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

1. 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

2. 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

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