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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

  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

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

  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

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