The Eukaryotic Cell; the nervous system

Created by njose528 

Upgrade to
remove ads

nucleus

contains all of the the DNA in an animal cell (except for a small amount in the mitochondria). Only eukaryotes have nuclei. DNA cannot leave the nucleus (thus transcription must take place in the nucleus through nuclear pores). RNA leaves the nucleus through nuclear pores.

nuclear envelope or membrane

nucleus wrapped in a double phospholipid bilayer called this. The nuclear envelope contain large holes where RNA can exit but DNA cannot.

nucleolus

contained w/i the nucleus where rRNA is transcribed and the subunits of the ribosomes are assembled. Not separated from the nucleus by a membrane.

endocytosis

process where cells acquire substances from the extracellular environment. There are several types of endocytosis.

phagocytosis

to eat. The cell membrane protrudes outward to envelop and engulf particulate matter.

pinocytosis

to drink- nonselective, extracellular fluid is engulfed by small invaginations of the cell membrane

Exocytosis

the reverse of endocytosis

Eukayrotic cell

contains a thick maze of membranous walls called the endoplasmic reticulum (ER) separating the cytosol (aqueous solution inside the cell) from the ER lumen or cisternal space (the extracellular fluid side of the ER). Although there are many compartments in a cell, it can be divided into two sides: the cytosol and the ER lumen. In order to reach the cytosol, a substance must cross a membrane via passive or facilitated diffusion, or active transport, but it can reach the ER lumen via endocytsis

granular or rough ER

ER near the nucleus has many ribosomes attached to it on the cytosolic side, giving it a granular appearance. It synthesizes virtually all proteins not used in the cytosol. Proteins synthesized on the rough ER are pushed into the ER lumen and sent to the Golgi.

Golgi apparatus or Golgi complex

a series of flattened of flattened, membrane bound sacs. The golgi modifies and packages proteins for use in other parts of the cell and outside the cell. The end-product of the Golgi is a vesicle full of proteins. These protein filled vesicles may either be expelled from the cell as secretory vesicles, released from the Golgi to mature into lysosomes, or transported to other parts of the membrane.

secretory vesicles

release their contents through exocytosis. Secretory vesicles also act as the vehicle with which to supply the cell membrane with its integral proteins and lipids. In the reverse process, endocytoic vesicles made at the cell membrane are shuttled back to the Golgi for recycling of the cell membrane.

Lysosomes

contain hydrolytic enzymes that digest substances taken in by endocytosis. Lysosomes come from the Golgi.

agranular or smooth endoplasmic reticulum

ER, which lacks ribosomes. The site of lipid synthesis including steroids. The smooth ER also helps detoxify some drugs.

adipocytes

cells containing predominately fat droplets. Such cells are important in energy storage and body temperature regulation.

Peroxisomes

vesicles in the cytosol. They inactivate toxic substances such as alcohol, regulate oxygen concentration, play a role in the synthesis and the breakdown of lipids, and in the metabolism of nitrogenous bases and carbohydrates.

cytoskeleton

anchors some membrane proteins and other cellular components, moves components w/i the cell, and moves the the cell itself. Two major types of filaments in the cytoskeleton are microtubules and microfilaments.

microtubules

larger than microfilaments and are involved in flagella and cilia construction, and the mitotic spindle apparatus. They are rigid hollow tubes made from a protein called tubulin. In humans, cilia are found only in the fallopian tubes and the respiratory tract.

axoneme

The major protein of each flagellum and cilium, contains 9 pairs of microtubules forming a circle around two lone microtubules in an arrangement known as 9+2. Cross bridges made from a protein called dynein connect each of the outer pairs of microtubules to their neighbor. Remember Eukaryotic flagella undergo a whip-like action, while prokaryotic flagella rotate.

Microfilaments

squeeze the membrane together in phagocytosis and cytokinesis. They are also the contractile force in microvilli and muscle. The polymerized protein actin forms a major component of microfilaments. Are also active in cytoplasmic streaming (responsible for amoeba-like movement).

centrosome

microtubulues have a + and - end. The - end attaches to a microtubule organizing center (MTOC) in the cell. A microtubule grows away from an MTOC at its + end. The major MTOC in animal cells is the centrosome.

centrioles

function in the production of flagella and cilia, but are not necessary for microtubules production.

cellular junction

there are 3 different types of junctions or attachments that connect animal cells: tight junctions; desmosomes; and gap junctions. Each junction performs a different function.

Tight junctions

form a watertight seal from cell to cell that can block water, ions, and other molecules from moving around and past cells. Tissue held together by tight junctions may act as a complete fluid barrier.

desmosomes

join two cells at a single point.

gap junctions

small tunnels connecting cells. They allow small molecules and ions to move between cells

mitochondria

the powerhouse of the eukaryotic cell. Remember the krebs cycle happens here.

endosymbiont theory

mitochondria may have evolved from a symbiotic relationship between ancient prokaryotes and eukaryotes. Like prokayotes, mitochondria have their own circular DNA that replicates independently from the eukaryotic cell. However, most proteins used by mitochondria are coded for by nuclear DNA, not mitochondrial DNA.

mitochondrion

MEMORIZE THE PARTS OF THE MITOCHONDRION AND ITS PURPOSE. RELATE THE PARTS TO RESPIRATION DISCUSSED IN BIOLOGY LECTURE 1. Mitochondria are surrounded by two phospholipid bilayer. The inner membrane invaginates to form cristae. It is the inner membrane that holds the electron transport chain. Between the inner and outer membrane is the intermembrane space.

extracellular matrix

stuff that surrounds the cell and that is formed by the cell itself

intercellular communication

in multicellular organisms, cells must be able to communicate each other so that the organism can function as a single unit. Communication is accomplished chemically via 3 types of molecules: 1) neurotransmitters; 2) local mediators; 3) hormones. These methods are governed by the nervous system, t.he paracrine system, and the endocrine system. Neurotransmitters travel over very short intercellular gaps; hormones travel throughout the organism via the bloodstream.

Distinctions between neurotransmitter and hormonal mediated communication

Neurotransmitters are released by neurons. Neuronal communication tends to be rapid, direct, and specific. Hormonal communication, on the hand, tends to be slower, spread throughout the body, and affect many cells tissues in many different ways.

paracrine system

local mediators are released by a variety of cells into the interstitial fluid ( fluid between the cells) and act on neighboring cells a few millimeters away. Local mediators may be proteins, other amino acid derivatives, or even fatty acids.

Nervous system

allows for rapid and direct communication between specific parts of the body resulting in changes in muscular contractions or glandular secretions. Included are the brain, spinal cord, nerves and neural support cells, and certain sense organs such as the eye, and the ear.

neuron

functional unit of the nervous system. It is a highly specialized cell capable of transmitting an electrical signal from one cell to another via electrical or chemical means. Cannot divide and depends on glucose for energy, but do not depend upon insulin to obtain glucose. All neurons have a basic anatomy consisting of many dendrites, a single cell body, and usually one axon with many small branches.

dendrites

receive a signal to be transmitted. Typically the cytosol of the cell body is highly conductive and any electrical stimulus creates a disturbance in the electric field that is transferred immediately to the axon hillock. If the stimulus is great enough, the axon hillock generates an action potential in all directions, including down the axon. The axon, carries the action potential to a synapse, which passes the signal to another cell.

action potential

disturbance in the electrical field across the membrane of a neuron. Throughout the action potential, the Na+/K+ pump keeps working. 1) membrane is at rest. Sodium and potassium channels are closed. 2) Sodium channels open and the cell depolarizes. 3) Potassium channels open as sodium channels begin to inactivate. 4) Sodium channels are inactivaed. Open potassium channels repolarize the membrane. 5) Potassium channels close and the membrane equilibrate to its resting potential. An action potential is all or nothing; the membrane completely depolarizes or no action potential is generated. In order to create an action potential, the stimulus to the membrane must be greater than the threshold stimulus.

resting potential

established mainly by an equilibrium between passive diffusion of ions across the membrane and the Na+/K+ pump. The Na+/K+ pump moves 3 positively charge sodium ions out of the cell while bringing 2 positively charged potassium ions into the cell. As the electrochemical gradient of Na+ becomes greater, the force pushing the Na+ back into the cell also increases. The same thing happens to potassium. When all rates reach equilibrium, the inside of the membrane has a negative potential difference (voltage) compared to the outside.

voltage gated sodium channels

integral membrane proteins that change configuration when the voltage across the membrane is disturbed. Specifically, they allow Na+ to flow through the membrane for a fraction of a second as they change configuration. As Na+ flows into into the cell, the voltage changes still further, causing more sodium channels to change configuration, allowing still more sodium to flow into the cell in a positive feedback mechanism. Since the Na+ concentration moves toward equilibrium, and the k+ concentration remains higher inside the cell, so that is positive on the inside and negative on the outside. This process is called depolarization

voltage gated potassium channels

the neuronal membrane also possesses these. The potassium channels are less sensitive to voltage change so they longer to open. By the time they begin to open, most of the sodium channels are closing. Now K+ flows out of the cell making the inside more negative in a process call repolarization.

hyperpolarization

the potassium channels are so slow to close that for a fraction of a second, the inside membrane becomes even more negative than the resting potential. Passive diffusion returns the membrane to its resting potential. The entire process just describes is called the action potential.

synapse

neural impulses are transmitted from one cell to another chemically or electrically via a synapse. The transmission of the signal from one cell to another is the slowest part of the process of nervous system cellular communication, even though it occurs in a fraction of a second.

electrical synapses (uncommon)

don't involve the diffusion of chemicals, thus they transmit signals much faster then chemical synapses and in both directions.

chemical synapse

small vesicles filed with neurotransmitter rest just inside the presynaptic membrane. When an action potential arrives at a synapse, these channels are activated allowing Ca²⁺ to flow into the cell. This causes some of the neurotransmitter vesicles to be released through an exocytotic process into the synaptic cleft. The neurotransmitter diffuses across the synaptic cleft via Brownian motion. Slowest step in the transfer of a nervous signal, and that it can only transfer a signal in one direction. A more common synapse that is unidirectional.

neurotransmitter

The postsynaptic membrane contains neurotransmitter receptor proteins. When the neurotransmitter attaches to the receptor proteins, the postsynaptic membrane becomes more permeable to ions. Ions move across the postsynaptic membrane proteins, completing the transfer of the neural impulse. The neurotransmitter attaches to to its receptor for only a fraction of a second, and is released back into the synaptic cleft. A

second messenger system

receptors may be ion channels themselves, which are opened when their respective neurotranmitter attaches, or they may act via a second messenger system activating another molecule inside the cell to make changes. G-proteins commonly initiate second messenger systems.

support cells

nervous tissue contains many support cells called glial cells or neuroglia. Neuroglia are capable of cellular division, and, in the case of traumatic injury to the brain, it is the neuroglia that multiply to fill any space created in the central nervous system.

Oliogodendrocytes (type of support cells)

wrap many times around the axon in the central nervous system system creating electrically insulating sheaths called myelin. In the peripheral nervous system, myelin is produced by Schwann cells. Myelin increases the rate at which an axon can transmit signals.

white matter

mylineated axons. Only vertebrates have myelinated axons.

gray matter

neuronal cell bodies

nodes of Ranvier

tiny gaps between myelin

saltatory conduction

when an action potential is generated down a mylineated axon, the action potential jumps from one node of Ranvier to the next as quickly as the disturbance moves through the electric field between them.

Neurons may perform one of three functions

1)Sensory(afferent) neurons - receive signals from a receptor cell that interacts with its environment. The sensory neuron then transfers this signal to other neurons. 99% of sensory input is discarded by the brain

2) Interneurons

transfer signals from neuron to neuron. 90% of neurons in the human body are interneurons.

3) Motor (efferent) neurons

carry signals to a muscle or gland called the effector. Sensory neurons are located dorsally (toward the back) from the spinal cord, while motor neurons are located ventrally (toward the front of abdomen)

nerves (called tracts in the CNS)

neuron processes (axons and dendrites) are typically bundled together to form nerves.

nervous system

has two major divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).

central nervous system

consists of the interneurons and support tissue within the brain and the spinal cord. The function of the CNS is to integrate nervous signals between sensory and motor neurons.

PNS

handles the sensory and motor functions of the nervous system. The PNS can be further divided into the somatic nervous system and the autonomic nervous system.

somatic nervous system

designed primarily to respond to the external environment . Contains sensory and motor functions. its motor neurons innervate only skeletal muscles. The cell bodies of somatic motor neurons are located in the ventral horns of the spinal cord. These neurons synapse directly on their effectors and use acetylocholine for their neurotransmitter. The motor functions can be consciously controlled and are considered voluntary.

ANS

The motor portion of the ANS conducts these signals to smooth muscle, cardiac muscle, and glands. The function of the ANS is generally involuntary. The motor portion is divided into two systems: sympathetic and parasympathetic. Automatic pathways are controlled by the hypothalmus.

sympathetic

deals with fight or flight responses. For instance, its action on the heart would be to increase beat rate and stroke volume; it works to constrict blood vessels around the digestive and excretory systems in order to increase blood flow around skeletal muscles. Signals originate in neurons whose cell bodies are found in the spinal cord. The postganglionic neurons of the sympathetic nervous system use either epinephrine or norepinephrine (also called adrenaline and noraadrenaline).

Parasympathetic

focus on rest and digest. slows the heart rate and increase digestive and excretory activity. Signals originate in neurons whose cell bodies can be found in both the brain and the spinal cord.

lower brain

consists of the medulla, pons, hypothalmus, thalmus, cerebellum, and basal ganglia. It integrates subconcious activities such as the respiratory system, arterial pressure, salivation, emotions, and reaction to pain and pleasure.

higher brain (cortical brain)

consists of the cerebrum or cerebral cortex. The cerebral cortex is incapable of functioning without the lower brain. It act to store memories and process thoughts.

sensory receptors

somatic sensory neurons are incapable distinguishing between different types of stimuli, and are not designed to be the initial receptors of such signals. In stead the body contains 5 types of sensory receptors. Sensory receptors transduce physical stimulus to neural signals.

Path of Light as it enters the eye

Light reflects off an object in the external environment and first strikes the eye on the cornea. From the cornea, the light enters the anterior cavity, which is filled with aqueous humor. Light then enters the lens. The eye then focuses light on through the vitreous humor and onto the retina.

cornea

nonvascular and made largely from collagen.

lens

spherical shape, but stiff suspensory ligaments tug on it and tend to flatten it. These ligaments are connected to the ciliary muscle.

ciliary muscle

circles the lens. When the ciliary contacts, the opening of the circle decreases allowing the lens to become more like a sphere and bringing its focal point closer to the lens; when the muscle relaxes, the lens flattens increasing the focal distance.

retina

covers the inside of the back (distal portion) of the eye. It contains light sensitive cells called rods and cones. Cones distinguish colors and rods don't.

iris

colored portion of the eye the creates the opening called the pupil. In a dark environment the sympathetic nervous system contracts the iris dilating the pupil and allowing more light to enter the eye. Ina bright environment the parasympathetic nervous system contracts the circular muscles of the iris constricting the pupil and screening out light.

The ear

The ear is divided into three parts: The outer ear, the middle ear, and the inner ear.

The Path of a sound wave through the ear

The auricle or pinna is the skin and cartilage flap that is commonly called the ear. The auricle functions to direct the sound wave into the external auditory canal. The external auditory canal carries the wave to the tympanic membrane or eardrum. The tympanic membrane begins the middle ear. The middle ear contains three small bones. 1. the malleus; 2. the incus and 3. the stapes. These three small bones act as a lever system translating the wave to the oval window. The wave in the inner ear moves through the cochlea where movement is transduced into neural signals which are sent to the brain.

The middle ear contains three small bones. 1. the malleus; 2. the incus and 3. the stapes.

Like any lever system, these bones change the combination of force and displacement from the inforce to the outforce. The displacement is actually lessened which creates an increase in force. In addition , the oval window is smaller than the tympanic membrane, acting to increase the pressure.

cochlea

As the waves moves through the cochlea, the alternating increase and decrease in pressure moves the vestibular membrane in and out. This movement is detected by the hair cells of the organ of Corti and transduced into neural signals, which are sent to the brain. Detects sounds

semicircular canals

located in the inner ear and is responsible for balance. Each canal contains fluid and hair cells. When the body or the head position changes with respect to gravity, the momentum of the fluid is changed impacting on the hair cells, and the body sense motion. Detect orientation and movement of the head.

The Nose and mouth

The senses of smell and taste are called olfactory and gustory, respectively. These senses involve chemoreceptors. Different chemoreceptors sense different chemicals. There are only four primary taste sensations.

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set