HCAS133 - Lecture 5 – The Nervous System, the Endocrine System, and Senses

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HCAS133 - Lecture 5 - The Nervous System, the Endocrine System, and Senses Majority of content within this lecture is extracted from https://www.oercommons.org/courses/anatomy-and-physiology-4/view Lesson 1 – Nervous System Tissue Introduction The nervous system is a very complex organ system. In Peter D. Kramer’s book Listening to Prozac , a pharmaceutical researcher is quoted as saying, “If the human brain were simple enough for us to understand, we would be too simple to understand it” (1994). One easy way to begin to understand the structure of the nervous system is to start with the large divisions and work through to a more in-depth understanding. The nervous system can be divided into two major regions: the central and peripheral nervous systems. The central nervous system (CNS) is the brain and spinal cord, and the peripheral nervous system (PNS) is everything else ( Figure 12.2 ). The brain is contained within the cranial cavity of the skull, and the spinal cord is contained within the vertebral cavity of the vertebral column. Figure 12.2 Central and Peripheral Nervous System The structures of the PNS are referred to as ganglia and nerves, which can be seen as distinct structures. The equivalent structures in the CNS are not obvious from this overall perspective and are best examined in prepared tissue under the microscope.

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 2 Basic Structure and Function of the Nervous Tissue Nervous tissue, present in both the CNS and PNS, contains two basic types of cells: neurons and glial cells. A glial cell provides a framework of tissue that supports the neurons and their activities. The neuron is the more functionally important of the two in terms of the communicative function of the nervous system. To describe the functional divisions of the nervous system, it is important to understand the structure of a neuron. Neurons are cells and therefore have a soma , or cell body, but they also have extensions of the cell; each extension is generally referred to as a process . There is one important process that every neuron has called an axon , which is the fiber that connects a neuron with its target. Another type of process that branches off from the soma is the dendrite . Dendrites are responsible for receiving most of the input from other neurons. Figure 12.8 Parts of a Neuron The major parts of the neuron are labeled on a multipolar neuron from the CNS. Looking at nervous tissue, there are regions that predominantly contain cell bodies and regions that are largely composed of just axons. These two regions within nervous system structures are often referred to as gray matter (the regions with many cell bodies and dendrites) or white matter (the regions with many axons). Figure 12.3 demonstrates the appearance of these regions in the brain and spinal cord. Figure 12.3 Gray Matter and White Matter A brain removed during an autopsy, with a partial section removed, shows white matter surrounded by gray matter. Gray matter makes up the outer cortex of the brain. (credit: modification of work by “Suseno”/Wikimedia Commons)

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 3 Basic Functions The nervous system is involved in receiving information about the environment around us (sensation) and generating responses to that information (motor responses). The nervous system can be divided into regions that are responsible for sensation (sensory functions) and for the response (motor functions). But there is a third function that needs to be included. Sensory input needs to be integrated with other sensations, as well as with memories, emotional state, or learning (cognition). Some regions of the nervous system are termed integration or association areas. The process of integration combines sensory perceptions and higher cognitive functions such as memories, learning, and emotion to produce a response. Sensation . The first major function of the nervous system is sensation—receiving information about the environment to gain input about what is happening outside the body. The senses we think of most are the “big five”: taste, smell, touch, sight, and hearing. Those five are all senses that receive stimuli from the outside world and of which there is conscious perception. Response . The nervous system produces a response on the basis of the stimuli perceived by sensory structures. An obvious response would be the movement of muscles, such as withdrawing a hand from a hot stove, but there are broader uses of the term. Integration . Stimuli that are received by sensory structures are communicated to the nervous system where that information is processed. This is called integration. Stimuli are compared with, or integrated with, other stimuli, memories of previous stimuli, or the state of a person at a particular time. How does the brain function? Imagine you are about to take a shower in the morning before going to school. You have turned on the faucet to start the water as you prepare to get in the shower. After a few minutes, you expect the water to be at a temperature that will be comfortable to enter. So, you put your hand out into the spray of water. What happens next depends on how your nervous system interacts with the stimulus of the water temperature and what you do in response to that stimulus.

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 4 Found in the skin of your fingers or toes is a type of sensory receptor that is sensitive to temperature, called a thermoreceptor . When you place your hand under the shower ( Figure 12.15 ), the cell membrane of the thermoreceptors changes its electrical state (voltage). The amount of change is dependent on the strength of the stimulus (how hot the water is). This is called a graded potential . If the stimulus is strong, the voltage of the cell membrane will change enough to generate an electrical signal that will travel down the axon. The voltage at which such a signal is generated is called the threshold , and the resulting electrical signal is called an action potential . In this example, the action potential travels—a process known as propagation —along the axon from the axon hillock to the axon terminals and into the synaptic end bulbs. When this signal reaches the end bulbs, it causes the release of a signaling molecule called a neurotransmitter . Figure 12.15 The Sensory Input Receptors in the skin sense the temperature of the water. The neurotransmitter diffuses across the short distance of the synapse and binds to a receptor protein of the target neuron. When the molecular signal binds to the receptor, the cell membrane of the target neuron changes its electrical state, and a new graded potential begins. If that graded potential is strong enough to reach threshold, the second neuron generates an action potential at its axon hillock. The target of this neuron is another neuron in the thalamus of the brain, the part of the CNS that acts as a relay for sensory information. At another synapse, the neurotransmitter is released and binds to its receptor. The thalamus then sends the sensory information to the cerebral cortex , the outermost layer of gray matter in the brain, where conscious perception of that water temperature begins. Within the cerebral cortex, information is processed among many neurons, integrating the stimulus of the water temperature with other sensory stimuli, with your emotional state (you just aren’t ready to wake up; the bed is calling to you), memories (perhaps of the lab notes you have to study before a quiz). Finally, a plan is developed about what to do, whether that is to turn the temperature up, turn the whole shower off and go back to bed, or step into the shower. To do any of these things, the cerebral cortex has to send a command out to your body to move muscles ( Figure 12.16 ).

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 5 Figure 12.16 The Motor Response On the basis of the sensory input and the integration in the CNS, a motor response is formulated and executed. Types of Neurons, Glial Cells, and Myelin You will note that the words 'groups' and 'types' when referring to neurons are used interchangeably according to the author. (GLIAL CELLS, n.d.) There are many neurons in the nervous system—a number in the trillions. And there are many different types of neurons. They can be classified by many different criteria. The first way to classify them is by the number of processes attached to the cell body. Using the standard model of neurons, one of these processes is the axon, and the rest are dendrites. (Molnar & Gair, 2019) Figure 12.9 Neuron Classification by Shape Unipolar cells have one process that includes both the axon and dendrite. Bipolar cells have two processes, the axon and a dendrite. Multipolar cells have more than two processes, the axon and two or more dendrites. Unipolar cells have only one process emerging from the cell. Unipolar cells are exclusively sensory neurons and have two unique characteristics. They are mostly located in the special senses. Pseudounipolar neurons are unipolar neurons with a single axon that splits in two. They are associated with ganglia and often connect the peripheral nervous system to the central nervous system.

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 6 Bipolar cells have two processes, which extend from each end of the cell body, opposite to each other. One is the axon and one the dendrite. Bipolar cells are not very common. They are found mainly in the olfactory epithelium and as part of the retina. Multipolar neurons are all of the neurons that are not unipolar or bipolar. They have one axon and two or more dendrites (usually many more). With the exception of the unipolar sensory ganglion cells, and the two specific bipolar cells mentioned above, all other neurons are multipolar. Multipolar neurons are the most common in the nervous system Glial Cells Glial cells, or neuroglia or simply glia, are the other type of cell found in nervous tissue. They are considered to be supporting cells, and many functions are directed at helping neurons complete their function for communication. The name glia comes from the Greek word that means “glue.” There are six types of glial cells. Four of them are found in the CNS and two are found in the PNS. Table 12.2 outlines some common characteristics and functions. Glial Cell Types by Location and Basic Function CNS glia PNS glia Basic function Astrocyte Satellite cell Support Oligodendrocyte Schwann cell Insulation, myelination Microglia - Immune surveillance and phagocytosis Ependymal cell - Creating CSF Table 12.2 Figure 12.11 Glial Cells of the CNS The CNS has astrocytes, oligodendrocytes, microglia, and ependymal cells that support the neurons of the CNS in several ways.

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 7 Figure 12.12 Glial Cells of the PNS The PNS has satellite cells and Schwann cells. Myelin The insulation for axons in the nervous system is provided by glial cells, oligodendrocytes in the CNS, and Schwann cells in the PNS. Whereas the manner in which either cell is associated with the axon segment, or segments, that it insulates is different, the means of myelinating an axon segment is mostly the same in the two situations. Myelin is a lipid-rich sheath that surrounds the axon and by doing so creates a myelin sheath that facilitates the transmission of electrical signals along the axon. Action Potential and Neuron Communication The nervous system is characterized by electrical signals that are sent from one area to another. Whether those areas are close or very far apart, the signal must travel along an axon. The basis of the electrical signal is the controlled distribution of ions across the membrane. Transmembrane ion channels regulate when ions can move in or out of the cell, so that a precise signal is generated. This signal is the action potential which has a very characteristic shape based on voltage changes across the membrane in a given time period. The membrane is normally at rest with established Na + and K + concentrations on either side. A stimulus will start the depolarization of the membrane, and voltage-gated channels will result in further depolarization followed by repolarization of the membrane. A slight overshoot of hyperpolarization marks the end of the action potential. While an action potential is in progress, another cannot be generated under the same conditions. While the voltage-gated Na + channel is inactivated, absolutely no action potentials can be generated. Once that channel has returned to its resting state, a new action potential is possible, but it must be started by a relatively stronger stimulus to overcome the K + leaving the cell. The action potential travels down the axon as voltage-gated ion channels are opened by the spreading depolarization.

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 8 Figure 12.24 Stages of an Action Potential Plotting voltage measured across the cell membrane against time, the events of the action potential can be related to specific changes in the membrane voltage. (1) At rest, the membrane voltage is -70 mV. (2) The membrane begins to depolarize when an external stimulus is applied. (3) The membrane voltage begins a rapid rise toward +30 mV. (4) The membrane voltage starts to return to a negative value. (5) Repolarization continues past the resting membrane voltage, resulting in hyperpolarization. (6) The membrane voltage returns to the resting value shortly after hyperpolarization. Watch the following 2 minute, 43 second video by MediMationz to learn about action potential. As you watch the video, consider the following: action potential  What effects does K+ and Na+ ions have on action potential?  How about if the stimulus wasn’t strong enough to hit threshold? ANSWER:  The cell membrane polarization, depolarization, and hyperpolarization depends on the concentration of the two ions K- and Na+.  If the stimulus is not strong enough to reach threshold, no action potential will be fired (According to the All-or-None law). Lesson 1 Completed! Thank you! You have completed this lesson. Please scroll down to complete a short, ungraded Knowledge Check activity. Check Your Knowledge 1 1. Which of the following cavities contains a component of the central nervous system? a. abdominal b. pelvic c. cranial (Correct: C) d. thoracic 2. Which part of a neuron transmits an electrical signal to a target cell? a. dendrites b. soma

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 9 c. cell body d. axon (Correct: D) 3. What ion enters a neuron causing depolarization of the cell membrane? a. sodium (Correct A) b. chloride c. potassium d. phosphate Lesson 2 – Anatomy of the Nervous System The nervous system is responsible for controlling much of the body, both through somatic (voluntary) and autonomic (involuntary) functions. The structures of the nervous system must be described in detail to understand how many of these functions are possible. CNS The brain and the spinal cord are the central nervous system, and they represent the main organs of the nervous system. The spinal cord is a single structure, whereas the adult brain is described in terms of four major regions: the cerebrum, the diencephalon, the brain stem, and the cerebellum. A person’s conscious experiences are based on neural activity in the brain. The regulation of homeostasis is governed by a specialized region in the brain. The coordination of reflexes depends on the integration of sensory and motor pathways in the spinal cord. Brain The Cerebrum The iconic gray mantle of the human brain, which appears to make up most of the mass of the brain, is the cerebrum ( Figure 13.6 ). The wrinkled portion is the cerebral cortex , and the rest of the structure is beneath that outer covering. There is a large separation between the two sides of the cerebrum called the longitudinal fissure . It separates the cerebrum into two distinct halves, a right and left cerebral hemisphere . Deep within the cerebrum, the white matter of the corpus callosum provides the major pathway for communication between the two hemispheres of the cerebral cortex. Many of the higher neurological functions, such as memory, emotion, and consciousness, are the result of cerebral function. Figure 13.6 The Cerebrum The cerebrum is a large component of the CNS in humans, and the most obvious aspect of it is the folded surface called the cerebral cortex.

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 10 The lateral sulcus that separates the temporal lobe from the other regions is one such landmark. Superior to the lateral sulcus are the parietal lobe and frontal lobe , which are separated from each other by the central sulcus . The posterior region of the cortex is the occipital lobe . Figure 13.7 Lobes of the Cerebral Cortex The cerebral cortex is divided into four lobes. Extensive folding increases the surface area available for cerebral functions. The temporal lobe is mainly associated with auditory and taste sensations. The parietal lobe is mainly associated with somatosensation. The frontal lobe is mainly associated with motor functions, it has Broca’s area that is responsible for the production of language or controlling movements responsible for speech; in the vast majority of people, it is located only on the left side. The occipital lobe is mainly associated with visual sensation. The Diencephalon The diencephalon is deep beneath the cerebrum and constitutes the walls of the third ventricle. The two major regions of the diencephalon are the thalamus and the hypothalamus ( Figure 13.11 ). Thalamus The thalamus is a collection of nuclei that relay information between the cerebral cortex and the periphery, spinal cord, or brain stem. All sensory information, except for the sense of smell, passes through the thalamus before processing by the cortex. Axons from the peripheral sensory organs, or intermediate nuclei, synapse in the thalamus and thalamic neurons project directly to the cerebrum. Hypothalamus Slightly anterior to the thalamus is the hypothalamus , the other major region of the diencephalon. The hypothalamus is a collection of nuclei that are largely involved in regulating homeostasis. The hypothalamus is the executive region in charge of the autonomic nervous system and the endocrine system through its regulation of the anterior pituitary gland. Other parts of the hypothalamus are involved in memory and emotion as part of the limbic system.

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 11 Figure 13.11 The Diencephalon The diencephalon is composed primarily of the thalamus and hypothalamus, which together define the walls of the third ventricle. The thalami are two elongated, ovoid structures on either side of the midline that make contact in the middle. The hypothalamus is inferior and anterior to the thalamus, culminating in a sharp angle to which the pituitary gland is attached. Brain Stem The midbrain and hindbrain (composed of the pons and the medulla) are collectively referred to as the brain stem ( Figure 13.12 ). The structure emerges from the ventral surface of the forebrain as a tapering cone that connects the brain to the spinal cord. Attached to the brain stem, but considered a separate region of the adult brain, is the cerebellum. The midbrain coordinates sensory representations of the visual, auditory, and somatosensory perceptual spaces. The pons is the main connection with the cerebellum. The pons and the medulla regulate several crucial functions, including the cardiovascular and respiratory systems and rates. The cranial nerves connect through the brain stem and provide the brain with the sensory input and motor output associated with the head and neck, including most of the special senses. The major ascending and descending pathways between the spinal cord and brain, specifically the cerebrum, pass through the brain stem. Figure 13.12 The Brain Stem The brain stem comprises three regions: the midbrain, the pons, and the medulla. The Cerebellum The cerebellum , as the name suggests, is the “little brain.” It is covered in gyri and sulci like the cerebrum and looks like a miniature version of that part of the brain ( Figure 13.13 ). The cerebellum is largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord. It accounts for approximately 10 percent of the mass of the brain.

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 12 Figure 13.13 The Cerebellum The cerebellum is situated on the posterior surface of the brain stem. Descending input from the cerebellum enters through the large white matter structure of the pons. Ascending input from the periphery and spinal cord enters through the fibers of the inferior olive. Output goes to the midbrain, which sends a descending signal to the spinal cord. The Spinal Cord The description of the CNS is concentrated on the structures of the brain, but the spinal cord is another major organ of the system. Whereas the brain develops out of expansions of the neural tube into primary and then secondary vesicles, the spinal cord maintains the tube structure and is only specialized into certain regions. The anterior midline is marked by the anterior median fissure , and the posterior midline is marked by the posterior median sulcus . On the whole, the posterior regions are responsible for sensory functions and the anterior regions are associated with motor functions. Regions of the spinal cord: Immediately adjacent to the brain stem is the cervical region, followed by the thoracic, then the lumbar, and finally the sacral region. The spinal cord is not the full length of the vertebral column because the spinal cord does not grow significantly longer after the first or second year, but the skeleton continues to grow. The nerves that emerge from the spinal cord pass through the intervertebral formina at the respective levels. As the vertebral column grows, these nerves grow with it and result in a long bundle of nerves that resembles a horse’s tail and is named the cauda equina . The sacral spinal cord is at the level of the upper lumbar vertebral bones. The spinal nerves extend from their various levels to the proper level of the vertebral column. Figure 13.14 Cross-section of Spinal Cord The cross-section of a thoracic spinal cord segment shows the posterior, anterior, and lateral horns of gray matter, as well as the posterior, anterior, and lateral columns of white matter. LM × 40. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 13 PNS The PNS is not as contained as the CNS because it is defined as everything that is not the CNS. In describing the anatomy of the PNS, it is necessary to describe the common structures, the nerves and the ganglia, as they are found in various parts of the body. Ganglia A ganglion is a group of neuron cell bodies in the periphery. Ganglia can be categorized, for the most part, as either sensory ganglia or autonomic ganglia, referring to their primary functions. The most common type of sensory ganglion is a dorsal (posterior) root ganglion . Nerves Bundles of axons in the PNS are referred to as nerves. The outer surface of a nerve is a surrounding layer of fibrous connective tissue called the epineurium . Within the nerve, axons are further bundled into fascicles , which are each surrounded by their own layer of fibrous connective tissue called perineurium . Finally, individual axons are surrounded by loose connective tissue called the endoneurium ( Figure 13.21 ). Figure 13.21 Nerve Structure The structure of a nerve is organized by the layers of connective tissue on the outside, around each fascicle, and surrounding the individual nerve fibers (tissue source: simian). LM × 40. (Micrograph provided by the Regents of University of Michigan Medical School © 2012) Nerves are associated with the region of the CNS to which they are connected, either as cranial nerves connected to the brain or spinal nerves connected to the spinal cord. Table 13.3 shows the cranial nerves, and figure 13.24 shows the spinal nerves. Cranial Nerves Mnemonic # Name Function (S/M/B) Central connection (nuclei) Peripheral connection (ganglion or muscle) On I Olfactory Smell (S) Olfactory bulb Olfactory epithelium Old II Optic Vision (S) Hypothalamus/ thalamus/midbrain Retina (retinal ganglion cells) Olympus’ III Oculomotor Eye movements (M) Oculomotor nucleus Extraocular muscles (other 4), levator palpebrae superioris, ciliary ganglion (autonomic) Towering IV Trochlear Eye movements (M) Trochlear nucleus Superior oblique muscle

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 14 Tops V Trigeminal Sensory/ motor - face (B) Trigeminal nuclei in the midbrain, pons, and medulla Trigeminal Mnemonic # Name Function (S/M/B) Central connection (nuclei) Peripheral connection (ganglion or muscle) A VI Abducens Eye movements (M) Abducens nucleus Lateral rectus muscle Finn VII Facial Motor - face, Taste (B) Facial nucleus, solitary nucleus, superior salivatory nucleus Facial muscles, Geniculate ganglion, Pterygopalatine ganglion (autonomic) And VIII Auditory (Vestibulocochlear) Hearing/ balance (S) Cochlear nucleus, Vestibular nucleus/ cerebellum Spiral ganglion (hearing), Vestibular ganglion (balance) German IX Glossopharyngeal Motor - throat Taste (B) Solitary nucleus, inferior salivatory nucleus, nucleus ambiguus Pharyngeal muscles, Geniculate ganglion, Otic ganglion (autonomic) Viewed X Vagus Motor/ sensory - viscera (autonomic) (B) Medulla Terminar gangna serving thoracic and upper abdominal organs (heart and small intestines) Some XI Spinal Accessory Motor - head and neck (M) Spinal accessory nucleus Neck muscles Hops XII Hypoglossal Motor - lower throat (M) Hypoglossal nucleus Muscles of the larynx and lower pharynx Table 13.3

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 15 Figure 13.24 Nerve Plexuses of the Body There are four main nerve plexuses in the human body. The cervical plexus supplies nerves to the posterior head and neck, as well as to the diaphragm. The brachial plexus supplies nerves to the arm. The lumbar plexus supplies nerves to the anterior leg. The sacral plexus supplies nerves to the posterior leg. Circulation and CNS The CNS has a privileged blood supply established by the blood-brain barrier. Establishing this barrier are anatomical structures that help to protect and isolate the CNS. The arterial blood to the brain comes from the internal carotid and vertebral arteries, which both contribute to the unique circle of Willis that provides constant perfusion of the brain even if one of the blood vessels is blocked or narrowed. That blood is eventually filtered to make a separate medium, the CSF, that circulates within the spaces of the brain and then into the surrounding space defined by the meninges, the protective covering (Dura matter, Arachnoid matter, and Pia matter) of the brain and spinal cord.

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 16 The blood that nourishes the brain and spinal cord is behind the glial-cell–enforced blood- brain barrier, which limits the exchange of material from blood vessels with the interstitial fluid of the nervous tissue. Thus, metabolic wastes are collected in cerebrospinal fluid that circulates through the CNS. This fluid is produced by filtering blood at the choroid plexuses in the four ventricles of the brain. It then circulates through the ventricles and into the subarachnoid space, between the pia mater and the arachnoid mater. From the arachnoid granulations, CSF is reabsorbed into the blood, removing the waste from the privileged central nervous tissue. The blood, now with the reabsorbed CSF, drains out of the cranium through the dural sinuses. The dura mater is the tough outer covering of the CNS, which is anchored to the inner surface of the cranial and vertebral cavities. It surrounds the venous space known as the dural sinuses, which connect to the jugular veins, where blood drains from the head and neck. Figure 13.17 Meningeal Layers of Superior Sagittal Sinus The layers of the meninges in the longitudinal fissure of the superior sagittal sinus are shown, with the dura mater adjacent to the inner surface of the cranium, the pia mater adjacent to the surface of the brain, and the arachnoid and subarachnoid space between them. An arachnoid villus is shown emerging into the dural sinus to allow CSF to filter back into the blood for drainage. Lesson 2 Completed! Thank you! You have completed this lesson. Please scroll down to complete a short, ungraded Knowledge Check activity. Check Your Knowledge 2 Which lobe of the cerebral cortex is responsible for generating motor commands? temporal parietal occipital frontal (Correct: D) What region of the diencephalon coordinates homeostasis? thalamus epithalamus hypothalamus (Correct: C)

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 17 subthalamus Which of the following meninges from the outer covering? Dura mater (Correct: A) Pia mater Arachnoid mater Subdural Lesson 3 – Somatic Nervous System and Autonomic Nervous System Somatic Nervous System The somatic nervous system is traditionally considered a division within the peripheral nervous system. However, this misses an important point: somatic refers to a functional division, whereas peripheral refers to an anatomic division. The somatic nervous system is responsible for our conscious perception of the environment and for our voluntary responses to that perception by means of skeletal muscles. A more complex example of somatic function is conscious muscle movement. For example, reading of this text starts with visual sensory input to the retina, which then projects to the thalamus, and on to the cerebral cortex. A sequence of regions of the cerebral cortex process the visual information, starting in the primary visual cortex of the occipital lobe, and resulting in the conscious perception of these letters. Subsequent cognitive processing results in understanding of the content. As you continue reading, regions of the cerebral cortex in the frontal lobe plan how to move the eyes to follow the lines of text. The output from the cortex causes activity in motor neurons in the brain stem that cause movement of the extraocular muscles through the third, fourth, and sixth cranial nerves. This example also includes sensory input (the retinal projection to the thalamus), central processing (the thalamus and subsequent cortical activity), and motor output (activation of neurons in the brain stem that lead to coordinated contraction of extraocular muscles). The somatic division of the central nervous system include Sensory perception, Central processing, and motor responses. Automatic Nervous System The autonomic nervous system is often associated with the “fight-or-flight response,” which refers to the preparation of the body to either run away from a threat or to stand and fight in the face of that threat. Adrenaline starts to flood your circulatory system. Your heart rate increases. Sweat glands become active. The bronchi of the lungs dilate to allow more air exchange. Pupils dilate to increase visual information. Blood pressure increases in general, and blood vessels dilate in skeletal muscles—time to run. Similar physiological responses would occur in preparation for fighting off the threat. However, the autonomic nervous system is not just about responding to threats. Besides the fight-or-flight response, there are the responses referred to as “rest and digest.” Heart rate will slow. Breathing will return to normal. The digestive system has a big job to do. Much of the function of the autonomic system is based on the connections within an autonomic, or visceral, reflex. Lesson 3 Completed! Thank you! You have completed this lesson. Please scroll down to complete a short, ungraded Knowledge Check activity. Check Your Knowledge 3 1. Which of these physiological changes would not be considered part of the sympathetic fight-or-flight response?

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 18 a. increased heart rate b. increased sweating c. dilated pupils d. increased stomach motility (ANSWER: D) 2. The following responses happen as a result of what part of the nervous system: slow heart rate, normal breathing, and digestive system is activated? a. Rest and Digest (ANSWER: A) b. Sympathetic Nervous system c. Somatic Nervous system d. All of the above 3- The somatic division of the central nervous system include the following, except: a. Sensory perception b. Central processing c. motor responses. d. Fight or flight (ANSWER: D) Lesson 4 - Senses Introduction Senses can be classified as either general or specific. A general sense is one that is distributed throughout the body and has receptor cells within the structures of other organs. Mechanoreceptors in the skin, muscles, or the walls of blood vessels are examples of this type. General senses often contribute to the sense of touch, as described above, or to proprioception (body movement) and kinesthesia (body movement), or to a visceral sense , which is most important to autonomic functions. A special sense is one that has a specific organ devoted to it, namely the eye, inner ear, tongue, or nose. Gustation (Taste) Until recently, only four tastes were recognized: sweet, salty, sour, and bitter. Research at the turn of the 20th century led to recognition of the fifth taste, umami, during the mid- 1980s. Umami is a Japanese word that means “delicious taste,” and is often translated to mean savory. Gustation is the special sense associated with the tongue. The surface of the tongue, along with the rest of the oral cavity, is lined by a stratified squamous epithelium. Raised bumps called papillae (singular = papilla) contain the structures for gustatory transduction. Within the structure of the papillae are taste buds that contain specialized gustatory receptor cells for the transduction of taste stimuli. Olfaction (Smell) Like taste, the sense of smell, or olfaction , is also responsive to chemical stimuli. The olfactory receptor neurons are located in a small region within the superior nasal cavity ( Figure 14.4 ). Figure 14.4 describes the process of smell.

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 19 Figure 14.4 The Olfactory System (a) The olfactory system begins in the peripheral structures of the nasal cavity. (b) The olfactory receptor neurons are within the olfactory epithelium. (c) Axons of the olfactory receptor neurons project through the cribriform plate of the ethmoid bone and synapse with the neurons of the olfactory bulb (tissue source: simian). LM × 812. (Micrograph provided by the Regents of University of Michigan Medical School © 2012) Audition (Hearing) Hearing, or audition , is the transduction of sound waves into a neural signal that is made possible by the structures of the ear ( Figure 14.5 ). The large, fleshy structure on the lateral aspect of the head is known as the auricle ; which directs sound waves toward the auditory canal. The canal enters the skull through the external auditory meatus of the temporal bone. At the end of the auditory canal is the tympanic membrane , or ear drum, which vibrates after it is struck by sound waves. The auricle, ear canal, and tympanic membrane are often referred to as the external ear . The middle ear consists of a space spanned by three small bones called the ossicles . The three ossicles are the malleus , incus , and stapes , which are Latin names that roughly translate to hammer, anvil, and stirrup. The malleus is attached to the tympanic membrane and articulates with the incus. The incus, in turn, articulates with the stapes. The stapes is then attached to the inner ear , where the sound waves will be transduced into a neural signal. The middle ear is connected to the pharynx through the Eustachian tube, which helps equilibrate air pressure across the tympanic membrane. The tube is normally closed but will pop open when the muscles of the pharynx contract during swallowing or yawning.

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 20 Figure 14.5 Structures of the Ear The external ear contains the auricle, ear canal, and tympanic membrane. The middle ear contains the ossicles and is connected to the pharynx by the Eustachian tube. The inner ear contains the cochlea and vestibule, which are responsible for audition and equilibrium, respectively. The inner ear is often described as a bony labyrinth, as it is composed of a series of canals embedded within the temporal bone. It has two separate regions, the cochlea and the vestibule , which are responsible for hearing and balance, respectively. The neural signals from these two regions are relayed to the brain stem through separate fiber bundles. However, these two distinct bundles travel together from the inner ear to the brain stem as the vestibulocochlear nerve. Sound is transduced into neural signals within the cochlear region of the inner ear, which contains the sensory neurons of the spiral ganglia . These ganglia are located within the spiral-shaped cochlea of the inner ear. The cochlea is attached to the stapes through the oval window . Figure 14.7 Cross Section of the Cochlea The three major spaces within the cochlea are highlighted. The scala tympani and scala vestibuli lie on either side of the cochlear duct. The organ of Corti, containing the mechanoreceptor hair cells, is adjacent to the scala tympani, where it sits atop the basilar membrane. Equilibrium (Balance) Along with audition, the inner ear is responsible for encoding information about equilibrium , the sense of balance. A similar mechanoreceptor—a hair cell with stereocilia— senses head position, head movement, and whether our bodies are in motion. These cells are located within the vestibule of the inner ear. Head position is sensed by the utricle and saccule , whereas head movement is sensed by the semicircular canals . The neural

HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 21 signals generated in the vestibular ganglion are transmitted through the vestibulocochlear nerve to the brain stem and cerebellum. Figure 14.11 Linear Acceleration Coding by Maculae The maculae are specialized for sensing linear acceleration, such as when gravity acts on the tilting head, or if the head starts moving in a straight line. The difference in inertia between the hair cell stereocilia and the otolithic membrane in which they are embedded leads to a shearing force that causes the stereocilia to bend in the direction of that linear acceleration. Vision Vision is the special sense of sight that is based on the transduction of light stimuli received through the eyes. The eyes are located within either orbit in the skull. The bony orbits surround the eyeballs, protecting them and anchoring the soft tissues of the eye ( Figure 14.13 ). The eyelids, with lashes at their leading edges, help to protect the eye from abrasions by blocking particles that may land on the surface of the eye. The inner surface of each lid is a thin membrane known as the palpebral conjunctiva . The conjunctiva extends over the white areas of the eye (the sclera), connecting the eyelids to the eyeball. Tears are produced by the lacrimal gland , located beneath the lateral edges of the nose. Tears produced by this gland flow through the lacrimal duct to the medial corner of the eye, where the tears flow over the conjunctiva, washing away foreign particles.

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 22 Figure 14.13 The Eye in the Orbit The eye is located within the orbit and surrounded by soft tissues that protect and support its function. The orbit is surrounded by cranial bones of the skull. Movement of the eye within the orbit is accomplished by the contraction of six extraocular muscles that originate from the bones of the orbit and insert into the surface of the eyeball ( Figure 14.14) Figure 14.15 Structure of the Eye The sphere of the eye can be divided into anterior and posterior chambers. The wall of the eye is composed of three layers: the fibrous tunic, vascular tunic, and neural tunic. Within the neural tunic is the retina, with three layers of cells and two synaptic layers in between. The center of the retina has a small indentation known as the fovea. The retina has two types of photoreceptors: rods (Function in dim light, and responsible for black/white vision), and cones (Function in day light, and responsible for colored vision). Lesson 4 Completed! Thank you! You have completed this lesson. Please scroll down to complete a short, ungraded Knowledge Check activity. Check Your Knowledge 4 1. True/False: General and special senses are the same but are located in different body areas.

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 23 a. True b. False (Answer: B- False, they are different in structure, function, and body location) 2. The photoreceptor cones of the retina function during ______; while rods function during_____: a. Day time, Night time b. Dim light, Night c. Day light, Colors d. Black and white, night (ANSWER: A) 3. The _____ ear is responsible for encoding information about Equilibrium (Balance): a. Outer b. Middle c. Inner (Correct: C) d. Tympanic membrane Lesson 5 – Endocrine System Overview of Endocrine System Communication is a process in which a sender transmits signals to one or more receivers to control and coordinate actions. In the human body, two major organ systems participate in relatively “long distance” communication: the nervous system and the endocrine system. Together, these two systems are primarily responsible for maintaining homeostasis in the body. In contrast to the nervous system, the endocrine system uses just one method of communication: chemical signaling. These signals are sent by the endocrine organs, which secrete chemicals—the hormone —into the extracellular fluid. Hormones are transported primarily via the bloodstream throughout the body, where they bind to receptors on target cells, inducing a characteristic response. As a result, endocrine signaling requires more time than neural signaling to prompt a response in target cells, though the precise amount of time varies with different hormones. Endocrine Glands and Hormones The endocrine system consists of cells, tissues, and organs that secrete hormones as a primary or secondary function. The endocrine gland is the major player in this system. The primary function of these ductless glands is to secrete their hormones directly into the surrounding fluid. The interstitial fluid and the blood vessels then transport the hormones throughout the body. The endocrine system includes the pituitary, thyroid, parathyroid, adrenal, and pineal glands ( Figure 17.2 ).

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 24 Figure 17.2 Endocrine System Endocrine glands and cells are located throughout the body and play an important role in homeostasis. The ductless endocrine glands are not to be confused with the body’s exocrine system , whose glands release their secretions through ducts. Examples of exocrine glands include the sebaceous and sweat glands of the skin. Although a given hormone may travel throughout the body in the bloodstream, it will affect the activity only of its target cells; that is, cells with receptors for that particular hormone. Once the hormone binds to the receptor, a chain of events is initiated that leads to the target cell’s response. The major hormones of the human body and their effects are identified in Table 17.2 . Endocrine Glands and Their Major Hormones Endocrine gland Associated hormones Chemical class Effect Pituitary (anterior) Growth hormone (GH) Protein Promotes growth of body tissues Pituitary (anterior) Prolactin (PRL) Peptide Promotes milk production Parathyroid Parathyroid hormone (PTH) Peptide Increases blood Ca2+ levels Adrenal (cortex) Aldosterone Steroid Increases blood Na+ levels Adrenal (cortex) Cortisol, corticosterone, cortisone Steroid Increase blood glucose levels Adrenal (medulla) Epinephrine, norepinephrine Amine Stimulate fight-or-flight response Pineal Melatonin Amine Regulates sleep cycles

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 25 Pancreas Insulin Protein Reduces blood glucose levels Pancreas Glucagon Protein Increases blood glucose levels Testes Testosterone Steroid Stimulates development of male secondary sex characteristics and sperm production Ovaries Estrogens and progesterone Steroid Stimulate development of female secondary sex characteristics and prepare the body for childbirth Table 17.2 The hormones of the human body can be divided into two major groups on the basis of their chemical structure. Hormones derived from amino acids include amines, peptides, and proteins. Those derived from lipids include steroids ( Figure 17.3 ). These chemical groups affect a hormone’s distribution, the type of receptors it binds to, and other aspects of its function.

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 26 Hormone Class Components Examples Amine Hormone Amino acids with modified groups (e.g. norepinephrine’s carboxyl group is replaced with a benzene ring) Peptide Hormone Short chains of linked amino acids Protein Hormone Long chains of linked amino acids Steroid Hormones Derived from the lipid cholesterol Figure 17.3 Amine, Peptide, Protein, and Steroid Hormone Structure Regulation of Hormone Secretion To prevent abnormal hormone levels and a potential disease state, hormone levels must be tightly controlled. The body maintains this control by balancing hormone production and degradation. Feedback loops govern the initiation and maintenance of most hormone secretion in response to various stimuli. Hormones are released upon stimulation that is of either chemical or neural origin. Regulation of hormone release is primarily achieved through negative feedback. Various stimuli may cause the release of hormones, but there are three major types. Humoral stimuli are changes in ion or nutrient levels in the blood. Hormonal stimuli are changes in hormone levels that initiate or inhibit the secretion of another hormone. Finally, a neural stimulus occurs when a nerve impulse prompts the secretion or inhibition of a hormone.

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 27 Aging of the Endocrine System As the body ages, changes occur that affect the endocrine system, sometimes altering the production, secretion, and catabolism of hormones. For example, the structure of the anterior pituitary gland changes as vascularization decreases and the connective tissue content increases with increasing age. This restructuring affects the gland’s hormone production. For example, the amount of human growth hormone that is produced declines with age, resulting in the reduced muscle mass commonly observed in the elderly. The adrenal glands also undergo changes as the body ages; as fibrous tissue increases, the production of cortisol and aldosterone decreases. Interestingly, the production and secretion of epinephrine and norepinephrine remain normal throughout the aging process. A well-known example of the aging process affecting an endocrine gland is menopause and the decline of ovarian function. With increasing age, the ovaries decrease in both size and weight and become progressively less sensitive to gonadotropins. This gradually causes a decrease in estrogen and progesterone levels, leading to menopause and the inability to reproduce. Low levels of estrogens and progesterone are also associated with some disease states, such as osteoporosis, atherosclerosis, and hyperlipidemia, or abnormal blood lipid levels. Testosterone levels also decline with age, a condition called andropause (or viropause); however, this decline is much less dramatic than the decline of estrogens in women, and much more gradual, rarely affecting sperm production until very old age. As the body ages, the thyroid gland produces less of the thyroid hormones, causing a gradual decrease in the basal metabolic rate. The lower metabolic rate reduces the production of body heat and increases levels of body fat. Parathyroid hormones, on the other hand, increase with age. This may be because of reduced dietary calcium levels, causing a compensatory increase in parathyroid hormone. However, increased parathyroid hormone levels combined with decreased levels of calcitonin (and estrogens in women) can lead to osteoporosis as PTH stimulates demineralization of bones to increase blood calcium levels. Notice that osteoporosis is common in both elderly males and females. Increasing age also affects glucose metabolism, as blood glucose levels spike more rapidly and take longer to return to normal in the elderly. In addition, increasing glucose intolerance may occur because of a gradual decline in cellular insulin sensitivity. Almost 27 percent of Americans aged 65 and older have diabetes. Lesson 5 Completed! Thank you! You have completed this lesson. Please scroll down to complete a short, ungraded Knowledge Check activity. Check Your Knowledge 5 1. Endocrine glands ________. a. secrete hormones that travel through a duct to the target organs b. release neurotransmitters into the synaptic cleft c. secrete chemical messengers that travel in the bloodstream (Correct: C) d. include sebaceous glands and sweat glands 2. How many hormones are produced by the posterior pituitary?

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HCAS133 – Lecture 4 - The Nervous System, the Endocrine System, and Senses 28 a. 0 b. 1 c. 2 (Correct: C) d. 6 3. Which of the following hormones contributes to the regulation of the body’s fluid and electrolyte balance? a. adrenocorticotropic hormone b. antidiuretic hormone (Correct: B) c. luteinizing hormone d. all of the above 4- The secretion of thyroid hormones is controlled by ________. TSH from the hypothalamus b. TSH from the anterior pituitary (Correct: B) c. thyroxine from the anterior pituitary d. thyroglobulin from the thyroid’s parafollicular cells Lecture Recap We discussed two of the most important systems in integration, regulation, and control: the Nervous and Endocrine systems. Starting with nervous tissue, the fundamental unit of the nervous system and the glial cells. We then transitioned to the divisions and anatomy of the nervous system. We then discussed the various general and special senses in the body. Finally, we discussed the endocrine system, along with its glands and their hormonal secretions, to end it with aging of the endocrine system. Next lecture, we will discuss the digestive, lymphatic, and immune systems. References GLIAL CELLS. (n.d.). Content.byui.edu. https://content.byui.edu/file/a236934c-3c60- 4fe9-90aa-d343b3e3a640/1/module6/readings/glial_cells.html MediMationz. (2010, January 22). Action potential . YouTube. Retrieved April 15, 2022, from https://www.youtube.com/watch?app=desktop&v=U0NpTdge3aw Molnar, C., & Gair, J. (2019, May 1). 16.1 Neurons and Glial Cells . Opentextbc.ca; BCcampus. https://opentextbc.ca/biology/chapter/16-1-neurons-and-glial-cells/

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HCAS133 - Lecture 5 – The Nervous System, the Endocrine System, and Senses

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