Communication Chapter 7: Signals from the eye and ear are transmitted as electro-chemical changes in the membranes of the optic and auditory nerves

Nerves are bundles of neuronal fibres identify that a nerve is a bundle of neuronal fibres The units which make up the nervous system are the nerve cells or neurones. There are 3 types: Sensory neurones: transmit impulses from sense organs to neurones in the CNS Connector (inter) neurones: connect sensory neurones with motor neurones, usually in the brain and spinal cord. Motor neurones: transmit impulses from the CNS to muscles and glands

Nerves are bundles of neuronal fibres identify that a nerve is a bundle of neuronal fibres Each neurone has 3 parts: Cell body: contains the nucleus. This forms the grey matter of the CNS Dendrites: fine branching extensions which conduct nerve impulses towards the cell body Axon: a single, long extension which conducts impulses away from the cell body. This forms the white matter of the CNS The cell bodies of neurones are usually situated in the grey matter of the brain or the spinal cord. Some occur outside the CNS in clusters called ganglia. Ganglia co-ordinate impulses.

Nerves are bundles of neuronal fibres identify that a nerve is a bundle of neuronal fibres Dendrites and axons are collectively referred to as neuronal fibres. They consist of fluid-filled tubes, often surrounded by a fatty, insulating cover called the myelin sheath. The myelin sheath is gradually built up as concentric layers which are produced and supported by special cells (Schwann cells) on the outside.

Nerves are bundles of neuronal fibres identify that a nerve is a bundle of neuronal fibres The cell body of a neurone is usually in the brain or the spinal cord, while the axon or the dendrites usually extend, as part of a nerve, towards a sensory organ of an effector organ. Nerves can often stretch over a long distance, for example from the spine to the hand.

Nerves are bundles of neuronal fibres identify that a nerve is a bundle of neuronal fibres Nerve fibres are able to transmit messages rapidly along their entire length and pass them to a successive neurone, over small gaps called synapses.

Nerves are bundles of neuronal fibres identify that a nerve is a bundle of neuronal fibres The myelin sheath has small gaps called the nodes of Ranvier between the Schwann cells. The ion channels that function in the action potential are concentrated in the node regions of the axons. Also, extracellular fluid is in contact with the neuronal membrane only at these nodes.

Nerves are bundles of neuronal fibres identify that a nerve is a bundle of neuronal fibres The action potential actually ‘jumps’ from node to node, skipping the insulated regions of the membrane between the nodes. The greater the insulation through the myelin sheath, the faster transmission of the nerve impulse.

Nerves are bundles of neuronal fibres identify that a nerve is a bundle of neuronal fibres The nervous system is made up of millions of neurones. The sensory or motor fibres of the neurones are gathered into bundles called nerves. The bundle is held together by a connective tissue sheath.

Neurones and nerves perform a first-hand investigation using stained prepared slides and/ or electron micrographs to gather information about the structure of neurones and nerves Link to video https://www.youtube.com/watch?v=Sscgbhp33Fw

Neurons transmit signals by electrochemical changes in their membranes identify neurones as nerve cells that are the transmitters of signals by electro-chemical changes in their membranes Signals are transmitted by nerves in the form of electricity along the neuronal membrane, and by chemicals from one neurone to the next. This is why its called an electrochemical change.

Neurons transmit signals by electrochemical changes in their membranes identify neurones as nerve cells that are the transmitters of signals by electro-chemical changes in their membranes NEURONS CONTAIN IONS Nerve impulses are electrical signals which are produced by the plasma membrane (cell membrane) of the nerve cell. The human body as a whole is electrically neutral, having almost the same number of positive charges as negative charges.

Neurons transmit signals by electrochemical changes in their membranes identify neurones as nerve cells that are the transmitters of signals by electro-chemical changes in their membranes A potential difference exists across every cell’s plasma membrane. The side of the membrane exposed to the cytoplasm is negative while the side exposed to the extracellular fluid is positive. Voltage is always measured between two points and is called potential difference or simply potential. The flow of electricity from one point to another is called a current and it can be made to do work.

Neurons transmit signals by electrochemical changes in their membranes identify neurones as nerve cells that are the transmitters of signals by electro-chemical changes in their membranes The differences on either side of the membrane result in a cellular voltage, which is called the resting membrane potential and measures about 70 millivolts. It is written as -70mV, which indicates that the inside of the membrane is negative. The membrane is said to be polarised.

Neurons transmit signals by electrochemical changes in their membranes identify neurones as nerve cells that are the transmitters of signals by electro-chemical changes in their membranes This arises because neurones contain ions (charged particles). Positively charged ions = cations. Negative charged ions = anions. When either of these is found in a solution, the solution is then an electrolyte solution. The cytoplasm of a cell and the extracellular fluid are both electrolyte solutions, but they differ greatly from each other.

Neurons transmit signals by electrochemical changes in their membranes identify neurones as nerve cells that are the transmitters of signals by electro-chemical changes in their membranes Cell membranes are impermeable to proteins and most organic phosphates, so these are kept inside the cytoplasm. The membranes are selectively permeable to Na+, K+ and Cl-. When the ion channel pores are open, ions can move from one side of the membrane to the other. Each channel allows only a specific type of ion to diffuse through it.

Neurons transmit signals by electrochemical changes in their membranes identify neurones as nerve cells that are the transmitters of signals by electro-chemical changes in their membranes DEPOLARISATION AND ACTION POTENTIAL Changes in the environment of a neurone can affect the permeability of the plasma membrane to ions and therefore change the membrane’s potential. Any environmental factor which causes such a change is called a stimulus and neurones are highly reactive to stimuli.

Neurons transmit signals by electrochemical changes in their membranes identify neurones as nerve cells that are the transmitters of signals by electro-chemical changes in their membranes A cell’s membrane potential can change in response to appropriate stimulation. A positive shift in membrane potential, for example from -70mV to -10mV, is called a depolarisation. If the depolarisation is strong enough, this flow of ions causes the neurone to generate a nerve impulse or action potential.

Neurons transmit signals by electrochemical changes in their membranes identify neurones as nerve cells that are the transmitters of signals by electro-chemical changes in their membranes Action potentials are transmitted from neurone to neurone across small gaps called synapses. Chemicals known as neurotransmitters diffuse across the gap from one neurone to the membrane of the receiving neurone, causing an electrical response. The movement is in one direction only. synapses = the junctions between the end of one axon and the dendrites of a receiving neurone

Graphical representation of an action potential present information from secondary sources to graphically represent a typical action potential Page 84-85

A threshold must be reached to generate an action potential define the term ‘threshold’ and explain why not all stimuli generate an action potential The threshold is the amount of positive change in membrane potential which is required before an action potential is produced. The depolarisation must reach a threshold, which is at least 15mV more positive than the resting potential of -70mV. EPSP = excitatory postsynaptic potential

A threshold must be reached to generate an action potential define the term ‘threshold’ and explain why not all stimuli generate an action potential No action potential is produced if the depolarisation is below this level. This is one of the reasons why not all stimuli generate an action potential. Also, each stimuli produces either a full action potential or none at all.

A threshold must be reached to generate an action potential define the term ‘threshold’ and explain why not all stimuli generate an action potential Each action potential is a separate event. Therefore, a cell cannot produce another action potential until the previous one is complete.