The Human Nervous System.docx

The Human Nervous System The Nervous System has three steps; - Gather information about surroundings - Process and integrate information - Inform parts of the body that need to be informed The Central Nervous System consists of the brain and spinal cord The Peripheral Nervous System consists of sens...

The Human Nervous System The Nervous System has three steps; - Gather information about surroundings - Process and integrate information - Inform parts of the body that need to be informed The Central Nervous System consists of the brain and spinal cord The Peripheral Nervous System consists of sensory receptors, sensory neurons, motor neurons, and end plates Neurons A neuron is a nerve cell. (1) Dendrites : Collects impulses from other neurons of sensory cells Cell body: Control centre of the cell Nerve Impulse: Electrical impulse travelling along axon Myelin sheath: Insulates and protects axon as well as speeding up impulse Axon: Carries impulses away from the cell body to other neurons, muscles, or glands Schwann cells: Secretes myelin sheath Presynaptic knobs: Increase contact with the effector Movement of Nerve Impulse - Nerve impulses are either sent or not sent - The stimulus has to be of a certain strength, called its threshold, before it will cause an impulse to be triggered - All nerve impulses are exactly the same. The brain tells if a message is strong or weak by using the frequency of nerve impulses arriving per second. The more impulses per second, the stronger the stimulus - When the impulse has passed, the process resets itself, ready for the next impulse to be transmitted Synapses A synapse is the space between neurons. - An impulse arrives at the presynaptic knob - Neurotransmitter vesicles move to the surface and burst, releasing a transmitter substance, such as acetylcholine - The acetylcholine diffuses across the very narrow synapse quickly - It attaches to specific receptor sites on the post-synaptic swelling - This triggers an impulse in the next neuron, or it may stimulate an effector - The transmitter substance is then inactivated by an enzyme, such as cholinesterase - The inactive form of the transmitter substance then diffuses back across the synapse where it is reabsorbed into the presynaptic knob (2) Painkillers Substances called prostaglandins are produced by damaged tissue. These increase the sensitivity of pain receptors. Aspirin and ibuprofen both work by inhibiting the synthesis of prostaglandins. Neuron Types Sensory Neurons - Carry impulses from receptors e.g., sense organs to the Central Nervous System - Found in the dorsal root of spinal cord - Cell body is outside the Central Nervous System - Cell body is at end of a short branch along the length Motor Neurons - Carry impulses from The Central Nervous System to effector organs - Found in ventral root of spinal cord - Cell body inside Central Nervous System - Cell body is at one end Interneurons - Connect sensory to motor neurons in the Central Nervous System - Found in central nervous system only - Cell body inside Central Nervous System - Cell body at one end - No myelin sheath (3) The Brain The brain is the interpreting center for the senses. It stores information both in short-term and long-term memory. The brain is divided into three sections: the forebrain, the midbrain, and the hindbrain. The forebrain is the part of the brain that is more developed in humans than in any other species. (4) Cerebrum - Is made of two hemispheres and is connected by the corpus callosum - Controls thought, logic, will, intelligence, memory and activities connected with sense organs - The right hemisphere controls the left-hand side of the body - The left hemisphere controls the right-hand side of the body - The left side is dominant for hand use, language, math’s, and logic - The right side specialises in art, music, shape recognition, and emotional responses Cerebellum - Controls balance and muscular co-ordination - Affected by alcohol. Hypothalamus - Regulates the internal environment by monitoring osmoregulation, appetite, thirst, body temperature etc. - Assists the hormonal function of the pituitary gland Pituitary Gland - The Master Endocrine Gland as it secretes a large number of hormones - Controlled by hypothalamus Medulla oblongata - Links the brain to the spinal cord - Regulates heart and breathing rates Spinal Cord - Transmits impulses to and from the brain and controls many reflex actions - The spinal cord has an inner grey matter and outer white matter with 31 pairs of spinal nerves - The meninges are three layers of protective tissue that surrounds the brain and spinal cord (5) A reflex action is an automatic response to a stimulus, not involving the brain, which protects or minimises damage to the body. A reflex arc is the nerve pathway involved in a reflex action. An example of a reflex action is a ‘knee jerk’. In a Knee Jerk, the patellar tendon is stretched by a sharp tap. Stretch receptors in the muscle are stimulated. An impulse is sent to the spinal cord in the waist via the sensory neuron. This synapses with the motor neuron and an impulse are sent to the motor end plate and stimulates the extensor muscle in the leg to contract, and the leg jerks out. Nervous System Disorders – Parkinson’s Symptoms - Shuffling gait - Limb tremors Causes - No definitive cause - It’ s thought that repeated knocks to the head can damage the dopamine-producing cells Treatment - No cure - The drug, levodopa, a pre-cursor of dopamine, can cross the blood-brain barrier to ease symptoms for a while - Deep brain stimulation using implanted electrodes has been very successful