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Nervous System

Nervous System. Neurones. Basic unit of nervous system, also known as a nerve cell. Form Grey Matter of nervous system. Consist of long projections or processes known as AXONS and DENDRITES. Although a nerve cell contains a nucleus it cannot divide or multiply as most other cell. Axons.

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Nervous System

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  1. Nervous System

  2. Neurones • Basic unit of nervous system, also known as a nerve cell. Form Grey Matter of nervous system. • Consist of long projections or processes known as AXONS and DENDRITES. • Although a nerve cell contains a nucleus it cannot divide or multiply as most other cell.

  3. Axons • 1 per nerve cell • Carry impulses away from cell body • Most are myelinated - myelin increases rate of impulse transmission • (Refer to diagram)

  4. Dendrites • Many short processes • Receive and carry incoming impulses towards cell bodies • Axons and dendrites form White Matter of nervous system

  5. Neurone Behaviour • Triggered by a stimulus to produce nerve impulses. • Level at which stimulus is strong enough- threshold. • Speed of transmission of impulse can be affected by- myelin sheath, cold and diameter of cell.

  6. Action Potentials • Initiated by stimulation of sensory nerve endings or by passage of an impulse from one cell to another. It is due to movement of ions across cell plasma membrane- sodium and potassium- active transport. In resting stage membrane is polarised- sodium higher outside and potassium inside. Causes a different electrical charge on each side- Resting membrane Potential.( inside +, outside -)

  7. In resting stage ions diffuse – potassium outwards, sodium inwards- due to increased membrane permeability. Sodium floods in causing Depolarisation and creating an action potential. Potassium then floods out returning the neurone to its resting state. Restimulation is not possible at this time. Sodium/potassium pump returns cell to its resting state.

  8. Types of nerves • Sensory or Afferent nerves- respond to different stimuli outside and inside body eg senses, balance, posture, involuntary activity. • Motor or Efferent nerves- transmit to effector organs eg muscles and glands.

  9. Synapse and Neurotransmitters • Always more than one neurone involved in transmission of impules • No physical contact between neurones. • Impulses cross at Synapse via Synaptic Cleft. • Chemicals required- secreted in synaptic knobs and released into cleft by diffusion. • Have a short lived effect. • Include- nor adrenaline, adrenaline, serotonin, dopamine, acetylcholine, histamine.

  10. Central Nervous System • Consists of brain and spinal cord. • Completely surrounded by 3 layers of tissue- the Meninges • Dura Mater • Arachnoid Mater • Pia Mater

  11. Ventricles of Brain • 4 irregular shaped cavities or ventricles - • Right and Left Lateral Ventricles • Third ventricle • Fourth Ventricle

  12. Cerebrospinal Fluid • Secreted by Choroid Plexus • Rate of 0.5ml per minute- 720ml per day • Clear, slightly alkaline fluid consisting of- water, glucose, mineral salts, plasma proteins, small amounts of creatinine and urea, a few leucocytes. • Functions- supports and protects brain and spinal cord, maintains a uniform pressure around structures, acts as a cushion and shock absorber and keeps brain and spinal cord moist.

  13. Brain

  14. Brain • Consists of –cerebrum, midbrain, pons, medulla oblongata and cerebellum. • Receives about 15% of cardiac output- 750ml blood per minute.

  15. Cerebrum • Largest part of brain. Right and left hemispheres. Superficial part is made up of grey matter- forms cerebral cortex. Deeper layers consist of white matter. Has many furrows or convolutions, which greatly increase the surface area. • Hemisphere- 4 lobes • Frontal • Parietal • Temporal • Occipital

  16. Functions of Cerebral Cortex • Mental activities- memory, intelligence, sense of responsibility, thinking, reasoning, moral sense and learning • Sensory perception- pain, temperature, touch, sight, hearing, taste, smell • Initiation and control of skeletal(involuntary) muscle contraction

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