Copy of 6 - Nervous System and Special Senses PDF

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ANATOMY & PHYSIOLOGY

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Lesson 6: Nervous System and Special Senses Please submit to me in webmail for grading. Please answer in complete sentences. You may use a different color or highlight your answers. At the end of this lesson, you will be able to do the following: ●

Describe the organization of the nervous system and how the nervous system contributes to homeostasis

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Identify the anatomical structures of the nervous system and special senses and their functions

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Explain how an electrical impulse is conducted through a nerve

KEY VOCABULARY Topic 1: Organization of the Nervous System Central nervous system (CNS): The brain and the spinal cord Peripheral nervous system (PNS): A system of nerves that connects the outlying parts of the body with the central nervous system Somatic nervous system: A division of the peripheral nervous system; also called the voluntary nervous system Autonomic nervous system: The division of the nervous system that functions involuntarily; innervates cardiac muscle, smooth muscle, and glands Neuron: Cells of the nervous system specialized to transmit messages throughout the body Afferent (sensory) neurons: Nerve that carries impulses to the brain and spinal cord from the skin and sense organs. Also called sensory neurons. Efferent (motor) neurons: Nerves that carry impulses away from the brain and spinal cord to the muscles and glands. Also called motor neurons. Topic 2: Central Nervous System Meninges: The membranes that cover the brain and spinal cord Cerebrospinal fluid (CFS): The fluid produced by choroid plexi; fills the ventricles and surrounds the central nervous system Topic 3: Peripheral Nervous System Nerve: Bundle of neuronal processes (axons) outside the central nervous system.

Endoneurium: A delicate connective tissue sheath that surrounds each fiber in a nerve. Fascicles: A bundle of nerve or muscle fibers bound together by connective tissue. Epineurium: A tough, fibrous sheath that binds together the fascicles in a nerve. Mixed nerves: Nerves containing the processes of motor and sensory neurons; their impulses travel to and from the central nervous system. Topic 4: Special Senses Sclera: The firm white fibrous outer layer of the eyeball; protects and maintains eyeball shape Cornea: The transparent anterior portion of the eyeball Choroid: A vascular membrane containing large pigmented cells that lies between the retina and the sclera. Iris: The opaque contractile diaphragm perforated by the pupil and forming the colored portion of the eye. Pupil: An opening in the center of the iris through which light enters the eye Ciliary body: The intraocular eye muscles that change the shape of the lens. Aqueous humor: Watery fluid that fills the anterior cavity of the eyeball. Retina: The innermost layer of the eye. It contains the visual receptors called rods and cones. The rods and cones receive the light impulses and transmit them to the brain through the optic nerve. Rods: One of the two types of photosensitive cells in the retina Cones: The intraocular eye muscles that change the shape of the lens. Optic nerve: The second cranial nerve that carries impulses from the retinas to the brain. Macula lutea: Images are projected onto the area of the retina. Fovea centralis retinae: The area of the retina that has the sharpest vision. Vitreous humor: The transparent jelly-like substance inside the eyeball. NOTES AND ACTIVITIES Topic 1: Organization of the Nervous System Functions of the Nervous System

A: sensory input B: motor output Organization of the Nervous System A: brain and spinal cord B: cranial and spinal nerves C: afferent D: sense organs E: efferent F: voluntary G: skeletal muscles H: cardiac and smooth muscle, glands I: parasympathetic J: sympathetic

Neurons

A: cell body B: axon C: axon terminal

A: cytoskeletal elements B: cell body C: nucleus D: dendrite

Myelin A: skin of scalp B: bone of skull C: pia mater D: subdural space

Neuron Classification Interneurons A: Peripheral nervous system

Multipolar neuron A: dendrites B: cell body C: axon

Bipolar neuron A: dendrite B: cell body C: axon

Unipolar neuron A: dendrites B: cell body C: short single process D: axon

Supporting Nerve Cells Neuroglial cells of the CNS a: astrocyte b: microglial cell c: ependymal cells d: oligodendrocyte e: sensory neuron with Schwann cells and satellite cells Neuroglial cells of the PNS 1: schwann cells 2: satellite cells

Nerve Impulses: Depolarization and the Action Potential

b: stimulus initiates local depolarization c: depolarization and generation of the action potential d: propagation of the action potential e: repolarization f: restoration of ionic concentrations via sodium-potassium pump

Nerve Impulses: Repolarization A: depolarization and generation of the action potential B: propagation of the action potential C: repolarization

Nerve Impulses: Neurotransmitters

1: action potential arrives 2: vesicle fuses with plasma membrane 3: neurotransmitter is released into synaptic cleft 4: neurotransmitter binds to receptor on receiving neuron’s membrane 5: ion channel opens 6: ion channel closes

Reflexes

1: receptor 2: sensory neuron 3: integration center 4: motor neuron 5: effector

Reflexes All reflexes have five elements:

1: A sensory receptor 2: An effector organ 3: Sensory neurons 4: Motor neurons 5: CNS integration center

Nervous System and Homeostasis Topic 2: Central Nervous System Anatomy of the Brain A: cerebral hemisphere B: diencephalon C: cerebellum D: brain stem

Lobes of the Brain

1: parietal lobe

2: occipital lobe

3: temporal lobe

4: frontal lobe

Diencephalon

A:thalamus B: hypothalamus C: pineal body Major Structures of the Brain Stem 1: midbrain 2: pons 3: medulla oblongata

Reticular Formation

A: radiations to cerebral cortex C: descending motor projections to spinal cord E: reticular formation

B: auditory impulses D: visual impulses F: ascending general sensory tracts (touch, pain, temperature)

G: cerebellum Meninges

A: dura mater Cerebrospinal Fluid

B: arachnoid matter

C: pia mater

The cerebrospinal fluid (CFS) is a watery broth similar to the composition of blood plasma. It contains less protein than blood and more vitamin C. The CSF creates a watery cushion to protect the fragile nervous system. The blood-brain barrier is composed of the least permeable capillaries in the human body. This barrier only allows water, glucose, and essential amino acids to diffuse into the brain. Metabolic wastes such as urea, toxins, proteins, and most drugs are prevented from entering the brain. Fats, respiratory gases, and fat-soluble molecules easily cross the blood-brain barrier, which is why alcohol, nicotine, and anesthetics affect the brain. Spinal Cord The spinal cord is approximately 17 inches long, and serves as the two-way conduction pathway to and from the brain, and its major reflex center. The spinal cord is enclosed in the vertebral column, and like the brain is cushioned and protected by the meninges. Thirty-one spinal nerves arise from the spinal cord and serve the body area close by. The gray matter of the spinal cord resembles a butterfly or the letter “H” in cross section. The gray matter surrounds the central canal of the cord, which contains CSF. Neurons with specific functions are located in the gray matter of the spinal cord. The white matter is composed of myelinated fiber tracts, some traveling to higher centers, some traveling from the brain to the cord, and

some conducting impulses from one side of the spinal cord to the other. Topic 3: Peripheral Nervous System Nerves

A: endoneurium B: perineurium C: epineurium Cranial Nerves

D: axon E: myelin sheath

Twelve pairs of cranial nerves serve the head and neck of the body. Only the vagus nerves extend to the thoracic and abdominal cavities. The cranial nerves are numbered and their name reveals the most important structures they control. Cranial nerves can be identified by name, number, course, and function. Most cranial nerves are mixed nerves, excluding the optic, olfactory, and vestibulocochlear (acoustic nerve), which are only sensory in function.

Spinal Nerves A: cervical B: thoracic C: lumbar D: sacral E: coccygeal

Autonomic Nervous System

Topic 4: Special Senses Eyes

Sclera:The whites of your eyes are the sclera, the outer covering of the eyeball. The anterior part of the sclera, the cornea, is what permits light to enter the eyeball. The cornea’s job is not to simply let the light shine in but to refract (bend) it.

Choroid:The second layer of the eyeball is the choroid, a dark-brown membrane that provides the blood supply to the eye. Its anterior portion consists of the iris (the colored part of the eye; it’s composed of smooth muscle), the pupil (the opening in the center of the iris that permits the light rays to enter), and the muscular ciliary body that is attached to the lens (located behind the pupil) and pulls the lens to change its shape so it can focus incoming light on the retina.Between the cornea and lens is the aqueous humor, a fluid the ciliary body releases to maintain the anterior eye shape as well as nourish the eye itself.

Retina:The retina contains the receptor cells: the rods and cones. The rods help in dim light and to see shades of gray; the cones aid you in bright light and with colors.As the lens focuses light rays on the retina, nerve impulses travel on the optic nerve to the brain. The optic disc is where the optic nerve meets the retina and the retinal blood vessels enter and exit the eyeball; it is also known as the “blind spot” because there are no receptors at that connection point.When the light reaches the retina, it strikes a yellowish spot next to the optic disc, the macula lutea. At the center of the macula is a depression called the fovea centralis retinae. Made primarily of cones, this is your clearest point of vision.Between the lens and the retina is a gel-like substance called the vitreous humor, which helps the eyeball keep its overall shape.

A: ciliary body B: cornea C: iris D: pupil E: aqueous humour F: vitreous humor Eyes: External and Accessory Structures

G: sclera H: choroid I: retina J: fovea centrails K: optic nerve

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Extrinsic eye muscles: tiny muscles that connect the eyeball to the orbital cavity of the face Palpebrae (eyelids): flaps that close over the eyeballs to protect them from intense light, foreign objects, and impact Conjunctiva: a mucous membrane that lines the underside of the eyelids and protects the eye Lacrimal apparatus: the structures that produce, store, and remove tears

Light’s Pathway

Light rays are bent in the eye as they encounter the cornea, aqueous humor, lens and vitreous humor. The refractive, or bending, power of the cornea and humors is constant, but the lens can be changed by altering its shape to be more or less convex, so that light can be properly focused on the retina. The image formed on the retina from the light-bending activity of the lens is a real image. It is reversed, upside down and smaller than the object. Physiology of the Eye

Axons carry impulses from the retina and are bundled together at the posterior aspect of the eyeball, leading to the optic nerve. The optic chiasma is where the fibers from the medial side of each eye cross over to the opposite side. The fiber tracts that result are the optic tracts. The optic tract fibers synapse with neurons in the thalamus, whose axons form the optic radiation which run to the occipital lobe of the brain. There they synapse with the cortical cells and visual interpretation, or seeing, occurs.

Ears The ear is responsible for hearing and our sense of balance. Receptors that respond to the movement of fluids are called mechanoreceptors. The outer ear is composed of the pinna or auricle, the shell-shaped projecting part which collects and directs sound waves into the external acoustic meatus (or external auditory canal), containing cerumen (earwax) produced by the ceruminous glands.

The external ear ends at the tympanic membrane (eardrum) which vibrates in response to sound. The middle ear or tympanic cavity is a small cavity containing three small bones, called ossicles and are named according to their shape: Hammer (malleus) Anvil (incus) Stirrup (stapes) which presses on the oval window of the inner ear Movement against the oval window moves the fluids of the inner ear. The inner ear is separated into bony chambers called the osseous or bony labyrinth. The bony labyrinth is divided into three sections: the cochlea, the vestibule, and the semicircular canals. The cochlea is a snail shell-shaped bone that is connected to the oval window and contains plasma-like fluid called perilymph which helps to transmit sounds. A membranous labyrinth, which contains a thicker fluid called endolymph, is suspended in the perilymph. Hearing Mechanism

A: outer ear Equilibrium

B: middle ear

C: inner ear

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Static equilibrium receptors: detect changes in the position of the head with respect to the pull of gravity. For example, a diver swimming at night (no visual cues) knows whether she is right-side up or upside down because of her static equilibrium receptors. Dynamic equilibrium receptors: detect angular movements of the head, and are essential to providing equilibrium during movement, such as when you are dancing.

Olfactory Receptors and Smell

The receptors for the sense of smell are called olfactory receptors and are located in the roof of the nasal cavity. The olfactory receptor cells are neurons covered with olfactory hair (cilia). When the receptors are stimulated, the impulse is transmitted along the olfactory nerve. Taste Buds and Taste

Taste receptors are located in the tongue and are called taste buds which are found on the numerous papillae (peg-like projections). There are specific cells that respond to chemicals called gustatory cells which are surrounded by the epithelium cells of the tongue. Gustatory hairs protrude from the gustatory cell through the taste pore. When stimulated, the cranial nerves (facial, glossopharyngeal, and vagus) carry taste impulses to the gustatory cortex of the brain....