The Nervous System

The nervous system Functions Receive information from internal/external environment or other nerve cells Integrate the information and produce an appropriate output signal Conduct the signal Transmit the signal to other nerve cells, glands, or muscles

The nervous system Structural regions of typical vertebrate neurons Dendrites respond to external signals through the binding of receptor sites Cell body serves as the integration center and carries out basic metabolism 3. Axon conducts signals long distances 4. Synaptic terminal releases neurotransmitters to communicate with other cells

Receive signals from other neurons. Synaptic terminals: Dendrites: Receive signals from other neurons. Synaptic terminals: Bring signals from other neurons. Cell body: Integrates signals; coordinates metabolic activities. Action potential starts here. Myelin: Insulates the axon and speeds conduction. Arrows indicate direction of travel of action potential. Exposed areas of axon. Figure: 24-01 Title: A neuron, showing its specialized parts and their functions. Caption: Dendrites of other neurons receive signals. Synaptic terminals: Transmit signals to other neurons.

The nervous system Mechanisms of neural activity 1. Electrical signals and membrane potentials a. Resting potential b. Action potential

action potential threshold resting potential Figure: 24-02 Title: An action potential makes the inside of a neuron positive Caption: A recording (by oscilloscope) of the electrical events in a neuron. The resting potential is about 60 millivolts negative with respect to the outside. When the neuron is stimulated to threshold, the inside rapidly becomes positively charged. Shortly thereafter, the resting potential is reestablished.

The nervous system Mechanisms of neural activity Communication between neurons a. Synapses 1) Presynaptic neurons 2) Postsynaptic neurons b. Neurotransmitters and ion gradients c. Excitatory and inhibitory potentials

An action potential is initiated. presynaptic neuron postsynaptic neuron 1 An action potential is initiated. 2 The action potential reaches the synaptic terminal of the presynaptic neuron. synaptic vesicle synaptic terminal Figure: 24-03 Title: The structure and operation of the synapse. Caption: The synaptic terminal contains numerous vesicles that enclose a neurotransmitter for which the postsynaptic neuron has membrane receptors. When the neurotransmitter binds to postsynaptic receptors, ion channels open, causing a postsynaptic potential in the postsynaptic cell. 3 Synaptic vesicles release neurotransmitter. gap dendrite of postsynaptic neuron neurotransmitter ion channel closed 4 Receptor binds neurotransmitter and opens ion channel. plasma membrane of postsynaptic neuron

Figure: 24-T01 Title: Some important neurotransmitters. Caption:

The nervous system Operation of the nervous system 1. Four basic requirements a. Determine the type of stimulus 1) Wiring patterns in the brain 2) Nervous system monitors which neurons are firing

The nervous system b. Signal the intensity of the stimulus Operation of the nervous system b. Signal the intensity of the stimulus All action potentials are of the same magnitude Frequency of action potentials signals intensity 3) Number of firing neurons signals intensity

gentle touch; 1 fires slowly, 2 is silent (a) Gentle touch gentle touch; 1 fires slowly, 2 is silent (b) Moderate pressure Figure: 24-04 Title: Determining the intensity of a stimulus. Caption: Consider two touch receptors that have endings in adjacent patches of skin. (a) A gentle touch elicits only a few action potentials from one sensory neuron but none from another. (b) Moderate pressure stimulates only the first receptor, which now fires faster, informing the brain that the touch is more intense than before. (c) Strong pressure activates both receptors, firing the first one very fast and the other more slowly, thus signaling that the pressure is very intense and centered over the faster-firing receptor. moderate pressure; 1 fires more rapidly, 2 is silent (c) Strong pressure strong pressure: both 1 and 2 fire

The nervous system c. Integrate information from many sources Operation of the nervous system c. Integrate information from many sources Convergence of many neuron signals to fewer neurons d. Initiate and direct the response 1) Divergence—signals sent from a few decision-making cells to many neurons controlling the responses

white matter (contains myelinated axons) gray matter (contains cell bodies of motor and association neurons) dorsal root (contains axons of sensory neurons) central canal dorsal root ganglion (contains cell bodies of sensory neurons) Figure: 24-06 Title: The spinal cord in cross-section. Caption: peripheral nerve ventral root (contains axons of motor neurons)

The nervous system Operation of the nervous system Neural control of behavior a. Pathway contains four components 1) Sensory neurons—respond to a stimulus 2) Association neurons—activate motor neurons 3) Motor neurons—activate muscles or glands 4) Effectors—usually muscles or glands

The nervous system Neural control of behavior b. Simple behavior – the reflex c. Complex behaviors

Step 1: a painful stimulus activates a pain receptor dorsal root association neuron sensation relayed to the brain Step 2: signal transmitted by a sensory neuron REFLEX ARC receptor stimulus Step 5: effector muscle causes withdrawal response Figure: 24-07 Title: The pain-withdrawal reflex. Caption: This simple reflex circuit includes a sensory neuron that has pain-sensitive endings in the skin and a long fiber leading to the spinal cord. The sensory neuron stimulates an association neuron in the spinal cord, which in turn stimulates a motor neuron in the cord. An association neuron also sends the signal to the brain, informing it of the danger. effector ventral root Step 3: signal transmitted within the spinal cord Step 4: activation of a motor neuron stimulates the appropriate muscle

The human nervous system A. Peripheral nervous system Somatic nervous system—controls voluntary movement Autonomic nervous system—controls involuntary responses a. Sympathetic division—energetic and stressful activities b. Parasympathetic division—leisure and maintenance activities

Figure: 24-05 Title: The organization and functions of the vertebrate nervous system. Caption:

The human nervous system B. Central nervous system (CNS) 1. Brain a. Functions 1) Integration: senses, processes, and directs responses

The human nervous system Brain Structure 1) Hindbrain a) Contains the medulla, pons, and cerebellum Controls automatic functions of breathing, heart rate, blood pressure, swallowing, sleeping, and coordination of movements 2) Midbrain a) Contains the reticular formation Center for relay control and filtering sensory messages

FOREBRAIN (within dashed blue line) meninges cerebral cortex skull FOREBRAIN (within dashed blue line) corpus callosum hypothalamus thalamus pituitary gland Figure: 24-08 Title: The human brain. Caption: A section through the midline of the human brain reveals some of its major structures. MIDBRAIN cerebellum pons HINDBRAIN medulla spinal cord

The human nervous system Brain Structure 3) Forebrain a) Thalamus shuttles sensory information to the cerebrum and limbic system b) The limbic system controls instincts and emotions i) The limbic system includes the hypothalamus, amygdala, and hippocampus c) The cerebral cortex produces thoughts and perceptions i) Damage to the cerebral cortex

cerebral cortex thalamus hypothalamus hippocampus amygdala Figure: 24-09 Title: The limbic system and thalamus. Caption: In this view of the brain, the left cerebral cortex is transparent. hypothalamus hippocampus amygdala

higher intellectual functions Visual Association Area hand Primary Motor Area Primary Sensory Area Sensory Association Area leg trunk arm higher intellectual functions Visual Association Area hand face tongue Primary Auditory Area Primary Visual Area Figure: 24-10 Title: The cerebral cortex. Caption: Structural (colored) and functional (labeled) regions of the human left cerebral cortex. A map of the right cerebral cortex would be similar, except that speech and language are less well developed there. Speech Motor Area memory language comprehension and formation

The human nervous system B. Central nervous system (CNS) (cont.) 2. Spinal cord a. A cable of axons protected by the backbone b. Conducts signals to the brain c. Spinal cord injuries

The human nervous system C. The brain and the mind 1. Brain and mind research 2. Left-brain functions 3. Right-brain functions D. Memory and learning 1. Working memory 2. Long-term memory 3. Learning involves the hippocampus 4. Neither is well understood