BY4: The reflex arc
A reflex action is a rapid, involuntary response resulting from nervous impulses initiated by a stimulus. The action is involuntary in that the brain is not involved. Reflex actions are generally protective in function. The following describes a typical reflex action – the nerve pathways involved in the flexion of the arm in response to touching a hot surface.
Stimulus: the hot surface
Receptor: temperature receptors (thermoreceptors) and pain receptors (nociceptors) in the skin
Sensory neurone: sends nerve impulse (a series of action potentials) into the spinal cord
Relay (intermediate) neurone: connects sensory neurone to motor neurone in the grey matter of the spinal cord
Motor neurone: sends impulse to an effector organ/tissue (muscle)
Response: arm muscles contract and the hand is removed from surface
Action Draw an annotated diagram of the nervous pathways of this reflex arc
Although many reflexes are protective, actions such as blinking, coughing and swallowing are also co-ordinated by reflexes.
With any reflex action there is also a pathway for impulses to be sent to the brain via ascending nerve fibres that originate at synapses in the grey matter of the spinal cord. The ascending nerve sends nerve impulses up the spinal cord in the white matter. The brain may store this information or it may relate the information with sense data from, say, the eyes. As a result of receiving this extra information impulses may be sent from the brain to modify the response. Sometimes the response is over-ridden by the brain along inhibitory nerve fibres.
A reflex action is a rapid, involuntary response resulting from nervous impulses initiated by a stimulus. The action is involuntary in that the brain is not involved. Reflex actions are generally protective in function. The following describes a typical reflex action – the nerve pathways involved in the flexion of the arm in response to touching a hot surface.
Stimulus: the hot surface
Receptor: temperature receptors (thermoreceptors) and pain receptors (nociceptors) in the skin
Sensory neurone: sends nerve impulse (a series of action potentials) into the spinal cord
Relay (intermediate) neurone: connects sensory neurone to motor neurone in the grey matter of the spinal cord
Motor neurone: sends impulse to an effector organ/tissue (muscle)
Response: arm muscles contract and the hand is removed from surface
Action Draw an annotated diagram of the nervous pathways of this reflex arc
Although many reflexes are protective, actions such as blinking, coughing and swallowing are also co-ordinated by reflexes.
With any reflex action there is also a pathway for impulses to be sent to the brain via ascending nerve fibres that originate at synapses in the grey matter of the spinal cord. The ascending nerve sends nerve impulses up the spinal cord in the white matter. The brain may store this information or it may relate the information with sense data from, say, the eyes. As a result of receiving this extra information impulses may be sent from the brain to modify the response. Sometimes the response is over-ridden by the brain along inhibitory nerve fibres.
Generation of a reflex arc. The reflex arc is normally protective in and is involuntary. However, other reflex actions may involve blinking, coughing and swallowing food. The receptor will detect a stimulus in either the external or internal environment and initiate a nerve impule being sent down the sensory neurone to the spinal cord. Here the sensory neurone synapses with a relay (intermediate) neurone and passes the nerve impulse to a motor neurone in the grey matter. The motor neurone acts as the effector nerve and carries the nerve impulse away from the spinal cord to an effector organ/tissue such as the muscles. Here an appropriate response is initiated. The sensory neurone in the grey matter can also synapse with an ascending nerve which carries the impulse up to the brain. This information can be combined with other sensory information (such as from the eyes) to form a memory. Certain reflex actions (such as blinking) can be controlled by inhibitory nerve fibres from the brain that prevent the reflex action occurring.
Please see video below for information about different receptors in the body (that detect stimuli from both the external and the internal environment):