Nervous System
Representative Nervous Systems
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
Two Divisions of PNS
- 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
- Predominantly composed of motor neurons
Hindbrain
- 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
Midbrain
- 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
Forebrain - Diencephalon
- 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
Cerebrum - Telencephalon
- 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
Three Main Types of Neurons
- 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
Reflex Arc
- 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