Presentation on theme: "NERVOUS SYSTEM Its function is to control and co-ordinate the parts of the body."— Presentation transcript:
NERVOUS SYSTEM Its function is to control and co-ordinate the parts of the body.
CENTRAL NERVOUS SYSTEM(CNS) PERIPHERAL NERVOUS SYSTEM (PNS) BRAIN receives and sends out messages. SPINAL CORD connects the brain to the rest of the body. CRANIAL NERVES carry messages directly to and from the brain. SPINAL NERVES carry messages to and from the spinal cord. Coordinating center for incoming and outgoing information Carry info. between organs such as skin, heart, eyes, ears and the CNS.
Peripheral Nervous System Somatic Nervous System Sensory and motor neurons under conscious control VOLUNTARY e.g. controls skeletal muscles Autonomic Nervous System Motor neurons that function without conscious control INVOLUNTARY e.g. controls heart rate, blood pressure, digestive muscles, breathing
NERVE CELLS There are two types: 1.Glial cells – non-conducting / important for structural support and Schwann cells make myelin 2.Neurons - Specialized cells that can carry electro-chemical messages called NERVE IMPULSES Neurons can be classed according to function. Sensory neurons Interneurons – link neurons Motor neurons
Direction of impulse ReceptorDendrite Cell body Axon Branches forming synapse These sense and relay info. from the environment to CNS Baroreceptors (detect pressure) Chemoreceptors (detect chemicals) Photoreceptors (detect light) Osmoreceptors Thermoreceptors SENSORY NEURONS
MOTOR NEURONES These carry impulses from the CNS to an EFFECTOR (a muscle or a gland or an organ). Direction of impulse DendritesCell body Axon Nerve endings on a muscle Both sensory and motor neurons are very long (up to 1m in a human). This helps to reduce the synapses (connections) needed.
Neurons can also be classified structurally Several dendrites, one axon, found in brain and spinal cord Single dendrite, single axon, found in inner ear, retina of eye and olfactory area of brain Dendrite and axon are fused and extend from cell body, found in peripheral nervous system
The importance of myelin Many neurons have axons that are covered in a fatty substance called myelin. This insulates the axons so it stops impulses jumping from one axon into others next to it. The myelin sheath also increases impulse speeds. Direction of impulse Myelin sheath
NERVES NERVE CELLS (FIBRES) NERVE A nerve is a bundle of nerve fibres (cells). Most nerves carry a mixture of sensory and motor fibres.
SYNAPSES Nerve impulses can travel at up to 100m per sec but when they reach the end of a cell they have to cross a gap called a SYNAPSE. IMPULSE Impulse arrives at the end of first neuron. TRANSMITTER chemical is released from vesicles. TRANSMITTER diffuses across the gap When TRANSMITTER reaches second neuron it starts a new impulse.
The synapse The gap between neurones is called a synapse. Messages are sent across this gap using chemical messengers. End of neurone (Axon terminal) Chemical is released by one neurone and detected by the next Impulse travels along axon to the terminal An impulse travels through the neurone
Serotonin Normal functions –Emotions –Judgment –Sleep Imbalances –Depression –Suicidal behavior –Anxiety –Impulsive behavior –Eating disorders Glutamate/GABA Normal functions Involved in most facets of brain function Imbalances Memory disturbances Sleep disturbances Anxiety
Dopamine Normal functions –Mood –Movement –Memory Imbalances –Movement disorders –Schizophrenia –Addiction Endorphins Normal functions Relieve pain Induce euphoria
REFLEXES These reactions are:- Fast Automatic Unlearned Do not involve the brain Often designed to protect the body
Examples :- COUGHINGRemoves particles from breathing system PUPIL REFLEX Automatically adjusts the eye to light intensity WITHDRAWAL REFLEX Removes arm or leg from a painful stimulus to prevent damage.
Motor neurone Sensory neurone Effector (Biceps) Receptor in skin Spinal cord REFLEX ARC The path taken by an impulse during a reflex eg Withdrawing hand from a painful stimulus.
Reflex arc Finger touches hot object Receptor in skin detects stimulus Sensory neurone sends impulse to spinal cord Motor neurone picks up impulse from sensory neurone and sends impulse to the effector Effector (muscle) moves hand away from danger Gap between neurones is called synapse
REFLEX ARC IN SPINAL CORD Grey matter White matter Sensory neuron Motor neuron Interneuron Synapse Dorsal root of spinal nerve
SEQUENCE OF EVENTS 1. Skin of hand touches a hot surface. 2. Temperature receptors in the skin start an impulse 3. Impulse travels up the spinal nerve of the arm in a sensory neuron. 4. Impulse passed to relay neurone in spinal cord 5. Impulse travels down the spinal nerve of the arm in a motor neuron. 6. Impulse causes BICEPS muscle to contract bending the arm and pulling the hand away NB Although the brain is informed it does not have time to stop the reaction.
The reflex is fast because:- The impulse does not need to travel through the brain so it only involves two synapses. Synapses delay a reaction because of the time taken for transmitter to diffuse across the gap between neurones.