Nervous System

All animals have a nervous system except for sponges
Nerve net * Simplest nervous system * Cnidarians (jellyfish, hydras, anemones) * Neurons connect to each other in a network * Activation of neurons in one area leads to activation of all or most neurons
Echinoderms * Slightly more complicated * Nerve ring around mouth connected to larger radial nerves extending to arms * Mouth and arms operate independently
Planaria * Nerve cords extend length of animal connected by transverse nerves * Collection of neurons in head form cerebral ganglia * Basic integration of sensory input and motor output
Annelids * Same basic structure * More neurons * Ventral nerve cords have ganglia in each segment * Rudimentary brain
Simple mollusks * Similar to annelids * Pair of anterior ganglia * Paired nerve cords
Trend toward cephalization: increasingly complex brain in the head
Insects – Drosophila * Brain has several subdivisions with separate functions
Advanced mollusks * Well- developed brain with subdivisions
Chordates
CNS: brain and nerve cord * Brain and spinal cord in vertebrates
PNS: all neurons that are outside of the CNS
In certain invertebrates with a simple nervous system, the distinction is less clear

Somatic nervous system: primary function to sense external environment and control skeletal muscles * Sensory neurons receive stimuli – heat, vision, smell, taste, hearing, touch – and transmit to CNS * Motor neurons control skeletal muscles * Controls many voluntary responses
Autonomic nervous system: regulates homeostasis and organ function * Predominantly composed of motor neurons * Involuntary – usually cannot be consciously controlled * Sensory neurons detect internal body conditions * Efferent nerves of autonomic nervous system are further divided * Act on same organs with opposing actions * Sympathetic division * Fight-or-flight * Increased heart rate, faster breathing, relaxed airways * Parasympathetic division * Rest-or-digest * Slow heart rate, promote digestion

Medulla oblongata * Coordinates basic reflexes and bodily functions that maintain normal homeostatic processes * Controls heart rate, breathing, cardiovascular function, digestion, swallowing, and vomiting
Cerebellum * Overall function of the cerebellum is to maintain balance and coordinate hand-eye movements * May have significant cognitive functions
Pons * Serves as a relay between the cerebellum and other areas of the brain * Regulates rate and depth of breathing

Processes sensory inputs of several types, including vision, olfaction, and audition
Tracts pass this information to other parts of the brain for further processing and interpretation
Brainstem: medulla oblongata, pons and midbrain * Reticular formation * All three parts of brainstem contain nuclei contributing to the reticular formation * Maintains and controls alertness and sleep * Regulation of respiration and cardiovascular systems

Thalamus * Relays sensory information to the cerebrum * Also sends outputs from the cerebrum to other parts of the brain * Gets input from all sensory systems except olfaction
Hypothalamus * Produces hormones regulating pituitary gland, which regulates hormone secretion from other glands * Great importance for homeostasis of the body and the control of behavior
Epithalamus * Structures with various roles in the production of cerebrospinal fluid, control of food and water intake, and rhythmic and seasonal behaviors * Pineal gland produces melatonin
Cerebral cortex * Surface layer of gray matter on the cerebrum * Contains 10% of neurons in the brain * Integrate information from other nervous system structures and creates outgoing signals
Brain has two halves or hemispheres with four lobes each * Frontal lobe: conscious thought and social awareness * Parietal lobe: receives and interprets sensory input from visual pathways and somatic pathways * Occipital lobe: vision and color recognition * Temporal lobe: language, hearing, and some types of memory * Corpus callosum: connects the cerebral hemispheres * Severing this connection was used in the past to treat severe epilepsy * Hemispheres can function independently * Process different types of information * Left hemisphere: understanding language and producing speech * Right hemisphere: nonverbal memories, recognizing faces. and interpreting emotions

Basal nuclei * Involved in planning, learning, and fine-tuning movements * Complex circuitry to initiate or inhibit movements * Affected in Parkinson disease * People with disease have trouble initiating movement
Limbic system * Include the olfactory bulbs, amygdala, and hippocampus * Primarily involved in formation and expression of emotions * Role in learning, memory, and perception of smells * amygdala – understand and remember emotional situations, recognize emotional expressions in others * hippocampus – establish memories for spatial locations, facts, and sequences of events

Sensory Neurons: detect information from the outside world or internal body conditions * Afferent neurons – transmit to CNS
Motor Neurons: send signals away from CNS (efferent neurons) to elicit response
Interneurons or Association Neurons: form interconnections between other neurons

Stimulus from sensory neurons sent to CNS, little or no interpretation (few or no interneurons), signal transmitted to motor neurons to elicit response
Quick and automatic response