemical signal and then changes back to electrical siganl in next neuron. Signals take thousandths of a second to travel down the length of a neuron. Seems like a long process but in actually it is very quick. Function: To receive electrical signal from axon and release neurotransmitters (chemical signal) into the synapse.

Types of Neurone Sensory neurons: transmit nevre impulse from sensory organ to CNS (brain and spinal cord). Interneurons: integrate data and send appropriate signals to other interneurons or to motor neurons. They are found in the CNS Motor neurons: transmit nerve impulses from CNS to effector organs.

The Nerve Impulse An electrical current that runs down the length of an axon. It starts at the beginning of the axon and ends at the axon terminals.

ELECTROCHEMICAL PROPERTIES OF A NERVE IMPULSE Generation and transmission of a nerve impulse depend on membrane proteins of a neuron. There are three main types of membrane proteins which involve nerve impulse. These proteins are voltage sensitive proteins. Na-K pump proteins Na channels (Gates) K channels (Gates)

Resting Potential Resting potential is the potential difference (almost -70mV) of neurons membrane when there is no stimulus. The cytoplasm of neuron is (-) charged with respect to outside of neuron. Neuron is called polarized. This potential difference is due to concentration difference of Na and K ions. The outside of neuron has 10x more Na ions than cytoplasm; cytoplasm has 10x times more K ions than outside. The concentration difference of Na and K ions are kept by Na-K pump proteins. These proteins pump Na ions to outside, K ions to inside by active transport.

Action potential Nerve impulse of a neuron is called action potential. When a neuron is stimulated, Na channels open. Na ions diffuse into the cytoplasm. So, cytoplasm becomes (+) charged with respect to outside. Outside of the cell membrane becomes (-) charged with respect to cytoplasm. Membrane potential difference change changes from -70mV to +40mV. The membrane is called depolarized. This potential difference causes Na gates close and K gates open. Repolarization starts.

Repolarization Na gates are closed. K gates are open. K ions diffuse out. So outside becomes + charged, inside – charged. Na-K pump proteins pumps 3Na ions to outside 2K ions to inside.

The Synapse

The junction across which a nerve impulse passes from an axon terminal to a neuron, muscle cell, or gland cell. It occurs between axon end of a pre-synaptic neuron and dendrites of post-synaptic neuron. TRANSMISSION ACCROSS THE SYNAPSE When the nerve impulses reach to axon end, they are transmitted by neurotransmitter proteins through synaptic cleft. Neurotransmitters are chemicals that transmit nerve impulse from one neuron to next one.

Steps in ChemicalTranmission When the nerve impulse reaches to the axon end, it causes to open Ca++ channels on the membrane and Ca++ ions flow into the axon end. The Ca++ ions induce a few vesicles containing neurotransmitters fuse with the pre-synaptic membrane and release their contents into the synaptic cleft (exocytosis). Neurotransmitters bind to the receptors of the next cell’s membrane.

4. Binding of neurotransmitter to the receptor proteins causes action potential in the post-synaptic neurone ( By opening the Na+ channels which are placed next to receptor proteins – Na ions flow in -> depolarization of post synaptic neuron) 5. The inactivated neurotransmitters are taken back by the pre-synaptic neuron by endocytosis and they are used for synthesis of new neurotransmitters.

Types of Neurotransmitters Acetylcholine - voluntary movement of the muscles Noradrenaline - wakefulness or arousal Dopamine - voluntary movement and emotional arousal Serotonin - memory, emotions, wakefulness, sleep and temperature regulation Adrenaline Glutamic acid