Biology Meiosis Quiz

Human Biology 112

• This book is the seventeenth edition of Human Biology
• It covers material for health science
• The author is Dr. Gamal Sharawy
• Contact information is provided for the author.

Chapter 14 / Nervous System

• The nervous system has two major divisions:
  • Central Nervous System (CNS): consists of the brain and spinal cord
  • Peripheral Nervous System (PNS): consists of nerves lying outside the CNS
• CNS functions:
  • Receives sensory input
  • Processes and integrates sensory input
  • Generates motor output
• PNS functions:
  • Carries sensory information to the CNS
  • Carries motor information from the CNS to effectors.
• Types of nerves:
  • Sensory (afferent) nerves: carry sensory information
  • Motor (efferent) nerves: carry motor information from CNS to effectors (muscles, glands, organs)
  • Somatic sensory nerves: signals from skin, muscles, joints, special senses
  • Visceral sensory nerves: signals from body organs.
  • Somatic motor nerves: control skeletal muscles (voluntary)
  • Autonomic motor nerves: control smooth muscle, cardiac muscle, and glands (involuntary)
    • Sympathetic division ("fight or flight")
    • Parasympathetic division ("rest and digest")

Nervous Tissue

• Two types of cells:
  • Neurons: greatly outnumber neurons
  • Neuroglia: support and nourish neurons.
    • Microglia: phagocytic cells removing bacteria and debris
    • Astrocytes: structural support and metabolic support to neurons
    • Oligodendrocytes: form myelin sheath in CNS
    • Schwann cells: form myelin sheath in PNS
• Three types of neurons:
  • Sensory neurons: carry signals from sensory receptors to CNS.
  • Interneurons: communicate between sensory and motor neurons
  • Motor neurons: carry signals from CNS to effectors

Myelin Sheath

• Covers long axons, not short ones
• Formed by Schwann cells (PNS) or oligodendrocytes (CNS) wrapping around the axon.
• Gives nerve fibers a white appearance and acts as an insulator.
• Important for nerve regeneration in the PNS.
• Multiple sclerosis (MS): myelin breaks down, preventing information transmission

Synapse

• The region of close proximity between axon terminals of one neuron and the dendrite or cell body of another.
• Synaptic cleft: a small gap separating sending and receiving neurons.
• Neurotransmitters: molecules that transmit action potentials across the synapse.
• Stored in synaptic vesicles in axon terminals
• Many neurotransmitters exist.
  • Ex. acetylcholine, norepinephrine, dopamine, serotonin, glutamate, GABA
• Nerve signals travel along axon to axon terminal.
• Calcium ions enter terminal → stimulate synaptic vesicles.
• Neurotransmitter is released into synaptic cleft & binds to receptor proteins on receiving membrane

Excitation & Inhibition

• Depending on the neurotransmitter, the receiving neuron's response can be:
  • Excitation: sodium ions diffuse into the cell
  • Inhibition: potassium ions exit the cell
• Removal: enzymes inactivate or reabsorb neurotransmitter from the synaptic cleft. Prevents continuous stimulation.

Neurotransmitter molecules

• Acetylcholine and norepinephrine are active in both CNS and PNS.
  • In PNS, ACh excites skeletal muscle but inhibits cardiac muscle. Norepinephrine generally excites smooth muscle.
• Serotonin is involved in thermoregulation, sleeping, emotions, and perception.

Resting Potential

• The potential energy of a neuron at rest.
• Exists because the plasma membrane is polarized (i.e., there is a more positive charge outside the cell, more negative charge inside due to potassium ions (K+) diffusing out and negative inside due to proteins).
• Measured in millivolts (mV).

Action Potential (Depolarization)

• The process of conduction of nerve signals in axons.
• A stimulus activates the neuron, causing sodium gates to open, and sodium rushes into the cell, making the inside of the axon positive compared to the outside.
• Threshold: the minimum voltage for an action potential to occur.

Repolarization

• Na+ channels close, and K+ channels open.
• K+ flows out of the cell, making the inside of the cell negative again.
• Sodium-potassium pump restores ions to their initial positions, restoring resting potential.

Unmyelinated Axons

• Action potentials stimulate adjacent parts of the axon membrane, producing an action potential.
• Conduction can be slow (1 m/s).

Myelinated Fibers

• Action potentials only occur at nodes of Ranvier.
• This is called saltatory conduction and is much faster (100 m/s).

Refractory Period

• The period of time immediately after an action potential during which the axon cannot conduct another action potential.
• Ensures one-way direction of signal from cell body down the axon.

CNS (Central Nervous System)

• Protected by bone (vertebrae [spinal cord], skull [brain])
• Wrapped in meninges (membranes)
• Meningitis: infection of the meninges
• Cerebrospinal fluid: Found in spaces between the meninges.
• Cushions and protects the CNS; it is produced by ventricles in the brain and circulates into the cardiovascular system.
• Lumbar puncture: Fluid withdrawal for testing.
• Composed of two types of nervous tissue:
  • Gray matter → contains cell bodies and short nonmyelinated axons.
  • White matter → contains myelinated axons grouped in bundles (tracts).

Brain

• Largest part of the brain.
• Divided into four lobes: frontal, parietal, temporal, and occipital.
• Communicates with and coordinates activities of other parts of the brain. (Communicates via corpus callosum, an extensive bridge of nerve tracts)

Spinal Cord

• Extends from the base of the brain through a large opening in the skull called the foramen magnum.
• Travels in the vertebral canal.
• Functions: communication pathway, gateway for pain signals, transmits motor signals from brain to muscles and internal organs; center for thousands of reflex arcs (also creates reflex arcs for internal organs).

PNS (Peripheral Nervous System)

• Cranial nerves (12 pairs) arising from the brain; spinal nerves (31 pairs) arising from the spinal cord.
• Ganglia (collections of nerve cell bodies outside the CNS)
• Nerves →collections of axons outside the CNS.
• Two divisions:
  • Somatic PNS: nerves serving the skin, skeletal muscles, and tendons.
  • Autonomic PNS: regulates cardiac and smooth muscles, organs, and glands.

Autonomic Nervous System

• Divided into two systems with opposing responses:
  • Sympathetic division: active during emergency situations (fight-or-flight) → increases heartbeat & dilates airways, inhibits digestive & urinary organs
  • Parasympathetic division: active during relaxed states (rest-and-digest) → promotes digestion, slows heart rate

Endocrine System

• Organs produce chemical signals called hormones, regulating other organs.
• Works very closely with the nervous system to maintain homeostasis
• The hypothalamus & pituitary glands are in the center of the brain. The posterior and anterior pituitary glands are the parts of the pituitary gland
• The thyroid and parathyroids are located in the neck.
  • The thyroid gland is located in the throat.
  • The parathyroids are four tiny glands located on the posterior surface of the thyroid.
• The thymus gland is attached to the heart
• The adrenal glands are on top of the kidneys
• The pancreas is endocrine and exocrine gland
• The testes and ovaries are located in the groin.

Hormones, Their Actions & Functions

• The table will list different endocrine glands, their hormones, and their target tissues/organs. The table will also outline their chief functions.

Hypothalamus

• Produces two hormones ADH & oxytocin stored and secreted by the posterior pituitary; it acts as the link between the nervous and endocrine systems
• Posterior pituitary and anterior pituitary glands are similar because both are controlled by the hypothalamus. Anterior pituitary gland is also controlled by hypothalamus through a portal system; produces releasing and inhibiting hormones → controls other glands
  • FSH (follicle stimulating hormone)
  • LH (luteinizing hormone)

Endocrine System & Nervous System

• Both systems can affect homeostasis and regulate other systems by using chemical signals
• Negative feedback mechanisms are used

Reproductive System

• Male: testes produce sperm, male sex hormones. Testes develop in the abdominal cavity then descend into scrotum (to avoid high body temperature).
• Female: ovaries produce eggs and female sex hormones. The uterus houses the developing fetus, with the cervix leading to the vagina.
• Both: Gonads, ducts, glands.
• Spermatogenesis:*
• Occurs in seminiferous tubules in testes
• Produce 4 sperms starting just after puberty and continuous.
• Spermatogonium → primary spermatocytes (mitosis) → secondary spermatocytes (meiosis I) → spermatids (meiosis II)→ sperm
• Oogenesis:*
• Occurs in ovaries
• Produces one egg and two or three polar bodies
• Starts prior to birth and completes after puberty (and stops after menopause).
• Primary oocyte → secondary oocyte & first polar body (meiosis I) → secondary oocyte & second polar body (meiosis II).
• Polar bodies hold discarded chromosomes.

Cell Cycle Control

• Checkpoints delay the cell cycle to ensure that conditions are met.
• External signals, such as hormones and growth factors, can stimulate cell division.
• Genes (proto-oncogenes and tumor suppressor genes) stimulate or inhibit the cell cycle and prevent apoptosis

DNA Biology & Technology.

• DNA is a double helix with complementary base pairs (A-T, C-G).

• DNA replication is semiconservative, producing two identical DNA molecules.

• Genes are segments of DNA with instructions for a specific trait.

• RNA is transcribed from DNA and translates into proteins.

  • Types of RNA: mRNA, rRNA, tRNA

• Three stages: initiation, elongation & termination

Mitosis vs Meiosis

• Mitosis: produces two genetically identical diploid daughter cells; Chromosome number remains constant.
• Meiosis: produces four genetically different haploid daughter cells; Chromosome number reduces by half.
• Steps and processes differ between the two functions with their respective results.

Test your knowledge of meiosis and its role in sexual reproduction. This quiz covers key concepts such as chromosome numbers, the comparison of sperm and egg cells, and the implications of the absence of meiosis. Dive into the fascinating world of cellular reproduction and understand the significance of meiosis in producing gametes.