Unit 4 Anatomy😾

Rods

# Pigments: 1 (noncolor) Sensitivity/Functionality: High sensitivity; function in dim light Acuity: Low acuity (many rods converge into one ganglion cell) Density in Retina: More numerous (20 rods for every cone) Location: Mostly in peripheral retina

Conss

# Pigments: 3 (color) Sensitivity/Functionality: Low sensitivity; function in bright light Acuity: High acuity (one cone per ganglion cell in fovea) Density in Retina: Less numerous Location: Mostly in central retina

Compare and contrast the functions of the parasympathetic and sympathetic divisions

* Role of parasympathetic: "Rest & digest" ("D" division [digestion, defecation, & diuresis (urination)]; * Role of sympathetic: "Fight-or-flight" ("E" division; "EEEE") exercise, excitement, emergency, embarassment.

List the types of neuroglia and cite their functions

1. CNS Astrocytes: Branching cell that clings to neurons and their synaptic ending • brace neurons and anchor them to nutrient supply lines 2. CNS Microglial Cells: Small, oroid cell with long, thorny processes • phagocytize microorganisms engendering neurons 3. CNS Ependymal Cells: Squamous or columnar cells that line central cavities • beating of cilia helps circulate CSF. Helps form a permeable barrier 4: CNS Oligodendrocytes: Branching cell with fewer processes than an osteocyte • wrap process around nerve fibers to produce myelin sheath that insulates neurons 5. PNS Satellite Cells: Branching cell that surrounds cell bodies • brace neurons and anchor them to nutrient supply lines 6. PNS Schwann Cells: Branching cell with processes • surround nerve fibers in PNS to form myelin sheath that insulates nerves

Distinguish between excitatory and inhibitory postsynaptic potentials

1. Excitatory: The binding of these neurotransmitters to the postsynaptic membrane opens up chemically-gated ion channels allowing Na+ and K+ to diffuse simultaneously through the membrane but in opposite directions with the Na+ influx being greater than the K+ efflux. This results in a net depolarization of the membrane. 2. Inhibitory: The binding of these neurotransmitters to the postsynaptic membrane opens up K+ or Cl- channels but Na+ channels are not affected. This causes K+ to move out of the cell or Cl- to move into the cell, causing the charge on the inner face of the membrane to become more negative. This results in a net hyperpolarization of the membrane, causing the postsynaptic neuron to be less likely to "fire".

Describe graded potentials and name several examples

1. Graded Potential: A short-lived, localized change in a membrane potential that dissipates quickly and declines with increasing distance from the site of initial depolarization. Nonetheless, they are essential in initiating action potentials. Examples include the receptor of a sensory neuron excited by some form of energy or a postsynaptic potential due to a neurotransmitter binding to the membrane of that nerve cell. 2. Action Potential: A long-distance signal that does not decay with distance. Only cells with excitable membranes (neurons and muscle cells) can generate action potentials. They are activated by graded potentials that spread toward the axon along the dendritic and cell body membranes.

Outline the three levels of the motor hierarchy

1. Highest Level (Precommand): The cerebral cortex is at the highest level of our conscious motor pathways, but is not the ultimate planner and coordinator of complex motor activities. The cerebellum and basal ganglia play this role, and are therefore at the top of the motor control hierarchy. These structures precisely start or stop movements, coordinate movements with posture, block unwanted movements, and monitor muscle tone. 2. Middle Level (Projection): Motor cortex conveys information to the spinal cord descending tracts, which is under the direct control of this level of motor control. 3. Lowest Level (Segmental): This level consists of reflexes and spinal cord circuits that control automatic movements.

Describe the ANS controls

1. Hypothalamus: Main integration center at the top of the ANS control hierarchy. The anterior region directs parasympathetic functions and the posterior region directs sympathetic functions. 2. Brain Stem: The reticular formation exerts the most influence but the medulla regulates heart rate, blood vessel diameter, and gastrointestinal activities. The midbrain controls pupil diameter and lens control. 3. Cortical Controls: The cerebral cortex modifies the ANS at a subconscious level via the limbic system.

Explain how action potentials are generated and propagated along neurons

1. Resting State: All gated Na+ and K+ channels are closed. Only the leakage channels are open. Sodium- potassium pump maintains potential. 2. Depolarization: Na+ channels open, allowing Na+ entry into the cell. This causes the cell interior to become progressively less negative. When it reaches a critical level called the threshold, between - 55 and - 50 mV, depolarization becomes self-generating urged on by positive feedback. 3. Repolarization: Na+ channels are inactivating and K+ channels open allowing K+ to exit. As Na+ entry declines, the internal negativity of the neuron is restored. 4. Hyperpolarization: Some K+ channels remain open, and Na+ channels reset. As a result of the excessive K+ efflux, the inside of the membrane become more negative. 5. Resting State: All gated Na+ and K+ channels close and the sodium-potassium pump redistributes the ions.

Describe the general structure of a nerve

A cord-like organ that consists of parallel bundles of peripheral axons (some myelinated and some not) enclosed by successive wrappings of connective tissue.

Define a neuron, describe its important structural components, and relate each to a functional role

A neuron (nerve cell) is the structural unit of the nervous system. They have extreme longevity and can function for a lifetime. They cannot divide and be replaced if destroyed (amitotic). Lastly, they have a high metabolic rate and require continuous and abundant supplies of oxygen and glucose. The neuron has a distinct structure Look at diagram on notes

Define autonomic nervous system and explain its relationship to the peripheral nervous system

A system of motor neurons that innervate smooth muscle, cardiac muscle, and glands. It is a motor subdivision of the peripheral nervous system and has a certain amount of functional independence.

Identify the major ascending and descending pathways

Ascending Dorsal Column - Medial Lemniscal Pathways: Transmit sensory information from skin and proprioceptors to opposite somato sensory cortex o Ascending Spinothalamic Pathways: Transmit pain and temperature as well as crude tough and pressure to opposite somatosensory cortex o Ascending Spinocerebellar Pathways: Transmit proprioceptor impulses to same side of cerebellum o Descending Corticospinal (2x): Transmit motor impulses from pro central Gyrus to opposite side of body o Descending Tectospinal: Turn neck so eyes can follow a moving object o Descending Vestibulospinal: Transmit motor impulses to same side of trunk and limbs to maintain balance o Descending: Rubrospinal: Alternate route to corticospinal tract to achieve voluntary movement o Descending Reticulospinal (2x): Transmit impulses concerned with muscle tone and visceral functions

Explain the structural and functional divisions of the nervous system

Central Nervous System (CNS): • Structure: consists of the brain and spinal cord, which occupy the dorsal body cavity. • Function: interpret sensory input and dictate motor output based on reflexes, current conditions, and past experiences Peripheral Nervous System (PNS): • Structure: consists of cranial nerves, spinal nerves, and ganglia (collection of neuron cell bodies) • Function: communicate between the CNS and the rest of the body 1. Sensory (Afferent) Division: • Structure: consists of somatic nerves (from skin, skeletal muscles, and joints) and visceral nerves (from organs within the ventral body cavity) • Function: convey impulses to the CNS from sensory receptors located throughout the body 2. Motor (Efferent) Division: • Structure: consists of motor nerves • Function: convey impulses from the CNS to the muscles and glands (effector organs) • It consists of two parts: a. Somatic Nervous System: • Structure: consists of somatic motor nerve fibers which are voluntary • Function: conduct impulses from the CNS to consciously control skeletal muscles b. Autonomic Nervous System: • Structure: consists of visceral motor nerve fibers which are involuntary • Function: conduct impulses from the CNS to regulate the activity of smooth muscles, cardiac muscles, and glands

Define plexus and name the major plexuses of the body

Except for T2 - T12 (these nerves supply the intercostal muscles), there exists several complicated interlacing nerve networks, known as a nerve plexus, lateral to the vertebral column. This allows for redundancy in innervation to the muscles in the limb. As a result of the nerve plexus, each muscle in a limb receives its nerve supply from more than one spinal nerve. For each nerve plexus, briefly describe the body region innervated by each: o Cervical Plexus: o Brachial Plexus: o Lumbar Plexus: o Sacral Plexus:

Outline the events that lead to sensation and perception

For sensation to occur a stimulus must excite a receptor and action potentials must reach the CNS. The stimulus must first match the specificity of the receptor (touch receptor sensate to pressure, stretch, and vibration but not to light). The stimulus must also be applied in the area the receptor monitors. The stimulus must then be converted into the energy of a graded potential, called transduction. Lastly, the graded potentials must reach threshold in order to open up the sodium channels on the axon and generate an action potential. Perceptual Level: At this level, the sensory input is interpreted in the cerebral cortex. o Pain perception: caused when nociceptors are activated by extremes of pressure and temperature or chemicals released by injured tissue. These synapse in the spinal cord and ascend to the brain via the spinothalamic tract. The brain and spinal cord have endogenous opioids that play an inhibitory role in suppressing pain signals which decreases the perception of pain in the brain.

Trace the pathway of light through the eye to the retina, and explain how light is focused for distant and close vision

I moves sequentially through the cornea, aqueous humor, lens, vitrous humor, and then passes through the entire neural layer of the retina to excite the photoreceptors (rods and cones). • Distant vision: The ciliary muscles are completely relaxed which causes the lens to be stretched flat, which decreases the amount the light is bent as it passes through it, allowing for distant vision. • Close vision: The ciliary muscles contract causing the lens to bulge and increasing the amount the light is bent as it passes through the lens. Additionally, the size of the pupil is reduced preventing light from the extreme edges of the lens from entering the eye. Lastly, the medial rectus muscles rotates our eyes inward to direct the light rays toward the fovea.

Trace the visual pathway to the visual cortex, and briefly describe the steps in visual processing

In order for perception to occur, the physiological signal that starts in the retina must travel to the visual cortex. The visual pathway to the brain begins with the optic nerve fibers (ganglion cell axons) from the retina. The retinal ganglion cells merge in the back of the eyeball to become the optic nerve, which crosses at the optic chiasma to become the optic tracts. The optic tracts send their axons to neurons within the lateral geniculate body of the thalamus. Axons from the thalamus project through the internal capsule to form the optic radiation of fibers in the cerebral white matter. These fibers project to the primary visual cortex in the occipital lobes. Visual processing begins in the retina and occurs when the action of light on photoreceptors hyperpolarizes them, which causes the bipolar neurons from both the rods and cones to ultimately send signals to their ganglion cells.

Define resting membrane potential and describe its electrochemical basis

Like all cells, neurons have a resting membrane potential. However, unlike most other cells, neurons can rapidly change their membrane potential. This ability underlies the function of neurons throughout the nervous system. The resting membrane potential is due to the cytoplasmic side of the membrane being negatively charged relative to the outside of the membrane, thus making the membrane polarized.

Locate the limbic system and the reticular formation, and explain the role of each

Limbic System: internal structures to include the amygdala, cingulate gyrus, fornix, and hippocampus. Deals with emotions and memory Reticular Formation: white matter that form three broad columns along length of brain stem. Promotes consciousness

List the major lobes, fissures, and functional areas of the cerebral cortex

Lobes: frontal, parietal, temporal, occipital, and insula Fissures: longitudinal and transverse cerebral Sulci: central sulcus, parieto-occipital sulcus, and lateral sulcus Gyri: precentral gyrus and postcentral gyrus

Classify general sensory receptors by stimulus detected, body location, and structure

Look at PNS and ANS guided notes

Name the 12 pairs of cranial nerves, indicate the body region innervated by each as well as it sensory/motor function

Look at PNS and ANS guided notes

Describe the structure and function of accessory eye structures, eye layers, the lens, and humors of the eye

Look at Special Senses guided notes

Describe the structure and general function of the outer, middle, and internal ears

Look at Special Senses guided notes

Describe how meninges, cerebrospinal fluid, and the blood-brain barrier protect the CNS

Meninges are three connective tissue membranes that cover and protect the CNS, protect blood vessels and enclose venous sinuses, contain cerebrospinal fluid, and partition the brain The dura mater: is the most durable, outermost covering that extends inward in certain areas to limit movement of the brain within the cranium. The arachnoid mater: is the middle meninx that forms a loose brain covering. The pia mater: is the innermost layer that clings tightly to the brain.

Identify the three major regions of the brain stem, and note the functions of each area

Midbrain: controls vital functions like heartbeat and respiration Pons: responsible for relaying messages between the cerebrum and the cerebellum Medulla Oblongata: the nerves cross over so the left hemisphere controls the right side of the body and vice versa

Define a neurotransmitter

More than 50 different neurotransmitters have been identified and are the language of the nervous system. Neurotransmitters are classified chemically and functionally. Functionally, neurotransmitters are either excitatory or are inhibitory.

Describe the events that convert light into a neural signal

Phototransduction: Process by which light energy is converted into a graded receptor potential. • Light will hyperpolarize the photoreceptors, which then stop releasing their inhibitory neurotransmitter. No longer inhibited, the connected bipolar neuron will depolarize and release a neurotransmitter onto ganglion cells, which is converted into an action potential. The action potential is transmitted to the brain along the ganglion cell axons that make up the optic nerve. • At the X-shaped optic chiasm, fibers from the medial aspect of each eye decussate (cross over to the opposite side) and fibers from the lateral aspect of each eye do not decussate. • The action potential continues on via the optic tracts and synapse with nuclei in the thalamus, which then project via white matter fibers to the primary visual cortex in the occipital lobe where the image is interpreted. • Output will pass to the frontal cortex for further processing and decision making.

Describe sound transduction

Process by which movement of the hair cells is converted into a graded receptor potential. • The deflection of the hair cells causes ion channels to open. • K+ and Ca2+ from the fluid flow through the open channels, creating a graded depolarization. • This causes release of a neurotransmitter which facilitates transmission of impulses to brain. • The impulse travels through the brain stem and projects to the thalamus. • The axons of the thalamic neurons project to the primary auditory cortex, which provides conscious awareness of sound.

Name the major regions and ventricles of the adult brain

Regions: frontal, parietal, temporal, occipital, and insula Ventricles: lateral, third, cerebral aqueduct, and fourth

List the basic functions of the nervous system

Sensory input, integration, motor output

Describe the general function of the basal nuclei

Smoothing out motor activity

Compare and contrast the motor endings of somatic and autonomic nerve fibers

Somatic Nerve Fibers: As each axon branch reaches its target, a single somatic muscle fiber, the ending splits into a cluster of axon terminals that branch treelike over the junctional folds of the sarcolemma of the muscle fiber. When a nerve impulse reaches an axon terminal, acetylcholine (ACh) is released via exocytosis, diffuses across the synaptic cleft, and attaches to receptors on the sarcolemma. This results in a graded potential called an end plate potential. The end plate potential spreads to adjacent areas of the membrane where it triggers the opening of voltage-gated sodium channels. This event causes an action potential to propagate along the sarcolemma, which stimulates the muscle fiber to contract via the sliding filament theory discussed previously. The synaptic cleft at this neuromuscular junction contains a structure not seen at other synapses called a basal lamina. This structure contains acetylcholinesterase, the enzyme that breaks down ACh. b. Autonomic Nerve Fibers: The synaptic vesicles at motor ending of smooth muscle, cardiac muscle, and glands contain either acetylcholine or norepinephrine, both of which act indirectly on their targets via second messengers. Consequently, autonomic motor responses tend to be slower than those induced by somatic motor fibers.

Name the components of a reflex arc and distinguish between autonomic and somatic reflexes

Somatic Reflex Arc: Many of the body's control systems are reflexes. Reflexes occur over highly specific neural paths called reflex arcs. All reflex arcs have 5 essential components: 1. Receptor: Site of the stimulus action 2. Sensory Neuron: Transmits afferent impulses to the CNS 3. Integration Center: One or multiple synapses between a sensory and a motor neuron, via interneurons. 4. Motor Neuron: Conducts efferent impulses from the integrating center to an effector organ. 5. Effector: Muscle fiber or gland cell that responds to the efferent impulses by either contracting or secreting.

Describe the sound conduction pathway to the fluids of the internal ear

Sound waves (vibrations) in the air must be propagated through membranes, bones, and fluids to stimulate receptor cells in the spiral organ. Below is a synopsis of how this occurs: • Sound waves enter the external acoustic meatus and strike the tympanic membrane which cause it to vibrate at the same frequency. • The motion of the tympanic membrane is amplified and transferred to the oval window via the auditory ossicles. Since the oval window is smaller than the tympanic membrane, the pressure wave is amplified. • The pressure wave travels into the fluid of the cochlea, which activates hair cells (receptor cells) in the spiral organ causing action potentials to be sent to the brain.

Classify neurons by structure and function

Structural: a. Multipolar Neuron: Have three or more processes (one axon and rest dendrites) Major type of neuron in CNS b. Bipolar Neuron: Have two processes (one axon and one dendrite) Rare neuron found in special sense organs c. Unipolar Neuron: Have a single short process that divides, T-like, into proximal and distal branches Found mainly in PNS as sensory neurons Functional: a. Sensory (afferent) Neuron: Transmit impulses from sensory receptors toward the CNS b. Motor (efferent) Neuron: Transmit impulses away from the CNS to effector organs to involve muscles and glands c. Interneuron (association): Lie between motor and sensory neuron, mostly in CNS, to facilitate integration between PNS and CNS

Define a synapse and distinguish between electrical and chemical synapses

Synapse: A junction that mediates information transfer from one neuron to the next neuron or to an effector cell Electrical: These are less common and happen when ions flow directly from one neuron to the next. These occur in synapses in the hippocampus, a region involved in emotions and memory. Chemical: These are specialized to allow the release and reception of chemical messengers called neurotransmitters.

Define peripheral nervous system and list its components

The PNS provides links from and to the world outside our bodies. The PNS consists of sensory receptors, peripheral nerves and their associated ganglia, and efferent motor endings

Describe the structure and function of the cerebellum

The cerebellum consists of two hemispheres, marked by convolutions and separated by the vermis. It is connected to the brain stem by superior, middle, and inferior peduncles. The cerebellum processes and interprets impulses from the motor cortex and sensory pathways and coordinates motor activity so that smooth, well-timed movements occur. It also plays a poorly understood role in cognition.

Describe the location of the diencephalon, and name its subdivisions and functions

The diencephelon includes the thalamus, hypothalamus, and epithalamus ans encloses the third ventricle. The thalamus is the major relay station for (1) sensory impulses ascending to the sensory cortex, (2) inputs from subcortical motor nuclei and the cerebellum traveling to the cerebral motor cortex, and (3) impulses traveling to association cortices from lower centers. The hypothalamus is an important control center of the autonomic nervous system and a pivotal part of the limbic system. It maintains water balance and regulates thirst, eating behavior, gastrointestinal activity, body temperature, and the activity of the anterior pituitary gland. The epithalamus includes the pineal gland, which secretes the hormone melatonin.

Compare the roles of the cerebellum and basal nuclei in controlling motor activity

The key center for "online" sensorimotor integration and control is the cerebellum. The cerebellum lacks direct connections to the spinal cord. It acts on motor pathways through the projection areas of the brain stem and on the motor cortex via the thalamus to fine tune motor activity. The basal nuclei recieve inputs from all cortical areas and send their output back mainly to premotor and prefrontal cortical areas via the thalamus. Compared to the cerebellum, the basal nuclei appear to be involved in more complex aspects of motor control.

Differentiate between a nerve and a tract and between a nucleus and a ganglion

Tract- CNS, collection of axons Nerves - PNS, collection of axons Nuclei - CNS collection of nerve bodies Ganglia - PNS collections of nerve bodies

Compare and contrast light and dark adaptation

• Light adaptation occurs when we move from darkness into bright light. The pupil constricts, reducing the amount of light that enters the eye. The rod system turns off and the cone system takes over. • Dark adaptation occurs when we go from a well-lit area into a dark one. The pupil dilates, allowing more light to enter the eye. The cones stop functioning and the rods will take over, but slowly, which accounts for the phenomena that initially we can't see in the dark but over time eyes adapt allowing adequate dim-light vision.

Describe how we are able to differentiate pitch and loudness, and to localize the source of sounds

• Pitch: Sound waves of different frequencies (pitch) activate hair cells in different positions along the length of the cochlear membrane. Impulses from specific hair cells are interpreted as specific pitches. • Loudness: Louder sounds cause larger deflections of the hairs, thereby causing larger graded potentials. As a result, they release more neurotransmitter and generate more frequent action potentials. The brain interprets more frequent action potentials as greater loudness. • Localization of Sound: Relative intensity and timing of the sound waves reaching the two ears help localize the sound. If the intensity and timing cues are the same for both ears, the sound source is directly in front, in back, or overhead. When the timing in one ear is more vigorous and earlier than the other ear, the sound is coming from one side.