Synapses

Adjacent neurons do not touch each other. There is a small gap separating them. This gap or synaptic cleft plus the adjacent neurons forms a synapses. A synapses is therefore the junction across which a nerve impulse passes from an axon terminal to a neuron, a muscle cell or a gland.

• when a nerve impulses reach the terminal branches of axons, they cause vesicles in the pre-synaptic knob to burst, releasing neurotransmitters which diffuse across the synaptic gap • the neurotransmitters carry impulses across the gap - a chemical process which stimulates receptors in the post- synaptic membrane to initiate nerve impulses.

• they make sure that the flow of impulses is in one direction only • they allow the dispersal of impulses to many other neurons as neurotransmitters • they allow the “filtering out” of continual unnecessary stimuli

It is the functional unit of the nervous system. It is the pathway followed by impulses from a receptor to an effector to bring about a reflex action

Is a fast, automatic response by an effector organ, a muscle or a gland, to a stimulus received by a receptor organ. Reflexes may be: - somatic which activate skeletal muscles - autonomic which activate muscle and glands

Brain- controlling reflexes such as sneezing, breathing, blinking Spinal cord - controlling primitive reflexes such as the knee jerk

Reflex arcs bring about reflex actions that: • enable the body to respond quickly to stimulus • provide inborn safety mechanisms which serve mainly to protect the body from danger

• Receptor eg skin - responds to stimuli and generates impulses • Sensory neuron - carries impulse to CNS • Connector neuron - acts as reflex centre • Motor neuron - carries impulses to an effector organ • Effector - brings about change

• The receptors that respond to pain generate impulses in sensory neurons • the impulses are conducted along sensory neurons to the grey matter in the spinal cord • here the impulses make synaptic contact with the connector neurons which act as reflex centres • from connector neurons impulses make synaptic contact with motor neurons which conduct them to the effector • the effector, brings about a response by contracting very quickly to pull the finger away from the pin