Adv Biology 1-2

The Nervous System Consists of the brain, spinal cord and supporting cells. Purpose: Sensory input-conduction of signals to the brain. Integration-interpretation and formulation of response. Motor output-create a response.

Nervous System cont’d Central nervous system (CNS) is the brain and spinal cord. Site of integration. Peripheral nervous system (PNS) is the nerves outside the CNS. Includes ganglia (sing.: ganglion) a cluster of neuron cell bodies. Where sensory input and motor output occur.

Neurons Neuron-the functional unit of the nervous system. Sensory neuron-carry impulses from sensory receptors to the spinal cord. Sensory receptor-structure that picks up stimulus from the environment. Motor neuron-carry impulses from spinal cord and create a response. Interneuron-neuron in the brain or spinal cord. Relay impulses to and from the brain, interpret and formulate responses.

Neurons cont’d Three parts to a neuron: Cell body-enlarged part of the neuron, where the nucleus is. Dendrite-thin branches off the cell body, receive and transmit impulses to the cell body. Axon-long extension off the cell body, carries impulses from the cell body. The axon is insulated by the myelin sheath.

Action Potentials The cell membrane has a charge of -65 to -70 mV. Inside is negative, outside is positive. Changing the charge of the membrane creates an action potential. The action potential creates an electrical current (nervous impulse) that travels to and from the brain.

Action Potentials cont’d Stimulus-anything that generates a nervous impulse. The stimulus must be great enough to create an action potential (all or nothing response). Stimulus causes gates to open, Na+ ions enter, K+ ions flow out. Moving ions create an electric current (impulse). The impulse moves down the dendrite to the cell body to the axon.

Action Potentials cont’d Synapse-junction between neuron and the next. At the end of the axon, the impulse releases neurotransmitters into the synapse. Neurotransmitters cross the synapse and create an action potential on dendrites of the neighboring neuron. Open gates, allowing Na+ and K+ to enter/exit.

Action Potentials cont’d The impulse travels from sensory neurons to interneurons in the spinal cord to interneurons in the brain. Brain interprets and sends out an impulse down the spinal cord to the motor neurons. Motor neurons create the desired response.

Action Potentials cont’d Refractory period-time after an impulse is sent. During the refractory period, the neuron cannot send another impulse. The neuron runs pumps to remove Na + and bring in K +. The potential is reset and the neuron can make another impulse.

Reflexes Reflex-unconscious response to a stimulus. Reflex arc-pathway an impulse of a reflex travels. Sensory receptor to sensory neuron to spinal cord. Spinal cord sends it back out along a motor neuron closely associated with the sensory neuron. Motor neuron creates a response.