The Nervous System chapter 37 Gathering, analyzing and responding to stimuli - information from internal and external environment - via nerve cells, aka neurons All domains detect and respond; only animals have a NS

Neuron Circuitry a one-way loop 2) Interneurons in brain, spinal cord analyse incoming info, send msg to… 1) Receptors attached to sensory neurons receive stimuli, direct impulse to… receptor interneuron 3) Motor neurons to effectors for response effector

Neurons interact chemically Information travels down the axon as a charge (action potential) but breaches the gap between neurons chemically, via neurotransmitters Direction of impulse axon Vesicles release neurotransmitters via exocytosis dendrite One dendrite can receive info from many axons

Reflex arc spinal cord directs response - msg to brain after the fact message to brain patellar reflex Pain, blinking,, etc. Interneuron in cord relays to motor neuron moro reflex

2 NS divisions CNS - central nervous system brain, spinal cord (+20 billion interneurons!) PNS - peripheral nervous system receptors, sensory neurons effectors, motor neurons

Receptors photoreceptors mechanoreceptors nociceptors chemoreceptors Attached to sensory neurons photoreceptors 10 million sensory neurons! mechanoreceptors nociceptors chemoreceptors

Effectors Terminal end of motor neurons muscles glands Half million motor neurons! muscles glands

NS architecture PNS motor sensory CNS brain spinal cord autonomic respond take in brain spinal cord autonomic somatic Involuntary internal stimuli glands, heart, etc Voluntary external stimuili > skeletal muscle effector Somatic, autonomic work together to maintain homeostasis Exception; reflexes are somatic Ex: as body temp drops, somatic causes shivering, autonomic constricts surface blood vessels sympathetic parasympathetic ‘rest & digest’ ‘fight or flight’